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Re: Bravo to the command team!




----- Original Message -----
From: Richard D. Burgan <wc8j@raex.com>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, January 09, 2001 7:05 AM
Subject: [amsat-bb] Bravo to the command team!


> Hi All,
>
> I think today's AMSAT Special Bulletin 008.01 regarding the
> status of AO-40 is really good news.  There are some negatives
> in that some functions have been lost but AO-40 is still very
> capable.  Thanks to all of the AMSAT command team for your
> hard work.
>
> There are specific points that I would like to see clarified
> in order to help us understand the AO-40 status better.  They
> are:
>
> In the What's Next section of the bulletin Dr. Meinzer uses
> the phrase "ongoing mass loss".  What is he referring to?
> Does this indicate that the spacecraft is still loosing mass
> or that it will in the future?  If reorienting the spacecraft
> could take advantage of it it must mean the mechanism is
> understood.  Is this true?  I am sure clarification would be
> greatly appreciated by all.

Let me try to clarify.

There had been a suspicion [as reported] of a propellant leakage, though
this had not been characterized initially.  However, observations of the
changes to AO-40's orbit could not be explained or even adequately
approximated by any combination of natural forces, of which the computations
included:

-- Earth Gravity (using up to an 8th-order gepotential model)
-- Lunar & Solar Gravity
-- Atmospheric Drag
-- Solar Radiation Pressure

Evaluation of AO-40's orbit changes most notably indicated a decrease in
perigee altitude that was inconsistent with the above forces.  The
hypothesis was that since AO-40 has essentially the same orientation it had
for the perigee boost thruster firing, a leak out the 400N thruster nozzle
would have a positive acceleration at perigee and a negative acceleration at
apogee (since the spacecraft is spin stabilized).  This deceleration at
apogee would, in turn, cause an unnatural decrease in the perigee altitude.

Thus a thrust component directed toward the spacecraft's spin-stabilized
orientation was added to the above computations.  The amount of [estimated]
thrust was varied in the calculations until there was a match to AO-40's
observed orbital behavior.  This more or less corroborated the propellant
leak hypothesis.  Furthermore, finding a good fit for the thrust gives an
excellent estimate of the rate at which the propellant mass is being lost.

73, Ken N2WWD


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