65 votes

If the Apollo mandate were delivered today, would the mission vehicle(s) and profile be similar?

A big difference is that you wouldn't need to leave someone in lunar orbit. We now have experience and confidence in the remote operation of an uncrewed vehicle. So you could have a crew of two ...
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  • 57.5k
50 votes
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Why isn't a centrifuge used for astronauts on the space station?

The short answer is it would cost a lot of money. In order to get a 1G force, you'd either need something really big, or rotating very fast. For example, the reference design for the space colonies ...
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  • 1,666
47 votes

What is "mission design"? What do mission designers do (if such a designation exists)?

Yes, there are people whose sole job is "mission design." They design the trajectory that a spacecraft should follow to fulfill its mission and all of the maneuvers needed for that to happen....
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  • 5,775
37 votes
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Requirements to orbit Pluto

This mission study came up with a 900 kg nuclear-electric-propulsion spacecraft launched on an Ariane V with a C3 of 100 km2/s2 and a Jupiter gravity assist along the way. 1.05 kW electrical power at ...
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  • 57.5k
37 votes
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Exactly why does Starship need to be this big for interplanetary travel?

A lot of launch costs are independent of rocket size. It's no cheaper to clear the flight path for a smaller rocket, for example. It also takes a lot longer to do 10 launches instead of one large ...
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36 votes

Why did the space shuttle's altitude go down after reaching 108,000m?

The drop in acceleration around 40s into the flight is the shuttle throttling down to reduce the aerodynamic load on the vehicle. It then accelerates when past this point. The drop in acceleration at ...
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  • 4,015
36 votes

Why doesn't JWST use ion thrusters?

Since the L2 point is unstable, JWST needs engines to maintain it's orbit. It uses mono-propellant engines which have given it a 10 year (maximum) lifespan. The JWST uses bi-propellant engines (...
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  • 62.9k
34 votes

Would it have been any more difficult to build the space station without the space shuttle?

I do not think your assertion that "other rockets were just as capable of performing the task at that time" is correct at all. I'd love to hear your counterexamples, if you have any. Perhaps you are ...
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32 votes
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Why doesn't the New Horizons probe fly any nearer than 10,000 km from Pluto?

The long distance to the Sun mandates long exposure times. The New Horizons spacecraft needs to be relatively stable and its pointing accurate throughout these long exposure times. New Horizons does ...
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  • 62.9k
32 votes

Would it have been any more difficult to build the space station without the space shuttle?

Launching and assembling the ISS in its current design could not have been accomplished without the STS (Shuttle system), but that is largely because the ISS was designed with the STS in mind as its ...
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  • 1,699
31 votes
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Is this really Rosetta's orbit around 67P?

This was one of the questions just now during the Rosetta press briefing. This video was shown during the presentation: The triangular trajectory are hyperbolic ...
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  • 75.3k
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
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Is this plot of deep space trajectories correct? Did most launch retrograde from Earth? Why do some change direction between planets?

The diagram you show is the digital version of a drawing by someone with an Etch-a-Sketch: completely inaccurate. The diagram below is accurate, showing Pioneer 10 & 11 and Voyager 1 & 2 ...
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  • 17.9k
28 votes
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What powers New Horizons?

Space is basically a vacuum, so there's no air resistance. A probe that's been launched will travel at the same speed indefinitely. Because New Horizons is moving away from the Sun, it loses some ...
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  • 121k
27 votes
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Why weren't Saturn V and the Soviet N-1 Moon rockets made larger in order to simplify Lunar missions?

In order to use the direct ascent method of landing on the moon, which is where the entire vehicle descends and leaves the moon, you would need a rocket an order of magnitude bigger than the Saturn V, ...
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  • 18.7k
26 votes

How much did we know about lunar soil conditions prior to Apollo 11?

The uncrewed Surveyor probes landed on the moon before Apollo did. They provided visual images of the landscape and pictures of soil samples that were dug up robotically. All the visual indications ...
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26 votes

How hard is it to fly through the tail of a comet? Has it been done?

Ulysses, the shuttle-launched joint NASA/ESA probe to study the sun's polar regions, ran through three comet tails, more or less by chance. Ulysses Catches Record for Catching Comets by Their Tails ....
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26 votes

How will DART be able to hit a 170 meter rock dead-center at over 6000 m/s? What technologies will be use and how will they work together?

Didymos will be roughly 11 million kilometers (6.8 million miles) from Earth at the time of the DART impact.The round trip time for a radio signal from DART to the control center on Earth will be ...
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  • 46k
25 votes
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Why explore Ceres?

Dawn has several mission objectives, including to continue testing the Ion Thruster. But why Ceres? Ceres and Vesta were chosen, because they have contrasting content, one icy and one rocky. Also,...
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  • 2,871
23 votes

Requirements to orbit Pluto

This is probably the easiest to answer if we take the same mission profile and just track from the Pluto flyby backwards. I'll make some rather broad assumptions and first order approximations, like ...
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  • 75.3k
23 votes

What typically gets sent to the ISS?

If you want an example manifest for one logistics flight, that's available. Search terms...suggest "ISS Cargo Manifest" From SpaceX 2 Cargo Manifest (see link for details) 81 kg of crew ...
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23 votes

Why doesn't JWST use ion thrusters?

@DavidHammen's answer goes a long way towards answering, especially in that the space telescope's bus was finalized quite a long time ago when ion propulsion was much less a proven long-term reliable ...
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  • 148k
22 votes
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Why does NASA's Juno spacecraft only have a one year primary mission?

While many missions have been able to continue beyond their design lifetimes (Cassini and the Mars Exploration Rovers being prominent examples), the type of mission and orbit Juno must undertake to ...
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22 votes

What powers New Horizons?

Propulsion Until someone solves the N-body problem every spacecraft needs some kind of propulsion to correct its course during the mission. New Horizons uses a Hydrazine based propulsion system ...
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  • 7,078
22 votes
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Were the consoles in mission control computers or terminals for displaying information?

Since you have tagged the question apollo-program, I will explain the Apollo era consoles. Sources are from this Ars Technica article, which interviewed flight controller Sy Liebergot. The flight ...
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  • 46.3k
21 votes
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Has Luna been used for gravity assist for interplanetary probes?

The STEREO satellites used multiple gravitational assists from the Moon to significantly decrease the amount of fuel needed to put those two satellites into heliocentric orbits. The first flyby ...
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  • 62.9k
21 votes

Why weren't Saturn V and the Soviet N-1 Moon rockets made larger in order to simplify Lunar missions?

During the early part of the Apollo program, the "direct ascent" mode was favored and Lunar-orbit rendezvous (LOR) was considered far too complex. In fact, the specifications of the Apollo service ...
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21 votes
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How an americium-241 RTG would differ from one using plutonium-238?

Power and Mass From this paper (emphasis mine): The specific power of an 241Am-fuelled RTG cannot match that of a 238Pu system (except perhaps at small power output levels); however, the design work ...
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  • 9,834
20 votes

Has a spacecraft ever docked with the same space station twice in one mission?

The first, experimental redocking was performed on Soyuz 29 (though by crew of Soyuz 31) with the Salyut 6 station. Afterwards, the maneuver was repeated several times, usually between different ...
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  • 52.4k
20 votes
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Are launch windows to Mars avoided if they result in landings during dust storm season?

Are launch windows to Mars avoided if they result in landings during dust storm season? No. It's pretty well known that the gusts of wind on Mars are relatively harmless to a person standing on Mars (...
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