NASA designated Landsat-7 Earth observation satellite as objective for planned Restore-L mission.
NASA is seriously planning robotic service mission on Low Earth Orbit. Since 2009 all NASA efforts which are referring to refueling, tuning or servicing satellites in space are developed by Satellite Servicing Capabilities Office (SSCO). This institution remaining inside NASA and is able to use all necessary technologies developed by Agency to reach its ultimate goal. This objective is to create affordable technology which could be used by U.S. space industry to become a leader in servicing satellites in orbit and change experimental status of present technology to something which is utilized regularly and commercially available.
One of the key programs developed by SSCO was Restore-L; it is planned mission of robotic spacecraft, which will be equipped in various instruments helping in refueling other satellite in space. In spite of main objective of testing technology of autonomic rendez vous, docking (basically catching other spacecraft with special robotic arm) and refueling, this technology is planned to be utilized in future space exploration planned by NASA including manned mission to Mars, Asteroid Redirect Mission or Wide-Field Infrared Survey Telescope (WFIRST) mission.
It seems that works on Restore-L are quite advanced, because in May 2016 NASA decided about moving forward in time first experimental mission. New date was set for 2020, and recently on June 23, 2016, it was announced that first object of experiment was chosen. It will be Landsat-7, Earth observation satellite manufactured by Lockheed Martin and launched on April 15, 1999. Weighing 2200 kg satellite was placed on orbit on almost circular orbit with following parameters: 669 km x 698 km with inclination at 98.2°. Landsat-7 was operated jointly by NASA, NOAA and US Geological Survey; data provided by satellite, containing high resolution pictures, were utilized for general monitoring, disaster relief, cartography and planning.
Restore-L spacecraft will be equipped in autonomous navigation system and avionics which will be used during flight and rendez vous. This system was named RAVEN (Relative Navigation System-upgraded version of ARGON system tested in 2013 under MISSE-7 and STP-H4 programs) and will based on computers, cameras and proximity sensors; system will be heavily complicated due the fact that rendez vous will be performed with speed at least of 16000 km/h and necessary course corrections will be performed in real time. Spacecraft will be also equipped with robotic arm and special set of tools and sensors to perform refueling (it is worth to remind that Landsat-7 was not equipped with any special valve for in-orbit refueling). Robotic arm was not designed from the scratch, but its construction was based on DARPA Spacecraft for the Universal Modification of Orbits and Front-end Robotics Enabling Near-term Demonstration (FREND) project which was developed in the mid-2000. Arm will be equipped in multiple joints to provide seven degrees of freedom combined with force and torque sensors in the end of arm. Equipping arm with cameras will provide full control of the refueling and attaching process. Next important part of the Restore-L is refueling system called Propellant Transfer System (PTS). Its construction is based on oxidizer tank, pumps, flow, temperature and pressure sensors, special hose (first tests in low gravity were performed already in 2013) and oxidizer nozzle tool. System will operate with high pressure providing fast, bubble free, and requiring very little power flow from Restore-L oxidizer tank to Landsat-7. Refueling nozzle is designed to operate with Landsat-7 valve, which was not originally designed to be opened in space. It will provide sealed connection during refueling and next it will close properly valve of satellite to avoid leakage. Restore-L will be powered with solar arrays and will be equipped for propulsion to perform rendez vous. Still details on propulsion were not unveiled, but surely it will be throttable propulsion with possibility of multiple burns combined with advanced maneuver thrusters system.
Restore-L will be first mission in history which covers refueling on Low Earth Orbit. Commercial companies like Orbital ATK offer similar solutions for GEO satellites (Orbital ATK have signed already contract for refueling satellites operated by Intelsat with first mission ot their MEV in 2019). GEO satellites are usually large and expensive spacecrafts, and their operators are interested in investing money in refueling technology in spite of costs, because price for new satellites is also very high. Satellites operating on LEO are often research satellites which are extremely useful, but commercial companies are not interested in independent development of refueling technology due the low probability of refunding such investment. NASA effort will be surely support for space industry, not to mention about obvious savings for NASA or DoD.
On picture above: vision of Robotic Refueling Mission experiment performed on ISS.