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To All Members of AMSAT-NA,
The following statement is addressed to those members of AMSAT-NA who have requested an explanation of the December 2000 incident that took place on P3D. This statement has been prepared and developed by Robin Haighton, VE3FRH, President of AMSAT-NA, with input and review from other AMSAT-NA members.
As you are aware, Phase 3D was launched on November 16, 2000 into an almost perfect geosynchronous transfer orbit (GTO) by an Arianespace launch vehicle (AR-507) from Kourou, French Guiana. Within a few hours of launch excellent telemetry was being received from the 2 meter beacon, and amateur radio stations worldwide started downloading data with great accuracy, due in part to the strong signal strength. The original plan was to use the 70cm beacon. However, for reasons not yet known, the 70cm transmitter signal was not heard.
Before the satellite could be regularly used for general amateur radio communications, it was necessary to carry out orbital changes, stabilize the satellite, open the solar panels, etc. The first changes to the orientation of the satellite were carried out using the onboard magnetorquing system. This worked well and after relatively few orbits the attitude of (now) AO-40 was 270/0, and ready for operation of the 400 Newton motor. Among the many components which comprise this motor system, there are several valves which control pressurizing helium and fuel. During construction of the satellite it was noted that one of the helium valves had a tendency to "stick" when operated. Both of these valves were sent back to the manufacturer for inspection and repair. Both valves were inspected and one valve was repaired, followed by return and re-installation into the system.
On the first attempt to fire the 400N propulsion system, it failed to operate, possibly due to a sticking helium valve. Before the second attempt, it was determined that the fuel tanks could be pressurized (by helium) to their correct pressure over a five minute period, and although this was about one-tenth of the normal helium flow rate, it was still adequate for the planned three minute motor burn.
On the second attempt to fire the 400N motor, all systems appeared to respond correctly at first. At the three minute mark the internal timer transmitted a signal for the main solenoid valve to close, which should have shut off the fuel to the motor. Telemetry shows that the signal was sent and received, but the motor did not shut off for two or three more minutes, placing AO-40 into a higher apogee orbit than was planned at that time.
To understand how this may have happened, it is necessary to be aware that the fuel for the 400N motor is made up of two components, hydrazine (MMH) and nitrogen tetraoxide (N2O4), with each component contained in two separate tanks, both of which could be pressurized by helium. Helium could also be applied to the solenoid motor valve, the output of which operates the two fuel valves which start (and stop) the fuel flow. These valves are actually part of the 400N motor and are located inside the motor itself.
On the solenoid motor valve there is an evacuation port that allows excess helium at the output port of the valve to escape when closing the valve. It is believed that this evacuation port was blocked and that the output port remained pressurized beyond the three minute mark of the motor operation -- thus the motor continued to burn for an extended period of time.
Between the fuel tanks and the 400 Newton motor there are fuel isolation valves which are pressure operated by the helium system. When the pressure in the helium manifold had been reduced to approximately 6 Bar (100 psi) the fuel isolation valves closed and prevented any additional fuel from entering the motor, stopping the burn. At this time it is possible that the main motor valves were still open, due to the trapped pressurized helium that had not vented at the solenoid motor valve.
Approximately twelve minutes after the motor shut down, a second anomaly occurred. This was detected when the motor solenoid valve changed from closed to open, possibly caused by fuel migrating in the lines between the isolation valve and the 400N motor. The motor could have also "burped" or "popped" as the fuel mixed and then ignited.
High pressure helium (180 Bar) is fed to the motor system via a high pressure on/off valve and a regulator valve -- reducing the pressure to a nominal 15 Bar level. It is then fed to the low pressure helium manifold. Because of the longer 400N burn, a program for testing the high pressure helium valve was written to "cycle" the valve (to insure proper functioning) and uploaded to AO-40.
On December 11, 2000, while cycling the helium valve, a sudden loss of signal from AO-40 occurred. It is believed that during this exercise the system became pressurized and that a leakage of fuel was the end result. Initial thoughts were that the spacecraft was completely dead and that chances of recovery were remote, with the possibility that AO-40 was in multiple pieces. However, with help from NORAD, it was determined that the satellite was in one piece, with a possibility of some recovery. At least two automatic resets passed without hearing from the spacecraft. It was decided to try and hear the general beacon on the S band (2.4 GHz) transmitter. On Christmas Day 2000 the second attempt to activate the S-band transmitter was successful, and since that day downlink telemetry has been recovered on a regular basis.
The following items have been found to be working; the 2 meter, 70cm, and 1.2 GHz receivers, the S-2 (2.4 GHz) transmitter, the magnetorquing system, the YACE camera, IHU-2 and the high-gain antennas. The following items are believed not to be working; the 2 meter and 70cm transmitters and the omni-directional antennas.
