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Emerging Technology from the arXiv

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GPS Satellites Could Solve Flyby Anomaly

Spacecraft flying past Earth undergo a puzzling change in speed and nobody knows why. The next generation of navigation satellites could help, say scientists

  • September 19, 2011

Now that the Pioneer anomaly has been more or less laid to rest, the outstanding space-based puzzle of the moment is the flyby anomaly.

This is how the arXiv Blog described the phenomena back in 2008:

“On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.

Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.

The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.

And people finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.”

Nobody knows what causes these strange hiccups in spacecraft speed but there is no shortage of theories, some of which we’ve discussed here and here.

If scientists are ever to get to the root of this phenomenon, they need to have a way of measuring it repeatedly, unambiguously and in detail.

But flyby’s are few and far between. And even when they do occur, NASA’s Deep Space Network which monitors spacecraft from the ground is not designed to study the effect in detail.

The most serious problem is that the network cannot follow spacecraft when they are very close to Earth. This results in a gap in communications during a flyby lasting a few hours, just when the most interesting effect is happening.

As a result, the fly-by anomaly has never been caught in flagrante. Instead, it arises as the difference between the observed and expected velocity after a flyby.

Today, Orfeu Bertolami at the University of Porto in Portugal and a few buddies suggest a way out of this conundrum. They say the next generation of global navigation satellite systems ought to be able to help. These should be capable of detecting the expected change in speed of just a few millimetres per second.

These guys calculate that a microsatellite fitted with a device capable of receiving signals from any of the satellite navigation systems would cost less than $15 million. And it might be considerably less if the necessary gear was bolted onto an existing spacecraft intended for a flyby or the kind of highly elliptical orbit likely to demonstrate the anomaly .

That’s chickenfeed to most space agencies and that means we’re likely to see an attempt to measure the phenomenon in the not too distant futur..

The agency most likely to take the bait is the European Space Agency which is about to deploy a GPS rival constellation called Galileo.

If it needs a scientific mission to raise the profile of Galileo and show off its potential, it need look no further.

Ref: arxiv.org/abs/1109.2779: Probing The Flyby Anomaly With The Galileo Constellation

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