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34 votes
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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 ...
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32 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'...
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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 ...
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29 votes
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Nuclear Explosion in Space

You can detonate nuclear bombs in space, it's been done several times. There are technical challenges to it but nothing too complex. In an atmosphere much of the damage from a nuclear weapon is from ...
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27 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 ...
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27 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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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  • 121k
18 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, ...
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  • 118k
17 votes

Could we detect a nuclear explosion near Proxima Centauri?

If you can detect unusually large quantities (superabundance) of Xe-129 or higher isotopes of Xenon that would naturally only be present in trace amounts without explosions of thermonuclear weapons, ...
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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 ...
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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 ...
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15 votes
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Could we detect a nuclear explosion near Proxima Centauri?

Assuming best case? According to this page, about half the energy from a normal nuclear explosion is radiation. That means we can simplify it to all energy radiated for an order of magnitude estimate....
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14 votes
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Dangers of launching a nuclear thermal rocket

It's not dangerous. The core would never be operated on Earth, and so would not become radioactive like you're thinking. A nuclear reactor on Earth that has been in operation is extremely ...
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13 votes

Nuclear thermal rocket specific impulse calculation uses 1 amu, is that wrong?

Some of the hydrogen will be disassociated. For the reaction mass that is not dissociated, and passes through the engine in the form of diatomic hydrogen, in addition to the three translational ...
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12 votes
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Nuking the Sun?

What would happen? Not much. The Sun is mindbogglingly vast. Even our biggest nuclear bombs don't fuse more than 1 ton of hydrogen. Compare that with the Sun's 620 million tons burned per second: the ...
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  • 121k
12 votes

What are the economics of Nuclear Thermal Propulsion?

Any sensible answer to your question should make an implicit assumption on the number of engines to be ordered overall. That is, we need to know the number of planned manned flights to Mars and other ...
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  • 11.3k
12 votes
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Will Roscosmos et.al attempt to revive nuclear-engine space technology violate the OST?

Whether the reported article is accurate? It's rather bad in my opinion. The news is outdated and incorrect. This part was completely incorrect: After a multi-decade hiatus, both NASA and the ...
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  • 62.9k
11 votes

Nuclear Explosion in Space

Is it possible? As depicted in that awful movie? No. The concept in general? Yes. A nuclear standoff explosion is widely regarded as the best, most realistic approach to diverting an incoming ...
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  • 62.9k
11 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 ...
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  • 57.5k
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 ...
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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 ...
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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. ...
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10 votes

What are the economics of Nuclear Thermal Propulsion?

In the past 6 years NASA and the DOE have put a fair amount of effort into estimating the cost to recapture NTP technology assuming either graphite based or tungsten CERMET fuel. The estimates to ...
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10 votes

How could a fast powerful rover on Mars be powered electrically?

An option not mentioned so far are solar power satellites. A large antenna in orbit could focus a tight, high-power microwave beam on the rover. From a low Mars orbit (300 km), a 1 km antenna could ...
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  • 57.5k
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 ...
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9 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 ...
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8 votes
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Detecting a Nuclear powered vehicle from outer space (at least 8 AU or further out) feasible?

I sometime see this quote in forum arguments against "Klingon/Romulan-style" cloaking in video games that tries to be close as possible to real-life I gather the "World Building" Stack exchange might ...
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