kensat

KENSAT — Edge-AI Compute in Orbit

A 2U CubeSat that runs a large language model on-orbit. A power-gated NVIDIA Jetson Orin Nano executes neural-network inference in space, and the results are downlinked over a custom UHF radio link to amateur ground stations.

KENSAT’s mission is to demonstrate autonomous AI compute on a small satellite — taking a GPU-class accelerator and a quantized LLM out of the data center and running them inside the tight power, thermal, and reliability envelope of a 2U CubeSat. The on-board computer wakes the Jetson only when needed, runs an inference within a measured energy budget, and frames the output for downlink. Everything else in the spacecraft — the flight software, the UHF radio and its RF matching networks, the power system, and the antenna-deployment hardware — exists to get that compute on orbit, keep it alive, and get its results to the ground.

Why it’s hard. Edge AI in orbit means treating a multi-watt accelerator as a scheduled, fault-tolerant load: powering it from a battery-backed bus only in defined windows, dissipating its heat passively in vacuum, recovering it if it hangs, and surviving the brownouts and resets that come with switching that much current on a small satellite. KENSAT is built end to end around that problem.

Mission profile: a 520 km sun-synchronous orbit, operating UHF amateur radio at 437.08 MHz for beaconing, telemetry downlink, and command uplink. Telemetry — including downlinked inference results — is intentionally unencrypted so amateur operators worldwide can receive and decode it.

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Radio link (for receiving stations)

KENSAT beacons openly on the UHF amateur band — no encryption, no keys. Anyone with a 70 cm receiver and a G3RUH-capable TNC (Direwolf, gr-satellites, SatNOGS) can decode it.

Beacon / downlink frequency	437.080 MHz
Transmitter	Mode U — GFSK 1k2 AX.25 G3RUH
Modulation	GFSK
Baud	1200
Framing	AX.25 UI, NRZI + G3RUH
Source callsign	KO6IKZ
Beacon interval	~10 s
Status	active
Encryption	none — telemetry is open by design

Everything in the info field is plain ASCII. Frames are identified by their first token:

Frame	Carries
BCN	Housekeeping beacon: cumulative sequence number, boot count, reset cause, uptime, body rates, uplink frames received
LLM	One per on-orbit inference: Jetson temperatures and peaks, power, RAM, model-load and inference times, result CRC-32, and how many text frames to expect
TXT	The text the on-board LLM generated, as numbered chunks — s= result, c=<k>/<m> chunk, h= CRC-32 of the whole result
ACK	Acknowledgement of a received telecommand

A result is sent one chunk per beacon cycle and the whole set twice, because the link has no ARQ. To reassemble: group by s=, order by c=, concatenate, and check h= (standard CRC-32). ground-station/llm_downlink.py does this for you, from live decoder output or a saved log.

Command uplink is a short authenticated ASCII telecommand (Si4463 native framing, CRC-16) that can inhibit the transmitter, ping the spacecraft, uplink a prompt of up to 256 characters for the LLM in a single frame (which starts the inference), or run a library prompt. Formats, verbs and the reasoning behind them are in firmware/obc/README.md.

Decoders, the result reassembler and an end-to-end test harness live in ground-station.

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System at a glance

        ┌──────────────────────────────────────────────┐
        │  Burn-Wire Board (custom)                     │  Slot 4 (top)
        │  Antenna-release driver · resistive heating   │
        ├──────────────────────────────────────────────┤
        │  Radio Board (custom)                         │  Slot 3
        │  Si4463 UHF transceiver + AS179 T/R switch    │
        │  Jetson Orin Nano (edge-AI payload)           │
        ├──────────────────────────────────────────────┤
        │  EPS Board (custom)                           │  Slot 2
        │  2S2P 18650 pack · rails · hardware watchdog  │
        ├──────────────────────────────────────────────┤
        │  Pumpkin MB + PPM D1 (PIC24FJ256GB210)        │  Slot 1 (bottom)
        │  OBC — always-on C&DH, Salvo RTOS             │
        └──────────────────────────────────────────────┘
              104-pin CubeSat Kit Bus (H1/H2)

   UHF dipole ── U.FL ── matching network ── AS179 ── Si4463 ── SPI ── PIC24

Boards interconnect over the 104-pin CubeSat Kit Bus. The PIC24 is the always-on flight computer; it talks to the EPS over I²C, drives the Si4463 radio over SPI, controls and exchanges data with the Jetson over UART, and fires the antenna-deployment burn wires over GPIO.

