Preliminary analyses of the Induced Environment Contamination Monitor (IECM) measurements obtained from the STS-2 mission are given by the Instrument Scientists and their colleagues. These first comprehensive measurements of the Space Shuttle induced contamination environment are encouraging, and future flights of the IECM are planned to further define this environment.

The Humidity Monitor measured zero relative humidity during ascent, reflecting the environment provided by the cargo bay dry nitrogen gas purge prior to launch. The Dew Point Hygrometer correspondingly indicated a dew point below its measuring range of -6.7°C (20°F).

Sampling the rapidly changing environment of the Shuttle cargo bay is a challenging requirement. In our approach to meeting this requirement, 1 four time-integrated samples and one rapid acquisition sample were collected to determine the types and quantities of contaminants present during ascent and descent of the Shuttle. Residual gas analyses were made prior to opening the bottles after flight, and analyses for volatile organics were subsequently performed. Analyses for the presence of reactives (HC1 during ascent and NO, NO₂, and NH₃ during descent) were also completed. Pressure profile measurements were obtained to help determine the standard volumes of the sampled environment.

The Cascade Impactor on the IECM is an aerosol sampling instrument using three cascade impaction-type nozzles of progressively smaller diameter, with coated quartz crystal oscillators as collection plates. In this manner, particle size discrimination into three ranges (5 μm and larger, 1 to 5 μm, and 0.3 to 1 μm) is accomplished.

The Optical Effects Module (OEM), built by Advanced Kinetics, Inc., Costa Mesa, California, performed inflight measurements of the ultraviolet (253.7 nm) transmittance and diffuse reflectance of five optical samples at regular intervals throughout the orbital mission. The objective of the OEM was to monitor the effects of the deposition and adhesion of both molecular species and particles on optical surfaces in the Shuttle cargo bay environment.

The purpose of the Temperature-Controlled Quartz Crystal Microbalance (TQCM) system on STS-2 was to measure condensible molecular flux in the payload bay of the Space Shuttle as a function of temperature, direction, and time.1 Five quartz crystal microbalance sen-sors were located in the IECM to measure molecular adsorption in each of the Orbiter axes, +X (fore), -X (aft), +Y (starboard), -Y (port), and -Z (up, perpendicular to payload bay). The temperature of each sensor was controlled by a thermoelectric device so contamination could be measured as a function of four preset temperatures: +30, 0, -30, and -60°C. When orbital altitude was reached, the TQCM sensors began their orbital measuring cycle routine (Figure 1). The sensors were commanded to 80°C for 30 min, which was used as an initial clean-up. They were then stepped through a program of 2-nr collection periods at each temperature with a 30-min, 80°C period between each collection period. The collection periods progressed in descending order from +30 to -60°C and, then the cycle was repeated. Since the STS-2 orbital phase lasted approximately 53 hrs, the TQCM system completed four cycles and was in the fifth when the mission was terminated.

Efforts continue regarding the analysis of particulate contamination recorded by the Camera/Photometers on STS-2. These systems were constructed by Epsilon Laboratories, Inc. and consisted of two 16-mm photographic cameras, using Kodak Double X film, Type 7222, to make stereoscopic observations of contaminant particles and background. Each was housed within a pressurized canister and operated automatically throughout the mission, making simultaneous exposures on a continuous basis every 150 sec. The cameras were equipped with 18-mm f/0.9 lenses and subtended overlapping 20° fields-of-view. An integrating photometer was used to inhibit the exposure sequences during periods of excessive illumination and to terminate the exposures at preset light levels. During the exposures, a camera shutter operated in a chopping mode in order to isolate the movement of particles for velocity determinations. Calculations based on the preflight film calibration indicate that particles as small as 25 μm can be detected from ideal observing conditions. Current emphasis is placed on the digitization of the photographic data frames and the determination of particle distances, sizes, and velocities. It has been concluded that background bright-ness measurements cannot be established with any reliability on the STS-2 mission, due to the preponderance of Earth-directed attitudes and the incidence of light reflected from nearby surfaces.

