Latest GPS Satellite Set to Healthy

January 9, 2008

The U.S Coast Guard's Navigation Center (Navcen) confirmed that the GPS IIR-18 (M) launched from Cape Canaveral December 20 was set to healthy on January 2.

The satellite, dubbed SVN57, joins the four IIR-M satellites and 12 operational IIR satellites currently in the GPS constellation, which comprises 31 operational satellites overall. GPS IIR-18 (M) will be replacing SVN36, which in turn will replace SVN37, and be placed in orbital slot C1, according to the U.S. Air Force. The orbital initialization progress from the time of launch breaks down like this (in reverse chronological order; provided by the U.S. Air Force):

2 Jan 21:00Z — SVN57 was set healthy to users today at 20:41 Zulu (Z). All subsystems continue to operate nominally.
26 Dec 21:00Z — The navigation payload initialization was successfully accomplished today. The time line of events include:

L1 transmitter on at 17:54Z
L2 transmitter on at 17:55Z
confirmed monitor station tracking at 18:24Z
completed legacy signal adjustments at 19:57Z
L2C on at 20:41Z
M code on at 20:46Z

Projected date for setting the space vehicle (SV) healthy to users is 2 Jan. The NDS payload will be initialized 14:00-18:00 Jan 08.
24 Dec 00:00Z — The clock and MDU have both been turned on and all telemetry looks nominal. A passive support has been accomplished by AEP to validate they could receive telemetry prior to hand-off. The LADO operations are wrapped up and 2SOPS will take over shortly.
23 Dec 20:30Z — Solar array deployment was successfully accomplished at 19:01Z. After successful three-axis transition, sun acquisition was initiated. Sun search hold was completed at 19:25Z. This mission experienced the quickest Earth acquisition to date, with sun nadir pointing occurring at 19:42Z. The NAP antenna was deployed at 19:51Z and the W sensor antennas were successfully deployed at 19:55Z. All SV subsystems remain nominal. The next events are SPU drift configuration, redundancy management configuration, and power management configuration. The plan is to complete clock and MDU initialization this afternoon and hand off the SV (space vehicle) to AEP. 2SOPS will monitor SV state of health via AEP for the next two days and then we will conduct nav payload initialization on the 26th.
23 Dec 09:30Z — The 51-10 rpm despin initiated at approximately 08:16Z with a burn duration of 22 minutes and resulted in a final spin rate of 9.77 rpm. The 10-1.3 rpm despin initiated at approx 09:00Z with a burn duration of 5 minutes and resulted in a final spin rate of 1.26 rpm. The next major event is the deployment of the solar arrays scheduled for 19:20Z. The clock and MDU turn on times have been moved up to approx 22:00Z on 23 Dec. All SV subsystems, as well as the control segment, are performing nominally.
23 Dec 07:00Z — Final orbit analysis indicates a post AKM drift rate of -.9765 deg/day (West) which will result in an on-station date of 16 Jan 08 in slot C1. Mission planers had targeted a drift rate of -1 deg/day to allow time for another SV to be repositioned starting on 8 Jan. The AKM efficiency was 99.9692 percent and the final inclination is 54.96 degrees. The next maneuvers are the 51-10 despin scheduled for 08:20Z and the 10-1.3 despin scheduled for 09:10Z. The DRAM scheduled for 24 Jan is canceled. All SV subsystems, as well as the control segment, are performing nominally.
22 Dec 23:45Z — Apogee kick motor (AKM) burn was successfully initiated at 23:19.57Z. The burn time was nominal and all telemetry indications show a good burn. The final orbit analysis will be available in about 6 hours. All SV subsystems remain nominal. Initial despin of the spacecraft will begin 23 Dec at 08:45Z.
21 Dec 23:30Z — Trim 2 is canceled. All SV subsystems, as well as the control segment, are performing nominally. The latest MES is shown below.
21Dec 1630Z — Although the CSPM burn, using the 5-pound thrusters, was only planned to get the SV within 7 degrees of the AKM targeting angle, we ended up only 0.86 degrees off. As a result, a small TRIM1 was conducted at 15:30Z. The burn, using the 0.2-pound thrusters, was 2 minutes and 6 seconds in duration. The final Sun Z after the burn was 77.87 degrees compared to a target of 77.89 degrees. The SV spin rate remained unchanged at 49.3 RPM. Attitude data will be collected over the next orbit to determine if the second fine spin precession maneuver, currently planned for 22 Dec 04:45Z, will be required. The AKM burn, which will put us in our mission orbit, is still scheduled for 22 Dec at 23:21.09Z. All SV subsystems, as well as the control segment, are performing nominally.
21Dec 00:30Z — CSPM was successfully executed on time at 23:31Z. The final Sun Z was almost perfectly on target at 76.85 degrees, compared to a planned 76.80 degrees. The SV spin rate slowed slightly to 49.3 RPM, which is expected. All SV subsystems remain nominal. Attitude data will be collected over the next two orbits in preparation for the first fine spin precession maneuver (TRIM1), which is currently scheduled for 21 Dec 15:30Z. TRIM 2 remains on its nominal time line at 22 Dec 04:45Z while the AKM burn will move out 5 minutes to 22 Dec 23:21Z.
20 Dec 2230Z — Mission GPS IIR-18(M) successfully launched at 20:04Z today, five minutes into the planned 14 minute launch window. The five-minute delay was due to a collision avoidance (COLA) restriction from the ISP. Six hours prior to launch, we were notified that the Diego Garcia ground station was red and may not be green for launch. Diego is not a mandatory asset for launch but the loss of Diego ground station for our fine spin precession maneuvers would have ultimately caused a delay in the AKM maneuver from apogee 9 to apogee 13 and added risk to the mission.
The mission planners quickly conducted a re-plan of the mission using LION and BOSS (ground stations for the TRIM) maneuvers and were able to hold AKM to apogee 9. As a result of the launch five minutes into the window and the change in maneuver planning, all maneuvers in the attached MES will likely change slightly. Updates will be provided prior to each maneuver. The first command was successfully sent from Schrieffer and received by SVN57 at 21:24 Zulu.
Our spin rate and Sun Z are as expected and all SV subsystems are nominal at this time. The first SV maneuver will be the coarse spin precession maneuver (CSPM) now scheduled for 23:31 Zulu.