See docs/system-architecture.md for the full spec: pinouts, bus map, operational modes, deployment state machine, power budget, and thermal analysis.

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Subsystems

Subsystem	What it is	Highlights
firmware/obc	PIC24 flight software (C, Salvo RTOS)	Fault-tolerant antenna deployment with flash-persisted state, AX.25 beacons, Si4463 driver, IMU, SD/serial-flash logging, command parser
radio	Custom 437 MHz UHF radio board	Si4463 + AS179 T/R switch, ESP32-S3 firmware, KiCad 2-layer design
radio/rf-design	RF matching-network design & test	Custom scikit-rf optimizer over LCSC-stocked parts, CPWG parasitic modeling, ADALM-Pluto SDR test bench
eps	Electrical power system board	2S2P 18650 pack, regulated rails, hardware watchdog (KiCad)
burnwire	Antenna-release deployment board	Redundant nichrome burn-wire driver (KiCad)
jetson	Edge-AI payload	Jetson Orin Nano running a quantized LLM (llama.cpp/TinyLlama) over UART, systemd daemons, thermal management
ground-station	SDR ground station & decoders	ADALM-Pluto RX/TX, AX.25 beacon decoder, DSP diagnostics, end-to-end test harness
docs	System documentation	Architecture spec, radio guide, Jetson startup, debug notes

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Engineering highlights

• An LLM running in orbit. The payload is an NVIDIA Jetson Orin Nano running a quantized TinyLlama model under llama.cpp. The always-on PIC24 keeps it powered down, then — on schedule or command — switches on its rail through a high-side load switch, waits for the Jetson to boot and signal READY over UART, dispatches a prompt, collects the generated text, powers the Jetson back off, and queues the result for downlink. The whole cycle is bounded by a measured per-inference energy budget so a single run can’t drain the pack. Prompts come either from a library pre-loaded on the payload — so the mission produces results with no uplink at all — or from the ground, uplinked as a single 256-byte prompt field that the OBC runs as soon as it arrives. (docs/system-architecture.md §6.2, jetson/)

• Treating a GPU as a spacecraft load. Running multi-watt edge compute on a 2U bus is a systems problem: the EPS sizes a battery-backed rail and a hardware watchdog around the Jetson’s draw, the OBC power-gates it and can recover a hung payload by cutting power, and the design accounts for dissipating its heat passively in vacuum, where there’s no convection. (docs/system-architecture.md §8.1)

• Fault-tolerant by construction. Both the inference cycle and the antenna burn-wire release are one-shot, flash-persisted state machines that survive the brownouts and resets that come with switching large currents: attempt counts are written before energizing, success flags only after completion, and the RF-silence hold fails safe toward staying quiet. (details)

• A complete UHF link to get results down. TX / RX / antenna matching networks were designed with a custom scikit-rf grid-search optimizer that models PCB traces as CPWG transmission lines (elliptic-integral method) and snaps to real LCSC part values, then validated on an ADALM-Pluto SDR loopback bench (gain sweep, harmonics, insertion loss). Inference output is framed as AX.25 and downlinked openly. (radio/rf-design)

• Signal-integrity-aware bus design. The Si4463 SPI bus crosses two board-to-board connectors; the design derates the clock and adds series termination accordingly. (docs/spi-debug-notes.md)

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Repository layout

kensat/
├── docs/             System architecture spec + guides
├── firmware/obc/     PIC24 flight software (app/ + bsp/)
├── radio/            UHF radio: ESP32 firmware, KiCad board, RF design
├── eps/              Electrical power system board (KiCad)
├── burnwire/         Antenna deployment board (KiCad)
├── jetson/           Edge-AI payload daemon + systemd units
└── ground-station/   SDR scripts, beacon decoder, diagnostics

Building

• OBC firmware depends on proprietary vendor SDKs (Pumpkin CubeSat Kit BSP, Salvo RTOS) that are not redistributed here. See firmware/obc/BUILD.md.
• Radio firmware builds with arduino-cli for the ESP32-S3.
• RF design / ground-station tools are Python; see the requirements.txt in each directory.

License

Original work in this repository is released under the MIT License. Proprietary vendor SDKs the firmware builds against are not included and are not covered by that license — see the LICENSE file and firmware/obc/BUILD.md.

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KENSAT — UHF amateur satellite, 437.08 MHz. Telemetry is open and unencrypted by design, in the tradition of the amateur radio community.