Retrograde burn

Definition

A retrograde burn is a maneuver performed by a spacecraft to decrease its velocity relative to a celestial body, typically used to lower its orbit or bring it back to a desired trajectory. This burn involves firing the spacecraft's engines in the opposite direction of its current motion, effectively slowing it down. Understanding retrograde burns is crucial for executing orbital maneuvers and transfers, as they enable spacecraft to adjust their orbits and positions for successful missions.

5 Must Know Facts For Your Next Test

1. Retrograde burns are essential when a spacecraft needs to enter a lower orbit or deorbit back to a planetary surface.
2. Performing a retrograde burn requires precise calculations of timing and thrust to achieve the desired change in velocity.
3. The effectiveness of a retrograde burn depends on the current speed and altitude of the spacecraft, as well as gravitational influences from nearby bodies.
4. Retrograde burns can also be critical for rendezvous maneuvers where one spacecraft needs to match or intercept another's orbit.
5. In some missions, such as returning from Mars, retrograde burns are necessary to ensure safe re-entry into Earth's atmosphere.

Review Questions

• How does a retrograde burn impact a spacecraft's orbital dynamics?
  • A retrograde burn directly impacts a spacecraft's orbital dynamics by decreasing its velocity. This reduction in speed leads to a change in the spacecraft's orbit, allowing it to transition to a lower altitude or a different trajectory. By understanding this relationship, engineers can plan maneuvers that effectively navigate the complexities of space travel.
• What factors must be considered when planning a retrograde burn for a mission returning from another planet?
  • When planning a retrograde burn for a mission returning from another planet, several factors must be considered including the spacecraft's current velocity, altitude, and the gravitational influence of the celestial body. Additionally, mission planners need to account for fuel requirements, timing for the burn relative to the planetary position, and the trajectory needed to ensure a safe re-entry into Earth's atmosphere.
• Evaluate how retrograde burns are used in conjunction with other orbital maneuvers like Hohmann transfers and prograde burns.
  • Retrograde burns are often used alongside Hohmann transfers and prograde burns to effectively manage spacecraft trajectories. For instance, while Hohmann transfers facilitate efficient movement between orbits with minimal fuel use, retrograde burns can lower an orbit post-transfer or assist in rendezvous missions. By evaluating these maneuvers collectively, mission planners can create complex trajectories that optimize fuel usage and time efficiency for space missions.

Related terms

Hohmann Transfer Orbit: An efficient method of transferring between two orbits using two burns, one to leave the initial orbit and one to enter the target orbit.

Delta-v: The change in velocity required for a spacecraft to perform maneuvers, including burns, to alter its trajectory.

Prograde Burn: A maneuver that increases a spacecraft's velocity by firing its engines in the same direction as its current motion, used to raise its orbit.