Sunday, August 30, 2009

Exoplanet Incineration

If anything makes a planet a less promising candidate for colonization that orbiting so close to its parent star that the dayside hemisphere is heated to 2400 K, it is the prospect that said planet is on the brink of its final swan dive, about to plunge into the star. But that is just the spectacle that Sky & Telescope offers in its latest indulgence in gratuitous celestial violence.

The doomed planet, Wasp-18b, was never going to be a prime colonization spot at any distance from its stellar parent, since it is about 10 times the mass of Jupiter, only slightly below the 13 Jupiter mass lower limit for brown dwarfs. If it ever had moons it lost them when it migrated inward from where it formed (by current theory), beyond the 'snow line, to its present close orbit just 2.2 million km above the surface of the star Wasp-18 itself. This star is no red dwarf, but a sunlike star, class F6 (a bit hotter than the Sun), and about a billion years old.

Tidal forces should doom the planet in no more than a million years. Orbiting much faster than the star's period of rotation, it is tidally spinning up the star - and spinning itself down in the process, transferring its orbital angular momentum to the stellar parent that will presently dine on it. (Two myths for the price of one - Chronos eating his children and Icarus flying too close to the sun.)

The odds of us finding a planet so near to its final plunge are likened to the chances of drawing two red aces - rare, but not flukishly so. Which doesn't keep the article from indulging in a little pr0n about how All Our Theories Could be Wrong. But a doomed planet is not all that unlikely, and a lot more fun.

Related links: I recently contemplated the demise of Betelgeuse, and colliding protoplanets.

Thursday, August 27, 2009

Space Warfare VII: Kinetics, Part 2 - The Killer Bus

If we are dealing with deep space warfare, interplanetary or interstellar, we are probably in a setting with regular, extensive space travel, passengers and freight. These people throw a lot of luggage around, and they throw it fast. The whole interplanetary economy is based on their ability to do so, and do it (relatively) cheaply. Which makes kinetics, unlike lasers or other weapons, a 'natural' outgrowth of civil space travel.

So, why build a costly 10,000 ton space battlecruiser just to deliver a few dozen kinetic missiles of a few tons each? Cut out the middleman. Build a 10,000 ton killer bus - or buy an obsolescent cargo hauler at scrap price. It won't be cheap, but it will be a great deal cheaper than a reusable warcraft, and it allows you to use its full delta v to build up impact speed, and its entire mass (less expended fuel) as punch. A few thousand tons of that mass can go into an armor faceplate, making it harder to zap.

Now let's throw some luggage. Suppose a closing rate of 30 km/s, and assume that defensive laser fire will burn through the armor and wreck the bus at 3000 km = 100 seconds from the target. At that point the bursting charges go off and break up the bus into a cloud of fragments. Big ones and little ones, but say they average 10 kg - a million of them, delivering an average punch equal to rather more than a ton of TNT.

Let the wreckage fly apart at up to 25 meters per second. When the fragment cloud passes the target it will be 5 km across, with a cross section of about 20 million square meters - meaning a chunk of nasty for every 20 square meters of target cross section. Now, just how big is your laser battlestar? If it is 20 meters in diameter across the aspect facing the attack, it is in line for about 15 whacks, giving you 6 or 7 seconds of zapping time per frag on collision course.

The total mass you need to zap is about 150 kg, requiring up to 8 gigajoules to fully vaporize - thus average beam power of 80 MW. (And you'll generate up to a couple of dozen GJ of waste heat you'll have to get rid of, if you survive.) You can probably get away with less beam power by slapping frags aside instead of fully vaporizing them, but this is fairly unpredictable. And in orbital space you'll have a complex computational problem determining which four out of those million or so frags you need to zap. Plus, I'll let my killer bus carry a few dozen kinetic target seekers, released just before the bus frags, so the target seekers are mixed into the clutter of fragments till they light up their deflect motors to make intercept in the last few seconds.

Or you can sidestep the entire fragment cloud with a fairly modest lateral burn - a minimum 25 meters per second, though you had better add some safety margin, and unless you have very powerful deflect thrusters you must allow for acceleration time. Minimum acceleration is 50 milligees, pushing you to 50 meters per second, but again some safety margin is wise. This is a basic limitation of (unguided) kinetics - they can be sidestepped, which beams cannot be at less than light-second ranges.

You also have the option of turning the killer bus's closing rate against it by attacking it with kinetics - which can be launched along its track well in advance, at no great speed relative to you, since you see the killer bus coming and know you're at the end of the line. This is a Kirklin mine, named for Kirk Spencer, who proposed them on SFConsim-l. The countermeasure is another, smaller Kirklin mine, leading to a theoretically infinite regress of counter-counter-countermines. In practice it granulates at the minimim size/cost of effective guidance or buckshot-aiming.

