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Radar tracking is used for Earth satellites and big enough asteroids. As the FH-launched Tesla Roadster is leaving the Earth-Moon system and it is quite small object (the car + the payload adapter are much smaller than telco satellites, but the second stage is possibly still attached and is a bit bigger), my question is:

For how long (or how far from Earth) will it be picked by orbital tracking radars? Can it be significantly longer if it is specifically targetted? Could for example the Arecibo Observatory be used to pick it even in the asteroid belt or is it just too small?

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According to the JPL Horizons team (emailed to me), they expect it to be visible in sky survey telescopes through April. It will thus almost certainly continue to be tracked during that period of time. The largest telescopes can detect it until June, but it seems doubtful that someone will use one of these large telescopes to track this object, as the time is very valuable for these large telescopes.

The predictions beyond there are pretty good, but not all of the effects are being utilized to track it super accurately. My guess is that if it comes within 0.2 AU or so of Earth, it will be detected again with fairly minimal disruption in it's detection.

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We will be able to track it directly by radar for only a short time - days perhaps, but since we know the speed and trajectory with fairly high precision we will be able to locate the area of space it currently occupies indefinitely and perhaps someday track it if it comes close to Earth again. The final burn sent it into a heliocentric orbit with an apogee well beyond Mars (which is 1.55AU or about 141M miles)and into the Asteroid belt (3.2 AU or approx 291M miles).

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    $\begingroup$ It does strike me that knowing the details of size, distance, location, colour, composition etc. might make it a good target for calibrating and testing some of our more powerful telescopes. One can imagine that new deductions about other objects could be made on the back of the data. If this is so we might find it being seen more distant and more often than the simple pleasure of spotting a car in space could justify. $\endgroup$ – meesern Feb 9 '18 at 9:15
  • $\begingroup$ Just to add to this, there is a great answer to What is the current record for the farthest detection of a “dead” spacecraft? that addresses radar, and I've shown some calculations explaining that Roadster could theoretically be seen as far as about 1AU using Hubble, though that probably wouldn't be actually done, in this answer. $\endgroup$ – uhoh Feb 10 '18 at 16:48

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