| Date: | 1997-04-17 16:00:00 | |
| Sender: | P. Schwintzer, R. Biancale, A. Sinclair <prd@dfd.dlr.de (PRD)> | |
| Subject: | [SLR-Mail] No. 53: Tracking Request for Diadem 1-C, 1-D | |
| Author: | P. Schwintzer, R. Biancale, A. Sinclair | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-04-17 16:00:00 UTC Message No. 53 ******************************************************************************** Author: P. Schwintzer, R. Biancale, A. Sinclair Subject: Tracking Request for Diadem 1-C, 1-D REQUEST FOR A SLR TRACKING CAMPAIGN OF DIADEME 1-C, 1-D SATELLITES starting from April 21th, 1997 by P. SCHWINTZER (GFZ), R. BIANCALE (GRGS) A. SINCLAIR (EUROLAS) to the SLR International Community -------------------- Dear colleagues, As you know, gravity field improvement is a major theme in our geodetic community. For determining the long-wavelength part, we use a lot of satellites at different inclinations, different altitudes, different eccentricities,... Old data gathered long time ago (30 years) continue to be used (optical and laser data) and are very useful, especially at moderate and low inclination where no geodetic satellites have been recently launched. But the precision of old laser data is now comparatively poor with respect to modern precision (120 cm versus centimeter level nowadays). Moreover new geodetic satellites will be launched in the years to come (i.e. CHAMP in 1999), new gravimetric and altimeter data will be available and all that will entail a new generation of Earth gravity models. Our proposal is very simple: Why do not reobserve old but useful geodetic satellites as DIADEME Satellites which have an inclination of great interest (inclination of about 40 degrees, perigee 550/570 km, apogee 1080/1730 km) rather than to continue to use very old data of poor precision with a poor tracking coverage? The present time is very well suited to observe them because the solar activity is minimum. In the frame of CHAMP and in the frame of future new effort in gravity modelling, GFZ and GRGS propose the SLR community to reinitiate the tracking of DIADEME 1-C (Cospar nb: 6701101), DIADEME 1-D (Cospar nb: 6701401) for a limited period of 6 months (3 months is the period of perigee). Both satellites were launched by CNES in 1967 and have 144 corner-cubes reflectors distributed on the satellite body and on the solar panels. The link budget and visibility should be comparable to AJISAI satellite. The tracking campaign will start on April 21, 1997. At that time the satellites should be illuminated by the sun in a favourable way to make the tracking easier. This proposal was presented to the CSTG Laser Ranging Subcommission in November 1996, and was subsequently reviewed and accepted by the individual networks, NASA, WPLTN and EUROLAS. GFZ/D-PAF agrees to generate and distribute the orbit predictions for both satellites under the form of IRVs and time bias which will be stored in the CDDIS and EDC data bases under the usual conventions. Please note that a pre-campaign was initiated last fall (11 passes have been observed and analysed). A priori, everything seems to be correct. On behalf of GFZ, GRGS, EUROLAS we thank warmly all involved people, particularity from all the SLR stations distributed around the world for cooperating in this 6 month campaign dedicated to the Earth gravity field improvement. Tracking Recommendations The Diademe satellites carry retro-reflector arrays on the base of the satellites and also on the solar panels. When ranging at high elevation these will give a twin-peaked distribution at returns, separated by about 45 cm, with the returns from the base being shorter in range. At an elevation of about 45 degrees these peaks will merge, and at a low elevation of 30=B0 they will separate again by about 10 cm, with the returns from the array now being shorter in range. It is recommended that tracking should be carried out at high return rates, so that the shorter range peak will dominate. Normal points should be formed in 15 second bins, and it is requested that both normal points and full rata data should be sent to the data centres. P. SCHWINTZER (GFZ) R. BIANCALE (GRGS) A. SINCLAIR (EUROLAS) On April 16, 1997 Point of contact: Dr. Richard Biancale CNES/GRGS/GTP 18, Avenue Edouard Belin 31401 Toulouse CEDEX H France Tel.: +33-61-33-2978 Tel.: +33-61-25-3098 email: biancale@sc2000.cst.cnes.fr From: prd@dfd.dlr.de (PRD) ******************************************************************************** |