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Zerraspace — Starcatcher Class Heavy Transport
Published: 2014-08-29 14:59:10 +0000 UTC; Views: 3342; Favourites: 23; Downloads: 47
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Description
Physical Specifications:
- Dimensions: 100 m diameter at main body, 104 m diameter radiation shield, 210 m length (dimensions for engine only without trailing cables)
- Composition: primarily high-emissivity graffold (folded graphene) scaffolding, tungsten carbide / boron carbide radiation shield, skin is layered with high emissivity graffold and Whipple shield
- Dry Mass: roughly 100,000 tons
- Wet Mass: potential maximum of 200,000 to 325,000 tons at STP, 100 to 225 Megatons at 100 MPa depending on fuel type used (hydrogen or helium isotopes)
- Engine: antimatter-initiated fusion with Medusa-style sail, maximum thrust power of 100 PW
- Thrust/Weight: designed for up to continuous 1 G acceleration
- Powerplant: 300 MW Brayton Cycle generator with argon working fluid, heat provided by ICF reactor
This is a continuation of my work started with the starfighter, in this case a mixed traffic heavy duty transport, a workhorse befitting of a massive interplanetary or interstellar economy. The enormous propulsive power required for such loads would fry all but the largest engine bells, hence it relies on a lightweight sail, and trails behind on long tethers to avoid intercepting the worst of the exhaust: it’s the sight of the brilliant trail contained within the sail that gave this class its name, Starcatcher. With an even larger sail it could become a suncatcher, using mere sunlight to accelerate, but as is it can still benefit from beamed power stations to push it ahead.
At full power the ship burns tons of fuel per second, enough that it could be set up to rely on fusion charges, specially shaped to direct the blast towards the sail and further reduce ship exposure. Nevertheless, most Starcatchers rely on antimatter catalyzed fusion. This allows them to run more steadily at low accelerations where the bombs would require a low pulse rate (their spaced-out pushes would give quite a jarring ride), and moreover, it’s quite a bit safer, as bombs might be set off or stolen for use as weapons, but gaseous fusion fuel on its own is pretty tame, and these ships only need micrograms of antimatter for every journey, not enough to be much of a threat (beyond that of a few tons of gas in a truck’s fuel tank, at least). This does run the risk of leaving one stranded if all its antimatter stores run out, as the Starcatcher’s ICF reactor is too feeble to provide meaningful propulsion, hence this is distributed amongst several containers, spaced apart to keep any one from damaging the others if it blows up. Their distance also serves to minimize heat flow from the main body, as the antimatter must be stored at very low temperatures for easy containment, temperatures at which thermodynamics limit even ideal refrigerators to single digit efficiencies: the only consolation is that the cooled spaces are so small that this translates to only a few spare watts of waste heat.
As it generally runs regular routes the Starcatcher is meant to be automated, with a huge retinue of loaders and tugs filling and emptying it, attaching and detaching load modules, and pulling it into and out of range of docking stations that it may safely activate its drive. There is a crew accompanying any passenger runs, but they are easily bunked in a spare habitation module in one of the attached carriers, hence the ship proper requires no life support of its own. In those cases where it must venture into uncharted or potentially dangerous territory, or where the cargo is too important to be left unattended, a special section must be attached to house mission overseers. The Starcatcher does accommodate them, in its own way – the radiation shield protrudes over the edge of the ship, covering any who would have to work on the sides.
The beauty of the design is that acceleration can be traded off for cargo capacity, allowing the Starcatcher to act as either a swift passenger service or a slow cargo crawler. As a high speed ship, typical payload mass is 800,000 tons (for a total mass of some million tons), and it will accelerate at 1 G over the course of one day to 1000 km/s, after which it’ll coast at this speed for most of the remainder of the journey, crossing 0.576 AU/day. It could go faster, but at the cost of a higher mass ratio (with helium-3 fuel, this can be as low as 1.1), and it can still make incredible time – Mars is accessible within a week, the inner Jovians within three, and the ice giants within two months. With just double that weight of fuel and lugging a whole 100 million ton payload (mass ratio of nearly 1.002), maximum acceleration drops to about 10 milligees, allowing for a top velocity of 19.422 km/s that can be reached in a little over 2 days, equivalent to 0.011 AU/day or 4.086 AU/year. Alternatively, that’s equivalent to a delta-v of 38.845 km/s, more than sufficient for Hohmann transfers between any of the planets, and much better can be managed by compressing the fuel for higher mass ratios. Taken to its ultimate limits, the Starcatcher could manage a staggering mass ratio of 225 (not that this is practical, as it assumes negligible payload), allowing a maximum velocity of 0.176 c (delta-v of 0.352 c) or even higher if part of the acceleration were taken up by beaming it ahead, and it transforms into a potential interstellar voyager – a true Starcatcher, indeed.
