In reply to Terry Blanton's message of Fri, 31 Mar 2023 10:22:49 -0400:
Hi,
[snip]
>https://www.universetoday.com/160516/the-first-all-electrical-thruster-the-ivo-quantum-drive-is-headed-to-space/
Phosphorous-32 has a power to weight ratio of 2.9E6 W/kg. Compare this to the
measly 340 W/kg of the solar panel
previously mentioned, and it becomes obvious that a short half lived
radioisotope would be very advantageous as power
source in a real Mars mission where the mass of the craft is not trivial.
However P32 has a half life of only 14.3 days, so it had better be a quick
"there and back mission". :)
For Cesium-137 we get 876 W/kg (HL = 30 yr)
Americium-241 we get 112 W/kg (HL = 432.7 yr)
Polonium-210 we get 144000 w/kg (HL = 138 days)
Pu-238 => 568 W/kg (HL = 87.7 yr)
For something like a Mars mission I think Po-210 might be best suited, as it
has a half life of 138 days, which means
that a trip taking a few days shouldn't be much of a problem. Besides, the
Russians don't seem to have a problem getting
hold of it. (IIRC there has been at least one case of Po-210 poisoning.)
Of course "full" shuttle loads could be taken to Mars, then swapped for empty
ones that are brought straight back.
Isotopes with a long half life have an advantage that the power remains almost
constant during the mission.
To achieve an acceleration of 1g (2 day trip to Mars), a power density of 189
W/kg is needed. Dividing this number by
the power densities given here above tells you what fraction of the total mass
needs to be fuel. (I think?)
So for Po-210 we get 189/144000 = 0.131% or roughly 1 kg of fuel / tonne of
spacecraft. Upon return, most of this still
exists, so it just need to be "topped up".
(Note that web site advertises "zero" fuel, but they mean zero chemical fuel,
and no reaction mass, but neglect the
input of solar energy which should rightly be counted as fuel.)
CF would of course change all this.
Cloud storage:-
Unsafe, Slow, Expensive
...pick any three.
