The International Space Station (ISS) receives fuel primarily through resupply missions launched from Earth. These missions deliver propellant needed for altitude maintenance, attitude control, and reboosting to counteract atmospheric drag.
Methods of Fuel Delivery
Fuel is delivered to the ISS via unmanned cargo spacecraft. These spacecraft are launched by various international partners. Key methods include:
- Progress (Russia): This unmanned cargo spacecraft regularly delivers propellant, along with other supplies, to the ISS.
- Cygnus (Northrop Grumman): This U.S. cargo spacecraft also delivers fuel to the ISS.
- HTV (Japan): The H-II Transfer Vehicle (HTV), also known as Kounotori, delivered supplies including propellant until it was retired.
- Dragon (SpaceX): The Dragon spacecraft can deliver supplies to the ISS, but SpaceX doesn't offer this capability as part of their Commercial Resupply Services.
Types of Fuel Used
The ISS relies on a combination of propellants for its various propulsion needs. The two main types are:
- Gaseous H/O Rockets (High Thrust): These rockets utilize gaseous hydrogen and oxygen.
- Hydrazine (for traditional chemical rockets): This is a common monopropellant used for attitude control and orbital adjustments.
- Resistojets (Low Thrust): These systems can potentially utilize waste fluids, although this is still in development and not the primary source of propellant at present.
Purpose of Fuel
The fuel delivered to the ISS serves several crucial functions:
- Altitude Maintenance: The Earth's atmosphere, though very thin at the ISS's altitude, still exerts drag. This causes the ISS to gradually lose altitude. Regular reboosting maneuvers are required to maintain its operational orbit.
- Attitude Control: The ISS needs to maintain a specific orientation in space for solar panel efficiency, scientific experiments, and communication. Fuel is used to power thrusters that control the station's attitude.
- Orbital Adjustments: Minor orbital adjustments may be necessary to avoid space debris or to optimize the station's position for specific activities.
Future Considerations
While the ISS currently relies on resupply missions from Earth, future technologies may enable in-situ resource utilization (ISRU), allowing the station to generate its own propellant from resources found in space. This could significantly reduce the cost and complexity of maintaining the ISS in the long term.
In summary, the ISS gets its fuel through regular resupply missions launched from Earth by various international partners. This fuel is crucial for maintaining the station's altitude, attitude, and orbital position.
