[ExI] powersats

[Keith Henson]

On Thu, Mar 27, 2008 at 3:03 PM, Tom Nowell <nebathenemi at yahoo.co.uk> wrote:
> I've been following the "getting big loads into orbit"
>  discussions, and I'm quite a fan of the subject.
>   The space elevator does require amazing materials,
>  but they are theoretically possible. The problem is,
>  given space junk (all but the lowest part of the
>  cable) and monatomic oxygen attack (the lowest part),
>  how do you keep repairing it in time? The wikipedia
>  article on space tethers
>
>  http://en.wikipedia.org/wiki/Space_tether

The Wikipedia article does not consider moving cable type elevators.
That deals with the monatonic oxygen because the fast moving cable is
one exposed briefly.  The space elevator project assumes a fleet of
ion engine space tugs and 5 years of gathering up the junk and pushing
it out to GEO where it becomes the counterweight.

>  mentions the SEDS-2 experiment was expected to last 2
>  weeks, but was cut after 3.7 days. (the wiki article
>  includes references to your space elevators, skyhooks
>  which don't reach the ground, satellite orbit
>  alteration with tethers - all articles accessible from
>  the main one).
>
>  I like the idea of the launch loop - 2000km iron cable
>  track moving at 14km/s, using magnetism to accelerate
>  loads. There's something pleasingly Isembard Kingdom
>  Brunel about the whole concept, and while it has
>  issues it doesn't use any materials that don't
>  currently exist. (The potential dealbreaker on this on
>  is control circuits capable of adjusting the capable
>  every microsecond).

It's fundamentally a reliability problem.  Given nanotech I feel it
could almost certainly be done, but given nanotechnology, you don't
need it.  :-(  It's still an awesome idea.  The inventor, Keith
Lofstrom, contributed the variable speed cable going up 50 miles so
the payloads don't go supersonic in the lower atmosphere.

>  Laser launch looks very feasible - the heat exchanger
>  rockets seem doable with today's technology, it's just
>  the control system that would require serious R&D. The
>  only issue with this launch type is that it launches a
>  huge number of very small packages skywards - Keith,
>  how small a package can you get away with for powersat
>  construction?

A ton perhaps.  Operated 20 hours a day they would be launching 100,
one ton payloads an hour.  If you need to cycle the lasers less often,
then you would have to send up large payloads.  Rockets at 1%
efficient would take 20 5GW power sats making H2 and O2.  I don't have
the power consumption of laters.

>  Railgun/gas gun/launch track technologies - there
>  exist several possibilities for boosting things to
>  orbit with short,massive acceleration - I doubt solar
>  cells would survive it.
>
>  The overall space launch market isn't huge at the
>  moment (55 launches in 2005, according to one report I
>  read - couldn't find what the total launch mass was
>  though). Power satellites require a massively bigger
>  capability than at present. On the other hand, massive
>  launch capabilities won't be developed unless there's
>  an industry crying out for it. So, keep on designing
>  the power satellites - it will keep the hope of space
>  resource utilisation going.
>
>  Tom

Done at all it would be an integrated business proposal package.

Keith