unisat

CubeSat 3U — Operations Guide

Profile key: cubesat_3u · Mass cap: 4.0 kg · Volume: 3405 cm³ Template: mission_templates/cubesat_3u.json · BOM: hardware/bom/by_form_factor/cubesat_3u.csv

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1. Mission class

UniSat TRL-5 reference profile — every subsystem in the project is characterised against this envelope. 3U is also the most common professional CubeSat size worldwide: single 1U payload bay plus 2U platform for EPS / ADCS / comms.

Suitable for: Earth observation, technology demonstration, rideshare constellations (Kepler, Lemur), university flagship missions.

2. Physical envelope

Parameter	Value
Mass cap	4.0 kg
Dimensions	100 × 100 × 340.5 mm
Volume	3405 cm³
Power generation	~8.0 W orbit-average (body-mounted)
Nominal consumption	6.0 W
Battery	2P3S 18650, ~60 Wh

Add deployable solar panels for ~20 W generation if the mission budget allows; not assumed in the default BOM.

3. Regulatory context

• CDS rev 14 §3.1 — 3U standard.
• ITU: UHF + S-band coordination, or deep-space DSN request for very niche missions.
• Launch provider: NanoRacks, ISILaunch, D-Orbit ION, SpaceX Rideshare — well-trodden ICDs.
• Orbital-debris: end-of-life plan required (< 25-year decay for LEO).

4. Subsystem matrix

Subsystem	Status
Reaction wheels ADCS	✅ (3 axes, first allowed here)
Magnetorquer detumble	✅
Star tracker	⚠ (optional, adds 150 g)
UHF telemetry	✅
S-band downlink	✅
GNSS	✅
Camera (12 MP)	✅
Payload	✅
Propulsion	⚠ (cold-gas fits, electric needs 6U+)

5. Build

make target-cubesat-3u

Compile-time macro: MISSION_PROFILE_CUBESAT_3U=1 (also the default when no -D is passed). Sets:

• PROFILE_FEATURE_WHEELS=1 (first profile that allows this).
• PROFILE_FEATURE_SBAND=1.
• PROFILE_FEATURE_IMAGERY=1.
• PROFILE_FEATURE_RADIATION=1.

6. Mission config

cp mission_templates/cubesat_3u.json mission_config.json

Key fields:

• orbit.altitude_km / inclination_deg — default 550 / 97.6° SSO.
• subsystems.adcs.tier — wheels (first profile where this resolves).
• subsystems.adcs.star_tracker — true if fitted.
• subsystems.payload.type — your payload.
• mission.telemetry_hz — 1.0 Hz default; up to 4 Hz if S-band pass budget permits.

7. Mass & volume validation

Metric	Value	Status
Total mass	3.55 kg	≤ 4.0 kg ✅ (11 % margin)
Volume used	1180 cm³	35 % of 3405 cm³ ✅

Adding a star tracker + extra battery cells uses ~70 % of the remaining margin — still flight-approvable.

8. Typical mission phases

startup → deployment → detumbling → nominal ⇌ science / comm_window / low_power
                                        ↓ fault
                                    safe_mode
                                        ↓ ack
                                    nominal

Reference timings:

Phase	Nominal duration
startup	5 min (post-release)
deployment	30 min (antennas, panels)
detumbling	30–90 min (B-dot)
nominal	ongoing
science	10–20 min bursts / orbit
comm_window	6–10 min passes
low_power	eclipse-driven, ~30 min
safe_mode	until ground ack

9. Testing checklist (ground qualification)

Legend: [x] = verified in software / CI / SITL (passes in the current release); [ ] = requires bench hardware, RF range test, or flight-day field activity — team must sign off manually.

• Thermal-vacuum: -20 °C to +60 °C, 5 cycles, 6 h each (typical launch provider ICD).
• Random vibration: 14 g-rms, 3 axes, 2 min each.
• Shock: half-sine 1500 g, 0.5 ms, one shot per axis.
• EMC: MIL-STD-461E CE102 / RE102.
• Thermal cycling: 8 cycles from -40 °C to +85 °C at board level.
• Radiation: 60Co TID to 2 krad (see docs/hardware/radiation_budget.md).
• 48-hour soak: UNISAT_SOAK_SECONDS=172800 pytest flight-software/tests/test_long_soak.py.
• End-to-end SITL: scripts/simulate_mission.sh mission_config.json ≥ 1 orbit.

10. Flight-day checklist

Same as 2U plus:

• Reaction-wheel bias torque characterised and stored in NV memory.
• Magnetic offset of final satellite measured and encoded in ADCS config.
• Star-tracker dark-frame calibration uploaded if fitted.
• Downlink key rotated at T-7 days; KeyRotationPolicy.counter_used == 0.

11. Known limitations

• Magnetic torquers lose authority near the magnetic equator — 3U reference attitude accuracy is 0.5° with wheels, 2° without.
• Deep-space or beyond 800 km requires a rad-hard secondary OBC; UniSat 1.x targets ≤ 700 km.
• Propulsion-on-3U budgets are tight — stick with attitude impulse (magnetorquer + wheel desat), not station-keeping.

12. Post-flight debrief

This is the reference profile; log the most data:

• Every pass: AX.25 PCAP, raw telemetry, command log, image thumbnails.
• Daily: SoC profile, wheel momentum, FDIR fault count, reboot count.
• Weekly: orbit decay trend from TLE vs. prediction, SADM + thermal performance.
• Monthly: science data products, publication-ready plots.

Canonical location: docs/operations/flight_reports/ with sub-folders by month.

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