(Rose, re second link: The last two letters were missing: http://www.nasa.gov/mission_pages/gpb/index.html)

What a beautiful piece of technology.

Unfortunately, the theory met some unexpected problems in practice:

http://space.newscientist.com/article/dn...dId=space_rss20 (20 May 2008)

"The probe's data was unexpectedly noisy due to solar flares in March 2005 that interrupted the satellite's observations, as well as unexpected torques on the gyroscopes that changed their orientation, mimicking relativistic effects...The noisy data meant that GPB could not measure the effects as precisely as astronomers had by firing laser beams at mirrors left on the Moon by the Apollo astronauts."