[Server-sky] Drag and LEO thinsat experiments

Jonathan "Duke" Leto jonathan at leto.net
Fri Jul 5 21:20:27 UTC 2013


I am very interested in the software side of these things.

Would it be useful or interesting to have web-based software for
research and development people, like us, can do simulations and get
real data from a web browser? That seems like it will lower the
barrier to entry exponentially, in terms of "doing useful stuff" to
make Server Sky a reality.


On Mon, Jul 1, 2013 at 6:57 PM, Keith Lofstrom <keithl at kl-ic.com> wrote:
> Some thoughts about microgravity thinsat tests.
> Take a look at http://server-sky.com/Drag .  The air drag at ISS
> altitudes (350-400km) and below is way too high to maneuver
> thinsats - they are tissue paper in a hurricane.  Once thinsats
> drop below 1000km altitude, they will re-enter in weeks;  below
> 400km, re-enter in hours, unless they are shielded from air drag.
> Thinsats in light pressure accelerate away from the sun at
> around 20 μm/s².  At ISS altitudes, the orbital drag is 200
> times higher, -4000 μm/s², rapidly slowing down and losing
> altitude.  That is 15 m/s per hour, dropping orbit altitude
> by 30 kilometers, which doubles the drag in an hour, which
> doubles the drag in half an hour, ...
> A 1U cubesat has an area of 0.01m²and weighs 1kg, 200 times the
> mass and 0.4 times the area of a thinsat, so the drag acceleration
> is 500 times lower, about -8μm/s².
> ISS accelerates at -0.2μm/s² because of drag.  Small, but it adds
> to drop the orbit by 10s of kilometers over months - putting ISS
> in denser atmosphere, decreasing the decay rate and requiring
> frequent rocket reboost.  ISS flexes, turns, outgasses - certainly
> not perfect vacuum and zero gravity.
> Imagine testing a thinsat inside of a transparent container to
> protect it from air drag.  If the container is in the portion of
> its orbit moving towards the sun, and slowing at 20μm/s², it will
> track the light pressure acceleration of the thinsat and the
> thinsat can maneuver inside the container.  That is way more
> acceleration than ISS, a bit more than a slowing cubesat.
> But if the cubesat deploys a larger transparent plastic bag,
> that could add enough drag to match the thinsat's 20μm/s²
> light pressure acceleration for a small portion of a 92
> minute ISS-altitude orbit.  A full size 20cm thinsat won't
> fit in a small bag, but for testing a 5cm thinsat will do
> fine.  A small thinsat turns four times faster, facilitating
> short duration experiments.
> A proposed experiment:
> Make a cubesat with small TV cameras, an S-band transmitter,
> a bluetooth transmitter, and a small deployable tent with a
> 5cm baby thinsat inside.   The baby thinsat has InP solar
> cells and electrochromic thrusters controlled by a single
> chip bluetooth receiver/CPU.  The cubesat commands the captive
> baby thinsat to manuever, the behavior is captured by the
> cameras and flash memory, to be slowly transmitted to the
> software radios on ISS.
> As the cubesat drags and slows down, the orbit will drop
> and move forwards in orbit, eventually falling out of range
> of ISS and re-enter.  If the drag tent stays deployed,
> the cubesat will come down in less than two weeks.  That
> will result in a few dozen experimental passes.
> Also, developing a low-mass deployable drag tent from a
> cubesat might be a useful technology for other cubesats.
> If their orbit takes them near some other LEO asset, it
> slowing down and missing a collision could save $$$$$ in
> liability.
> A lot of handwaving, but a concept for an experiment that might
> refine into something practical.  CHECK MY NUMBERS please!
> Keith
> --
> Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
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Jonathan "Duke" Leto <jonathan at leto.net>
Leto Labs LLC http://letolabs.com
209.691.DUKE http://duke.leto.net

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