(A spinoff of this thread.)
I thought it would be interesting to have a thread where we could discuss atmospheric mining (primarily of helium-3) in Jupiter, Saturn, Uranus and Neptune, and which planet is actually most profitable in the long run.
Here's the thing: The gas giant closest to the Inner System (Jupiter) is also the one with the greatest gravity. Uranus has the lowest gravity, but is an insane distance from most potential buyers. Saturn is middle of the road in both aspects. Fuck Neptune.
Using a Hohmann transfer orbit (the most energy-efficient travel path), here are the travel times and delta-v required to go from orbit around the various gas giants to Mars orbit:
Jupiter-Mars: 37 months. 21,956 m/s --- 100% J, 100% J
Saturn-Mars: 78.5 months. 16,392 m/s --- 212 % J, 75% J
Uranus-Mars: 200.1 months. 13,177 m/s --- 541% J, 60% J
Neptune-Mars: 376.3 months. 14,093 m/s --- 1017% J, 64% J
Getting to orbit from "mining height" should require roughly the same proportions of delta-v. (With some exceptions: See below.) So far, it seems like Uranus wins in the long run thanks to lower reaction mass costs, right? That's what I thought! But then NewtonPulsifer made me aware of the blatantly obvious fact that if we're using hydrogen as reaction mass, we can simply get it from the same place we get the helium-3 (since the atmospheres are, you know, over 80% hydrogen). It can't be a huge cost. If the cost of creating metallic hydrogen is small enough, it seems that Jupiter wins in terms of profitability, to the cheer of greedy biocons everywhere.
Still, most recent suggestions for helium-3 extraction I've seen discussed in the scientific literature seems to favor Saturn and Uranus over Jupiter, due to Jupiter's gravity and magnetic field. It feels like I'm missing something, possibly due to the gap between EP-technology and the technology being discussed today.
In addition to gravity and distance, there are the following factors to consider:
Jupiter:
+: Not as windy as Saturn.
-: Has far more erratic weather than Uranus and Neptune.
-: Murderous magnetic field of doom.
Saturn:
+: You spin me right round; rapid rotation period makes it easier to get into orbit.
-: Has far more erratic weather than Uranus and Neptune.
-: Much faster winds than Jupiter.
-: Rings might pose navigational problems.
Uranus:
+: Has more predictable weather than Jupiter and Saturn.
+: Has calmer winds than Neptune.
+: Very, very cold: Makes liquefying helium easier?
-: Weird axial tilt.
Neptune:
+: Has more predictable weather than Jupiter and Saturn.
-: Has faster winds than Uranus.
In addition to all this, we have the composition of the atmospheres themselves to think about!
Jupiter: Hydrogen 89.8%, helium 10.2%.
Saturn: Hydrogen 96.3%, helium 3.3%.
Uranus: Hydrogen 82.5%, helium 15.2%, methane 2.3%.
Neptune: Hydrogen 80.0%, helium 19.0%, methane 1.0%
Oh, and of course we must also take into consideration the price of both helium-3 and the ships themselves (not to mention maintenance of the entire infrastructure).
And probably a thousand other factors I haven't mentioned and/or considered. It's like it's rocket science or something.
Does anyone have any idea how to sort this all out, and how to figure out which planet is, in the long run, the most profitable to invest in?
—
President of PETE: People for the Ethical Treatment of Exhumans.
I'm saying there's multiple fusion fuels.
Why use He-3?
In economic terms it means other fusable fuels can be used instead of He-3.
In fact if you check out
http://en.wikipedia.org/wiki/Nuclear_fusion#Neutronicity.2C_confinement_...
you'll see Tritium-Deuterium fusion is far and away the best power density, but also generates a lot of neutrons. Those neutrons would eventually make your fusion rocket radioactive - to the point you couldn't use it any more. So if ditching the fusion motor and getting a new one is cheap, there's no need to use He-3.
If you could get He-3+He-3 fusion working there would be zero neutrons. One problem with that is a He-3 only fusion reactor creates most of its energy as x-rays, not alpha particles. You'd need a good/clever way to contain and convert those x-rays to usable heat and power.
However I think EP may be using He-3/Deuterium fusion in their ships, not He-3 only. I'm not sure.