September 24, 2004

Demeter debuts science mission

Launched on 29 June, the Demeter microsatellite (Detection of Electro Magnetic Emissions Transmitted from Earthquake Regions) is now on orbit and operational. But before embarking on its mission to study electromagnetic disturbances in the ionosphere associated with earthquakes and tremors, the satellite first had to undergo in-orbit checkout. Throughout the summer, the project team and scientists minded the first newborn in the Myriade series to monitor its flight performance.
20 September 2004

One month of checks, tests and calibrations

The month-long in-orbit checkout phase began for Demeter on 29 June, as soon as it reached orbit. A few hours after separating from the launcher and deploying its solar array, the satellite established contact with ground stations and initial data confirmed it was in great shape.
Payload checkout operations began early in July. This phase involved verifying the onboard computer, telemetry system, science data acquisition and processing unit, and the magnetic and electric sensors. A key step keenly awaited by the project team was successfully accomplished when the five booms supporting the magnetic and electric sensors were deployed.
These operations were complicated by the fact that Demeter was out of range of ground control stations at the time.
The remaining tasks were to check the quality of science measurements and the effectiveness of electromagnetic shielding, to ensure that satellite equipment does not interfere with natural waves recorded by instruments.

After this battery of tests, the Demeter mission was ready to begin science operations in August. Two minor hitches—quickly corrected—interrupted operations for a few days, one requiring a new version of the flight software to be uploaded.
Did you know?
Obviously, visual inspection of a satellite once it is on orbit at an altitude of over 700 km is impossible. So, how can we check that its instruments have deployed correctly? The answer is indirect measurements. For Demeter, thermal engineers provided the first clue: the sudden variation in temperature of the magnetic sensor boom indicated it had moved away from the body of the satellite, confirming it had deployed.

First science data coming in

The science instruments have been operating for a few weeks now and the satellite has already obtained some unexpected data. Demeter’s ability to record signals all along its orbit has revealed natural emissions of previously unknown extent. For example, it has recorded quasi-periodic “whistler”-type waves generated in both hemispheres and propagating as far as the equator. These waves have been observed on several consecutive orbits, confirming their temporal and spatial extent.

It is still much too early to say whether Demeter will help scientists to reveal the inner rumblings of our planet. The satellite has already observed almost at nadir more than 10 tremors of a magnitude of more than 5, and a cursory analysis of the data has not uncovered anything in particular. Scientists will need to acquire a series of measurements and study phenomena statistically before drawing conclusions.

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