Again, I would like to thank the Atomic Rockets website for help gathering data, as well as the Pennsylvania State University (developer of the AIMStar and ICAN probes) for guiding my research into potential use of antimatter, and the user T.Neo of the Speculative Evolution site for her enormous feedback and inspiring the ideas that set this off.
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Comments: 9
I don't quite understand the diagram here. You discribe it as being a Medusa using antimatter catalyzed fusion bombs, but the diagram shows fuel tanks, ignition lasers, and and ICF reactor. Which is it? I understand these are two completely different drives using completely different principles.
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That was poor wording on my part; I said it could use fusion bombs, but usually uses antimatter catalyzed fusion. The process itself is just what you'd expect - pellets of the fusion fuel are released and allowed to drift till they're much closer to the sail than the ship. At this point, lasers are used to compress it (I've since been told that ion particle beams would probably be better for this), and antimatter is launched against it to provide the energy that starts the process. What differs here is that propulsion is achieved by having the sail intercept the blast, with thrust arising from its debris and radiative pressure.
Using antimatter catalysis makes it easier to start the fusion process, and eliminates the need for self-reliant bombs which could go off or be stolen for use as weapons (the mass of antimatter required is small enough that it isn't worth using for such purposes either). Having a Medusa sail intercept the blast rather than a magnetic ship nozzle allows the ship to be farther from the blast center reducing radiation and heat exposure, and makes for easier construction: it puts the ship under tension rather than compression, which we have stronger materials for, and the sail does not need to be rigid - it'll be blown to size by the blast - or cooled - no need for superconductors, and the sail's area already serves as its own giant radiator.
Possibly adding to the confusion is that the ship has an ICF reactor; that's built into the ship's main body, and is only used for providing power when it is not actively thrusting. It also provides a recourse to keep the ship running (if not thrusting) should the antimatter stores be exhausted.
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Absolutely beautiful! I'm a big fan of the Medusa idea, for both romantic and practical reasons, and I am so happy to see someone create such a great depiction of one. The antimatter-catalyzed fusion is an excellent touch as well, solving the proliferation problem handily while increasing the spacecraft performance.
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I forgot to ask, the Medusa model on Atomic Rockets features a winch to smooth out the shock of detonation. Is there a similar feature at work here?
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Huh, this never turned up in my Notifications... Yes, you're right on the money. In this case, the winches are right under the protruding ring. Having so many (1400 of them! That was not fun to model) would probably require a fairly advanced control system to manage, but also allows for very precise manipulation of the sail, which is critical for steering. That being said, these chords are so long that the time necessary for the stretch to propagate throughout the whole length might go a long ways toward smoothing the sudden acceleration all on its own!
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Cool design. I like the way you use the sail. You've certainly come up with some really interesting designs.
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I love idea of a plausible way to store anti-matter and its use in Goldilocks explosions. 0.176c is also a great speed for near/intermediate-future sci-fi because if you have ships that take 2k just to reach Alpha Centauri then those same ships could conceivably be rendered irrelevant by tech advances before they have enough time to make a real impact depending on how the world building is set up in regards to FTL. 0.176c would allow colonization of most of the Local Bubble in a century or two, if you'll pardon me for thinking out loud and stating the obvious, and it would allow for a lot of interesting Balkanized interstellar empires before FTL is developed and optimized. Perhaps if it took 1,000 years to get a solar system wide civ up and running there could also be an intermediate 1,000 year period of slow interstellar colonization before FTL and then maybe another 1,000 years could go into perfecting the FTL. By then it would be 5,000 AD so if you wanted a timeline where the main story starts at 10,000 AD and most of space remains unexplored then I guess that means throwing in a bunch of dark ages or decreasing the density of advanced civilizations. By the way, how do you acquire anti-matter before storing it?
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Both this ship and the last were developed for the same story universe as VotVP, and though they're merely part of the backdrop and don't notably feature within said story, I do intend to use this universe and various points in its history for other works where they'll be more important. There's already a basic framework for the timeline - early FTL travel stunted solar system development as man sought more preferable Earth-like worlds outside it, but economic and sociopolitical upheavals combined with the relative rarity of conveniently habitable worlds and the time needed to fill them slowed expansion to a crawl, so by the time of VotVP (around 3500 AD) only 20 worlds are meaningfully inhabited, and of these only a couple besides Earth have populations exceeding hundreds of millions. That being said, I do like your suggestions here, particularly since the ship's mechanics would let it fit in both in settings utilizing FTL and those that do not, so I might apply them elsewhere. The principle behind this design isn't all that complex, so it wouldn't be much a stretch for something similar to develop in another place.
