Thursday, December 31, 2009

Space Warfare IX: Could Everything We Know Be Wrong?

International Space Station and Earth
Or at least 'it depends?'

The broad mainstream tradition of space SF tradition is to treat planets as analogous to island countries, with their surrounding orbital space as 'offshore waters.' In the more picaresque settings an occasional orbital station around some backward colony planet might become a Free Haven, welcoming all comers with no questions asked and fewer answered. But as a rule, any planet that wants to count for anything controls its own orbital space. Or at least someone does, such as a trade federation.

In this type of setting, where entire regions of local space are normally under a single authority, any enemy must come from some other local region, arriving from deep space. The attackers might come from Mars, or Callisto, or Sigma Draconis IV, without really changing the story line.

And much of what I have said here follows from that assumption. An approaching deep space force can be detected at Stupendous Range, its orbit telegraphing its region of origin and therefore probably its intent. It can then be engaged at merely Enormous Range, at the translunar fringe of orbital space or even beyond.

But what if both the attacker and defender are in Earth orbital space to begin with?

In Cold War days there was a whole subgenre that dealt with orbital warfare, in a near future setting - back when that meant circa 1965 - and a Cold War context. Much more recently a micro-genre of alternate history rocketpunk has appeared, centering on World War II. The most notable example is Ministry of Space, but I believe there are others.

In fact an all out war between Earth powers would reduce Earth's inner orbital space to a no man's land. Low orbit is too vulnerable to surface-launched kinetics, and shuttle types are especially vulnerable during ascent and return. Forces in high orbit or deep space would be cut off from their home bases for the duration, on both sides. In an early-space setting they'd have plenty on their hands to survive, let alone conduct operations against each other.

But suppose that, in a century or two, Earth orbital space is home to a welter of stations, habs, ships, and other platforms. Some belong to national governments, some are jointly operated (like the ISS today), or belong in various ways to a host of entities such as NGOs and private firms. Over time, how these spacecraft are 'flagged' may have as little to do with actual ownership as it does at sea today.

Ships at sea have to put into port sooner or later, entering someone's territorial waters. Spacecraft, other than shuttle types, remain in space, merely docking with other spacecraft from time to time. In these circumstances, so long as someone can pay the bills a flag of convenience is barely short of outright autonomy.

I have discussed this previously in the context of rethinking space piracy, and have also discussed alternatives to the familiar 'Westphalian' world of absolute sovereign states.

Independent or quasi-independent space habs are as plausible in Earth orbital space (or Mars, etc.) as they are in the asteroid belt, and perhaps more so. The asteroids have raw material, but Earth and its orbital space have the markets (and source of immigrants). If cycler ships are used, Earth orbital space is probably the one destination they all call at each time around.

Most likely an ambiguous welter of authority in space will merely provide billable hours for lawyers. But if Earth orbital space is home to increasingly autonomous powers, they can have rivalries, crises, and potentially warfare. What would a war between rival stations or habs in Earth orbital space be like?

It would have to be 'limited,' because of the great vulnerability of spacehabs to attack. But this is true of civil space infrastructure wherever it is located, so it does not distinguish orbital warfare from any other kind of space warfare. Or, in the postnuclear age, from any kind of warfare that any player can hope to survive.

The most obvious difference from the familiar vision of interplanetary (or interstellar) warfare is that travel times are suddenly much shorter. As was noted in the comment thread on orbital combat, mission durations in orbital space look more 'air force' than 'navy.'

The space you are fighting in is also a lot more cluttered, including with neutrals. Of course, 'cluttered' is a relative term. Earth orbital space is vast, taking hours or days to cross at even at orbital speeds. But compared to the months of interplanetary travel it is cheek by jowl. And the clutter may include neutrals whom you do not wish to draw into the war.

Which changes a lot of familiar assumptions. Everyone sees everything? Not behind that big round planet they don't, unless they have an eye on the other side. But even more to the point, we can't see through ships' hulls, let alone human minds, and the change of time scale changes the sort of missions we may undertake.

Imagine a suspicious ship departing a neutral space station.

In a traditional setting, absent magical drives we couldn't do much more than log its orbit. Intercepting and inspecting it would take months. If human inspection is called for you'd need a fairly large ship for long term habitability, and you are committing ship and crew to that one mission for perhaps a year or so. Which means that such missions will be costly, and rare.

Now shift the story into Earth orbital space. Intercept and inspection mission can now be performed in hours to a few days, by a much smaller craft with only short term habitability - which makes such missions far more practical.

For the same reason the 'suspicious spacecraft' itself becomes more plausible. Slipping a covert military craft into the civil traffic flow is cumbersome when civil traffic is months en route. It works a lot better on a time scale of hours to a few days.

Even the manned space fighter starts to be plausible in this environment. Its role is not precisely analogous to an atmosphere fighter, more nearly to a helicopter gunship, for example escorting the craft that carry boarding and inspection teams.

Fighting could and probably will erupt not in the middle of nowhere, but in genuinely crowded space - even amid the constellation of spacecraft that surrounds any large commercial station. A demand is refused, negotiations go pear shaped, and suddenly shooting erupts.

Here we are fighting at Hollywood range, and with civil and neutral craft nearby, posing rules of engagement decisions not to be entrusted to garden variety robotics. Teleoperation is an uncertain option. Jamming can't be ruled out in these close situations - and when split second decisions matter, a little light lag goes a long ways.

Putting human pilots aboard your escort gunships is no longer frivolous.

This sort of space environment is not confined to Earth orbital space. It can appear wherever you have extensive traffic in a small region of space, with no one local power in a position to regulate it all.

No technological assumptions need to be changed to bring about this state of affairs, only political and social assumptions about who can travel where in space, and whether high traffic local regions of space are typically under a single local authority that can defend them (or attack other local regions) as a unity.

The meta point is that a lot of what I have said here about Realistic [TM] space warfare is driven not just by technology but by (hidden) assumptions about who is fighting and what they are fighting over. Change those assumptions and you may get surprising results.

Happy New Year, and have at it!

The excellent image is from Astronomy Picture of the Day.

Related links: Piracy in space, and post-Westphalian worlds.

Wednesday, December 23, 2009

Glint of a Distant Lake

Lake Glint on Titan
This wonderful Cassini image, via Sky & Telescope, shows reflected sun glinting off Kraken Mare, an ethane lake on Titan.

The Ethane Lakes of Titan ... how cool is that?

And a Merry Christmas to all, or its like, by whatever custom you celebrate this solstitial holiday!

Wednesday, December 16, 2009

Space Warfare VIII: Orbital Combat

Orbital Combat
You cannot land on a planet or moon, or leave it - including, notably, Earth - without passing through its surrounding orbital space. This gives orbital space great strategic importance.

I have used 'orbital space' a good deal on this blog without ever defining what it means. Any formal definition would be somewhat arbitrary (like 'the threshold of space') but generally a planet's orbital space is the region dominated by its gravity. Think of it as close enough that you orbit the planet rather than just taking up a nearby solar orbit. (Or orbit a moon instead of its parent planet.)

For orbital space to have distinctive characteristics, major orbit change maneuvers must also require a substantial effort, a delta v of at least a few hundred meters per second - enough that chemfuel burns are costly in propellant consumption, while high specific impulse burns are time consuming.

Ceres, with an escape velocity of 0.51 km/s and low orbit velocity around 0.35 km/s, is about the minimum size for strategically significant orbital space. Neatly, and not entirely by coincidence, this corresponds to the minimum size for a 'dwarf planet,' shaped (literally!) by geological forces.

Significant zones of orbital space thus surrounds the eight major planets, the Moon, Ceres itself, the four big moons of Jupiter, Titan and six other moons of Saturn, four moons of Uranus, and Triton, along with Pluto and a growing list of outer system objects. We are interested in visiting most of them, and might one day be interested in fighting over them. (This last may not really be very likely, but it is possible, and makes for good thud and blunder space stories.)

