Sentinel Collective
Shared Sentinel 1U CubeSat · 100 Founding Backers Per Satellite
Technical Overview
Sentinel Collective is shared ownership of a Sentinel 1U CubeSat — the same 1U platform documented in our internal engineering blueprints, funded by a community of up to 100 founding backers instead of a single buyer. $29 puts your name on the satellite manifest. Once a campaign reaches 100 backers, that Sentinel 1U enters the build queue using the bill of materials and subsystem design below. All 100 backers on a funded satellite share access to its UHF/VHF amateur radio link for emergency messaging and GPS-independent positioning.
Subsystem Blueprints
Structure
- ·1U PC/104-compatible frame, 100×100×113.5 mm
- ·6061-T6 aluminum, Type II black anodize
- ·8.5 mm rails per CubeSat Design Spec Rev 14
- ·14.1 Grms vibration tolerance (Falcon 9 spec)
- ·2× redundant deployment kill switches
Primary structure: Endurosat 1U Structure (P/N ES-STR-1U), with Pumpkin Inc. CubeSat Kit 1U qualified as a backup supplier. Four PC/104 boards (EPS, OBC, COMMS, Payload) stack bottom to top on M3 hex standoffs, torqued to 0.4 N·m in a star pattern. Current best estimate mass: 877 g against a 1,330 g CubeSat Design Spec maximum — 453 g of margin.
Electrical Power System
- ·3× body-mounted GaAs solar panels (+X/+Y/+Z)
- ·SpectroLab XTE-SF cells, 29.5% BOL / 26% EOL
- ·~2.8 W average orbital power, nadir-pointing
- ·Li-ion 2S1P 18650 pack, 10 Wh (8 Wh usable)
- ·Endurosat EPS 1U (ES-EPS-1U), MPPT 4-channel
Each solar face delivers ~3.2 W peak when sun-normal; averaged across an orbit with nadir pointing the array nets ~2.8 W. Battery: 2× Molicel INR-18650-P42A cells in 2S1P (7.4 V nominal, 10 Wh), discharged to a maximum 80% depth of discharge. Eclipse (33 min/orbit) draws the pack down at roughly 1.1 W; sunlight (62 min/orbit) is power-positive at the 2.8 W average load.
On-Board Computer
- ·STM32H753, ARM Cortex-M7 @ 480 MHz
- ·2 MB internal flash + 128 MB NAND
- ·FreeRTOS v10.5
- ·Hardware watchdog (Maxim DS1390)
- ·Battery-backed RTC, ±3 ppm (Abracon AB1815)
Endurosat OBC (ES-OBC-1U) or an equivalent custom STM32H7 board. Telemetry runs at 1 Hz housekeeping / 10 Hz attitude. SEL immunity characterized to 43 MeV·cm²/mg on the STM32H7 part. A hardware watchdog forces reset on lockup independent of firmware state.
Communications
- ·Downlink: 437.525 MHz, GMSK 9600 baud, AX.25
- ·Uplink: 145.825 MHz, AFSK 1200 baud, AX.25
- ·0.5 W TX power, 10% max duty cycle (FCC Part 97)
- ·Deployable half-wave dipole, 320 mm extended
- ·Endurosat UHF Type II transceiver (ES-UHF-TRX-II)
Both frequencies sit inside IARU Region 2 satellite sub-bands (145.800–146.000 MHz and 435.000–438.000 MHz). The dipole deploys via a spring-loaded nichrome burn-wire mechanism (0.28 A, 3-second burn) and matches from its 72 Ω intrinsic impedance to the 50 Ω feedline with a simple L-network (47 nH series, 15 pF shunt). VSWR target: <1.5:1 at 437.525 MHz, verified pre-integration with a NanoVNA.
Attitude Determination & Control
- ·Passive magnetic stabilization
- ·AlNiCo bar magnet (Z-axis aligned)
- ·2× Permalloy hysteresis rods for damping
- ·Honeywell HMC5983 3-axis magnetometer
- ·6× photodiode coarse sun sensors
- ·±15° pointing, detumble in <2 orbits
No reaction wheels or thrusters — pointing is entirely passive, using a permanent magnet to align the satellite Z-axis with Earth's magnetic field and hysteresis rods to damp residual tumble within two orbits of deployment. This keeps mass, power, and part count low at the cost of pointing precision, acceptable for an omnidirectional UHF/VHF link.
