# Which two satellites had a 44% probability of collision at 2017-01-07 21:53 UTC?

I saw this message on space-track.org:

The JSpOC has identified a close approach between two non-maneuverable satellites in a sun-synchronous orbit (approximately 800km altitude) with a time of closest approach at 21:53:00 UTC (16:53 EST) on 7 January 2017. The probability of collision has been predicted as high as 44%. Affected operators have been notified.

Which two satellites are involved? I'd like to calculate the ground location below where the two orbits intersect in the unlikely even that there will be an "Earth-shattering Kaboom!" but I can not find an event at January 7, near 21:53 in Socrates.

The multiple answers to this question are worth reading for additional background.

edit: @Chris noted that today's Spaceflight 101 article discusses this particular conjunction.

note: Marvin the Martian has appeared on the NASA Mission patch of Mars Exploration Rover (Spirit).

Or perhaps this is more appropriate for a potential collision:

• I suspect at least one of the satellites is a classified one, which would explain the lack of available details. Still... Jan 7, 2017 at 13:04
• This article gives a couple of potential candidates, but until it's publicly released, we don't know for sure. Jan 7, 2017 at 15:57
• I sure hope they aren't "Kessler" and "Syndrome"! Jan 7, 2017 at 20:31
• > The close approach predicted at 21:53:00 UTC on 7 Jan 2017 has passed without incident. The JSpOC has confirmed that both satellites are being tracked as single objects, indicating that no collision has occurred. Jan 8, 2017 at 1:41
• I fixed the title so that it will still be valid tomorrow.
– user
Jan 8, 2017 at 11:35

First of all, it was a miss. Whew!

The close approach predicted at 21:53:00 UTC on 7 Jan 2017 has passed without incident. The JSpOC has confirmed that both satellites are being tracked as single objects, indicating that no collision has occurred.

A few tidbits that might help narrow it down:

1. The percentage is very high, which means the objects must be large.
2. They are in a Sun-Synchronous orbit.
3. Neither object can maneuver. This means they are either inactive, or have fuel depleted.

The most popular theory, although it might never be confirmed publicly, is DMSP F15 & Meteor 1-26. DMSP F15 is a military weather satellite, meaning it's exact orbital predictions are likely classified (Or at least not for public release), which would explain why the difficulties in identifying the satellites. Meteor is a defunct USSR weather satellite.

• #1 is not necessarily true. Jan 8, 2017 at 3:10
• Considering the announcement was made many hours in advance, they must have known the position of the objects such that the 1 STD uncertainty was about the size of the satellites. For that uncertainty to be small, the objects had to be large, which would also increase the likelihood of collision. Not huge, mind you, but not likely debris either, something at least the side of a trash can would be large enough, with larger antennas/ solar panels. Jan 8, 2017 at 3:20
• That's a fair point. Jan 8, 2017 at 3:30
• @Chris et al. There's an implicit "with respect to uncertainties in predicted minimum separation of conjunction" in #1. There is also an explicit "as high as" (44%) in the original announcement. Except for a few notable exceptions (space stations, invisible alien monitoring posts, and Big Boy-shaped weapons, i.imgur.com/qaCiA3t.gif and youtu.be/ARXqNc5DGXU) most artificial objects are at most a half-dozen meters in scale, so in this case somebody, somehow is determining the positions of possibly non-GPS enabled objects to GPS-like precision, roughly speaking.
– uhoh
Jan 8, 2017 at 6:59