sevenperforce

Four of each animal is also not nearly enough to create any sort of sustainable population, either. If you want a small temporary breeding population of tasty or useful animals, a few hundred embryos per desired species might be enough. But if you want a permanent sustainable population you will need 100,000 individuals minimum in order to have enough genetic diversity for the population to survive in the wild, and that is if you have already achieved 95%+ terraforming on the target world. If the trip only takes 45 years, why would most of the passengers have never seen Earth? Is artificial gravity based on linear acceleration, centrifugal acceleration, or handwaved? Handwaved selectable artificial gravity is technology on a level with Alcubierre FTL drive.

The SABRE engine cannot use kerosene, by definition, because it is an airbreather that requires you to dump LH2 through a precooler. But you wouldn't actually need LH2 to get Skylon to orbit. Strengthen the frame, replace the SABRE engines with a pair of steel-ducted Merlin 1D clusters, and fill it up with kerolox. It would carry triple the payload to orbit. Mass fraction wouldn't be as good, but that doesn't really matter because kerosene is cheap as heck and simple to tank. The proposed Skylon vehicle is REALLY big.

It is a battery, not a capacitor. That was my first question as well.

Perhaps a regular hypersonic transport between two nodes carrying a series of time-sensitive cargo packages + passengers?

The problem is that it actually has to be used in order to generate revenue. Intriguing. I wonder how large an average shipment is. Partial passenger/partial cargo is a possibility if there is some regular need...

You really would want to go cargo, simply because the LV requirements are thus rendered substantially less onerous and you have a lot more flexibility. Unfortunately, I can't think of any suitable cargo either. There's really nothing in the world that needs to be shipped in bulk to the other side of the world in a matter of hours...at least, not so desperately that people would pay for a suborbital spaceflight to accomplish it. I suppose there are certain particularly expensive consumables with short lifetimes that could be harvested and shipped to high-end restaurants, etc., but the demand would not be high enough to be a major driver. That leaves you with human cargo, with all its nasty "keep the cargo alive and air-conditioned" requirements. There's a glimmer of hope here, because while the difference between hypersonic and supersonic flight may be fairly low, supersonic options don't currently exist, and there is a big difference between hypersonic and subsonic flight. Subsonic flight means a trip to the other side of the world can take a day or longer; supersonic cuts this to several hours...suborbital hypersonic means no two points on the globe are more than an hour apart. There's a fair probability that the ability to commute around the world would prove attractive to enough people/businesses to service at least one or two routes from the start. I don't know what the maximum viable ticket price would be. Ideally, you could use existing airports by adding a dedicated spaceport terminal at lower cost than building an entirely new launchpad. The suborbital/orbital transition would probably be accomplished by having some portion of the passenger cabin be replaceable with an extended fuel tank. E.g., you can take 30 people to the other side of the world in an hour for $90,000 each, or you can take 10 people to orbit for $350,000 each. Well, this is a suborbital spaceflight, not a high-altitude sustained hypersonic flight. With a steep ascent and re-entry trajectory, only two sonic booms reach the ground. LH2 is a non-starter, I think. You need to be able to run on RP-1. Or LP/LNG at the very least. That's not a bad thing. A high propellant mass fraction is okay...you WANT to be able to carry a lot of fuel...and high density means better T/W ratios and a smaller overall vehicle, which drives down vehicle reuse costs. Yeah, but the horse is a lot closer to the cart than the rapid-reuse-orbital-flight version.

I just realized something. Chemistry is a compression algorithm for a subset of physics. There are certain physical particle interactions which happen the same way every time and thus can be represented in abbreviated form. Biology is a compression algorithm for a subset of chemistry. Psychology is a compression algorithm for a subset of biology. Sociology is a compression algorithm for a subset of psychology. A neat way of thinking about it, anyway. The supercomputer could "compress" by simulating chemistry rather than physics when particles were in the correct energy ranges, and so forth.

Lithium-7 has a vanishingly low probability of absorbing the high-energy neutrons in a nuclear reactor. It needs ultra-high-energy fusion neutrons for the absorption to have any reasonable probability.

SSTO RLV proponents often argue that once a vehicle with rapid reuse potential exists, it would create the market which would enable it to be cost-effective. Unfortunately, it's doubtful than anyone will bother to build or design such a craft unless the market for rapid small-payload LEO launch already exists. This creates a chicken and egg problem, where the market won't exist until the launch vehicle does, and the launch vehicle won't exist until the market does. It's possible, however, that a launch vehicle could be designed for a broader market, thus becoming available without requiring the rapid small-payload LEO launch market to exist first. From an economic/investment standpoint, it is much more attractive to build a vehicle which can use an existing market than it is to build a vehicle on the speculation that it will create a nonexistent market. Such a market could potentially be realized in a similar way to how we first got into space: using the same vehicles for suborbital and orbital flights. The US and the USSR both figured out that the gigantic missiles they were planning to use to lob nukes on suborbital trajectories could, when properly staged, be used to boost payloads into orbit. Many orbit-capable vehicles would make excellent hypersonic suborbital transports, suitable for transporting a large payload between any two points on Earth in an extremely short time. With a decent-sized fleet of such vehicles* servicing regular hypersonic transportation around the globe, you would have the support infrastructure necessary to service those same vehicles on orbital flights, either with reduced payloads or with a launch assist stage. The question, then: does such a market exist? Is there a need for large cargo (or, on the other hand, passenger transport) to be whipped around the world in a matter of hours, regularly? Who would pay, and what is the probable market saturation? *Skylon could potentially serve such a role, as it likely has excellent suborbital hypersonic flight capacities. It's not ideal, though, because it requires a great deal of LH2.

