Jonas_B._Bjarnø
Please do share on your experiences with a star tracker! I'm about to
start experimenting. I can for sure put one up to 100kft on a balloon
and get a pretty good idea if it will "Really" function.
So what sensor are you using in the camera?
Because if CMOS would work I'd be all for that for power reasons.
Monroe
-------- Original Message --------
Subject: [AR] Re: Star Tracker
From: Jonas_B._Bjarnø <sveskemos@xxxxxxxxx>
Date: Fri, December 28, 2018 2:37 am
To: arocket@xxxxxxxxxxxxx
That's erroneous information. Any properly designed star tracker will
have no problem staring at the sun for extended periods of time. It'll
give you no attitude solutions of course, but there will be no damage to
the sensor. Again let me stress that a LOS-capable star tracker
necessarily must be wide-field-of-view, hence the thermal management
issue of looking at the sun typically only entails a temperature rise on
the order of 10-15deg.
The baffles are there for another purpose entirely. They allow you to
operate the star tracker with the Earth, Sun, Moon etc. *close* to the
FOV. Its for stralight protection and in some cases as a thermal
radiator, nothing else.
/J
Den 12/27/2018 kl. 04:07 PM skrev Monroe L. King Jr.:
I found something I don't like about Star Trackers they need a baffle to
block the sun because the sensor can't handle the sun. That sucks! Too
easy to kill one.
How about using a FSD?
FSD (Fast Switchable Diffusor)
The polarizer-free FSD switches between clear and light-scattering
states. The open state exhibits over 83% transmittance while the closed
state effectively diffuses light.
I wonder if these Star Trackers could function sufficiently with 17%
less light?
These are non mechanical solid state and could be triggered by another
sensor.
To bad polarization (LCD) won't work because that cuts more like 50%
Not sure what the thermal issues would be.
Monroe
-------- Original Message --------
Subject: [AR] Star Tracker
From: "Monroe L. King Jr." <monroe@xxxxxxxxxxxxxxxxxx>
Date: Tue, December 25, 2018 9:32 pm
To: "Arocket" <arocket@xxxxxxxxxxxxx>
I'm going to have to split this topic off the Spin Stabilized thread.
Ok I'm looking at 2 Star trackers
1: Nasa Low Cost Star Tracker Software Highly accurate attitude
information for low cost COTS hardware.
2: OpenStarstacker a robust, high performance startracker
The camera for the Nasa tracker is the Lumenera LW230 monochrome with
FUJINON HF35SA-1 35mm lens and a star database from Hipparcos catalog
Position computation is derived from Euler Angles not Quaternions
The attitude is computed as a set of Euler angles: right ascension (RA),
declination (Dec), and roll. The first two Euler angles are computed by
using a linear system that is derived from vector algebra and the
information of two identified stars in the image. The roll angle is
computed using an iterative method that relies on the information of a
single star and the first two Euler angles.
The OpenStarstracker uses Bayesian startracker algorithms (Solar System
based frame of reference) and a star database from the same catalog
Hipparcos
The camera is left up to you to choose and they have a calibration
technique where you send an image from the camera and the it tries to
determine if your camera will work.
The position is accomplished by Using OpenCV centroiding and the
positional math I can not find a reference to but they must use Euler
angles, Quarternions or DCM (Direction Cosine Matrix) as far as I know.
So I'm offering this up so people can punch holes in the
quality/usefulness issues of actually trying to fly a spacecraft using
them.
Monroe