Abstract
Current investigations on space tethers include their application to space debris deorbiting, specifically on the set of manoeuvres performed by a chaser tug to change the orbital parameters of a target body. Targets can be cooperative spacecraft at the end of their life or uncontrolled objects such as defunct satellites without clearly available capturing interfaces. In this latter case, a link joining tug and target may be misaligned with the target body inertia axes, influencing the attitude of both bodies; in case of rigid links, torques transmitted during tugging operations may overcome the tug attitude control system. This issue is clearly less significant in case of non-rigid connections, such as tethers; furthermore, with such connections the chaser can remain at a safe distance from the target during the whole deorbiting operation. On the other side, the initial phase of tethered space debris removal manoeuvres can be influenced by transient events, such as sudden tether tension spikes, that may cause longitudinal and lateral oscillations and, in case of resonance with the target attitude dynamics, could represent a serious issue for tug safety. In this paper it is proposed to provide the tug with a tether deployer mechanism capable to perform reel-in and reel-out, smoothing loads transmission to the target and damping oscillations. This concept is validated through a representative test campaign performed with the SPAcecRraft Testbed for Autonomous proximity operatioNs experimentS (SPARTANS) on a low friction table. A prototype of the deployer is manufactured and the deployment and rewind of a thin aluminium tape tether is proven. Test results include the verification of the tether visco-elastic characteristics with the direct measurement of spikes and oscillations and the estimation of the proposed system damping capabilities.
Highlights
Since the introduction of the space tether concept [1], a wide number of applications from orbital momentum exchange devices to electrodynamic systems have been proposed; a complete review can be found in [2,3,4,5]
It consists of a Cold Gas Actuator (CGA) propulsive unit, employing two nozzles, a tank, and the relative fluidic system, and a deployment/reel-in subsystem, composed by a rotating reel, a system of pulleys to control the tape deployment, and a motor coupled to the reel to brake it during deployment and actuate it during reel-in operations
The facility consists in a 3 × 2 m test table and a spacecraft test mock-up; a Motion Capture (MC) system with 6 infrared cameras tracks the motion of the mock-up
Summary
Since the introduction of the space tether concept [1], a wide number of applications from orbital momentum exchange devices to electrodynamic systems have been proposed; a complete review can be found in [2,3,4,5]. Despite efforts to reduce new spacecraft influence on the debris environment (e.g., [14, 15]), the recent plans for large constellations [16, 17] are constantly scrutinized and their short and long term influence on the space debris environment stability is under evaluation [18,19,20] In this context the scientific community is evaluating further mitigation strategies, considering both the utilization of enhanced protections [21] and the implementation of post mission disposal (PMD) [22] and active debris removal (ADR) [23] operations. The advantages of tether systems are not limited to the disposal manoeuvre, as flexible connections between two modules reduce the loads transmitted between them with respect to solid joints With such connections the vehicles involved can remain at a safe distance while maintaining a physical connection. The prototype, while designed principally for the ETPACK kit tether deployment, can be employed for tethered systems formation flight and space tugging, thanks to the capability to control both the tether deployment and retrieval
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