The IECM quadrupole Mass Spectrometer, developed by the Space Physics Research Laboratory, operates over the range of 2 to 150 amu. The Mass Spectrometer is able to measure from approximately 108 1 to 106 M atoms or molecular/cm²/sec/0.1 sr and uses sintered zirco-nium getter pumps to provide collimation to 0.1 sr. Each amu pulse count is integrated for 2 sec, accomplishing a full sweep in 300 sec, alternating with an equal number of steps on the water peak (amu 18). Thus, the full cycle requires 600 sec, or 10 min. This cycle is repeated throughout the mission unless commanded to other modes .f Also incorporated in the instrument is a ²²Ne, H₂180 gas release system which is designed to provide a measure-ment for evaluating differential scattering cross sections for collisions at Orbiter speeds (8 km/sec). To accomplish this measurement, the gas is released as the Orbiter is maneuvered to scan the Mass Spectrometer/gas release pointing vector from 180 to 0° with respect to the Orbiter velocity vector.

The performance of the IECM on STS-2 was normal throughout the mission, responding properly to all commands and sequencing the instruments in proper order and mode. Although this first IECM flight provided initial data for all phases of the mission, the on-orbit phase was limited to essentially "early mission" time by the shortened flight.

A unified, systematic plan is presented for contamination control for space flight systems. Allowable contaminant quantities, or contamination budgets, are determined based on system performance margins and system-level allowable degradations. These contamination budgets are compared to contamination rates in ground environments to establish the controls required in each ground environment. The use of feedback from contamination monitoring and some contamination control procedures are discussed.

The issue of Shuttle payload processing facility cleanliness has risen in importance in the past months. With the commencement of actual Shuttle flights and with quickly approaching launch dates for so many Shuttle flown payloads, spacecraft representatives are becoming concerned over the cleanliness capabilities of processing facilities, in particular, the Eastern Launch Site (ELS) facilities. To put spacecraft people's minds at ease, a series of environmental verification tests is being performed and preliminary results have recently become available. This paper presents a method for evaluating this test data and specifically addresses test data obtained in the Launch Complex 39A, Rotating Service Structure (RSS), Payload changeout Room (PCR), in December of 1980.

An optical model for contamination effects has been developed for the SAGEII/ERBS instru-ment. This model describes instrument throughput efficiency and response characteristics as a function of molecular contamination thickness for indexes of refraction representative of Shuttle/ERBS/SAGE II contaminants at seven spectral wavelengths between 0.385 and 1.02 micrometers. Contamination effects are treated as thin film coatings on selected optical elements which cause changes in those elements reflection/transmission/absorption characteristics. SAGE/AEM in-orbit performance data were used to estimate the optical constants for the contaminants. SAGE and SAGE II are radiometers that spatially scan the sun through the Earth's atmosphere with a narrow field-of-view in spectral intervals from visible to the near infrared.

Judicious selection of materials, processes and preflight conditioning procedures provide a direct means of contamination control for spacecraft systems/instruments. Selecting low outgassing materials/processing and performing proper preflight cleaning and thermal vacuum conditioning can result in spacecraft hardware with a low intrinsic contamination potential. In an attempt to establish some quantitative effects of various processing/conditioning procedures, some recent Micro-Volatile Condensible Material and Vacuum Optical Degradation tests were performed. These tests established material outgassing rates and the optical transmittance of collected contaminant. Experimentally determined results are given which show the effect that specific material processing and thermal vacuum treatments have on outgassing behavior and contaminant vacuum ultraviolet (UV) transmittance.

One of the problems in spacecraft contamination assessment has been the scarcity of data on the effects of contaminants on optical surfaces. This study measured the effects of collected volatile condensable material (CVCM) on bidirectional reflectance distribution function (BRDF) in situ and the effects of particles on BRDF monitored ex situ. Low scatter mirrors were scanned from 1 to 600 off the specular beam at wavelengths of 10.6 μm and 0.633 μm. The in situ BRDF tests were performed with CVCM from Chemglaze Z-306 over 9922 primer (thickness from 60 to 110 nm), M-773 adhesive (thicknesses from 20 to 95 nm), and multilayer insulation (thickness 57 nm). The effects of vacuum ultraviolet radiation on the CVCM's BRDF was also determined. Ex situ BRDF tests were performed using four different size polystyrene spherical particles (5.2 to 22.2 μm mean diameters) and four different particle density distributions (from 0.56% to 98%)