Bear in mind that I am discussing a fairly modest midfuture tech. If you have uber-fast drive engines you can have much faster kinetics - with destructive effect going up as the square of velocity, while the evasion/countermeasures time window goes down inverse linear to velocity.

A killer bus is not an elegant weapon - but we are discussing battles, not costume balls. It is a brute force weapon, prose in motion, but it relies on standard transport technology that every spacefaring society will have. For this reason I tend to think of kinetics as particularly appropriate in less intensely militarized settings, such as rival trade federations that can raise semi-scratch forces in a crisis. (Of course, other industrial applications might also make high power laser tech readily available.)

And there is another curious property of kinetics that I only thought of while writing this. If your primary weapon is kinetics, most of your military procurement is expendables. A laser-armed enemy finds that their lasers are all 'defensive,' because you really have few if any targets to use offensive lasers against. There is not really much reason for kinetic-missile battlecruisers. Against the most heavily defended targets you expend a killer bus; against lesser targets you can deploy kinetics from modified transport types, with the only 'warships' being rear echelon sensor and command platforms.

In short, kinetics and lasers are not just alternate weapon options, they are highly 'assymetrical.' In the current era this has the connotation of insurgency, but in past era main forces of major powers have sometimes been similarly assymetrical - think Roman legions versus Parthian horse archers. If the tech is such that the weapons are in approximate balance, they may be deployed by different types of polities (or other power-exercising entities). Or, lasers may be the characteristic weapon of operational defense, deployed aboard orbital battle stations, while kinetics, which like to be thrown fast, are a characteristic weapon of attack.

Related links: Another kinetic weapon, the 'Lancer,' was discussed in my post on space fighters. And previously in this series:

I - The Gravity Well
II - Stealth Reconsidered
III - 'Warships' in Space?
IV - Mobility
V - Laser Weapons
VI - Kinetics, Part 1

Tuesday, August 25, 2009

Space Warfare VI: Kinetics, Part 1

Space travel technology is largely about making vehicles go really, really fast. So it is a bit surprising that kinetic weapons have played such a minor role in science fiction space battles. They never appeared in any story I recall reading when I was growing up - in fact, I don't recall ever reading a story that featured kinetics used against enemy spacecraft. [But see update below.]

'Strategic' kinetic bombardment of planets appeared in Heinlein's The Moon is a Harsh Mistress, and has been popular for slagging planets ever since we learned what an asteroid impact did to the dinosaurs. But using asteroids as bombs is lame. If you are out to wipe out a planet, just nuke the bejeezus out of it rather than spending months or years deflecting an asteroid. So much for kinetic WMD. The remainder of this discussion is about tactical combat between spacecraft, i.e. Space Battles. And because it came out long, I've split it into two posts.

Curiously enough, the first - and often prescient - known attempt to describe Realistic [TM] space tactics, by Malcolm Jameson in 1939 (scroll down a couple of screens) did feature kinetic 'mines,' but the idea was not taken up. Death rays remained far more popular in the early Golden Age, while the rocketpunk era, though more given to missiles, assumed they would carry nukes. It was the 1950s, after all, the age of nuclear hand grenades. At least they were rocket propelled! Current generation ABM technology does use kinetic weapons (kinetic kill vehicles, KKVs, being the favored jargon). But they still haven't caught on in science fiction.

The basic metric of kinetic weapons is that anything hitting you at 3 km/s - a rock, a throw pillow, whatever - delivers 4.5 megajoules of kinetic energy per kg of mass. For comparison, TNT delivers about 4.2 megajoules, meaning that at impact speeds much above 3 km/s a conventional explosive warhead merely adds insult to injury. And kinetic energy goes up with the square of velocity, so an impactor hitting at 100 km/s delivers a whallop equal to about 1000 times its mass in TNT. This is Robinson's First Law, and someone at SFConsim-l duly coined the 'Rick' as a measure of kinetic punch. As a rough and ready measure, Ricks = (Vi / 3)^2, where Vi is impact velocity.

Now, 3 km/s is pretty much the slow end of space speeds. Your encounter speed will probably be at least that much unless you make an orbit matching burn before the shooting starts. Spacecraft with electric drive - which are likely in any setting with regular human interplanetary travel - can be expected to go around ten times faster, give or take, thus delivering a whallop of ~100 Ricks. Smack! That will hurt.