At the time of this bulletin (March 16, 2001) we still do not know the status of the arcjet motor - which is an important item, needed to position the satellite for future use. We do know that the satellite has lost mass, and we attribute this to the loss of bi-propellant fuel from the 400N motor. The satellite spin rate had increased as the overall weight decreased, but by using the magnetorquing system the spin rate is now nearly down to a usable 5 RPM. In addition, the heat pipe system (which became unusable at the higher spin rates) has now become effective again.
Soon AO-40 will be able to be reoriented so that the high-gain antennas will face the Earth, and the arcjet motor will be tested. Following the reorientation it will be possible to test the remaining systems on board the spacecraft and to determine which systems and bands will be available for future operations and under what conditions.
As we all learn more about the status of the satellite, additional bulletins will be posted on AMSAT-BB, and placed on the AMSAT-NA, AMSAT-DL and AMSAT-UK web sites. Meanwhile, all those involved in the recovery of AO-40 are to be congratulated for their skills and perseverance, and may their hard work continue to bring us an operational satellite.
Robin Haighton VE3FRH
AO-40 is currently transmitting the following message in the A-Block MOTD:
Magnetorquing!! At Orbit # 172: ALON=212 / ALAT=45 / SPIN=5.8
[ANS thanks AMSAT-NA for this information]
The 2001 AMSAT-NA Annual Symposium is scheduled for October 5-6, 2001 in Atlanta, Georgia. This is the first "Call For Papers" to be presented during the 2001 Symposium.
Papers may be presented by the author during the Symposium, or simply offered for inclusion in the Symposium Proceedings publication.
The subject matter should be of general interest to amateur radio operators involved in satellite communications. Suggested topics include; operating techniques, antenna design and construction, spacecraft design and construction, current mission status, proposed satellite missions, telemetry acquisition and relay, satellite microwave projects, etc.
A brief abstract of the proposed paper (in outline format) should be submitted as soon as possible. The final date for abstracts is June 30, 2001. Copy-ready papers must be received no later than August 15, 2001.
Electronic submittal is preferred. The format must be either MS Word compatible or in plain text. For security purposes, Symposium chairman Steve Diggs, W4EPI, is asking authors to condense the document file and send it as an e-mail attachment. W4EPI's e-mail address is firstname.lastname@example.org.
[ANS thanks Symposium Chairman, Steve Diggs, W4EPI, for this information]
As this edition of ANS was being broadcast, the crews of Discovery and the International Space Station were spending a full day packing the Leonardo cargo module on the station before they detach Leonardo from the complex and secure it in the shuttle payload bay for the trip home.
Two more full days of joint work remain before Discovery is scheduled to undock from ISS. A third and final re-boost of ISS will also take place using the shuttle's small steering jets to raise Alpha by a little over two statute miles. Altogether, Discovery will leave Alpha a little more than seven miles higher than when it arrived.
The ISS Expedition-2 crew is getting right to its school contacts! The John B. Reible School, in Santa Rosa, California is scheduled for the week of March 26th, with the Vicksburg, Mississippi High School group scheduled for early April.
Late breaking news: Randy, KG3N, reported "this morning I heard astronaut Susan Helms calling CQ onboard the International Space Station. I gave her a call (and using the NA1SS callsign) she came back to me. I was able to talk to her for 45 seconds." It appears Susan will be very active (as promised).
[ANS thanks NASA and ARISS for this information]
When the space station Mir returns to Earth over the remote South Pacific in a few days, it will be big news. Several organizations (such as CNN) are planning live coverage of the de-orbit as it happens. The Russian outpost is the heaviest thing orbiting our planet other than the Moon itself!
During its 15-year stint in space, Mir has set endurance and space adventure records, along with providing hundreds of amateur radio contacts between ham radio satellite operators and onboard cosmonauts and astronauts.
Scientists expect the space station to put on a good show when it returns. Mir is put together much like an erector set. It's an assortment of solar arrays, laboratories and living quarters that was not designed for aerodynamic flight through the atmosphere. Mir has a core module and five other components weighing about 143 tons in all. With a cargo ship and an escape capsule attached, it weighs up to 154 tons. The modules are arranged in a T-shaped structure, 86 by 96 by 99 feet.
The station will quickly fall apart as it descends toward Earth. "We expect Mir to break into six or more main pieces when it hits the atmosphere," said Nicholas Johnson at NASA's Johnson Space Center. Each piece will resemble a blazing meteor that spits smaller fireballs as the pieces crumble and burn.
[ANS thanks NASA for this information]
ANS news in brief this week includes the following:
Link to the weekly report on satellite ...
ISS . Mir . 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
Please send any amateur satellite news or reports to the ANS Editors at email@example.com, or to ANS Editor Dan James, NN0DJ, at firstname.lastname@example.org.
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This week's AMSAT News Service bulletins were edited by AMSAT News Service editor Dan James, NN0DJ.