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Satnews Daily
March 20th, 2009

GOCE Going Great Guns

GOCE liftoff After liftoff 17 March, ESA's GOCE spacecraft is performing very well, having achieved an extremely accurate injection altitude of 283.5 km, just 1.5 km lower than planned.

The Mission Control Team is now working round-the-clock shifts to implement a series of critical check-out procedures and are now conducting the complex and critical Launch and Early Operations Phase (LEOP) for GOCE, which was successfully launched into a polar orbit at 15:21:13 CET on a Rockot launcher. Following the liftoff, separation of GOCE from the launcher and first acquisition of signals from the spacecraft were confirmed by Flight Operations Director Pier Paolo Emanuelli during a long day working with the Mission Control Team in the Main Control Room from two hours before until 10 hours after launch.

GOCE satellite (from animation) During the three-day LEOP, on-board flight control systems will be thoroughly checked-out and the spacecraft brought step-wise through several modes of operation to achieve a stable, fully functioning status. Communications with the Gravity field and steady-state Ocean Circulation Explorer (GOCE) spacecraft during LEOP are being enhanced by a network of four ground tracking stations, which are providing additional communications capacity. The spacecraft is currently in Coarse Pointing Mode, the most basic level of functioning, which was entered immediately after separation from the launcher. Current work includes preparing the spacecraft to switch to Extended Coarse Pointing Mode (ECPM), which enables a higher level of autonomous flight control. ECPM also includes orienting the satellite so as to minimise the cross-section exposed to the atmosphere, thus limiting altitude decay. As planned, GOCE is orbiting in free flight and the electric-ion propulsion has not yet been switched on.

GOCE Flight Operations Center team in main control Another crucial LEOP step is calibrating the on-board magnetometers, which enable full attitude control to be established; this was done overnight. Later, the team will issue commands to switch on the Satellite-to-Satellite Tracking Instrument — a state-of-the-art GPS (Global Positioning Satellite) receiver on board GOCE that has been specially adapted to operate in a low-Earth orbit environment. As well as supporting scientific data analysis, the SSTI will also provide real-time navigation data to the on-board orbit control system. ESA's Space Operations Centre (ESOC) Flight Dynamics team is also providing round-the-clock support, and will perform a series of calculations to enable the spacecraft to be switched into Fine Pointing Mode. FPM is a higher level of functioning that can be maintained indefinitely while the on-board scientific instruments are commissioned. This is planned for 18:00 CET on March 19th. Once GOCE is switched into Fine Pointing Mode tomorrow evening, and the additional ground tracking stations supporting LEOP are released (nominal communications will be provided via ESA's ESTRACK station at Kiruna, Sweden), the LEOP phase will be formally over.

(Credits: ESA + Medialab. Top—GOCE launch — Midstory — GOCE satellite — Bottom — GOCE Flight Control Team in Control Room)