# Hybrid-Compliant System for Soft Capture of Uncooperative Space Debris
## 2 Space Debris Capture
### The Capturing Phase  
An ADR mission consists of a succession of several crucial phases. From the launch of the spacecraft from Earth to the moment the chaser satellite, coupled with the debris, burns into the atmosphere, five general phases can be noted: berthed standby (the chaser satellite is on board and attached to the hosting platform), ejection (includes the launch of the rocket until the ejection of the payload), Far-Range Approach (arrive at hold point, close enough to the target), capturing, and post-capture (ready to de-orbit).  
The capturing phase is the most crucial one. With little cooperation between the servicer and the target (no communication link, no fiducial markers, nor capture interfaces), capturing uncooperative debris is today one of the biggest challenges. Indeed, mission  
Figure 2: Small objects’ apogee and perigee distribution in LEO organised by main shapes.  
failure and debris generation can occur more easily during that phase and the consequences can be dramatic.  
Figure 3 describes the concept we propose for the capturing phase. It includes three sub-phases, pre-capture (approach guidance and control), soft-capture, and hard-capture; these are in charge of the approach preparation, the impact absorption and stabilization, and the securing of the debris attachment.  
* **Pre-Capture** The servicer satellite's guidance navigation and control (GNC) rendezvous and synchronizes its motion with the debris. The ADR system is, at first, undeployed inside the CubeSat architecture, as displayed in Figure 4, and is then deployed. At the end of the pre-capture approach, there is a relative distance \(d_{t}\). Thus, only a translation motion is required to capture the debris.  
* **Soft Capture** In this sub-phase, the servicer satellite's thrusters are turned on to approach the debris and achieve the first contact. The first impact between the capturing mechanism and the debris must occur softly. Because of this, we propose a hybrid-compliant system for soft capture. It combines passive and active compliance with components that will reduce shocks and residual vibrations and actively control the contact time to avoid motion-reaction effects. It is assumed that the mechanism's tip will remain in contact with the debris for a finite time \(t_{c}\), long enough to ensure that the hard capture mechanism secures the debris.  
Figure 4: Undeployed hybrid-compliant system. _The gray cylinder at the back of the system is for illustration purposes only._  
Figure 3: Concept of operations of our proposed capturing phase.  
* **Hard Capture** This sub-phase aims to secure the link between the servicer satellite and the debris, resulting in a reliable bond ready for deorbiting. After the soft capture, the hard capture mechanism will activate to fold and embrace the shape of the debris.  
Figure 5 presents a general view of the proposed hybrid-compliant system for soft capture integrated into the CubeSat frame. This paper focused on the soft capture sub-phase. Details of the pre-capture and hard-capture sub-phases are out of the scope of this paper. Indeed, the system being at an early-stage design, we assume that the motion synchronization between the servicer and the debris had already been established in the pre-capture phase. Besides, the de-orbiting phase is considered out of the scope of the paper, as it is up to the servicer satellite using the proposed concept to decide how to demise the whole system with the debris attached.