Earth and Mars have escape velocities of several km/s, on the same order as interplanetary transfer speeds. (Escape speeds from the giant planets are higher still, but in strategic terms their moon systems are like miniatures of the Solar System, and a somewhat different strategic beast.)

This means that typical encounter speeds in Earth and Marsr orbital space are fairly high, even after making the burn from interplanetary transfer orbit. In low Earth orbit, encounter speeds can range from 4 km/s for circular orbits with a 30 degree difference in inclination, up to 22 km/s for a retrograde encounter just below escape velocity. Even at lunar distance a head-on encounter at escape velocity means a relative speed of 2 km/s.

Which makes orbital space a kinetic shooting gallery. A defender can pre-position kinetic target seekers as 'mines' on retrograde orbits, while an attacker coming from deep space needs hardly more than a tap to send kinetics onto a retrograde approach. Moreover, so long as they are below escape velocity, kinetic target seekers will not hurtle off into the void, but keep coming around.

What applies to kinetics also applies to ships. Ships in orbital space do not encounter each other as ships on crossing orbits in deep space do, one flash-past and off they go into the void on their separate paths, needing dozens of km/s of delta v to reverse track and re-engage. Ships orbiting a planet, so long as they are below escape velocity, will swing back around for repeated passes.

And it gets better. Orbital space (specifically, low orbit) is the domain of the Oberth effect. Imagine a target seeker in an elongated elliptical Earth orbit, so that it whips around perigee at 11 km/s, a shade under escape velocity. Let it have a small chemfuel booster good for 3 km/s of delta v. (The booster will have about twice the mass of the target seeker itself.)

Fire the booster at perigee and the target seeker is booted to 14 km/s, well above escape velocity. And its departure speed 'at infinity' will be 8.7 km/s (14 squared - 11 squared). Any target coming from deep space will have its own approach velocity, making for encounter speeds upwards of 12 km/s. A similar boot from low Mars orbit gives a departure speed of 6.2 km/s, and encounter speeds upwards of 10 km/s.

Finally, orbital space has the planet itself at the center of the maelstrom, giving spaceships a rare opportunity to crash, and providing a big exception to the rule that 'everyone sees everything.' You don't see anything through a solid planet or moon, and remote sensor probes can be burned out.

All of this ought to make orbital space militarily ... intriguing. Maneuvering there is more complex than in 'flat' space. Kinetics can be deployed cheaply and effectively as a sort of mine warfare.

And it matters, because a large proportion of strategic objectives will surely be in some planet's or moon's orbital space - or on the planet, subject to attack or blockade by whoever controls its orbital space. In any setting where planets are important, a good case can be made that most combat will take place in their orbital space.

Serious space warfare games, like Attack Vector, respond to all of this potential by avoiding orbital combat like the plague. This is for good reason. No one has yet figured out to sim convincing orbits in a board game, and not for lack of trying. This is no bar to fiction writers, who only have the problem of getting things right, or at any rate convincing.

But there is one other important consideration for orbital combat in a setting. Most of the interesting complications belong only to the near or midfuture, and become progressively less significant at higher techlevels. The planet or moon remains a physical obstacle, but its surrounding winds and currents matter less to steamships, so to speak, than to sailing ships. The shooting gallery effect matters only if kinetics approaching at 3-15 km/s are effective weapons, while orbital maneuvers are trivial for ships with torch drives.

So if you measure speeds as a fraction of c, don't have the captain fretting over approach orbits and defensive orbital mines.

The image is from commenter Luke, via Atomic Rockets. (It actually shows a laser zap, not a kinetic strike, but still portrays realistic orbital combat.)

Related posts: See the June, July, August, and September archives for previous posts in this series, plus the battles of the spherical war cows. And a much earlier post on space fighters.

Sunday, December 13, 2009

Mission to the Spice Islands

Da Gama Reaches India
It was not mainly about gold, it was about pepper. Europeans used a lot of it, and went to enormous efforts to get their hands on it. Shake or grind it with due respect: If the asteroid belt were known to have anything we want as badly as some of our ancestors wanted pepper, we might already be there.

Gold did figure in at the start, no surprise, and so did Prester John. Persisting rumor or legend placed a Christian kingdom somewhere in India, then a thoroughly vague term meaning 'way off east somewhere.' A Portuguese royal younger son became interested in Prester John, in the rather grubbier African gold trade, and - alas, but you knew it was coming - in the grubbiest African trade of them all.

The age of exploration was on, and one of the first things discovered was original sin.

Henry the Navigator's establishment at Sagres was not a 15th century NASA, and the Portuguese caravel was not a nautical revolution (though it was developed amid an ongoing revolution in nautical technology). In fact the lateen-rigged caravel turned out to be a bit of a technological dead end that faded away in the 16th century.

But what Henry and his shipwrights did was still remarkable; they took a handy, seaworthy type used mainly for deep sea fishing and modified it specifically for exploration. And Henry's captains pushed systematically along the coast of Africa, into waters then unknown to Europeans. They (re-) discovered Madiera in 1420, and the Azores in 1427.

They kept going after Prince Henry died. At last in 1488 Bartolomeu Dias rounded Cape Horn, and the way to the East was open. Ten years later da Gama reached India. The fabled wealth of the East, and especially pepper, was at last in direct reach.

And the world was changed. No need to beat the point to death, but good old Christopher Columbus was just trying to go one better on the Portuguese, armed with a gross underestimate for the size of the Earth and sublime ignorance that there was a continent in the way. Lucky for him there was. But it was the Portuguese who got the ball rolling.

No one, so far as I know, had ever explored before in the systematic way they did. There had been explorers: Pytheas, Hanno the Navigator, and the unnamed, semilegendary Phoenician whose circumnavigation of Africa was reported by Herodotus even though he did not believe it. But those were all one-offs.

The Chinese were doing it just as systematically, and at the same time. Zheng He's last expedition ended in 1433; the Portuguese had already reached the Azores and in 1434 they rounded Cape Bojador, pushing into waters unknown to Europeans since Hanno. It was a remarkable historical coincidence.

Unlike the great treasure junks the caravels were small, perhaps 20 meters long and 50 tons capacity - about a third the length and a thirtieth the displacement of their Chinese contemporaries. Handy and well suited to inshore work, to our eye they seem far better suited to exploration. Columbus thought the Santa Maria was too big and clumsy.

But the comparison is misleading. The Chinese treasure fleets had small handy ships, and more to the point the Chinese fleets were not sailing into entirely unknown waters. They were not so much survey missions as 'commercial exploration' and flag showing. When it comes to cargo capacity and sheer coolness factor, the great treasure junks could give value for money.

And most of all to the point, China had perhaps 50 times the resources of Portugal. A timely and interesting link from Winch of Atomic Rockets gives estimated GDPs in 1600. Portugal is not listed, but Spain and China are: Ming China, $96 billion; Philip II's Spain, $7.4 billion. Portugal a century earlier would have been at most perhaps $2 billion. Sending out a few hundred men aboard a squadron of caravels was as heavy a burden on Portugal as sending 30,000 men aboard a treasure fleet was for China.

So why did Portugal's program of exploration succeed, while China's was cancelled and forgotten? The reason can't be things like decentralization versus centralization or government versus private initiative. Both were more or less the same on those counts, pushed by government factions and supported by the merchants, shipbuilders, and such who benefited.

There are no doubt a host of other factors. The Chinese court eunuchs had domestic rivals who wanted to cut them down to size, while Henry the Navigator was a royal younger son who seemed out to make none of the trouble that royal younger sons can make.

But I believe the more important reason is that the Chinese treasure fleets had absolutely nothing to do with broader Chinese concerns of the time. The Indian Ocean produced nothing that the Chinese wanted the way Europeans wanted pepper, and it was irrelevant to the empire's security concerns. (Whereas central Asia was all too relevant.) Seafaring itself was incidental to most of China's population.

It was much different with Portugal, a small country with a substantial fishing population that would readily go to sea for anything more profitable. More important, Portugal shared the reconquista heritage and crusading enthusiasm of neighboring Castile, and shared with much of Western Europe a late medieval fascination with knighthood and quests that gave us Sir Thomas Malory's Le Mort d'Arthur.