Which actually casts a bit of doubt on the familiar image of kinetic missiles, at least for offensive use. If your encounter speed is 30 km/s (or even a 10 km/s stroll) there is not much need for a booster stage - just toss your kinetics out the hatch. Yes, they'll need a deflect motor to steer them into the target, but your encounter speed will do the heavy work. Guidance issues aside, Jameson had it pretty much right back in 1939.

Purple/Green. This is the popular expression, in the haunts of SFConsim-l and similar places, for the unending debate about missiles v lasers. The argument boils down to saying that while kinetics can be launched from outside laser range, they have to pass through laser range to hit a target, giving defensive lasers a chance to zap them first. The most effective zapping is at relatively long range, wrecking the guidance system and deflect motor so that the kinetic misses. Neener neener neener.

Of course, even a lump of molten wreckage will do it for you if it hits you anyway. A favored solution of mine is kinetic fragmentation, the shotgun approach. Place a small bursting charge in a big kinetic target seeker. If it is crippled it blows itself apart into a cloud of fragments, and (depending on burst range, etc.) one or two will hit, unless they are zapped to a fare-thee-well, vaporizing them. Or at least partly vaporizing them, the flash-off of the vaporized portion (maybe) serving to knock them aside.

As seen by the target, the dangerous fragments are the ones that appears to hang in one place - if a frag shows any lateral drift, it is on its way to missing you. This simplifies defensive targeting - at least in flat space. In orbital space, however, you are swinging at curveballs - and batting .300 probably won't be good enough. In orbital space the problem of determining which frags might hit you is, shall we say, non-trivial.

But for the kinetic attacker, the most effective countermeasure to laser defense may be simply to throw a lot of mass. The more you throw, the more the defender has to zap, and at some point you overwhelm him. Which is why the second part of this discussion will propose a new kinetic weapon: the Killer Bus.

Update: I was mistaken; I did read a book in my teens that featured kinetics: Arthur Clarke's Earthlight. See the comments thread for some details.

Saturday, August 22, 2009

Bad Science Fiction & Fantasy Book Covers

Via Carla, for your weekend entertainment and edification, a wonderfully British site, Good Show Sir.

Little further discussion on my part is required. On the whole, and consistent with my bookstore experience, fantasy covers are worse than SF covers, but SF-oriented Baen Books seems to be staking a claim as the capital of the bad-cover universe.

Thursday, August 20, 2009

Yesterday's Tech Revolutions: Galleasses

English galleass Hart, 1546

Naval planners in the early 16th century had a problem. None of them knew that they were 'naval planners,' but that was not a problem. They knew their assignment: To build warships for the King of England, or the Most Serene Republic of Venice, or at any rate for someone. Their problem was that that some years earlier the French had applied bell making technology to heavy guns, with spectacular results.

The new generation of artillery, bronze muzzle-loading cannons and culverins, were lighter than conventional bombards, safer and more reliable, and immensely more powerful. On land they rendered all existing fortifications obsolete and brought about a new type of fort, the trace italienne, built low and massive behind a ditch – the prototype of 18th century Vauban forts, and ultimately of fortifications up to and including present day firebases.

At sea the new heavy guns were equally problematic. Medieval naval warfare followed a combined arms doctrine, a mix of slow but sturdy and high-built round ships, similar to large transports and functioning as mobile castles, and faster, low-built rowing ships, galleys and smaller 'barges,' that served roughly as seagoing cavalry. The rowing ships had offensive punch (including putting troops ashore), while the big round ships provided defensive strength and logistic support.

Both types could be adapted to carry heavy guns. Galleys carried them above the prow, 'keel mounted,' serving as a super-ram or (more often in practice) to give a blast at 'cloth burning range' across the deck of an enemy ship just before boarding it. Lofty round ships were suddenly far more vulnerable to direct galley attack. Soon after 1500 a partial solution was found: The big ships could also carry heavy guns mounted on the lower decks, positioned to provide all-round defensive fire (though firing directly forward remained a problem). Henry VIII's Mary Rose, build in 1509, sunk in 1545, and recovered from the seabed of Portsmouth in 1982, was an early example of the type.

Mounting a dozen or so bronze great-guns aboard a carrack was very expensive, and while the resulting ship could stand up to galley attack it was inflexible and could not take the initiative against much more maneuverable galleys. Planners looked for alternative ways to bring heavy guns into play at sea, and hit on a couple of related solutions. The ship pictured above, the English 'galleass' Hart, built in 1546 – by no accident soon after the loss of the Mary Rose – was one of them.

In overall design Hart, like her near-sisters Tiger, Bull, and Antelope, is a fairly large sailing ship, with four masts as was common at the time, but longer and narrower than usual and without the lofty fighting 'castles' fore and aft. Her relatively cut-down prow allows her to carry heavy guns firing forward over her galley-style beak, and she carries a row of medium-caliber guns along the broadside of her upper deck above oar ports on her lower deck.

