Nibb31

When designing a spacecraft, you really have to keep in mind what you're building it for. - Do you want to launch crew to LEO and bring them back safely? => Soyuz, Dragon, DreamChaser, CST-100... - Do you want a versatile manned spacecraft for BEO => Apollo, Orion... - Do you want cheap access to LEO => Ariane 6, Dragon 9-R... - Do you want a spaceship that looks cool => Space Shuttle The whole point of building a spacecraft with wings is stupid. You need a massive launcher for all that extra hardware that is only used for the last 10 minutes of the flight.

The whole point of a Space Shuttle was to bring back and reuse the most expensive part of the launcher: the engines. If you are launching a complete airframe just to bring back the same airframe, and throwing away a huge rocket to do so, then what's the point of launching that airframe in the first place? Wings, hydraulics, landing gear, and tiles serve no purpose in space. You're better off throwing away a smaller/cheaper rocket and bringing back the meatbags in a smaller/cheaper capsule. Buran didn't make sense economically. It's only purpose was for the USSR to have a Shuttle because the US had one. The Soviets knew that it didn't make sense, but they also also knew that the US STS didn't make sense either. Consequently, they figured that the STS must have had a secret military purpose, so they concluded that needed to match it and cancelled the Spiral/MAKS/BOR program which was more promising.

Skylon is effectively 4 old geezers working in their shed for the past 20 years. I applaud folks who can think out of the box, but Skylon is such a radical design that basically 90% of it unproven technology. The design could only achieve SSTO if the optimistic theoretical margins are met, and as everybody knows in the aerospace industry, budgetary and performance criteria are rarely met at 100%. Any slight reduction in performance or extra weight in the actual flight article will render the whole thing useless. And of course, it also implies that the whole thing makes sense financially, which it doesn't. It's orders of magnitude more complex than something like the A380 or the B787 to design, with unproven manufacturing techniques, a whole new engine technology and an entire infrastructure to develop, yet they expect it to cost half the price. They also expect to build dozens of them, which implies that there is a market for hundreds of flights per year, which there simply isn't. Let's see a working model of their engine reach hypersonic speed on a scale model or on a testbed aircraft and then we'll start talking.

Seriously, the problematic is the same as for MarsOne. Permanent life on Mars is unfeasible without very heavy transport to Mars, heavy landing techniques, closed-loop life support, and solutions to the radiation and low-gravity issues. We are decades away from developing any of these technologies to a readiness level that would allow human lives to rely on them. In the next decade or two, we might be able to pull off a manned landing and return, but a permanent colony is orders of magnitude more complicated.

Dear Mr Musk, If you go to Mars to die there, can I have your stuff? Yours sincerely, Nibb31

I'd rather have a solid cable or truss structure than a rotating joint that could spring a leak or jam with catastrophic results. You're going to need lubrication, thermal control for the friction, appropriate sealing, and spare parts. And good luck replacing a joint like that in EVA if you have something like the SARJ failure that happened on the ISS. The complexity introduces a whole bunch of extra failure modes that you could definitely live without, because if a ball bearing fails or jams, the forces would rip your ship to pieces. Moving mechanical parts in space are problematic, which is why they are usually kept to a minimum. Large moving mechanical pressurized parts are even harder. Rotating the entire ship is much easier. It was done for Apollo, although not for gravity. As long as you keep things in balance, there is no reason it wouldn't work on a larger ship.

Operational crew is 6, with 9 on-board during rotation periods. The ISS can hardly operate with only 3 crew members, and they certainly couldn't do any science.

Gemini XI actually tried passive attitude stabilization of two spacecraft connected by a tether in order to create artificial gravity, but with mixed results.

It'll probably launch once or twice, and then it will be cancelled because of the infrastructure cost for 1 launch every two years. It'll be ironic if it endures the same fate as Energia.

It'll probably launch once or twice, and then it will be cancelled because of the infrastructure cost for 1 launch every two years.

Why would they need to? In any case, there is always at least 2 Soyuz docked at the ISS to serve as lifeboats, which is why the ISS supports 6 crewmembers.

We don't even know if artificial gravity is actually desirable on an interplanetary journey. There have been no tests or experiments on its long term effects. We have no idea how much is necessary, or safe, or for how long. For all we now, current bone-loss medication, or some future treatment, might be enough. It's really a shame that the CAM module was cancelled on the ISS, because before we ever send people off on a long term interplanetary journey, we are going to need to build a couple of centrifuges in LEO and spend a couple of years testing the long term effects. There are also easier ways to generate gravity than to have a spinning ring, with complicated joints and axles. Why not just spin the whole ship for example?

I don't see why it wouldn't work. The only reason communism can't work on Earth is because humans are humans. In an ideal organization, with ideally motivated individuals, it's probably the most efficient system. See Star Trek. I think it's actually more probable that space-faring species, with a civilization that spans thousands of years and advanced technology, must have streamlined itself into a highly efficient and rational society that puts the common interest of the group before concepts like personal greed and private property.

