ARISSat-1 Orbit Decay Prediction
Subject: ARISSat-1 (37772) decay
From: DeYoung James
Date: Tue, 15 Nov 2011 09:29:31 -0800 (PST)
First, thank you Mineo for reading the AMSAT Journal and making several of
my papers available on your web site. My AMSAT Journal paper published in
the March/April 2011 issue is actually still fairly valid for the scenarios
shown in the paper. The solar flux has turned out to be somewhat higher than
was used/predicted in the paper. This has caused the atmospheric densities
to be higher which results in higher decay rates. When I wrote the paper I
had this nagging feeling that stopping the release height scenarios at 370
-km was not going to be high enough. We are very fortunate that the ISS was
boosted to such a height before release of ARISSat-1 and not after release!
There is a valuable lesson, I think, to be made with respect to predicting
satellite decay dates far into the future. The future state of the atmosphere,
i.e. the atmospheric density that the satellite will pass through is poorly
predictable in the long-term, say starting greater than a week or two into
the future. Predictions of satellite decay dates months in the future should
be evaluated with the understanding that your date of prediction errors may
be large. The errors are due to the future uncertainties of the orbital path
which grow quickly with time in a prediction. The atmospheric density is not
the only source of error. Your orbit model, the integrator, and the accounting
of the gravitational and drag forces among others will affect your results.
Predictions of satellite decay dates are not do-and-forget. The general
process is to make a prediction, get new measured observations of the height
in the future, and at some point re-do your prediction when the errors become
significant to you. With that all said here is my current prediction using
the same tools used in the AMSAT J. paper and produced as of 2011 November
13th. The decay of ARISSat-1 (37772) will happen nominally on 2012 January
30th with a 10% rule-of-thumb error allowance of 18 days around this date.
The errors may be larger than the rule-of-thumb indicates!
Subject: Re: ARISSat-1 (37772) decay
From: Mineo Wakita
Date: Wed, 16 Nov 2011 20:36:44 +0900
Hello Jim, N8OQ.
Thanks for your very valuable reply.
Because it has the effect of the atmosphere density, I think that
the re-entry into the earth's atmosphere of ARISSat-1 will be
really earlier than April 9, 2012.
I added your this reply below the following my URL,
JE9PEL, Mineo Wakita