Wednesday, December 28, 2011

A Place to Call Home

Lunar eclipse above the Rockies
Extrasolar 'Earths' are still in the news, for a fairly loose definition of 'Earth'. Thanks to the Kepler mission the news stream of 'Earths' is likely to continue. Upwards of 200 candidates have been identified, most of which will probably not turn out to be false positives.

Surely some of the not-false-positives will orbit within their parent stars' habitable zones, calling for more detailed investigation. We will then search for signs of atmospheric water vapor, and especially oxygen - a substance so unstable and corrosive that its presence in significant quantities probably indicates life, and complex life at that.

Meanwhile, last post's comment thread drifted to a familiar topic in these parts: permanent, large scale human habitation in space. The 'large scale' part, especially, tends to pushes this subject beyond the Plausible Midfuture, which will have its work cut out producing a 'substantial' human population in space.

(Today's persistent space population is six. If it increases by an average 2 percent per year there are a decidedly modest 250 people in space circa 2200; at 3 percent per year some 1500. At 4 percent per year the space population is close to 10,000 people by 2200. Not so shabby, really. But bear in mind that all such compound interest calculations eventually bump up against something.)

Set aside the question of why - other than sheer coolness - we would colonize space at all. Also set aside, for now, those niggly questions about affording it.

An important, under-discussed aspect of space habitats is whether most humans can readily adapt to living in a can - and, if so, how big a can it takes. This issue was first pointed out to me in an email exchange with Matt Picio, a longtime regular at SFConsim-l. It came up again in the last discussion thread.

Putting it a more immediate way, how long can we be comfortable with never going outdoors? And what qualifies psychologically as being outdoors? We already know something about this without having to go into space, as the phrase 'cabin fever' suggests. Experience with nuclear submarines provides a baseline; so does over-winter habitation in Antarctica. But these habitats are on the same order of size as ordinary ships and buildings.

Space habs, intended for long-term occupation, are generally imagined to be at least an order of magnitude larger in sheer size, and an order of magnitude less cramped for their occupants. We do not have any examples on this scale to go by.

In popular imagination there are supposed to be Manhattanites who have no interest in riding the subway to the outer boroughs, let alone visiting the Big Sky Country. (They may or may not exist in any significant numbers.) But Manhattan is not an enclosed can - even its canyon streets are open to the sky. If Manhattan were domed over, would Central Park still feel like a park, or merely an indoor garden?

The question may not be purely a matter of (habitable!) physical space. Parallax depth from our binocular vision becomes 'infinity' at a few hundred meters; other cues (perspective; haze or lack of) can extend this to kilometers. My subjective impression is that mountain cabins on valleys less than a km or two wide feel confined.

Other factors both physiological and psychological could come into play. How rich an ecosystem is required for a healthy variety of smells and sounds?

Does it matter whether we are talking about an O'Neill-esque spacehab or a domed hab on a planetary surface? Does it count as 'going outside' if you have to stay in a vehicle or put on a spacesuit? I have also noticed, during long train rides, that in spite of the spectacular view from the dome car the impulse to step out of the train during station stops becomes very strong.

Presumably these concerns would not arise on a habitable planet, whether naturally so or terraformed. (But can we be completely sure of this?) And they may not matter for gigastructures approaching planetary dimensions, with rich ecosystems to match, and means other than domes or bulkheads to hold in the air.

But the overall point is that long-term human habitability may involve constraints going well beyond those that apply to spaceships that reach their destinations in a few months.


This image of the recent lunar eclipse above the Rocky Mountains comes, as so often, from Astronomy Picture of the Day. And a link to Atomic Rockets, just on general principles.

Sunday, December 11, 2011

A Supersized 'Earth'

Kepler-22b and inner Solar System
For your entertainment and edification, a short note on Kepler-22b, the exoplanet that has caused a flurry of 'habitable planet' stories in the mass media.

Is it actually habitable? The short and accurate answer is that we don't know. All we really know directly about Kepler-22b are its orbital period and size. But the first of these - not quite 290 days - yields an average orbital distance (semi-major axis) of 0.849 AU. In the Solar System that would fall close to midway between Venus and Earth.

The G5 parent star, however, is a shade smaller, cooler, and dimmer than Sol. Its estimated luminosity is 0.79 solar, meaning that the planet, at its average distance, receives just about 10 percent more light - and therefore heat - than Earth does. The planet must shed that heat by radiation, and a quick-and-dirty temperature estimate, based on the 4th power law of radiation to temperature, makes it 2.3 percent warmer than Earth - about six or seven degrees C.

In fact, the paper announcing the discovery comes up with an equilibrium temperature of 262 K for Kepler-22b, as compared to 255 K for Earth.

Radiative equilibrium is only a starting point for planetary conditions. How much heat a planet actually absorbs depends on how much light is reflected, or its albedo (0.29 for Earth). And its radiative temperature, in the IR, is measured at the top of any greenhouse layer in the atmosphere. The radiative equilibrium temperature is only a starting point.

But - assuming similar albedo and greenhouse heating to Earth - the surface temperature would also be a few degrees warmer than Earth. Which is easily inside the habitable range.

Pause here to note that most of what makes global warming problematic for our civilization is abrupt change in climate, not a somewhat warmer climate per se. An Earthlike planet with stifling tropics but mild subarctic zones would still be eminently habitable for humans.

Now for the caveats. For one, in spite of the cool illustration above (via Sky & Telescope) we do not know Kepler-22b's orbital eccentricity. Most extrasolar planets, unless so close in that their orbits have been tidally circularized, have notably more eccentric orbits than Earth does; this one could be searing hot at periastron, freezing cold at apoastron.

And we do know Kepler-22's size, 2.38 Earth radii, so it cannot really be very Earthlike at all. The radius corresponds to a volume 13.5 times Earth's. If it is primarily rocky its mass is proportional, with surface gravity well above 2g. On the other hand it could be a 'water giant,' with roughly earth-sized rocky core and a hydrosphere thousands of miles deep. Ocean is far too weak a term.

Earthlike it is not, whatever its composition. But it is hard not to speculate. Suppose that a rocky core has a radius of 1.38 x Earth's (and probably a bit denser), with a hydrosphere above.

Planetary mass is then close to 5 Earth masses. Surface gravity is about 0.9 g, and low-orbit velocity is around 11 km/s - similar to Earth's escape velocity. Getting back off after 'landing' on the hydrosphere would be tough, but not as tough as getting there in the first place, since it is 600 light years away.

So ... speculate!

Bonus science destructiveness news: Thanks to regular commenter 'Thucydides,' five cataclysmic events to think about.

Wednesday, December 7, 2011

Science Fiction versus Fantasy

The Course of Empire
Mostly this is not much of a fight. These two subgenres of Romance happily coexist (along with horror) in the same section of the bookstore.

This juxtaposition need not have been inevitable. Horror, at least, could as easily have been shelved along with mysteries. Both have a lot of dark stuff, not to mention shared roots going back to Edgar Allen Poe. In other respects, both SF and fantasy have a good deal in common with historical fiction - all set in worlds different from the everyday present, usually markedly so. But hist-fic seems generally shelved in with general fiction, presumably because its worlds are 'real.'

It is only by coincidence that I bring this up right after the death of Anne McCaffrey, whose Pern setting amounted (IIRC) to a fantasy setting framed within a mostly offstage SF setting.

Exactly how SF and F are to be distinguished from one another is a vexed, long-discussed issue, and now we are going to vex it some more. I have tended to favor the robust if simplistic rule that if it has a spaceship it is SF, if it has a sword it is fantasy, and if it has both it is science fantasy. Which works pretty well as practical guidance, but of course there is more to it than that.

