| Date: | 1998-04-22 06:00:00 | |
| Sender: | David Carter, NASA <[Mailed David L. Carter <dcarter@eib1.gsfc.nasa.gov>]> | |
| Subject: | [SLR-Mail] No. 113: GFO-1 Mission Support Message | |
| Author: | David Carter, NASA | |
| Content: | ******************************************************************************** SLR Electronic Mail 1998-04-22 06:00:00 UTC Message No. 113 ******************************************************************************** Author: David Carter, NASA Subject: GFO-1 Mission Support Message Dear Colleagues: Following the successful launch of the GEOSAT Follow-On 1 (GFO-1) Satellite on February 10, 1998, the GFO-1 spacecraft Mission Operations Group has been working to bring the satellite on-line and position GFO-1 for the GEOSAT Exact Repeat Orbit (ERO). Orbit adjustments to lower the apogee and increase the perigee have been successfully conducted. Preliminary results indicate that the resultant orbit is within 300 meters (high) and is drifting west approximately 2 km/day. A pair of burns (about 1 km/sec) occurred today, Friday, April 17th and will be followed by a pair of fine-tune burns (about 10 cm/sec) on or about Tuesday, April 21st. ERO should be established by the last pair of burns. There still remains a problem with the onboard GPS receivers. The inability of the GPS receiver to lock track GPS satellites has continued. JPL is working on special masking of the GPS constellation to limit the search by the GFO GPSR to 4 specified satellites in each orbit arc. This on-going problem has increased the need for SLR to support the altimeter portion of the GFO-1 mission. As was stated in a previous message, NASA Headquarters has requested that NASA Goddard Space Fight Center´s Space Geodesy Networks and Sensor Calibration Office (SGNSCO) provide SLR support of the GFO-1. A number of NASA supported scientists will use this data for ocean, polar, and geophysical science studies. To most effectively support these studies, the best possible accuracy and precision must be obtained from GFO-1. International SLR support is needed to improve the overall precision orbit determination, including gravity model tuning, reference frame adjustment, and measurement calibration. International SLR support of GFO-1 is requested to commence following the establishment of the GEOSAT ERO. This should occur approximately by April 21st. NASA SLR will generate acquisition data that will be distributed to all SLR organizations by conventional methods following the establishment of the ERO and the verification of all onboard subsystems. The TIV´s for the GFO-1 mission will be transmitted to the individual stations, to the CDDIS acquisition data accounts under the directory SLR_USERS:[ATSC], and the EDC computer facility. The weekly files available on the CDDIS will be named GFOmmddeph.TIV, where GFO is the three-letter acronym for GFO-1, mm is the two-digit month, dd is the two-digit day of the month, and eph is the three-digit current ephemeris number. Following successful tracking of GFO-1, all data, field generated normal points (FGNP), are to be sent daily to the CDDIS. The FGNP´s will be contained in daily files on the CDDIS in the directory SLR_DATA:[SLRQL.GFO.yyyy], where yyyy is the four digit year of the data. The daily filenames will be in the form NEW_Qlyymmdd.GFO where yymmdd is the two-digit year, two-digit month, and two-digit day of the date the data was merged. The following numbers are forms of identification and data information for the GFO-1 satellite: COSPAR #: 9800701 SIC #: 8501 NORAD #: 25157 NORMAL POINT BIN SIZE: 30 sec Currently, all NASA SLR stations will support the GFO-1 mission in the following four phases: Initial Acquisition, Intensive Tracking, Operational, and periodic Special Intensive Tracking Campaigns. A summary of these phases with planned durations are provided below. This mission has been thoroughly discussed at previous CSTG SLR/LLR sub-commission meetings and it is requested that the global SLR community supports the GFO-1 mission in a similar fashion. 1) Initial Acquisition Phase: Priority: Top Priority Purpose: Achieve stable SLR Orbit for acquisition data generation Duration: 1-3 days Start Date: Tentatively, April 21-22, 1998 2) Intensive Tracking Phase: Priority: Top Priority Purpose: Altimeter Calibration Cross-comparisons of orbits produced by SLR and GPS Tuning of the gravity model Tuning of the non-conservative force model Duration: Approximately four 17-day orbital cycles 3) Operational Phase: Priority: Below TOPEX/Poseidon Purpose: Precise Orbit Determination Duration: Remainder of GFO-1 planned 10-year mission 4) Intensive Tracking Campaigns: Priority: Top Priority Purpose: Validation, Cross-calibration of orbits produced by SLR and GPS Duration: Each campaign will last approximately one 17-day cycle Thank you in advance for supporting the GFO-1 project. If there are any changes to the current schedule, an update will be provided via SLR mail. Best Regards, David Carter NASA Satellite Laser Ranging Networks Manager David L. Carter NASA/GSFC Code 920.1 Greenbelt, MD 20771 301-286-6319 dcarter@eib1.gsfc.nasa.gov [Mailed From: ”David L. Carter” ******************************************************************************** |