Project Objective

An automated tethered spacecraft simulator in the Flat Floor Robotics Lab (FFRL) will enable higher fidelity in-space servicing, assembly, and manufacturing (ISAM) demos and enable the development of other tether-based capabilities, such as debris capture/removal, Electric Sail deployment, etc.

Project Description

In-Space Servicing, Assembly, and Manufacturing (ISAM) covers a wide range of activities that are and will be necessary to enable long-lasting and high-performing spacecraft and payloads. Tethered satellites are a promising tool for enabling ISAM activities. Small tethered satellites, or space tugs, can housed on larger spacecraft, such as the International Space Station (ISS) or Gateway, and deployed for servicing, assembly of structures, photography and data collection, structure deployment, etc. When these activities are complete, the space tug can be reeled back to its host spacecraft via an electric wench. These vehicles would have more maneuverability and flexibility in motion (and in application) than larger spacecraft.

FFRL houses a 44 by 86 foot epoxy flat floor that uses air bearings to simulate zero gravity in two dimensions. Air bearing vehicles have been used as spacecraft simulators for decades. This project will develop autonomous flight capabilities for small spacecraft simulators in the FFRL - closer to CubeSate-size than larger, bulkier simulators used for past testing. The space tug will be able to autonomously approach a specified location, following a specified trajectory, on the air bearing epoxy floor. Once developed, this vehicle will be available for a variety of Flat Floor testing, as the space tug is customizable to different needs and capabilities. The basic functions of the simulator are derived from previous air bearing vehicles, utilizing paint pall tanks for on-board solenoid valves, allowing the simulator to propel itself on an air bearing.

Key to this development are two navigation sensors systems available in the FFRL. An Indoor Positioning System from Marvelmind Robotics utilizes ultrasonic beacons to calculate and report real-time positioning with an accuracy up to two centimeters. This serves well as a coarse positioning system but does not reach the level of precision needed for space activities. The second is the Smart Video Guidance System (SVGS), the newest generation of the original Video Guidance System (VGS) developed in the FFRL and flown on the Space Shuttle. SVGS has sub-millimeter accuracy and will be used in junction with the Marvelmind system to provide inputs to the simulator's new control system.

Project Results and Conclusions

Maneuverable Automated Tethered Spacecraft (MATS) simulator construction is complete, with a new thruster configuration, new microcontroller, and integrated avionics box. The Indoor Positioning System and SVGS are integrated into the avionics system. Some of the pneumatic components have been upgraded to aid in mounting and assembly. The simulator can be maneuvered wirelessly from a PC ground station with keystrokes from a human operator. Other status functions on the simulator can be toggled via a graphical user interface (GUI) on the ground station. A pressure sensor was implemented to report low pressure on the thruster's air tanks.

Work is continuing to properly implement autonomous flight capabilities. Due to reliability issues with the Indoor Positioning System, this function may be removed and replaced entirely with the SVGS. The tether reel and mechanism prototype that controls tether direction is complete and will soon be integrated with the simulator's hardware and software. Users will be able to toggle the reel to be pulled out (by the flight of the simulator) or retracted (pulling the simulator back to ground station).

The current keystroke control, combined with the new thruster configuration, has greatly improved maneuverability of the platform. This already allows for improved repeatability of flights of the simulator, such as those used for previous ISAM demonstrations on the epoxy floor. The autonomous flight capabilities will be fully implemented in mid-2025.

• This project will produce an autonomous spacecraft simulator that can perform approaches and maneuvers with minimal operator inputs, via a closed loop control system.
• This simulator will allow for more complex and higher fidelity demonstrations, and will directly enable experimentation options to close critical gaps related to MSFC’s and the agency ISAM portfolio (experimentation to join two space structures together, inspection of joins, and assembly of modular structures).
• This project synergizes with in-space laser welding developments from MSFC's welding group, and will lead to future collaboration.
• This project supports future work on Electric Sail tether deployment. E-Sails are a promising deep space propulsion capability, and deployment demos were previously conducted in the FFRL in 2017. The MATS simulator is a stepping stone to future work in this area.
• After this project, the MATS simulator will be available for FFRL engineers and internal/external customers to use for their work.