Can Sustained Nuclear Chain Reactions Achieve Constant Acceleration in Space?

[wllsrvive]

Is it possible to make an object travel with a constant acceleration using sustained nuclear chain reaction in space?

 

[russ_watters]

Yes. A nuclear powered ion engine could provide constant acceleration for years. That's constant according to the spacecraft , btw...

 

[Freshtictac]

I'd say no. The first thing anyone must consider about space technology is safety. Would you consider volunteering to hop on a radioactive propulsive vehicle knowing you can't get out if something goes wrong? If in fact you did get out in the event something went wrong, where would you go? Deaths by radiation are not only gruesome but from what i understand extraordinarily painful.
Perhaps you consider an unmanned vehicle?
Well, no to that as well. Suppose it's guidance was altered by some undiscovered gravity anomaly and pointed the sucker right at something other then the intended target. Not only would millions of dollars in equipment would be lost but also damage to the unintended target could be catastrophic to possible life there.

 

[russ_watters]

The first thing anyone must consider about space technology is safety. Would you consider volunteering to hop on a radioactive propulsive vehicle knowing you can't get out if something goes wrong?

Absolutely. The radioactivity isn't much of a concern at all.

If in fact you did get out in the event something went wrong, where would you go? Deaths by radiation are not only gruesome but from what i understand extraordinarily painful.

So are deaths from fire.

Perhaps you consider an unmanned vehicle?

Indeed, such vehicles already exist:
http://en.wikipedia.org/wiki/Deep_Space_1#NSTAR_ion_engine
That craft fired its engine for just under two years, continuously. It was solar powered, though.

Well, no to that as well. Suppose it's guidance was altered by some undiscovered gravity anomaly and pointed the sucker right at something other then the intended target. Not only would millions of dollars in equipment would be lost but also damage to the unintended target could be catastrophic to possible life there.

Spacecraft are guided, so that's not an issue.

 

[Freshtictac]

Absolutely. The radioactivity isn't much of a concern at all. So are deaths from fire. Indeed, such vehicles already exist:
http://en.wikipedia.org/wiki/Deep_Space_1#NSTAR_ion_engine
That craft fired its engine for just under two years, continuously. It was solar powered, though. Spacecraft are guided, so that's not an issue.

I am by far not an expert, but after russ's comments about radiation not being much of a concern I further researched and found Uranium-235 to be a constant base for these types of "engines". The substance alone is hazardous and when undergoes a reaction may result with gamma radiation... that stuff that mad hulk mad... not so good for homo sapian sapian...

also other possible substances are known to be radioactive as well... plutonium, thorium, and uranium would fit into the category of these materials with radioactive capabilities.

 

[DaleSwanson]

https://secure.wikimedia.org/wikipedia/en/wiki/File:HEUraniumC.jpg
http://www.lm.doe.gov/land/sites/oh/fernald_orig/50th/photos/85-193.jpg
http://www.corbisimages.com/images/67/F1B0F0FC-C457-4761-AD93-705DC67DE8E8/IH081416.jpg

Those are some random pics I found of people holding uranium in their hands. Uranium is not particularly dangerous (not much more dangerous than lead). Just because something is radioactive does not mean it is automatically deadly and evil. If I was going into space on a properly engineered spacecraft , a nuclear power plant would be near the last of my concerns.

As russ pointed out fires in a spacecraft would be just as bad (and much more likely) as any nuclear accident. I think nuclear powered subs would be a good analogy. There are certainly plenty of people willing to be on them.

Unmanned spacecraft often use RTGs for power, which use a small amount of radioactive material to generate heat and in turn power. The reason the are used for unmanned spacecraft doesn't have to do with safety, but rather because they are only used farther from the sun than humans have ever gone.
https://secure.wikimedia.org/wikipedia/en/wiki/Radioisotope_thermoelectric_generator

Lastly, I'd like to point out that if you are leaving low Earth orbit, i.e., going to the moon, then there is already plenty of radiation in space.

 

[qraal]

Is it possible to make an object travel with a constant acceleration using sustained nuclear chain reaction in space?

Nuclear fission allows, in theory, exhaust velocities of 12,000 km/s. Accelerating at 1 m/s^2 means that can be sustained for 12 million seconds with a fuel mass 1.72 times the vehicle's mass - long enough? Of course you can go faster, but the fuel mass increases rapidly, exponentially even. Unless you can get more fuel on the fly... What were you planning? A long trip?

