news@cs.vu.nl (news) (03/19/89)
One of the thning the current shuttle mission has done (Ok, I know, the shuttle has landed a couple hours ago) is to put a communication satelite in orbit. This satelite should improve the communication between the shuttle and groundstations. Until now, I've been told , only during 30% of the flighttime communication with the ground was possible. With this new satelite, is should besomewhere around 80%. Question: Why was it only 30% until now. I guess that when the shuttle flies over Rusia, there might be a gap in communication, but only 30%??? Wheren't there any satelites upthere already, who could do the job? Serge Wallagh From: wallagh@tjalk.cs.vu.nl (Wallagh Serge R) Path: tjalk.cs.vu.nl!wallagh
henry@utzoo.uucp (Henry Spencer) (03/21/89)
In article <2099@botter.cs.vu.nl> wallagh@cs.vu.nl () writes: >Until now, I've been told , only during 30% of the flighttime communication >with the ground was possible... > >Question: Why was it only 30% until now. I guess that when the shuttle flies >over Rusia, there might be a gap in communication, but only 30%??? >Wheren't there any satelites upthere already, who could do the job? For data relay as well as voice, it's not an entirely trivial job. In the beginning, launching a complete set of relay satellites for itself was to be one of the shuttle's first jobs. In practice, an upper-stage failure on the first such launch delayed further ones until the problem could be straightened out. The second relay satellite was Challenger's payload. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
fireman@tippy.uucp (03/22/89)
By the way, 30% was too low. The new satellite won't change coverage,
it has been at about 80% since the last mission when they deployed a TDRS.
The only place where there is no coverage is around the Indian Ocean area,
where they lose the signal for about 10 minutes. The satellite just
deployed will replace one of the current TDRSs, and that satellite will be
moved and become an on-orbit spare.
Rob Dale - tippy!fireman@newton.physics.purdue.edujohnson@ncrcce.StPaul.NCR.COM (Wayne D. T. Johnson) (03/22/89)
In article <1989Mar20.191412.23335@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >In the >beginning, launching a complete set of relay satellites for itself was to >be one of the shuttle's first jobs. If my memory is right, there were originally to be 3 TDRS in orbit. Six were build and 2 each (one was a spare) were given to the French and another country (my memory fails me here) as well as 1 to be launched on the shuttle. The French dropped their 2 plus one borrowed from the US on the ocean floor. Or was this another satellite I'm thinking of? -- Wayne Johnson (Voice) 612-638-7665 NCR Comten, Inc. (E-MAIL) W.Johnson@StPaul.NCR.COM or Roseville MN 55113 johnson@c10sd1.StPaul.NCR.COM These opinions (or spelling) do not necessarily reflect those of NCR Comten.
mcdowell@cfa250.harvard.edu (Jonathan McDowell) (03/22/89)
From article <1194@ncrcce.StPaul.NCR.COM>, by johnson@ncrcce.StPaul.NCR.COM (Wayne D. T. Johnson): > If my memory is right, there were originally to be 3 TDRS in orbit. Six were > build and 2 each (one was a spare) were given to the French and another country > (my memory fails me here) as well as 1 to be launched on the shuttle. The > French dropped their 2 plus one borrowed from the US on the ocean floor. Or > was this another satellite I'm thinking of? No, it is another satellite you're thinking of. The only TDRS on the ocean floor is the one we dropped there with Challenger. TDRS is an entirely U.S. project. You may be confused with GTE's Spacenet satellite or one of INTELSAT's satellites, both much smaller US built commercial comsats which were delivered by Ariane to the Atlantic Ocean. Possibly you are also thinking of the Global Atmospheric Research Program which had an international set of weather satellites in geostationary orbit. Two were American, one European and one Japanese. (the Europeans built their own, we didnt have to 'give them' any. The Japanese bought two from us but the replacements they use today are mostly home built). At the moment for reasons which totally escape me, there are to be only two operational TDRS in orbit plus a spare, rather than three operational ones which would give full coverage. TDRS-E and F are on the manifest to go up in a few years as backups. Jonathan McDowell
henry@utzoo.uucp (Henry Spencer) (03/23/89)
In article <1194@ncrcce.StPaul.NCR.COM> johnson@ncrcce.StPaul.NCR.COM (Wayne D. T. Johnson) writes: >If my memory is right, there were originally to be 3 TDRS in orbit. Six were >build and 2 each (one was a spare) were given to the French and another country >(my memory fails me here) as well as 1 to be launched on the shuttle. The >French dropped their 2 plus one borrowed from the US on the ocean floor. Or >was this another satellite I'm thinking of? I think you're confusing TDRS with something else. The US has never given any of them away, and the Europeans have no booster that could launch one. The only TDRS on the ocean floor is the one that was aboard Challenger. The other three that have been built are all in orbit (although the first, launched by an early shuttle flight, is not in good shape), and at least one more is planned. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
tca@ut-emx.UUCP (Tobin C. Anthony) (03/29/89)
The reason that there are only two operational TDRS satellites is for sheer economic reasons. NASA only wants to have one TDRS ground station and they want to keep it at White Sands. Both TDRS spacecraft can see White Sands from their positions. Having a third TDRS would require an additional ground station on the opposite side of the Earth from White Sands. The logistical implications of maintaining this site and have it communicate with WS must have been cost-prohibitive. The TDRS system covers 85% of satellite orbits anyway. Tobin C. Anthony tca@gunaco.ae.utexas.edu
sw@cbnewsl.ATT.COM (Stuart Warmink) (03/30/89)
In article <11563@ut-emx.UUCP>, tca@ut-emx.UUCP (Tobin C. Anthony) writes: > [..............] NASA only wants to have one TDRS ground station and they > want to keep it at White Sands. Both TDRS spacecraft can see White Sands > from their positions. Having a third TDRS would require an additional > ground station on the opposite side of the Earth from White Sands. [...] In theory, the 3rd TDRS could communicate with White Sands via one of the other two TDRSs. In practice, as Tobin said, 85% coverage is good enough, especially considering the extra cost of launching and maintaining an additional TDRS. By the way, does anyone know if TDRS-D has reached its operational position yet, or is it still being checked-out? -- ------------------------------------------------------------------------------ "PENTAGON OFFICIALS ARE CONCERNED ABOUT | Stuart Warmink, Whippany, NJ, USA AN ANTIMATTER SHORTAGE" ("WHAT'S NEW") | sw@cbnewsl.ATT.COM (att!cbnewsl!sw) -----------> My opinions are not necessarily those of my employer <-----------
phil@titan.rice.edu (William LeFebvre) (03/30/89)
In article <354@cbnewsl.ATT.COM> sw@cbnewsl.ATT.COM (Stuart Warmink) writes: >In theory, the 3rd TDRS could communicate with White Sands via one of the >other two TDRSs. In practice, as Tobin said, 85% coverage is good enough, Besides....with 100% coverage, the flight controllers would *never* be able to take a bathroom break :-) (They normally take their breaks during Loss Of Signal times). William LeFebvre Department of Computer Science Rice University <phil@Rice.edu>