Flywheels / NEO Retrieval

Ian Woollard wrote,

"LOX isn't very easy to store in space; some refrigeration is probably
required,"

Is that true? What is the background temperature in the shade, and what
is the temperature at which LOX boils?

Ron

Ian Woollard ian.woollard@...
10/21/01 06:27 PM

Hall thrusters can run on LOX or other propellents if they have to.
The electrical efficiency is reduced, but you can probably save
money by adding more solar panels. I think that a solar panel
gives 1 kw per 40 kg, but I don't have a figure for the cost of
solar panel per kg off hand; but I doubt its as high as $100,000
per kg.

LOX isn't very easy to store in space; some refrigeration is
probably required, but with that much power around, I doubt it
would be a show stopper.

> In a message dated Mon, 1 Oct 2001 7:12:17 PM Eastern Daylight Time,
Ian Woollard ian.woollard@... writes:
>
>>For a probe weighing 500kgs, attached to a rock weighing 1 tonne
>>the final mass is 1.5 tonnes. Let's assume we use a Hall thruster
>>with an ISP of 1600 seconds (exhaustVelocity is 9.81 * 1600 =
>>~16,000km/s).
>>
>>This means that for a deltaV of 3 km/s [sounds ok, maybe even high
>>if we slingshot around the moon AND aerobrake at the earth] so the
>>initial mass before you head for home is:
>>
>>1.81 tonnes i.e. ~310 kgs of fuel.
>>
>>That's not all that much. Sure its going to be slow, you'd have to
>>wait many months, and you'd have to add more fuel for the way out,
>>but on the way out the probe is going empty so guesstimate for
>>doubling the fuel load and it probably comes out about right, i.e.
>>1.4 tonne initial vehicle drags back 1 tonne of rock plus itself,
>>
> So that means for an outlay 310 kg of Xenon propellant we get 1 tonne
of PGM.
>
> According to http://www.chemicool.com/elements/
>
> Xenon costs $100,000/kg
>
> Compared to:
>
> Platinum, $47000/kg - $47M/tonne
> Osmium, $77000/kg - $77M/tonne
> Iridium, $42000/kg - $42M/tonne
> Rhodium, $130000/kg - $130M/tonne
>
> I am surprised to see here that the cost of the Xenon is a large part of
the overall spacecraft cost, this is unusual. 310 kg of Xenon costs $31
million ! This is probably at least 50% of the overall spacecraft cost
- wow !
>
> Assume $60M overall mission cost...the mission could still make a profit
for Osmium and Rhodium, but not for Platinum and Iridium.
>
>>Doubling up the power and adding many more thrusters would multiply
>>up the time you can thrust for and double the thrust levels.
>>
> Since the cost of propellant is so high, doubling up on thrusters/power
could be attractive...
> the percentage cost increase would be small and the mission performance
would be dramatically improved.
>
>>Hall thruster are supposed to work with other, cheaper,
>>propellents, like oxygen, but I don't have performance figures for
>>that. The cost of xenon is huge, IRC, it comes from liquifying air
>>
> Hmm, we definitely need those performance figures.
>
>>so there's no theoretical limit to supply. Hall thrusters can be
>>run on oxygen with 10% of something else [probably xenon or argon],
>>that might be another approach for the propellent.
>>
> Yes, that would reduce the cost of propellant by a factor of ten.
> So if the performance is halved we get an improvement of specific
performance
> for propellant cost increase of a factor of five.
>
> But since I estimate propellant (Xenon) cost is about 50% mission cost,
> we would wnat our performance to fall be less than 50%. Otherwise, we
> might as well stick to the Xenon.
>
>>I think this may compare quite favourably with going to the moon.
>>In LEO you can probably stuff the rock in the back of a Space
>>Shuttle or something or send it to the ISS for analysis.
>>
> ISS does not have any mineral analysis capabilities.
>
> The analysis laboratories on Earth are much better equipped than
anything we could put into