Tag Archives: radar

Chandrayaan-1: the Lost and Found Lunar Orbiter

This is pretty cool. ┬á­čśë

On October 22, 2008, India joined the elite group of nations which have successfully sent spacecraft to orbit the Moon. ┬áThe mission was successful, conducting joint operations with NASA’s Lunar Reconnaissance Orbiter and LCROSS impactor, deploying an impactor of its own to help search for lunar ice (and making India only the fourth country to place its flag upon the Moon), and providing the first definitive proof of water ice in the lunar soil. ┬áThe mission was cut short, however, when the spacecraft abruptly stopped responding to ground commands on August 29, 2009. ┬áThe cause of the failure was never determined, but it had been experiencing issues in several systems, including the star tracker that keeps its antenna aligned with Earth.

Like other deep space spacecraft, the moment it stopped transmitting it became impossible to track from Earth — the Moon is much too far away to track such small objects (in Chandrayaan-1’s case, about 1.5 meters by 1.5 meters) by radar.

Or is it?

As international governmental and private space programs grow at an astonishing rate, it has become clear that space traffic will increasingly become a problem not just in Low Earth Orbit (LEO) and in the immensely valuable Geostationary Earth Orbit (GEO, the province of most communications satellites) but in deep space as well. ┬áThe recent move of the MAVEN spacecraft to dodge Mars’ innermost moon, Phobos, also underscores the hazards. ┬áSo JPL conducted a study to see whether lunar spacecraft actually┬ácould be tracked from Earth. And guess what — they can!

JPL’s first target was LRO, because it’s an active spacecraft and therefore its real position is known with exquisite precision. ┬áHaving located it with ground-based radar, the team moved on to something trickier: the Chandrayaan-1 spacecraft. ┬áLunar spacecraft are difficult, because the Moon is so lumpy that a) dead spacecraft don’t stay long unless their orbits are fairly high, and b) orbits can be difficult to predict over long timescales. ┬áNevertheless, they found it. ┬áChandrayaan-1 is dead, but not gone, and certainly not forgotten.


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Close Encounter of the Binary Kind

No, I don’t mean visits from alien computers. ┬á­čśë ┬áI mean that the first radar images of asteroid┬á2004 BL86, which flew by Earth earlier today, are in — and it’s got a companion. ┬á(Okay, so the moon isn’t big enough to call this a binary asteroid, but otherwise I was gonna have to make a “that’s no moon” joke, okay? ­čśŤ ) ┬áThis animation is composed of 20 individual images taken by the┬á70-meter “Mars” telescope at NASA’s Goldstone facility in California. ┬áRadar images are a bit like ultrasound pictures — the camera is actually “above” the asteroid in this picture, illuminating it with radio waves so a computer can reconstruct an image out of the reflected radio signals.



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