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Thread: Satellite Novice Wants to Learn More ...

  1. #1
    Registered User
    Join Date
    May 2019
    FLA and the Berkshires

    Satellite Novice Wants to Learn More ...

    ... about, well, satellites. I've learned a lot since joining the forum, but, considering that I've been out of the "microwave" game for such a long time, I realize that there's still a lot more to learn.

    I was just reading the "D15 moving from 103W to 101W" thread and, specifically, the accompanying narrative linked to the first post. As said narrative is essentially a request to move a satellite, I, naturally, wanted to know if (and/or how) this move impacted the first technical document I ever read on this forum: Gary Toma's TPN Map (Domestic tab). It would appear, based on Gary's TPN Map, that this move has already occurred and, once again, based on Gary's spreadsheet, that "D15" is presently synchronized at 100.85 W.L. (a.k.a., 101).

    So, as the title of this thread suggests, I started to do some research on communication satellites and, more to the point, those used by DirecTV (DTV). In the narrative, DTV is specifically requesting to move a satellite -- therein named "T15" -- from 102.75 degrees W.L. to 100.85 degrees W.L. My first novice questions are: Why is DTV calling their satellite "T15" while Gary Toma seems to call it "D15"? Is this difference because the satellite in question is a Direct Broadcast Satellite (DBS)? Does W.L. stand for West Longitude? This one seems to shift backward to absolute beginner status, but Gary doesn't specify anything other than "D15 @101" in his spreadsheet.

    I also watched a video interview with Bob Hall, Director of the Commercial Space Operations Center (somewhere in PA?). Although the fellows in the video referred to the satellite in question, Intelsat 29e, as a "GEO" (a.k.a., geosynchronous) satellite, it quickly became clear that this particular satellite was recently damaged and was "drifting" due to leaking fuel and pieces coming off of it. Before I get to the matter of "drifting," I'd like to ask why a GEO satellite needs fuel on board at all? Is it because the satellite has some sort of propulsion system used to correct its position (assumedly from time to time)?

    Back to drifting ... I noticed that DTV, in the narrative I previously mentioned, is asking to "drift" their T15 satellite. If these GEO satellites do have propulsion aboard, why is DTV employing the word "drift" to suggest precise positioning, while Bob Hall is using the word "drifting" to describe a failing satellite that's moving uncontrollably?

    Although I'm sure that any response(s) will spark some sort of an ensuing discussion, I think that I'll leave it there for now. As I recently stated in the first forum thread I created, we satellite novices have to start somewhere.

    Thanks for your time ~ Hand
    Last edited by HandLogger; 05-17-2019 at 08:27 PM.

  2. #2
    Senior Member
    Join Date
    Jul 2015
    Directv used to name all their satellites with 'D'x so e.g. D15. After the AT&T acquisition, they started referring to them with 'T'x. I guess that's what AT&T wanted. D15 and T15 are the same satellite.

    All geosynchronous satellites need fuel to maintain their orbit. Space may be a vacuum, but there's stuff like the solar wind which affects the Van Allen belts etc. which can 'drag' the satellite so they won't stay in a proper orbit for long without correction. They are also required to reserve some fuel to boost the satellite to a so-called 'graveyard orbit' a couple hundred miles further out than geosynchronous when it is at the end of its life.

    When Directv is talking about 'drifting' T15, they basically mean using propellant to either lift it to a slightly higher orbit than geosynchrous, or drop it to a slightly lower orbit. Either way the Earth would rotate slightly faster or slower than it does, allowing it to move with very little fuel expended. Once it gets to where it wants to be, it uses more propellant to go back to the correct distance so it can remain over a fixed spot on the Earth.
    Last edited by slice1900; 05-17-2019 at 09:54 PM.

  3. #3
    Super Moderator Tom Speer's Avatar
    Join Date
    Jul 2015
    Adirondack Mtns, NY and Eastern NC
    One of the problems with AT&T's desire to rename all of their satellites acquired in the merger with DirecTV, is that the list of geosynchronous satellites at the FCC still refer to them with the names in their original authorizations. The only one that AT&T has succeeded in renaming at the FCC is T11. Even though AT&T received a STA (Special Temporary Authority) to move "T15" to 101, It is still shown as licensed as "DirecTV 15" at 103. All of the data that we keep and refer to, and the software we use to produce the weekly TPN map, as well as the Satellite Transponder Information thread is organized by the original DirecTV names. The soon to be launched T16 will carry that name in anything that I produce, because it is the only name it has ever had.

    The one consistent thing is the satellite call sign, but no one can remember those.
    Last edited by Tom Speer; 05-18-2019 at 01:54 AM.
    Tom Speer, N2HF, Part of the DataDigesters team. A Migratory Common Loon

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