ESA Science & Technology - Herschel spacecraft ready for fuelling

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.

Weighing the Herschel spacecraft in the S1B building. Credit: ESA
Close-up of the mass measurement device. Credit: ESA	Weighing the Herschel spacecraft  in the S1B building. Credit: ESA

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 CCU containing the Herschel spacecraft detaches from the airlock at S1B  ... Credit: ESA	... and starts the journey to S5. Credit: ESA
The CCU travelled the 5 km from S1 to S5 in convoy. (Image credits: top left and right and lower left: Credit: ESA; lower right: Credit: ESA-CNES-ARIANESPACE/Optique vidéo du CSG - L. Mira)

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.

The CCU arrives at S5 late in the afternoon of 27 March and completes the docking with the S5 airlock. Credit: ESA

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.

	The Herschel spacecraft in the S5B building ready for hydrazine fuelling. The platforms (seen in the photograph to the left) will be used at a later stage for Helium filling. Credit: ESA