Herschel spacecraft ready for fuelling
9 April 2009Having completed all functional tests the Herschel spacecraft has been moved from the S1B building to the S5B building where the hydrazine fuelling activities will be performed. Everything is in place for fuelling to be completed this week.
On 26 March, while still in the S1B building, the Herschel spacecraft was weighed in order to record the dry mass. This measure will provide the baseline from which the total Herschel spacecraft mass at launch will be calculated once the hydrazine fuelling operation has been completed.
The spacecraft weighing involves inserting a load cell between the crane and the Herschel Vertical Lifting Device (VLD) and then performing a successive series of mass measurements: with the VLD itself, with the VLD and calibrated masses, with the VLD and the Herschel spacecraft, and finally again with the VLD and calibrated masses to achieve the best possible accuracy.
On the morning of 27 March the Herschel spacecraft was placed on top of the launch adapter (ACU) and the combined unit was loaded onto the payload transport container, the CCU, for transport to the fuelling building, S5B.
The CCU is a large transport container used to transfer spacecraft between the different satellite preparation sites (S1, S3, S5 and BAF) at CSG. It protects the spacecraft against shock and vibration, and provides a cleanroom-like environment with standard cleanroom levels of cleanliness, relative humidity and pressure.
The Herschel spacecraft was transported the 5 km distance between S1B and S5B in the CCU arriving in the afternoon of 27 March. It docked with the S5B airlock and once the cleanroom conditions had been re-established in the airlock the CCU was opened and the CCU pallet with the spacecraft on top pushed into the main fuelling hall. The Herschel spacecraft was then released from the flight adapter and lifted onto the stand to be used for the RCS fuelling.
Preliminary preparations have been made for the fuelling operations: the fuelling team has completed the mandatory safety training exercises and preparatory activities that are required prior to beginning the hazardous fuelling activities and 5 hydrazine-filled tanks have been moved to the S5 building. Everything is now in place for fuelling operations to be completed this week.