Schiaparelli's fuel tanks are filled
2 February 2016The hazardous task of fuelling Schiaparelli, the ExoMars 2016 entry, descent, and landing demonstrator module, has been safely completed at Baikonur. The module now has sufficient fuel on board to power the thrusters it will use while descending through the Martian atmosphere in October this year.
|Operators in protective gear while fuelling Schiaparelli. Credit: ESA -T. Walloschek|
The 600 kg Schiaparelli module is equipped with nine thrusters, clustered in groups of three. These will be activated about 1.3 km above the surface of Mars to slow the spacecraft down to less than 2 km/h when about 2m above the surface. At this point, the thrusters will be switched off and the module will drop to the ground.
The thrusters are powered by hydrazine, and the hazardous task of filling the fuel tanks with this toxic fuel and the successive pressurisation of the propellant tanks to launch pressure was completed on Sunday evening, by a dedicated team from Thales Alenia France who are in Baikonur specifically to take care of fuelling the module.
There are three 17.5 litre tanks on Schiaparelli. Each of these was filled with about 15 kg of hydrazine. But hydrazine on its own is not sufficient and the spacecraft also needs helium for its pressure regulated propulsion system to function.
A high-pressure helium tank on the module had been filled with 15.6 litres of helium and brought to flight pressure (at approximately 170 bar pressure) before the hydrazine fuelling. This helium is used to pressurise the propellant tanks and bring the propulsion system to the correct operating pressure.
While on the ground, closed pyro valves prevent the propellant from reaching the thrusters. Once in space, when the thrusters are eventually needed, the pressurised helium will be released into the propellant tanks to "push" the hydrazine into the propellant feed lines and towards the combustion chambers where the fuel will be ignited and forced out of the thruster nozzles. That process relies inherently on the helium pressure upstream of the hydrazine, which is maintained, via a pressure regulator, to the required operating pressure.
|Supplies for fuelling. Credit: ESA - B. Bethge|
Fuelling operations began on Thursday when Schiaparelli was moved from the clean tent area of the cleanroom, where it had been for the other preparatory activities, into the dedicated fuelling area. Preparations and safety checks were carried out on Friday and the actual hydrazine fuelling was done on Saturday, taking about two hours to complete the fuel transfer. On Sunday, the system was brought up to launch pressure, and by Sunday evening Schiaparelli could be declared to be fully fuelled and was ready to be brought back to the main cleanroom.
The fuelling team will be busy for another few days as they take care of decontaminating the fuelling equipment so that it can be transported back to Cannes.
|An operator in protective gear while working near Schiaparelli. Credit: Thales Alenia Space/Imag[IN]|
Now that Schiaparelli has been fuelled additional safety precautions will be implemented for all activities that are carried out in the vicinity of the module.
In practice, the presence of the hazardous fuel onboard Schiaparelli means that anyone working close by will need to carry a gas mask and wear an anti-acid protective suit. All personnel working in the cleanroom have had special safety training for what to do in case of a declared emergency, and as an additional safety measure, hydrazine detectors will be placed around the spacecraft.