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Dawn isn't the best we can do, though, because it's solar powered. Even in the inner solar system, solar power can't give you nearly as much power as you can ge

Dawn isn't the best we can do, though, because it's solar powered. Even in the inner solar system, solar power can't give you nearly as much power as you can get from a decent radioisotope thermoelectric generator, and in the outer solar system you can fuhggedaboudit. If we wanted to send a probe to the middle of nowhere right now and had a billion or two to do it we'd strap our best ion drive to our best RTGs and then send it via a Jupiter slingshot. No idea how fast we could get it. Of course it would continue to accelerate until the power or the propellant ran out.

dalke 14y ago
The New Horizons RTG puts out 300W of electrical energy (and more as heat). The solar arrays on Dawn can supply "10 kW at Earth and 1.4 kW at Ceres". Wikipedia says the NSTAR thrusters on Dawn requires 2.3 kW. How do RTGs help? Let's say they somehow do (perhaps I have the numbers wrong). How much more delta V would you get using an RTG? Twice the delta V as solar panels? Note: momentum transfer goes as the square root of the energy, so you would need 4x as much power as Dawn uses. On the other hand, you wouldn't be carrying heavy panels.) If so, 20km/s is about what a Jupiter or Saturn flyby gives. So RTG+ion thruster+Jupiter is about equivalent to the Jupiter+Saturn part of Voyager. Except Voyager also used the outer gas giants. My point is that to get the same speed you'll need at least both of Jupiter and Saturn lined up right, and preferably at least one of Uranus or Neptune. Your proposal isn't enough.
- planetguy 14y ago
  I must admit that you've surprised me with the numbers on solar vs RTG. (I've learned something today!) But of course you can always strap multiple RTGs together. According to wikipedia's article on RTGs the most efficient ones produce about 4 watts per kilogram, so you'd need a couple of tons of 'em to equal Dawn's 10 kW at Earth, well in excess of Dawn's mass. Solar panels still rapidly become useless (like the square of the distance from the sun) as you get further out, of course.
danielweber 14y ago
Solar is way denser than an RTG in terms of power per kilogram, at least out to Jupiter and probably to Saturn as well. This doesn't mean that RTGs don't have value. They are continuous and keep things warm, which may be very important depending on your mission.

dalke 14y ago

The New Horizons RTG puts out 300W of electrical energy (and more as heat). The solar arrays on Dawn can supply "10 kW at Earth and 1.4 kW at Ceres". Wikipedia says the NSTAR thrusters on Dawn requires 2.3 kW. How do RTGs help? Let's say they somehow do (perhaps I have the numbers wrong). How much more delta V would you get using an RTG? Twice the delta V as solar panels? Note: momentum transfer goes as the square root of the energy, so you would need 4x as much power as Dawn uses. On the other hand, you wouldn't be carrying heavy panels.) If so, 20km/s is about what a Jupiter or Saturn flyby gives. So RTG+ion thruster+Jupiter is about equivalent to the Jupiter+Saturn part of Voyager. Except Voyager also used the outer gas giants. My point is that to get the same speed you'll need at least both of Jupiter and Saturn lined up right, and preferably at least one of Uranus or Neptune. Your proposal isn't enough.

planetguy 14y ago
I must admit that you've surprised me with the numbers on solar vs RTG. (I've learned something today!) But of course you can always strap multiple RTGs together. According to wikipedia's article on RTGs the most efficient ones produce about 4 watts per kilogram, so you'd need a couple of tons of 'em to equal Dawn's 10 kW at Earth, well in excess of Dawn's mass. Solar panels still rapidly become useless (like the square of the distance from the sun) as you get further out, of course.

danielweber 14y ago

Solar is way denser than an RTG in terms of power per kilogram, at least out to Jupiter and probably to Saturn as well. This doesn't mean that RTGs don't have value. They are continuous and keep things warm, which may be very important depending on your mission.