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According to https://en.wikipedia.org/wiki/List_of_TDRS_satellites TDRS-C and TDRS-E were launched, but are "in storage". The citation (https://www.nasa.gov/directorates/heo/scan/services/networks/txt_tdrs_fleet.html) redirects to a page which doesn't mention what that means.

While I understand that an orbiting satellite can be a "spare" in case the main satellite malfunctions, how can a satellite be both launched and in storage at the same time?

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  • $\begingroup$ The geo graveyard belt orbital regime is valuable as a storage and disposal location for derelict satellite space debris after their useful economic life is completed as geosynchronous communication satellites. Artificial satellites are left in space because the economic cost of removing the debris would be high, and current public policy does not require nor incentivize rapid removal by the party that first inserted the debris in outer space and thus created a negative externality for others. - en.wikipedia.org/wiki/Supersynchronous_orbit $\endgroup$ – Vinicius Monteiro Aug 27 '18 at 17:43
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Look at the very page you're linking in your question:

TSRS-C is retired. When they quit using it they boosted it 300 miles farther out so it wouldn't be a navigation hazard to other synchronous satellites. It's called a storage orbit, hence the satellite is in storage.

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  • $\begingroup$ @RonJohn I found the 300 mile bit by following the reference link from the Wikipedia article. $\endgroup$ – Loren Pechtel Aug 26 '18 at 21:46
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    $\begingroup$ How did I miss that?? :( $\endgroup$ – RonJohn Aug 26 '18 at 21:47
  • $\begingroup$ @RonJohn consider asking a new question, something like "Could TDRS 3 and 5 (C and E) be 'turned on' again and possibly even moved back to GEO if needed for some reason, or are they permanently and irreversibly shut down?" If you're not interested, I'll ask it. $\endgroup$ – uhoh Aug 27 '18 at 1:20
  • $\begingroup$ @uhoh I would be surprised if they didn't burn most of it's remaining fuel--get it as far away from the active satellites as possible. $\endgroup$ – Loren Pechtel Aug 27 '18 at 2:01
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    $\begingroup$ I'm not convinced TDRS-C is retired. the document linked from wikipedia shows TDRS-4 retiring on the date attributed to it in wikipedia. I suspect a error by the wikipedian responsible. $\endgroup$ – JCRM Aug 27 '18 at 11:33
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Storage just means that they're launched and still in geosynchronous orbit but not actively used.

You can see the status of the Tracking and Data Relay Satellite (TDRS) Fleet on this NASA graphic:

TDRS Fleet Graphic

Of the eleven TDRS satellites successfully launched into space, nine are still functioning and two (TDRS-1 and TDRS-4) are not. The two non-functional satellites were boosted into a super-sync orbit. Two of the nine functioning satellites (TDRS-3 and TDRS-5) are in storage.

From that you can determine two things. Stored doesn't mean retired, because the retired satellites are boosted in a super-sync orbit, but the stored satellites remain in geosynchronous orbit. Stored also doesn't mean non-functional, because the two stored satellites are counted with the nine functional satellites.

It's then not much of a leap to conclude that these two functional satellites in geosynchronous orbit are not currently being used, but are available to be taken out of "storage" and put into service if necessary.

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