The multi-disciplinary character at Onera
CENTOR
Designs for Reusable Orbital Transfer Vehicles
Context, location and objectives
The Centor project (Designs for Reusable Orbital Transfer Vehicles) is connected with the theme of designing future space systems. The project's aim is to prepare tools and a methodology for designing Orbital Transfer Vehicles (also called OTV) capable of executing new types of missions requiring several high amplitude orbital transfers. The different groups of missions that can be considered are as follows:
- Maintenance missions (called OOS, for On-Orbit Servicing): refuelling, repairs, replacing sub-systems.
- Reconfiguring orbital systems (modification of mission orbit of small satellites, maintenance of a constellation).
- Removing space debris from orbit or placing it in a disposal orbit (limited, as fully cleaning 10,000 pieces of debris of more than 10 cm is unrealistic).
- Identifying and cataloguing satellites and debris in orbit.
- Transferring a payload to a high-energy orbit (LEO, MEO), in addition to a launch system with access to the lower orbit only.
Aero-assistance is a technology being studied as priority. It uses atmospheric forces (drag and lift) to modify the vehicle's orbit without using fuel. This technique can be used to reduce the propulsion requirements by 25 to 30 % of a two-way transfer between a low equatorial orbit and the geostationary orbit.
The project includes two types of activities:
- Development of tools, models and databases in various disciplines pertaining to design of space vehicles.
- Exploration of multi-disciplinary design methodologies that integrate these various tools. Two application scenarios were studied: a vehicle entirely propelled by cryogenic propulsion and an aero-assisted vehicle also using cryogenic propulsion.
Contribution of work
The Centor work has been used to develop capabilities in Onera in various disciplines needed for studying orbital vehicles and also atmospheric re-entry vehicles (because the required disciplines are common to the aero-assisted orbital vehicles). During the project, several tools and models were developed in the following disciplines:
- Mission analysis.
- Trajectory optimization.
- Guidance/piloting.
- Vehicle architecture design.
- Mass budget assessment and dimensioning of various sub-systems.
- Propulsion system.
- Thermal control.
- Aerothermodynamics.
- Space environment.
- HT materials.
Some tools show real progress in relation to previous tools, such as the FAST aerothermodynamics tool (Fast Aerothermodynamics Solver for Trans-atmospheric vehicle/systems) that is used to estimate the thermal flows and aerothermodynamic coefficients of an aero-assisted (or re-entry) vehicle much faster than standard tools and with satisfactory precision.
Furthermore, the work done by Centor, represents real experience in multi-disciplinary optimization (MDO) applied to a space vehicle. This experience is complementary to Doom PRF (focused on methodological aspects of the MDO), which has applications in the aeronautics and missile fields. This work has especially been used to explore the possibilities offered by aero-assistance and to become familiar with OTV performances having large maneuvering capabilities. The Centor multi-disciplinary design work has provided two preliminary sizings of vehicles for a space debris inspection/identification mission of a space debris in the optical domain (observation from a few kilometers with a 100 kg telescope).
Prospects The tools and models developed in Centor, as well as the multi-disciplinary design experience may be reused and developed for later work on future orbital systems (or re-entry vehicles). There are numerous possibilities for new missions that can be executed by orbital vehicles. A potentially interesting mission identified during the project is the use of an OTV for identifying/inspecting space debris. Such a vehicle may form the orbital component of a space surveillance system.
In the medium term, a possible development could be an in-flight demonstration of aero-assisted vehicle (in Earth orbit).
Some results
"All-propulsive" OTV with cryogenic propulsion
Aero-assisted OTV with cryogenic propulsion
Orbital transfer by aerobraking
Distribution of heat flow on the heat shield, calculated with the ATD FAST platform
Key words
Space transport, orbital transfer, orbital systems, MDO, multi-disciplinary optimization (MDO)
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