| Date: | 1997-03-04 16:00:00 | |
| Sender: | Bill Purdy, Naval Research Laboratory <DSGJEH@cdslr3.atsc.allied.com> | |
| Subject: | [SLR-Mail] No. 44: TiPS NEWSLETTER | |
| Author: | Bill Purdy, Naval Research Laboratory | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-03-04 16:00:00 UTC Message No. 44 ******************************************************************************** Author: Bill Purdy, Naval Research Laboratory Subject: TiPS NEWSLETTER Hello again. TiPS is still in one piece, and going strong. The = survival to date is now almost 8 months. We´ll be continuing to track = TiPS through September 1997. We have struggled to get enough data to = calculate the libration amplitudes lately for a variety of reasons that = I´ll discuss later. We have seen that the in plane libration amplitude = is now down to 4 degrees, +3, -1. Satellite Laser Ranging (SLR) We´ve learned a lot about what does and does not work with SLR for TiPS. = It turns out that regular libration solutions of the TiPS system = requires far more capability than presently exists in the global SLR = network. Here´s what works best: Lots of data is needed for good, regular solutions. We would like ten = passes per day. This is only practical when there are 30 or more = terminator opportunities a day. We only see 30 or so days like this a = year for TiPS. - It is especially helpful to get data returns from both end bodies, = Ralph and Norton. =AD Switching from one end body to the other during a single pass is = especially helpful. - Data from two SLR stations simultaneously is very helpful in = pinning down the solution. Why is it so difficult to solve TiPS motion with SLR? - No SLR returns from center of mass. With out a direct measurement = of the center of mass of the tethered system, we must simultaneously = solve for the orbital parameters and the libration parameters, all from a = single set of data. TiPS center of mass is approximately a quarter of = the way up the tether so it was impossible to place a retro reflector = there. If the center of mass is very close to one of the end bodies the = problem becomes a good deal easier. - The large libration amplitude of TiPS further complicates the = problems of acquiring data and solving for the behavior. Simply put, = less motion narrows the playing field. - The global SLR network is great at working on single body = satellites. They typically require terminator assist only for the first = day or two of tracking a retro reflector equipped satellite. - We are simply using the SLR network for something it was not = designed or optimized to do. However..... We are very proud of the work we have done in getting the solutions. = Believe me, it hasn´t been easy. The things we have learned so far are = entirely due to 1) the insight and dedication of the TiPS flight = operation team and 2) the dedication and expertise of the people who make = the SLR the powerful tool that it is. Particular credit goes to the = tireless efforts of Jim Barnds in coaxing tether solutions out of the = data. Visual Data The Air Force Maui Space Surveillance System (MSSS) has been tasked to = track TiPS with their telescopes day and night. Unfortunately telescopes = don´t quite work rain or shine. All the weather you have seen flooding = the Pacific Northwest this winter has usually passed over Hawaii on the = way. As such we´ve gotten very limited data from MSSS. We expect the = data flow to improve with the weather. Our use of visual data from telescopes is promising. It can and has been = used to correlate the SLR based solutions and to get solutions for the = out of plane libration. However we are only presently getting support = from one station and the wheather has given us fits. We would be interested in hearing about any other telescope sites we = might be able to get observations from. Our minimum optical requirements for gathering librational data from = videotapes are: -Tether shown at suitable size to be able to get a good measure of orientation. Both end masses do not need to be visible, so long as a fair length of tether is. -Enough stars in the background to be able to determine the velocity = vector. -Time tag displayed on screen or at start of tape to be able to assign a time to any frame to an accuracy of at most a few seconds. Ideally the time tag would always be displayed on screen. Future plans We will be getting great terminator observing conditions from late March = through early April. We will be combining radar data with the SLR Data = in this period. This will be one last try at getting a solution that we = can maintain without terminator acquisition. We are not getting our = hopes up as we´ve finally come to grips with the degree of difficulty. = This should be however, our best chance because we have the most = experience, the libration angles are low and we have the assistance of = radar data. We will be tasking several organizations to analyze the TiPS libration = data. The goal is to improve the understanding of long term tether = dynamics and the prediction thereof. Check out our website at http://hyperspace.nrl.navy.mil/TiPS. We´ve = updated the website recently with the addition of the libration amplitude = data. Please send me updates for my email list. A while back my computer´s = hard drive crashed. Believe me, it is worth the time to back up your = hard drive. We´ll that´s about it. See you later, Bill Purdy From: DSGJEH@cdslr3.atsc.allied.com ******************************************************************************** |