There are theoretical differences - so to speak - between the science-rooted world view (typically) presumed in SF and the magical/mystical/demireligious world view implied by most fantasy. More consequential are the practical differences - science is, well, science, while magic is an art. (Read the posts that follow that one for further discussion.)

Several attempts have been made to 'rationalize' fantasy settings, giving them an SF infrastructure. The ones I have read - notably by Niven and L Sprague de Camp - have tended to clunk. They had no magic, in the literary sense. Explaining magic takes the art out of it, and does what a lecture on nutrition does to a fine meal. The Pern book likely avoided this problem by putting the SF frame on the shelf and reading like traditional fantasy.

Another interesting line of argument contrasts the political undertones of SF and fantasy - the former tending to be broadly liberal, the latter deeply hierarchical and essentially reactionary. I introduce this point in a mealymouthed way because my monkey's google fu is weak. Just a few weeks ago I read an essay or blog post making this point. It was by a pretty well known SF writer, but I can't remember his name, and searching has failed to turn it up. Suggestions by the hive mind would be welcome!

This argument's logic and examples are impeccable, but I can't entirely buy it - and can't entirely put my finger on why I don't quite buy it. It is true that 'traditional' fantasy (as distinct from urban fantasy and the like) is backward-looking, rooted in the social conditions of the agrarian age, while SF looks forward to a post-industrial age.

Is it simply that the Scouring of the Shire is so cool? I've read a revisionist version (which seemed distinct from the one linked - once again reports from the hive mind are welcome), but the Scouring was still cool.

The political interpretation of genre makes for an easy segue to fretting over what has happened to SF/F since their bookstore pairing became the norm, by around 1970. Swords have done better than spaceships, with fantasy becoming considerably the larger of the two genres, as measured by book production and sales.

By further (non-?) coincidence all this happened at just about the same time that space travel became a reality - and turned out to be so difficult and costly as to make the classical SF space future look somewhat ... fantastic. Indeed, much of the modern-era growth in SF itself has been in quasi-fantasy directions, notably including retro-SF that looks as firmly backward as traditional fantasy, if not quite as far.

The flip side may be urban fantasy, bringing fantasy tropes into the post-industrial era.

Yet in spite of the controversies and stereotypes, the two genres do coexist pretty well, to the point where I can more or less take for granted that readers here will be familiar with fantasy tropes. The similarities are, in the end, more consequential than the differences, and more central to the great Romance genre to which they both belong.


The image, besides being entertainingly lurid, illustrates a theme common to SF and fantasy, and provides an excuse to link the page at Atomic Rockets where I found it.

Saturday, December 3, 2011

Distance 119+ AU

Curiosity Rover Launch
A discussion of SF and Fantasy is pending here, but in the meanwhile, a little weekend science news.

According to the Voyager website at NASA, Voyager 1 is currently nearly 120 AU from Earth - 119.862 AU, to throw in a few extra decimal places. (Follow the link to see a real-time distance updating.) Its distance from the Sun is just over 119 AU, a more relevant measure - the distance from Earth will actually shrink during by next (northern hemisphere) summer, when Earth swings around to the same side of the Sun as Voyager.

Voyager 2 is a slightly more modest 97 AU from the Sun. Pioneer 10, which lost contact with Earth a few years ago, is at a similar distance.

We grump about human spaceflight a lot around here, but stop to think about the fact that a human-built spacecraft is now nearly 120 AU from the Sun - still in operating condition, still investigating the heavens.

Meanwhile the Mars Science Laboratory mission, including the rover Curiosity, is on its way to Mars. The image above, from Astronomy Picture of the Day (APOD), shows its launch.

Not on its way to the inner moon of Mars, sad to say, is Phobos-Grunt, which fell out of contact on entering Earth parking orbit. Mars has a remarkable history of eating space missions. According to Wikipedia, Russian engineers still have some faint hope of establishing contact and perhaps even sending the spacecraft to a near-Earth asteroid. Otherwise, RIP.

In spite of setbacks, the exploration of the Solar System (and its environs) continues.

Tuesday, November 22, 2011

Whose Space Futures?

Perseid meteor seen from ISS
This blog has a fairly international readership. If Google Analytics are anything to go by, nearly half of you come from outside the US, and about a quarter from outside the Anglosphere. This probably has much more to do with the virtues of the Internet than any virtue of mine.

Space itself has been an international environment, so far. Which probably has much more to do with its perceived lack of immediate economic or power-political value than with anyone's virtue. Like Antarctica it is interesting enough to establish a presence there, but not enough for the major powers to go to the mat over it.

A frequent topic on this blog has been the colonization of space - how likely it is (or isn't), and under what circumstances it might happen. I am not the only one raising the question. Charlie Stross has brought it up a couple of times, at least.

As he notes, and this is pretty much a no-brainer, the 'Murrican SF conception of the space future is highly colonization-centric. It is firmly and understandably rooted in the experience of the New World (by those populations for whom it was new), and especially the Wild West. Thus Bat Durston and Firefly.

My excessively vague impression is that, elsewhere, the conceptions of the space futures are quite different. The contrast that is most striking in my mind is between Heinlein's rip-roarin' interplanetary future and Clarke's crumpets-and-tea version. (For both writers I am thinking mainly of their earlier work. Later Heinlein annoyed me; later Clarke merely bored me.)

Of the two, Clarke's future now strikes me as far closer to a plausible midfuture than Heinlein's. For one thing - but a very important thing - his Solar System was essentially the one we actually live in, with only one habitable planet, Earth.

Heinlein's Solar System - with its habitable Venus and near-habitable Mars, not to mention native civilizations on both worlds - was wonderful but baroque, largely outdated even by the 1950s. In a lot of ways classic Heinlein reads like steampunk disguised as rocketpunk.

2001: A Space Odyssey is, no surprise, firmly in the Clarkean universe, and resembles the real world space program on 1960s steroids. There is a Moon base, or more than one (the Russians presumably have their own), and commercial space travel, but no hint of incipient Heinleinian colonization.

Having said this much, I have no real sense of how non-US perceptions of a space future have developed over the years, or how much part permanent colonization has played in these images. So I want to toss this out to non-US readers in particular: Does the whole space colonization debate even seem salient, or just a parochial 'Murrican concern?

What is the human engagement with space all about, anyway? And while we are at it, what is the relationship between actual space travel and space as a setting for fiction, Romance or otherwise?


The image, from APOD, seems like one that Clarke would particularly have appreciated: a Perseid meteor entering Earth's atmosphere, as seen from above.

Monday, November 7, 2011

Is Realism Unrealistic?

ISS spacewalk
Realism is viable so long as you only want to do realistic things. Exploring space is realistic. Mining it, colonizing it, or fighting Epic Battles in its far reaches are all operatic things. None of them is impossible. But all are highly unlikely, at any rate in the readily foreseeable future, given technology as we know it.

In fairness to me, I have generally discussed the 'plausible midfuture,' a time and place that is characterized as plausible, but not necessarily most likely, or even very likely at all. But that doesn't do away with the problem. Does an implicit requirement for 'plausibly' demi-realistic technology amount to an unrealistic constraint when applied to essentially operatic settings?

Or, putting it another way - and bringing it down to cases - given that deep space warfare is pretty damn unlikely under the technological restraints I have discussed here, does the Space Warfare series really provide any useful help for writers or gamers who want to make their space battles more convincing. Wouldn't they really be better off to adopt the operatic technology of their choice, then work out the implication for combat under those conditions?

This came up in a recent comment thread, in which John Lumpkin's novel, Through Struggle, the Stars, got taken in vain. I have not read the book, so I have no informed opinion on how convincing his setting is. But the question raised is much more general - does putting 'realistic' spaceships in a setting of space colonies make it less plausible than allowing a technology that would justify deep space travel as convenient and cheap?

