Telemetry framing & protocols
Also known as AX.25, CSP, CCSDS, Kaitai Struct
AX.25, CubeSat Space Protocol (CSP), CCSDS reed-solomon/convolutional coding, Morse CW beacons and Kaitai Struct decoders for small-satellite downlinks.
- Document
- SQ-SS-012
- Updated
- Reading time
- 1 min
In this tab
Why uncoded AX.25 loses marginal passes
Amateur-band CubeSats historically transmitted uncoded UI frames with HDLC bit-stuffing and a 16-bit CRC[1]. Because HDLC aborts the entire frame if a single bit flips inside an flag sequence—and because uncoded 2- requires for [2]—uncoded AX.25 wastes low-elevation passes. Adding a Reed–Solomon outer code (correcting up to byte errors per block) or a rate-, constraint-length- convolutional inner code provides of coding gain.
Framing overhead and open-source decoding
| Protocol / Scheme | Header & Parity | FEC capability | Ground decoding ecosystem |
|---|---|---|---|
| CW (Morse) / RTTY | Minimal | Human/narrowband integration | Audible on any SSB receiver; fallback survival beacon |
| UI (HDLC) | 16–20 B callsign + 2 B FCS | None (error detection only) | Direwolf, Soundmodem, gr-satellites[3] |
| CSP + RS(255,223) | 4 B CSP header + 32 B RS parity | Corrects up to 16 B per 255 B block | libcsp, gr-satellites[3] |
| AO-40 / CCSDS concatenated | Sync marker + convolutional + RS | Corrects burst & random bit errors | CCSDS/SatNOGS pipeline |
Publishing a machine-readable Kaitai Struct (.ksy) telemetry definition and a gr-satellites YAML descriptor before launch allows hundreds of ground stations to decode and dashboard housekeeping frames from the very first orbit[4].
References
- [1]nadir lab. (2026). PocketQube-class picosatellites: architecture, flight heritage, and a multi-method post-flight analysis of Grizu-263A [Preprint]. nadir lab. Research Monographs (SQ-R-001).Read on nadir lab.
- [2]Proakis, J. G., & Salehi, M. (2008). Digital Communications (5th ed.). McGraw-Hill.
- [3]Estévez, D. (n.d.). gr-satellites: a GNU Radio out-of-tree module with decoders for amateur satellites.github.com(accessed 20 October 2026)
- [4]Kaitai Project. (n.d.). Kaitai Struct: a declarative language for describing binary data structures.kaitai.io(accessed 20 October 2026)
Cite this SatWiki entry
@misc{nadirlab2026telemetry,
author = {{nadir lab.}},
title = {{Telemetry framing \& protocols}},
year = {2026},
month = oct,
howpublished = {nadir lab. SatWiki SQ-SS-012 (Rev. 1)},
url = {https://nadirlab.space/wiki/telemetry-protocols/}
}nadir lab. (2026). Telemetry framing & protocols. nadir lab. SatWiki (SQ-SS-012, Rev. 1). https://nadirlab.space/wiki/telemetry-protocols/
TY - ENCYC AU - nadir lab. TI - Telemetry framing & protocols T2 - nadir lab. SatWiki PY - 2026 ET - Rev. 1 C1 - SQ-SS-012 UR - https://nadirlab.space/wiki/telemetry-protocols/ ER -