DIRECTV Satellite Discussion DLA-1 @95W

Discussion in 'DIRECTV General Discussion' started by egakagoc2xi, Aug 18, 2014.

  1. harsh

    harsh Beware the Attack Basset

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    I don't think that's an fair assessment of what a TLE represents. The TLE is a model, not a data point. It is representative of the orbit until something is done physically to change the orbit.
     
  2. harsh

    harsh Beware the Attack Basset

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    To suggest that the TLE interpretation software available to the consumer/hobbyist is any less accurate than software that more technical people might use is elitist snobbery. TLEs are a straightforward mathematical model and as you're so fond of pointing out, they are derived from observations.
     
  3. HoTat2

    HoTat2 Hall Of Fame

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    I thought the actual mathematical "model" were things like "SGP," "SGP4," "SDP4," "SGP8," "SDP8" ect. the various satellite calculation programs base their computations upon. Then when combined when input with the TLE data sets compute a satellite's position and speed at at any given point in it's orbit.

    But whatever the case, I agree that AIUI an aging TLE is not the cause of inaccuracy in the predicted orbit results of a program as long as the orbit doesn't change since it's epoch. But the inaccuracies come from the accumulated errors of the programs themselves as they continue to extrapolate further away from that TLE's epoch.
     
  4. doctor j

    doctor j Hall Of Fame DBSTalk Club

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    TLE 15 published
    Only slight changes.
    Still no "parked"

    Doctor j
     
  5. LameLefty

    LameLefty I used to be a rocket scientist

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    A TLE is a snapshot based on data as of a specific point in time. It is not a model. It's BASED on a model. But if you took time to actually learn the underlying mathematics (or just read HoTat2's post ;) ) you'd know that. Again, you're much better served to stick with what you KNOW not what you can regurgitate from a Google search.

    Uh, no. It's not "elite snobbery." Real satellite operation pros generally use STK, usually with all the bells and whistles. It's both more accurate and FAR more capable than stuff downloaded from an open-source repository, or even things purchased.

    But once again, you missed my point, which wasn't to knock hobbyist software (a lot of which is just fine for our purposes and a lot more accessible than STK) - rather, it was to point out that the TLE's available to the public are NOT the data satellite operators use to drive their own birds; they may use the data for other objects as part of their overall planning purposes - especially for objects in stable configurations and orbits which haven't changed significantly in weeks, months or years - but they do not use Space Command's "best guess" TLEs that are being release and discussed here to plan maneuvers and get status updates on their own spacecraft.. Instead, they'll use their own internal data (probably with something like STK and a real-time command/control software module interfaced to it).
     
  6. James Long

    James Long Ready for Uplink! Staff Member Super Moderator DBSTalk Gold Club DBSTalk Club

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    I agree that is your opinion - and disagree with your conclusion. The location at epoch is trivial given an accurate TLE. The location after epoch is a prediction based on the assumption that nothing changed. Assuming where a satellite is works OK for us amateurs. The professionals are not looking at TLEs to see where their satellites are. They know better.
     
  7. harsh

    harsh Beware the Attack Basset

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    A TLE represents the non-variable parameters of a mathematical function that represents a dynamic model. It is derived from measurements but the only variable is time.

    http://en.wikipedia.org/wiki/Mathematical_model

    The model should be valid until some external influence (a burn) changes the non-variable parameters.
     
  8. harsh

    harsh Beware the Attack Basset

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    I don't disagree with this.

    What I disagree with is your assertion that a TLE is only valid for an instant. If that were the case, they would simply give Euclidean or more likely polar coordinates and a simple vector to describe direction and speed.
     
  9. HoTat2

    HoTat2 Hall Of Fame

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    Since the 30 day STA for IOT and then transfer to it's actual licensed slot at 95.05W officially begins today. I wonder if the next TLE will show it parked?
     
  10. LameLefty

    LameLefty I used to be a rocket scientist

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    Challenge: explain "non-variable", "parameter," "mathematical function" and "dynamic model." Without using a computer, based on your own education. ;)

    And here's a hint to get you started: that definition is misleading you; the TLE isn't the "dynamic model" - the mathematical function is the dynamic model. But I'm sure you knew that already, right? You should've learned it in undergraduate orbital dynamics or spacecraft operations class. You did take those, right? After all, you sure do Google a good game ... :)
     
  11. LameLefty

    LameLefty I used to be a rocket scientist

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    Once again, you're conflating concepts you apparently don't fully grasp.

    A TLE represents a snapshot of an orbit; it is is a set of parameters that, when used with the corresponding mathematical model, depicts - to more or less accuracy, depending on any number of factors - the "best approximation" of an object's orbit AS OF THAT INSTANT. That mathematical model may be propagated forward in time to predict the location and the velocity of that object at some arbitrary future time, but again - only to a more or less accurate degree, depending on any number of factors.