As I have noted here before, my bias toward realistic-style spacecraft (and other details of a setting) is essentially aesthetic. Magitech is inherently arbitrary. It is well done if it holds together with internal consistency, but it is still arbitrary. And just on the level of purely visual aesthetics I was heavily influenced by the early space age, when we started getting pictures showing how things in outer space actually look.

Oddly enough, by the way, I have never seen Hollywood successfully capture this look, especially the brightness of spacecraft in full sunlight at 1 AU. In some cases this may be because Hollywood loves gothicism in space, but I suspect the real reason is much more basic: No studio lighting is anything near as bright as direct sunlight.

(Although APOD doesn't mention it, the dim lighting of the spacewalk scene above suggests that it was taken while the ISS was passing over Earth's nightside, illuminated only by floodlights and sucy, not direct sunlight.)

Speaking of Hollywood spaceships, the Venture Star in Avatar may not be quite as realistic as it looks. Its appearance, with big radiator wings and so forth, is very much Plausible Midfuture, suggestive of a gigawatt-output nuclear electric power plant ... but the drive is capable of reaching relativistic speeds at more or less 1 g. I'm not gonna do the math here, but that drive is putting out waaaaay more than a gigawatt of thrust power. Those impressive-looking radiators couldn't shed much more than the ship's galley heat.

See? This is the sort of problem you get into when you start running the numbers for our favorite space scenarios. And the problems exist at multiple levels of meta-ness, from the sorts of technical issues I just mentioned up to (at least) the question of what relationship science fiction settings can or should have to 'the future.'


Sunday, October 30, 2011

Space Liners

Liner-freighter 'Silk Road'
In the last comment thread, commenter papa noted a very natural first guess: that the title was a riff on the musical Showboat, and that the post topic would thus be space liners (rather than military showboating).

Thread drift duly followed, so that the rest of last thread can usefully be read as 'pre-comments' on this post.

If you do a Google Images search on battlecruiser, images of space warcraft handily predominate over, you know, actual seagoing battlecruisers. Do the same for space liner and you get a strange grab bag of images - the first row on my screen includes two aerospace vehicles (one from the film 2001), a very stylized deep space craft (from a Maldives stamp), a car, a bicycle, and a pullcart for garbage cans. Spaceliner as a single word brings up mostly bicycles, plus a fair number of buses.

This little search adventure confirmed something I already knew from my traffic stats: We geeks are a rather bloodthirsty lot, at least in imagination.

It also showed me something a bit disappointing that I didn't know. Space liners do not seem very well established as a trope. Even the Evil Website has only one reference (relating to the film The Fifth Element). Yet a future of large scale space travel, interplanetary or interstellar, might reasonably be expected to include space liners, so they are worth considering here.

First, some definition of terms, then a bit of future-history speculation. The minority of Google images showing spacecraft of any sort are dominated by aerospace planes, like 2001's Pan Am shuttle. (Melancholy note that the commercial tie-in was to a now-defunct airline.)

Operators of aerospace liners have a perfect right to leave off the 'aero-' part, but for this discussion I have in mind 'real' space liners that operate entirely in space, especially those making long trips through deep space, interplanetary or interstellar. And I am concerned here with spacecraft intended for travel, from one planet (station, whatever) to another, not the spacegoing equivalent of cruise ships.

(The spacegoing counterpart of the cruise ship is - at least for a long time to come - the orbital hotel. It has simpler operating and emergency procedures, and offers a scenic view for the whole time, not just near departure and arrival.)

If we have anything more than minimal human travel into deep space, we will presumably have the space liner's more utilitarian counterpart, the interplanetary transport. (Some technology assumptions, notably cycler stations, more or less eliminate this role, but I'm somewhat doubtful of these approaches.)

Commenter Tony made a suggestion last thread that early transports, at least, may have only a minimal dedicated crew - the passenger manifest providing needed most of the needed skillsets as well as the scut labor. After all, these early passengers will be trained specialists on assignment to outpost destinations, whatever the institutional details.

I tend to agree. Indeed, as I noted in comments, early passenger transports may have no permanently assigned crew. If they are lightly shielded to save penalty mass, a couple of round trips might rack up a substantial fraction of lifetime radiation exposure, making ship's crew a non-viable career path. And the people being transported to and from deep space outposts reasonably include propulsion techs, along with mission controllers who can function as pilots.

Somewhere along the time line, however, VIPs will muscle or bribe their way onto the passenger manifests. The first of these will make no difference in terms of accommodations - like today's pioneer orbital tourists, they will bunk and eat alongside working crew/passengers. At some later point, VIP passengers, whether bureaucratic or paying, will become numerous enough that First Class accommodations will be provided for them.

At this point the true space liner begins to take form, even if its chrysalis is just a corridor or two within the hab of an otherwise-utilitarian transport. As suggested in the last thread, even the transports will be relatively comfortable, because their travel times are in weeks or months. First Class accommodations may offer slightly larger cabins, or roomettes instead of bunkrooms, but their most distinctive - and expensive - feature will be stewards and other hotel staff.

If bases and outposts do evolve into incipient colonies (by no means a given!), travel will become more commercialized and purpose-built space liners will evolve. These may still have some equivalent of steerage class for passengers who do much of the work of maintaining their hab spaces - at least the basics like making up their own bunks and providing galley services. But they will also have First Class and intermediate level accommodations.

Yes, there is also the possibility of that old SF standby, Cold Sleep, or some other means of snoozing for most of the passage. But the more we learn about humans biologically the more complicated we turn out to be, and I don't think we can count on this.

In any case, by this point we are well beyond the 'Plausible Midfuture.' Will the liners, or at least their First Class sections, have spacious atrium areas with gardens and the like, to provide the illusion of not traveling through space while confined in a can? If your setting is operatic enough to have full-blown space liners, I wouldn't rule this out - though a lot of the spaciousness may be artful illusion.


The image at top is one I made several years ago, representing the liner-freighter torchship Silk Road. Due to the (improbably!) high acceleration no spin is needed, and the passenger pods are shamelessly based on rail passenger cars - even to the 'baggage car' clamped onto the passenger section.

The image below has nothing to do with space liners. It is a Blackpool (UK) 'Boat' - so named for obvious reasons. It is about as cool as streetcars get, and this one sometimes runs in regular service on the SF MUNI's F Market line.

Brighton Boat

Monday, October 10, 2011

Showboats in Space

It has been Fleet Week in San Francisco, which invites consideration of the things military forces do besides fighting wars. One of these, assisting first responders in civil disasters, figured in this year's Fleet Week.

But mainly Fleet Week is about showing off. It featured a 'parade of ships' coming into port (where I used my el cheapo phone camera to snap USS Antietam, CG-54, above), and three days of air shows - the first time I've ever walked to an air show. Sunday's Blue Angels performance had to be cut short because of intruding fog. (I had already watched them on Friday and Saturday.) An hour later the fog completely dissipated.

On an international note, this year's Fleet Week had a substantial Canadian presence: four ships and the Snowbirds, the RCAF's precision flight demonstration squadron.

But, ahem, on to the point of this post. In grand-strategic perspective, 'showing off' is arguably the primary mission of military forces. War-fighting is merely their most important secondary mission, the one they will be forced back onto if they fail in their primary mission.

Put another way, truly successful militaries deter, and achieve their wielders' objectives without a fight. Fighting battles and winning them is second-best, and might be regarded as a fail-safe mode. Fighting and losing, or surrendering without a fight, are both failure modes. (Which is worse depends on particular circumstances.)

To be sure, much military showing-off is an implicit display of war-fighting capabilities, and by no means is all or even most of it aimed directly at prospective enemies. Air show demonstration squadrons such as the Blue Angels and Snowbirds illustrate both of these points.