Gold, spice, landed estates, adventures in exotic lands, and fighting Muslims (in a pinch, any 'paynims' would do) all got swirled together in the late medieval European imagination, and it was a powerful high. In literature it would produce Amadis of Gaul and his endless successors, the fantasy quest adventures of the 16th century. In retrospect it was embarrassing and often worse, but it had big consequences. It explored the world and conquered a fair part of it.

Pepper would help. But ultimately we will be propelled into space by the power of cool.

Related posts: Zheng He, Leif Ericson, and - from the early days of this blog - the roots of fantasy fiction.

Monday, December 7, 2009

Like a Virgin ...

Virgin Galactic's SpaceShipTwo was officially rolled out today, bringing suborbital space tourism one step closer to really happening.

Future generations may have their share of mirth over the choice of name, particularly in our current less than chaste era. They can also ponder the iconography of the logo, a young woman in a tastefully impractical spacesuit. I hope they have a good laugh, because that will mean that SpaceShipTwo did well enough to be remembered.

I've had mixed feelings in the past about suborbital tourism, which is in some ways a gimmick, less demanding by an order of magnitude (at least!) than getting into orbit, the real ticket to Space. On the other hand it can't hurt, and may be a proving ground for technologies and streamlined operating procedures that will in time allow cheaper orbital flight.

Here's to a wonderful first time!

Friday, December 4, 2009

'She Blowed Up REAL Good ...!'

Eta Carinae
This week the Sky & Telescope website gives us not one but two chances to indulge in gratuitous astronomical violence.

The first is a supernova detected in a remote galaxy in 2007, estimated to be about 100 times more powerful than mere 'ordinary' supernovae. A star of about 150 to 240 solar masses blew itself entirely apart. No remnant neutron star, no black hole, no nothing, just the expanding fireball.

They don't make bangs like that in our galaxy any more, not for the last few billion years. To get them you need stars of enormous mass that form only in the first generation, when there are no elements heavier than helium. The observed supernova is probably in a dwarf galaxy only just now forming stars. In our part of the universe the only remnants of these high power blasts are ... us. (And planets, etc.)

But our home galaxy is still perfectly capable of lesser bangs from conventional supernovae, and a prime candidate is Eta Carinae. In the 19th century it flared up for several decades to become one of the brightest stars in the sky, then faded to 5th magnitude. The Hubble image tells the story: a vast eruption, its expanding cloud now partly concealing the massive binary star within.

Evidence points to 'a new unstable phase of mass loss,' which sounds duly ominous. And all you have to do is look at the image to see that Eta Carinae, like a bad girl in a Victorian novel, is heading for a tragic but spectacular fate.

Related post: Betelgeuse is also living on borrowed time.

Tuesday, December 1, 2009

Mission to the Western Ocean

The space banquet has been troubled by the ghost of Leif Ericson all along, archeological confirmation of Norse voyages having been unearthed right at the start of the space age. Only some years later (at least for Westerners) did another ghost turn up at the feast: Zheng He, the Muslim eunuch who led the great Chinese 'treasure fleets' to the Indian Ocean nearly a century before the Portuguese got there from the other direction.

The Chinese may have gone farther than that. A 15th century Venetian monk and geographer, Fra Mauro, reported that a large 'zoncho' - junk - from the Indian Ocean sailed sailed 2000 miles into the Atlantic before turning back. The illustration on his map shows a ship of European type, but the artist was probably working from a second or third hand account, and knew only that the 'zoncho' was big.

(By the way, the Chinese probably did not 'discover America' in 1421 or any other year. File that one alongside the aliens who built the Pyramids.)

One puzzle about the treasure fleets turns out to have a simple (likely) explanation. The largest ships are reported to have been enormous, upwards of 150 meters long, even close to 200 meters. But Europeans later found that the maximum safe length for seagoing wooden ships was 60-70 meters, about 200 feet. Yes, the Chinese used very different constructional methods, but wood is wood, and early modern Europeans were not chumps when it came to wooden shipbuilding.

It is now thought that the mega junks were used only for river service on the Yangtze, while the largest ships in the treasure fleet were comparable in size to the largest European Indiamen a few hundred years later, with a load capacity of about 1500 tons. Which is just what you'd expect.

But the much bigger and sobering puzzle about the treasure fleets is the way their voyages suddenly ended. There was a power shift at the imperial court. The court eunuchs (among whom was Zheng He) had supported the voyages, and when they fell out of favor the budget ax soon fell. The treasure ships were laid up and left to rot away. More axes fell than that. Building large seagoing ships was forbidden, and China's entire maritime capacity rotted away. A hundred years later Europeans showed up, and the rest is history.

It makes a great cautionary story. Cut the NASA budget, and the next thing you know the red haired devils are at the door. Or something like that.

The real story is more complicated. For one thing, the treasure fleets were stupendously big and expensive. Really big, perhaps five or ten times the fleet tonnage of a Spanish treasure flota or a convoy of Indiamen. A vast and economically disruptive effort was called for to build the treasure fleets and send them out.

Imperial China was capable of it; whether it was a good idea was no doubt a matter of dispute. It was good if you were a merchant or timber supplier, or a member of the court with a taste for Indian or Middle Eastern luxuries, not so good if you were paying taxes for some fairly nebulous benefits.

So it is not surprising that there was a reaction. The whole enterprise had no deep foundations in China's economy or its political interests. It was a matter of imperial prestige, and only by one measure of prestige - fleets of junks impressed no one in Central Asia, far from any ocean. By comparison the British East India Company was deeply rooted in the folkways of England. (Crumpets and tea, anyone?)

The backlash, when it came, was as extravagant as the voyages themselves, but it did not cause the 'century of humiliation' 500 years later. Shipbuilding was banned, but the sky was big and the Emperor far away, and oceangoing Chinese shipbuilding did not cease. China lost the Opium Wars for other reasons, in another era.

If there is any warning here for space advocates it is about needless gigantism, and arguably the old hare and tortoise story. Perhaps the post-Apollo letdown was fortunate in that it happened early, before the inevitable backstroke could develop too much force. The post-Apollo program has been more modest, but in spite of setbacks it has proven fairly robust.

Related posts: Leif Ericson, a retrospective and prospective, a Solar System for this century, and thoughts on colonization.

Monday, November 23, 2009

Mission to Vinland

Norse Ship
In the course of a work gig, I lately read up on Leif Ericson. I have noted him before on this blog, a gloomy Nordic presence at the space banquet. His claim to fame is as the second to last person to discover America, proof that mighty voyages do not always have mighty results. (The connotations of 'mighty' depending, of course, on perspective.)

To recap the story, Leif was the son of Eric the Red - an even more unwelcome guest at the space banquet, since he founded the Norse colony in Greenland that ultimately failed, its life support technology overwhelmed by the Little Ice Age.

Leif heard that another Norse seaman had sighted land west of Greenland, bought the man's ship, and went to see for himself. He found a couple of rather bleak islands, then one that was a lot less bleak. He dubbed it Vinland.

Up until 50 years ago this whole story hung only on the saga accounts, glimpsed along with King Arthur and the Trojan War across the misty frontier between history and legend. Then archeologists dug at L'Anse aux Meadows, on the northern tip of Newfoundland, and found a Norse outpost.

Leif's colonization effort was shortlived - mostly due to short tempered Vikings - and it is not certain that a 'colony' was the intent, rather than a base camp for resource exploitation. A chance encounter at sea more than 300 years later indicates that the Greenland Norse were still sailing as far as one of Leif's intermediate islands, Markland (possibly Labrador) to gather timber.

In short, the entire Vinland episode was a matter of a small frontier settlement looking for additional resources to tap in neighoring regions, a process that would be repeated scores of times after 1492. Leif Ericson, like Christopher Columbus, had no idea that he was 'discovering America.' But Columbus did know that he was looking for a major trade route, one that if it panned out would bring fabulous wealth to Spain (and, from his Genoese perspective, poke one in the eye of the Venetians).

