Protecting the Apollo Sites

Several years ago, our team member Metzger contacted by Astrobotics to provide guidelines for visiting the Apollo landing sites to avoid damaging them. Metzger advocated with NASA headquarters to develop guidelines, and a team was put together led by Rob Kelso of NASA/JSC. Metzger wrote the sections of the guidelines related to plume effects protection. Because we have an inadequate understanding of the plume effects, and because the modeling is still very immature, it was not possible to create very reliable guidelines. The team took the approach that this would be a “living document” that is revised as our understanding of the physics improves. We are currently working toward an update of the document.
The following is a summary of the artifacts on the Moon and the guidelines to protect them.

Types of U.S. Artifacts on the Moon

  • Apollo lunar surface landing and roving hardware
  • Unmanned lunar surface landing sites
  • Impact sites (e.g., Ranger, S-IVB, LCROSS, LM ascent stage)
  • Experiments left on the lunar surface, tools, equipment, misc. EVA hardware
  • Specific indicators of US human, human-robotic lunar presence, including footprints, rover tracks, rocks fractured to take samples, etc.
    • NOTE: not all anthropogenic indicators are protected as identified in the recommendations

Some Representative Artifacts

The following are copied from the NASA document.

An annotated diagram of various components related to lunar exploration. Items include an ALSEP central station, RTG, passive seismic experiment, and a lunar surface magnetometer.

Two pieces of scientific equipment on a lunar surface. On the left is a solar wind spectrometer, and on the right is a suprathermal ion detector/cold cathode ion gage.

Two images: a heat flow experiment with epoxy-fiberglass probes on the left, and a laser ranging retroreflector with fused silica glass reflectors on the right, both situated on a lunar surface.

The image shows four figures from a lunar mission: a solar wind experiment (B9), a hammer and feather demonstration (B10), the U.S. flag (B11), and a gnomon (B12) on the Moon’s surface.

Image of a Lunar Roving Vehicle on the moon, with labeled parts including aluminum frame and seats, fiberglass fenders, nylon seat belts, zinc-coated tires, silica radiators, and MLI/betatcloth insulation.

Image of a Lunar Module Descent Stage with labels highlighting thermal and micrometeoroid protection materials, and the engine nozzle extension made of aluminide-coated niobium.

Some of the Main Guidelines

Landing

  • Land 2 km away from the artifacts on a tangential approach.
  • The purpose of the tangential approach is in case the descent engines fail, the spacecraft is guaranteed to crash at least 2 km away, removing the possibility of crashing directly on the artifacts.

Diagram depicting possible approach paths during descent. Blue circle represents descent plane keep-out radius with an 'X' in the center. Estimated error boundary is shown with dashed lines.

  • Keep plume reflection planes pointed away from the artifacts, since enhance erosion rates and higher ejecta angles occur on those planes.

Diagram depicting multiple engine spacecraft ejecta paths with orange arrows indicating maximum ejecta flux ('rooster tail') and green arrows denoting minimum ejecta flux.

 

  • Land behind natural terrain barriers to block the spray as much as possible
    • 2 km distance reduces but does not eliminate damage
    • Damage is cumulative with each visiting spacecraft
    • Terrain barriers are for ALARA principle, “As Low As Reasonably Achievable”

Low Altitude Flyby

  • Hoppers translating within 2 km should remain higher than 40 m
  • Ensure no dust motion
  • Hoppers never get within a 45 degree cone of artifact boundary
  • Ensure no propellant droplets deposited on artifacts

Diagram of lunar surface with two rectangular objects, labeled "Apollo Site Exclusion Radius (AB)" and "Plume." Droplets are shown inside a 45-degree cone, coming from the plume.

Avoid Damaging Spacecraft That Are In Orbit

  • Collision Avoidance (COLA) windows should be assessed to protect orbiting spacecraft
  • Ejecta travels higher than orbital altitudes
  • Impact velocities will be relative to spacecraft motion, putting it into the hypervelocity impact regime
  • Can expect multiple impacts if spacecraft is at trajectory node same time as ejecta

Some of the Additional Guidelines (in Addition to Plume Effects)

  • Rover keep out zones, varying for each site
  • Linear wheel speed of rovers
  • Use direct approach and backtrack to avoid excessive disturbance of soil

Link to NASA Document

For Additional Information