PHEBUS uses a sensitive sensor in the extreme UV (55-155nm) requiring to be kept under vacuum continuously to guarantee its performance. From the manufacture of the detector to the launch, the detector was connected to a system allowing it to be kept under vacuum. An interface was provided for this purpose directly on the detector.
Two versions of the pumping system have been developed to meet different constraints.
First Pumping system: PS # 1
A first specific pumping system was designed, manufactured and tested at LATMOS to ensure this vital function after integrating the instrument into the satellite, and as long as the satellite is on the ground.
This “PS # 1” pumping system remained attached to the MPO satellite for more than 3 years (from late April 2015 to late August 2018), almost permanently, guaranteeing the performance of the EUV detector. with a mass of 13kg, it is composed of a couple of primary and turbo-molecular pumps. Two vacuum gauges allow to measure the vacuum level in the system and a normally closed valve allows to isolate the detector in case of pressure rise (failure of pumping, power failure,…); A “Getter” pump (passive chemical pump) then takes over to ensure a correct vacuum level for a few days, until the fault is corrected.
A control bay (EGSE) allows to control and monitor the whole system.
Second Pumping System :”PS # 2″, certified “ATEX”
The last weeks of activities before the launch of the satellite were carried out as part of the Ariane 5 launch campaign in Kourou, Guyana. Due to the presence of propellant (satellites, Ariane 5), operational constraints apply in order to limit the risk of explosion. Risk areas are identified: This is called “ATEX Zone” (for “explosive atmospheres”).
Several levels of risk exist, imposing different levels of constraints. Since the first pumping system is not compatible with an ATEX environment, these constraintshave necessitated the development of a new pumping system “PS#2” whose design takes into account the risk of explosion. Like PS#1, this pumping system was designed, assembled and tested by the LATMOS and certified “ATEX” by Centrexpert with the support of the Centre National d’études Spatiales (CNES).
PS#2 is essentially passive. It uses two “Getter” pumps in parallel to keep the detector under vacuum. The pumping function therefore does not require any power supply. An ATEX vacuum gauge and 2 ATEX temperature probes are the only energized parts of the system.
Installing the Pumping group PS # 2
PS#2 was installed on the satellite and connected to the EUV detector in Kourou at the end of August 2018, a few days before the entry of the satellites into the ATEX zone and their filling in propellant.
Definitive disconnection of the pumping unit
PS#2 was permanently disconnected from PHEBUS on October 10, 2018. The removal of the pump allowed the installation of the Parking Bracket (protection of the entrance of the PHEBUS baffle) and the thermal cover of MPO around the PHEBUS baffle to be finalized.
A few hours later, the cap was installed on Ariane 5 banning any access to the satellite. On October 20, Bepi was in space!