Leif Ericson was not looking for a major trade route, only a supply source for a remote settlement. The Greenland Norse were too few to exploit it, and no one else had any practical need for it. In space terms, Vinland was just one more outer-planet moon that turned out not to warrant follow-up missions. A great story in its own right, but not, after all, a story of failed discovery.

Friday, November 20, 2009

The Weather on Mars

Dust Devil Trails on Mars
Hat tip to Anita for reminding me about this striking image, via Astronomy Picture of the Day, from the Mars Reconnaissance Orbiter. The swirly patterns are formed by dust devils that blow aside reddish surface dust to reveal dark material just beneath it.

I am old enough to be reminded of the Nazca lines, geoglyphs made by ancient peoples in a South American desert, that figured prominently in 'ancient astronauts' crankery. The patterns are entirely different, but you can imagine a playful intelligence at work here. 'Dust devil' is an apt term - think of the Tasmanian Devil in old Warner Bros. cartoons. Dust devils on Mars can reach 8 km in height, and have extended the life of Mars rovers by blowing the dust off their solar panels.

Once again Mars evokes an offworldly American Southwest. The Bat Durston theme is quintessentially SF, perhaps the very heart of 'Murrican SF, but oddly enough it never entirely applied to the old, rocketpunk era Mars. The old Mars, Percival Lowell's Mars, was a desert world indeed, but a desert of vast flat plains (the better for the canal system).

No one dreamed that Mars had both the highest mountain and the largest canyon in the Solar System. By pleasing irony, Lowell's observatory is not so far from the Grand Canyon.

Lowell's Mars was flat because it was a slowly dying world, its topography long since worn down by its desert winds. Real Mars fall from Earthlike grace more quickly, its atmosphere now too thin for its winds to wear down Olympus Mons. The forces that break mountains have faded along with the forces that make them. Now the winds of Mars produce only dust devils. (And the occasional planetwide dust storm.)

Yet the dust devils are also a reminded that Mars is not quite dead. Winds swirl across its surface; from time to time liquid water still flows there. It is still a world with weather.

Related Post: I noted in March that in spite of appearances, Mars is fiercely unlike Arizona.

Friday, November 13, 2009

Lunar Water: 'We Practically Tasted It'

IR Spectrum From L-CROSS
My post before last turns out to have been premature. I should have known better. Even at the press conference just after impact the L-CROSS team seemed just a bit chipper and smooth, especially for guys whose heavily promo'd sky show had just gone bust. Their media leaks a few days ago were also just a bit coy. (And given the subject, 'leak' is a singularly appropriate term.)

The sky show may have been a bust for the Earth audience, but it was no bust for the instruments aboard the L-CROSS probe, or the Lunar Reconnaissance Orbiter passing 50 km overhead.

Cutting to the chase, team leader Anthony Colaprete reports that that they found water, and 'We didn't find just a little bit, we found a significant amount.' In fact, 100 kg of water vapor were detected in the plume. (The illo above is from the Sky & Telescope article, where it is explained.)

Colaprete wouldn't give an estimate for what fraction of the soil that might be, but on the face of it that is quite a lot, and apparently counts only vapor - ice either vaporized by the impact heat, or perhaps sublimating from crystals exposed to space, especially if kicked up high enough to be hit by sunlight.

A brew of other compounds was also detected, one of the inevitable candidates being ethanol. I hope that pans out, if only to see the estimates of how many fifths are locked up in the lunar regolith. However, the first potable moon juice will surely come from a still tucked away in the life support plant.

Tuesday, November 10, 2009

On Colonization

Colony Planet from 'Firefly'
A post at SFConsim-l leads me to revisit a trope I have commented about here before. Space colonization, as imagined in SF and 'nonfiction' space speculation, is - surprise! - a riff on the English colonization of America, an experience shared by Clarke and Heinlein, albeit from different perspectives. Historically sort of colonization was driven first and foremost by cheap land.

This should be no surprise, any more than the American colonial analogy itself. It is like hydraulics. Provide a cheaper place to live and people will drift toward it, sometimes even flood toward it.

And the heart of the nutshell, as Heinlein once put it, is that there is no cheap land in space because there is no land at all. Land doesn't just mean a solid planetary surface (those are dirt cheap). Land means habitat, and in space the only way to have any is to build it youself. Which makes it expensive, especially since you have to build it up front.

Water can be pumped uphill, and people can be pulled toward expensive places to live by compensating attractions, or pushed there by pressures. But it is not a 'natural' process, and it can easily be reversed, hence ghost towns in rugged, played-out mining regions.

The sort of colonization envisioned in the rocketpunk era, most explicitly in books like Farmer in the Sky, but implicit in the consensus future history of the genre, is just plain unlikely, almost desperately unlikely, this side of the remote future or the Singularity, whichever comes first.

This is not the only possible sort of colonization. People have traveled afar, often spending their adult lives in some remote clime with no intention to settle there, marry, and raise a family, hoping instead to make their fortune and return home. The ones who don't make their fortune may end up staying, but that was not the plan.

Political colonialism often follows this pattern. The British colonized India, but I've never heard that any significant number of Britons settled there. (Human nature being what it is they did leave an Anglo-Indian population behind.)

A similar pattern has been common for trading outposts through the ages, whenever travel times have been prolonged. Even today, with one day global travel, people live abroad for years or even decades as expatriates, not emigrants. This, I believe, is a far more plausible scenario for the long term human presence in space than classic colonization. (And human nature being what it is, a mixed population will leave someone behind.)

Meta to this discussion - and not all that meta - is the delicate cohabitation of 'nonfiction' space speculation and science fiction. Space colonization has been driven first and foremost by story logic. For a broad range of story possibilities we want settings with a broad range of human experience. For this we want complete human communities, which means colonization in something like the classic SF sense.

But who are we trying to kid? Science fiction, particularly hard SF, is not known for engaging the whole range of human experience. This is no knock on it; all the branches of Romance are selective. The truth is that we want space colonies so that they can rebel against Earth, form an Empire, and generally play out History with a capital H, with lots of explosions and other cool stuff along the way.

I've suggested before on this blog that you can, in fact, get quite a lot of History without classical colonies. But another thing to keep in mind is that story logic doesn't necessarily drive real history. We may have an active spacefaring future that involves practically none of the story tropes of the rocketpunk era.

As a loose analogy, robotic diving on shipwrecks has done away with all those old underwater story tropes about divers trapped in a collapsing wreck, or bad guys cutting the air hose, but it has not at all done away with the somber magic of shipwrecks themselves, something the makers of 'Titanic' used to effect.

On the other hand, Hollywood has made two popular and critically acclaimed historical period pieces about actual space travel, and the stories are both an awful lot like rocketpunk.

Related posts: A Solar System for This Century.

Friday, November 6, 2009

Cold and Dry

Moon Above Desert
This seems to be the current forecast for the Moon's polar craters, as it presumably has been for the last few billion years, and will continue to be for the next few billion.

Not much (only one heavily processed image) has come out officially from the L-CROSS team since their mission scored a lunar bull's eye, minus the photogenic plume that was supposed to be the media highlight of the show. But in the grand old aerospace industry tradition of using Aviation Leak to get the story out, the L-CROSS team dropped some hints in the online Sky & Telescope about what is going on behind the scenes.

The impact did produce a plume, but it was about 10 times less massive than expected. Why it was so sparse is not yet known and may never be fully known, but new hypervelocity impact modeling suggests that debris may have gone more 'out' than 'up.'

There's also mention of the Centaur booster stage 'collapsed into itself when it hit.' I am not quite sure what to make of that last part. You'd expect any tank structure to 'collapse into itself' when it slams into the Moon at 1.5 km/s. But fans of kinetic weapons, including me, take note: There is a lot that we do not know about uber-fast impacts.

As for what was in the faint plume, Sky & Telescope gives contradictory hints, noting that the IR signature of water vapor is conspicuous (and implicitly absent), but also broadly hinting that when an L-CROSS public announcement comes, in a couple of weeks, the team may reveal that it did detect water. But not, I suspect, very much of it. What they did detect, rather oddly, is mercury.

