On Mon, Jun 11, 2018 at 1:59 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Sat, 9 Jun 2018, Craig Fink wrote:all rolled into one.
You missed the part about powering this arcjet with a nuclear battery
with 300 watts tops and some of that used elsewhere. The month long burn
is really to gather and store the energy in the superconducting magnet
storage ring. The engine runs in only short bursts.
You want some numbers, ok. Lifetime of a nuclear battery 50 years with
40 of those a thrusting from object to object in the Kepler Belt...
Hold it. Are you proposing this for *New Horizons*, or for a fantasy
Kuiper Belt Tour mission? They're not the same thing. New Horizons is a
Pluto mission, and that was key to getting it funded; everything else NH
can do is a bonus, and bonuses don't get to drive the spacecraft design.
Both, neither and entirely something else. Don't forget Dawn and Curiosity
That's 40 years averaging at half the power 150 watts... Energy budge is
50 Megawatt-hours added to 100 kg of propellant, ah gees I don't have a
feel for that. How about metric, 1.8 gigajoule per kilogram of
propellant? Sure sounds like a lot.
Kinetic energy is 0.5*m*Ve^2, and actually forget the 0.5 because you're
lucky if the propulsion system is 50% efficient at turning electricity
into jet kinetic energy. So Ve is about 45_km/s, i.e. Isp circa 4500_s,
which is ion-engine territory. So forget the hydrogen; you need xenon or
mercury.
For a 400_kg dry mass, that's a total delta-V of just under 10_km/s.
Which may sound like a lot, but actually isn't all that impressive for a
Kuiper Belt Tour -- the distances are really long out there. NH went
screaming past Pluto at just under 14_km/s, and even so needed nearly a
decade to get there.
Actually, none at all, because you can't. :-) There are no
commercial [Pu-238] suppliers, period. The only organizations
which have any are the US and Russian governments...
Russians? Ah, those Russians use a different kind of paperwork, Rubles!
Rubles? Ho ho. Hard currency is what's wanted. And alas, even that
doesn't hypnotize them the way it used to. Trying to bribe...
