Purging sucesfull

Purging the low pressure branch of the Attitude and Orbit Control System (AOCS) is a nominal operation. It is made necessary by the CryoSat-2 AOCS design to prevent a pressure build up in the low pressure branch which is not desirable for several reasons. The pressure build up is caused by the unavoidable leak of the mini pressure regulator between the High Pressure and the Low Pressure branches of the AOCS. This purging operation is planned to be done regularly once CryoSat-2 will be in Orbit. Due to the unexpected storage period duration, since the tank has been fully pressurized, it was necessary to perform the same purging operation on the ground today.

The snapshot below shows the Pressures, before the purging:

• in the High Pressure Branches A and B respectively HPT-A=267,1 and HPT-B=267,6 Bars
• in the Low Pressure Branch A and B respectively LPT-A =3,6 and LPT -B=4 Bars.

The procedure says that the purging needs to be done when the Pressure in the Low Pressure Branch is above 3,5 Bars. Therefore Low Pressure Branches A and B have to be purged today.

The short movie below, shot on the Control Ground System Screen, shows in real time the purging of the Low Pressure Branch B by mean of thruster activation (OCT B1) for 10 seconds. The pressure drops from 4 to 2,7 Bars (unfortunately, due to movie conversion, the display of LPT-B Pressure is hardly readable, but the appearing and disappearing green rectangle shows the 10 seconds thruster activation that causes this pressure drop)

1 hour later, the pressure in branches A and B stabilizes and the final measurements can be recorded (LPT-A and B = 2,9 bars).

Purging successful!
Let's only wish now that next time, this operation will be done not on the ground,...but in space :-)

Note: This activity was performed by Gehrard from ASTRIUM, arrived at Baikonur on Friday 12/3/2010. We are therefor, as from this date, a team of 2 to babysit Cryosat-2.