What "issue with radiation"? We knew about radiation in the 1960's. This was for use on the moon, which has worse radiation exposure than Mars (the moon is closer to the sun and lacks an atmosphere)

http://www.astronautix.com/cra...

For 12 years I lived about 4 blocks away from a decommissioned research reactor, and downwind and downstream of a major reactor complex. Never caused me concern because I've actually looked into the statistics and understand a concept called comparative risk. People rant and rave about "nuclear" just how bad and dangerous something becomes, simply by attaching an adjective to it. My mother is still alive thanks to nuclear technology. In her case the nuclear medicine used to treat her cancer 30 years ago.

Can you show your math? I just did the same with a 1km impactor blown into 2million chunks (one thousandth the mass chixulub), resulting in enough energy to light the continental US on fire. Chuxulb weighing in at 1E15 kg (low estimate), smashed into 20m pieces (the same as Chelyabinsk) would result in 1E8 pieces (Chelyabinsk weighing in at 10000 tonnes) , each dumping 500kt of energy into the atmosphere, or 2.09E23J. That's enough to raise the temperature of the ENTIRE atmosphere of the planet by 40 degrees (2.09E23J / 1005 specific heat of air / 5E18kg mass of atmosphere)

It's not just the energy of things landing on your head. All that energy still goes somewhere, it doesn't just magically dissipate just because you've blown it into little pieces. Sure you don't get one big crater that puts enough dust into the atmosphere to cause global winter. You lite the hemisphere on fire which generates enough soot to cause a global winter. Note the fireball for Chixulub was in the hundreds of kms in diameter

Lets take a 1km object, assuming a standard density carbon chondrite meteorite, it weighs in at 1.6E13 kg. Assuming we manage to blow it up into 20m chunks (about the same as the Chelyabinsk meteor). That's just shy of 2 million separate pieces, each dumping about 500kt of energy into the atmosphere or or about 3.5E15J of energy. This is enough to raise 5 billion cubic meters of air by a 1000C, or enough to lite the continental US on fire. This is just based on the pure conversion of energy released into heating of air. No radiative thermal effects have been taken into account. Note this for a smaller object. Chixulub was 10 times bigger

Just how big of a nuke do you think we have? A 1km stony asteroid has a gravitational binding energy equivalent of a 500 megaton bomb (i.e. you would need a bomb 10 times bigger than the largest ever built to blow up a 1km asteroid, assuming 100% of the energy was absorbed into the structure of the asteroid) A question, would you prefer getting hit in the arm with a 30mm round (losing your arm) or several dozen 9mm rounds,

No, because those millions of small pieces release the same amount of energy into the Earth system, just now into the atmosphere now rather than the planet surface. Rather than ejecting material, earthquakes, tsunamis, you flash fry the hemisphere.

Or to put it another way (to more accurately reflect the energies involved), would you rather be hit in the arm by a 30mm round (taking your arm off), or hit by several dozen 9mm rounds. The problem isn't the impact, its all the kinetic energy needs to go somewhere. Either into the Earth which vaporizes rock and spreads it around, or in the atmosphere that flash cooks the hemisphere

It's all about statistics and comparative assessment of risk. It comes down to how likely is an individual person to be killed or injured in a motor vehicle accident vs. being killed or injured by "highly toxic radio nucleotides which last tens of thousands of years" released during a launch failure? The answer is, or course, that you are orders of magnitude more likely to be harmed in a car accident (or slipping in the shower) than you would by an RTG launch. Surrounding it with hyperbolic descriptors such as "toxic" or "highly harmful" doesn't make any difference to the statistics, nor the fact that each of us make the choice to participate in far more risky endeavors on a daily basis. Adding the word "nuclear" to something that has a 0.0000001% of killing you, means it still has a 0.0000001% of killing you. Besides Pu-238 (used in RTGs) has a half life of 87 years. So it most definitely wont be hanging around for "tens of thousands of years"

As I indicated in my original post. RTGs are designed to survive (and have successfully survived) both launch accidents and re-entry's

Then god forbid you drive to work today. It's just not worth it to risk a car accident, after all just because you've had a perfect "not dying in a car crash" record so far, it meaningless. Or are you one of those people that hear the word "Nuclear" and flee in abject terror. You must be shocked, absolutely shocked that you probably have nuclear material in your home (smoke detector) or that thousands of lives a day are saved using nuclear medicine (my mother was one). But hey Fukushima. RTGs are designed to handle worst case launch accident or re-entry scenarios. Even if they did somehow breach and release some of their Pu-238, the odds of if harming someone are so insignificant, that if it worries you, I cant imagine how you manage to go outside while dealing with the constant fear of being, shot, run over and struck by lightning. Never mind that full blown nuclear reactors carrying far greater quantities of highly radioactive material have burned up in the atmosphere several times, with zero, absolutely zero harm to anyone.

Ooops, yes, mixed up my isotopes.

Read my response to the other poster. Kosmos 954 carried a BES-5 nuclear reactor on board, NOT a RTG. These are very very different technologies. If someone just sees the word "Nuclear" and starts running for the hills, then it's pretty clear they aren't even willing to learn.

Kosmos 954 carried a BES-5 nuclear reactor not a RTG, these are very very different technologies. Besides I remember how we all died in 1977