Her mission was to serve as an anti-galley escort. Though slower than the French galleys she was intended to fight she could at least force them back with her heavy bow guns. And if the galleys swarmed in, even though she lacked the high fighting castles of conventional big ships her powerful secondary armament could give them a very hot reception.

These 'galleasses' performed very well in skirmishes against galley squadrons. The Venetians, about the same time, built galleasses of quite different design (oversized galleys, converted from merchant galley hulls) but similar mission, and they did an impressive job of shooting up Turkish galleys in the opening stages of the Battle of Lepanto in 1571. The Venetian galleass type is the one usually mentioned in modern books, though it turned out to be a dead end largely because of geostrategic developments that sidelined the Mediterranean in the 17th century.

Galleasses of the English type, however, had a big future ahead of them – and not one their designers originally had in mind. Probably they were not an English invention, most likely originating in Spain or Portugal, though Henry VIII built one big ship of the type, called simply the Great Galley, as early as 1515. Though effective against galleys they were pigs under oar-power – but swans under sail. And their broadside secondary armament, intended for defense against swarming galleys, turned out to be highly effective in offense.

So larger versions abandoned the lower-deck oars, replacing them with more broadside guns, until the secondary armament became the main armament. This variant type got a variant name, galleon, and ended up as the ancestor of the classic broadside-armed sailing man-of-war. (Some smaller models retained oars well into the 18th century – in an unusual Hollywood concession to accuracy the Black Pearl in 'Pirates of the Caribbean' is fitted for sweeps, as was Captain Kidd's rather similar ship, Adventure Galley.)

No, I am not recommending space galleasses for your constellations of combat spacecraft, though aerial galleasses might fit nicely into those flying-ship settings for graphic novels. But the evolution of the galleass, from anti-galley ship to the ancestor of the frigate and two-decker, is a good example of the impact of changing technology and requirements. Space warcraft of a future era may well develop over time in a comparable way, designed initially for one mission and gradually tranformed to perform a very different one involving different primary weapons and tactics.

This blog has a known weakness for the 16th century, particularly its women, real or fictitious.

Tuesday, August 18, 2009

A Sky Without Betelgeuse?

Orion's premier red supergiant was the first star ever to have its diameter measured by interferometry, and the first to be directly imaged as a disk, by the Hubble in 1996. Only a handful of extrasolar stars can be thus observed, Betelgeuse and Antares among them. This image of Betelgeuse is a new one, reported in Sky & Telescope a couple of weeks ago. (Yes, I'm playing catch-up here.)

Betelgeuse's stellar stats are widely available but always worth repeating. At 640 light years away it is one of the nearer supergiants, with a total luminosity (mostly in the IR) about 100,000 times brighter than the Sun. The measured diameter depends on the wavelength you use - the star probably has no sharply defined surface - but comes to about 900 solar diameters, comparable to the size of the asteroid belt.

And astronomically speaking, it is not long for our sky. An artist's conception shows it boiling ominously, with bubbles the size of the orbit of Mars. Betelgeuse is blowing off an Earth mass or so every year, and - also rather ominous - its diameter seems to have decreased about 15 percent in the last 15 years.

In fact, Betelgeuse is in a pre-supernova state ... but just how pre-? I initially misread one of the researchers' linked press releases, saying that it expected to blow 'in the next few thousand to hundred thousand years' as 'in the next thousand years.' It sort of jolted me. But even the correct statement amounts, in astrophysical terms, to any time now.

Whenever Betelgeuse goes off, it will be hard to miss. No supernova has been observed in the Milky Way since 1604, and the brightest recorded one, in the year 1004, was of a star 7100 light years away - more then 10 times the distance to Betelgeuse. The supernova of 1054, that formed the Crab Nebula, was 4000 light years away. The Geminga supernova was only some 550 light years away, but it went off 300,000 years ago.

So the Betelgeuse supernova will be at least dozens of times brighter than any observed in the historical era, perhaps a hundred times brighter, nearly as bright as a full moon. Wow!

Yet afterwards, as the first commenter on the Sky & Telescope article noted, it will be rather strange not to have the familiar figure of noble Orion in the sky anymore. It is the first constellation I ever recognized, and because at the start of each season I see it rising in the southeast, on its side, I think of its figure as representing not a giant but an exotic stringed instrument, its strings running from Betelgeuse to Rigel, with the Belt stars as pegs on the soundboard. Without Betelgeuse the instrument's symmetry will be broken, the music of the spheres altered.

