[Server-sky] Drag and LEO thinsat experiments

Tue Jul 2 06:22:30 UTC 2013

"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."

It's been proposed (sorry for the vagueness, there's some ITAR
sensitivity here from my source) that PhoneSat become a kind of
standard cubesat bus. It will lack S-band of course but will have a
camera and bluetooth.

The "tent" could double as a de-orbiting mechanism later in flight.
There's been some persuasive talk of a standard for deorbiting cubesat
using this technique

   http://repository.tudelft.nl/view/ir/uuid%3A49d86db1-8909-4464-af1b-fe1655c9c376/

If there could at least be an option in the standard for tent-fabric
transparency, there might be other space-sci/tech uses for it, by
other researchers who'd like long-duration nanogravity themselves,
together with solar insolation. Well, OK, maybe only other solar-sail
researchers. But still.

Regards,
Michael Turner

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

On Tue, Jul 2, 2013 at 10:57 AM, 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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