Flying loops in wingtip-tight formation may be a combat maneuver, but it certainly displays piloting skills and aircraft performance that are relevant to combat. But the more immediate objective of demonstration squadrons - as of much military display - is as a recruiting tool. Though come to think of it, being able to recruit troops is also combat-relevant.

The role of military display has generally been understated in the recent era. The books I read on the history of ships tended to denigrate the gilt-work of 17th century 'great ships,' though it served very well for conveying their royal owners' wealth and power.

The shift of attitudes can perhaps be pinpointed to a little more than 100 years ago, when the world's navies abruptly went gray as their armies went khaki. Not that the impulse toward display actually disappeared - at almost that exact moment, 'armored cruisers' gave way to battlecruisers, showboats par excellence, which is why their name survives in SF.

Which brings us to space. Space forces, strictly speaking, have some disadvantages when it comes to military display - in particular, being a long ways from most of the people they might impress. Space fighters, in the strict sense, can't go thundering a couple of hundred meters over the rooftops of Pacific Heights. Only atmospheric craft can do that.

The curious flip side of this is, of course, that the Space Race was all about (quasi-) military display on the grandest scale. In this case the hardware had no specific warfighting role at all. It didn't need to. Everyone understood that if you could hit the moon, you could nail Moscow or Washington.

But the Space Race soon ended, and I doubt there will be a repeat in the next few decades, even among emerging great powers. (Are the Chinese really going to impress India all that much by doing what Americans and Russians did 50 years ago?)

On the other hand, space might still have a future as a place to display technological prowess. And if, as I suspect, war 'as we have known it' is becoming obsolescent, the role of quasi-military display could become even more prominent than in the past. The obsolescence of war is not about moral betterment but pervasive mutual deterrence.

And deterrence is fundamentally all about showboating.


Wednesday, September 28, 2011

World of Two Suns

Planets orbiting a binary star
Rocketpunk Manifesto has never claimed to be a space news blog, so I make no apology for being the last space blog in the known universe to mention last week's report of a planet found orbiting both components of a double star. (There is no indication - yet - of more than one planet in this system; see illo note at the end of this post.)

I will apologize for slower posting of late, the excuse being a couple of new work gigs I'm still breaking in.

But back to the world of two suns. The interesting thing about this - apart from the discovery itself - is that when I was growing up, and for long afterwards, the standard wise advice for any SF writer aiming for a speck of hardness was to avoid binary-star planets like the plague.

Any such planet was liable to be hurled out of its birth system. Even more to the point it was unlikely to form in the first place, disrupted before birth by the processes that formed a binary star in the first place. Which meant that in hard SF perspective, any planet of a binary might as well be 1930s baroque, with the blue sun rising as the red sun was sitting and the orange sun was at midafternoon.

Not for the first time - and surely not for the last - elegant inference has been trumped by observation.

Certainly not for the first time in the history of extrasolar planet discoveries. The first such worlds to be found, in 1993, were so hard to wrap our collective mind around - three planets orbiting a pulsar - that they were not fully acknowledged as 'real' planets.

Then came 51 Pegasi b, in 1995. The star is suitably sunlike, but no one expected a planet comparable in mass to Jupiter to be orbiting several times closer in than Mercury. And basically things have stayed weird ever since.

Before 1995, I'd venture that most people (who thought about it at all) expected more or less the same thing I did. Extrasolar planetary systems, when we found them, would mostly have the same overall organization as the Solar System. They'd have some rocky terrestrial inner planets between about 0.3 and 3 AU, and some gas giants out beyond the 'snow line.' Beyond the gas giants would be nothing much.

Details would vary, of course. Some systems might have only two or three planets, others well over a dozen. A few with planets bigger than Jupiter - even approaching brown-dwarf mass - and other systems with only Saturns or Neptunes. Most of these planets, big and small, would be on near-circular orbits, in striking contrast to the highly eccentric orbits typical of binary and multiple stars. The spacing of their orbits would likely be suggestive of 'Bode's law.'

By the current more or less official count of the Paris Observatory there are now 687 confirmed extrasolar planets. And precisely none of them are in systems with an overall architecture like I just described.

As I have noted here before, this is (probably) at least in part an artifact of observational 'selection effects.' Most of those 687 planets have been discovered by techniques that have a technical bias in favor of large planets close to the parent star. Indeed, a duplicate of the Solar System would be only at the threshold of detectability.

All the same it is starting to be just a little bit odd that so few known extrasolar planetary systems are even kinda sorta like the Solar System. Looking at the Paris Observatory website, there is just a hint that planets are more common around 5 AU - Jupiter distance - than around 4 AU or 6 AU. Some even have fairly circular orbits.

But all in all, the planets and planetary systems we have been finding have amazingly little in common with the ones we expected.

I don't want to draw very many large conclusions from this, except perhaps that 'large conclusions' are likely to be wrong. In particular, note that this particular discussion is entirely about the physical (and observational) facts about astronomical bodies, not about future human societies that might investigate those worlds, or seek to do more than investigate them.

But they are interesting, in themselves and for their possible place in human affairs, SFnal or otherwise.


The image comes from - but just to keep things interesting, it illustrates a discovery made last fall, not last week.

Tuesday, September 13, 2011

At the Speed of Story

Shuttle Endeavor docking to the ISS
Spaceships in science fiction, as was first noted by a commenter in the early days of this blog, always travel at the speed of plot. This observation is recurrent, including in comments on the previous post.

The title is a mashup of this principle with Teresa Nielsen Hayden's dictum that plot is a literary convention, while story is a force of nature.

All of which goes to explain why this blog is, in some respects, a futile effort. When story collides with other considerations (such as realistic space travel), story invariably wins.

I have first-hand experience of this problem, which I will be delving into further in upcoming posts. Suffice it for now to say that when a cool technology led me to a story, the story took over completely. And I mean completely. Among other things, not one but two battle sequences ended up on the cutting room floor. They had become distractions from the story; therefore they had to go.

There are, at best, some limited protective measures. The most obvious is to go with the flow. If your story calls for fighter jocks, you are going to need fighters for them to fly. These don't necessarily have to be space fighters - if a planetary atmosphere is handy, air fighters are legit - but you will certainly need fighters of some sort.

The implausibility of space fighters won't get you off that hook. You'll have to either make them plausible - or else say the hell with it and go with implausible ones. This is an eminently safe option. The great majority of readers will neither know nor care. Of the relatively few who do care, most will forgive you. Especially if they like the story.

Other options are available. A radical but straightforward one is to avoid telling a story. This is the strategy I have followed in this blog. I've posted only a handful of fiction snippets here, and most of those had nothing to do with space. (My only actual rocketpunk SF has been a couple of paragraphs in a very early post.)

There is a modest but real interest in 'nonfiction' space speculation. It is not too hard to find blogs or other websites that discuss and describe imaginary spacecraft without trying to tell stories in which they figure. But such is the power of story that it is always lurking, waiting for a chance to intrude. To identify your laser star or killer bus as belonging to the Zorgon Empire is to invite speculation about where or what Zorgon is and how it became an empire. Warning lights flash and sirens warble, because you are now under intrusion by an incipient story.

I ought to note here that all of this applies not just to the details of spaceships and the like, but to the entire setting. I have mentioned a few times here that there are plausible space futures that are simply not very story-conducive. But the comment threads for those posts always veer toward how to get a story out of it.


Last post I mentioned that there are no known cases of spacecraft docking maneuvers being filmed from a third spacecraft. There turns out to be an almost-exception: The image of the Shuttle Endeavor - on its final mission - docked up to the ISS comes was filmed from a nearby Soyuz. It comes from this rather interesting blog.

Wednesday, August 31, 2011

Will Hollywood Ever Be Accurate About Space?

Scene from
As a change of pace from Mars exploration mission architecture, and by popular demand - or, at any rate, the suggestion of regular commenter Geoffrey S H - a few thoughts on Hollywood and outer space.

