RE: Final trajectory (Re: 2021-035B decay estimates)

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Mon, 10 May 2021 07:46:40 -0400
Marco Langbroek responded to Bob Christy:

> > Half way between then and now is December 2012. The median date of the list is Jan 2013.
> The "SBIRS era" started about the same time.
>
>
> Well, before SBIRS there was DSP of course. Starting in the mid-1990-ies, the US
> DoD started to share DSP detections of meteoric fireballs with astronomers
> researching meteoric fireballs. First occasionally, now rather routinely (see
> https://cneos.jpl.nasa.gov/fireballs/).

I believe that suspicion that the +/-1 min. prediction intervals are derived from missile warning satellites is well founded.

This 1985 document is relevant, despite its age:

https://archive.org/details/MilitaryInSpace/Space-377

Specifically:

d. Decay Window. A time interval of uncertainty
about the final decay trajectory. The decay window is
calculated as ± 20 percent of the time difference
between the time of the last observation and the
predicted final decay trajectory time. When verified
by a visual sighting, the decay window for the final
prediction is ± 1 minute. Historically, this gives 95
percent confidence that the final prediction is within
the stated decay window for intermediate predictions
(for example, 10 days to 2 hours prior to decay). For
the final prediction, the ± 20-percent decay window
is a 68-percent confidence that the actual final decay
trajectory is within the stated window.

So we know that the +/-1 min. windows are "verified by a visual sighting."

TIP messages date back to the 1960s - long before the existence of operational missile warning
satellites. I do not know whether the +/- 1 min. window was used then, but I suspect it was. I do
know that in the early 1960s, special efforts were made to use US military personnel around the
world to try to spot decays visually, because many of the reports (negative and positive) ended up
in the Project Bluebook UFO files, which I successfully mined for re-entry sightings.

It makes sense that with the advent of the DSP missile warning satellites in the 1970s, that they
would have been used to detect and track re-entries. Such satellites use IR sensors, not visual,
but it would be no conceptual leap to include them as the basis for +/-1 min. windows. My
impression (not based on any statistics) has been that the +/-1 min. window is reported too often
to be the result of purely visual sightings, which are rare. Bob's statistics showing 548
TIP +/-1 min. windows since 2004 bears that out. My table of re-entry visual sightings lists just
61 from 2004 through 2017, or about 4.4 annually.

Ted Molczan


> -----Original Message-----
> From: Seesat-l <seesat-l-bounces+ssl3molcz=rogers.com_at_satobs.org> On Behalf Of Marco
> Langbroek via Seesat-l
> Sent: May-10-21 6:34 AM
> To: Bob Christy <bob_at_zarya.info>; Seesat-L <seesat-l_at_satobs.org>
> Subject: Re: Final trajectory (Re: 2021-035B decay estimates)
>
> Op 10-5-2021 om 10:41 schreef Bob Christy via Seesat-l:
>
> > Half way between then and now is December 2012. The median date of the list is Jan 2013.
> The "SBIRS era" started about the same time.
>
>
> Well, before SBIRS there was DSP of course. Starting in the mid-1990-ies, the US
> DoD started to share DSP detections of meteoric fireballs with astronomers
> researching meteoric fireballs. First occasionally, now rather routinely (see
> https://cneos.jpl.nasa.gov/fireballs/).
>
> - Marco
>
>
> -----
> Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
> e-mail: sattrackcam_at_langbroek.org
>
> launchtower:    http://launchtower.langbroek.org
> Station (b)log: http://sattrackcam.blogspot.com
> Twitter:        _at_Marco_Langbroek
> -----
> _______________________________________________
> Seesat-l mailing list
> http://mailman.satobs.org/mailman/listinfo/seesat-l


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Received on Mon May 10 2021 - 06:47:41 UTC

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