Cargo Resupply Spacecraft Product

Overview

A cargo resupply spacecraft delivers food, spares, experiments, and propellant to a crewed station and disposes of its trash on the way down. The vehicle described here carries about 3,500 kg of pressurized cargo in 27 m³, launches at roughly 7,500 kg, and flies the entire mission — launch dispersions, orbit phasing, rendezvous, and docking — without a pilot. It splits into two sections: the Pressurized Cargo Module, a pressure vessel the crew enters after docking, and the Service Module, which carries everything that burns, stores energy, or thinks.

Cargo module

The Cargo Pressure Shell is a friction-stir-welded aluminum-lithium cylinder holding station atmosphere at 101 kPa. Cargo ships almost entirely as soft stowage: standardized Cargo Transfer Bag units (Cargo Transfer Bags, sized in half, single, and double modules) strapped into Cargo Rack frames that restrain them through 4–6 g launch loads. A Late-Load Hatchway accessible on the pad lets time-critical items — biological samples, fresh food — be installed about 24 hours before liftoff.

Once docked, the module becomes a temporary room of the station. Two Ventilation Fan units exchange air with the station so CO2 cannot pool around working crew, and Cargo Bay Light illuminates the unloading. Unloading and repacking with disposal cargo typically takes the crew 30–60 hours spread over weeks.

Propulsion

The Service Module uses storable hypergolic propellants — monomethylhydrazine fuel and nitrogen tetroxide oxidizer — because they ignite on contact, need no ignition system, and keep for months in orbit. Four titanium Propellant Tank vessels feed the engines through the Propellant Valve Set; internal propellant management devices use surface tension to keep liquid over the outlets in microgravity. Two composite-overwrapped Helium Pressurant Tank bottles store helium at about 31 MPa, regulated down to push propellant to the engines — the whole system is pressure-fed, with no turbopumps to fail.

The Main Engine performs phasing burns during the 1–3 day chase and the final deorbit burn. Twenty-four RCS Thruster units in redundant strings handle attitude control and the fine translation pulses of final approach, where control authority of a few millimeters per second matters.

Power

Two deployable Solar Array Wing wings generate 4–5 kW from triple-junction GaAs cells on rigid Solar Panel substrates. Each wing launches folded under Hold-Down Release Mechanism restraints, unfolds on spring-driven Deployment Hinge joints, and tracks the Sun through a slip-ring Array Drive Assembly. During the ~36 minutes of eclipse each orbit, two Battery Pack units carry the load; each pack is built from Li-ion Cell, 18650 cells with a BMS Board for balancing and Thermal Fuse protection, inside a Battery Enclosure designed to contain a single-cell thermal runaway. The Power Distribution Unit switches and fuses every load on the 28 V bus.

Guidance, navigation, and docking

Three Flight Computer units run in a voting triplex so that any single failure during proximity operations produces a safe abort rather than a collision. Far-field navigation differences the vehicle's GPS Receiver state against GPS data relayed from the station, good to a few meters. Inside about one kilometer the Rendezvous Sensor Suite take over: the Rendezvous LiDAR ranges against retroreflectors on the station, Proximity Camera vision solves full relative pose from docking-target features, and the Thermal Imager keeps tracking through orbital night. Attitude comes from the Star Tracker pair and Inertial Measurement Unit gyros; the S-band Transceiver carries both ground telemetry and the direct proximity link the station crew can use to command a hold or retreat.

Approach follows mandatory hold points (typically 350 m, 250 m, 30 m) along the docking axis at closing rates near 0.05 m/s. At contact the Soft-Capture Ring petals engage the station port and damp the residual energy; twelve Structural Hook then pull the interfaces together, the vestibule is leak-checked with Pressure Sensor readings, Umbilical Connector pairs mate station power and data, and the crew opens the Docking Hatch.

Thermal control and disposal

The Thermal Control System system is mostly passive: MLI Blanket Set blankets isolate the vehicle from the ±120 °C orbital radiative swing, Heater Set films keep hypergol lines above their ~2 °C freezing point, and Body Radiator panels dump avionics heat. Hundreds of points in the Thermistor Set feed the heater loops.

At end of mission the vehicle departs loaded with trash, performs its deorbit burn with the main engine, and breaks up over the South Pacific uninhabited area — disposal by design, which is why the pressure shell needs no heat shield and the structure can stay light.