Communications (COMMS)

Also known as COMMS, TT&C, Radio, RF

Carries telemetry, telecommands and payload data between spacecraft and ground. Small satellites span VHF and UHF amateur bands, S, X and Ka band and optical links; the link budget decides whether a link closes.

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SQ-SS-004
Updated
20 Oct 2026
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8 min
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Definition#

The communications subsystem consists of the radio or optical links that bring the state of the spacecraft (telemetry) down, take commands (telecommands) up and move payload data. Telemetry, tracking and command together are called TT&C. VHF and UHF are the most mature bands for small satellites; UHF, S, X and Ka are the bands commonly considered. Industry carries TT&C mostly in S band[1], whereas small satellites in amateur bands usually do it in UHF.

Choosing a band#

Band selection trades data rate against complexity. In UHF, simple wide-beam antennas and cheap ground stations suffice, but channels are narrow and rates low. S and X band allow megabits to hundreds of megabits per second, at the price of directional antennas, attitude control towards Sun and ground, and spectrum licensing. Optical links can bring down orders of magnitude more data per pass than radio.

For a PocketQube the antenna alone decides much: a quarter-wave monopole at 437 MHz is 171 mm long, more than three times the edge of a 1P, so every UHF PocketQube depends on a deployable antenna[2].

Ground segment#

Missions in amateur bands can be heard by , an open-source network of volunteer stations around the world; its database lists transmitter frequencies, modulations and observations of each satellite[3]. NASA missions may use the Near Space Network; others choose anything from their own stations to commercial pay-per-pass services. Existing constellations such as Globalstar and Iridium can relay data as well[1]. The ground segment entry covers stations, networks and operations.

Landmark demonstrations#

The two MarCO spacecraft, the first interplanetary CubeSats, relayed InSight’s landing on Mars to Earth almost in real time[4]. Each 6U carried a UHF receiver for InSight’s 8 kbit/s transmission and a flat reflectarray high-gain X-band antenna that behaves like a parabolic dish[5].

On the optical side, the TBIRD payload of MIT Lincoln Laboratory and NASA, launched on Transporter-5 in May 2022, downlinked 4.8 TB without errors in a single pass of about five minutes at 200 Gbit/s in June 2023[6]. It flew on the 6U PTD-3 spacecraft[7].

References

  1. [1]NASA Small Spacecraft Systems Virtual Institute. (2026). Communications. State-of-the-Art of Small Spacecraft Technology (2026 edition), Chapter 9. NASA Ames Research Center.nasa.gov(accessed 20 October 2026)
  2. [2]nadir lab. (2026). PocketQube picosatellites: A review of standards, mission trends and miniaturization constraints, with lessons learned from Grizu-263A, Türkiye’s first PocketQube [Preprint]. nadir lab.Read on nadir lab.
  3. [3]Libre Space Foundation. (2026). SatNOGS DB — satellite and transmitter database.db.satnogs.org(accessed 20 October 2026)
  4. [4]NASA Jet Propulsion Laboratory. (2019). The MarCO mission comes to an end.jpl.nasa.gov
  5. [5]NASA Jet Propulsion Laboratory. (2018). InSight landing press kit: Mars Cube One (MarCO).jpl.nasa.gov
  6. [6]MIT Lincoln Laboratory. (2024). NASA's record-breaking laser demo completes mission.ll.mit.edu
  7. [7]Krebs, G. D. (2026). PTD 3. Gunter’s Space Page.space.skyrocket.de(accessed 20 October 2026)
  8. [8]Friis, H. T. (1946). A note on a simple transmission formula. Proceedings of the IRE, 34(5), 254–256.doi:10.1109/JRPROC.1946.234568
  9. [9]Proakis, J. G., & Salehi, M. (2008). Digital Communications (5th ed.). McGraw-Hill.
  10. [10]ITU-R. (2023). Recommendation P.618: Propagation data and prediction methods required for the design of Earth-space telecommunication systems. International Telecommunication Union.itu.int
  11. [11]Doroshkin, A. A., Zadorozhny, A. M., Kus, O. N., Prokopyev, V. Y., & Prokopyev, Y. M. (2019). Experimental study of LoRa modulation immunity to Doppler effect in CubeSat radio communications. IEEE Access, 7, 75721–75731.doi:10.1109/ACCESS.2019.2919274
  12. [12]Fernandez, L., Ruiz-De-Azua, J. A., Calveras, A., & Camps, A. (2020). Assessing LoRa for satellite-to-Earth communications considering the impact of ionospheric scintillation. IEEE Access, 8, 165570–165582.doi:10.1109/ACCESS.2020.3022433
  13. [13]International Amateur Radio Union. (2026). Amateur satellite frequency coordination.iaru.org(accessed 20 October 2026)
  14. [14]International Telecommunication Union. (2020). Radio Regulations, Edition of 2020. ITU.
  15. [15]The CubeSat Program, Cal Poly SLO. (2022). CubeSat Design Specification, Rev. 14.1 (CP-CDS-R14.1). California Polytechnic State University.nasa.gov

Cite this SatWiki entry

@misc{nadirlab2026comms,
  author       = {{nadir lab.}},
  title        = {{Communications (COMMS)}},
  year         = {2026},
  month        = oct,
  howpublished = {nadir lab. SatWiki SQ-SS-004 (Rev. 3)},
  url          = {https://nadirlab.space/en/wiki/comms/}
}