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 ...
- 167k
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'...
- 4,548
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 ...
- 21.4k
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 ...
- 2,391
27
votes
Accepted
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 ...
- 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....
- 8,954
21
votes
Accepted
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 ...
- 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 ...
- 8,001
19
votes
Accepted
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. ...
- 58.5k
19
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, ...
- 121k
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 ...
- 126k
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, ...
- 76.5k
17
votes
Accepted
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 ...
16
votes
Accepted
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 ...
- 8,414
15
votes
Accepted
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....
12
votes
Accepted
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 ...
- 126k
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 ...
- 58.5k
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 ...
- 5,475
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 ...
- 11.5k
11
votes
Accepted
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 ...
- 8,001
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.
...
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 ...
- 58.5k
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 ...
- 121k
10
votes
Accepted
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 ...
- 149k
10
votes
Accepted
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 ...
- 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 ...
- 21.4k
9
votes
Accepted
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 ...
- 126k
8
votes
For a hypothetical high-power nuclear spacecraft, where does the waste heat go?
As you stated, radiation is the only method of removing excess heat from a conventional spacecraft in vacuum. Designing a spacecraft to radiate heat appropriately is important and yes, it does add ...
- 4,350
8
votes
Accepted
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 ...
- 5,178
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 ...
- 167k
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