SB SAT @ AMSAT $ANS-075.01<BR>PHASE 3D / AO-40 SPECIAL BULLETIN<P>AMSAT NEWS SERVICE BULLETIN 075.01 FROM AMSAT HQ<BR>SILVER SPRING, MD, MARCH 16, 2001<BR>TO ALL RADIO AMATEURS<BR>BID: $ANS-075.01<P>To All Members of AMSAT-NA,<P>The following statement is addressed to those members of AMSAT-NA<BR>who have requested an explanation of the December 2000 incident that<BR>took place on P3D. This statement has been prepared and developed by<BR>Robin Haighton, VE3FRH, President of AMSAT-NA, with input and<BR>review from other AMSAT-NA members.<P>As you are aware, Phase 3D was launched on November 16, 2001 into<BR>an almost perfect geosynchronous transfer orbit (GTO) by an<BR>Arianespace launch vehicle (AR-507) from Kourou, French Guiana.<BR>Within a few hours of launch excellent telemetry was being received<BR>from the 2-meter beacon, and Amateur Radio stations worldwide started<BR>downloading data with great accuracy, due in-part to the strong signal<BR>strength. The original plan was to use the 70-cm beacon, however,<BR>for reasons not yet known, the 70-cm transmitter signal was not heard.<P>Before the satellite could be regularly used for general Amateur Radio<BR>communications, it was necessary to carry out orbital changes, stabilize<BR>the satellite, open the solar panels, etc. The first changes to the<BR>orientation of the satellite were carried out using the onboard<BR>magnetorquing system - this worked well and after relatively few orbits<BR>the attitude of (now) AO-40 was 270/0, and ready for operation of the<BR>400 Newton motor. Among the many components which comprise this<BR>motor system, there are several valves which control pressurizing helium<BR>and fuel. During construction of the satellite it was noted that one of the<BR>helium valves had a tendency to "stick" when operated. Both of these<BR>valves were sent back to the manufacturer for inspection and repair.<BR>Both valves were inspected and one valve was repaired, followed by<BR>return and re-installation into the system. <P>On the first attempt to fire the 400-N propulsion system, it failed to<BR>operate, possibly due to a sticking helium valve. Before the second<BR>attempt, it was determined that the fuel tanks could be pressurized (by<BR>helium) to their correct pressure over a five minute period, and although<BR>this was about one-tenth of the normal helium flow rate, it was still<BR>adequate for the planned three minute motor burn. <P>On the second attempt to fire the 400-N motor, all systems appeared to<BR>respond correctly at first. At the three minute mark the internal timer<BR>transmitted a signal for the main solenoid valve to close, which should<BR>have shut off the fuel to the motor. Telemetry shows that the signal was<BR>sent and received, but the motor did not shut off for two or three more<BR>minutes, placing AO-40 into a higher apogee orbit than was planned at<BR>that time. <P>To understand how this may have happened, it is necessary to be aware<BR>that the fuel for the 400-N motor is made up of two components,<BR>hydrazine (MMH) and nitrogen tetraoxide (N2O4), with each component<BR>contained in two separate tanks, both of which could be pressurized by<BR>helium. Helium could also be applied to the solenoid motor valve, the<BR>output of which operates the two fuel valves which start (and stop) the<BR>fuel flow. These valves are actually part of the 400-N motor and are<BR>located inside the motor itself.<BR> <BR>On the solenoid motor valve there is an evacuation port that allows<BR>excess helium at the output port of the valve to escape when closing the<BR>valve. It is believed that this evacuation port was blocked and that the<BR>output port remained pressurized beyond the three minute mark of the<BR>motor operation - thus the motor continued to burn for an extended<BR>period of time.<BR> <BR>Between the fuel tanks and the 400 Newton motor there are fuel isolation<BR>valves which are pressure operated by the helium system. When the<BR>pressure in the helium manifold had been reduced to approximately<BR>6-Bar (100 PSI) the fuel isolation valves closed and prevented any<BR>additional fuel from entering the motor, stopping the burn. At this time<BR>it is possible that the main motor valves were still open, due to the<BR>trapped pressurized helium that had not vented at the solenoid motor<BR>valve.<P>Approximately twelve minutes after the motor shut down, a second<BR>anomaly occurred. This was detected when the motor solenoid valve<BR>changed from closed to open, possibly caused by fuel migrating in the<BR>lines between the isolation valve and the 400-N motor. The motor<BR>could have also "burped" or "popped" as the fuel mixed and then ignited.<BR> <BR>High pressure helium (180 Bar) is fed to the motor system via a high<BR>pressure on/off valve and a regulator valve - reducing the pressure to<BR>a nominal 15 Bar level. It is then fed to the low pressure helium manifold.<BR>Because of the longer 400-N burn, a program for testing the high<BR>pressure helium valve was written to "cycle" the valve (to insure proper<BR>functioning) and uploaded to AO-40.<P>On December 11, 2000, while cycling the helium valve, a sudden loss<BR>of signal from AO-40 occurred. It is believed that during this exercise the<BR>system became pressurized and that a leakage of fuel was the end result. <BR>Initial thoughts were that the spacecraft was completely dead and that <BR>chances of recovery were remote, with the possibility that AO-40 was in <BR>multiple pieces. However, with help from NORAD, it was determined<BR>that the satellite was in one piece and still in it's known orbit, with a<BR>possibility of some recovery. At least two automatic resets passed<BR>without hearing from the spacecraft. It was decided to try and hear the<BR>general beacon on the S-band (2.4 GHz) transmitter. On Christmas Day<BR>2000 the second attempt to activate the S-band transmitter was<BR>successful, and since that day downlink telemetry has been recovered<BR>on a regular basis.<P>The following items have been found to be working; the 2-meter, 70-cm<BR>and 1.2 GHz receivers, the S-2 (2.4 GHz) transmitter, the magnetorquing<BR>system, the YACE camera, IHU-2 and the high-gain antennas. The<BR>following items are believed not to be working; the 2-meter and 70-cm<BR>transmitters and the omni-directional antennas.<P>At the time of this bulletin (March 16, 2001) we still do not know the<BR>status of the Arc-jet motor - which is an important item, needed to<BR>position the satellite for future use. We do know that the satellite has<BR>lost mass, and we attribute this to the loss of bi-propellant fuel from the<BR>400-N motor. The satellite spin rate had increased as the overall weight<BR>decreased, but by using the magnetorquing system the spin rate is<BR>now nearly down to a usable 5 RPM. In addition, the heat pipe system<BR>(which became unusable at the higher spin rates) has now become<BR>effective again.<BR> <BR>Soon AO-40 will be able to be re-orientated so that the high-gain<BR>antennas will face the Earth, and the Arc-jet motor will be tested.<BR>Following the re-orientation it will be possible to test the remaining<BR>systems on board the spacecraft and to determine which systems and<BR>bands will be available for future operations and under what conditions.<P>As we all learn more about the status of the satellite, additional bulletins<BR>will be posted on AMSAT-BB, and placed on the AMSAT-NA, AMSAT-DL<BR>and AMSAT-UK web sites. Meanwhile, all those involved in the recovery<BR>of AO-40 are to be congratulated for their skills and perseverance, and<BR>may their hard work continue to bring us an operational satellite.<P>73,<P>Robin Haighton VE3FRH <BR>President AMSAT-NA <P>[ANS thanks AMSAT-NA for this information]<BR>