First, the short answer to the question posed in the title: Yes - when it has to be. That is, when the audience knows the reality, or at least has some notion of the reality, and would laugh at obvious faketude.

Which will not be for some time to come - namely, when enough people are traveling in space for actual space footage to become a familiar commonplace.

Until then, Hollywood will be completely indifferent to space realism. See this page at Atomic Rockets. Scroll down about halfway, to Hollywood Reasons.

In principle, how real spacecraft maneuver should already be familiar. We have been performing successful rendezvous and docking maneuvers since 1965, meaning 46 years of impeccably realistic maneuvers by spacecraft in space, and in close proximity to each other. But so far as I'm aware, in none of these operations has a third spacecraft been handy nearby to film the maneuver from a photogenic angle.

More to the point, rendezvous and docking is conceptually cool, but in purely visual terms it is only slightly more exciting than watching paint dry.

The day may come when docking and undocking are standard bits of stock footage, used the same way snippets of an airliner pulling up to the gate are used, to convey arrival or departure of a character. But the time and attention given to such snippets will be minimal, unless justified by some plot complication - say, a squad of police in hot pursuit, trying to arrest someone before a departing ship undocks. In which case the whole scene will get a lot more attention.

How accurate this attention will be is another matter. The scenario itself invites some interesting legal and practical questions. When a plane pulls away from the gate, or a ship from a pier, it is still within the jurisdiction of the airport or harbor - but once a spacecraft unlatches from a station, is it still within the station's jurisdiction?

Enforcing jurisdiction has its own points of interest, but in any case, don't expect Hollywood to care, any more than most cop movies today care about what would really happen in equivalent situations.

Anyway, space cops are a sideshow. Let's be honest: What you're really interested in is space battles. The usual Hollywood treatment of these, from Trek and Star Wars and on through various TV shows, is pretty risable. Space dreadnoughts fight at Trafalgar range, space fighters do barrel rolls and Immelmann turns, and an implausibly spectacular (and, especially, noisy) time is had by all.

There are a few honorable exceptions - a silent rifle shot in Firefly, and most notably the Starfury fighters in Babylon 5, which sometimes actually maneuvered like spacecraft.

How did they get away with that? I'll venture a two-part answer: First, the fliparound and retrofire maneuver is visually impressive and somewhat self-explanatory - you don't need to understand the underlying physics to appreciate its coolness. Second, J. Michael Straczynski, or someone in his development team, guessed that a small but significant part of the show's core audience would appreciate the maneuver and the logic behind it, and say "Way Cool!" Which would cue in other viewers that something way cool had just happened.

Which is useful guidance on how to make similar effects appear again. You will never convince Hollywood to replace cool by non-cool for the sake of mere realism. You have to offer a cool alternative to the existing conventions.

As one example, combat range. I can think of scenarios where spacecraft might start shooting at very close range (say, an exchange of prisoners/hostages goes pear shaped, or whatever). But most space combat situations imply Stupendous Range, or at least enormous range, certainly far too great for the rival combatants to both show visible details in the same frame.

World War II newsreel footage already solved this problem: Good guy battleship shown firing toward the right, cut to bad guy battleship shown firing to the left. We know and understand this convention - but you still need to convince the director to forego showing both the Enterprise and the Klingon battlecruisers at once.

My solution would be to use a handy moon as a prop. (It isn't like moons are hard to find out there.) Now you can have one ship firing in the direction of a distant moon - then cut to the other ship firing back, with the moon as a nearby planet-scape. Stupendous Range is instantly and vividly conveyed.

Stepping back a bit, I should acknowledge that what exactly constitutes 'realistic' space combat is rather more complex and ambiguous than simply making a nod to Sir Isaac Newton.

As has been previously discussed/argued about here on this blog, space warfare does not just involve physics; it also involves power politics and economics. In the Plausible Midfuture, at least, any space warfare is most likely to a) be fought between rival Earth powers, b) be confined almost exclusively in Earth orbital space, and c) involve only robotic or remote-piloted vehicles. None of which offers much place for space armadas, colonial rebellions, or other classic SF space warfare tropes.

All of which having been said, we'd still be inclined to stand up and cheer for space battles that have even a superficial ring of plausibility.

Good plot and characterization might also be helpful, but that is another discussion.

Anyway, discuss.

The image, via Atomic Rockets, is a scene from The Wrath of Khan - concerning 'three-dimensional thinking' in a battle between spacecraft with a thoroughly two-dimensional aesthetic.

Thursday, August 18, 2011

A Mission to Mars

Surface of Mars
Speculation about Mars missions produces an irresistable temptation to design paper spaceships, and I won't even try to resist. So here we go:

My bias, as expressed last post, is for reaching Mars and returning on fast transfer orbits, making the one way trip in approximately three months. Allowing a few weeks on (or at least orbiting) Mars, the mission can be done in six months and change.

The alternative is using Hohmann transfer orbits, more or less, and accepting an 18-month round trip. This can be done with chemfuel rockets, and broadly speaking we already know how to do that part. What we don't know is how to send humans into space for 18 months and get them back in good health.

Six months corresponds to the currently accepted mission duration for the ISS. Going much longer will be much harder on the crew. On the other hand, the 'fast' six-month mission calls for an electric drive; even nuclear thermal comes up short.

An electric drive with sufficient performance is semi-speculative. The Dawn probe has three (redundant) ion thrusters with a combined mass of 129 kg, thus 46 kg each, while its solar wings come in at 204 kg. Each thruster delivers 92 mN of thrust from 2600 watts of electric power.

The combined mass of one thruster plus solar wings thus comes to 247 kg, just about 0.01 kW/kg. We need power performance about 100 times better, approaching the figure of merit I have often mentioned here, 1 kW/kg is the standard figure of merit.

The reason for using this figure of merit shows up in sims done on the Rocketpunk Manifesto TravelPlanner. Specifically I looked at a baseline vehicle capable of putting on 29 km/s of delta v in 60 days of acceleration, allowing a 30-day coasting period. This is more efficient than a classical brachistochrone orbit, which expends energy and propellant on putting on speed, then (literally!) turning around and taking it back off again.

Exhaust velocity is a little over 30 km/s, giving a mass ratio of 2.5: given a departure mass from Earth orbit of 250 tons, the 'dry' mass that reaches Mars orbit is 100 tons.

Rated drive power is 15 megawatts. The propulsion system (thrusters and power supply combined) is allowed 50 tons, half the 'dry' mass of the ship. This corresponds to a power density of 0.29 kW/kg - or, putting it reciprocally, 3.45 kg of drive mass - thrusters and power supply - per kilowatt of drive power output. As a gearhead reference point that corresponds to 5.65 lbs per horsepower.

I allow 30 tons for fuel tankage, keel structure, and general equipment. Which leaves just 20 tons for the gross payload - life support hab, stores, and crew. This ship is half engine, not a very balanced design. But this is what you need if drive power density is limited and you want to get to Mars in a few months.

My math fu is not equal to the task of actually determining travel time to Mars for a given mission delta v. But this handy delta v calculator, can do it. According to the calculator, burns totaling 27.33 km/s of delta v are needed to get from a high (100,000 km) Earth orbit to low (500 km) Mars orbit in 90 days.

The calculator assumes a brisk 10 milligees of acceleration. The sims have a much more modest acceleration, averaging half a milligee. (And if the drive is solar electric its acceleration performance will be halved at Mars distance from the Sun. Therefore the calculator estimate quite optimistic, but clever mission design could probably squeeze out some improvements.

At least, to a first approximation, this provides some idea of what it takes to reach Mars in a few months.

But the mission profile is for a one-way trip, implying that the vehicle must refuel at Mars orbit. One day this may be a routine operation, but it will certainly not be routine the first time. Really we should be capable of a round trip with onboard propellant - requiring twice the mission delta v, about 55 km/s.

