Cargo resupply missions are robotic spaceflights that deliver food, water, experiments, spare parts, fuel, and other supplies to astronauts living in orbit. They make long duration space stations possible because crews cannot carry everything they will need at launch. These missions also return scientific samples to Earth or dispose of trash by burning up in the atmosphere.
Understanding resupply helps students connect orbital motion, spacecraft control, and real engineering logistics.
Key Facts
- Orbital speed near the International Space Station is about 7.7 km/s.
- A cargo spacecraft must match the station's orbit before docking or berthing.
- Delta-v, written Δv, is the change in velocity needed for maneuvers.
- Circular orbit speed is v = sqrt(GM/r), where r is distance from Earth's center.
- Travel time after launch can range from a few hours to several days depending on the rendezvous plan.
- A reentering disposal vehicle slows due to atmospheric drag, converting kinetic energy into heat.
Vocabulary
- Rendezvous
- Rendezvous is the process of bringing two spacecraft to nearly the same orbit, position, and speed.
- Docking
- Docking is when a spacecraft connects itself to a station using its own guidance and docking mechanism.
- Berthing
- Berthing is when a robotic arm captures a visiting spacecraft and attaches it to a station port.
- Delta-v
- Delta-v is the total change in velocity a spacecraft must produce to complete a maneuver or mission.
- Reentry
- Reentry is the phase when a spacecraft enters a planet's atmosphere and is slowed by drag and heating.
Common Mistakes to Avoid
- Thinking the cargo ship flies straight up to the station, which is wrong because the station is moving sideways at orbital speed and the vehicle must enter a matching orbit.
- Confusing docking and berthing, which is wrong because docking is self-connection while berthing uses a robotic arm to attach the spacecraft.
- Assuming rockets keep firing the whole time in orbit, which is wrong because spacecraft usually coast and use short engine burns for course corrections.
- Ignoring relative speed near the station, which is wrong because even small speed errors can create large safety risks during final approach.
Practice Questions
- 1 A cargo spacecraft is 20 km behind the station along the same orbit and closes the gap at 5 m/s relative speed. How long will it take to reach the station's position if the speed stays constant?
- 2 A resupply vehicle carries 2600 kg of cargo at launch and 650 kg is food and crew supplies. What percentage of the cargo is food and crew supplies?
- 3 Explain why a cargo spacecraft must approach the station slowly during final rendezvous even though both objects are traveling around Earth at about 7.7 km/s.