Spacelab-1 (SL-1) Mission on Flight STS-9
Spacelab-1 was a pioneering first joint NASA-ESA Shuttle mission (STS-9, Columbia), a 10-day flight with a 6 member crew from Nov. 28 to Dec. 8, 1983 (launch from KSC (Kennedy Space Center) at Cape Canaveral, FLA, landing at Edwards AFB, CA). The prime objective of the mission was to demonstrate the ability to conduct advanced scientific research in space, with astronauts and payload specialists working in the Spacelab module and coordinating their efforts with scientists at the POCC (Payload Operations Control Center), of NASA/MSFC located at the Johnson Space Center (JSC), Houston, TX, for the Spacelab-1.
The mission marked the maiden flight of Spacelab, the first purpose built space laboratory. An important aspect of the Spacelab and Shuttle concept was the fact that the payload instruments could be re-flown many times over.
Figure 1: Cutaway view of the Shuttle with the SL-1 payload (with PM & two pallets), image credit: NASA
The Spacelab facility itself was a large modular and reusable laboratory designed by ESA to fit into the payload or cargo bay of the US Space Shuttle, connected to the Orbiter crew compartment by a long tube (tunnel). The goal of the Spacelab program was to provide a ”shirt sleeve” environment which allowed scientific experiments to be performed in LEO (Low-Earth Orbit) on a routine basis.
The overall architecture and concept of the Spacelab structure consisted of pressurized laboratory modules (core module, experiment module) and unpressurized pallets that could be used in various combinations/configurations for different types of science missions (i.e., operation of exposed instruments). The core module contained supporting systems, such as data processing equipment and utilities for the pressurized modules and pallets (if pallets were used in conjunction with the pressurized modules). The experiment module provided more working laboratory space and contained only floor-mounted racks. 1) 2)
The PM (Pressurized Module), with a volume of 75 m3 (4.1 m diameter and 7 m in length), was the principal element of the mission providing the astronauts with a comfortable working environment. The inner walls of the PM were furnished with standard instrument racks.
The SL-1 mission was the first of two flights comprising the so-called Spacelab VFT (Verification Flight Test) program. The SL-1 configuration consisted of an interconnected Spacelab transfer tunnel, a long module (7 m in length and 4.06 m of outer diameter), and a single pallet. The CPSE (Common Payload Support Equipment) included the SWAA (Spacelab Window Adapter Assembly), SAL (Scientific Airlock), and an aft-end cone-mounted viewport assembly. Furthermore, the SL-1 configuration, included experiment hardware in the pressured module and on the pallet, representing five broad areas of investigation. Also included throughout the configuration was hardware comprising the Spacelab-1 VFI (Verification Flight Instrumentation) system to provide for the acquisition of additional data required to accomplish the objectives of the VFT program. The total mass of the Spacelab-1 facility at launch was 15,088 kg (total payload mass of about 3,000 kg). 3) 4)
Launch: The launch of the Spacelab-1 mission took place on Nov. 28, 1983 (STS-9 flight on Columbia) from KSC (Kennedy Space Center).
Orbit: Perigee of 240 km, apogee of 257 km, inclination = 57º, period = 89.5 minutes (a total of 167 orbits were flown during the mission). The launch represented the northern-most inclination (57º) of any US manned flight (to cover also observations in the region of middle Europe).
Figure 2: View of the SL-1 Pressurized Module the cargo bay as seen from the Orbiter cabin (image credit: NASA)
Figure 3: The pallet of SL-1 loaded with atmospheric and plasma physics instruments (image credit: NASA)
Table 1: Legend to Figure 4
Figure 5: The crew of flight Spacelab-1 (image credit: NASA)
The 6-man crew of SL-1 was divided into two teams, each working 12-hour shifts for the duration of the mission. John W. Young, Robert A. Parker and Ulf Merbold formed the Red Team, while Brewster H. Shaw, Owen Garriott and Byron K. Lichtenberg made up the Blue Team. Ulf Merbold was the first foreign citizen (Germany, ESA astronaut) to participate in a Shuttle flight.
Subset of the Spacelab-1 sensor complement: (Metric Camera, MRSE, Grille, ISO, SOLSPEC, SOLCON, ACRIM, ALAE)
The first Spacelab mission, positioned in the payload bay of the Space Shuttle, carried a multi-disciplinary payload intended to demonstrate that good science could be done on short shuttle flights.
