83

Reliability. Any rotating station needs non-rotating components: solar panels need to face the Sun, radiators need to be shadowed, docking points need to be non-moving, and so on. Making a rotating joint that can last decades is hard; if the hub of a rotating station seizes up, the resulting accelerations are likely to tear the station apart and kill ...


60

Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would going much slower help you? No, it would not, because simply carrying the book is exhausting to you. You would never be able to hold the book up for an entire ...


50

I'll add one or two more items to Mark's excellent list. Stability - large rotating platforms (and they have to be large to produce useful artificial gravity) are subject to all sorts of precession. Cost. The ISS was not cheap. Now imagine just getting maybe 50 ISS' worth of mass into orbit, assembled, and then enough fuel to spin it up.


49

LAGEOS satellites This has, in a way, already been done, with the Laser Geodynamics Satellite (LAGEOS) satellites. LAGEOS satellites, (the second of which was launched from the shuttle on mission STS-52), have a projected orbital lifetime of over 8 million years. They are in a very stable medium Earth orbit. They are completely passive, but are ...


43

From STS-3, the tank was left unpainted, the brown color is the natural color of the insulation foam, see this PDF. The color would get darker from exposure to the sun. The tanks of STS-1 and 2 were painted white, but this took several hundred kg of paint, and after STS-1 and 2 tests showed that the paint wasn't necessary.


43

NASA have deployed 4 rovers to Mars, and are working on the fifth. ESA is working on nr. 6. Sojourner: tiny, limited. Spirit and Opportunity (MER): much larger than Sojourner. No reuse possible. Spirit and Opportunity were identical. Curiosity: much larger than MER. No reuse possible - but it does use technologies proven on MER, like the suspension design. ...


41

Neither has much financial purpose without the other. A BFR cannot perform any useful function without an upper stage, and that is the BFS. Since the whole platform is a major investment in a new architecture, they are starting with the smaller piece - the BFS. Since it uses some of the same engines as the BFR, it can act as a testbed for both BFR and BFS ...


37

It's a good question, followed by many relevant responses so far. I'll focus on the physiology aspects. Research had been conducted for decades prior to ISS launch on creating artificial gravity through spinning. The short of it is: the human balancing system (inner-ear plus brain) cannot not handle the spinning motion on the scales of what humans could ...


31

Elon Musk stated in a news conference after the Falcon Heavy launch that the BFS will be the focus because they think they understand designing booster rockets pretty well, and thus they decided to focus on the more difficult piece first. He answers this in response to a question that starts at 20 minutes 52 seconds here, and speaks specifically to starting ...


29

Ars Technica has a pair of articles that give some insight in why it's desirable to use new designs: NASA has been working on an updated version of the F-1 (the first stage engine for the Saturn V). Some of the major differences: Another clear difference is the construction of the exhaust nozzle itself. The F-1's nozzle was made up of two parts: the first ...


29

A solar sail with an areal density of $1~\mathrm{kg}/\mathrm{km}^2 = 1~\mathrm{mg}/\mathrm{m}^2 =0.001~\mathrm{g}/\mathrm{m}^2$ is impossible by known materials science because graphene has an areal density of $0.77~\mathrm{mg}/\mathrm{m}^2$. Being a single atomic layer of a light atom, graphene is the absolute lower bound for the areal density of pretty ...


27

There was a proposal to add an experimental rotating habitat: Nautilus-X. One of those wonderfully tortured backronyms: Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration - eXperimental. Its primary purpose was to extend how long humans could live in space not only through artificial gravity, but also storage for consumables, ...


26

For supersonic flow, the Sears-Haack body offers less drag than the shorter teardrop that's optimal in the subsonic regime. Sears-Haack is pretty similar to the German V-2 rocket body. (Note that the proportions of this particular example aren't part the definition of the Sears-Haack shape; for minimal drag you'd have to have an impractical body of infinite ...


26

Has any research into actually producing anything larger than the F1 been seriously carried out? The M-1 was a hydrogen engine just a little larger than the F-1. Parts of it were built and tested and the engine would likely have worked just fine if completed and flown. Lack of need for a super-heavy lift vehicle larger than a Saturn V prevented it from ...


25

I think you answered your question in the first sentence. I am reminded of this image: Aerodynamics is but one (albeit a large one) of many concerns in the systems engineering of a rocket. Others include manufacturability, propulsion, changing flight regimes, safety, structures, economics, etc... All of these seem to have converged on a simple, more-or-...


