14 DAY TRIAL // Physicist Phil Metzger warns about the danger of flying rocks that could have energies high enough to smash concrete poles, and punch holes through chain link fences, during the blast off of the solid rocket engines that lift the space shuttles. The exhaust of the engines can blast concrete pieces from the flame trench, as large as a half a meter in diameter, so people and equipment must be kept at a safe distance.
The effect is greatly amplified on objects with low gravitational fields such as the Moon, which could potentially pose a threat to future NASA missions which plans to create a long term outpost. Spacecrafts coming and going to the Moon could blast large amounts of debris that would fly for long distances. However, large objects like boulders should pose no problems due to the fact that spacecrafts are less massive than those used on Earth, and don't need much energy to lift from the lunar surface due to its low gravity. This has also been proven by the Apollo 6 mission, which made movies during liftoff from the Moon's surface, showing that a debris not larger than gravel was thrown off by the engine's exhaust.
On Earth, small particles such as dust or sand, blasted by the solid fuel rocket engines, travel a relative small distance, and rapidly fall back to the surface, as a result of the presence of a thick atmosphere. However, the Moon barely has any atmosphere, and tiny particles and gravel can travel long distances at high speeds.
In 1969, NASA launched its second manned mission to the Moon, which landed only 200 meters away from the robotic probe Surveyor 3 launched only two years before. As the crew of the Apollo 12 mission, approached the probe to photograph it, they realized that its white surface had turned to brown in two years of activity, only the side facing the Lunar Module being cleaned by the blast of the engines.
The dust collected from the Surveyor 3 probe showed that the sandblast resulted only in creating particle ranging from 1 to 10 micrometers in diameter, that created 30 to 60 micrometers craters across its surface, some of them infiltrating the inside of the probe, and even the Surveyor's camera. This could pose problems to future lunar outposts, as high-speed clouds of sand could grind their reflective coatings, windows, or completely destroy the vital solar panels, and cause mechanical failure.
Clouds of dust created by exhausts can theoretically travel all the way around the Moon. By analyzing the marks created on the surface of the Surveyor 3 probe, Metzger calculated that the particles of dust could actually have speeds close to those of the exhaust gases produced by the lunar module engine. Particles traveling at speeds of 1.7 kilometers per second can travel as far as half the way around the Moon, anything over 2 kilometers per second would travel all the way around it.