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RE: Bravo to the command team!

See below.  JAK

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Ken Ernandes
Sent: Tuesday, January 09, 2001 5:27 AM
To: Richard D. Burgan; amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] 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

-- 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

[...After subtracting off the real effects of the above itemized
forces (which are not zero).  In my experience estimating drag effects is
difficult, especially near solar max. which is (unfortunately) where we are.

Jan W3GEY]
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