Ok, I have some serious questions about Star Trackers. In order to
rewrite the code on the Ardupilot to obtain a position from a star
tracker, I need to know a lot more about them. I'm not the kind of guy
that can plug and play anything I'm going to have to know what's going
on.
When we did Ardusat Jole and Jerome from Spark where here and Jerome was
working on the code for the sat. But none of the code had anything to do
with attitude control.
My first question is can you test a Star Tracker from earth? Can it get
a position from a single frame?
I also wonder if the spacecraft is tumbling can it get a position? What
roll rate and tumble can a star tracker handle?
The camera would matter in this right?
I've done a lot of work with some software called "Optic Tracker" I use
it for opticaly tracking balloons and rockets and UAS projects. I also
use it for tracking my telescope if a star tracker can be used from
earth (this is why I'm supposing they can't work from earth) Why don't
telescope tracking systems use it?
And here's where I show the limits of my skills in Ardupilot Euler
angles and quaternions are the positional math used by Ardupilot in the
current versions using Kalman filtering. What kind of math does a star
tracker use?
My last question at the moment is: how difficult is it really to go from
an earth frame of reference to an inertial, body fixed from an earth
fixed frame?
Can I even do this?
I admit the math is beyond me. But if I can get these things into boxes
I'm a guy that is really good at putting boxes together using other
peoples work in the math department. If I can get a grasp on the basic
principals involved no matter how complex the final project is.
Help me out here get me in the ballpark?
I've been working with Andrew Trigwell and a few other guys at Ardupilot
for almost 10 years now and they do like me and they will help me. But I
never tie them up to teach me anything because at that point I'd become
a burden. I'm just a water boy waiting for the right opportunity.
You follow?
Monroe
-------- Original Message --------
Subject: [AR] Re: Star Trackers, was Re: Re: Spin stabilized rocket
From: Ivan Vuletich <ivan.vuletich@xxxxxxxxxxxx>
Date: Tue, December 25, 2018 3:50 am
To: arocket@xxxxxxxxxxxxx
A quick Google turned up OpenStarTracker http://openstartracker.org/, ;
which looks real interesting.
According to the forum, it can run on a BeagleBone Black, but I haven't
been able to find anything on minimum camera specs.
On 25/12/2018 17:51, Ray Rocket (Redacted sender ar0cketman for DMARC)
wrote:
On Mon, 12/24/18, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
Beyond maybe 75,000km, sun sensors and star trackers
are about your only choice for external
attitude reference. Fortunately,
lightweight miniature star trackers, e.g. the
Sinclair ST-16, are now very good: point
one at any part of the sky not too close to the Sun, and
half a second later it reports full
three-axis attitude to sub-arcminute precision.)
Wow, starting at only $120,000!
I always wondered at the lack of F/OSS star tracker code. Should be able
to easily run on something like a Raspberry Pi,
Interestingly enough, NASA licenses a Linux compiled star tracker code:
https://technology.nasa.gov/patent/TOP2-265
"Low Cost Star Tracker Software - Highly accurate attitude information for
low cost COTS hardware"
Ah, just a question of proper search terms. Google's suggestion of [star
tracker matlab code] seems to be a sweet spot.
Ad Astra,
Ray