A second sim shows a lighter and more powerful drive engine, close to the 1 kW/kg figure of merit, putting out 30 megawatts and providing twice the specific impulse. This more powerful engine has a mass of 30 tons, allowing 40 tons gross payload. Realistically speaking this is close to the minimum performance requirement for a practical Mars craft - which is why 1 kW/kg is regarded as the figure of merit for fast space propulsion.

This spacecraft is strictly a crew transfer vehicle, intended to get the crew from high Earth orbit to low Mars orbit and back. Electric drive is completely unsuited to planetary landings, so any mission profile like Mars Direct is ruled out. Everything needed to land on Mars, live and work there for a time, and return to Mars orbit, can be sent on a slow orbit.

Since the mission departs from high Earth orbit, there must be a prior phase in which the ship, assembled in low orbit, spirals out, then is met by a crew ferry. In principle the ship could return to high Earth orbit and be met there. More likely at least on early missions, the payload will include an Earth return capsule for the crew (and samples of Mars material), with the interplanetary bus being expended.

This post is conceptually quite incomplete - really it only talks about the interplanetary bus. But I want to get it posted, so here it is.


The image of Mars' surface is from Astronomy Picture of the Day.

Wednesday, August 10, 2011

Destination: Mars

ESA Mars Lander
The first human interplanetary mission will, more likely than not, go to the Red Planet. Apart from the Moon it is the easiest major body in the Solar System for us to reach. Its surface bears evidence of rivers and seas, and liquid water may still occasionally flow there. The similarity of its landscapes to the American Southwest is an illusion, but it remains a candidate for life, and its chief rivals - Europa and Titan - are far more distant and hard to reach.

A single image (of an artifact, for example) could of course change all this. But for now at least, Mars is the likely first place to go.

I am not concerned with pure stunt missions, whether by some multi-billionaire or an emergent great power. For this discussion I presume that a human mission to Mars is intended to explore Mars. Yes, other motivations will surely be in the background, involving the usual suspects. But the more serious the exploratory intent, the more likely that going to Mars will lead to further developments rather than end up as a costly one-off.

This does not mean that every individual mission must 'do science.' The engineering demands of safe human interplanetary travel justify what amount to shakedown missions, say, a manned flyby that does nothing but demonstrate our ability to perform the transfer mission. But the program as a whole should be aimed at advancing our knowledge of Mars.

The model here is not Apollo but the robotic deep space program, which in spite of some embarrassing failures (feet/second != meters/second), has in all been a profound success.

A first implication is that a human mission will be undertaken only when robotic missions reach diminishing returns. It is no doubt true that a geologist with a hammer could learn more about Mars in a day than our rovers have learned over years. But the cost of sending that geologist would be very much greater than the next few rovers. And human missions are subject to some constraints, such as landing where it is safe to land.

My instinct in thinking about a Mars program is to proceed cautiously and incrementally - unmanned tests of the vehicle, then a human flyby, then orbit without landing, and only then a full-on landing. I am not sure that each of these stage is strictly necessary, and there are alternate possibilities, such as a visit to a NEO, that would similarly exercise spacecraft and procedures.

And some of these missions - notably, orbiting without landing - might be able to 'do science' on an important and relevant scale. In particular, a crew on Mars orbit can operate surface vehicles and manipulators remotely, but without significant light lag - like steering a minisub from the surface, not steering a rover from Pasadena.

This is as good a place as any to note that 'going to Mars' combines at least two very distinct space missions: the deep space journey to Mars orbit and back, lasting at least months and perhaps most of two years; and landing on Mars, working there for weeks, and lifting back off to Mars orbit. This in itself is reason to test the Mars orbital capability before the surface landing.

Mars Direct argues in effect for a very different functional division - in effect a one way trip to the surface of Mars, then use of a second pre-positioned (and pre-fueled) spacecraft for the trip back. This feels cut-rate and precarious to me, not least because Zubrin is so much like a real estate promoter, not quite trustworthy on principle.

To be sure, there's no reason this architecture couldn't be tested in an unmanned mission, but I also have doubts about packing the hab elements into form factors suited to Mars landing and liftoff. It seems like awfully cramped crew quarters for such a long mission, or else a much larger cabin than you need to carry the crew and some rock samples from the surface to Mars orbit.

In any case, as longtime readers know, I have bias in favor of fast human travel using high ISP propulsion - most likely solar electric, though perhaps nuclear electric - for getting to Mars orbit and back. Faster travel means less exposure to radiation and weightlessness, the main health hazards of prolonged spaceflight.

Solar electric has now been successfully flight tested by the Dawn mission. A fast (~3 month) trip to Mars requires a much higher drive power/mass ratio, which may not be attainable. But solar electric space propulsion is far from technical maturity, and it may well be able to approach the 1 kg/kW standard for fast travel. .

Electric drive pretty much precludes the Mars Direct approach anyway, since an electric spacecraft is ill-suited to aerobraking, and doesn't need it. The surface components of the mission can be sent separately - a Hohmann transfer is fine, since the crew isn't aboard until the Mars landing.


The image, from a European proposal for Mars exploration, is recycled from an earlier post on interplanetary exploration.

Monday, July 25, 2011

Cold Equations

The title, of course, evokes one of the all time notorious science fiction stories - from geek perspective perhaps the notorious SF story: 'The Cold Equations.' I have been in the bashing school regarding that story, on the grounds that the most basic safe operation procedures should have prevented it, and more broadly because it is anvilicious. (No, I won't link the Evil Website. If you want the link, google it.)

A fair literary response is that the anviliciousness is the point - people may argue about the story, but if you've read it you remember it.

This post is not about the story itself, but about those cold equations, specifically as they relate to reaching Earth orbit. And for that purpose, the grump about the story is, if anything, understated. Realistically, the spacecraft in the story should not have had anywhere a stowaway could hide in the first place. It would be like stowing away in a Formula I racing car.

The cold equations we are specifically interested in are handily available at the Atomic Rockets site. Orbital velocity in low orbit is about 7.8 km/s. Add the potential energy from being about 300 km up, and the kinetic energy needed to reach low orbit corresponds to about 8.2 km/s.

There are also some unavoidable losses from air friction and gravity. In a vertical launch, 1 g of your initial thrust just goes to hovering, adding nothing to your speed. A horizontal launch allows aerodynamic lift to do that work, but means more aerodynamic drag.

If your launch site is at low latitude you also get up a few hundred meters/second of rotational velocity as a freebie.

These variables are, well, variable, depending on vehicle configuration and launch site. But taken together, expect to burn some 9-10 km/s in delta v to reach orbit.

Now we can play with some (very crude!) virtual orbiters. Captain Obvious reminds you that these numbers are not remotely authoritative: for one thing, I routinely round off numbers to 2-3 significant figures.

The highest performance propellant mix that we can really count on is H2-O2, which is good for an Isp in the range of 420-455 seconds, corresponding to an effective exhaust velocity around 4.2-4.5 km/s. Performance in atmosphere is lower. Delicately ignore that for the moment.

Cutting to the chase - and in the best case - getting to orbit calls for a mission delta v equal to at least twice the drive's exhaust velocity. For an SSTO that corresponds to a mass ratio of e^2, or 7.39, or an 86 percent propellant fraction.

To simplistically model more conservative assumptions, again set effective exhaust velocity at 4.5 km/s (still ignoring atmosphere!), while equivalent mission delta v is 10 km/s. In that case the mass ratio rises to 9.23, for an 89 percent propellant fraction.

This is the truly cold equation, because it puts convenient space flight pretty much out of the running. In the ideal case, if your launch mass is 1000 tons, 860 tons of that will be propellants, with the remaining 140 tons for the tankage, thrust structure, engines, minor items such as the guidance package, and (oh yes) a payload. With more conservative assumptions you have 890 tons of propellants and 110 tons for everything else.

