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35 votes
Accepted

What was the result of the propellant predictions in the last chapter of "Ignition!"?

Chemical rockets will never have more than 600 seconds specific impulse. Storing free radicals in propellant to defeat this limit is impractical. Validated. Chemical rockets in use top out at 450-460 ...
Russell Borogove's user avatar
31 votes

Is it true that nuclear rockets cut the journey to Mars in half?

The biggest challenge of our Mars journey is the journey time (9 months). Well, maybe. More likely, the biggest challenge is making it economically worthwhile to support a viable colony. But if you'...
Nathan Tuggy's user avatar
  • 4,567
31 votes

Why do nuclear rockets (e.g. NERVA) have such poor Thrust-to-Weight ratios?

At their core nuclear rockets working by heating a working fluid and running it out a nozzle are still constrained by the same physics as a chemical rocket where exhaust temperature cannot be much ...
GremlinWranger's user avatar
28 votes

Why are RTGs different colors?

The big difference between the two darker RTG fins (Black and Grey) and the white RTG fins, is that the white fins were destined for use in an atmosphere (Mars). The presence of an atmosphere, even ...
Josh King's user avatar
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28 votes
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Why are RTGs different colors?

Answer: Thermal radiating coating technology has improved, so they are no longer forced to be sub-optimally black in visible light. They can now be white and reflect incident sunlight to improve ...
uhoh's user avatar
  • 149k
23 votes
Accepted

How does NASA have permission to test a nuclear engine?

The nuclear test ban treaty bans testing nuclear weapons. It does not ban nuclear reactors. A nuclear rocket engine of the type proposed by NASA would be a thermal nuclear rocket: https://en.wikipedia....
Slarty's user avatar
  • 9,560
21 votes
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Can a nuclear detonation on Moon destroy life on Earth?

Probably not. Just to give you an idea, lunar rocks hit the Earth on a somewhat regular basis. The power required to have a rock hit Earth is equivalent to that of making a 450 m crater. This comes ...
PearsonArtPhoto's user avatar
  • 121k
21 votes

Why do nuclear rockets (e.g. NERVA) have such poor Thrust-to-Weight ratios?

The one exception to this fact is Project Orion Not quite. Project Timberwind was a solid-core NTR using a pebble-bed reactor design that combined high Isp with a moderate T/W of 30. The DUMBO NTR ...
Starfish Prime's user avatar
20 votes

What does it mean for a launcher to be 'nuclear-certified'?

Really what it means is "Category 3" certified, with an additional review of a self-destruct situation to prevent breaking the nuclear payload. Category 3 is also what is required to launch humans, ...
PearsonArtPhoto's user avatar
  • 121k
19 votes
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How does the launch risk for a plutonium RTG and a uranium fission reactor compare?

The probability and consequences of a release of Pu-238 from an RTG in a launch accident are very low, due to the protections in place for such an incident. It's not like they never thought of that. ...
Mark Adler's user avatar
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18 votes

Is it possible to covertly put an EMP weapon into an ISS-like orbit by masquerading it as a legitimate launch?

Classified satellites are launched all the time. For example, fourteen KH-11 espionage satellites were launched between 1976 and 2013, and we still have no idea what they look like. So you can launch ...
Hobbes's user avatar
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17 votes
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Would a nuclear propelled spaceship still need a storm shelter?

The basic idea here is to turn to have the shield you have towards the Sun. That does actually work, because the radiation from the Sun is directed, with a few exceptions: First, inside a planetary ...
SE - stop firing the good guys's user avatar
16 votes
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How does propellant flow work in a nuclear thermal rocket?

You have the same problem in any rocket. The pressure at the pump outlet must be higher than the chamber pressure. What you are missing, is that the density of your propellant drops by heating, both ...
Rikki-Tikki-Tavi's user avatar
11 votes

Bombing the Moon: how much debris would there be in stable orbit?

The empirical answer is that there is absolutely no risk of debris reaching a permanently stable orbit. If so, then there would already be a lot of such because of the millions of impacts that the ...
Everyday Astronaut's user avatar
11 votes

Would it be possible to send a nuclear bomb to Europa and make a hole in the ice of more than 11 km?

You may not send a nuclear bomb into space if you're one of the 105 countries that have signed the Outer Space Treaty that, among other things, forbids deploying nuclear weapons or any other kinds ...
Camille Goudeseune's user avatar
11 votes
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Are nuclear thermal engine designs limited to about twice the Isp of existing chemical rocket engines? If so, why; what's the limiting factor?

