Re: TDRS desginations
Wed, 28 Aug 1996 16:52:52 -0400

I've been following the discussions about the TDRS with some interest, having
seen one launched in 1989  - STS-29 Discovery/TDRS D (the only launch I have
ever had the privilege and pleasure to actually see first hand).

Out of curiosity, I had often wondered if it were possible to actually see
TDRS D from my home near Washington DC, even if only telescopically (I
presume if any geostationary satellites would be visible at all, due to their
size and extent of their arrays, the TDRS series would probably be among

In agreeing with Steve Walter's assertion, I had always understood TDRS D to
be TDRS 4 (although, after reading Phil Chien's argument that it should
instead be TDRS 3, I can appreciate his point, as well).  Consequently, when
I first displayed the real time location of TDRS 4 on my screen about a year
ago, using an element set I had retrieved from Dr T S Kelso's Air Force Inst.
of Technology site (, I found it
positioned over the Pacific ocean.  Thus, barring moving to Hawaii, that
pretty much shot any hope I had of ever spotting the STS-29 payload actually
in orbit.  

But with these recent Seesat postings on the confusion over TDRS number
designations, I realized, really for the first time, that the original Kelso
element set I used may have in fact had TDRS D as TDRS 3.  I retrieved a new
set and checked the launch date designations (TDRS D being launched in March
1989), and, sure enough, found 89021B was listed as TDRS 3, agreeing with
Philip Chien's designation scheme.  I had used the wrong satellite.

So, again out of curiosity, this morning I went back and retrieved another
element set, this time from NASA's Goddard Space Flight Center
(, and found the same TDRS D (89021B) listed
as TDRS 4 - just as Steve Walter said it was.   

In fact, this is how the NASA GSFC and KELSO/AFIT TDRS satellite designations
compare, side by side:

                NASA GSFC     Kelso/AFIT
13969U 83026B     TDRS 1        TDRS 1 
19548U 88091B     TDRS 3        TDRS 2
19883U 89021B     TDRS 4        TDRS 3
21639U 91054B     TDRS 5        TDRS 4
22314U 93003B     TDRS F6       TDRS 5
23613U 95035B     TDRS F7       TDRS 6

(And this is apparently why, as Jay Respler pointed out, the same number is
confusingly used for different TDRS satellites - not every one is on is the
same page.)

Does this all have a happy ending?  I don't know.  All I know is that TDRS D,
the one I saw launched in 1989, the one I thought was high over the central
Pacific, is instead somewhere near the NE coast of Brazil, putting it about
31-degrees over my SE horizon, and has been patiently waiting for me to
finally get my scope out and try to find it.  I'll let you know. 

Jim Cook (