Thrust chamber health monitoring

With the arrival of the reusable space propulsion systems, the new field of propulsion system health monitoring is emerging. Health monitoring consists of measuring and reviewing engine operating parameters which will warn of engine deterioration or abnormal operation well in advance of any failure. The health monitoring data can be used to establish that an engine should be repaired or replaced, thereby avoiding a future flight failure. This paper presents a status report on the development of a health monitoring system for regeneratively cooled thrust chambers. The system employs a single measurement with a simple nonintrusive sensor to monitor the operation of the engine. The basic measuring and sensor concept is explained and the results of both laboratory and engine firing tests with the health monitoring system are presented.     

The Development of Systems Engineering

Systems engineering is described as the design of the whole as distinguished from the design of the parts. Systems engineers create the architecture of the system, define the criteria for its evaluation, and perform tradeoff studies for optimization of the subsystem characteristics. In addition to their own brains, the principal tool of systems engineers is the computer. Systems engineering has evolved during a long series of major developments, in particular the intercontinental ballistic missile (ICBM) program. The major growth of systems engineering is expected to be in the improvement of its tools and in the enlargement of the range of problems to which it is applied.     

The sondrestrom radar and accompanying ground-based instrumentation

The Sondrestrom radar facility, funded by the NSF Upper Atmospheric Facilities Program, is operated and managed by SRI International. The facility is located on the west coast of Greenland, just north of the Arctic Circle, near 75 deg invariant magnetic latitude. The principal instrument at the facility is the incoherent scatter radar. The incoherent scatter technique allows the direct measurement of ionospheric electron number density, ion velocity, and electron and ion temperature along the radar beam. Because the radar antenna is fully steerable these parameters can be determined as functions of horizontal distance and altitude. Additional ionospheric quantities can be derived using these measured parameters. As part of the ISTP mission, the radar will measure the spatial (horizontal and altitudinal) and temporal variations of ionospheric parameters including electron density, large scale electric field. conductivity, currents, and energy input. Repetitive measurements define variations of parameters with local time, as well.     

An ultra stable optical bench for the magnetic survey satellite

An optical bench has been designed and built that must hold the alignment of five optical elements to deflections of 1–2 arc s during orbital operation. In addition, it must suffer no alignment changes during the launch and prestabilization phase of the mission. Severe weight constraints, in conjunction with the thermal and structural requirements, led to the choice of graphite fiber reinforced epoxy egg crate core and face sheets for the bench construction. Active temperature control was necessary to meet thermal deflection objectives, and novel kinematic mountings were required to prevent spacecraft bending from deflecting the bench. The structural and thermal analyses both show that the mission objectives can be met with margin by the present design. No adverse effects from launch are expected, and the maximum thermal bending is expected to be less than 2 arc s.     

Trojans in habitable zones

With the aid of numerical experiments we examined the dynamical stability of fictitious terrestrial planets in 1:1 mean motion resonance with Jovian-like planets of extrasolar planetary systems. In our stability study of the so-called "Trojan" planets in the habitable zone, we used the restricted three-body problem with different mass ratios of the primary bodies. The application of the three-body problem showed that even massive Trojan planets can be stable in the 1:1 mean motion resonance. From the 117 extrasolar planetary systems only 11 systems were found with one giant planet in the habitable zone. Out of this sample set we chose four planetary systems--HD17051, HD27442, HD28185, and HD108874--for further investigation. To study the orbital behavior of the stable zone in the different systems, we used direct numerical computations (Lie Integration Method) that allowed us to determine the escape times and the maximum eccentricity of the fictitious "Trojan planets."     

Lunar orbital science

Summary Orbital science has, to the present, concentrated on studies of force fields, particles, and visible photography. Cameras have been the major scientific instrument (it could be debated that for geodesy and gravity the entire spacecraft represents an instrument), and geology has been the principle benefactor. Photography has also been essential for the manned landing program, which would not have been possible on the schedule followed without the detailed Lunar Orbiter pictures.Orbital tracking data indicates that the Moon is almost homogeneous with perhaps a slight increase in density with depth. Significant analysis of the higher gravity harmonics have identified localized, near surface gravity highs that appear to be associated with circular maria. The Moon does not have a significant magnetic field of its own, and the solar wind appears to impinge directly on the surface. Russian and United States evidence on micrometeorite fluxes near the Moon is conflicting, but probably there is a decrease in flux compared to that near the Earth.Photographic evidence indicates that both impact and volcanic action has shaped the lunar surface. Mass movements of surface material and surface erosional effects are clearly evident. Surface water in the past, or near surface permafrost now, are definite possibilities to explain the sinuous rills. Faulting, both regional and local, is evident, as is probably horizontal layering near the surface.The United States space program is embarking on a broad program of orbital science including nearly the entire spectra of remote sensing. Approved orbital missions extend through 1972 and will be carried out in conjunction with manned landings. Emphasis will be placed on determining the extent and degree of surface variations between and within lunar provinces and the nature and strength of the lunar spectrum. Information obtained from the surface missions and the returned lunar samples will be invaluable in helping us to design orbital instruments and interpret the results.Missions after 1972 undoubtedly will carry more sophisticated instruments that will give us definitive information on the geochemical nature of the lunar surface and interior.Copies of NASA-issued documents may be obtained by writing to the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Information about, and data from, U.S. space missions, including photographs, can be obtained from the National Space Science Data Center, Code 601, Goddard Space Flight Center, Greenbelt, Maryland 20771.