Launch and Early Operations of the first in-space demonstration of a green propulsion system
The Prisma mission is a unique opportunity to demonstrate the novel “High Performance Green Propulsion” HPGP technology in space, and thus take a significant step to towards its use in future space applications. The HPGP propulsion system is used both for providing the required delta-v for the Prisma main satellite manoeuvres and as an experiment with the objective to demonstrate performance in space. Delta-v is nominally generated in an autonomous and combined operation of the HPGP and Hydrazine propulsion systems while the performance measurements are performed with one propulsion system at the time.
 
The HPGP propulsion system uses the first “Green” monopropellant qualified for space flight, which is the ADN-based LMP-103S.

HPGP propulsion system
The Prisma HPGP system consists of one diaphragm-type propellant tank with a capacity of 5.5 kg (i.e. 4.5 L) of propellant, two service valves, one pressure transducer, one system filter, one isolation latch valve and two 1 N monopropellant thrusters, see figure 1.



 
Figure 1. 1 N HPGP Thruster during test
 

The hydraulic schematic is shown in figure 2.

 
Figure 2. The HPGP Hydraulic Schematic

The system operates in blow-down mode, meaning that the feed pressure decreases proportional to the amount of consumed propellant. The nominal Beginning of Life (BOL) feed pressure is 1.85 MPa at 20 ˚C. With a blow-down ratio of 3.7:1, the feed pressure will decrease to 0.5 MPa when all propellant is consumed. The thrust will due to the change of feed pressure decrease from its beginning of life from nominally 0.9 N to 0.27 N.
 
The propellant and the pressurant gas are stored in the tank and are separated by means of a diaphragm. The pressurant (helium) acts on the flexible diaphragm and pushes the propellant via the system filter to the thruster propellant flow control valve.
 
The thruster requires preheating prior to firing. When the firing command is given, the series redundant propellant Flow Control Valve (FCV) opens and enables the propellant to enter into the thrust chamber. The propellant decomposes and ignites in the pre-heated reactor bed, thus generating hot gases and thereby thrust.
 
The pressure transducer and tank temperature sensor are utilized for propellant gauging.


Figure 3. The HPGP Propulsion System Layout

The planned operations for the HPGP system are shown below.

Figure 4. The HPGP Propulsion System Layout
 
The operational modes for HPGP 1 are summarized in figure 4.