89 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

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 ...
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60 votes

Why are all space initiatives designed to get to space overnight when in Nature all extreme feats are achieved in a gradual process

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 ...
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  • 381
54 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

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. ...
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51 votes

What would be the (most difficult) challenge to make a 10,000 year satellite?

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 ...
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43 votes
Accepted

Why isn't there research to build a standard lunar, or Martian mobility platform?

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. ...
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  • 121k
42 votes
Accepted

Why is SpaceX building the Big Falcon Ship before the Big Falcon Rocket?

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 ...
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  • 6,377
41 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

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 ...
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32 votes

Why is SpaceX building the Big Falcon Ship before the Big Falcon Rocket?

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 ...
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  • 118k
31 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

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 ...
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  • 7,376
30 votes

How realistic is the 1 kg/km² solar sail in "Death's End"?

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 ...
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29 votes

Why design new rocket engines instead of using the existing types?

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). ...
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  • 121k
26 votes
Accepted

What is the ideal shape for a rocket?

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 ...
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26 votes
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How realistic would the Sea Dragon engine be to produce given today's technology?

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 ...
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25 votes

What is the ideal shape for a rocket?

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 ...
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25 votes

What would be the (most difficult) challenge to make a 10,000 year satellite?

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 ...
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  • 57.5k
22 votes

What would be the (most difficult) challenge to make a 10,000 year satellite?

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 ...
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  • 7,186
22 votes
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Overcoming the speed of light thanks to ion thrusters

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 ...
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  • 63.1k
21 votes
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Becoming an astronaut with engineering background

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 ...
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  • 7,074
20 votes
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How did they solve Saturn V pogo oscillation problems?

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 ...
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20 votes
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How hot do rocket engine nozzles get?

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 ...
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20 votes

How realistic is the 1 kg/km² solar sail in "Death's End"?

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. ...
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19 votes
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How does the Saturn V Dynamic Test Stand work?

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 ...
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17 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

O'Neil cylinders have a very large minimum radius of several kilometers for a reason, or several reasons in fact. One can't just spin up a small station to simulate gravity and expect a person to be ...
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  • 279
16 votes
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How does a space probe differ from a satellite in terms of materials used and size?

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. ...
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  • 121k
16 votes

What led NASA et al. to decide the ISS should be a zero-g station when the massive negative health and quality of life impacts of zero-g were known?

The other answers are good, but I think we miss something. Imagine a spacewalk around a rotating space station. With the current technology, we do need regular spacewalks. Everything dropped doesn't ...
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  • 1,692
16 votes

Which US Air Force career should I be in for the best chances at becoming some sort of electrical engineer at SpaceX?

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, ...
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  • 148k
15 votes

Why do pressure fed engines have combustion instabilities?

The issue with Sea Dragon and pressure instability is that the likelihood of pressure instability increases exponentially as the size of the combustion chamber and nozzle diameter increases linearly. ...
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15 votes

What would be the (most difficult) challenge to make a 10,000 year satellite?

The biggest challenges are going to be what people have already mentioned - the funding (don't skirt over that comment, you did ask for the challenges), an energy source for 10,000 years, and how to ...
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  • 5,148
15 votes

Are and should satellites use wireless communication internally, rather than cables?

Radio may reduce some complexity, but it will introduce problems that wiring doesn't have. Limited bandwidth. Interference. You can separate wiring so it doesn't influence each other. Can't do ...
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