[time-nuts] GPS interference and history...

Jim Lux jimlux at earthlink.net
Fri Jan 13 00:25:27 EST 2012

On 6/9/11 1:06 PM, J. Forster wrote:
> Ha!
> Nuclear power in space is poltically utterly impossible in the US. There
> is huge opposition to RTGs, never mind even the thought of reactors.

Hmm.. when I was working on Prometheus aka Jupiter Icy Moons Orbiter 
(JIMO) there was a guy from NASA HQ who gave a talk at the Lunar & 
Planetary Institute about flying reactors.  His basic idea was that 
there is a fraction of people who will object to ANY nuclear power in 
orbit, be they 1 ounce Radioactive Heating Units (RHUs.. pretty much in 
every Mars mission we've flown) or RTGs or full on nuclear reactors 
(JIMO was going to fly a 300kWthermal/100kW electrical reactor being 
developed by the folks who do submarine reactors)

So therefore, the "incremental pain" from flying a reactor is small.

> Solar is not really practical either. The sun puts out about 1 KW/Sq.M in
> EO, and solar cell efficiency is<20%; so 10 KW needs 50 Sq.M of
> stabilized pointing cells.

A bit more than 1 kW/sq m (thats more like earth surface).. I think 1.3 
is more of a typical number above the atmosphere..

30% is more like what we get with triple junction enhanced solar cells, 
I think, but there's a whole lot of factors that go into it.

In any case, there are lots of commercial COMSATs in GEO with tens of kW 
of solar panels (yes, many, many square meters).  The power available on 
those things (to those of us used to deep space scientific missions) is 
gargantuan.. They're running more than a hundred TWTAs with hundreds of 
watts each.  And the L band ones (Sirius/XM) are BIG tubes.

But, for instance, Juno, which is on it's way to Jupiter has solar 
panels that are enormous (since it's NOT nuclear powered).   ABout 60 
square meters which produce just under 500W at the orbit of Jupiter 
(5AU, so 1/25th what they generate at earth)..

That would be about 200W/square meter in earth orbit (which I concede is 
about your 20%)

> -John

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