ERMES: Design and preliminary simulations for an autonomous docking manoeuvre

Abstract

In the last decades, small satellites have played an important role in space missions. Due to their reduced dimension and costs, they became affordable to smaller companies and research laboratories to conduct scientific experiments and technological demonstrations in space. In addition, the number of these satellites has considerably increased due to their wide use in technological, scientific and commercial domains. In this scenario, autonomous architectures, as well as miniaturized mechanical subsystems for small satellites, are continuously investigated.
 Experimental Rendezvous in Microgravity Environment Study (ERMES) is a student project that focuses on the simulation of an autonomous docking manoeuvres between two CubeSats mock-ups equipped with miniaturized Guidance Navigation and Control systems and mechanical docking interfaces. ERMES aims to integrate different subsystems for autonomous docking, to increase the Technology Readiness Level and to study possible applications for in-orbit servicing. This paper deals with the design and development of the tests for autonomous docking manoeuvres between two CubeSats mock-ups to be performed in a reduced-gravity environment during a parabolic flight. A Target-Chaser configuration has been selected, where the Chaser is fully active and the Target is cooperative. The Chaser is equipped with a miniaturized cold gas propulsion system with eight thrusters to control its attitude and position; in contrast, the Target has a set of three reaction wheels to control only its attitude. The tested miniaturized mechanical docking interfaces employs a probe-drogue configuration. The most demanding aspect of the development phase will be the dedicated software for the proximity navigation. The reduced-gravity conditions will be achieved during a campaign of parabolic flights thanks to the participation to the European Space Agency “Fly Your Thesis!” programme 2022.

Autonomous docking manoeuvre Testing in the framework of the ERMES experiment

“…It is worth highlighting that although choosing an accelerated release impacted negatively the duration of the manoeuvre, it also guaranteed that the Chaser would complete it before any collision could interfere. As shown in 11, during Flight#2 and #3, despite some exceptions in Flight#1, the duration of the accelerated manoeuvres and their counterpart is negligible [38]. Regarding the performances of the localization system, the video tracking gives consistent results with the reconstruction of the Chaser.…”

“…This assumption guarantees a linear trend of the exit pressure with respect to the total pressure (p 0 1 ) as shown in Eq. 1 [33]. To induce sonic conditions at the end of the nozzles, the system must be characterized by high p 0 and expansion coefficient (ξ).…”

“…6. As a consequence of this particular configuration, it is possible to control each DoF by actuating a unique combination of 4 out of the 8 total thrusters at the same time [34]. Tab.…”

“…These commands contain information on the DoF to correct, which are interpreted as the group of four electrovalves (see Tab. 2) to be opened, as well as the duration of the thrust impulse (number of "cycles") [34]. Since the electrovalves implemented have an opening time of 4 ±1 ms, the LLS has been designed to ensure actuation delays lower than 1 ms.…”

“…The "failures" in the remaining manoeuvres were mainly due to mistakes committed by the Chaser, who failed to close the distance and dock in time, or to unexpected disturbances that ended the manoeuvres prematurely [38]. The g-jitter is a primary example of these disturbances.…”