But if you gotta go, what a spectacular exit!

Related links: I previously wrote about the pleasures of both sky observing and, more recently, armchair astronomy.

Monday, August 17, 2009

Tough Guide: Nanotech

There are two types of nano-scaled machines in the Known Galaxy. One kind does the same things that other machines do, only smaller. They scrape scale off the insides of microtubes, or the plaque off your teeth, which is why dental assistants are unknown on the more advanced Planets. Nano-touchscreens were a failure, because even Really Aliens lack tentacles small enough to use them. Taken as a group, such nanomachines are pervasive and commonplace, fascinating to tech geeks but ignored by everyone else, especially since you can't see them except through an expensive nanoscope.

The other kind of nanomachine does everything, and does it faster and cheaper, leaving the mere laws of physics and mechanics in the dust - well, not quite dust. Especially, these nanomachines make more nanomachines, which ought to give any Planets that develop this form of nanotech an enormous industrial advantage over everyone else. Unfortunately, what nanomachines of this type do best is to turn everything in reach into gray goo, including Planets so careless as to invent them. This must effectively limit their spread, since the Known Galaxy has not yet been turned into gray goo.

Nanotech of the gray goo type seems to have had a brief period of vogue in SF in the years around the turn of the third millenium CE. After a short time, however, the nanotech subgenre vanished, leaving no identifiable traces. It is speculated that all such works, along with their authors, were turned into gray goo.

Related links: Here is the original Tough Guide to the Known Galaxy. This blog previously took on Elevators and the Singularity.

Thursday, August 13, 2009

My Other New Blog: TecTrends Monitor

I am now blogging about tech industry trends and news for an SF Bay Area company, TecTrends / Information Sources. I've been reading and summarizing tech press articles for them for a while, and started noticing patterns of articles, trends that show up in several trade journals at about the same time. I suggested a blog to discuss these trends, they liked the idea, and we launched it yesterday.

Right now the blog, TecTrends Monitor, is extremely plain vanilla - Wordpress does very little hand holding, and I'll have to figure out style sheets and such before I can do things like adding the company logo to the header. And so far the only post is my welcome message. Drop by and leave a comment anyway!

Posting will be fairly sporadic at first, due to budget constraints, but I'm looking forward to this! (No, of course I won't be deserting Rocketpunk Manifesto - bloggo ergo sum!) If the comment threads are anything to go by, my readership here is not lacking in tech geekitude, so some of you might want to keep an eye on TecTrends Monitor in the weeks to come.

And getting paid to blog - how cool is that?

(While I'm at it, also a hat tip to The European Courier, where I write commentary about US politics more or less monthly.)

Tuesday, August 11, 2009

Worlds in Collision

Colliding protoplanets
Most exoplanet discoveries are no longer Big News, since the excellent Paris Observatory exoplanet site now lists nearly a planet for each day of the year. (Currently 360, to be exact.) But the discovery of ex-exoplanets still warrants special mention, and gets it from Sky & Telescope (plus a discussion thread at SFConsim-l, including a link to the original paper). A star with the catchy name HD 172555, a young, Vega-like Class A star 95 light years away in the constellation Pavo, is surrounded by what researchers using the Spitzer Space Telescope expected to be a protoplanetary disk.

Instead it turned out to be just the opposite – a debris ring from the collision of two protoplanetary bodies, estimated to be the size of Mercury and the Moon. The observed IR radiation comes from enough glassy silica dust to form an asteroid over 300 km across, along with about a hundred times that much SiO2 gas that hasn't condensed back into particles yet. Nothing was said about larger pieces of wreckage, which wouldn't be detectable with current instruments. The smashup was pretty recent, too, perhaps less than a thousand years ago, which is why we get to observe wreckage skidding across the freeway lanes, as it were.

A demolition derby phase is in fact an expected stage of planet formation, so all is not lost for HD 172555. Earth probably took a more glancing whack from a Mars-sized object in its early history, which wrote finis for the unlucky intruder in our orbital space, but knocked enough chrome detailing off Earth to coalesce into the Moon.

For your added entertainment value, Sky & Telescope links to this NASA video of what happens when protoplanets go bump in the night.

Related Links: In the early days of this blog I wrote twice about non-wrecked exoplanets.

Monday, August 10, 2009

Space Warfare V: Laser Weapons

Beams are the classic science fiction space weapon par excellence, ever since HG Wells' Martians zapped Edwardian England at the dawn of SF. For half a century they were almost pure magitech. Then came lasers, and laser weapons have now zapped targets in tests. What's more, they are almost precisely 'heat rays,' just like the ones in the pulps.

