Space communications covers all transmission of data between spacecraft and ground stations (space-to-ground links), between satellites (inter-satellite links, ISL), and between satellites and end-user terminals (direct-to-device). It is the nervous system of the commercial space economy.
RF links dominate current infrastructure. Ka-band (26.5–40 GHz) and Ku-band (12–18 GHz) are the workhorses for broadband SATCOM. The Shannon limit constrains throughput for a given bandwidth; link budget engineering (EIRP, G/T, rain fade margin) determines system performance. LEO mega-constellations (LEO Mega-Constellations) — Starlink, OneWeb, Amazon Kuiper — exploit lower path loss and lower latency (~20 ms vs ~600 ms for GEO) to deliver broadband from low-cost phased-array terminals.
Optical inter-satellite links (OISL) use laser beams between satellites to carry high-throughput backbone traffic without going to ground. See Optical Inter-Satellite Links. Starlink’s Gen 2 OISL operates at ~100 Gbps per link. Key technical challenge: pointing, acquisition, and tracking (PAT) of a diffraction-limited beam across thousands of km while both platforms vibrate and thermally flex.
Direct-to-cell (see Direct-to-Cell / LEO SOS (Lynk, AST SpaceMobile)) eliminates the need for specialised terminals; Starlink, AST SpaceMobile, and others use unmodified 4G/5G handsets as terminals. Regulatory co-ordination with terrestrial mobile networks is the primary constraint.
Investment relevance: ground-segment hardware (phased-array antennas, optical terminals, ground-station-as-a-service) and spectrum management are the fundable wedges. Pure satellite manufacturing and launch are dominated by vertically integrated players. Quantum-secured SATCOM (QKD via satellite) is an early-stage opportunity for sovereign-assured communications.
Frontier
- Can OISLs achieve sufficient pointing stability on low-cost small-sat platforms without deformable mirrors?
- What is the practical data-rate ceiling for direct-to-device LEO broadband without licensed spectrum refarming?
- How does QKD via satellite scale to a commercial service model?