March 31, 2002

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AO-40 Update

AO-40 ground control station W4SM recently reported on the latitude drift of AO-40's sub-satellite (apogee) point. The sub-satellite point of latitude at apogee is a function of argument of perigee and the inclination of the satellite's orbit. The greater the inclination, the more the variability.

Argument of Perigee (ArgP) needs a drawing to fully visualize, but it represents the angle between the perigee of the orbit and the point where the orbit crosses the equatorial plane headed north (ascending node). If ArgP = 0 or 180, then apogee is over the equator. When ArgP is less than 180 degrees, the apogee is in the southern hemisphere. When ArgP is greater than 180 degrees, apogee is in the northern hemisphere. For AO-40, ArgP is currently ~32 degrees, and increasing 0.3251 degrees each day. The duration of a full cycle is a little over 3 years.

Inclination is a measure of the tilt of the orbital plane with respect to the Earth's equatorial plane. For satellites with highly elliptical orbits such as AO-40, the inclination is subject to significant solar/lunar forces which tend to alter it in a non-linear fashion. AO-40's inclination has been increasing from about 5.2 degrees in mid-2001, to the current value of 7.3 degrees. Orbital element integration, factoring in solar, lunar, and terrestrial forces show that inclination will continue to increase until it peaks at approximately 10.3 degrees in the spring of 2004. As AO-40's inclination and eccentricity change due to these forces, the rate of change of ArgP will fluctuate very slightly as well.

From a northern hemisphere perspective, the low point for elevation of AO-40 at apogee will occur in the fall of this year. Apogee elevation will then improve, peaking 18 months later (in the spring of 2004).

AO-40 is currently experiencing eclipse periods of nearly 30 minutes. During a recent eclipse period, both the magnetorquers and beacon were on when the IHU detected that the battery was running low, triggering the low-voltage software-which turned the S-2 transmitter off.

For the last three orbits, the battery voltage during the final 45 seconds of the eclipse period has dropped to the point where it has triggered S-2 shutoff.

The shutoff is set very conservatively and the scheduling software has restarted the S-2 transmitter at MA=15 nominally each time. W4SM lowered the shutoff threshold by one count, and this should be sufficient to prevent further eclipse shutoffs for this cycle. If not, additional adjustments will be made.

The current perigee eclipse cycle runs through June 19th. From August 13th to September 18th, AO-40 will experience much longer non-perigee eclipses that peak at 165 minutes duration. During these eclipses the S-2 transmitter will be turned off by the scheduler.

[ANS thanks the AO-40 team for this information]

Second Call for Papers

This is the second call for papers for the 17th AMSAT-UK Colloquium, to be held at Surrey University, Guildford, Surrey, United Kingdom. The dates are July 26-28, 2002.

AMSAT-UK invites speakers to submit papers about amateur radio space and associated activities for the event and for the Proceedings document to be published at the same time.

There will be awards for the best presentations.

Offers of Papers should be submitted as soon as possible; the final date for full documents to be received is mid-June 2002.

Submissions should be sent to:

Internet e-mail:

Terrestrial mail:

        Richard Limebear, G3RWL
        60 Willow Road
        Enfield EN1 3NQ
        United Kingdom

AMSAT-UK also invites anyone with requests for program topics to also submit them to G3RWL.

[ANS thanks Colloquium organizer Richard Limebear, G3RWL for this information]

ANS in Brief

ANS news in brief this week includes the following:

Weekly Satellite Report

Link to the weekly report on satellite ...

All Satellites
ISS . RS-12 . RS-13 . RS-15 . AO-10 . UO-11 . UO-14 . AO-16 . DO-17 . WO-18 . LO-19 . FO-20 . UO-22 . KO-23 . KO-25 . IO-26 . AO-27 . FO-29 . TO-31 . GO-32 . SO-33 . PO-34 . SO-35 . UO-36 . AO-40 . SO-41 . SO-42 . NO-44 . MO-46

Please send any amateur satellite news or reports to the ANS Editors at, or to ANS Editor Dan James, NN0DJ, at

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This week's AMSAT News Service bulletins were edited by AMSAT  News Service editor Dan James, NN0DJ.