What will happen to the IMAGE satellite during its first month after launch?

Orbit Activation Timeline

Orbital Activation Timeline. Within the first hour after launch, the spin axis of the satellite will be in the plane of the orbit and the rotation of the spacecraft is slowed to 2 +/- 2 rpm. The nutation of the spacecraft is damped. The spin axis of the satellite would need to be commanded to a new orientation, and there was some discussion that until the magnetometer sensors were tested, we do not have verification that the spacecraft could automatically reorient to the proper direction. But it was felt that the magnetometers had already been tested to death and that there was no need to do this on orbit. If a problem was found, it would not be possible to upload new software at that time anyway given all the other things that would be going on on the ground. Because the high voltages to the HENA would be turned on after Day 10, sometime before then the spacecraft needed to be outgassed but exactly when this would happen was left up in the air.

Reorientation of the spacecraft would take 7 days under autonomous spacecraft control and no science instrument operations would take place during that time. CIDP power would be off and the instrument 'Survival Heaters' would be on. At Day 7 the RPI antennas would be deployed to 120 meters by Day 15. By Day 19 they would be deployed to 160 meters, by Day 23 deployment reaches 210 meters, and by Day 32 the antennas are at full 250 meter deployment. The axial antennas wil also be deployed on Day 32. The reason that the antenna deployment is performed in 4 stages is that the spacecraft orientation and spin rate must be corrected back to their nominal values (??). By the first deployment the spin rate has increased to 13 RPM. The successive deployments only increase the spin up to 1/2 rpm. The spacecraft is spinned up to 13 rpm so that the tip masses on the antennas feel the right centrifugal force to allow antenna deployment. Then on Day 15 the antennas are deployed out to 120 meters. The spin up of the spacecraft takes 8 days. The actual deployment only takes a few hour. The deployment despins the spacecraft to about 1 rpm because of angular momentum ( ice scater ) conservation. The other deployments follow a similar schedule. The space craft is spun up to about 1.5 rpm over the course of 4 days and then the antenna is reeled out some more which despins the spacecraft back to about 1 rpm. There was some concern that if one of the wires did not deploy completely, should the opposite wire not be deployed fully, but this was set aside since it is better for RPI to have 1/2 a dipole working at full extension than neither side being a full dipole.

The CDIP is turned on 3500 seconds after launch after third stage separation, so that the HENA shutter can be opened for outgassing. The HENA and CDIP are turned off again at 4900 seconds after launch, and after satellite spin up on Day 15, the CIDP is turned on again and the RPI antenna deployers are turned on. The CDIP begins thermal control of the spacecraft on Day 15. On Day 16, the RPI is turned on and switched to Mode 6 ( receive only..18 watts) to verify the deployment, EUV, FUV and MENA are turned on, and the FUV and MENA doors are opened. The spacecraft continues to be spun up to 1.5 rpm for the second stage of the RPI antenna deployment. There is no identifiable reason why the asymetric deployment of the RPI antennas should affect the other. The impact would not be to cause the spacecraft to wobble, but simply to shift the spin axis of the spacecraft parallel to its initial axis which should not make any difference to the other instruments. One of the reviewers still recommended that, rather than continue with the deployment of the other antennas that the deployment should be stopped until tests could be made that it was still safe to proceed.

LENA is turned on and its shutter is opened on Day 17. On Day 19 the RPI antenna is deployed to 160 meters, the attitude is again verified, and spin up Number 3 starts on Day 20. FUV and EUV high voltage power supplies are turned on which could be very pyrotechnic if something serious goes wrong. The RPI antenna is deployed to 210 meters and the spacecraft attitide verified on Day 23. The FUV and EUV are run in their science mode to collect first science images to verify data link. By Day 27 LENA, MENA and HENA high voltage power supplies are turned on and spin up Number 4 happens on Day 25. By Day 34 The RPI antennas have already been fully deployed and the satellite spin rate has been trimmed to 1/2 rpm and the RPI instrument is now in normal operaton mode. The two 'Z-axis' antennas for RPI would also be deployed. RPI would then do a transmission test and its affect upon the other instruments, particularly the FUV-WIC instrument with its large unprotected entrance aperture, would be carefully studied.

By Day 35 the FUV, EUV and MENA instruments enter their normal operation mode. By Day 40 LENA experiences its first 'resurfacing event'. Al the other instruments have now begun work in their normal science operatons mode. The LENA instrument converts incoming neutral atoms into detectable ions by their impact upon a tungsten plate. The efficiency with which this conversion occurs depends on the number of impurity atoms that the tungsten plate collects, so that every 10 days the plate has to be heated to drive out (evaporate) the impurity atoms. This process is called resurfacing and draws about 100 watts of spacecraft power. LENA also equires DSN contact and a 30 day checkout period commences for this instrument. There was some discussion over why DSN contact was needed at all other than the experimenters being perhaps overly nervous about their 'new baby', but the LENA scientists said that they need to verify the resurfacing process. At Day 70 LENA goes to full operations and this begins the 2 year observing mode for IMAGE which was proposed to NASA and funded by the NASA MIDEX program. Depending on the quality and usefulness of the science data to the scientific community, there is some hope that NASA will approve an 'extended mission' timeline with up to 2 years additional satellite operation.


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