    Please, leave space navigation, satellite design, launch and operations to those who actually know what they're talking about. Correcting your misstatements, mistakes and outright errors provides us all with hours of amusement, but it does clutter up these threads. :)
     
  12. James Long

    James Long Ready for Uplink! Staff Member Super Moderator DBSTalk Gold Club DBSTalk Club

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    The TLE does not tell you what changed after the epoch ... which makes it more unreliable every instant that passes after the epoch. There could have been a controlled burn or total system failure. You won't know anything has changed until a new TLE is published.
     
  13. harsh

    harsh Beware the Attack Basset

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    The assumption is that nothing other than time changed. If the TLE shows movement, we know it isn't parked and won't be parked until another burn has happened.
     
  14. harsh

    harsh Beware the Attack Basset

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    The people that do all of these things don't live in an exclusive bubble that you seem to insist exists. We are all subject to the same laws of physics.

    You're not generally correcting or improving anyone's understanding, only working overtime in an attempt to cast mine as incorrect.
     
  15. harsh

    harsh Beware the Attack Basset

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    The non-variable parameters of a TLE are the external inputs (burns). Absent these parameters, the orbit is reasonably well described by the TLE until a subsequent burn.

    The magic of what I'm trying to do is that I'm not talking down to the audience or any particular member of it.
     
  16. slice1900

    slice1900 Well-Known Member

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    He is improving the understanding of others, by pointing out where and how you're (as usual) wrong.
     
  17. slice1900

    slice1900 Well-Known Member

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    I don't feel LameLefty is "talking down to the audience". He knows way more about this than I do, so I'm happy to listen to him. You may have slept in a Holiday Inn Express last night, but that doesn't mean you know as much about this as he does.
     
  18. James Long

    James Long Ready for Uplink! Staff Member Super Moderator DBSTalk Gold Club DBSTalk Club

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    And as you have already agreed ... the people actually controlling the satellite are not working on assumptions.

    TLEs available to the public are a fun way for us to see the characteristics of movement at each epoch. Don't take the fun out of it with false assumptions. The last available TLE (#15) is now over 53 hours old.

    01 Thu Oct 16 18:57:03 EDT
    02 Thu Oct 16 18:57:03 EDT
    03 Thu Oct 16 18:57:03 EDT
    04 Fri Oct 17 07:24:41 EDT
    05 Fri Oct 17 10:38:24 EDT
    06 Fri Oct 17 13:15:50 EDT - Driftrate 228.1713 deg/day East - Inclination 5.9509
    07 Sun Oct 19 06:15:57 EDT - Driftrate 192.3722 deg/day East - Inclination 3.0928
    08 Mon Oct 20 13:29:38 EDT - Longitude 179.1517 West (at Epoch) Driftrate 131.0083 deg/day East - Inclination 1.6043
    09 Mon Oct 20 17:39:19 EDT - Longitude 168.9015 West (at Epoch) Driftrate 47.8362 deg/day East - Inclination 0.3071
    10 Tue Oct 21 03:42:48 EDT
    11 Wed Oct 22 01:25:19 EDT
    12 Wed Oct 22 14:05:52 EDT - Longitude 136.7086 West (at Epoch) Driftrate 16.5253 deg/day East - Inclination 0.1714
    13 Thu Oct 23 14:11:41 EDT - Longitude 134.7611 West (at Epoch) Driftrate 1.8351 deg/day East - Inclination 0.0723
    [Note: Longitude 120.1167 West if you were still assuming TLE 12 at 14:14:41 on Thursday. When did the change occur? TLEs do not tell us that!]
    14 Fri Oct 24 01:21:54 EDT
    15 Fri Oct 24 07:24:21 EDT - Longitude 133.0399 West (at Epoch) Driftrate 1.9092 deg/day East - Inclination 0.0707


    One can assume the satellite reached the target on Friday @ 8:28p EDT following the last TLE known. Or one can assume, as you suggest, that the satellite is still moving east at 1.9092 deg/day (as reported in the latest known TLE). I believe the first assumption is safer ... but we won't know until we see TLE #16 and #17, etc etc etc.
     
  19. carl6

    carl6 Moderator Staff Member DBSTalk Club

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    LameLefty does in fact have degrees and working experience in this field. He actually is a "rocket scientist" (among other things). I think it's great that we can benefit from his knowledge and first hand experience in this area.
     
  20. harsh

    harsh Beware the Attack Basset

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    Absent an understandable explanation of what the facts are, it isn't bettering anyone's (your's or mine) understanding.
     

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