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Nicodemus

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Spacecraft Velocity Anomolies [Feb. 29th, 2008|11:29 am]
Nicodemus
We've known about the unaccounted acceleration of crafts moving through deep space for a while now. It's been given the name Pioneer Anomaly since it was first seen in the tracking data from Pioneer 10 and 11.

In essence, the craft are not traveling along the trajectories predicted. In fact, they are receeding slightly "slower" (relatively speaking) than they should be; the magnitude of the observed difference is increasing, indicating that there's some sun-ward acceleration which, although very small, cannot be accounted for.

There are many possible explanations without having to revise gravitational physics. Most people put it down to either a forgotten detail of Pioneer spacecraft design (e.g. long-term outgassing) or systemic problems in how data was collected and recorded (on varying computer hardware over decades). But it remained one of the great mysteries of astrophysics.

Now it looks like the mystery has deepened! The NEAR spacecraft was launched in '96 to visit the asteroid Eros. Recent observations show that the crafts speed is off by 13 mm/sec (measured with a precision of 0.1 mm/sec). At first blush, it seems that we have an observation of the Pioneer Anomaly closer to home on a different type of spacecraft. Other mission trajectories are being studied. We might finally uncover some more clues to this puzzle!

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but rather, 'Hmm, that's funny...'" --Isaac Asimov
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[User Picture]From: yasha_taur
2008-03-01 05:36 am (UTC)
Ummmm...... NEAR 'landed' on Eros. It was not designed for a real landing, but they did it anyways. And I am pretty sure that they have not had any radio contact with NEAR since shortly after the landing.....

So how are they determining this?
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[User Picture]From: nicodemusrat
2008-03-01 06:28 pm (UTC)
That's true... It could be that this is recent analysis of the data? (Gotta keep those grad students busy somehow!) Article doesn't make it clear.
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