[Orekit Users] Re: picosatellite biomagnetorquer experiment - request for answers/ideas/comments

[Michael Turner <michael.eugene.turner@gmail.com>]

On Tue, Jun 19, 2012 at 10:04 AM, Zac Manchester <zacinaction@gmail.com> wrote:
[snip]
> - The Sprites will be spin-stabilized in a sun-pointing attitude upon
> deployment.  This will ensure they have solar power whenever they are on the
> day side of the Earth.

I see this approach as potentially very good for my project, for
several reasons:

(1) Simpler modeling/sensing of the initial orbits. A batch of ejected
sprites should all experience very similar aerodynamic drag. I expect
this means they'll disperse slowly, even as drag becomes ever more
significant. If slight magnetorquing on my project's sprite changes
its drag characteristics by enough, it's possible that its orbital
path will diverge significantly from the group. Detection of any such
divergence (if possible) might constitute evidence of magnetorquing.

(2) Known initial conditions. I was concerned about the need to model
of a wide variety of tumbling scenarios, and, once my project's sprite
was flying free, to sense which scenario most closely approximated the
real situation. A known initial attitude and rotation rate should make
modeling easier.

(3) Alignment with experimental agenda. Spin-stabilization for
sun-pointing is already part of a longer-term, more ambitious plan.
"Biomagnetorquing" is a proposed way to maintain a sun-pointing
attitude over a long period of time (years), by periodically growing
and manipulating the required magnets, then recycling the materials.
Showing that magnetotactic microorganisms in a permanent, fixed magnet
can perform magnetorquing on a sun-pointing spacecraft helps support a
proof-of-concept for that scenario -- even though, in this case, the
torque actually perturbs the craft *away* from (direct) sun-pointing.

> - I'm trying to tune the antenna vibration frequencies so that they can act
> as nutation dampers to damp out attitude disturbances.

I'm surprised that this can be done at such small scales.

> - The current Sprite boards have a magnetometer and gyro.  The magnetometer
> allows sensing the Earth's magnetic field, which can give partial attitude
> information (up to an arbitrary rotation about the local B field vector).
>  The gyro gives the body-frame angular velocity vector.  With these two
> measurements, quite a lot can be gleaned about the attitude dynamics of a
> Sprite.



> - It's quite possible your permanent magnet will mess up the magnetometer
> readings.  You might be able to subtract its effects out as a constant bias,
> but you'd have to try that out with a development board (coming, I promise
> ;-)
>
> Let me know if you have any other questions.
>
> - Zac
>
> On Thu, Jun 14, 2012 at 4:03 AM, Michael Turner
> <michael.eugene.turner@gmail.com> wrote:
>>
>> Dear Orekit list members,
>>
>> I have a question about Orekit capabilities. Zac Manchester is copied
>> on this e-mail because he's making the relevant spacecraft; Kartik
>> Madiraju is copied because I've engaged him on related (but somewhat
>> tangential) issues related to magnetorquing. Please remove them from
>> the CC list if they ask to be dropped.
>>
>> I've been contributing to the Orekit wiki, but so far only at the
>> level of copyediting -- fixing typos, small grammatical errors, etc.
>> I'd hoped to learn more orbital dynamics by osmosis, so that I could
>> answer any questions I might have on my own. Unfortunately, I have
>> several other projects competing for my time. At this point, I can
>> only say that helping with the Orekit wiki has improved my orbital
>> dynamics *vocabulary* a little, while also helping me appreciate what
>> a complex subject it is.
>>
>> Orekit might be very useful for one of my current projects. However,
>> I'd like to be sure, before committing to Orekit.
>>
>> The project involves KickSat sprites - picosatellites launched from a
>> Cubesat. For a quick overview, see the Wikipedia article about
>> KickSat:
>>
>>   http://en.wikipedia.org/wiki/KickSat
>>
>> and the video in the original Kickstarter solicitation
>>
>>
>> http://www.kickstarter.com/projects/zacinaction/kicksat-your-personal-spacecraft-in-space
>>
>> I have donated enough to KickSat qualify for the launch of a
>> customized sprite. I want to make this spacecraft part of a science
>> education project here in Japan, and in some other countries if
>> possible.
>>
>> My specific project involves attaching a lightly magnetized strip to
>> the sprite before launch, then measuring and transmitting the amount
>> of magnetorquing the sprite undergoes before it deorbits. For two
>> reasons, I'd like to be very sure of the theoretical *minimum* magnet
>> strength that could cause any measurable change in orientation.
>>
>> (1) a magnet that's too strong might be disqualified as potentially
>> interfering with other sprites in KickSat;
>>
>> (2) I hope to use biologically derived biomaterials (bacteria or algae
>> containing magnetosomes) to make the strip a magnet; the maximum
>> achievable strength might be quite low.
>>
>> Because these sprites have a very high ballistic coefficient, and will
>> be ejected from the Cubesat at around 300 km (?), they will deorbit
>> fairly soon (weeks?). So it's important to be able to filter out any
>> attitude changes that are due only to increasing atmospheric drag.
>>
>> Orekit appears to have models for atmospheric drag (though not much
>> wiki documentation yet on this?), and even the beginnings of a
>> tutorial about geomagnetic field modeling. In exchange for help with
>> questions, I would be more than happy to help flesh out any Orekit
>> documentation that already exists on these two topics, as needed. I
>> would also be happy to contribute to the Orekit documentation any
>> tutorial examples that come out of my own project.
>>
>> Regards,
>> Michael Turner
>> Project Persephone
>> Tokyo
>
>