Spacecraft

A PROVES Kit 1U bus with an AMSAT LTM payload

The spacecraft is built almost entirely from open-source PROVES Kit hardware. The one custom board is a PROVES V5d flight controller with its on-board radios removed and replaced by an interface to the LTM.

Subsystems

Payload: AMSAT LTM

A V/u linear transponder (SSB/CW, 30 kHz passband) with a 1200 bps BPSK telemetry beacon and a command receiver. It is a three-board PC-104 stack (transponder at the bottom, the ICR command receiver in the middle, and the LTI host interface on top), 92 × 90 × 33 mm, 130 g, running on 5–7 V. It has flight heritage on HuskySat-1, Fox-1E and MESAT1.

amsat.org → LTM

Flight controller: FC V5d LTM

RP2350 running CircuitPython, with an LSM6DSO IMU, LIS2MDL magnetometer, RTC and SD NAND. The RFM98/E28 radios are replaced by an MCP25625 CAN controller (1 Mbit/s) and a switched 5 V LTM supply that stays off at boot and is enabled after antenna deployment. The board also carries umbilical sense, console and telemetry lines and a host temperature sensor.

FC_V5d_LTM_mods_20261010 · firmware / ltm1 driver

EPS

The EPS sits on the flight controller: an LT3652 2S solar charger (8.38 V float, 1 A), a TPS54226 3.3 V rail, the TPS54225 5 V LTM rail, INA219 battery and solar monitors, per-face load switches, and TPS4H160 burn-wire and heater drivers.

Battery pack v2

Four 18650 Li-ion cells in 2S2P (NCR18650B class, about 48 Wh at 7.2 V), with an R5460 2-cell protector, back-to-back FETs and four TMP112 temperature sensors.

battery_pack_v2

Solar: XY Faces V2a

Six KXOB101K08TF mono-Si cells per face in 2s3p, with Schottky-isolated strings. Each panel also carries a MCP9808 temperature sensor, a VEML7700 light sensor and a DRV2605L-driven PCB magnetorquer coil. About 1.6 W per face at normal incidence (AM0, BOL).

XY_Faces_V2a

Antenna top cap v2c

A +Z endcap with burn-wire-released tape-measure elements, a CSD17576 burn FET, a balun, an MMCX feed and sun/temperature sensors.

antenna_top_cap_v2c

Structure

The PROVES 1U frame is made of 1.6 mm 5052 aluminium sheet with PA-12 feet, M2.5 self-clinching fasteners and normally-closed deployment switches. It has been vibration-tested to 20 g RMS and thermally cycled.

PROVES documentation

ADCS

Passive and magnetic. B-dot detumble uses the face PCB coils and the torque rods/air coil from the PROVES build. No pointing is required: the transponder and beacon work while the spacecraft tumbles, at the cost of the antenna-null allowance in the link budget.

System block diagram

 Solar faces x5 ──(2s3p, Schottky OR)──► LT3652 charger ──► 2S2P 18650 pack (6.0–8.4 V, VBUSP)
                                                                │
          ┌──────────────────────── FC V5d LTM ─────────────────┼─────────────────────────┐
          │  TPS54226 ─► +3V3 ─► RP2350, IMU, mag, RTC, SD, MCP23017, sensors            │
          │  TPS54225 ─► LTM_VSYS 5 V  (EN = MCP23017 GPB6, forced on by USB umbilical)  │
          │  MCP25625 ─► CAN 1 Mbit/s ─────────────┐                                      │
          │  TPS4H160 ─► burn wire, heater          │   I2C (LTM master) ─► MAX31725      │
          └────────────────────────────────────────┼──────────────────────────────────────┘
                                                   ▼  J30 harness
                                   AMSAT LTM-1 (LTI · ICR · Transponder)
                                    │ 2 m RX (uplink)      │ 70 cm TX (downlink)
                                    ▼                      ▼
                          V-band element (TBD)      Antenna top cap v2c

Mass budget

This budget is derived from the PROVES Atlas DAS component list (The-PROVES-Project-DAS), with the PROVES payload board and camera replaced by the LTM and its harness.

Component	Qty	Unit (g)	Total (g)	Source
Primary structure (PROVES 1U frame)	1	92.0	92.0	Atlas DAS
Flight controller (FC V5d LTM)	1	44.6	44.6	Atlas DAS
Battery pack board (battery_pack_v2)	1	44.6	44.6	Atlas DAS
Li-ion 18650 cells (2S2P)	4	46.0	184.0	Atlas DAS / NCR18650B
AMSAT LTM (3-board PC-104 stack)	1	130.0	130.0	amsat.org LTM page
LTM harness (J30 to H1/H2)	1	10.0	10.0	estimate
Solar panels (XY_Faces_V2a / Z)	5	2.5	12.5	Atlas DAS
Solar cells (KXOB101K08TF)	30	3.3	99.0	Atlas DAS
Antenna top cap (v2c)	1	42.7	42.7	Atlas DAS
Tape-measure antenna elements	2	0.1	0.2	Atlas DAS
Card brackets	6	4.4	26.4	Atlas DAS
L-brackets	4	2.4	9.6	Atlas DAS
Feet (PA-12)	8	2.1	16.8	Atlas DAS
M2.5 fasteners	44	0.3	13.2	Atlas DAS
M2.5 bolts + locknuts	16	1.0	16.0	Atlas DAS
Wire harnessing	1	170.0	170.0	Atlas DAS
Torque rod cores	1	81.0	81.0	Atlas DAS (2 rods combined)
Torque rod windings	2	4.0	8.0	Atlas DAS
Magnetorquer air coil	1	200.0	200.0	Atlas DAS
Current best estimate			1201
Contingency (5 %)			60
Maximum expected value			1261	CDS 1U limit 2000 g

Open design items

1. V-band (2 m) receive antenna. The antenna top cap's tape elements are about 0.18 m long, which is a 70 cm quarter-wave. The LTM's uplink is in the 144 MHz band and needs its own element (about 0.5 m quarter-wave) or a diplexed dual-band arrangement. The link budget assumes a dedicated V-band monopole.

2. Charger operating point. The LT3652 input-regulation threshold (about 8.44 V) and startup headroom need to be checked on the bench against the 2S panel's V_mp and V_oc at hot and cold temperatures. The power budget carries a 10 % operating-point loss for this.

3. FC V5d LTM layout. Parts are placed but not routed (87 ratsnest connections). The J30–LTM harness has not been designed yet.

4. LTM interface details. CAN termination, the host temperature-sensor address and health-message encoding all need to be confirmed with AMSAT. The interface follows AMSAT's partner documentation, which is not reproduced on this site.

5. Part-number reconciliation. The solar cell part (KXOB101K08TF vs SM101K07TF) and the battery protector variant differ between README, schematic and footprint in the source repositories.