GIOVE-B spacecraft in good health

April 30, 2008
Artist's impression of GIOVE-B in orbit
Artist's impression of GIOVE-B in orbit. Credits: ESA

A second test satellite for Galileo, Europe's rival to the US Global Positioning System, is "in good health" despite a hiccup that emerged after it was placed in orbit last Sunday, the European Space Agency said on Wednesday.

After its successful launch by a Soyuz Rocket from Baiknour on 27 April and accurate insertion into its target orbit by the Fregat autonomous upper stage, GIOVE-B is now completing its Launch and Early Operations Phase (LEOP), which will shortly give way to the platform commissioning phase.

Platform commissioning includes the on-board verification of all primary and redundant platform subsystems, namely telemetry and telecommand, propulsion, power, thermal control, and attitude and orbit control. GIOVE-B operations are being carried out from Telespazio's Fucino Space Centre in Italy.

Once the spacecraft platform has been commissioned, switch-on of the various payload elements can begin. First signal transmission is anticipated in the coming days.

Charging the batteries

Since the spacecraft had been running on battery power from just before liftoff - throughout the lengthy series of manoeuvres performed by Fregat to reach the intended orbit - the first tasks after separation from Fregat were to deploy the solar arrays and achieve Sun-pointing, so that battery charging could begin.

The first-choice method to turn the spacecraft for Sun-pointing is to use the reaction wheels. GIOVE-B is equipped with four gyroscope-like wheels driven by brushless electric motors. Altering the speed of rotation of these wheels allows the satellite to be rotated in space.

Use of the reaction wheels for initial pointing is the first choice because, once they are operational, the supply of electricity from the solar arrays is essentially unlimited. However, due to the battery discharge that occurred during pre-orbital flight, the spacecraft operations manual only allows a restricted time for these manoeuvres to be accomplished.

Attitude and orbit control

GIOVE-B's reaction wheels were slow to respond and stable Sun-pointing was not achieved within the specified time period. As a consequence, around five hours after launch it was decided to put the satellite into safe mode, and Sun-pointing was achieved using small engines known as thrusters.

The initial underperformance of the reaction wheels was found to have occurred due to a mismatch between the on-board avionics software and the reaction wheel calibration data. This has now been corrected by the uploading of a software patch to the spacecraft, leading to nominal performance.

Use of the thrusters is the second-choice method because one of the factors determining the operational life of GIOVE-B is the amount of propellant that the spacecraft carries. The thrusters are used for orbital station-keeping and conservation of propellant is important to maximise the lifetime of the spacecraft. Once the propellant is nearly exhausted, the thrusters' final task is to lift the spacecraft into a 'graveyard' orbit at the end of its mission - to free the orbit for the operational Galileo constellation.

Payload switch-on

Once the GIOVE-B spacecraft platform is fully commissioned, the navigation payload can be switched on. The rubidium and passive hydrogen maser clocks will be started first, followed by the navigation signal generator.

The final units to be turned on will be the transmit chain consisting of L-band solid-state power amplifiers that broadcast the Galileo signals to the Earth. First signal transmission is anticipated in the coming days and will be received and calibrated by In-Orbit Test (IOT) facilities deployed at ESA's ground station in Redu (Belgium) and at Chilbolton Observatory in the UK.

Source: ESA

Explore further: Technology-testing CubeSat hitchhiker on today's HTV launch

Related Stories

Technology-testing CubeSat hitchhiker on today's HTV launch

August 19, 2015

Today's HTV supply launch from Japan to the International Space Station also marks the arrival in orbit of one of ESA's smallest missions yet – a CubeSat which will test miniaturised technologies for space, set to be followed ...

Exoplanets 20/20: Looking back to the future

July 31, 2015

Geoff Marcy remembers the hair standing up on the back of his neck. Paul Butler remembers being dead tired. The two men had just made history: the first confirmation of a planet orbiting another star.

Mars Odyssey orbiter out of precautionary 'safe mode'

June 20, 2012

(Phys.org) -- NASA's Mars Odyssey orbiter has been taken out of a protective status called safe mode. Remaining steps toward resuming all normal spacecraft activities will probably be completed by next week.

What are extrasolar planets?

May 25, 2015

For countless generations, human beings have looked out at the night sky and wondered if they were alone in the universe. With the discovery of other planets in our solar system, the true extent of the Milky Way galaxy, and ...

On Pi Day, how scientists use this number

March 13, 2015

If you like numbers, you will love March 14, 2015. When written as a numerical date, it's 3/14/15, corresponding to the first six digits of pi (3.1415)—a once-in-a-century coincidence! Pi Day, which would have been the ...

Recommended for you

Image: Hubble sees a youthful cluster

August 31, 2015

Shown here in a new image taken with the Advanced Camera for Surveys (ACS) on board the NASA/ESA Hubble Space Telescope is the globular cluster NGC 1783. This is one of the biggest globular clusters in the Large Magellanic ...

New Horizons team selects potential Kuiper Belt flyby target

August 29, 2015

NASA has selected the potential next destination for the New Horizons mission to visit after its historic July 14 flyby of the Pluto system. The destination is a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits ...

Earth's extremes point the way to extraterrestrial life

August 26, 2015

Bizarre creatures that go years without water. Others that can survive the vacuum of open space. Some of the most unusual organisms found on Earth provide insights for Washington State University planetary scientist Dirk ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.