Recent research in propulsion technology combined with active aerodynamic concepts have led to the concept of spacecraft operating in Very Low Earth Orbits (VLEO). Using such an approach, a satellite could stay in an orbit of less than 200 km (i.e. lower than conventional LEO), for an extended duration in spite of the aerodynamic drag.
Satellite communication services operating from VLEO would benefit from the improved link budget and lower latency due to shorter transmission distance to ground terminals, and the reducedcoverage footprint could enable an increase in frequency re-use, or provide a degree of security against interception/interference.Such a system might also enable the use of lower transmit powers enabling operation at higher frequencies such as W-band. (Recent satellite network filings in the U.S. suggest that SpaceX is investigating such an approach). In addition, the reduce re-visit timeofVLEO may be of benefit in some use cases. If technically feasible, operation in VLEO orbits near the Kármán line (100 km) could evenopen the possibility of operating under a different (i.e. non-space) radio regulatory regime.The use of VLEO orbits is enabledby the emergence of air breathing engines that are expected to be relatively simple and inexpensive, in conjunction with active aerodynamic drag manoeuvre techniques. These elements may in turn enable more efficient deployment methods for VLEO spacecraft: the ongoingdevelopment of sub-orbital vehicles (e.g. Blue Origin, Space Ship Two, Space Rider) may provide an efficient option for injection into such VLEO orbits. Whilst the use of VLEO could offer certain benefits, it is expected that the impact on the overall system architecture and space segment design would be significant. E.g. payload accommodation, thermal dissipation, and power generation sub-systems would all be very different for such a spacecraft design.
The running EU-funded project DISCOVERER addresses the broaderfeasibility of using VLEO orbits, with a specific emphasis on their application to Earth Observation missions. The proposed ARTES activitywill therefore focus specifically on the feasibility and benefits for satellite communications. The activity shall first investigate the possible services and applications that could be offered from VLEO. Services shall be identified for which the combination of VLEO, with its favourable link budget, and the use of COTS on ground (e.g. mobile handsets or existing terrestrial base station technology) provide a tipping point that enables such services. The potential for M2M/IoT services utilising terrestrial protocols andterminals is of particular interest. The high-level economic feasibility and impact on satellite platforms shall therefore be addressed early in the study.
After selection of the most promising services and applications, the study shall derive system requirements for the satellite communication systems that could offer the identified services. There shall be a specific emphasis on understanding the impact on the satellite platform (and hence payload) when operating in VLEO, taking into account new propulsion or aerodynamic drag requirements combined with accommodation requirement for antenna, solar panel or other appendices. In addition an understanding of the environmental effects of radiation, atomic oxygen, and electrical charging shall be developed for operation in these orbits. Finally, the activity shall address the launch, deployment and orbital maintenance aspects of such systems in VLEO. System designs for the identified services shall be proposed, supported by simulations that provide insight in the overall performance ofproposed new services. The adaptations to existing user and ground segment design and operations shall be identified.
The activity outcomeshall therefore be to understand the potential viability and benefits of future VLEO telecommunications missions, and to propose the subsequent technological developments needed to enable tthe use of VLEO systems for satellite communications. The activity will be implemented via a phased approach - due to its forward-looking nature and will not continue if no credible new services orbenefitsare identified during its initial phase.