Payload — Messaging Relay
- ·Semtech SX1276 LoRa transceiver, 915 MHz
- ·−148 dBm receive sensitivity
- ·SAMD21G18A payload MCU (Arduino Zero compatible)
- ·4 MB SPI flash, 1,000+ stored messages @ 256 B
- ·Store-and-forward relay architecture
The payload board receives short messages over a 915 MHz LoRa uplink, stores them in onboard flash, and forwards them on the next ground station pass — the store-and-forward design behind the emergency messaging and GPS-independent location features described on the Collective page.
Bill of Materials
| PART | SPEC | SUPPLIER | LOCATION | EST. |
|---|---|---|---|---|
| 1U CubeSat Structure | 6061-T6 Al, anodized, CDS Rev 14 | Endurosat | ES-STR-1U | $850 |
| Electrical Power System 1U | MPPT 4-ch, 3.3V/5V/12V rails | Endurosat | ES-EPS-1U | $3,200 |
| On-Board Computer 1U | STM32H7, FreeRTOS, 128MB NAND | Endurosat | ES-OBC-1U | $7,500 |
| UHF Transceiver 437 MHz | 437.525 MHz, 0.5W TX, GMSK 9600 | Endurosat | ES-UHF-TRX-II | $4,200 |
| GaAs Solar Panels (×3) | 29.5% BOL, 80 cm² per face | Endurosat | ES-SOL-1U | $5,400 |
| 18650 Li-ion cells (×2) | Molicel INR-18650-P42A, 4,200 mAh | 18650BatteryStore | Online retail | $24 |
| Magnetometer HMC5983 | 3-axis, ±8 Gauss, I²C/SPI | Honeywell (Mouser) | US distribution | $12 |
| LoRa Module SX1276 | 915 MHz, −148 dBm sensitivity | Semtech (Mouser) | US distribution | $7 |
| MLI blanket + thermal tape | 10-layer Kapton/Mylar, 3M 8810 tape | Sheldahl / 3M | US distribution | $145 |
Assembly & Build Sequence
Endurosat EPS (14 wk), OBC (16 wk), UHF transceiver (12 wk), and structure (12 wk) are the critical path — order first. Solar panels run 16 weeks.
CDS Rev 14 compliant 1U frame, 6061-T6 aluminum, Type II black anodize for thermal control. Rail width 8.5 mm ± 0.1 mm, verified per CubeSat Design Specification.
Spot-weld 2× Molicel 18650 cells 2S1P, install battery protection PCB, verify the MPPT charge controller across all 3 solar channels on a bench power supply before integration.
Load FreeRTOS v10.5 on the STM32H753. Configure the hardware watchdog (DS1390) and battery-backed RTC (AB1815). Verify telemetry at 1 Hz housekeeping / 10 Hz attitude on the bench.
Cut and solder phosphor-bronze dipole arms to 160 mm each. Install the L-network match (47 nH / 15 pF) or ADT1-1WT balun. Verify VSWR <1.5:1 at 437.525 MHz with a NanoVNA before integration.
Align the AlNiCo bar magnet to the Z-axis, install 2× Permalloy hysteresis rods, mount the HMC5983 magnetometer and 6 photodiode sun sensors flush to each face.
EPS (bottom) → OBC → COMMS → Payload (top, nadir face). 4× M3 hex standoffs per board, star-pattern torque to 0.4 N·m. Route 24 AWG PTFE harness with JST PH connectors.
Bench-power the full stack, verify deployment switches and that the antenna burn-wire fires within spec (0.28 A, 3 s) and the beacon transmits. Then vibration test to 14.1 Grms (3 axes) and thermal-cycle −30°C to +60°C.
File the IARU satellite coordination request and FCC Part 97 space station notification before integration with the launch vehicle. See the regulatory note below.
How Sentinel Collective Works
Sentinel Collective campaigns are tracked in our own database, not a third-party crowdfunding platform: each campaign (a HAM Radio, Prepper/Survival, or Rural Community cohort, for example) opens with a target of 100 backers at $29 each. Current backer count and spots remaining are shown live on the Collective page.
When a campaign reaches 100 backers, that Sentinel 1U enters the build queue against the bill of materials and subsystem design documented above — the same engineering blueprint used for every Sentinel 1U we build, whether sold individually or funded collectively.
If a campaign does not reach 100 backers within 18 months of opening, every backer on it receives a full refund — we will not launch a satellite that does not have a full community behind it.
Regulatory note: the UHF/VHF links documented above operate in the amateur radio bands under FCC Part 97, which restricts use to non-commercial, no-pecuniary-interest operation. A commercial messaging service at scale requires either FCC Experimental Authorization or a Part 25 commercial license — both are open items in our frequency plan, not yet filed.