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ESA satellites flying in formation
Date:12/3/2008

eers had to overcome many challenges in order to put Envisat and ERS-2 into a tandem flight configuration. For instance, in 2001 ERS-2 lost the ability to be manoeuvred in the usual way by onboard gyroscopes, navigational tools that allow mission controllers to maintain the correct position of satellites.

The operational lifetime of satellite missions is normally determined by the functioning of onboard gyroscopes. Without them, the ESA team had to work out a way of positioning the spacecraft by operating onboard sensors in a new way.

Part of their creative solution involved using a device called the Digital Earth Sensor (DES), which is designed to provide the horizon line to allow basic checks on the spacecraft's position, and analysing Doppler frequency shifts in the signals of ERS-2's radar instruments.

ERS-2, launched in 1995, and Envisat, launched in 2002, have exceeded the time they were intended to stay in orbit. Since they remain operational and continue to provide quality data about our planet, engineers are trying to use as little fuel as possible so as not to shorten their lifetimes.

"The strategy is to align the tandem start date with an Envisat manoeuvre. Therefore, there is no need to spend extra hydrazine for Envisat. For ERS, the manoeuvre to place it in tandem position is such that the satellite drifts back to its nominal orbit without additional manoeuvre after the tandem campaign," ESA Mission Planner Manager Sergio Vazzana said.


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Contact: Mariangela D'Acunto
mariangela.dacunto@esa.int
39-069-418-0856
European Space Agency
Source:Eurekalert

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