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NASA Ames's feature CAPSTONE’s CubeSat Prepares for Lunar Flight says

CAPSTONE will use a hydrazine-fueled propulsion system during most of its three- to four- month journey to the Moon. This line of propulsion system, developed by Stellar Exploration Inc. of San Luis Obispo, California, is a recently developed and flight-proven system developed for use on CubeSats. The team recently completed a fueling and final test-fire of CAPSTONE’s propulsion system at Stellar Exploration’s facility and is integrating the system with the spacecraft.

But before CAPSTONE fires its own thrusters, Rocket Lab’s Electron rocket will launch the mission from Earth carrying the CAPSTONE spacecraft integrated onto its new Lunar Photon upper stage/spacecraft. For the mission, Lunar Photon will serve as an upper stage to get CAPSTONE to a highly efficient ballistic lunar transfer trajectory designed by Advanced Space of Colorado. About seven days after launch, after a series of orbit raising maneuvers and the final trans-lunar injection burn, Photon will release CAPSTONE. After the deep space, low energy transfer, the CAPSTONE spacecraft will insert itself into the near rectilinear halo orbit. At the same time, Lunar Photon will continue to a separate orbit for its safe disposal.

Question: Is there a fairly detailed outline of CAPSTONE's "highly efficient ballistic lunar transfer trajectory" from LEO to lunar near-rectilinear halo orbit? I'm having a hard time picturing when/where CAPSTONE separates from the Lunar Photon and where/how/how much later it inserts itself into NRHO.

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Advanced Space has a great webpage detailing Ballistic Lunar Transfers (BLT) with links to numerous papers/presentations about BLTs. They all seem to refer back to Advanced Space's CTO Dr. Jeffery Parker's PhD thesis (available here$^1$). The webpage has this summary:

BLTs are a type of low-energy transfer in which a spacecraft launches 1-2 million kilometers away from the Earth (where the Sun’s gravity perturbation becomes dominant), then returns to Earth with a larger radius of perigee than before and a different geocentric orbit plane. When designed with the proper geometry, it is possible to choose the perigee to coincide with the Moon’s orbit, bringing the spacecraft into the vicinity of the Moon. For many three-body target orbits, it is possible to design the transfer such that it arrives at the target orbit with very little insertion 𝛥V required. In the ideal case, the transfer is ballistic (zero deterministic 𝛥V) after launch. This type of transfer is being considered to deliver the Logistics Module, lander elements, and other cargo to the lunar Gateway.

From their Ballistic Lunar Transfers Quick Reference Guide is this figure (and text) showing what an example trajectory looks like:

example BLT

In a Scott Manley video interview with Rocket Lab CEO Peter Beck they show this high level Con Ops poster about the CAPSTONE mission:

CAPSTONE Rocket Lab Con Ops

Video cued at 30:30 where they begin discussing Lunar Photon & CAPSTONE:

Peter Beck says that Lunar Photon (aka Photon Interplanetary) needs to perform 8 burns total to raise the apoapsis and perform the final TLI over the course of about 8 days (the blurb in question says 7 days).

CAPSTONE is using an "outbound lunar flyby" to lower the C3 requirement for TLI, though this lengthens the time of flight until rendezvous with the Moon (from Ballistic Lunar Transfers Quick Reference Guide):

BLT C3 & transfer time

The exact transfer time is variable depending on launch date and TLI parameters. As a reference, the GRAIL mission used a BLT and had a transfer time of ~112 days (GRAIL-A):

grail trajectory

(Wikipedia)

References:

  1. J. S. Parker, “Low-Energy Ballistic Lunar Transfers,” University of Colorado Boulder, PhD Thesis, 2007.
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