AO-40 attitude & leak

• Subject: [amsat-bb] AO-40 attitude & leak
• From: Chris Hill <CRH_Telnet@xxxxxxxxxxx>
• Date: Tue, 09 Jan 2001 11:55:35 +0800

```Hi All,

What a great piece of news that the magnetorquers are working on AO-40!

I'm trying to deduce the direction in which the mass loss (leak) is
occuring on AO-40.  If I'm correct, the fact that the thrust developed is
decreasing perigee, means that there is a significant vector of that thrust
directed in the +z axis.

This is based on the premise that from a GTO, perigee is usually increased
by firing tangentially at apogee.  Likewise, it took a burn at perigee to
lift the apogee.

I could be wrong here...  thoughts, anybody?

Earlier, I had thought the leak was on the -z side of the satellite, which
is in accord with the U & L omni antennas not working...  but the omni's
may have failed due to damage elsewhere in the satellite, not necessarily
due to damage directly on the -z facet.

Presumably, the solution is to change the satellite attitude by something
approaching 180 degrees, thus having the thrust add to the orbital
velocity, not detract (attitude = 90/0).  This will cause best squint angle
to occur prior to perigee, not after.

Whilst an attitude of 90/0 gives a solar-illumination angle of about 28
degrees, 122/0 gives near-perfect solar-illumination, which would be useful
for providing the power budget to power the Arc-Jet.  If the arc-jet works,
then it should easily be able to lift the perigee height...  only problem
is, that the existing attitude of 270/0 (or thereabouts) is best suited to
an arc-jet burn at apogee to lift the perigee height.

So, what will happen next?  Perhaps the following:
- Use the magnetorquers to reduce spin further, then change attitude to
302/0, thus greatly improving communications, and bringing the batteries up
to full charge.
- Test the arc-jet with a very short burn at the unfavourable attitude of
302/0
- If the arc-jet works, bring batteries back to full charge, change
attitude to 270/0, then do a series of apogee burns at attitude 270/0 to
lift the perigee.
- If the arc-jet doesn't work, change attitude to 90/0, and wait until all
fuel has finished leaking...  the thrust will be helping to lift the
perigee height, however communications will be about the same as now.

...  and that's about as much guessing as I should do today!

Chris
vk6kch
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