The article also has one other interesting tidbit, though not from L-CROSS. Apparently an instrument aboard the Lunar Reconnaissance Orbiter determined that the surface temperature on the floor of those permanently shadowed are only about 35 K - much lower than anticipated, and making those spots the coldest known place in the entire Solar System.

And right in our local 'hood. How cool is that?

Saturday, October 31, 2009

Spaceship Design 102: Life Support

Growing Algae
Human life support is complicated, bulky, and it smells bad. If we only sent robots we would not have to mess with it. But if we go in person we have to deal with it. First, go to the life support page at Atomic Rockets.

To begin with we will need a cabin. Here there is a big difference between short missions, up to a day or two, and longer ones. Short term passengers can sit in airliner style seats, crew at their work stations, and the galley needn't be much more than a refrigerator and microwave oven. But as missions get longer you need bunk space for off duty crew, and at some point cabins or bunkrooms and a real galley.

From a comparison of railroad sleeping cars versus coaches, sleeping accommodations take up about 10 cubic meters per person, 2-4 times as much room as airliner style seating. Add a galley and dining compartment, storage space, and some this and that brings the minimum requirement to around 15 cubic meters per person, give or take.

(The ISS is much roomier, Wikipedia claiming a 'living volume' of 358 cubic meters for a crew of six, or nearly 60 m3 per person. But I don't know how living volume is defined, for example whether it includes working spaces. Total pressurized volume of the ISS is reported as about 1000 m3.)

Man does not live by bread alone, but along with water and oxygen it is a start. Human beings need about 5 kg/day in food, water, and oxygen, food accounting for about half the total. Unless you have regenerative life support you will need to carry it all with you. This does have the advantage of simplicity - we know how to do it, which is not the case for regenerative life support. For missions up to a few months the mass penalty is not excessive; 200 days' provisions and supplies come to about a ton per person, requiring about 3 cubic meters of storage space.

With storerooms, equipment bays, and assorted plumbing, our hab compartment for deep space transports may thus have a volume around 20 cubic meters per person. This in turn equates to about a ton or two per person for the basic hab pressure vessel, plus another ton or two of fittings and equipment, and for a 6 month mission a ton of consumables. So, altogether, each person (passenger or crew) carried by a transport class ship accounts for 3-5 tons of payload capacity.

In the rocketpunk era the standard way to reduce this was to carry passengers in Cold Sleep. But at our current level of knowledge this is magitech. We haven't a clue how to drastically slow down human metabolism, or even produce mere hibernation, let alone how to do it safely.

Another rocketpunk era classic was regenerative life support, those famous hydroponics tanks somewhere aft/below decks. Details were sometimes vivid, occasionally charming (fresh flowers in the wardroom of PRS Aes Triplex), rarely quantitative.

There is a rule of thumb that it takes 10 kg of food source biomass to support 1 kg of whatever is eating it: thus, for a purely vegetarian diet, about 0.75 tons of plant biomass per person. Biochemistry conveniently sees to it that the plants we eat also replenish our oxygen.

On this basis the break even point for regenerative life support is about 150 days. A 1953 (!) source cited at Atomic Rockets says 145 days. But this ignores the penalty mass of the hydroponics tanks. (Or aeroponics, whateva.) Greenhouse hydroponics on Earth seems to achieve yields of about 30-35 kg per square meter. One source mentions a 4 month growing season, suggesting that with year round operation we might do three times better, approaching 100 kg/m2.

Since we eat about a ton of food per year, this corresponds to about 10 square meters of growing surface per person. With access and working space perhaps 20 cubic meters per person - comparable, that is, to our estimate for living space, and probably with a comparable mass, about 3-5 tons per person, including a ton or so of biomass.

The structure and equipment mass needed to grow food shifts the tradeoff point: For missions less than about 2 years, the mass of stores plus storeroom capacity is less than the mass of a regenerative system. Most transport class ships - which for this purpose includes most military craft - are used for shorter missions that that, so they will dispense with the extra bulk and mass of full regenerative life support. They might have a garden deck, more for human factors than for its modest life support contribution.

There's also the little detail that we don't yet know how to do regenerative life support. This is one type of space research that can be done on Earth, and as space research goes it does not require a lot of expensive hardware. The Biosphere 2 fiasco doesn't prove a lot in and of itself, given the possible flake factor, but building a human supporting ecohab cannot be easy, or someone would have done it by now.

But we won't really need regenerative life support until we are establishing long term stations or bases. And my guess is that we'll learn the techniques gradually, in the process of reducing dependence on costly supplies from Earth. Regenerative life support is, on some level, a sophisticated form of gardening, and gardening has always called for patience.

Two other life support considerations: Radiation, and heat.

Without shielding, the cosmic radiation dose in deep space is about 400-900 millisieverts per year, where 1 Sievert = 100 old fashioned rems. The current career limit is 4 Sieverts for astronauts, 2 Sieverts and change for nuclear industry workers. Thus for long term habitation we will need enough shielding to diminish the penetrating radiation by about tenfold. This requires about 100 grams per square centimeter - a ton per square meter. And this shielding has to be applied all around, because cosmic rays can come at you from any direction.

This is not a problem for big permanent habs, but it is far too massive for transport class ships. This is one more reason to favor fast orbits for human travel. A ship's habitat might provide enough shielding to cut radiation by half, so that a 3 month tranfer mission provides about the same radiation exposure as a year living aboard a shielded hab.

And don't forget plain old heat management. An object at room temperature radiates about 400 Watts per square meter, which you will have to replace - but at 1 AU you are also exposed to a solar flux of 1400 W/m2 on surfaces directly facing the Sun. Managing heat, both from onboard power and solar flux, to keep the hab in the human comfort zone will be a constant task.

In fact, all of life support will be a constant task. In rocketpunk days maintaining the life support system was treated as an afterthought to the cool space stuff like astrogation and engineering. This is unlikely to be the case.

This being All Hallows' Eve, I'll just leave you with this thought for your contemplation: Cascading life support malfunction.

Related post: Spaceship Design 101.

Monday, October 26, 2009

History, From Above

ISS Above Ionian Sea
This image from Astronomy Picture of the Day - see it here in magnificent full size - gives a whole new meaning to 'overview of history.' Seen from the Shuttle Endeavor, the International Space Station passes above Sicily and heads east over the Ionian Sea, with the instep and heel of the Italian boot seen just to its left.

The Ionian Islands are the group above and to the right of the ISS, just off the coast of Greece. One of them is Odysseus' Ithaca (though it is uncertain whether his home was the same as modern Thiaki). The site of Troy is also hazily visible, straight up from the Ionian Islands about two thirds of the way to the limb of the Earth. The ISS will cover this distance in about 100 seconds, some three million times faster than Odysseus' trip home.

History's three greatest galley battles all took place within this field of view. Salamis (480 BC) is only hazily visible on the Aegean coast of Greece, but Actium (33 BC) was fought just off the lagoon to the left of the Ionian Islands, and Lepanto (1571) in the gulf just behind them.

In fact these waters are the Belgium of Mediterranean naval history: A disproportionate number of seafights have taken place here over the centuries, from Corcyra, the opening round of the Pelopponesian War in 31 BC, to Navarino (1827), the last fleet battle under sail, and Cape Matapan (1941). Also visible here is Taranto, Italy, where the British staged the first successful air raid against an anchored fleet more than a year before Pearl Harbor.

And in the time it has taken you to read this, the ISS will already be far to the east, gliding across the skies above the Silk Road.

Wednesday, October 21, 2009

Spaceship Design 101

Discovery (from 2001, the novel)
A lot of us would like some system for designing spaceships, at least in outline, for use in games, detailed fictional settings or physical or virtual 3D modeling.

The procedure I have seen most often begin by defining a hull. This gives you the main dimensions of the spacecraft, its surface area and volume capacity, perhaps along with constraints such as maximum load and drive acceleration. This is a natural approach. I used it for my battleship-era warship specification sim, SpringStyle, and it is retained by its independent offspring, SpringSharp.