These proportions are not, in themselves, impossible. The first and second stages of the Saturn V had dry weights of less than 8 percent and 6 percent of loaded weight respectively. But the first stage used denser kerosene and LOX with much lower performance, while the second stage used H2-O2 but had initial acceleration of only 1.04 g in near-vacuum, and at sea level would have been unable to lift itself off the pad.

For the current state of the art, the dry weight of the SpaceX Falcon 9 first stage is about 7 percent of load weight, but it also uses kerosene and LOX. A tank for H2-O2 would have to be much bulkier - about 3 times the volume capacity - and thus much heavier.

The bottom line is that an expendable SSTO might be viable, but offers no advantage over two-stage expendables. Any saving in operational simplicity (no staging separation or second stage startup) would be have to be balanced against the extremely narrow margins of the design.

Note that both Americans and Russians used 'one and a half stage' designs for their experimental ICBM models, Atlas and R-7 Semyorka - both of which went on to very successful careers as space boosters. Their designs allowed all main engines to be started on the launch pad. But later developments added a true second stage, and modern generation boosters have at least two stages, often with boosters strapped to the first stage.

The Shuttle was (we must now say was!) essentially a 'one and a half stage' orbiter, with recovery of the solid boosters, engines, and payload bay, but expendable main propellant tank.

Getting to a recoverable SSTO rocket would require a tech revolution - either dramatically stronger materials, or dramatically more powerful propellants. Neither is impossible. But likewise, neither is foreseeably in the cards.

An airbreather ascent, as proposed for Skylon, does not call for quite so big a tech revolution, but still requires a couple of very big pieces of undemonstrated technology - jet engines operating up to Mach 5+, then efficiently shifting into rocket mode, and a huge, lightweight airframe capable of handling the heat loads.

Skylon is awesomely cool, but just as awesomely demanding. I can't quite rule it out, but I wouldn't want to rely on it.

Two stages makes it all a lot easier, which is why two-stage boosters are now typical. A fully reusable TSTO vehicle is almost certainly possible. Whether it would be viable - that is to say, competitive with modern generation expendables - is a much iffier question.

And because I've made you wait so long even for this much, I will take up recoverable TSTO, and its alternatives, in an upcoming post.

Related Post: 'The Cold Equations' came up here previously, in the comment thread of a post about what constitutes hard SF.

The image of the X-37 unmanned spaceplane comes from the Christian Science Monitor (which in spite of its name and affiliation has had a good reputation over the years).

Saturday, July 16, 2011

A Visit To Vesta

Via Sky & Telescope comes word that the Dawn probe has reached the asteroid Vesta, going into orbit around it last evening (PDT). Unlike the abrupt arrival burns of chemfuel rockets, Dawn's arrival was a gentle transition from solar orbit to circum-Vesta orbit - the first arrival burn by an electric-drive spacecraft.

The image, taken a week ago by one of Dawn's cameras, shows Vesta as a suitably transitional object, not quite spherical, but also not potato-shaped like smaller asteroids. According to the S&T news note, Vesta probably underwent partial internal melting during its formation, and so has a distinct core and mantle. One of Dawn's tasks is to measure Vesta's mass - implying that we don't actually know yet precisely when Dawn entered Vesta orbit, only that at some point during its gradual burn it must have done so.

Dawn will spend about a year orbiting Vesta before moving on to the asteroid belt's sole full-fledged 'dwarf planet,' Ceres.

This coming week we will return to the vexed issue of reaching Earth orbit. (Yes, last week slipped past me.) But for now, let this be a reminder that exploration of the Solar System is underway and continuing.

In other news, a belated note that I have added my Twitter feed to the right-hand column on the main page, below the archive links. But I haven't taken time yet to add the little bird logo.

Thursday, July 7, 2011

Halfway To Anywhere

Heinlein famously said that once you are in low Earth orbit you are 'halfway to anywhere.' In strict terms of kinetic energy he was wrong. LEO is merely halfway to an independent solar orbit that escapes Earth, but then goes nowhere in particular. With nominal additional delta v, great ingenuity, and enormous patience, you could indeed exploit the 'interplanetary superhighway,' but in spite of the name that is the slowest way to get anywhere.

In more practical respects a case could be made that low orbit is a good deal more than halfway to anywhere. Once in orbit you can use high specific impulse propulsion to reach other worlds, then single-stage rockets to land on and take off from them. None of these maneuvers is as difficult as the brutal lift from Earth surface to orbit.

I have said relatively little on this blog about reaching Earth orbit, precisely because it is so difficult. Getting to orbit is the elephant in the room of space travel, an access ticket that costs about $10 million per ton, give or take.

This cost structure, I would argue, is due as much to modest traffic volume as to purely technical limitations. (More precisely, low traffic volume is one of the technical limitations, perhaps the most important one.) In the current era there are about 60-70 space launches each year, with total payloads probably equivalent to a few hundred tons to LEO.

And for this low traffic volume the familiar expendable multistage rocket is the optimal solution. The launch vehicles are (relatively!) simple and cheap, since they don't need the features - heat shields, wings or parachutes, landing gear or cushions, and so forth - that would be needed to recover them. (The associated ground support facilities can also be skipped.)

Moreover, expendable rockets are built on a production line, achieving some modest manufacturing efficiencies, albeit much less than true mass production (like cars) might allow.

Another way to look at this is that if we had a classic reusable orbiter, capable of being turned around for re-launch every few days, it would be grossly under-utilized. Total world traffic could be handled by one or two vehicles - prototypes, in effect - eliminating all the efficiencies of series construction and fleet operation.

Moreover, those one or two orbiters could not be optimized to match varied payloads and insertion orbits. Thus, most launches would fail to take full advantage of the orbiter's capabilities - meaning that those launches would cost more than, ideally, they should.

The Shuttle, now on the verge of its final flight, is in large part a testimony to misjudged traffic demand. For all of its design compromises and operational shortcomings - which, among other things, cost the lives of two space crews - it was not an outright failure. It proved that a semi-reusable spacecraft is technically and operationally possible.

If we were to build a second generation version we could do a considerably better job. (For one thing, it would not carry astronauts for routine payload launches.) But we will not build a second generation version, and nor will anyone else, at least not in the near future. There is not the traffic demand to call for developing and deploying it.

Note the contrast between SpaceX's Falcon and the 'alt space' proposals of earlier decades. Rather than try to revolutionize space lift, SpaceX has aimed at modest, incremental streamlining of familiar launch technologies. The Falcon doesn't look like the future. It just looks like another two-stage expendable rocket. Which is pretty cool in its own right.

A flip side of this discussion is that I am unpersuaded by the various radical launch alternatives - elevators, launch loops, even laser launch - that have been proposed in recent years. My gut reaction is that they all reek of desperation. Because the Shuttle failed to provide routine biweekly space flights, the thinking seems to go, we should abandon chemfuel rockets entirely in favor of almost purely speculative technologies. I doubt that this is either necessary or viable.

At some point in the plausible midfuture we may reach the point of wanting to put thousands rather than hundreds of tons into orbit each year. At that point - not earlier, and probably not later - we will have reason, and financing, to develop reusable orbiters.

I'm highly doubtful of classic SSTO rockets. The design would have to be too extreme, even with major improvements in materials technology. On the other hand, reusable TSTO is almost certainly technically achievable. It would have a much smaller payload fraction than expendable rockets, since the stages must come back for recovery. But if the traffic is sufficient, there is at least a fair chance of streamlining operations to the point where re-use of the launcher pays off.

Discuss. Be civilized.

Via APOD, the final Shuttle rollout.

