Ballistic Capture Orbit

Author: CislunarSpace

Website: https://cislunarspace.cn

Definition

A ballistic capture orbit is a low-energy unpowered capture trajectory that exploits the Weak Stability Boundary (WSB) theory. When a spacecraft's apogee distance relative to Earth greatly exceeds the lunar orbit radius, solar gravitational perturbation can gradually drive the spacecraft into the Moon's weak stability boundary, achieving temporary lunar capture without requiring a braking maneuver at perilune.

This approach saves approximately 15% of Δv compared to conventional Hohmann transfers to lunar orbit. The tradeoff is a longer transfer time, as the spacecraft follows a winding trajectory influenced primarily by solar gravity before naturally entering the lunar sphere of influence.

Japan's Hiten (MUSES-A) satellite, launched in 1990, was the first successful application of ballistic capture. After its primary mission, Hiten was redirected to the Moon using a WSB transfer, arriving in lunar orbit in 1991 without a dedicated lunar orbit insertion burn. NASA's GRAIL mission also employed a ballistic capture approach in 2012.

Key Properties

  • No braking burn: Capture occurs naturally through gravitational dynamics, eliminating the need for a costly orbit insertion maneuver
  • Δv savings: Approximately 15% less Δv than Hohmann transfers
  • Longer transfer time: Requires significantly more flight time than direct transfers
  • Solar perturbation dependent: Relies on the Sun's gravitational influence to redirect the spacecraft into the lunar WSB

References

  • Belbruno, E. (1990). "A New Lunar Transfer Route." AIAA/AAS Astrodynamics Conference.
  • Belbruno, E. & Miller, J. (1993). "Sun-Perturbed Earth-to-Moon Transfers with Ballistic Capture." Journal of Guidance, Control, and Dynamics.