Full tank , please!...

1,5 billion kilometers is roughly the distance Cryosat-2 will fly over its mission i.e. 3,5 years nominal and 2 years more (nice to have but not a mission requirement) at 717 kms altitude above the Earth with 16 orbits a day.

After the end of the rocket push and separation, the spacecraft will need energy to perform its maneuvers during the rest of the mission.

Pressurized Nitrogen is the CryoSat-2 "propellant' used by the Attitude and Orbit Control Subsystem (AOCS). This N2 gas is stored in a pressurized tank at ca 280 bars. After the tank, pressure is reduced to few bars and N2 flow will be ejected into space trough Attitude and Orbit thrusters. Short gas blows through the Attitude Control Thrusters, positioned on the 3 axes of the spacecraft, enable fine moves, whilst Orbit Control Thrusters on the X axis only allow maneuvers and orbit change.

For CryoSat-2, it has been calculated that 36,5 kgs (+/- 0,3) of Nitrogen will suffice to perform the (extended) mission.

Tank loading is then a very important step to prepare the spacecraft for the mission as well as to thoroughly check the tightness of all the "plumbing pipes and devices" of the AOCS subsystem.

Here is the set up for the tank loading activity:


On the right hand side, 2 sets of compressed Nitrogen bottles at 200 bars.

Note that the operators are not in the same room as the spacecraft for safety reasons. They are also protected by a removable protective wall opposite to the door (in brown) and close to the spacecraft in the next room.

Below, a close up view on:
- the computer which is used for Pressure and Temperature monitoring
- and on the left, the "Maximator'' that will "push" the Nitrogen gas to the spacecraft tank when the tank pressure will reached 200 bars (i.e. the same pressure of the compressed nitrogen in the bottles).



The screen snapshot below was taken just before the end of the tank loading activity and proves the successful performance of the activity.
As we can read:
-36,75kg* of nitrogen have been loaded and a final tank pressure of ca 279 bars.

* T3 and T4 Temperatures had to be balanced before the exact quantity of N2 gas can be calculated and the last Nitrogen top up can be made in order to complete the loading.



This activity was successfully completed this morning, Cryosat-2 gets then closer to its journey to space.