Pentagon tempted by private concept of “orbital fuel station”

The said agreement on R&D cooperation was signed on October 14 this year. Within its framework, technology is to be transferred to the AFRL, with the advisory and engineering support of the American armed forces.

Orbit Fab, involved in the cooperation, is an American startup specializing in the field of technologies related to satellite servicing, in particular the methods of delivering and injecting propellant into satellite systems and vehicles already operating in orbit. In June this year, with the support of SpaceX and the Falcon 9 rocket, Orbit Fab launched a miniature “space tank” demonstrator, the Tanker-001 Tenzing, on LEO.

The idea of ​​Orbit Fab is based on the deployment of small stations in orbit, to which satellite objects and ships could autonomously moor, in order to collect propellant by a special, unmanned (i.e. one that will work without additional mechanical guidance, using a robotic arm or manipulator) RAFTI high pressure valve (Rapidly Attachable Fluid Transfer Interface). The system is to be standardized (based on a common, unified access valve – on the side of the service station and the satellite) and appropriately adapted to be able to maintain airtightness and its functionality in the difficult conditions prevailing in space. Its material injection capacity is designed to include a pressure in the range of about 35 to 207 bar (500-3000 psi).

The American space force (US Space Force) would use new engineering capabilities to extend the life of their satellites, which, when they run out of propellant, are doomed to end the mission. Many times in such situations they still have useful and technically efficient on-board equipment, but the lack of the necessary fuel prevents their further use. At the same time, it is indicated that the new service capabilities would make it possible to significantly improve the economic cost of using satellite solutions to ensure national security.

In the segment of orbital satellite refueling, the US military is another entity striving to obtain specific technical capabilities. It is worth recalling that the assumptions regarding this aspect of spaceflight are also included in the Interplanetary Transport System project, which, after years of modification and development work on an adapted orbital rocket, has become what is today associated with SpaceX’s Starship program. This commercial project also involves orbital refueling, but for missions to Mars and in the future to other solar system bodies.

The very idea of ​​refueling in space has been the subject of engineering considerations for a long time. Pioneering work on this subject is combined with the Soviet space program, with the main continuation under the Russian program. Many decades ago, during the Salut program, the first successful attempts to transfer the material, at that time from the first versions of the Progress ship to the Salut 6 station, were to be carried out. Compressed gas was used to carry out the procedure. A similar method of refueling in space was later used at the Salut 7, Mir and ISS stations.

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The concept of using a service station with a RAFTI fuel valve. Picture: Orbit Fab

Let us add that, apart from Russia and the United States, the People’s Republic of China has its own solutions for orbital refueling. Four years ago, the CMSE agency (China Manned Space Agency) responsible, inter alia, for manned space flights, she announced that in low Earth orbit, the now defunct Tiangong-2 station refueled with fuel from the autonomous supply vessel Tianzhou-1. Back then, this procedure, which was controlled from the Chinese air traffic control center, took five days and was successful without any further information from the Chinese authorities.

Refueling in space is not easy. In an environment where there is no gravity, all fluids in the tanks float freely, which significantly complicates the transfer between vehicles – without the influence of gravity, the fuel must otherwise be “forced” to thrust. As mentioned, the Soviet designers used compressed gas for this purpose – another method is to use the pressure difference between the inside of the connected tanks and the space itself.

A separate issue here, however, is refueling considered through the prism of satellite servicing. The obstacle is not only a different size and mass specificity, but also a significantly larger scale of requirements for adaptation and integration of solutions enabling mooring, securing and ensuring the flow of substances.

So far, efforts in the field of satellite servicing are associated primarily with the project of the SpaceLogistics design office – a subsidiary of Northrop Grumman, which cooperates in this field with the Agency for Advanced Defense Research Projects (DARPA) – in the MEV (Mission Extension Vehicle) vehicle development program. . Equipped with a robotic arm and a grippy mooring clamp, this system can attach to orbital satellites and deliver them to pre-set orbital positions, serving as an additional propulsion module. In the future, it will also be able to carry out more demanding inspections and manipulations on satellite equipment.

Northrop Grumman has already launched two MEV service vehicles into orbit – the first (MEV-1) is now used as a propulsion module for the commercial Intelsat-901 satellite in a geostationary orbit mission. The successful attachment to GEO took place in February 2020. On the other hand, the second vehicle (MEV-2) in April this year successfully connected with another telecommunications satellite, Intelsat 10-02 (also on GEO).

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Pentagon tempted by private concept of “orbital fuel station”