Regarding antimatter production, this does a good job of explaining it. Basically if enough energy is applied to atomic nuclei, pair production will ensue as the energy is converted to the equivalent mass, producing a particle of normal matter and its complementary anti-particle (for the record, this also means that antimatter production will never exceed 50% efficiency, but in making it you also make fuel to annihilate it with, so this isn't a particularly big problem). This is done artificially via particle accelerators or large lasers speeding up electrons and plowing them into thin sheets of material, causing the charges of its atomic nuclei to divert them hence forcing the electrons to give up (and in doing so transmit) part of their energy as high frequency photons, which are absorbed and start the process. That being said, it seems any sufficient application of energy to matter is enough to get pair production started – natural antimatter production occurs all the time. It’s a byproduct of certain radioactive decay processes and thunderstorms, the quantum foam hypothesis holds that minute amounts are generated and annihilated all the time, some is made by the sun and winds up in the solar wind, and significant amounts can be found in cosmic rays (up to 1% of their particles) and orbiting planets in their radiation belts. NASA is currently looking for a way to sweep these belts for just that very purpose, but until that day we’re just going to have to settle with what we can make on Earth and hope to vastly improve production efficiency. You see, the produced particles tend to be highly energetic, sometimes enough to cause even more pair production, but generally this poses a problem as they’re moving at ludicrous speeds and must be decelerated and contained before they hit anything. This is the main hurdle facing viable antimatter production, and while some breakthroughs have been made, efficiency is generally quite appalling, with Fermilab’s on the order of 1 millionth of a percent (I wish I were kidding).
There are two things I should note here. Firstly, the above processes all produce antimatter subatomic particles, not anti-atoms and true anti-materials. While you could theoretically produce an antimatter variant of any element in the periodic table, only two elements have been successfully created – anti-hydrogen (as used in the Starcatcher) and anti-helium. Anti-atoms are even more difficult to make than anti-particles, as the only means we have of producing them currently is throwing the needed particles at one another and hoping they’ll stick, and the resulting anti-atom is neutral and hence cannot be contained electrically. Antihydrogen has been successfully stored for up to 16 minutes – that’s the best that can currently be claimed, but that is thousands of times better than the previous record (1/6th of a second), and quite a few techniques are on the drawing board for how to get around this, a few described in this article . The authors hold that frozen antihydrogen should be diamagnetic like its regular matter counterpart, in which case it could be suspended with static magnetic fields, and this is what I applied for the Starcatcher.
The other is one of the big catches with antimatter: unless you can harvest it naturally (and there isn’t as much around as I’m making it seem), it’s no use as a means of energy production. Pair production requires just as much energy to create the two particles as would be released by the two annihilating one another, so at best you’ll end up with right what you started with, and more likely than not you’ll incur losses from some inefficiency. Purely from an energy standpoint, you’d have been better off using the energy taken to create in the first place. It’s from the power density standpoint that artificial antimatter trumps all else – it contains as much energy as possible within the smallest possible mass, and allows you to release it as quickly as possible. The Starcatcher doesn’t use antimatter to propel itself directly, but to apply the needed energy to initiate fuel fusion so quickly as to minimize heat losses (which would be a major problem if it relied on lasers), and it’s the fusion that provides direct propulsion and power for the ship.
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Thank you again for the links and excellent commentary. From a purely economic standpoint I love where this seems to be going. Big energy relies primarily on fusion which means that either Lunar-based He-3 harvesting or ocean-based heavy water refinery, a la OGame, is king...unless a lot of smaller ships etc can get by with manipulation of exotic matter (Third Law extra-dimensional and/or mulitiverse-derived as opposed to straight up antimatter) components via use of battery-based or fossil fuel based electrical systems. Anyway, antimatter is still important because it allows a wider range of flexibility, which would be especially important for military applications as well as potentially business class rapid passenger transit via careful tweaking of warp drive tech, which would of course rely to some extent on antimatter. Thus, the cost of antimatter could be an important factor in explaining higher prices for premium starship components etc while also having a second tier system where less important freighters, clunkers, etc make do with slower transit, inferior tech, etc.
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