| Date: | 1999-07-12 23:57:00 | |
| Sender: | John J. Degnan <[Mailed John Degnan <jjd@ltpmail.gsfc.nasa.gov>]> | |
| Subject: | [SLR-Mail] No. 371: Beacon-C tracking Campaign | |
| Author: | John J. Degnan | |
| Content: | ******************************************************************************** SLR Electronic Mail 1999-07-12 23:57:00 UTC Message No. 371 ******************************************************************************** Author: John J. Degnan Subject: Beacon-C tracking Campaign for Based upon a recommendation of the Missions Working Group, the ILRS Governing Board has approved a six month tracking campaign for the old Beacon Explorer-C satellite. The campaign was proposed by Minkang Cheng of the University of Texas Center for Space Research to enhance our knowledge of the gravity field. Orbital predictions will be provided by AlliedSignal Technical Services (ATSC). The campaign will begin as soon as the orbital predicts become available from ATSC as will be announced by a subsequent SLRmail from ATSC. The ILRS tracking priority table will be updated at the same time. ILRS tracking priority will be assigned based on the standard ILRS criteria regarding satellite altitude and orbital inclination. We ask that each of the ILRS stations include this satellite in their schedules. The justification provided by Minkang Cheng follows this message. Sincerely, John J. Degnan Chairperson, ILRS Governing Board Dear Colleague, Analysis of the long-term SLR data from multiple satellites provides a unique capability for determining the secular and long period tidal variations in the Earth´s gravity field. The satellite solution provides a critical global constraint on the geophysical modeling to improve our understanding of the rheology of Earth, such as the mantle viscosity and anelasticity, and the postglacial rebound since the last ice age. The study for the temporal variations in the Earth´s gravity field from analysis of space geodetic measurements is currently supported by the National Aeronautics and Space Administrations under grant NAG5-5710. The ability to measure the long-term changes in the Earth´s gravity field from analysis of SLR data is based on the fact that mass variations within the Earth system produce detectable orbital perturbations, which depend on the orbital inclination and altitude of satellites. As a consequence, the requirement for both the long-term temporal and spatial distribution of the SLR tracking data (i.e., from the satellites at various inclinations and altitudes) is critical for separating the variations at different degrees and orders. Most of the current geodetic satellites are orbiting at inclinations ranging from 50 to 110 degrees. BEC satellite is the only useful target in a low inclination (41 degrees) with SLR tracking capability, and it can be used to extend the inclination coverage to improve the separation of the secular variations in the zonal harmonics. Use of the SLR data sets from 8 geodetic satellites, including Starlette, Stella, Ajisai, Lageos 1 and 2, Etalon 1 and 2, and BEC covering the period over 20 year through the end of 1995 has yielded the most accurate zonal rates with the highest degree (< 7) [Cheng, Shum and Tapley, 1997]. Except for BEC, extension of the 3-years SLR data by the end of 1998 from those satellites enables us to separate the secular zonal variations up to degree 10. However, the solutions for the higher degrees of the zonal rates are limited by the limited time span of the BEC data [Cheng and Tapley, 1999]. All of these satellites are currently tracked by the SLR network except for BEC, which was no longer tracked after June 30, 1986. To enhance the current capability of SLR data to monitor the long-term changes of the Earth´s gravity field, we request the inclusion of the BEC satellite in the regular tracking schedule by the global SLR network. The long-term SLR data sets from multiple satellites will be an invaluable geophysical time series and will play an important role for geodynamics study in conjunction with the GRACE mission. We appeal to you for support. Thank you for your consideration. Minkang Cheng, UTCSR Dr. John J. Degnan Chairperson, ILRS Governing Board Code 920.3, Geoscience Technology Office NASA Goddard Space Flight Center Greenbelt, MD 20771 USA Phone: 01-301-614-5860 Fax: 01-301-614-5970 E-mail: jjd@ltpmail.gsfc.nasa.gov [Mailed From: John Degnan ******************************************************************************** |