Bi-elliptic transfers

Definition

Bi-elliptic transfers are a type of orbital maneuver used to transfer a spacecraft from one circular orbit to another circular orbit at a different altitude, utilizing two elliptical arcs. This method involves an initial burn to enter an elliptical transfer orbit, followed by a second burn at the apogee of that orbit to achieve the desired final orbit. The bi-elliptic transfer is an alternative to the Hohmann transfer and is often more efficient in terms of fuel usage when dealing with large altitude changes.

5 Must Know Facts For Your Next Test

1. Bi-elliptic transfers are generally more fuel-efficient than Hohmann transfers when the altitude difference between orbits is significant, particularly when going to a higher orbit.
2. The initial burn in a bi-elliptic transfer can be smaller compared to a Hohmann transfer, which can save fuel when starting from low Earth orbit.
3. The total time of flight in a bi-elliptic transfer can be longer than in other methods due to the additional elliptical orbit phase.
4. Optimal conditions for bi-elliptic transfers depend on specific mission profiles, including the desired altitude change and spacecraft capabilities.
5. Bi-elliptic transfers can be especially useful for missions requiring precise insertion into higher orbits without expending excessive energy.

Review Questions

• How does a bi-elliptic transfer compare to a Hohmann transfer in terms of fuel efficiency and mission profiles?
  • A bi-elliptic transfer can be more fuel-efficient than a Hohmann transfer when the altitude difference between the initial and final orbits is large. While a Hohmann transfer is often preferred for smaller altitude changes due to its shorter time of flight, bi-elliptic transfers reduce fuel consumption during the initial burn, making them advantageous for specific mission profiles that require significant altitude increases.
• Explain the steps involved in executing a bi-elliptic transfer and how each phase contributes to reaching the final orbit.
  • Executing a bi-elliptic transfer involves three main phases: first, an initial burn places the spacecraft into an elliptical transfer orbit. Next, as the spacecraft reaches apogee, a second burn is performed to raise the perigee to the desired final circular orbit. This method utilizes two elliptical arcs, allowing for adjustments in velocity at both the initial and final positions, which helps achieve more efficient energy use during large altitude transitions.
• Evaluate how mission-specific factors influence the choice between using bi-elliptic transfers versus other orbital maneuvers.
  • Mission-specific factors such as the required altitude change, spacecraft capabilities, and available fuel significantly influence the choice of using bi-elliptic transfers over other orbital maneuvers like Hohmann transfers. For missions needing substantial altitude adjustments with limited fuel budgets, bi-elliptic transfers may provide a more efficient solution despite potentially longer travel times. Additionally, factors such as trajectory accuracy requirements and launch windows also play crucial roles in determining the optimal maneuver for successful mission outcomes.

Related terms

Hohmann Transfer: A type of orbital maneuver that involves two engine burns to transfer between two circular orbits, typically the most fuel-efficient method for small altitude changes.

Apogee: The point in an elliptical orbit where the spacecraft is farthest from the celestial body it is orbiting.

Delta-V: The change in velocity required for a spacecraft to perform a maneuver, critical in determining fuel consumption for orbital transfers.