But for deep space craft it is seriously misleading. Ships and aircraft, says Captain Obvious, move through a fluid medium that shapes and constrains their design. Deep space craft do not. Their overall design constraints are more architectural: supporting the craft against its own thrust, along with stresses from attitude change maneuvers, the thump of docking, thermal flexing, spin loads, and the various other kinds of abuse that spacecraft are subject to.

This is as good a time as any to point you to the Atomic Rockets pages on basic and advanced design.

I will argue that deep space craft have essentially two sections that can largely be treated separately from one another. One section is the propulsion bus - drive engine, reactor if any, solar wings or radiator fins, propellant tankage, and a keel structure to hold it all together. The other is the payload section that it pushes along from world to world.

There are both conceptual and economic reasons to treat them separately. Conceptually, because a propulsion bus might push many different payloads for different missions, such as light payloads on fast orbits versus heavy payloads on slow orbits. A little noticed but important feature of deep space craft is that you cannot overload them. They do not sink, or crash at the end of the runway, or even bottom out their suspension. They merely perform more sluggishly, with reduced acceleration and (for a given propellant supply) less delta v.

A very large station or hab might well have a modified ship drive as its main stationkeeping thruster. Or it may rely on a ship coupling to it, as the ISS is shunted by Soyuz craft docked to it.

Conceptual logic is also economic logic. The outfits that build drive buses would like to sell them to lots of different customers for a broad range of assignments.

This is not necessarily an argument for true modular construction, with drive buses hitching up to payloads on an ad hoc basis like big-rig trucks and trailers. Building things to couple and uncouple adds complexity, mass, and cost - plug connectors, docking collars, and so forth. Moreover, drive buses intended for manned ships need to be human-rated, not just with higher safety factors but provision for supplying housekeeping power to the hab, etc. But these things, along with differing sizes or number of propellant tanks, and so forth, can all be minor variations in a drive bus design family.

The payload we are most interested in is, naturally, us. The main habitat section of a deep space ship closely resembles a space station. It is likely that habs intended for prolonged missions will be spun, for health, efficiency, and all round convenience. (Flush!) The design of a spin hab is dominated by the spin structure and - unless you spin the entire ship - the coupling between the spin and nonspin sections.

Because ships' spin habs have the features of stations they may be used as stations, and again we can imagine design families, with some variants intended for ships and others as orbital platforms having only stationkeeping propulsion. Habs are the one major part of a deep space ship that correspond fairly well to our concept of a hull. Spin habs are entirely different in shape, but the shape is constrained; once you build it you can't easily modify it, beyond adding another complete spin section.

Pause to question another familiar convention here. Since at least Heinlein days spinning ships have typically been given a control room located on the spin axis, and perhaps nonspinning, where the astrogators can use their instruments unhampered. But isn't this equivalent to the circular astrogation slide rule? The navigators will do their normal work on monitors. In the inevitable space emergency there will no doubt be coelostats available, or other workarounds. But there's no reason not to locate the ship's main operating control room in the spin section, closer to the people who work there.

Though I'd be happy to be persuaded otherwise. I have always liked Heinlein's penthouse style control rooms at the forward/top end of the ship (plus the fact that he never called it a bridge). If Hollywood came calling I'd bend realism here in a nanosecond, not least because a 'top' control station is visually easy to understand, a sort of Aha! moment for viewers. But I suspect it is a minor cheat.

For those with bank cards at the ready, buying a deep space ship might be not unlike buying a computer. If your mission needs are fairly standard, you check off options on a menu. Those with more specialized requirements can select major components - perhaps a drive bus from one manufacturer, a main crew hab from another, along with custom payload sections, service bays, and so forth, assembled to your specifications.

In fact, both technology and probable historical development suggest that fabrication and overall assembly will be two distinct phases, carried on in different places, quite unlike either shipyard or aircraft assembly practice. In the early days, large deep space craft will be built the way the ISS was, assembled on orbit out of modules built on Earth and launched as payloads. In time fabrication may move to the Moon, or wherever else, but final assembly (at least of larger craft) will continue to be done at orbital facilities. I call them cageworks, on the assumption that a cage or cradle structure provides handy anchoring points for equipment.

For game or sim purposes, my advice would be to treat drive buses and hab sections as the primary building blocks for ships, whether these components are permanently attached to each other or simply coupled together. Both approaches might be in use.

A couple of provisos. All of the above applies mainly to deep space craft, especially with high specific impulse drives. Ships for landing on airless planets have some similar features. Ships that use rapid aerobraking, however, are aerospace craft and broadly resemble airplanes, even if they never land or even go below orbital speed.

And I have said nothing of warcraft. Kinetics are essentially just another payload. Lasers, and other energy weapons such as coilguns, probably draw power from the drive reactor, calling for some modifications in the drive bus. These things don't much affect the overall configuration. Armor protection would, but discussions here have left me doubtful of its value against either lasers or kinetics. Laser stars and other major warcraft may not be dramatically different in appearance from civil craft of similar size.

Monday, October 19, 2009

Thirty Planets

Extrasolar Planet
That is how many new discoveries are being reported at the Extrasolar Planets Encyclopedia website, along with three new brown dwarfs.

I was tipped off by a political blog, which linked to this CNN article. Yes, the article says 32 planets, but I'll go with the Paris Observatory. It may be a matter of updated information, since the observatory site links an email that references 29 plus 1.

No details yet about the newly reported planets - the image above, from the CNN site, seems to show a planet orbiting a double star, but it may just be a generic exoplanet from file footage, so to speak.

But thirty new planets (at least!) have swum into our ken. Wow.

Related posts: The California planet search team reported a haul of 28 planets in 2007.

Saturday, October 17, 2009

A Plume After All

L-CROSS Centaur Impact Plume
As it turns out, the L-CROSS mission did create a visible plume. Neener neener neener, says the Moon and the L-CROSS science team. I saw the news in the Los Angeles Times, dead tree edition, and it is online at Apparently the plume was imaged by a camera aboard L-CROSS itself, just not the imagery everyone was watching in real time. Judging from the stark contrast, they had to tweak up the contrast value to see it.

According to Anthony Colaprete, head of the team, the plume brightness was 'at the low end of our predictions.' (Do'h - that's why you didn't give us our show!)

Because I think of ice crystals as being bright, this does not seem positive for water, but that is probably an extremely naive interpretation. Much more to the point, the L-CROSS team evidently got plenty of good data, and over the next few weeks we may start to hear what they are learning from it.

Thursday, October 15, 2009

The Time Scale of Space II - Travel

A couple of posts back I looked at the historical time scale of space. Now let's look at the human time scale, the pace of travel.

We know how long this takes with current technology: about 9 months to Mars, and in the example of Cassini, three years to its Jupiter flyby and seven years to Saturn. Happily we do not have the choice of chemfuel or waiting for magic; the Dawn mission to Ceres and Vesta is already using that classic SF standby, ion drive. This is not suitable for large, human-carrying spacecraft, but other electric drives are.

Drive details matter less than the drive's power output, because for deep space travel with Realistic [TM] high specific impulse drives we must be concerned not only with speed (technically, delta v) but also acceleration. High specific impulse drives require enormous power in relation to thrust, and a top speed of 100 km/s will not get you to Mars quickly if it takes you a year to build up to it.

My convenient figure of merit for drive power density is one kilowatt per kilogram - on the same order as gasoline engines (and about 10x better than present day shipboard nuclear power plants.) At this power density, a drive with an exhaust velocity of 50 km/s has a thrust/mass ratio of 0.004, meaning it can just push itself along at 4 milligees. Attached to a ship, it might might waft it forward at 1 milligee or so.

By the bone crushing standards of SF acceleration - or actual Earth liftoff - this is feeble stuff, less than freight train acceleration. But keep it up for a month and you're booking along at 25 km/s - well above solar escape velocity for a tangential burn departing Earth's orbit.

