This object was tracked after launch by Catalina on two nights. Then we lost track of it.
In September 2012, Catalina found a "new", unidentifiable artsat. It went under the designation TR93D0F for over three years, getting picked up once or twice a year, but remaining unidentified.
In January 2016, though, in the course of trying to sort out a different object, I came across this page describing the new orbit used by IBEX. There was a maneuver in June 2011, putting it in a higher orbit. We had been relying on the orbital elements from JSpOC (Joint Space Operations Center). They hadn't noticed the maneuver, and simply propagated the pre-2011 trajectory forward to the present. (This sort of problem has happened before. In early 2015, the INTEGRAL satellite maneuvered, and JSpOC left it in the old orbit for about half a year.)
I had noticed earlier that TR93D0F didn't look like a good candidate for hitting the earth or moon, or getting ejected from the earth/moon system. Dave McComas, the PI for IBEX, kindly pointed me to a paper explaining why IBEX is in this new orbit: it puts IBEX into a 1:3 resonance with the moon; thus, at apogee, it's always 60 or 180 degrees from the moon, very similar to the way the Alinda group asteroids miss Jupiter with the same resonance. The paper also provides a graph of perigee distances between 2011 and 2021 that lines up nicely with the perigees of TR93D0F.
This object was picked up at Mt. Lemmon on 2016 February 8. Tracking it and identifying it turned into a bit of an epic saga; details are at the page linked above. As you can see by the above long list of IDs, it had been spotted several times; we just hadn't linked the pieces together before now.
Our current "object of mystery" is S509356 = WJ2AD07. This was picked up a couple of weeks ago by the SONEAR team in Brazil. They've been getting a fair number of artsats, most of which we've been able to ID quickly, but this one has remained a puzzler. In fact, we wondered if it might be a natural object for a while, but it's now clearly moving the way a rocket booster would, being pushed out by solar radiation pressure to a degree consistent with space junk. (Rocks are much more dense, and it's rare you can even detect the solar radiation pressure on them.)
Peter Vereš was able to find the object on several images from PanSTARRS over the preceding two months. That allowed me to link to WJ2AD07, an object tracked for about an hour from Catalina in May 2015. At the time, Eric Christensen at CSS and I swapped a few e-mails about it, but we didn't have a lot of data to work with, and it was "lost".
At this point, we can propagate the orbit back to the beginning of the Space Age in 1957. But I haven't found any matches to this object.
ExoMars and its booster got tracked as they were leaving us on 14 March, on purpose in some cases (ESA and a gent in South Africa deliberately looked for them) and by accident (the MASTER-IAC folks reported them as asteroids). It turned out to be a good thing that the objects were observed; the images showed that there was some debris around the booster that wasn't supposed to be there.
In the past, I've not really nudged people to observe departing spacecraft very much. But reasons to target them are accumulating. We get data useful for computing trajectories so we can ID these objects if they come back. If there's a malfunction, as happened with the ExoMars booster, the images may be our only way of knowing about it. (When the CONTOUR mission failed, a request for observations went out, in hopes of getting some information as to what had gone wrong; but it might have helped if somebody had been targeting it slightly before or after the malfunction occurred, rather than waiting for some time after the mishap.)
In addition, I've found that people working on these missions are often very interested to see an image of "their" spacecraft heading into Outer Darkness, something to frame and hang on the wall.
The SONEAR team picked up this object on 2016 April 24. Usually, satellites can be identified with the on-line satellite ID page, but this object didn't match anything listed.
However, the orbit looked very much like that listed for XMM in the JSpOC (Joint Space Operations Center) elements, except that the JSpOC elements had the object about three hours away. Which is a heck of a lot. Everything else -- eccentricity, inclination, argument of perigee, and longitude of ascending node -- matched pretty well. So I figured this was another case in which JSpOC was tracking a "ghost" object, with the actual satellite having moved a while ago.
To confirm this, I looked around the XMM-Newton site, found a 'help desk', and asked if they could provide perigee times. They could; their times matched those generated from the SONEAR orbit to within a minute. Which has made me confident that XMM = S509474.
(In early May, (Y00) got more data and linked in some 2016 April 18 observations. That has led to a much better orbit solution, matching the ESA perigee times nicely and further confirming the match.)