For solid core engines, yes, that's their limit. If so, what is the limiting factor? The exhaust velocity (and hence specific impulse) is linked to the heat of the propellant. The propellant can't ...
Starfish Prime's user avatar
11 votes

Nuclear or Solar power for satellites?

Virtually all satellites use solar power as power source. The exception is the true nuclear reactors, exemplified by the Soviet RORSAT series, which needed more power for their radar surveillance. ...
CuteKItty_pleaseStopBArking's user avatar
10 votes

What will be the best way to convert nuclear fusion energy into thrust for a rocket?

Exploding thermonuclear bombs behind a big, thick plate, with the payload on giant shock absorbers behind that, referred to as Project Orion, is practical today, and has been for decades. There is no ...
Mark Adler's user avatar
  • 58.2k
10 votes

What is the relationship (if any) between NASA's Kilopower project and its request for 40 kW reactor designs?

Kilopower is designed for at most 10 kW of power. I asked Patrick McClure, who is the engineer in charge of the Kilopower project at Los Alamos (2019 Humans to Mars summit) if they could scale it up ...
PearsonArtPhoto's user avatar
  • 121k
10 votes
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Lunar nuclear power system - how can hydrogen generated on the Moon be liquefied?

How would you cool and liquefy this hydrogen on the Moon? I guess one would have to do a serious study to find out for sure which way is more suitable in a given scenario, but I think passive cooling ...
uhoh's user avatar
  • 149k
10 votes
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Could a Nuclear-Thermal turbine keep a winged craft aloft on Titan at 5000m ASL?

It's absolutely impractical. Source: https://en.wikipedia.org/wiki/Kilopower Current designs: 1 kWe Kilopower reactor weighs 134 kg 10 kWe Kilopower is expected to mass 1500 kg The Artemis nuclear ...
Antzi's user avatar
  • 12.6k
10 votes

Could a Nuclear-Thermal turbine keep a winged craft aloft on Titan at 5000m ASL?

As Antzi correctly identifies, doing this via nuclear decay->heat->boiling fluid->turbine->electricity->electric motors->propellers is pretty marginal. In terms of serious ...
GremlinWranger's user avatar
9 votes
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How many nuclear fission reactors have been launched into space? How many are still there?

There's a new list on Wikipedia that has a better breakdown of Russian nuclear power systems in space. It lists 32 BES-5 thermoelectric reactors, 2 Topaz reactors, 5 RTGs and 2 '2 kWe' reactors. At ...
Hobbes's user avatar
  • 128k
8 votes

How much thrust can a nuclear thermal rocket provide?

The American NERVA program developed a design expected to produce up to 333kN (75klbf) of thrust in a 6.8 ton package, for a thrust to weight ratio of about 5:1. It was never completed or flown. NERVA ...
Russell Borogove's user avatar
8 votes

Lunar nuclear power system - how can hydrogen generated on the Moon be liquefied?

Cryogenic cooling typically works by cooling pressurised gas, releasing the pressure to reach even lower temperatures. The cooling itself uses boiling of some other gas with a higher boiling point (...
SE - stop firing the good guys's user avatar
7 votes

Is terraforming mars with only 4 nuclear bombs/penetrators in 10 years possible as this paper says?

I'm not an expert in any of the topics of the paper, but on a quick read I see it's full of naive assumptions about ratios -- to cover 1/20 the area requires 1/20 the energy release, 6% of cap ...
Russell Borogove's user avatar
7 votes
Accepted

Is it possible to use zinc powder as a NTR propellant?

I suggest you look into the chemistry of clay slip and slurries. For example, porcelain slip is very fluid and can pour through distribution channels in molds to form fine features, then sets up as a ...
Kengineer's user avatar
  • 1,748
7 votes

What kinds of nuclear reactors are suitable for operations in space? (Beyond thermionic and RTG)

The question is how to convert the heat from a fission reactor into electricity. Most systems that have been either built (Topaz) or proposed (SP-100) rely on thermionic conversion. This is the same ...
Mark Adler's user avatar
  • 58.2k
7 votes
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Is the Falcon 9 or Falcon Heavy allowed to launch nuclear material?

As far as I can tell Falcon 9 hasn't been certified to carry nuclear payloads. There's a separate certification process required https://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8715_0026_&...
Alan Birtles's user avatar
  • 2,066
7 votes

Nuking mars for colonization

Fusion bombs have existed for decades, they are called thermonuclear weapons, and are many thousands have been produced. A thermonuclear bomb uses a small fission bomb primary to cause the extreme ...
GdD's user avatar
  • 20.3k

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