Within a big, black-walled facility outside Denver, NASA’s Satellite Servicing Projects Division (SSPD) group successfully completed the most recent testing of three rendezvous and proximity operations sensors employed for satellite servicing applications and beyond. These sensors are required for autonomous rendezvous of spacecraft, which is an important technology for robotically servicing a satellite.
A model of a satellite aft end on a robot for simulated, controlled rendezvous at the Space Operations Simulation Center. Credits: NASA
Held at the Space Operations Simulation Center (SOSC) at Lockheed Martin, this round of testing involved the wide field-of-view visible camera, the Goddard Reconfigurable Solid-state Scanning Lidar (GRSSLi) sensor, and a Vision Navigation System (VNS) light detection and ranging (Lidar) sensor. These three instruments were tested alongside in different situations to assess their sensitivity and accuracy for eventual use in satellite servicing. All sensors contribute to helping a servicer “see” and move toward a client.
These sensors are the key to tackling the most difficult part of satellite servicing, the autonomous rendezvous. Our team was very pleased with the performance of these imagers in a space-like environment.
Bob Smith, Satellite Servicing Project Manager.
Two spacecraft must be coupled without any input or human control to autonomously rendezvous. A combination of sensors, algorithms and a computer are important to produce the precise maneuvers required for this difficult operation.
Several scenarios were simulated by the Engineers during testing at SOSC. To begin with, the three-instrument suite was set to a fixed position and viewed calibrated targets at known distances to calibrate their instrument’s distance and light sensitivity. Subsequently, Engineers employed a model of a satellite affixed to a moving robot, and instruments mounted on another robot to “fly” in the direction of the satellite to record data during this simulated, controlled rendezvous. Besides collecting distance and light measurements using GRSSLi and VNS, this test also enabled operators to test algorithms that establish the position and orientation or “pose” of a satellite while performing a simulated rendezvous.
The aim of SSPD is to demonstrate and mature technologies that are vital for satellite servicing, including the instruments resulting from these tested sensors. The instruments will feed very important data to a cutting-edge SpaceCube computer, which will process the data for autonomous tracking, approach and grasping of a client accordingly.
Enhanced performance for light intensity and range measurements by the imagers was substantiated by the testing conducted at the SOSC. From the results, it can be seen that the VNS is progressing on schedule as per the SSPD timeline.
Satellite servicing testing team was not the only team that was available. Additionally, there were also two teams from NASA’s Johnson Space Center in Houston that tested the VNS for applications specific to human exploration missions. One group collected data for feasible applications of autonomous rendezvous for visiting vehicles to the International Space Station. The second team gathered data that could be integrated into the design of Orion, NASA’s new exploration spacecraft, exclusively developed to carry Astronauts to destinations in deep space, including Mars. A long range testing and simulated rendezvous to a docking port mockup was carried out by both groups.
In a technology demonstration associated with this SOSC testing, SSPD is also currently executing the Raven mission on the International Space Station, which is helping NASA specifically design autopilot for spacecraft. Testing at SOSC helps Engineers develop algorithms and validate sensor performance using calibrated distances between two objects, while testing on the space station offers data on in-orbit functionality of sensors compared to ground testing, and is the best environment to test an infrared camera. Employing both flight-testing and ground-testing is part of the process of learning, perfecting and solving challenging engineering problems for space exploration.
At present, the three instruments are back from SOSC and at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, where the SSPD team is reviewing data to maximize and streamline their performance.
The data from this testing will help us build flight cameras and Lidar systems for making satellite servicing a reality.
Benjamin Reed, SSPD Deputy Division Director