[Server-sky] A kind of thinsat to help deorbiting small debris

[Michael Turner]

On Sun, Nov 17, 2013 at 7:38 PM, Keith Lofstrom <keithl at gate.kl-ic.com> wrote:
> When people talk about thousands or millions of potential debris
> objects, I'm not impressed.  The sphere below GEO is 300 billion
> trillion cubic meters, and almost all of those cubic meters are empty.

Specific /orbital ranges/ are the problem here, though.

> When I walk to the library, I navigate through a few thousand cubic
> meters of space filled with hundreds of unpredictable potential
> colliders, mis-operated by idiots yakking on their cell phones,
> rather than passive objects following Newton's laws to eight decimal
> places.  Accurately track the debris objects, and space becomes
> far safer than a crosswalk.

A lot of it is rather small for tracking purposes. Much of it consists
of tiny pieces chipped off larger pieces. Even paint flakes can cause
spider cracks and cratering in windows.

>>   http://www.bloomberg.com/news/2013-11-14/real-life-gravity-space-debris-spells-business-for-astrium.html#!
> ...
>
> Check out Star Inc's electrodynamic tether debris collector:
> http://www.star-tech-inc.com/id121.html

Nice. And I love ED tethers. But are they going send these after every
1-cm debris chunk out there?

> Some space advocates talk about extracting resources from the moon.
> Jerome Pearson points out that there are thousands of tons of high
> grade aluminum in orbit already - we call it debris because we
> don't know how to harvest it and re-use it (yet).

Some physical processes are virtually irreversible. I think current
modeling suggests that if they neutralize the big stuff, the small
stuff solves itself (or at least the situation stabilizes.) One would
hope so.

> Much of the unharvested aluminum is in highly eccentric, highly
> inclined orbits (Delta, GEO, and Molniya upper stages, mostly) and
> hard to bring to space processing facilities to melt and recast.
> However, there are two good uses as-is for cylinders of 5mm to 10mm
> aluminum-lithium tankage:  armor for ISS, and ballast for launch-weight
> reduced server sky thinsats.

Armor sort of begs the question. Ballast for thinsats sounds a lot
better. Ideally, there's some solution to the small-debris problem
where the solution actually /feeds on/ debris. If it helps bootstrap
Server Sky, one could hardly complain.

> Jerome posits twelve 100 kg EDDE systems to capture all the larger
> low earth orbit objects in 7 years.  But electrodynamic tethers
> don't work very well above 2000 km or so.  That is the /lower/
> practical altitude for light sails.  Light sails won't be effective
> moving a large rocket body, but they could move small bits of one
> if we laser cut pieces off of it (hovering a few millimeters away,
> not from thousands of kilometers, definitely not through a
> dispersive atmosphere).  One gram chunks would make dandy
> ballast for ultralight thinsats - less to launch from earth.

You'd want a pretty clean cut. Maybe only lasers can do that.

> But worst case, if we choose to reenter that valuable aluminum,
> remember that powdered aluminum is the main fuel component of
> solid fuel rockets.  Rendezvous some oxidizer and the appropriate
> combustor and nozzle with that aluminum, and it can make its own
> delta V.  It is far more difficult to deliver that kind of energy
> from the ground and through an atmosphere, because 99% of the
> time, any given LEO object is over the horizon from a ground laser.
> When and if an object appears, it isn't in view for very long.

It'll be back, though.

> Whatever you plan for dealing with an orbital object, you must
> still find it, very accurately.  Radar sensitivity decreases as
> the inverse fourth power of distance in vacuum; atmosphere adds
> more inaccuracies.

Sounds like we need more radar up there. Is that another possible
thinsat-edge-of-the-wedge? Oh wait: you address this below. How nice.

> ... The reason we don't "just get out of the way"
> of more space debris is that the tracking error for passive
> objects in high LEO is one kilometer.  If we knew where the stuff
> was to 10 meter accuracy, very little delta V would be needed to
> get out of the way of it, and we could confidently ignore a much
> larger quantity of objects in the short term.  With high precision
> tracking and orbit computation, we could also prioritize the
> likely colliders that need orbit change first.
>
> Server sky arrays make dandy illuminators for look-down synthetic
> aperture radar.  We can find small objects, and characterize their
> position and velocity to millimeters and to micrometers per second.
> You can't do that from the ground, or with small aperture, low
> power, lower frequency orbiting radars.  You also need a lot of
> computing to correlate and characterize the reflected energy.
> That is a similar calculation to sorting out uplink from millions
> of terrestrial internet customers.  Server sky will do radar until
> the internet business becomes profitable.

OK, then: is it /also/ worth making early thinsats mirror Distributed
LODR laser pulses for diverting debris onto more innocuous paths until
it can be recycled?

> We can already do that kind of hyper-accurate tracking of objects
> if they are designed to be found.  The LAGEOS laser geodesy
> satellites are tracked accurately enough to measure continental
> continental drift, with millimeter-per-year velocity accuracy.
> Most rocket bodies and fragments are NOT designed to be found;
> that could be fixed by pasting light weight, solar powered, RF
> fabric on inner and outer surfaces.  In other words, the solar
> cell and radio portion of thinsats.

Another potential market entry point, if debris tracking information
can be sold. To the extent that satellites can use station-keeping
thrust to evade tracked debris, perhaps the information would be
useful for reducing satellite insurance premia.

> BTW, the LAGEOS satellites the nearest neighbors to the M288
> orbits, and the only valuable assets we need worry about
> colliding with.  It's lonely up in the van Allen belt gap.
>
> Most "pollution" is valuable material we are too stupid to use.
> We drilled wells into oil formations for hundreds of years,
> hoping to find brine for making salt, before Thorla and McKee
> started selling the gunk that came out of their brine well as
> medicinal "Seneca Oil" in 1814.
>
> We will learn to do the same with space "debris".  The companies
> that get paid to remove it will profit handsomely from reselling
> it.  Stake your claims now - the Russians would probably be glad
> to sell the headache and responsibility for their orbiting
> derelicts for a little hard currency.

If only there were a way to stake claims. Is there? As things stand,
they would appear on balance sheets as liabilities, not assets. The
question is how to turn that around.

Note that LODR doesn't seem to be limited to deorbiting - it can also
nudge things into higher(-energy) orbits.

Regards,
Michael Turner
Executive Director
Project Persephone
K-1 bldg 3F
7-2-6 Nishishinjuku
Shinjuku-ku Tokyo 160-0023
Tel: +81 (3) 6890-1140
Fax: +81 (3) 6890-1158
Mobile: +81 (90) 5203-8682
turner at projectpersephone.org
http://www.projectpersephone.org/

"Love does not consist in gazing at each other, but in looking outward
together in the same direction." -- Antoine de Saint-Exupéry