| Date: | 1997-04-11 07:00:00 | |
| Sender: | Richard Eanes, University of Texas, Center for Space Research <[Mailed Richard Eanes <eanes@ramses.csr.utexas.edu>]> | |
| Subject: | [SLR-Mail] No. 49: New CSR Lageos-1 and Lageos-2 Predictions | |
| Author: | Richard Eanes, University of Texas, Center for Space Research | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-04-11 07:00:00 UTC Message No. 49 ******************************************************************************** Author: Richard Eanes, University of Texas, Center for Space Research Subject: New CSR Lageos-1 and Lageos-2 Predictions As the last Lageos-1 eclipse season began around the end of October 1996 the mismodeled non-gravitational accelerations began growing quickly and reached new record highs. The average along track acceleration peaked out above 10 picometers/s/s, well above its previous record. Worse, the imaginary part of the eccentricity excitation (the mean acceleration along the direction toward the ascending node) reached 500 mas/yr, more than doubling the old record of 200 mas/yr and even eclipsing the record for the real part of the eccentricity excitation (which has been showing large peaks since 1989). The large anomaly in the imaginary eccentricty excitation is good evidence that the Lageos-1 spin axis was nearly in the equator for the first time ever. My guess is that the spin-axis aligned forces on Lageos-1 will become harder and harder to predict now, and as a result, I will need to distribute Lageos-1 predictions more frequently (6 months?) than I have in the past (1 to 2 years). I am releasing the first of these more frequent predictions today. My thanks go to Philip and Roger from the Herstmonceux station for pointing out that the Lageos-1 predictions (CSR027) were getting hard to use even though the time bias was not too bad. The residuals don´t flatten well with a time bias and UT1 correction when the eccentricity errors get large. I´ve decided to make a new Lageos-2 prediction also, even though it is not absolutely necessary. I would like to hear your opinions about how often the Lageos predictions should be issued. The decision basically is a a tradeoff between the time you spend retreiving a new prediction vs. the time you spend coping with a suboptimal prediction. If you ever feel that you missed a Lageos pass because of poor predictions please tell me immediately. It would not be difficult to provide a new prediction each month. What is your preference? Here is the usual verbiage about the new predictions: New predictions for Lageos-1, Lageos-2 for April 1997 through July 1999 have been produced at the University of Texas Center for Space Research. The ephemerides are distributed in the form of daily ”tuned IRV´s” suitable for use in the IRVINT tracking software or its derivatives. This is the 28´th ephemeris distributed for Lageos-1 (GSFC ID 1155). For Lageos-2 (GSFC ID 5986) this is the 4´th ephemeris distributed. New Etalon-1 and Etalon-2 predictions are not yet required. The leap second at the end of June 1997 has been modeled, and another leap second at the end of June 1999 has been predicted. This prediction is quite uncertain, and should it prove incorrect new tuned IRV´s will be issued (if the ephemeris holds up that long!). When uncompressed, each of the IRV files has 3408 lines and 216408 bytes. They are available via anonymous ftp at CSR. Use ftp.csr.utexas.edu (129.116.190.30) and cd to pub/slr/ephemeris. The files are lg1irv28_tune, and lg2irv04_tune for Lageos-1 and Lageos-2 respectively. They are compressed using the unix command ”compress”, so the names listed above are followed by .Z in each case. Another file contains the Earth rotation predictions used in the generation of the new IRV´s. The columns in these files are: Modified Julian Date, x and y components of polar motion in arcsec, TAI-UTC and UT1R-TAI in seconds. There is a point every day. The file named irv28_pole_exp was used for both the Lageos-1 and Lageos-2 IRV´s. These files together with up-to-date UT1-TAI values from IERS should be used to derive the UT1 correction for SLR tracking operations. The files will also be made available at the EUROLAS Data Center and at the NASA CDDIS. You can request the files from Wolfgang Seemueller at the EUROLAS Data Center using e-mail address: edc@dgfi.badw-muenchen.de, or from Carey Noll at CDDIS using e-mail address: noll@cddis.gsfc.nasa.gov. I will be glad to respond to any questions about these predictions. I can be reached at e-mail address: eanes@csr.utexas.edu , or by phone at (512)471-7560, or fax at (512)471-3570. --------------------------------------------------------------------------- Richard Eanes, eanes@csr.utexas.edu, (512) 471-7560 Other Phone Numbers: (512) 471-5573 (CSR Secretary), -3570 (Fax) Campus Address: Mail and Express Delivery Address: University of Texas University of Texas Center for Space Research Center for Space Research Campus Code R1000 3925 W. Braker Lane, Suite 200 Austin, TX 78712-1085 Austin, Texas 78759-5321 --------------------------------------------------------------------------- [Mailed From: Richard Eanes ******************************************************************************** |