 

[Freshtictac]

Love how in all the pictures they're wearing protective gloves. The material may be relatively inert, but as Dave stated there's plenty of radiation in space already. I can only guess that in the near future producing more radiation in space will have catastrophic effects throughout. Just as it is inappropriate to dispose of waste here on Earth space will also hold these emission values... Adding to the problem hasn't solved much here where people are barely beginning to understand the impact of pollution.

I understand that many objects in physics may be theoretical. But what's the point of theory if your grandchildren will disprove it.

 

[russ_watters]

Love how in all the pictures they're wearing protective gloves. The material may be relatively inert, but as Dave stated there's plenty of radiation in space already. I can only guess that in the near future producing more radiation in space will have catastrophic effects throughout. Just as it is inappropriate to dispose of waste here on Earth space will also hold these emission values... Adding to the problem hasn't solved much here where people are barely beginning to understand the impact of pollution.

I understand that many objects in physics may be theoretical. But what's the point of theory if your grandchildren will disprove it.

You think those rubber gloves protect them against radiation?

You really misunderstand nuclear energy. Nuclear "waste" is not a pollutant in normal circumstances as it is never intended to be released into the environment. Even including accidents, nuclear energy is neither a major safety nor pollution problem - no western country has ever had a civilian nuclear energy accident that killed more than a handful of people or caused a substantial amount of pollution. The magnitude of the danger and environmental impact of nuclear energy is much smaller than that of chemicals both for regular use and in the event of accidents.

For accidents, the Russians are the world leaders in environmental destruction, but all of the world's deaths due to nuclear power excluding Russia total under 100. Yet we accept with barely the batting of an eyelash, the death of 20,000 people a year in the US alone due to coal power pollution.

 

[DaleSwanson]

Love how in all the pictures they're wearing protective gloves. The material may be relatively inert, but as Dave stated there's plenty of radiation in space already. I can only guess that in the near future producing more radiation in space will have catastrophic effects throughout. Just as it is inappropriate to dispose of waste here on Earth space will also hold these emission values... Adding to the problem hasn't solved much here where people are barely beginning to understand the impact of pollution.

I understand that many objects in physics may be theoretical. But what's the point of theory if your grandchildren will disprove it.

They are wearing gloves because uranium is a toxic metal, like lead. I'd want to wear gloves if I had to handle lead on a regular basis as part of my job.

Correct me if I'm wrong, but are you arguing that we are going to damage space by polluting it with radioactive materials? Space is a massive, virtually empty, expanse. There's nothing to damage there. Even if there were, the Sun contains more radioactive material and puts out more ionizing radiation than we as humans could ever hope to. As for the inner planets they are largely rocks, and there isn't much to radiate there. The outer planets and their moons would have quite a bit more care taken as they are more interesting. In either case though, contaminating with life from Earth (bacteria) is a more serious concern than radioactive material.

The point is that "nuclear" elicits an irrational fear in many people. This is frustrating because there is tremendous potential with the energy of nuclear power. Radiation can be dangerous, but so can toxic metals, and flammable materials. However, if the risks are understood and handled properly they can be mitigated greatly. Avoiding any possible risk, or waiting to do anything until we have perfect understanding will only lead to an end to advancement.

 

[qraal]

Love how in all the pictures they're wearing protective gloves. The material may be relatively inert, but as Dave stated there's plenty of radiation in space already. I can only guess that in the near future producing more radiation in space will have catastrophic effects throughout. Just as it is inappropriate to dispose of waste here on Earth space will also hold these emission values... Adding to the problem hasn't solved much here where people are barely beginning to understand the impact of pollution.

I understand that many objects in physics may be theoretical. But what's the point of theory if your grandchildren will disprove it.

Your statement is incoherent. Care to rephrase it?

 

[Freshtictac]

I thought the question was specifically addressed to whether it is possible by today's technological and scientific community. All I've heard is a lot of talk, and not much product. So in theory, which could be debated for decades or more, it could be refined to such a process as Dale suggests. But I wouldn't count on that unless you're smarter then Albert Einstein, who has many theories which have been dis-proven by today's scientific community.

 

[qraal]

I thought the question was specifically addressed to whether it is possible by today's technological and scientific community. All I've heard is a lot of talk, and not much product. So in theory, which could be debated for decades or more, it could be refined to such a process as Dale suggests. But I wouldn't count on that unless you're smarter then Albert Einstein, who has many theories which have been dis-proven by today's scientific community.

It's not a matter of theory, but practicalities. Different matter entirely. But it also is irrelevant to drag Einstein into the question since he doesn't forbid uniform rectilinear acceleration from the point of view of the accelerating reference frame. In fact relativity guarantees such is perfectly physical. What relativity violates is the naive Newtonian expectation that all observers will see the same motion.