Jacques Posted February 20, 2015 Posted February 20, 2015 Hi I had an idea that might interest some people here, and I would like to have some comment on that idea. There is a possibility that someday we will find a comet heading to earth and we will try to deviate it so it miss the earth. There are many senario's proposed, but mine is so simple: Take a big mass of nuclear fuel and crash it on one of the pole of the comet. Make it crash at a speed so the mass will penetrate between 10 and a 100 meter. The nuclear mass is subcritical so it wont detonate, but massive enough to come to a temperature of around 1000 Celsis. The interior of the comet is mostly water ice and the water will turn into steam that will exit by the entry hole providing some trust. Is it a realistic scenario to change the orbit of a comet ? How much fuel would be needed ? How long before the hole get to large ?
Greg H. Posted February 20, 2015 Posted February 20, 2015 It seems to me you'd be better off using the fuel to propel something larger at the comet to deflect it. Not crunching the numbers, but it seems like a more efficient use of a giant pile of radioactive material.
swansont Posted February 20, 2015 Posted February 20, 2015 Critical/subcritical is only an issue if you have fissile material. I doubt you'd be able to control a bunch of material to being safely subcritical and get it really hot. The other way is to just get shott-lived radioactive material. One huge problem is that if you have a mass that can get to 1000 ºC, it will already be at that temperature in the rocket. That's not good. 1
Jacques Posted February 20, 2015 Author Posted February 20, 2015 Swansont Does a nuclear reactor is critical or is it subcritical ? Can we used some uranium mixed with some moderator and have it warm enough but not explose ? Maybe I used a to hight temperature, but the idea is transform the ice into steam to propel the comet.
Mordred Posted February 20, 2015 Posted February 20, 2015 There was a proposal to use a laser, to obtain the same effect. No radiation fallout. This link covers some of the pros and cons of a variety of methods. Early warning being a major key factor in the best method. http://orbitalvector.com/Solar%20System/Asteroids%20And%20Comets/Redirecting%20Asteroids/REDIRECTING%20ASTEROIDS.htm
swansont Posted February 21, 2015 Posted February 21, 2015 Swansont Does a nuclear reactor is critical or is it subcritical ? Can we used some uranium mixed with some moderator and have it warm enough but not explose ? Maybe I used a to hight temperature, but the idea is transform the ice into steam to propel the comet. An operating reactor is nominally critical. That just means the fission reaction is self-sustaining. But reactors are fairly complex and aren't the sort of thing that react well to impacts and the like. You also lose the possibility of a simple convection-driven device because you're in outer space. You could avoid that by having a system you know is going to melt down, but then you run the risk of the contamination it causes falling back to earth. I'm wondering why a chemical system wouldn't suffice.
Mr. Astrophysicist Posted February 21, 2015 Posted February 21, 2015 Hi I had an idea that might interest some people here, and I would like to have some comment on that idea. There is a possibility that someday we will find a comet heading to earth and we will try to deviate it so it miss the earth. There are many senario's proposed, but mine is so simple: Take a big mass of nuclear fuel and crash it on one of the pole of the comet. Make it crash at a speed so the mass will penetrate between 10 and a 100 meter. The nuclear mass is subcritical so it wont detonate, but massive enough to come to a temperature of around 1000 Celsis. The interior of the comet is mostly water ice and the water will turn into steam that will exit by the entry hole providing some trust. Is it a realistic scenario to change the orbit of a comet ? How much fuel would be needed ? How long before the hole get to large ? Good question there. The hole to get large is a little vague. Some possible theories of it being radioactive, or chemical reaction of some sort in the comet causing it to explode to leave a big hole, or it being too high of its temperature that it will melt the ground. What is the ground? What other chemicals are there in the comet? I need more data to calculate the infinite possibilities of this theorem. Just solve it within all the information given or do you prefer to give me more? (This question also gives more questions than it answers, surprisingly). -1
Jacques Posted February 23, 2015 Author Posted February 23, 2015 Thanks for your answer and interest. The basic idea is somekind of mass driver, expelling some mass (water vapor) from the comet, but without all the mechanical part. I thaught of using nuclear power because of the higher power density, but it seam that you cannot control a nuclear reactor without some complex feedback mechanic. Maybe it would be possible to have a subcritical mass and have a neutron source turn on when in place. I was targeting the pole so it can work all the time.
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