Over short distances, relative to the length of the laser itself, laser beams cheerfully ignore the inverse square law that governs ordinary light sources. But thanks to diffraction, over long distance they are effectively subject to it. The formula for the spread of a laser beam (via Atomic Rockets, of course) is a close cousin to the formula for telescope resolution:

RT = 0.61 * D * L / RL


RT = beam radius at target (m)
D = distance from laser emitter to target (m)
L = wavelength of laser beam (m, see table below)
RL = radius of laser lens or reflector (m)

So an ideal diffraction-limited laser zapping in the near IR, with a wavelength of 1000 nanometers firing through a 2-meter telescope, has a spot size of 12.2 cm at a range of 100 km. (Before you break out your calculators, remember that the formula uses radii while my example uses diameters.) If your laser has an average power output of 1 megawatt, each square centimeter is getting hit with about 8.5 kilowatts – about 850,000 times the intensity of sunlight at Earth's surface. The target surface will get very hot, very quickly.

The most refractory material we currently know of, graphite, requires some 50 MW MJ [oops, energy = megajoules, not power = megawatts] to vaporize 1 kg – roughly the energy of 12 kg of TNT – and has a density of about 2.2 g/cm3. Cutting to the chase, our beam will burn through it at not quite a millimeter per second. Most metals are much less resistant to heat, so the laser will burn through metal hulls way faster). But if you substitute a 5 meter mirror – or a 400 nanometer beam, at the short end of the visible spectrum – you'll burn a smaller hole at half a centimeter per second. Or it will have the same spot size and burn rate at 250 km.

Lesson: For a given beam power, the bigger the mirror and shorter the wavelength, the greater the effective range. And lasers cannons, at least in the classical IR-visible-UV band, probably won't look much like guns, but perhaps more like a TV satellite dish.

Let's get a bit more SFnal about it and specify a 100 nanometer UV laser firing through a 10-meter telescope, with beam power of 1 gigawatt and range of 5000 km. Our spot size is unchanged, but each square centimeter is now getting hit with about 8.5 MW, and you'll burn through a meter of graphite in a second. This is some serious zapping. Or you can achieve a 1 mm/second burn rate at 160,000 km, more than half a light second.

Of course there is a tech challenge or two: Operating a laser cannon is loosely comparable to mounting a jet engine at the eyepiece of an observatory grade telescope. You will produce waste heat greater than beam power, probably several times beam power. But all this merely makes it difficult, not impossible. Real lasers presumably won't be as good as ideal ones, but there's no inherent reason why they couldn't come reasonably close to diffraction-limited performance.

Venturing further into SFness, if you make it a 0.1 nm X-ray laser with a 10-meter aperture you now achieve the same spot size and beam intensity at 10 million km. Since that is half a light minute, the target now can dodge, and because X-ray telescopes require an enormous focal length, your laser - and therefore the ship carrying it - may have to be, oh, perhaps 8 km long (see comment thread).

So much for laser basics. Now for the consequences.

If you can see it, you can zap it, and vice versa. As noted above, laser spot size is closely related to telescope resolution. If you can focus the beam to a couple of dozen centimeters, that is also the resolution your sensors can gain, simply by looking through the telescope between pulses. Which means that lasers of this precision don't just score random hits like World War I battleships; they fire at specific points on the target surface. (If mechanical or thermal limits preclude this precision, you won't get the penetrating burn-throughs described above, just scars burned along the hull surface.)

Thus the objective won't just be to blast an enemy ship but to mission kill it by zeroing in on critical systems – such as armament. In a laser battle, if you can hit the other guy effectively at all you can shoot the gun out his hand. But it gets better. What happens when two lasers are zapping each other? Their targeting optics are pointing straight at each other – so the optics concentrate the incoming beam right onto the laser itself. I have no idea what the effect is, but it could easily be dramatic. Laser engagements lend themselves to a mutual eyeball frying contest. Whoever zaps first, probably wins.

But there is another and even more curious implication of laser combat. So far I've been talking about beams concentrated down to blowtorch intensity, kilowatts or metawatts per square centimeter, able to burn right through refractory materials by heating the surface to thousands of degrees K. But what about mere scorch intensity? Say, the 50 watts/cm2 that causes primary thermal burns to humans and sets paper on fire. This won't burn through armor, but it will likely burn out delicate components such as sensor elements, or at any rate saturate and 'dazzle' them.

Thus laser weapons can blind the enemy, temporarily or permanently, at much greater range than they can do serious physical damage to structures. Our first modest laser has a scorch range of 1300 km; the more SFnal one a scorch range of 2 million km … and the jumbo X-ray laser has a scorch range of 2 billion km, about 14 AU. Spot size (and targeting resolution) is wider by the same proportion, dozens of meters. More rugged sensors are the solution, but it seems likely that weapon lasers can dazzle or blind targets at several times the range at which they can burn through armor.

