http://www.skyandtelescope.com.au 13Thr ough Space
AGILE’s happy accident
But spinning can provide much more than stability, as
the experience of the Italian AGILE satellite team so
vividly shows. Launched in 2007, Astrorivelatore Gamma
a Immagini Leggero (AGILE) is a wide-field gamma-ray
instrument that explores cosmic high-energy physics. The
initial aim was for the telescope to point in one direction for
a couple of weeks and then move on to another area until it
covered a large swath of sky. This worked well until the end of
2009, when the team hit a snag: The telescope’s inertia wheelthat kep the platform stable, malfunctioned.
Automatically AGILE switched into a safe mode: The
spacecraft swivelled so that its solar panels constinuously
faced the Sun, while the rest of the craft started spinning very
slowly (one revolution every 7 minutes) at right angles to the
direction of the Sun.
“It created a lot of debate,” recalls AGILE Principal
Investigator Marco Tavani (National Institute for Astrophysics,
Rome). “Some engineers said, ‘It’s finished, it’s the end of
AGILE,’ but others said, ‘No, it’s the exact opposite’.”by Benjamin Skuse TWIRLING TELESCOPES