During 2014 and 2015, NASA's Neutron star Interior Composition Explorer (NICER) mission proceeded success- fully through Phase C, Design and Development. An X-ray (0.2-12 keV) astrophysics payload destined for the International Space Station, NICER is manifested for launch in early 2017 on the Commercial Resupply Services SpaceX-11 flight. Its scientific objectives are to investigate the internal structure, dynamics, and energetics of neutron stars, the densest objects in the universe. During Phase C, flight components including optics, detectors, the optical bench, pointing actuators, electronics, and others were subjected to environmental testing and integrated to form the flight payload. A custom-built facility was used to co-align and integrate the X-ray "con- centrator" optics and silicon-drift detectors. Ground calibration provided robust performance measures of the optical (at NASA's Goddard Space Flight Center) and detector (at the Massachusetts Institute of Technology) subsystems, while comprehensive functional tests prior to payload-level environmental testing met all instrument performance requirements. We describe here the implementation of NICER's major subsystems, summarize their performance and calibration, and outline the component-level testing that was successfully applied.
Over a 10-month period during 2013 and early 2014, development of the Neutron star Interior Composition Explorer (NICER) mission  proceeded through Phase B, Mission Definition. An external attached payload on the International Space Station (ISS), NICER is scheduled to launch in 2016 for an 18-month baseline mission. Its prime scientific focus is an in-depth investigation of neutron stars—objects that compress up to two Solar masses into a volume the size of a city—accomplished through observations in 0.2–12 keV X-rays, the electromagnetic band into which the stars radiate significant fractions of their thermal, magnetic, and rotational energy stores. Additionally, NICER enables the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration of spacecraft navigation using pulsars as beacons. During Phase B, substantive refinements were made to the mission-level requirements, concept of operations, and payload and instrument design. Fabrication and testing of engineering-model components improved the fidelity of the anticipated scientific performance of NICER’s X-ray Timing Instrument (XTI), as well as of the payload’s pointing system, which enables tracking of science targets from the ISS platform. We briefly summarize advances in the mission’s formulation that, together with strong programmatic performance in project management, culminated in NICER’s confirmation by NASA into Phase C, Design and Development, in March 2014.
Space based laser missions have gained their popularity in areas such as: communication, power
beaming, ranging, altimetry, and Light Detection and Ranging. The capabilities of 1.0 micron lasers
offer a host of improvements in the knowledge gaps that exist and help promote our understanding
of our Earth and lunar environments as well as planetary and space science applications. Some past
and present National Aeronautics and Space Administration missions that have been developed for
increasing our universal knowledge of such environments and applications include: The Shuttle
Laser Altimeter, Mars Orbiter Laser Altimeter, Geoscience Laser Altimeter System, Mercury Laser
Altimeter, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, and Lunar Orbiter
The effort of contamination control depends on the specific performance goals, instrument designs,
and planned operating scenarios of such missions. Trace amounts of contamination have been
shown to greatly reduce the performance of 1.0 micron space based laser systems. In addition, the
type of contamination plays an important role in the degree of degradation and helps to define the
"contamination sensitivity" of the mission. A space based laser mission is considered highly
contamination sensitive and therefore requires an unprecedented contamination control effort.
We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 μm. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.
The Solar Terrestrial Relations Observatory (STEREO) is a pair of identical satellites that will orbit the Sun so as to drift ahead of and behind Earth respectively, to give a stereo view of the Sun. STEREO is currently scheduled for launch in November 2005. One of the instrument packages that will be flown on each of the STEREO spacecrafts is the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI), which consists of an extreme ultraviolet imager, two coronagraphs, and two side-viewing heliospheric imagers to observe solar coronal mass ejections all the way from the Sun to Earth. We report here on the inner coronagraph, labeled COR1. COR1 is a classic Lyot internally occulting refractive coronagraph, adapted for the first time to be used in space. The field of view is from 1.3 to 4 solar radii. A linear polarizer is used to suppress scattered light, and to extract the polarized brightness signal from the solar corona. The optical scattering performance of the coronagraph was first modeled using both the ASAP and APART numerical modeling codes, and then tested at the Vacuum Tunnel Facility at the National Center for Atmospheric Research in Boulder, Colorado. In this report, we will focus on the COR1 optical design, the predicted optical performance, and the observed performance in the lab. We will also discuss the mechanical and thermal design, and the cleanliness requirements needed to achieve the optical performance.
