BeppoSAX resumes operation without gyroscopes
Thanks to sophisticated gyroless attitude control software, developed
by Alenia Spazio, ASI’s BeppoSAX astronomical satellite is operating
again even without gyroscopes.
On October 29, 2001, the Italian Space Agency’s BeppoSAX (Satellite for
X-ray Astronomy) satellite recommenced scientific observation thanks to
new attitude control software, named Extended Science Modes 2 (ESM2),
designed and developed by Alenia Spazio, a Finmeccanica company.
The initial design of the attitude control subsystem (AOCS) of the
BeppoSAX astronomical satellite, built by Alenia Spazio for the Italian
Space Agency (ASI) and orbited on April 30, 1996, foresaw the use of
three permanently active gyroscopes and three reserve ones.
However, the limited life of these units, already demonstrated on other
satellites, led Alenia Spazio to design and develop software that
guaranteed the scientific pointing, using only one gyroscope (ESM1).
This software was used up to the degrading of the last gyroscope, in
September of this year, necessitating a gyroless reconfiguration of
the attitude control software.
Gyroless pointing techniques have already been adopted on other
satellites (Rosat, Soho and, most recently, ERS2), but in missions
with different characteristics to BeppoSAX that requires greater
complexity and autonomy to manoeuvre. The satellite, managed from
Earth and visible to the Malindi station in Kenya for only 10 minutes
per orbit, is able to carry out a variety of programmed pointing to
sources indicated by the scientists. Furthermore, it can detect Gamma
Ray Bursts in the Universe, rapidly pointing its instruments in the
direction of the burst to study its passage through the X-band.
Alenia Spazio’s new software, ESM2, principally uses the three on-board
Star Tracker sensors and orientates the satellite through the reaction
wheels. It can maintain the scientific pointing using only one star
sensor when the other two are blocked by the Earth. In the case of a
contemporary blocking of all three star sensors, ESM2 uses the Sun
sensor and the magnetometer (much less accurate), automatically
reacquiring an inertial attitude when one star tracker becomes
available again, calculating and correcting the error through small
redirections guided by a mini-star catalogue loaded on board.
The manoeuvres are made around the satellite’s axis using one star
sensor tracking two stars, or around any axis using the Sun sensor
and the magnetometer.
The new software works using algorithms based on robust logic to manage
the sensors and auxiliary functions such as an orbital propagator and
a model of the Earth’s magnetic field.
The flight test of ESM2 has proved that it can keep the BeppoSAX
mission profile unchanged, meeting all the pointing requirements of
the scientific instruments and carrying out a wide range of manoeuvres
to reach the sources to be observed: another success for this Alenia
Spazio-developed satellite whose use continues to be sought by
scientists around the world.
[NOTE: An image supporting this release is available at
http://www.alespazio.it/news/85.jpg (92KB)]