Realistic [TM] laser combat thus has rather little in common with the Hollywood image of gyrating ships zapping each other at smoothbore-cannon range. I'd argue that laser warcraft, like tanks, will typically have a single main weapon in order to provide it with the largest cost-effective optics and thus longer range. This may well be 'keel-mounted,' aimed by orienting the spacecraft (though the optics will likely provide for vernier adjustments).

Yes, this precludes maneuver while firing – but unless you're fighting at Stupendous Range, more than a light second, you can't dodge a laser beam anyway, while at ranges of hundreds or thousands of km tactical maneuver won't make much difference on the time scale of zapping. Railroad guns don't fire while the train is moving, and laser cannons will plausibly have equivalent constraints.

So if you want the furball combat effect, or anything close to it, you will need a workaround - such as an engagement in the clutter of orbital space, where the challenge is distinguishing hostiles from civil craft and stations you do not want to zap. Or, long range sensor blinding might produce a strange battle of lasers concealed behind armored ports, taking potshots like spaghetti-Western riflemen shooting from the windows of a ranch house.

The floor is open for discussion.

Related links: Previously in this series, The Gravity Well, Stealth Reconsidered, Space 'Warships', and Mobility. And earlier, my take on Space Fighters.

Wednesday, August 5, 2009

Science Fiction, Hard and Otherwise

Non-realistic space battle

This blog is not entirely about space, but space travel is, shall we say, a prominent topic of discussion. I recently got an email from a reader who made what might be a controversial observation: "I like my starships with a little bit of swoosh."

So, how much swoosh is a starship allowed to make, and who decides? One of the first good things I heard about Firefly, before I'd seen any episodes, was that it had a silent rifle shot in space. This alone was reason enough to check out into the next episode. As it turned out, if I was looking for Realism [TM] I'd have been better off sticking with the World Series, which was then chasing Firefly around the TV schedule. So far as scientific and technical realism goes it was modest even by Hollywood standards, which is to say not at all.

All the same Firefly hooked me, the first TV scifi show to do so since Babylon 5. It did have another sort of realism that I like, and which is also rare in Hollywood scifi – a milieu set in an era clearly not our own, with differences of clothing, customs, even language. By comparison, I was never tempted to try Battlestar Galactica because even its admirers agreed that its space military was portrayed as an operational and cultural dead ringer for the present day USN.

But mostly Firefly pulled me in because while at bottom it was a shameless Bat Durston, it was a really good Bat Durston. Story trumps realism, and character trumps everything.

Rocketpunk Manifesto deals largely with hard SF and Realistic [TM] future space tech mainly because these things are an interesting mental game in their own right. Spacecraft behave in ways almost entirely unlike terrestrial vehicles. If you want to have, say, a space battle – and judging from my traffic, a good many of you do – it is interesting to explore how it might play out within the constraints of known physical laws and foreseeable technology for exploiting them.

Also, of course, barring a Huge Scientific Revolution, this is the way actual future spacecraft will behave. Science fiction, especially hard SF, has a close if somewhat uneasy relationship to futurology and what might really happen. So much so that retro-futurism – portrayals of the future as it used to be – has become an established SF subgenre. Thus steampunk, inspired by the early SF of a century ago, and at least potentially rocketpunk, inspired by that of 50 years ago.

Hard SF also has a somewhat uneasy relationship with the rest of science fiction, not to mention the rest of literature. In emphasizing technical realism it occupies roughly the same place in SF that police procedurals do in the mystery genre. But there's also a case, as Eric Raymond argues, that hard SF is in some sense the core of SF – as SFnal as it gets. Which also puts it at the heart of the SF literary ghetto. To the general public, 'scifi' still means, especially, spaceships – even though Hollywood has made two successful and highly regarded historical period pieces about space travel.

There is a whole wing of SF criticism that is not especially happy about this, and subgenres such as slipstream make a fairly deliberate effort to emphasize the weird, and blur the lines between SF and the rest of Romance, and for that matter between Romance itself and 'mainstream' – a branch of literature that oddly enough is far more essentially concerned with realism than hard SF is. But I think Raymond is right in some important way; hard SF typifies what distinguishes SF from its genre cousins.

That said, the, um, hard truth is that even most of hard SF is, in its heart of hearts, space opera. My posts on space warfare are the most popular I've done on this blog, and probably are what brought a good many of you here. From a Realistic [TM] perspective, space armadas or 'constellations' are none too likely – it is indicative that even though the Space Age began amid superpower rivalry and continued that way for a generation, neither side ever found reason to build and deploy space warcraft. But it makes for cool space opera.