Also relevant...

Atom-by-atom is easy. But the universe is splitting atoms all the time. So it really needs to go quanta-by-quanta, which is not so easy. XKCD #505 is apt...

But wouldn't objects move back in during its million-year orbit? Nah. Planet 9's subtle adjustment to the sun's gravity well extends all the way across the solar system; it's not like its gravitational influence just drops to zero when you get far enough away. Otherwise the L3 Lagrange point wouldn't be a thing. Under my definition? No, it wouldn't be. Right now, the moon is tidally locked to Earth but Earth is rotating independently of the moon. When the dynamics of the system shift so that both Earth and the moon are tidally locked to each other, it will become a double-planet system. I mean, we would still probably call it "the moon" for the sake of history, but there's nothing wrong with recognizing such a change. After all, the Earth and the moon are already very close to being a double-planet system; the moon doesn't actually go around the Earth at all. They're just in very close solar orbits and the Earth's gravity perturbs the moon's solar orbit enough to tidally lock it and make it appear to orbit Earth.

Could have been a neutron star? I don't think so.

For anyone paying attention, they have rotated the F9 first stage and are lowering it onto the transport rings right now. http://www.portcanaveralwebcam.com/

Lithium-7 has a really low fast neutron cross-section and needs ultra-fast D-T fusion neutrons to actually fission into tritium and helium. Not enough neutrons to do it, even in an NTR.

'Twas pointed out to me elsewhere that Pluto is large enough to retain Rhea as a "real" moon -- that is, with the barycentre inside of Pluto. However, Pluto would still become tidally locked to Rhea in astronomically brief time. Thus, I propose an adjusted definition for "natural satellite". A natural satellite is a self-gravitationally-bound object orbiting a barycentre inside a larger body, too small to force mutual tidal locking with the larger body. This makes intuitive sense; if two objects are tidally locked then they are orbiting each other, even if the barycentre is within one body. A moon is a gravitationally-rounded natural satellite of a substellar object. A planet is a body large enough to have a moon. This cutoff is about 6.3e22 kg, comfortably greater than the mass of Eris but comfortably lower than the mass of Mercury. A dwarf planet is a gravitationally-rounded body too small to have a moon.

We can call them moonitoids Better yet, dwarf moons. It's forcing orbital periapse arguments for the other bodies, which is exactly what orbit-clearing gravitational dynamical dominance is supposed to do.

I may give this a shot in Demo. Won't come anywhere close to y'all's results, of course, but it will be an interesting design challenge.

Yeah. I was expecting them to drain the ignition fuel (pyrophoric TEA-TEB) but instead it appears they simply burned it off by triggering the reignition sequence. Presumably it was something they needed to do while they had the rocket firmly strapped down, before attempting to transport it. Speculation that this should have been done automatically on OCISLY but some part of the automated process failed.

Recovery updates.... I have been keeping up pretty closely with the live stream video to the stage 1 recovery. They have removed an access panel covering one of the engines and are going through what is apparently a pretty involved process. The workers are wearing fire protection suits, so they are probably setting up to remove the engine igniters.

Looks like a win, though it's a shame the landing legs didn't survive. Hint: try parallel-staging the landing boosters with radial decouplers, so you can ditch them at touchdown. I'll try now with a suborbital flight....

Yes, the cold-gas thrusters at the top were the first thing I noticed.

Talking about size, not aerodynamics or COM. If I didn't know better, I would think the landing video was a telephone-pole-sized rocket landing on a basketball-court-sized barge...not a 737-sized rocket landing on a football-field-sized carrier. I've asked people how large the booster looks and they say "a couple stories high" and I tell them it is twice as long as a semi-truck, landing on a football field, and their jaws drop.

It is. Pictures just don't do it justice. This is not a telephone pole, folks.

Yeah, a boneless creature has some serious advantages. Especially if they can survive in open air by respirating through their skin. It's even theoretically possible that a boneless creature could survive unprotected EVAs without difficulty. If they can handle the transition from high pressure to atmospheric pressure then that last atmosphere shouldn't be much of a problem if they can mitigate moisture loss. Ability to handle very high gees could lead to ground-based launches like launch cannons, especially because it is far easier to build a large underwater structure.