| Date: | 1996-09-02 18:00:00 | |
| Sender: | Bill Purdy <[Mailed EDC <slrmail@dgfi.badw-muenchen.de>]> | |
| Subject: | [SLR-Mail] No. 23: TiPS Support | |
| Author: | Bill Purdy | |
| Content: | ******************************************************************************** SLR Electronic Mail 1996-09-02 18:00:00 UTC Message No. 23 ******************************************************************************** Author: Bill Purdy Subject: TiPS Support I am writing this note to thank the international SLR community for their outstanding support of the TiPS mission. Your results have been and will continue to be crucial to our improving understanding of TiPS` dynamics. We greatly appreciate the work you have done for us. We have been working very hard using Geodyn to try to solve for the tether motion. As you can imagine, it is not very easy. We have gotten occasional solutions, but they take a lot of intervention by our analyst through many iterative runs. We have found that the problem is eased, of course, by larger quantities of data. The problem is also eased when we have returns for Ralph and Norton during the same time period. These are two areas where we have been especially well served by the international SLR community. The data quantity has been improved significantly by the whole community. The large quantity of stations in Europe has strong benefits for us in providing simultaneous data on Ralph and Norton. I publish a TiPS newsletter every few weeks. I have included the latest issue to inform you of the progress we have made. Your help has been indispensable to this progress. Again, thank you very much. Bill Purdy TiPS Program Manager bpurdy@space.nrl.navy.mil ---------------------------------------------------------------- TiPS Newsletter August 19, 1996 Hello again, TiPS Survival to date: 50 Days Things are steadily improving in our understanding of TiPS` behavior. The progress has been slower than we had been hoping for. Like everything else in the world, this has been much more difficult than it appeared. We have gotten some answers on the libration. We have determined that the in plane libration angle amplitude is between 20 and 40 degrees with an approximate period of 62 minutes and the out of plane libration angle amplitude is between 10 and 30 degrees with an approximate period of 52 minutes. We don`t yet know these angles to any better resolution. In these early stages it is a painstaking process to get a solution for the motion. The process begins with finding a time period where we received a lot of SLR data. We feed that data to our Geodyn software and look for a solution for all 6 orbital elements as well as for all of the parameters of the tether specific motion. The first answer is typically very poor, so then we adjust certain parameters in the initial guesses for the orbit and tether state or perhaps in the program and try again. We repeatedly iterate in this process slowly homing in on a solution that is valid. There is a good bit of cross checking the solution throughout this process. As you can imagine this takes quite a long time, and on some attempts we just have not had enough data to find a valid solution. I`m trying not to be too whiny, rather I`m trying to help you to understand why the answers have been slow to arrive. Our big improvement recently is that we now have a very accurate solution for the TiPS center of mass. This does two good things for us: 1) we now have an improved orbit prediction which will make it easier hit TiPS with the SLR lasers and therefore should get us more data. 2) It simplifies the iterative job of determining the system behavior, since the 6 variables of the orbit no longer need to be solved for. There are quite a number of new recipients of the newsletter, so I`m reprinting the summary of the TiPS system. TiPS basic system parameters Tether length: 4 kilometers Tether nominal diameter: approximately 2mm diameter Tether construction: Outer Layer is Spectra 1000 braid for strength, the core is acrylic yarn which will puff the outer braid out to the 2mm diameter to give it a larger cross section to improve its resistance to small micrometeroids. Tether breaking strength: approx. 200 pounds TiPS altitude/ orbit: 552 nmi, circular, 63.4 Degrees inclination Total weight: 118 pounds Weight of Ralph (lower end body): 83 pounds weight of Norton (upper end body): 23 pounds weight of tether: 12 pounds 18 laser retroreflectors on each end body Initial TiPS spin rate: 4 rpm Tips was deployed June 20, 1996 It took approximately 42 minutes to deploy the full 4KM tether. Experiment Development: Experiment Design, Build, Test and Integration: NRL Tether and Deployer: NASA-MSFC, Tether Applications Deployment Data System: NASA-MSFC Transmitter: NASA-Langley Dynamics Analysis: Lockheed Martin Astronautics, NRL, Tether Applications Flight Operations: Flight Ops Lead: NRL Satellite Laser Ranging Management: NASA-GSFC, NRL Satellite Laser Ranging Operations: Allied-Signal Technical Services Satellite Laser Ranging Stations: NASA, NRL/Starfire Optical Range, many European stations and many other international stations RF Tracking & Orbit Determination: US Space Command Telemetry Reception: Air Force Satellite Control Network Tether Data Analysis: NRL All of the tether data gathered will be made available to any interestedparty. We are in the process of setting up a web site which will be the starting point to access the data. Of course, I`ll be publishing the address as soon as the web site is up and running. We have a draft of our website. It is in the final review cycle, so hopefully I`ll be able to publicize it soon. My next newsletter will be in about three weeks, or sooner if we get some interesting new findings. Bill Purdy bpurdy@space.nrl.navy.mil [Mailed From: EDC From: Bill Purdy (8/19/96) ******************************************************************************** |