Monday, June 27, 2011

Space and Heresy

Longtime readers of this blog know that I am somewhat heretical regarding the human future in space. As I first argued a couple of years ago, outer space is profoundly unlike the New World - such an evocative phrase! - that Europeans encountered five centuries ago (and proceeded to loot and colonize).

This heresy has come up in, and spilled across, a couple of recent comment threads, especially the one for the previous post. (And yes, it was nearly three weeks ago. What can I say? June sort of slipped through my fingers.) As heresies go it raises enough interesting questions to deserve a front page post.

Space is, for one thing, a great deal more difficult to reach than the New World was. Europe's worldwide maritime expansion closely followed a tech revolution, development of the full-rigged ship. But this new technology could be and was employed off-the-shelf for oceanic missions. The Santa Maria was an ordinary freighter. If we could reach Mars aboard second-hand jetliners we would already have gone there.

And once you do get there, nothing in space is remotely conducive to human habitation. The traditional driver of settlement colonization (as distinct from strictly political colonization) has been cheap land. But there is no 'land' in space at all, at any rate in the Solar System. You have to manufacture it, building a hab or a sealed dome, then providing a working ecosystem inside.

It would be many times easier to build luxury condominium developments in Antarctica, or on the continental shelf.

Now, compare all of this to the Solar System of Heinlein's juveniles, where a lot of us got our basic conception of the space future. The space technology made a couple of iffy assumptions. Nuclear thermal drive was not only technically capable of lifting ships into orbit, but socially and politically acceptable as well. Moreover, the chemfuel alternative involved some very convenient magitech, namely monatomic hydrogen, stabilized by means Heinlein never went into.

If you wonder why our real world space tech is so much less convenient, those are sufficient reasons.

But even more than this, Heinlein's Solar System made Venus a 'shirtsleeves' habitable planet, while Mars required no more - or so it seemed - than a mask type breather device. (Heinlein's juveniles do not strictly form a single future history, and details vary, but they portray a broadly consistent future.)

Heinlein's Solar System also had at least two living extraterrestrial civilizations, on Venus and Mars, the local inhabitants having different characteristics in different stories. (The blue-elf Venusians in Space Patrol are entirely unlike the dragons in Between Planets.)

I belabor all of this because Heinlein's Solar System (in particular) had such an enormous impact on what we expect out of the human future in space. In the first years of space exploration we found out that the real Solar System is a very different place, but we have tended to hold onto the old tropes as far as possible, even when reconfiguring them - as in envisioning orbital habs in place of domed surface colonies.

Much of this is for the sake of Romance, i.e. stories. But space discussion often blurs story settings with 'real' possible futures. This blog is particularly guilty of doing so, and quite deliberately so. Space is no fantasy world, a creation of pure imagination. More than 500 people have gone there, and our machines have traveled across the Solar System.

Human interplanetary missions are clearly possible, to the point where we can discuss their architecture in considerable detail. They are merely horrendously expensive, to the point where there is no particular eagerness to pony up sufficient funds. Permanent human habitation in deep space is technically much iffier, particularly with respect to self-contained ecosystems. But it is surely possible, even without such ecosystems. Again, colonizing space is merely, with foreseeable tech, horrendously expensive.

And there is no obvious reason for doing it except that living in space would be Really Cool. For which people will spend a lot of money, but sometimes cool is just not affordable.

On the other hand, the future - not just the plausible midfuture I talk about here - is a Really Long Time. For that reason, saying we will never do something is the iffiest proposition of all. Who can say what our descendants might be doing in the year 22,011, or 2,002,011?

But in the next few hundred years, absent unforeseen breakthroughs in technology, we are more constrained. We might have true space colonies by 2211, but I think it is unlikely, and also unnecessary. Much more likely we will still be exploring space, mainly with machines though sometimes sending people, and perhaps setting up outposts in a few locations.

As a setting for space opera such a future is deficient, but it is a natural way for humans, at something like our techlevel, to come to grips with space.

For more contrarian argument, see author Jeffrey F. Bell. On the technical substance I tend to agree with him, though I would be a bit less quick to throw around 'impossible'. That said, Bell seems to have a remarkably well developed sense of martyrdom. No one ever expects the Spanish Inquisition, but space heresy is not exactly like getting on the wrong side of theological disputes during the 16th century.

Related Post: A Solar System For This Century.

The image of Archbishop Cramner being burned at the stake comes from a website about Anne Boleyn.

Tuesday, June 7, 2011

Sluggish Pickup, But the Mileage is Spectacular

This used-car dealership on mid Market St. has intrigued and amused me since moving to Babylon by the Bay.

Since ordinary batteries involve ions, I suppose the Chevy Volt or even a Prius could be said to use a form of ion propulsion, but how many people associate electric cars with 'ions'? In any case there is no indication that this place specializes in electric cars. Their website does not explain the name, but I can only guess that the name is intended to evoke ion propulsion for spacecraft.

The logo - for a business that touts itself as the bay area's 'newest car dealership' - sort of goes along with that connotation, I think. Doesn't it have a bit of Zeerust retro flavor?

Ion drive, in fact, is probably the only high specific impulse that qualifies as a trope, in the (correct) sense used by the Evil Website. A broad cross-section of people, not just geeks, have at least some vague sense that ion drive is an advanced and futuristic space drive, yet at the same time a 'real' one, not pure sci-fi jive. Perhaps its status was confirmed by Trek, either The Wrath of Khan or its TOS progenitor episode, in which ion drive was characterized as an archaic technology.

Nuclear-thermal propulsion, AKA atomic rockets, do not quite qualify as a high specific impulse drive, its classic form outperforming chemfuel by a modest factor of two or three. Fusion drive, much debated and belated at websites like this one, does not seem to me to have quite made the jump from geekdom to the broader public. The same applies to generic torch drive. Possibly Avatar will promote antimatter drive to trope status; only time will tell.

Compared to these latecomers, ion propulsion has an enormous headstart. Somewhat remarkably, Robert Goddard considered ion propulsion more than a century ago, in 1906. Konstantin Tsiolkovsky published on the subject in 1911 while Goddard performed actual laboratory experiments in 1916-17.

The rocketpunk-era books I read as a kid about Our Future in Space almost always mentioned ion drive, generally in the context of what I now call the plausible midfuture. I recall one book with great illustrations that portrayed an ion drive ship under the heading To the Stars. The next page had a photon-drive ship, To the Galaxies. The temporal implications of intergalactic STL travel were left undiscussed.

I don't have any specific recollection of ion propulsion in rocketpunk-era SF. Heinlein had no interest in space drives that lacked bone-jarring acceleration; his propulsion sequence thus went from nuke thermal to Ortega's mass-conversion torch to the unabashedly magitech Horst-Milne-Conrad impellor.

Clarke also never specifically mentioned ion drive, at least that I recall. He was usually rather cagey about deep space propulsion details, though I often got the impression that some sort of electric drive was implied.

Therein, of course, lies the rub. As I understand it, ion thrusters are in fact not suitable for deep space propulsion of large, human-carrying spacecraft. Their thrust is very low, even by high-ISP standards, and apparently the thrusters cannot readily be scaled up. Ion propulsion is now in service, used by the Dawn probe among others, but there are unlikely ever to be ion-drive ships.

But in trope terms - in the mind of the popular culture - ion drive is synonymous with electric space propulsion in general. Technologies such as VASIMR, while they do involve ionized plasmas, are not 'ion drive' in the strictly technical sense. But in some broader cultural sense they are indeed ion drives, technical details be damned. If it emits a faint blue or purple glow, produces gentle but steady thrust for days, weeks, months on end, it fits the cultural vision of ion drive.

Though I wouldn't recommend it for Bay Area freeways.

The image was taken from my el cheapo ('free') smartphone while riding a vehicle with electric drive: the F Market streetcar.