Speaker
Description
ESA under the umbrella of the Clean Space Initiative has promoted complementary activities in view of Active Debris Removal (ADR) missions.
One of the main challenges driving the complexity of the rendezvous and capture of a debris is its rotational state. In-orbit observations of defunct satellites do not show an ideal Gravity Gradient capture, but instead large angular rates letting the target in a permanent or quasi-permanent spinning state. The prediction and estimation of the angular rates of defunct satellites to be captured is therefore crucial for the design of the chaser and to confirm the feasibility of these critical operations.
This paper shares what we have been learning over the past years about the dynamic evolution of defunct satellites in Low Earth Orbit, how complex it is and how to do this assessment properly.
Such satellite is assumed to have been prepared for Design for Removal (D4R) during its development phase and to be equipped in particular with a Magnetic Detumbling System (e.g. automatic short circuiting of Magnetic Torquers), 2D Navigation Aids including features to support ground-tracking and attitude reconstruction, 3D Navigation Aids to support precise pose and attitude determination for the last phase of the capture and a Mechanical Capture Interface to allow its capture with a robotic gripper.
Due to the complexity of the YORP effect created by Solar Radiation pressure, together with the low authority of existing Passive Magnetic Damping Systems (short-circuited Magnetic Torquers and Eddy currents), the proposed verification process to assess the long-term dynamic evolution mainly relies on extensive simulation campaigns performed on a dedicated High-Fidelity simulator.
Although simulations tackle all dynamic configurations including tumbling at low angular rates, the spinning configuration deserves special understanding. Analytical models of spin-averaged and orbit-averaged torques developed by ESA and ABSpaceConsulting are shared, covering Gravity Gradient, Solar Radiation Pressure (YORP effect), S/C Residual Magnetic Dipole, atmospheric drag, Eddy currents and Magnetic Detumbling Systems. They are very helpful to interpret the complex behaviour shown by the simulations, identify S/C driving parameters and representative initial conditions, and sweep parameters accordingly.
Guidelines related to the set-up of a representative High-Fidelity simulator and to the simulation campaigns are proposed, to avoid artefacts and wrong conclusions, and with a suggested list of S/C and orbit driving parameters.
Representative simulations with their interpretation are presented, covering a variety of initial conditions for LEO missions, highlighting the impact of the sun elevation evolution and the criticality of Solar Arrays orientation with respect to the principal axes of inertia.
The post-launch attitude reconstruction to be performed in-orbit to confirm the feasibility of a planned ADR mission is another important verification step and the use of navigation aids developed by ESA is explained.
Preliminary conclusions and recommendations are finally proposed.
