Fresh Air Is Good for Satellites, Too

Very low Earth orbit (VLEO) is becoming popular for large satellite constellations. According to the European Space Agency (ESA), approximately 5,000 satellites are currently in this orbit, but the historic numbers are dwarfed by future satellite forecasts. The booming commercial space industry has proposed another 20,000 satellites for deployment into non-geostationary orbits, with about 13,000 approved by the FCC thus far. One SpaceX filing from March 2017 alone proposed 7,518 satellites in orbits between 336 km and 346 km altitudes.

VLEO satellites typically experience fast orbital decay and require significant propellant for periodic orbital maintenance maneuvers. A proliferated very low Earth orbit (pVLEO) constellation may require a larger initial number of satellites in orbit to provide communication coverage than existing proliferated LEO (pLEO) constellations. A game-changing concept, known as air-scooping electric propulsion (ASEP), could extend the life of these VLEO satellites by providing a means for periodic re-boosting to maintain orbital altitudes.

An ASEP satellite uses a solar array and electric propulsion to leverage ambient air as a propellant. This satellite design could offer economic and operational advantages transformational for lower-altitude orbital slots and potentially support a range of long duration missions. Without the finite limit of onboard propellant, an ASEP satellite could have an extended life — potentially reducing vehicle replacement rate and overall cost of the constellation.

Air-scooping satellites have the potential to reduce launch cost, improve mission performance for high-resolution Earth observation missions, reduce latency for satellite communications, and introduce new space tug servicing capabilities for existing satellites. With the emergence of pLEO communication satellites such as the OneWeb, SpaceX Starlink, and Amazon Kuiper commercial constellations, air-scooping satellites offer new advantages and capabilities.

60 Starlink satellites stacked together before deployment on May 24, 2019. Courtesy: SpaceX

Demand for connectivity to support enterprise and general consumer broadband and Internet of Things needs is driving the rapid design and deployment of pLEO communication constellations. Any company that can fly VLEO ASEP satellites, particularly for those constellations that support latency intolerant applications such as financial transactions and high-speed trading, autonomous vehicle navigation, multiplayer gaming, and remotely operated robotics that need near real-time capabilities, will have a strong competitive advantage.

The need for high-resolution Earth observation may stimulate industry investment. Additionally, NASA may be interested in a more ambitious goal: space tugging to remote outposts, such as the moon or the target for the James Webb Telescope. An ASEP-enabled space tug could reach high-altitude orbits, such as GEO and further then return to VLEO to refill the tank; introducing a reusable space tugging capability. A fleet of ASEP space tugs has the potential to disrupt the entire launch architecture by obviating the need for heavy lift vehicles, except for those satellites that require short station delivery timelines. While not yet achievable with the current state, future technology demonstrations could stimulate significant government and commercial interest.

Because of this growing interest, numerous companies and institutions are actively designing ASEP concepts. Technical hurdles remain, such as optimizing the air-scoop design and electric propulsion systems and developing durable materials to operate within the corrosive VLEO atmosphere. While ASEP technology is still immature, it is on the cusp of transitioning between research and development and demonstration phases. Once ASEP enabled satellites can be successfully demonstrated in VLEO, they could transform lower-altitude orbital slots into prime real estate to support a range of long duration missions.

This article is an excerpt from a?Game Changer?paper by The Aerospace Corporation's Karen Jones. The Game Changer series is dedicated to analyzing the impacts of new space technologies and the challenges of operating in an ever-expanding space domain.