Recent advances to enhance low Earth orbit space simulation

Abstract

Accurate ground-based simulation of low Earth orbit (LEO) conditions experienced by a satellite has proven to be a challenge. Recent progress that has been made toward the development of means for simulating portions of the LEO environment will be reviewed. A satellite in LEO has a speed relative to the atmosphere of approximately 8km∕s. The neutral atmospheric molecules exchange momentum upon collision with the surfaces of the satellite, leading to drag, lift, and moments, but ground facilities still have trouble simulating pure beams of ground state atmospheric gases at this speed. The most important atmospheric species, atomic oxygen, collides with ram-direction satellite surfaces with a relative energy of 5eV. The solar UV spectrum in LEO is a composite of many emission lines and continuum, which must be simulated using special lamp systems. Thruster plumes and outgassing molecules result in a contamination atmosphere close to the spacecraft surface. Energetic atomic oxygen atoms in the presence of solar UV radiation and contamination gases can produce synergistic effects that result in many chemical reactions on or in the vicinity of the outer satellite surfaces. These reactions can lead to structural or operational damage to various satellite components, such as a reduction in the effectiveness of thermal control paints, cleanliness of optical lenses, and the reduction of the output of solar cells. Several techniques for generating beams of 5eV atomic oxygen in the ground state will be reviewed as well as special diagnostic instrumentation developed to detect atomic oxygen. These are combined in space simulation chambers for a more complete study of materials degradation. Some electric thrusters exit directly to the vacuum of space. Their exhaust and plume simulation presents unique vacuum chamber pumping problems. Specially designed cryogenic pumps to simulate the conditions that these electric thrusters will experience in orbit will be described. Reference to inventories of space simulation chambers will be given.