# Tag Info

48

The speculation is that Galileo gradually sunk into thicker layers of Jupiter body, and eventually reached level where pressure squeezed its RTG battery so much the plutonium went supercritical. Galileo was powered by RTGs. That is a heat source powered by the decay of Plutonium-238. Nuclear decay rate does not change. It isn't affected by pressure, ...

32

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're just talking about the problems of transport, assuming the will to do it, sure, that's plausible enough. Now I have seen news coming stating that atomic or ...

30

The Galileo probe carried two radionucleid batteries, each one carrying 7.8kg of Plutonium-238. But Plutonium 238, while radioactive, is not the kind of Plutonium used for nuclear bombs. That's another isotope: Plutonium-239. That's a big difference, because only the kinds of Plutonium with odd isotope numbers are fissile. Fissile means, that they are ...

27

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 seconds, with a demonstrated test-stand record of 542 seconds. ~500km range rockets will use chlorine pentafluoride and a hydrazine derivative. As far as I ...

22

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 the blast wave which is caused by the heat and pressure of the explosion. This wave goes out from center of the explosion, and then back again as the pressure ...

21

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 as diffuse as Martian air, would allow increased heat transfer from the RTG fins via convection and conduction, vs. the space based versions which would entirely ...

21

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 from a 30m asteroid, roughly. The Tunguska event was caused by a 60m rock, and had an explosive power equivalent to that of a large nuclear weapon, around 15 MT. ...

19

The problem with using nuclear fission reactors as means of power to propel spacecraft is twofold: our own aversion to anything nuclear due to environmental hazards and the problem of reaction mass still persisting, regardless of your energy source longevity and power density per its own mass. Let's explain these points a bit more. The reaction mass problem ...

19

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. The radioactive material is not "widely dispersed". As for the numbers, the rate of decay is inversely proportional to the half-life. The half-life of U-235 is ...

18

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 pretty much what you want and nobody will know for sure what it is. A satellite that does nothing would be suspicious, so you'd have to stick your warhead ...

17

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, then yes. Potentially even millions of years after the event (Xe-129 has a half-life of 16 million years). It is hard to estimate what weapon yield would be ...

17

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, and in fact the final milestone in the Commercial Crew is to rate the system Category 3. It is required for any kind of sensitive launch. Note that man rated ...

16

Two alternatives (RTG or solar) were investigated in the Mars Science Laboratory Environmental Impact Statement. In summary, solar arrays would limit the MSL to operate between 5°N and 20°N, and for one Martian Year only if at exactly 15°N, whereas RTGs would permit it to operate for at least one Martian year anywhere from 60°S to 60°N. From page 2-1 (PDF ...

16

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 in chemical reactions, as well as by being fed through a nuclear core. For a nuclear thermal rocket some of the heated (and thus expanded) hydrogen is tapped ...

15

Yes they considered the disassosciation of hydrogen According to this source : Previous testing used a maximum temperature of 2,750° K, short of the 3000+° K design temperature for the NCPS. The NTREES facility is designed to test fuel elements and materials in hot flowing hydrogen, reaching pressures up to 1,000 pounds per square inch and ...

15

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. For reference I will use the Tzar bomba, the largest nuclear weapon ever tested. It was about 50 megatons worth of TNT. According to unit conversion , a ...

15

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 magnetosphere, charged particles are bent, and form radiation belts, for example the Van Allen belts. There, shielding is a bit more difficult. Secondly, that is ...

14

Yes it is possible to develop such a weapon. Example: Fractional Orbital Bombardment System It consists of a rocket and a warhead. The rocket would place the warhead into LEO where small on-board thrusters would guide the the warhead into place for it's controlled descent to the target. There was also a thermal protection system required but overall, this ...

14

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 radioactive due to the fission products, but the original fuel was not. The unburned U-235 fuel has a half-life of 700 million years, which means that its ...

13

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 degrees of freedom, heat energy is also put into the vibrational and rotational energy of the hydrogen molecule. So the energy stored is 6/2kT, not 3/2 kT as in the ...

12

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 important destinations, since fixed (sunk) costs of an NTR-based program are significant. The following ideas are based on a few NASA documents discussing NTRs. ...

12

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 Russian Federal Space Agency (which developed many of its own NTRs during the Cold War but never physically tested their designs) announced in April 2012 that they ...

12

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 nuke would add $10^{-9}$ to the Sun's output.

11

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 of weapons of mass destruction in outer space. Even disregarding that... By measuring the craters of bombs we exploded in the 1950's, we found that a crater ...

10

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 include fuel development, reactor development, reactor testing and infrastructure ranged from \$4 to 6 billion over 10 to 15 years. However, where there has been ...

10

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 other practical way to generate net energy from fusion, and there won't be for decades.

10

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 Moon has been subject to in the past. However, for human missions, the question should not only be about permanently stable orbits but also about orbits that ...

9

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 asteroid or comet, assuming some minimal amount of lead time. Weeks or months do not qualify as "minimal". We need a couple of years, at least, even with nukes. A ...

9

Of course, you can't simply "drop" the bomb — it would just stay in the same orbit as the satellite. The bomb would need a propulsion system (rocket) to decelerate. But this would certainly be possible.

8

This article, titled Nuclear Pulse Propulsion Re-Examined, was published in late '05. There is also this article, which was posted in early '12. Unfortunately, despite much Googling, I wasn't able to find any real research on the subject after about the '90s, when Project Medusa was started by NASA.

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