Design challenges and safety concept for the AVANTI experiment

Flight Demonstration of Autonomous Noncooperative Rendezvous in Low Earth Orbit

“…2, the off-line TM of AVANTI, together with GPS-raw data as well stored in the BIROS PPU, have been routinely processed by the experiment control center (ECC), also located in GSOC. Its main activities consisted in: (i) performing the relative precise orbit determination, benefiting from calibrated maneuvers information, to assess spaceborne navigation performance [32] and to re-initialize the onboard safety monitoring tool [15]; (ii) analyzing the extended TM to monitor the whole GNC behavior and to detect eventual anomalies; (iii) producing and validating the command timeline that encoded the high-level goals of subsequent phases of the experiment. These activities have been supported by dedicated tools of the AvantiSimulator, a QT-based C++ software environment (also featuring different on-need hardware-in-the-loop capabilities), evolved from the multi-satellite simulator test-bed in use in GSOC to design, integrate, validate, and support spaceborne formation-flying activities in the last decade [33,34].…”

“…For simplicity, time constraints are solved firstly to restrict the solution's domain. The remaining two tasks can be tackled sequentially thanks to the following peculiarities of the ROE framework: (i) the availability of a simple but accurate and complete closed-form state transition matrix for the perturbed relative motion; (ii) the geometrical meaning of each component of the ROE state; (iii) the possibility to easily and synthetically express the passive-safety property of a relative orbit as function of the ROE state components [15,39]; (iv) the functional structure of the relations between instantaneous variation of velocity in the local radial-tangential-normal (RTN) orbital frame and consequent effect on the ROE components [40]. All these features together allow transforming a time-dependent optimal control problem into a geometrical minimum-path problem in the ROE space, provided that the maneuvers scheduled to achieve each intermediate way-point are computed pursuing the same optimality criterion of the way-points planning step.…”

“…As detailed in Ref. [15], the noncooperative scenario of the AVANTI experiment required to develop a safety concept which does not rely on the continuous availability of any picosatellite tracking data. It is mainly based on the use of passively safe relative trajectories and it is then completed by the following additional safety measures: an onboard preventive action and a long-term reaction.…”

“…AVANTI firstly applied the one-orbit-minimum cross-track distance criterion throughout all rendezvous phases. And, to this end, it extended such principle to drifting relative orbits, resulting from nonvanishing relative semi-major axis encountered during a rendezvous or produced by the action of the differential aerodynamic drag [15].…”

Flight demonstration of spaceborne real-time angles-only navigation to a noncooperative target in low earth orbit

“…This peculiar relative motion is the consequence of the adopted passive formation safety concept which states that a minimum intersatellite distance will be guaranteed at any time, provided that δe and δi are properly phased. 16 The onboard autonomous guidance will have the task of reducing step by step the size of the spiral during the approach and of keeping the desired phasing of the relative eccentricity and inclination vectors.…”