On-orbit, self-contamination of a spacecraft is a concern facing instrument and spacecraft designers. While on the Earth, gases adsorb onto spacecraft surfaces. These gases are later released when placed in the vacuum of space. The rate at which the emitted gases are returned to the spacecraft by collisions with other gaseous molecules is known as the return flux. Models predicting the amount of gas released by a spacecraft that is returned to itself do exist, but these models have had very limited experimental testing. We describe a flight experiment designed to provide a test of these models and the analysis of the data obtained by that experiment. The experiment flew on a 1996 space shuttle mission and provided in-situ testing of the return flux models. Analysis of the limited data obtained by the experiment has determined the return flux is primarily due to collisions with the ambient atmosphere and not collisions with other gases released by the spacecraft. Limited measurements of the ambient atmosphere were also made.
The goal is the Active Cleaning for Space-systems (ACES) project is to develop and demonstrate a new means for on-orbit cleaning of particle contaminants from optical surfaces on satellites. This paper describes the rationale for on-orbit cleaning, a carbon dioxide (CO<SUB>2</SUB>) snow cleaning system, and a future Space Shuttle experiment with that system. The experiment and hardware designs are described in some detail to show how all experiment objectives will be met.
A TQCM coated with graphite was flown aboard a Spartan carrier in January 1996. During a flight of about 46 hours at an altitude of 305 km, the graphite reacted with the atomic oxygen (AO) in the environment and was eroded away. The 15-MHz TQCM's frequency dropped from 6800 to 4000 Hz in about 15 hours of exposure and was shown to be a strong function of the TQCM's orientation to the ram direction. The erosion rates for four different ram angels was measured and found to be both consistent and repeatable. The average graphite volume loss for the 61 degree and -62 degree ram angles was calculated to be about 2 X E-08 cm<SUP>3</SUP>/hr and for the 18 degrees and 19 degrees angles to be about 8.5 X E-08 cm<SUP>3</SUP>/hr, which is slightly less than previous flight data. The erosion data was then correlated with AO density numbers for the particular times and positions of the spacecraft in orbit. From this analysis, an equation was derived that shoed the carbon volume loss as a function of both atomic oxygen density and ram angle. For example, 1.59 E-07 cm<SUP>3</SUP>/hr would be the calculated carbon volume loss for a ram angle of 0- degrees and an AO fluence of 3.52 E+17 atoms/hr. The results of this data and analysis may lead to the development of a sensor capable of monitoring the AO fluence on a spacecraft.
The fraction of neutral molecules transmitted through a restrictive passage in molecular flow can be highly dependent on the shape of the reservoir from which the gas originates. A particular reservoir shape was investigated to determine its effect on the angular distribution of molecules entering two types of simple restrictive passages. It was determined that a reservoir consisting largely of two-dimensional shells imparted a bimodal distribution to the reservoir gas, resulting in lemniscate flux distributions for the gas entering a baffle network. A Monte Carlo code was developed and compared to analytical transmission probabilities calculated by Clausing. After establishing the validity of the code, the effects of lemniscate and Lambertian flux distributions for molecular flow were simulated for two-dimensional channels and right- angle bends for various length-to-height ratios. It was determined that the shape of the entrance distribution can play an important role in the calculation of transmission probabilities.