And the dialogue between hard SF and the rest of SF – and the rest of Romance – can be a productive one. Any FTL setting is, almost definitionally, not really hard SF, since the whole setting relies on women chanting in Welsh. But plausible-sounding tech can play the same role in faking realism that convincing-looking swordplay does in a swashbuckler or fantasy story. For fans of non-hard SF – even space fighters – I hope that this blog will at least give you twists and variations to think about. But if you're reading this, you probably already guessed that.

Related links: The dialogue in action: my post on space fighters is still getting comments after nearly two years. And the temple of hard SF information, Atomic Rockets, is as richly ornamented with non-hard artwork (including the image above) as a Gothic cathedral. I discussed rocketpunk as such early on (surprise!), and later mulled the possibility of hard SF.

Monday, August 3, 2009

Solar Power from SPAAACE ??!

The idea of beaming solar power down from orbital powersats is not exactly new. It was first proposed (that I know of) in 1968, and got a fair amount of attention during the energy-crisis years of the late 1970s and 1980s. I'll confess to having always regarded the idea as including an excessive coefficient of hype.

The theoretical advantages are straightforward enough. There's no night in space, no cloud cover, and sunlight is about 40 percent brighter than what reaches the earth's surface. All in all a solar installation in space delivers about two and a half times the power of the same installation on Earth, and delivers it steadily, requiring no storage system to keep the lights on at night. The disadvantage (apart from worries about cooking people or animals that stray into the surface rectenna that the power is beamed down to) is that you have to put the solar cells in geosynch orbit, An Expensive Thing To Do.

For this reason I've tended to think of space solar power as one of those things, like maglev tunnels under the oceans, that you shouldn't hold your breath waiting for.

But in my day gig I read the tech press, and was surprised to discover that my friendly local electric utility, PG&E, has signed an agreement with a company called Solaren to provide 200 megawatts of solar power from space. Not by some conveniently remote date like 2030, but starting in 2016, which according to my calendar is only seven years off.

The usual caveats apply. The whole thing has to jump through regulatory hoops, and PG&E is fronting no money. Perhaps it is just as well that they are not involved at the technical end, because they are not my favorite utility, and not just because they bill me. Back in the 1980s there was a big local stink about construction of the Diablo Canyon nuke plant, a few miles (upwind!) of where I live. I was a tad embarrassed when, in the middle of defending nuclear power to friends and neighbors, it turned out that PG&E reversed the blueprints and built a fair amount of the plant in mirror image to the intended design. (!) Yes, the error was fixed, and the plant has a fine safety record, but it did leave me wondering whether PG&E should be trusted with anything more complex than a dry cell.

For now, I'll assume that Solaren, at least, knows what they are doing.

In the meanwhile, let's play with some numbers. The current average cost of electric power is about a dime per kilowatt hour. Solar cells, so I am told, are now approaching a power density of 400 watts/kg. For a bit of margin let us say 300 watts/kg, or 7.2 kilowatt hours per day per kg, or a shade over 65,000 kWh over a service lifetime of 25 years. The current launch cost to LEO is about $10 million per ton, $10,000/kg, so the launch cost of our solar cell works out to 15 cents per kWh.

This is not great, but it is far from awful. LEO is not geosynch, where the powersat needs to be, but a solar powersat is uniquely well suited to using solar electric power to spiral out to its desired orbit. There's also the actual cost of the solar cells, and the rest of the setup, and the interest charge of paying up front for 25 years' worth of power. On the other hand, current electric power pricing reflect recession-level energy costs. Over the next few decades, juice is probably not getting cheaper, and barring catastrophe the world will be using more than the 15 TW it uses now (from all sources).

Let us suppose that, over the next 50 years, a terawatt of power supply is put in orbit, supplying a few percent of total world power. At 300 watts/kg that calls for 3.3 million tons of solar cells put into orbit - say 4 million tons for the whole shebang, including fuel for the spiral up to geosynch. This averages 10,000 tons per year for 40 years, on order of 100x current traffic volume. If anything can pull down launch cost it is lots of launches, with resulting economies of scale.

So. If average power cost near midcentury is 15 cents per kWh - probably an optimistic figure - and launch cost falls only by half, to $5 million/ton = 7.5 cents per kWh, launch cost becomes only half of what the installation earns in 25 years. I'm still ignoring the cost of the solar cells, but the ones in space provide more juice, and interest cost applies wherever you put them.

I'll be damned. This thing might actually work out.

Related links: Last year I discussed solar electric spacecraft.