Back on March 24, John Gardner asked about some TLEs that had future epochs. I forwarded the message to Tom Kelso of Celestrak for comment and have now received the following reply, which is posted here with his permission. AT: This appeared on SeeSat -- could you provide any enlightenment about how/why AT: SPACECOM generates "future" TLEs for these high-altitude objects? I think AT: the topic has come up before, but I don't remember the answer. AT: Posting the answer to SeeSat would be desirable -- I can relay it if you'd AT: rather not do it yourself. >Allen > I'm not sure I can answer your question. According to the way NORAD > 'describes' the process of generating element sets, this should not happen. > What it suggests is that someone is generating these element sets outside > of the normal process, which would make the quality of the data somewhat > suspect. Whether these are being produced by their own analysts or, more > likely, by someone else is hard to say. My guess would be that NORAD is not > able to track these objects adequately using the current Space Surveillance > Network. These objects are difficult to track with either radar or optical > systems. As a result, they probably went to one of the special radar sites, > such as Haystack, to do the tracking. Odds are that they have a different > process and even use different software to produce the data. While this > would make the data suspect, you should be cautious about results for these > objects anyway since the SGP4/SDP4 orbital model assumes low-eccentricity > orbits and so is not intended for tracking objects in these orbits (you are > violating one of the key mathematical assumptions used to develop the > model). I hope that answers your question to some extent, even if it isn't > the way you expected. Please feel free to share whatever portions of my > response with whomever you'd like. - TS > > Dr TS Kelso > CelesTrak WWW, http://celestrak.com > E-Mail: tskelso@celestrak.com ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Thu Apr 13 2000 - 12:27:28 PDT