The X-37B, operated by the US Space Force, is currently on its seventh mission (OTV-7), which began in December 2023, showcasing its capability for extended orbital operations.
This mission includes pioneering aerobraking maneuvers, allowing the X-37B to change its orbit using Earth's atmospheric drag, a technique that conserves fuel and marks a significant advancement in space technology.
Space.com
While most details of the X-37B's missions remain classified, its role in testing new space technologies for national security purposes has been acknowledged, with previous missions extending in duration, the last one lasting 908 days.
While most details of the X-37B's missions remain classified, its role in testing new space technologies for national security purposes has been acknowledged, with previous missions extending in duration, the last one lasting 908 days.
Livescience.com
Aerobraking technique details
Aerobraking is a spaceflight maneuver used to reduce the high point of an elliptical orbit (apoapsis) by flying a spacecraft through the atmosphere at the low point of the orbit (periapsis). The friction from the atmosphere slows down the spacecraft, effectively reducing its orbit without the need for significant fuel consumption. Here are some details about the technique:Purpose: Aerobraking is employed to lower a spacecraft's orbit around a planet with an atmosphere, such as Earth or Mars, to achieve a lower, more circular orbit for scientific studies or operational purposes. This technique is particularly useful because it reduces the need for fuel, which is crucial for spacecraft where payload capacity and cost are concerns.
Process:
- Initial Orbit: A spacecraft enters an elongated elliptic orbit with a high apoapsis after a relatively small propulsion burn.
- Aerobraking: The spacecraft then repeatedly passes through the upper atmosphere at its periapsis, where atmospheric drag slows it down. Each pass reduces the apoapsis, gradually bringing the orbit closer to the desired lower, more circular path.
- Monitoring and Adjustments: Since aerobraking requires precise knowledge of the atmosphere, the deceleration is monitored during each pass, and adjustments are made based on the data collected. This process can take several months, involving hundreds of passes for planets like Mars.
- Atmospheric Knowledge: A very detailed understanding of the target planet's atmosphere is necessary to plan the maneuver accurately. This includes understanding atmospheric density, composition, and temperature variations.
- Heat Dissipation: The kinetic energy lost during aerobraking is converted into heat, requiring the spacecraft to have adequate thermal protection.
- Control: Since no spacecraft can currently aerobrake autonomously, constant human oversight and support from space communication networks like the Deep Space Network are essential, especially towards the end of the process when passes are close together.
- Hiten Spacecraft: The first aerobraking maneuver was performed by the Japanese Hiten spacecraft on March 19, 1991, which adjusted its orbit around Earth.
- Mars Global Surveyor (MGS): In 1997, MGS was the first to use aerobraking as a primary method for orbit adjustment around Mars.
- X-37B: Recently, the X-37B spaceplane conducted aerobraking maneuvers to change its orbit around Earth, demonstrating this technique's application in highly classified national security missions.
Benefits: Aerobraking significantly reduces the fuel required for orbit adjustment, allowing for larger payloads or smaller launch vehicles, which can lower mission costs and increase the efficiency of space operations.
Aerocapture technique
Aerocapture is a sophisticated spaceflight technique designed to capture a spacecraft into orbit around a celestial body with an atmosphere by using that atmosphere to slow down the spacecraft from an escape trajectory or flyby into a stable orbit. Here are the key details:
- Definition: Aerocapture uses the atmosphere of a planet or moon to reduce the velocity of a spacecraft sufficiently to transition from a hyperbolic trajectory (which would otherwise result in a flyby or escape) into an elliptical orbit around the body. This is achieved through a single pass through the atmosphere, which contrasts with aerobraking, which involves multiple passes.
- Process:Approach: The spacecraft approaches the target body at high speed on a trajectory that would normally result in a flyby.
- Atmospheric Entry: The spacecraft enters the atmosphere at a carefully calculated point (periapsis) where the drag will be sufficient to slow it down but not so deep as to cause it to crash or burn up.
- Deceleration: Atmospheric drag significantly reduces the spacecraft's speed, converting kinetic energy into heat, which requires robust thermal protection systems.
- Orbit Insertion: After exiting the atmosphere, the spacecraft has slowed enough that its trajectory becomes an elliptical orbit around the body. A small burn at the apoapsis might then be necessary to adjust the orbit further, ensuring stability.
- Key Differences with Aerobraking:Single vs. Multiple Passes: Aerocapture is performed in one pass, while aerobraking involves multiple atmospheric passes to gradually reduce the orbit.
- Purpose: Aerocapture is used for capture from interplanetary speeds into orbit, whereas aerobraking is used to lower an already established orbit.
- Heat Shield Requirement: Due to the high speeds involved in aerocapture, a heat shield is essential to protect against the intense heat generated by atmospheric friction. Aerobraking might not require such protection as it uses the upper atmosphere over many passes, reducing the heat load per pass. Applications: Aerocapture has been proposed for several missions due to its fuel efficiency, particularly for missions to planets with atmospheres like Mars, Venus, or even Titan. It's especially beneficial for missions aiming to reduce the mass of the spacecraft by saving on propulsion fuel, allowing more scientific instruments or other payload to be carried.
Thermal Protection: The intense heat generated during the high-speed atmospheric pass necessitates advanced thermal protection systems.
Risk: There's a higher risk involved since the process is less forgiving than aerobraking; a miscalculation could result in the spacecraft being lost.
Examples and Research:
Although aerocapture has not been widely used in operational missions, it has been studied extensively for future missions. NASA has conducted studies and simulations, particularly for missions to the outer planets where conventional orbit insertion would require a significant amount of fuel.
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