| Date: | 1996-10-15 02:00:00 | |
| Sender: | John Degnan, GSFC/NASA <[Mailed EDC <slrmail@dgfi.badw-muenchen.de>]> | |
| Subject: | [SLR-Mail] No. 28: CSTG GPS LASER TRACKING CAMPAIGN | |
| Author: | John Degnan, GSFC | |
| Content: | ******************************************************************************** SLR Electronic Mail 1996-10-15 02:00:00 UTC Message No. 28 ******************************************************************************** Author: John Degnan, GSFC/NASA Subject: CSTG GPS LASER TRACKING CAMPAIGN CSTG GPS LASER TRACKING CAMPAIGN UPDATE DURATION OF THE CAMPAIGN As announced previously in April 1996, the first international CSTG GPS Laser Tracking Campaign will begin this Fall. A start date of October 20, 1996 has been selected. The full program will continue through November 20, 1996, but a more limited program addressing the GPS orbit in eclipse will continue through December 15 in order to collect laser range data on a significant number of GPS Earth-eclipse events . CAMPAIGN GOALS The goals of the first GPS tracking campaign are as follows: (1) SLR-derived Trajectory: To develop an all-SLR orbital trajectory, lasting initially for up to 4 weeks, for the GPS 35 and 36 satellites for the purpose of acquiring an intensive SLR data set which can be used for direct comparisons to GPS-derived ephemerides and other studies . (2) Continuous Multistation Tracking during GPS Eclipse Events: To provide continuous multistation (preferably 3 or more SLR sites) SLR tracking of GPS 35 during any eclipse episode. SLR tracking should begin 15 minutes before GPS enters the Earth´s shadow and continue for 30 minutes after GPS exits the Earth´s shadow. (3) GPS Phase Antenna Offset: To provide improved estimates of the GPS antenna phase center/laser retroreflector offset through ”near-simultaneous” (defined as over the same time interval) tracking of GPS 35 and/or 36 by multiple (four or more) SLR stations for several continuous intervals of one to two hours each. SUGGESTED METHODOLOGIES FOR ACHIEVING EACH OF THE GOALS (1) SLR-derived Trajectories: The first of these experiments will begin on October 20, 1996 and end November 20, 1996. This particular schedule has been chosen because: (1) passes of the GPS-35 and GPS-36 satellites largely occur at night at most of the stations capable of tracking them (except for the Australian sites) as shown in Figure 1; and (2) the NRL@SOR facility near Albuquerque, New Mexico will be online during this period . The latter station has a strong GPS tracking capability and adds needed redundancy in the Southwestern US for coverage of other satellites. It is anticipated that tracking coverage in the Southern Hemisphere will be sparse due to a lack of a GPS-capable SLR station in South America or Africa and the fact that most GPS-35 and 36 passes over the the two SLR stations in Australia will occur in daylight. The Australian and Asian stations are encouraged, however, to attempt daylight tracking of GPS. In all geographic regions, 15 minutes of SLR station tracking per hour from at least one SLR station will be the goal, day or night. In order to maintain an adequate data yield for other Low Earth Orbiting (LEO) satellites during the campaign, it is recommended that the stations in each region (Americas, Eurasia, and Western Pacific) be subdivided into two groups: (1) those stations with a demonstrated or potential GPS tracking capability and (2) stations which do not at present have such a capability. Stations in Group 1 should adjust their tracking priorities, under the guidance of their local networks, to meet the goals of the various GPS experiments while maintaining an adequate level of LAGEOS and lower satellite tracking for orbit maintenance and quality control activities. During the GPS Tracking Campaign, stations in Group 2 should carry the primary burden for LEO tracking up to and including LAGEOS altitudes. Networks are encouraged to continue to provide adequate geographic and longitudinal coverage for all satellites by scheduling and ”teaming” pairs or clusters of stations within a locality or region whenever possible. Although every SLR station is invited and encouraged to participate in this international GPS tracking campaign, the stations in Table 1have been assigned to Group 1 because of their demonstrated ability (or in some cases potential) to acquire SLR ranging data to GPS and are especially encouraged to GPS range data. The aforementioned Group 1 stations are further subdivided into ”regions” irregardless of their sponsorship or affiliation (i.e. NASA, EUROLAS, or WPLTN). Because of their unique geographic location which places them in a night tracking mode simultaneously with more than one ”region” during the November-December campaign period (see Figure 1), two stations , Maidanak and HOLLAS, have been assigned to more than one region. (2) Continuous Tracking during a GPS Eclipse: Information on GPS-35 eclipse events and stations which are in a position to track the satellite during these periods will be posted on the CSTG SLR/LLR Subcommission Home Page at the following WWW address: http://cddis.gsfc.nasa.gov/cstg/slr_cstg.html The networks (NASA, EUROLAS, and WPLTN) should attempt to provide continuous ”near-simultaneous” tracking of the event from multiple sites beginning 15 minutes before GPS enters the Earth´s shadow and continuing until 30 minutes after it emerges from the shadow. This portion of the campaign will extend through December 15 in order to collect data on eclipses which occur in the late November and early December time frame. (3) Antenna Offset: This episodic experiment will be highly subject to the vagaries of local and regional weather and should be coordinated and performed at an individual network level, i.e. NASA, EUROLAS, and WPLTN. It will require continuous and lengthy (1 to 2 hours per experiment) tracking of GPS from four or more sites within a ”region” simultaneously, and should only be scheduled when all or most of the ”regional” station passes are at night and are likely to enjoy good weather and visibility. It is therefore suggested that each of the aforementioned networks (i.e. NASA in the Americas, EUROLAS in Eurasia, and WPLTN in the Western Pacific) be responsible for scheduling the activities for the stations in their primary region. During this experiment, it is proposed that NASA coordinate the tracking activities (both GPS and LEO) of NASA sites in the Americas and that of the German station in Santiago de Cuba, that EUROLAS coordinate the activities of its own network extending from RGO to Maidenak but also including the SALRO system in Riyadh, and WPLTN will coordinate the stations spanning Maidenak to HOLLAS and including the NASA MOBLAS-5 site in Australia. Comments or suggestions regarding the proposed campaign should be addressed to the CSTG SLR/LLR Subcommission Chairman, John Degnan, via one of the following means: Address: Code 920.3, NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA Phone: 01-301-286-8470 FAX: 01-301-286-0213 Email: jjd@ltpmail.gsfc.nasa.gov, degnan@cddis.gsfc.nasa.gov This announcement, complete with figures as well as periodically updated information on the campaign, will be provided on the CSTG SLR/LLR Subcommission home page listed above. If you have information of general interest to the community regarding this campaign and would like to include it on our Web Site, please submit it to either John Degnan or to Carey Noll at the CDDIS (Noll@CDDIS.gsfc.nasa.gov). Interim analysis results from the campaign are also welcome. ---------------------------------------------------------------------------- Dr. John J. Degnan Head, Geoscience Technology Office Code 920.3 NASA Goddard Space Flight Center Greenbelt, MD 20771 USA Phone: (301) 286-8470 Fax: (301) 286-0213 Email: jjd@ltpmail.gsfc.nasa.gov Internet: jjd@ltpmail.gsfc.nasa.gov ---------------------------------------------------------------------------- [Mailed From: EDC ******************************************************************************** |