Here are outline characteristics for a small ship, with a 100 megawatt power plant and full load mass of 750 tons, half of it propellant:

Drive engine, 100 tons
Tankage and structure, 75 tons
Payload section, 200 tons

Propellant, 375 tons

Given an exhaust velocity of 50 km/s this ship has a mission delta v of 34.7 km/s. It burns off propellant at 80 grams/second for a total burn time of 4.375 million seconds, 51 days, giving it an average acceleration of 0.81 milligees. It can reach Mars in about three months - its delta v is sufficient for a two month orbit, but the prolonged burns will add another month; in fact, the ship is under power for more than half the trip.

Replace the payload section with a much larger one, 750 tons, and mission delta v falls to 17.0 km/s, just enough for the Hohmann transfer to Mars, plus the (inefficient) spirals a low-thrust ship must use to enter and leave a planetary gravity well. This is good enough for slow freight, which in a thriving space economy will be the great majority of traffic.

All of these details are pretty arbitrary, except for the important ones, the basic relationships of drive power output, acceleration, and specific impulse that determine how fast you can get wherever you are trying to go.

Our concern is with passenger traffic in the broad sense, human travel, and for that we want fast orbits. Orbit calculations are far above my math pay grade. Happily the Atomic Rockets site has a wealth of information plus some handy links. For those who want to play along at home, this online calculator will give you the orbit parameters, delta v requirement, and travel time for orbits ranging from the economical Hohmann transfer to semi-fast orbits at just below solar escape speed. For faster orbits a flat space approximation starts to give decent results.

For travel in the inner Solar System, at least out to Mars, I am partial to solar electric drive. It has about as good a prospect as nuke electric does of hitting the 1 kW/kg benchmark, and it has the enormous virtue of having practically no moving parts. Whereas a nuclear electric plant is the ultimate steampunk maintenance nightmare, a steam engine in space.

The only problem with solar electric is that it gasps for light beyond the orbit of Mars. Sunlight at Ceres has only a seventh of its intensity at Earth, so a drive good for 1 km/s per day at 1 AU now takes a week to put on 1 km/s. A trip that might take 6 months by nuclear electric drive might take 9 months by solar electric due to sluggish performance in the asteroid belt.

For outer system exploration a VASIMR style variable specific impulse drive also becomes handy, and is probably not too difficult to achieve. If, for a given drive power output, you double the specific impulse and halve your thrust and thus acceleration, your total power requirement is (ideally) unchanged, but total delta v is doubled, while your propellant consumption falls by a factor of four.

The result? With a VASIMR type drive, travel time increases not in direct proportion to distance, but as the 2/3 root of distance. Suitably tuned, the drive outlined here reaches the main asteroid belt in about 6 months, Jupiter in a year, Saturn in a year and a half, Neptune in three years, and Eris, beyond the Kuiper Belt near 90 AU, in about 7 years. (These are careful guesses, not worked out orbits!)

In rocketpunk days they did not blink at multi-year journeys, and you could say that the true first orbital mission was Magellan's, three years to go once around. We can explore Jupiter and Saturn; human missions to the outer planets and beyond are problematic, at this techlevel, on human factors grounds.

I've suggested that a benchmark for 'routine' travel is about three months, experience with submarines showing that being cooped in a can becomes progressively difficult beyond this time. Even aboard luxury liners, shipboard romances start getting complicated, and threats to the piano player get serious. Oh yes, also the little detail of radiation - the longer your travel time, the more shielding you need, meaning penalty mass.

This doesn't mean that we can't go to the asteroid belt, especially if it turns out to be full of Valuable Asteroid Stuff; it just means that cabin fever becomes a challenge. (As does radiation shielding.)

For the bloodthirsty among my readers, which is most of you, note that warlike expeditions will tend to follow slower orbits than civil passenger transports, because they had better carry delta v for a round trip, or least an abort to a friendly base. Drop tanks won't really speed you up, because their mass reduces acceleration, making transfer burns more sluggish. For a faster military trip you'll have to revert to staging, and ditch power plants as well as tanks.

Faster travel would be helpful - for peaceful as well as warlike purposes - but speeding things up will be surprisingly difficult. For faster orbits we must increase not only peak speed but acceleration; in fact, for brachistochrone and semi-brachistochrone orbits the required acceleration goes up as the square of peak speed. (To make the trip in half the time you must go twice as fast in half the time, calling for four times the acceleration.)

Halving travel time - three months to Ceres, six months to Jupiter - thus requires an eightfold increase in drive power density, into the same range as jet engines, several kilowatts per kilogram. For this we will probably need a drive that generates its power directly, rather than requiring a separate power plant. Fusion drive is the classic if speculative example, though there are alternatives.

So what does all of this mean? For some period in the midfuture, perhaps a lengthy one, the pace of travel will be more or less as outlined here - about three months to Mars, six to Ceres and other points in the main asteroid belt, a year to Jupiter. Coming next, a look at the social and political implications of these travel times.

Related post: Last year I wrote a bit on getting around the Solar System, under much the same tech assumptions I've described here.

Friday, October 9, 2009

Dark Flash

There is a story, no doubt apocryphal, about a cub reporter sent on his first assignment to cover a society wedding. He came back to tell his editor that there was no story because the groom never showed up.

This morning's L-CROSS mission press conference, which I just got done watching on NASA television, had a bit of that flavor. The underlying interest in L-CROSS centers on the search for lunar ice. But the short term payoff - the Hollywood money shot - was the bright plume that the Centaur stage impact was supposed to kick up from the lunar surface, expected to be visible from Earth through observatory telescopes.

No plume was visible, at least not in the early results. And it was clear at the press conference that neither the mission team nor the assembled media knew quite what to make of it. The mission team put on its dog and pony show, without the pony - even showing video footage that showed nothing but the shadowed floor of Cabeus crater. The media seemed just a bit annoyed at not getting their expected show. Not until near the end of the question period did anyone ask the question on my mind: What does it tell us that we didn't see the expected plume?

Apart from the missing - or unexpectedly dim - plume, the impact clearly yielded some 'interesting' data. Whatever happened to the debris plume, spectrometers took post-impact spectra that were clearly different from pre-impact spectra. A small (barely more than one pixel, about 20 meters) but conspicuous impact crater was imaged by L-CROSS just before it too impacted, and the mission team noted something else they evidently did not expect, a sodium flash.

Did the spectra also have any hint of water? (Or not?) The mission team was cagey about that, as you'd expect they would be unless Cabeus had erupted like a broken fire hydrant. When the head guy (I missed his name) said he hadn't yet examined the spectra for hints of water, a reporter drew laughs by saying 'Oh, come on!' But the mission scientist kept his poker face, and I can't guess whether he did or didn't see water indicators.

Perhaps most likely it is genuinely too early to tell. They saw something, including indicators of sodium, so conspicuous (and in a sense so uncontroversial) they could mention it even in this early going. But it will take analysis of the results to know what else they did or didn't find.

The one thing clear is that L-CROSS delivered a surprise, a dog that did not bark in the night.

Tuesday, October 6, 2009

The Time Scale of Space

Interplanetary Spacecraft
When is the space future supposed to happen? The question is raised by comments on the last couple of posts, especially some of Jean Remy's observations. Among space minded people today a sense of frustration and stagnation is pervasive. But this is largely a result of distorted historical perspective.

We entered space with a spectacular splash, due to particular circumstances, AKA the Space Race. Rather than working up gradually to a lunar expedition by building an orbital station first, as expected in the 1950s, we took it in one straight shot, then woke up with moon rocks in our pockets and a great big hangover. We did what? We went where?

Just as unexpectedly, satellites took over most of the jobs that the 1950s assigned to a space station. Instead of having immediate (and valuable/profitable) tasks, such as weather observation and telecoms relay, a space station is needed only for long term development. The same can be said of human spaceflight itself. Robotic spacecraft serve our current practical needs very well, and they are carrying out our first reconnaissance of the Solar System faster than anyone in the 1950s dreamed. We are not sending people up to watch hurricanes, we are sending them up to learn how to live and work in space.