It's both. Democracy is a principle. A republic is an implementation of that principle. Democracy is the notion that the people gets to vote. Direct democracy can lead to the rule of the mob and oppression of minorities and is generally impractical. Therefore, most modern democracies are republics and have some form of indirect vote in their system. In the US, the people gets to vote on their representatives. Whether that vote is direct or indirect is irrelevant, it's still a democratic process. A republic is a particular implementation of government where the power is in the hands of elected representatives. A republic isn't necessarily democratic. For example the Roman Empire or Ancient Greece were plutocratic republics, and China is a republic where nominated party members elect the representatives, not the people. The US, however, is a democratic republic, which is a form of democracy. Stating the opposite would be like claiming that the UK is not a democracy because it's a kingdom, when it is actually both.

Interesting article here: http://www.nature.com/news/planetary-science-lunar-conspiracies-1.14270

If you have an Android smartphone, I strongly suggest Sky Maps: https://play.google.com/store/apps/details?id=com.google.android.stardroid

Yes, it could be useful for building large structures, like sunshades, radiators, solar panels, or large antenna dishes. Pretty cool technology if they ever get it to work.

He-3 from the Moon is just about the most expensive and inefficient way to do fusion. There are much cheaper and more straightforward fusion fuels.

If they had any angular velocity relative to the station, they just had to hold on to tether as it would swing them around the station. The tether would just roll itself around the ISS and bring them towards the center in a spiral.

Plan changes are more efficient when done at a high apoapsis. You are going slower, so you need less delta-v to rotate the inclination. You would need to run the numbers, but it might be more efficient to raise your ap (best for it to coincide with the equatorial AN or DN), rotate your inclination, perform your Hoffman transfer, and rotate inclination again when you enter the SOI of your destination.

If I had that money to waste, I'd rather get myself a new computer to play KSP.

One word: Magic.

I don't buy that explanation. If they had any angular momentum, it was apparent that they were stationary relative to the ISS. Let me demonstrate my poor drawing skills: In this magnifiscent work of art, for them to appear stationary relative to the ISS as they were on screen, the station must have been spinning at a speed v while their own speed must have had a speed v' that corresponds to the exact same rotation period as the station for the length of the tether. If they were going only slightly faster or slightly slower, then the tether would have wrapped around the station and pulled them in. Basically, they had to be "geostationary" above the attachment point of the tether. What are the odds of those two speeds v and v' matching exactly out of pure coincidence? But ok, this is Hollywood. Let's imagine that their speed did match the exact rotation of the station. In that case, all they needed to do is to pull on the tether or to climb up it, as shown by the green arrow in my crappy diagram. They would have preserved the same absolute angular momentum v' but because the radius of the tether was different, their relative speed to the anchor of the tether would be much higher. Their speed v' would no longer be the magical "geostationary" speed that it was at the end of the tether and would have wrapped around the station and pulled them towards it in a spiral. The other point that doesn't make sense in this scene, is that as soon as Clooney detaches himself, Bullock is no longer pulled away from the station. She should have had the exact same angular momentum v' as before, yet she has no problem climbing back up on the tether to get back to the station. She could have done exactly the same thing with Mr Nespresso still attached.

After the free-return burn, they had calculated the re-entry trajectory for the weight of the CM at the end of a nominal Apollo mission. Of course, on a nominal mission, the weight of the CM would have included a certain amount of moon rocks and samples brought back from the surface, while most of the trash and used equipment was jettisoned with the LM. Luckily, someone at Houston spotted the mistake before they separated from the LM. They decided that it would be preferable to move some ballast from the LM into the CM, in order to approach the weight that was used for the calculations, rather than to rerun the calculations minus the weight of the rocks. Those calculations took several hours in those days, and would have probably required an adjustment burn, which they wanted to avoid. The shape of the Apollo capsule did have a positive lift/drag ratio when pointed at a certain angle, a bit like a wing: The following diagram shows (at an exagerated scale) what the re-entry profile looked like: Because the Apollo CM passively took the aerodynamic angle shown in the first diagram when it was 'heads down', the method for steering the lift up or down was to use thrusters to roll the CM left or right. - To reduce lift (phase 'I'), they would typically roll 2 minutes left, then 2 minutes right in order to maintain the trajectory - Then to provide more lift and go up (phase 'II'), they would roll the CM to a straight 'heads down' attitude. This trajectory allowed the capsule to lose speed in the upper atmosphere while not putting too much stress on the heat shield and not taking too many Gs. A direct dip into the lower atmosphere (without phases 'II" and 'III' in the diagram) would have caused a much more brutal deceleration and generated more heat for a longer period. Of course, because the Apollo 13 CM was lighter than it should have been, without the extra ballast it might not have dipped low enough into the atmosphere (in phase 'I') to be captured, resulting in an even worse day for the crew. Fascinating, isn't it?

Rutan is a great aircraft designer. However, he isn't an expert in spacecraft. The SS1 and SS2 are not spacecraft. They aren't even hypersonic, let alone orbital. They are atmospheric vehicles with passive attitude control and no thermal protection for re-entry. The SS1/SS2 concept simply doesn't scale to an orbital vehicle at all. To go orbital would need at least a second rocket stage, some sort of RCS, and a TPS. The actual vehicles would end up being twice as heavy, the mothership would have to be 10 times larger than it is making air-launch impractical, the feathered wing concept would be useless. It would have to be a totally different vehicle.