Aishling Dignam, Astroscale; Lucas Almeida Cypriano, Astroscale Ltd.
Keywords: space debris, ssa, optical sensor, calibration, instrumentation, imaging
Abstract:
Astroscales ELSA-d mission has demonstrated in-orbit servicing (IOS) techniques that are vital to performing End-of-Life (EOL) services, Active Debris Removal (ADR) and Life Extension (LEX) activities to address the risks created by the presence of debris. The End-of-Life Services by Astroscale demonstrator (ELSA-d), launched in 2021, is comprised of the Servicer and Client spacecraft, initially connected through a ferromagnetic docking system, which successfully performed a number of rendezvous proximity operations (RPO) in orbit. Following the completion of the demonstration activities, the onboard visible camera (VISCAM) has been repurposed to perform In-Space Situational Awareness (ISSA) imaging of catalogued debris objects. The VISCAM was designed for the sole purpose of executing RPO and, hence, was only intended for imaging objects at close range. In repurposing this camera for Space Situational Awareness (SSA) activities a number of capabilities had to be developed to capture images of debris objects, such as how to time the image acquisition and how to calibrate the camera that has no previous calibration for performing ISSA imaging.
With the VISCAM, various on-orbit calibration techniques are explored, including on-orbit flat fielding without any inbuilt onboard capacity. One consideration of an repurposed sensor is due to radiation damage. The ELSA-d VISCAM has is a large population of hot pixels present pixels with a readout level consistently greater than the background average. Annealing a sensor, heating the sensor and dissipating the heat back to nominal levels, is the conventional method of reducing the effect of hot pixels in an image. One such method is to use the Sun as a heat source for the camera, which is investigated here to use the ELSA-d attitude control to heat the VISCAM with the aim of reducing the hot pixel intensity.
Available sensors onboard satellites present an opportunity to yield more data about resident space objects and to this end, we present methods for calibrating cameras that were not designed for ISSA purposes to obtain useful observations. Different operational capabilities of the satellite and camera are considered; for example, a basic, uncalibrated camera with attitude control like VISCAM on ELSA-d. At Astroscale, these techniques are used to inform the imaging capabilities of our different platforms including a UK Space Agency-funded ADR mission to design a dedicated ISSA payload and also in informing our future ELSA-M ISSA imaging capabilities with RPO cameras.
Date of Conference: September 19-22, 2023
Track: SDA Systems & Instrumentation