True, there is a short-term crisis in US human spaceflight - our current architecture is nearing retirement, and its replacement is over budget and behind schedule at best, at worst a major Washington boondoggle. This is a temporary and parochial concern. Abandoning a reusable shuttle in favor of an 'old fashioned' capsule also feels like retrogression, but it merely accepts a reality: The Shuttle, like the Great Eastern, was too much too soon. The technology is not mature enough for an efficiently reusable vehicle, and the traffic does justify one.

Meanwhile people like Burt Rutan are experimenting with lower cost approaches to launch and initial ascent. Whether or not suborbital tourism succeeds as a business, and it might, this work will pay off when the launch market reaches the point of demanding reusable craft.

So what might we expect from here?

The current year round population in space is six. Suppose it were to grow, through the usual fits and starts, at an average 4 percent per year. First we'll try this out on the past. Run backward from 2009, this growth rate gives us three people in space in 1991 - about when Mir entered full service - and one person in 1963, soon after we started traveling in space at all. As predictions of the past go this is imperfect but not bad.

Now let's apply it to the future. Over the next few decades, growth is glacially slow:

2025: 11 people
2050: 30
2075: 80

So two generations from now there are still only 80 people living in space - barely enough for a robust orbital station and minimal outposts on the Moon and Mars. The space population passes 100 in 2081, and by 2101 there are a shade over 220 people in space - just enough, perhaps, to support the sort of travel infrastructure that the movie 2001 pictured for a century earlier.

But in the 22nd century, compound arithmetic starts to kick in:

2125: 568
2150: 1513
2175: 4034
2200: 10,753

More than ten thousand people in space is a lot. At this point the human Solar System begins to resemble our familiar image - large orbital stations; regular scheduled passenger service at least to the Moon and perhaps to Mars; space based industries - surely propellant production, likely some mining and fabrication as well.

Continue the same growth rate until 2300 and there are more than half a million people in space, the equivalent of a medium sized city and suggestive of at least incipient colonization.

Any compounding formula, carried far enough, becomes absurd. This one gives 1.4 billion people in space in 2500 and 3.5 trillion in 2700. In real life such trends bump up against something. Short of magitech on the one hand or catastrophe on the other, living in space will remain more difficult and costly than on Earth, so the population will probably settle in at some modest fraction of Earth's population - which might mean anything from a few hundred people to a few million.

But the real point is that the time scale examined here is not so different from the classic time scale of the rocketpunk era. Heinlein, after his early (and wildly space-optimistic) Future History, got cagey about specific dates. But the interplanetary futures of Space Cadet or The Rolling Stones generally seem to be set around the 22nd century, and much the same for Clarke's hard SF, aside from books directly linked to 2001. The scale of things was closer to what my formula predicts for the 23rd century. But a few decades this way or that, or even 100 years, is nearly a quibble on the time scale of centuries.

The truth is that human expansion into the Solar System was always going to be gradual, because the Solar System is so big. 'Murricans should have been particular aware of this, because of the prolonged colonial prelude to our national experience. It was 115 years from Columbus to Jamestown, and another 168 years to the the Declaration of Independence. On the same time scale, starting from 1969, we might expect the founding of Luna Base in 2084 and the inevitable Revolt of the Colonies in 2252.

Viewed in large historical perspective our space progress is just about on schedule.

Image of proposed HOPE Callisto mission ship via Atomic Rockets.

Related posts: I discussed our rate of progress on the 39th anniversary of Apollo.

Sunday, October 4, 2009

Some Sunday Afternoon Reading

A couple of links I have come across that relate to the last few posts on space access and space costs.

When Rocket Science Meets the Dismal Science. An analysis of orbit lift costs that uses much the same method I do, and reaches a similar result. (Which is reassuring!) In a nutshell, reusable orbiters are bigger, more complicated, more cantankerous, and therefore more expensive to build and fly than expendables are. Therefore you need a lot of traffic before they pay off.

Space Cynics. This blog isn't cynical about space itself, but it is a bit cynical - and not without justification - about what they call the 'alt-space' movement and (would-be) industry. Not guys like Rutan, who has a track record, but too many people who are fueled by technological and economic wishful thinking.

I have been harping on this subject a lot lately because it is so central to the enterprise of space. Things have not happened nearly as quickly as we expected. But the space community has been more evangelical than analytical about it. Somewhat meta, but how much have we really thought about the human presence in space since the rocketpunk era?

Back to links, and now on the nuts & bolts side, Space Launch Report is a handy site for finding out what is actually going up there. I was looking for year-by-year launch totals and found them here, at least back to 1998, along with descriptions of recent launches and a nice series on the Thor IRBM and its evolution into the Delta space booster.

Wednesday, September 30, 2009

Building Things in Space

Structural Fabrication Work
Construction in space, remarkably and wonderfully, is something we know that we can do, because we have done it. And it is worth saying something about, if only as a change from the distressingly popular subject of blowing things up in space.

To be sure, what we do now is only the final stage of assembly, and from kits. We all know how smoothly that can go. Like rendezvous and docking it might easily have been impractical, but it works about as well in real life as it did in Heinlein stories.

Thus we can build our ships in space, as big as we need them to be, instead of having to launch them all up from Earth. In this as in so much else, the ISS amounts to a training mission for deep space travel.

Actual fabrication of structures is another matter, but we are not likely to do it (other than as an experiment), or need to do it, for quite a long time to come. The reason lies in the odd economics of space travel, and Cobb's Law. If orbit lift is cheap, we can bring up the things we need. If it isn't cheap, we aren't up there either.

Cheap is a relative term when it comes to space travel, but I'll resort to my standard rule of thumb and say that with technical and economic maturity the major component parts of a spaceship - hab pods, tanks, drive units, radiator panels; some assembly required - might cost roughly a million dollars a ton, here on Earth at the factory gate. Launching them into space, along with assembly crews, might cost another $1 million a ton, making the on orbit flyaway cost $2 million per ton.

The good news is that this places deep space craft in the same broad range of cost, size for size and mass for mass, as jetliners, of which thousands are in regular service. The bad news is that the lunar spacecraft industry is strangled in the crib. It has no market unless its production cost at the factory cargo airlock can be brought down to twice Earth production cost at the factory gate. That is an awfully tough standard for a new industry on a new planet.

(If lift cost to orbit can be brought down to $100,000 per ton - which calls for the magic of heavy traffic demand, supporting regular flights by production vehicles - even food production is cast in doubt. $450/lb is a lot to pay for cornflakes. But cheap local produce from the ecohab is only cheap after someone has built the hab, and mastered space gardening techniques.)

More complete fabrication in space will grow partly out of special requirements for structures too big to lift and not suited to snap-together construction. But more than that it will evolve from the duct tape side of the equation. People will start modifying pods, authorized or otherwise. Over decades a boneyard of old structures and equipment will accumulate, begging to be repurposed. Orbital (or lunar, etc.) machine shops will appear to do this work.

And the machine shop is pretty much the basis for all industrial technology, a production line being simply a series of machine tools lined up and set up to run a standard job repeatedly.

Once space facilities can fabricate their own structures, the 'supply chain' economics changes. Now the lunar industry doesn't have to compete in the market for expensive prefabricated pods, but for much cheaper rolled aluminum and the like. Raw aluminum currently costs on order of $3000 per ton - even if the lunar cost were ten times greater, it would be cheaper than 'cheap' orbit lift.

A note of caution. As always in space economics there are some devils in the details. Inherently the trip from the lunar surface to lunar orbit and back, a round trip delta v of 3.2 km/s, is much cheaper than from Earth to LEO. A sensible, single stage vehicle can do it. But it will only be cheap when there is enough lunar traffic for frequent service, so that economies of scale can start to kick in.

So a lunar industry may have to start big - perhaps meaning for political reasons - to permit economies of scale in transportation, and likely in production as well. In the pristine world of economics there is no particular reason for this to happen, suggesting that politics might rear its ugly head.

Therein, presumably, would lie a tale.

Image from Atomic Rockets.

Related post: A Solar System For This Century.