As the overall mission and system prime SpaceTech established a technological baseline both, in terms of mission implementation and satellite design, for the first German servicing mission DEOS.
Main goals of the DEOS mission
- rendezvous with and berthing of a non-cooperative and tumbling spacecraft by means of a manipulator system accommodated on a servicing satellite
- docking of the spacecraft via a dedicated docking device
- servicing tasks in the coupled configuration as well as the controlled de-orbiting / re-entry of the spacecraft’s coupled configuration in the earth’s atmosphere at the end of the mission
|DEOS mission phases||DEOS communication concept|
In a Phase A contract to the German Aerospace Center DLR and leading a team of German small enterprises and university institutes, SpaceTech demonstrated the feasibility of the mission by establishing a concept for the different flight manoeuvres, including far and close range rendezvous as well as fly-around manoeuvres, by defining a realistic experiment program for the one year mission under consideration of environmental conditions and by providing an initial spacecraft design for the servicing as well as the client spacecraft.
In the Phase B, again in a direct contract to DLR, SpaceTech was responsible for the development of the client spacecraft. Furthermore, in subcontracts to OHB System and Kayser-Threde, SpaceTech was responsible for the launcher, the berthing / docking mechanism and the software of the automation and robotics instrument control unit.
DEOS Phase A
In the context of the Phase A study performed by SpaceTech GmbH, the user needs were defined in the functional specification, a concept for the implementation was traded, elaborated and detailed into a technical baseline design, and, last but not least, a realistic mission scenario for the experimental program was worked out. Using advanced simulation tools, the feasibility of the DEOS mission was demonstrated, as well.
DEOS space segment
The DEOS space segment consists of a Servicer and a Client spacecraft:
- The Client spacecraft simulates the multitude of characteristics of a spacecraft in need of service
- The Servicer tasks comprise constellation flight, rendezvous and fly-around, docking, berthing and in-orbit servicing
- The ground segment consists of a primary ground station and the Mission Control Centre
During critical mission phases (LEOP, proximity experiments) the primary ground station is temporarily amended by an adequate supplementary ground station network. Each spacecraft maintains a direct link to ground.
Furthermore the Servicer is able to receive the Client telemetry data for board-autonomous mission supervision purposes. Additional communication via geostationary relay satellites and their operating ground stations may be utilized depending on the availability of such system.
The following experiments will be performed where in general the complexity of the experiment execution is required to be stepwise increased over the mission period:
- Far formation flight between Servicer and Client including the identification of the dynamic parameters of the individual spacecraft
- Rendezvous manoeuvres consisting of approach manoeuvres of the Servicer to the non-cooperative Client, departing manoeuvres of the Servicer from the non-cooperative Client and fly-around and inspection of the non-cooperative Client by the Servicer
- Berthing of the non-cooperative Client by the Servicer’s manipulator system (see Figure 2) under different environmental and operational conditions as well as different attitude states of the Client (three axes stabilized, spinning and tumbling), as well as experiments in a dynamically coupled configuration controlled by the manipulator system under different operational conditions
- Docking of the Servicer at the cooperative Client under different operational environments
- Flight manoeuvres in a rigidly coupled configuration including attitude manoeuvres to identify the dynamic parameters of the rigidly coupled configuration as well as standard attitude and orbit manoeuvres
- On-orbit servicing tasks such as refueling and mounting of mechanical / electrical devices with the two spacecraft rigidly coupled via a mechanism different from the manipulator arm
- De-orbiting of the configuration rigidly coupled by the manipulator arm, executed as a purposive re-entry within a given re-entry corridor
Both spacecraft are to be injected together into the initial low Earth near polar orbit on the same launcher. The initial orbit altitude will be stepwise decreased during the planned one year orbit lifetime in order to increase the operational complexity caused by reduced contact time to the communication network. The near polar inclination of the orbit offers variable illumination conditions for the experiments over the life time.
The phase A of DEOS has been performed on behalf of the Agency of the German Aerospace Center funded by the Federal Ministry of Economy and Technology, funding code 50 RA 0802.
A German version of the information of this page is available at TIB Hannover.
DEOS Phase B
In phase B of DEOS a contract has been awarded by DLR agency to SpaceTech GmbH to design the platform for the demonstrator target spacecraft (Client).
The Client is executing different attitude manoeuvres to simulate a satellite being out of service, starting from an earth-oriented attitude mode at the beginning to a spinning and at least tumbling attitude behaviour increasing the complexity of the experimental program.
Within the experiments berthing operations by a manipulator system of the approaching Servicer spacecraft and docking will be executed. In the coupled configuration fixed by the manipulator system the Client is executing orbit manoeuvres for lowering the orbit altitude during the planned one year in-orbit period and will terminate the mission by a controlled atmospheric re-entry of the coupled configuration of Client and Servicer over the South Pacific.
The Client consists of a satellite platform and the on-orbit servicing payload. The platform equipment comprises the on-board computer, power control and distribution unit, two Li-Ion batteries, magnetometers, magnetorquers, gyroscopes, a coarse-Earth/Sun sensor, GPS system, a star camera with two camera heads, a S-band communication system, a cold gas (nitrogen) propulsion system for attitude control and a hydrazine monopropellant propulsion system for orbit manoeuvres. All platform equipment is redundant. For the power generation the satellite's circumferential surfaces are covered with GaAs triple junction solar cells. The accommodation of the equipment is shown in the following figure.
The payload of the Client consists of the passive part of the docking/berthing mechanism and the on-orbit servicing elements, a camera system and a refuelling demonstration system.
The phase B Client contract of DEOS was performed on behalf of the Agency of the German Aerospace Center funded by the Federal Ministry of Economy and Technology, funding code 50 RA 0922.. The responsibility for the overall mission, the Servicer spacecraft, the robotic system and GNC were contracted separately to OHB-System AG, Astrium GmbH and Kayser-Threde GmbH. A German version of the information of this page is available at TIB Hannover.