25

The problems would be many to transmit a radio signal for 10,000 years. However there is nothing about a 10,000 year lifetime that would violate physics. It would just be extremely difficult engineering. I would use a thermally driven Stirling engine for power, magnetic torquer for attitude control, and vacuum tubes for the electronics (which are much more ...


23

The material used for the seal is silicone rubber. Example materials considered for NDS iLIDS are: Parker S0383-70 (as part of Gask-O-Seal product) Esterline ELA-SA-401 Silicone rubber is the only class of space flight-qualified elastomeric seal material that functions across the expected temperature range. NASA Glenn has tested three silicone ...


22

To complement, not attempt to replace, the other answers, I would like to propose a difficulty I see nobody having mentioned so far, but which could potentially be very problematic over such long time scales. Micrometeorite bombardment. Even after only 15 years in low (550 km) Earth orbit, we know that the Wide Field Planetary Camera II (WFPC2) on Hubble ...


22

The expression $v_e = \sqrt{\frac{2Vq}{m}}$ is a non-relativistic approximation. This is quite valid when the exhaust velocity is small compared to the speed of light, which is the case for ion thrusters made to date (exhaust velocity is on the order of $10^{-4}c$). A more precise expression is $${v_e}^2\left(1+\frac{2Vq}{mc^2}\right) = \frac{2Vq}m$$ No ...


21

I thought it might be interesting (and hopefully helpful) to take a look at the education that astronauts actually have. For that, I decided to look at the list of current NASA astronauts (and current but not flight-eligible), and former NASA astronauts (there are some extremely interesting people in there, by the way). For the sake of this answer, I'm ...


20

Apparently the issue could not be addressed in time for the Apollo 13 mission as is evidenced by this note in the NASA archives available online. During the Apollo 13 flight the pogo effect had reappeared, this time on the second stage. Severe oscillations had forced an early shutdown (two minutes ahead of schedule) of the inboard engine. The NASA ...


20

There is a extensive summary report on possible improvements of solar sail materials: "Ultra-Thin Solar Sails for Interstellar Travel - Phase I Final Report" December 1999, Dean Spieth, Dr. Robert Zubrin When reading this report one has to keep in mind that they only look for the properties of the sail itself, not taking into account structural ...


19

I can answer the Shuttle part. The test in question was the Mated Vertical Ground Vibration Test (MVGVT). Here's how the stack looked in the test stand. Five configurations were tested Liftoff First stage (SRBs attached) early, mid, and late 2nd stage For the launch testing, the SRBs stood on hydrodynamic supports which "provided the vertical support ...


19

Direct measurement is difficult; I've seen some optical methods used but can't put a hand on them at the moment. Here are some calculated inner and outer wall temperatures for the Space Shuttle Main Engine, a regeneratively-cooled booster engine. The X axis is axial distance from the throat. I am pleased to see that both metric and English units are provided....


17

Nitrogen is a relatively inert diatomic (N2) gas, but also importantly, while there are other gases that refuse to react with much anything even more so, like e.g. Helium, Nitrogen is cheap since it's often a byproduct of industrial processes. It is also frequently readily available at scientific facilities in its liquid form for being an extremely ...


17

They're part of the SpaceX reusable launch system development program. The intent is to make both first and second stages of the Falcon 9 and the Falcon Heavy reusable by returning them both to the launch pad, where they are to make vertical landings. Their technology demonstrator, Grasshopper, made eight successful test flights. Yes, it reduces the payload ...


16

The big difference is in weight. Satellites in Earth orbit can be much heavier than deep space probes, simply because it takes a lot of energy to launch something into an Earth-escape trajectory. Satellites are often in the region of 8 tons, while deep space probes are rarely above 1 ton. The materials are mostly the same. Aluminium for the structure, the ...


16

Though many say that success directly reflects how hard one works or how motivated one is, there is a huge amount of random "luck" involved; being in the right place at the right time, meeting just the right people who may be helpful later, etc. This leads to the following advice. Choose a path that has you doing things that you really enjoy doing: ...


15

This answer is about OKB-1 (later known as TsKBEM, then NPO Energia, today known as RSC Energia) spacecrafts. I plan to edit, to make it more exact and detailed. Vostok and Voskhod. (3K) The chief conceptual designer was Konstantin Feoktistov. The administrative chain of all the people "responsible for the design" looked like that: Korolev (OKB-1. Chief ...


15

NASA has done an extensive report on this, and in fact, cryogenic hydrogen tanks are considered to be one of the greatest technical achievements that NASA managed. Much of this is specific to the Centaur upper stage, but here's a few interesting quotes from the article: Page 38 Bossart led Mrazek out into the factory yard, where a Centaur tank stood ...


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