From: Chuck Hemker (maahqjt.bbkmjzwosv@zeosoft.com)
Date: Tue Mar 05 2002 - 03:34:41 EET
On 02-Mar-02 Riley Williams wrote:
> Hi Chuck.
>
> I've to head out in a minute, so I'm just dealing with one aspect of
> your email and will do a fuller reply later...
>
>> With the discussion of TLE servers, one other thing I was thinking
>> would be nice is the ability to have multiple keps for a satellite
>> with a range of valid time for each.
>
>> If you go to the NASA spaceflight page to get the keps for the ISS
>> or the shuttle, they have multiple sets of keps with a range of time
>> that they're valid. That way you can do predictions after maneuvers
>> and such.
>
> There is one obvious problem with that idea - those "future keplers"
> are based on the INTENDED manoeuvres, and those aren't necessarily the
> ACTUAL manoeuvres that took place. Another problem is that the TLE
> format only specifies a start time from which the keplers can be used,
> and not a finish time at which they should stop being used.
I understand that they are based on intentions, but they are probably better for
predictions then just using the current keps. As an example, if I'm trying to
predict passes for the ISS for a few days from now, it would be better to use
keps that include their intended maneuvers. When the time gets closer to the
pass, it would be good idea to get updated keps that include any changes.
This is similar to coming up with predictions for a satellite for next week or
next month. It's as close as we can get right now, but I wouldn't want to
drive a set of rotators using these numbers. I'd try to get a new set of keps
before then. (Otherwise it would be like using an old set of keps)
The reason I mentioned this was because I saw the discussion about coming up
with a TLE server, and I though I'd mention it so someone could think about it
before coming up with a design.
As for the format, I haven't implemented anything and the only source I've found
so far for predicted keps has been the NASA spaceflight website, I was thinking
of just adding a begin time and an end time on a line or two after the normal
TLE. Then writing something to go to NASA site and parse them out of the web
page.
>
> The intent behind your suggestion could, however, be realized fairly
> easily by simply ignoring any keplers that quote a start time in the
> future. This would result in the "current" kepler from such a multiset
> being selected automatically, since the older ones would be marked as
> superceded (this happens already) and the future ones would be ignored
> (which probably doesn't happen at the moment). I'll have a look at this
> when I get back from child-minding this afternoon/evening.
>
> Best wishes from Riley.
>
> PS: I use British English, you use American English, hence the
> difference in spelling of "maneuvers" and "manoeuvres" above.
You should have seen my spelling before I ran it through a spelling checker. :)
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