The Hubble Space Telescope (HST) has been designed to accommodate changeout and/or repair of many of the primary instruments and subsystem components, in an effort to prolong the useful life of this orbiting observatory. In order to achieve the science goals established for this observatory, many HST instruments must operate in regimes that are greatly influenced by the presence of on-orbit propagated contaminants. To insure that the required performance of each instrument is not compromised due to these contaminant effects, great efforts have been made to minimize the level of on-orbit contamination. These efforts include careful material selection, performing extensive pre-flight vacuum bakeouts of parts and assemblies, assuring instrument assembly is carried out in strict cleanroom environments, performing precision cleaning of various parts, and most recently, the incorporation of a relatively new technology -- molecular adsorbers -- into the basic design of future replacement instruments. Molecular adsorbers were included as part of the wide field/planetary camera 2 (WFPC-2) instrument, which was integrated into the HST during the servicing mission 1 (SM1) in 1993. It is generally recognized that these adsorbers aided in the reductio of on-orbit contamination levels for the WFPC-2 instrument. This technology is now being implemented as part of the basic design for several new instruments being readied for the servicing mission 2 (SM2), scheduled for early 1997. An overview of the concept, design, applications, and to-date testing and predicted benefits associated with the molecular adsorbers within these new HST instruments are presented and discussed in this paper.
The Environmental Verification Experiment for the Explorer Platform (EVEEP) was launched in June 1992 and is flying on an Explorer Platform along with the Extreme Ultraviolet Explorer (EUVE). EVEEP consists of five Temperature-Controlled Quartz Crystal Microbalances (TQCMs) and the necessary electronics to control the sensors and prepare the data for downlink. Two of EVEEP's TQCMs were coated with Teflon prior to flight for atomic oxygen studies. The remaining three TQCMs were not coated and are dedicated to contamination accretion studies. The two Teflon coated TQCMs were designed to give a transient demonstration of the erosion of Teflon material caused by atomic oxygen. One of the coated TQCMs is located on the shade side of the platform and experiences only atomic oxygen erosion. The other TQCM is located on the sun side of the platform and demonstrates the effects of ultraviolet radiation on the atomic oxygen erosion rate. An analysis of the erosion rates is presented for each situation emphasizing the differences between the two erosion rates. The three uncoated TQCMs measure contamination due to direct flux emitted on-orbit. This data has been used to verify current contamination modeling techniques. There is one TQCM on each side of the platform whose sole view is of the back of the nearest solar array. These arrays were painted with TW1300 white paint. Since there are two separate TQCMs with similar views, a redundant check on the modeling techniques for this configuration was possible. A comparison between the on-orbit data and the results from the analytic contamination model is presented.
The transport of molecules, under vacuum conditions, from a source surface to a receiving surface is of major concern from the perspective of spacecraft contamination control. The transport phenomena involved is a complex mechanism comprising the physical characteristics of each surface, the properties of contaminant species participating, and the temperatures of both surfaces. Because of both the complex nature and the limited data available to describe such a phenomena, contamination modeling usually requires that a highly simplified engineering approach be undertaken. One area where this is particularly true is in the representation of the surface accommodation of incident molecules. When a molecule in the gas phase collides with the surface of a receiver it can either "stick" to that surface or be scattered away. Molecules accommodated by this surface become thermally equilibrated to the receiver temperature while the material that is not accommodated retains its original energy and undergoes specular reflection. The ratio of this thermally accommodated mass to the total incident mass is known as the "accommodation" or "sticking" coefficient. Most of the current theory and experimental work performed to date has been restricted to the accommodation coefficients of the rare gases in contact with metal surfaces3'10"1. UnfortUnately, the results generated by these studies cannot be made very useful to spacecraft contamination engineers who are predominantly interested in environments where contaminants are typically limited only to water and long-chain hydrocarbons. Because of this deficiency most current spacecraft contamination analyses are forced to rely on general mathematical expressions that consider the sticking coefficient to be only a direct function of the temperature gradient between the emitting and receiving surfaces. The major shortcoming of the simplified method presently in use is that it may provide an inadequate representation of the actual molecular transport occurring between surfaces. The purpose of this paper is, therefore, to study the nature of the transport mechanisms involved in the adsorption of high molecular weight gases on typical spacecraft surfaces, the overall concept of the sticking coefficient, and the quantitative and qualitative theory involved. In addition, this paper will examine some of the existing molecular accommodation data as it relates to spacecraft applications, as well as present new experimental data gathered by the Contamination Control Section of the Goddard Space Flight Center (GSFC). All this information will then be correlated and used to verify the accuracy of the most common sticking coefficient equations in use by contamination analyses.