Contamination budgeting for space optical systems basically starts at understanding the sensitivity of component performance, e.g. mirror reflectance, window transmittance, etc., to surface deposits. To evaluate contamination sensitivity for mirror coatings, eight types representative of those used in the vacuum ultraviolet, visible, and infrared were modeled assuming that the contaminant is uniformly deposited on the mirror surface. Parametric studies over a range of complex refractive indices combined with an examination of optical data available for several organic materials suggested division of the contaminant layer index into three categories, N = 1.5 + 0.1i, N = 1.5 + 0.5i, and N = 1.5 + 2.0i. Contaminant thickness sensitivity curves were then calculated for each of the selected mirror coatings. For comparative purposes, critical thicknesses for each type were extracted, assuming a reflectance loss of 10 percent was allowable. Critical thicknesses ranged from about 10Å. to 1000Å depending on the specifics of coating design and spectral region.

R. Kruger: The format I would like to follow in this session is to allow each of the panel members some 10 or 15 minutes to discuss his or her particular subject, and then we will open the meeting for a general discussion. With that, let me introduce the members of the panel. We will lead off with Jack Triolo. Jack is a member of the Goddard Space Flight Center and will be discussing planning for contamination con-trol. The next person who will speak is Harry Poehlmann. Harry is Manager of the Materials Engineering Department at Ball Aerospace Systems Division, and he will be discussing materials from the various aspects of space application. He will be followed by Jim Austin, also from Ball Aerospace, and Jim will be talking about fabrication, assembly, and transportation. Next, Gene Borson from the Material Sciences Lab of The Aerospace Corporation will discuss the aspects of integration and tests. Finally, Nancy Pugel of Martin-Marietta, Denver, will be talking about the contamination aspects of Shuttle integration. What we have tried to do is set an order like the flow of a spacecraft program. With that, I'd like to ask Jack Triolo to begin with his discussion planning for contamination control in the spacecraft program.

Simultaneous degradation of the infrared Earth Sensor Assemblies (ESA) on TIROS-N and Defense Meteorological Satellites, and cleanup or recovery of the ultraviolet channels in the Earth Radiation Budget (ERB) instruments on Nimbus satellites, have been observed. The simultaneous radiometric variations which occurred in the radiometer channels facing the spacecraft velocity direction started during a period of rapidly increasing solar activity. Mechanisms causing the optical degradation and cleanup of ESA and ERB channels were compared. These included radiation damage caused by charged particles, self contamination, exospheric reactions and micrometeoroids. Results of studies show that the presence of both atomic oxygen and oxygen ions of the 0I-type at satellite altitudes were the principal cause of the radiometric variations. Concentrations of these particles have been observed to increase with solar activity. The flux of this relatively static and reactive gas impinging on the front surfaces of the high speed spacecraft apparently cleaned the organic contaminant film off the ERB solar channels. This is similar to the way that ozone cleans organic contaminant films during optics manufacturing.

To extract the maximum information content of orbiting particulates from a remote-sensing particulate monitor there are three instrument design requirements: (1) the monitor must be an imaging coronagraph; (2) it must be capable of range-finding; and (3) it must yield absolute photometric measurements. When all three requirements are met, the number, size, and velocity distributions of the vehicle-induced particulates can be deduced. Examples of each of these requirements, as realized during the Shuttle-3 and Skylab-3 missions, are discussed. A design is presented for a coronagraph suitable as a particulate monitor for Shuttle missions.

Atmospheric optical emission measurements by the Visible Aircilow Experiment (VAE) on board the Atmosphere Explorer (AE-C, D and E) satellites have been analyzed and found to be contaminated at low altitudes. The contamination maximizes in the forward direction along the spacecraft velocity and is sensitive to the composition and density of the ambient atmosphere. Analysis at two different wavelengths suggests that the contamination is likely to have a diffuse band spectrum which is brighter toward the red. Some unknown processes which involve satellite surface materials and the incoming ambient particles are believed to be responsible for the contamination. A simulation model is presented here to account for the observed angular dependence.