A total of 73 experiments were carried out in the fields of atmospheric and plasma physics, astronomy, solar physics, material sciences, technology, life sciences, and Earth observations. In retrospect, the Spacelab -1 mission was highly successful, having proved the feasibility of the concept of carrying out complex experiments in space.
The Metric Camera is a DLR experiment in imaging technology. The Metric Camera is considered to be the first civil spaceborne experiment dedicated to photogrammetry; it was proposed and managed by Gottfried Konecny (PI) of the Institute of Photogrammetry and Surveying at the University of Hannover, Germany. At the start of the 1980s, spaceborne imagery for topographic applications could not be provided by Landsat imagery [Landsat-4 was launched July 16, 1984; TM (Thematic Mapper) provided a resolution of 30 m, and MSS (Multispectral Scanner) of 80 m, with both sensors on a swath of 185 km].
The Metric Camera was a slightly modified aerial survey camera of Carl Zeiss, Oberkochen, Germany, of the type RMK A (Reihenmesskammer A) 30/23. The Metric Camera was mounted on the optical-quality window in the ceiling of the Spacelab pressurized module. Objective: to test the mapping capabilities of high-resolution space photography on a large film format (23 cm x 23 cm). 8) 9) 10) 11) 12) 13) 14) 15)
Application: Topographic and thematic mapping. The metric camera provided high-resolution photographs and experimental results on planimetric and topographic mapping from a spaceborne platform. Analysis has shown that these images may be used for mapping at a scale of 1:100,000.
The RMK A30/23 camera consisted of the following elements:
- Camera body with optics and mounting brackets (the camera body consisted of a solid casting with the following parts: a) lens cone with shutter and focal plane frame, b) main motor with drive unit, c) blower motor, d) display for auxiliary data).
- Two film magazines containing aerial film of 24 cm width and 150 m in length
- Two filters (1 spare)
- RCU (Remote Control Unit)
- Camera suspension mount [the camera interfaced to the SWAA (Spacelab Window Adapter Assembly), an optically flat high-quality window via a camera suspension mount]
- Stowage containers (the camera, film magazines and filters were stowed in special containers in experiment racks during launch and landing).
Table 2: Instrument parameters of the Metric Camera (RMK A)
For metric camera operations, the Shuttle flew with the open cargo bay oriented towards Earth. In this flight attitude, the camera's optical axis looked vertically down to the Earth's surface. A total of 21 camera operations (exposure series) were taken which varied in duration from 2 to 18 minutes. During the mission, approximately 36 h were flown in this Earth-oriented attitude, of which 4.5 h were suitable for taking photographs over land. Actually, about 3 hours of these were used for camera operations to expose all the film material that was loaded in two magazines.
A total of 1019 photographs were exposed of which 546 were on CIR (Color Infrared) film and 473 on BW (Black and White) film. The CIR-film was KODAK Aerochrome Infrared Film 2443 and the B/W was KODAK Double-X Aerographic Film 2405.
The camera was installed inside the pressurized cabin of the Spacelab module under controlled environmental conditions. The average cabin temperature was 22º C with an air pressure of about 1020 mbar.
The operation of the camera was fully automatic, in that the start and stop of every exposure series (operation), as well as, the settings for every single exposure were stored in the onboard master computer and were transferred to the camera via a microprocessor. No exposure meter was used for the exposure control to avoid wrong exposure settings caused by single clouds over the target areas. 16)
The objective of the Metric Camera experiment was to test the capability of high resolution stereoscopic space images for compiling and updating topographic and thematic maps. About 50 major investigators participated in the evaluation of the image data and their final results were presented at a Metric Camera Workshop at DLR, Oberpfaffenhofen in February 1985. The results of the analog (film) imagery obtained can be summarized as follows:
• Ground resolution: 10-15 m (pixel equivalent)
• Planimetric accuracy: ± 10 m
• Height accuracy: ± 15 m
• Due to the limited ground resolution the maximum map scale that could be derived was 1:100,000.
Figure 6: Illustration of the Metric Camera (image credit: DLR)
Figure 7: View into the objective of the Metric Camera (image credit: Deutsches Museum)
Background: The Spacelab-1 mission was originally scheduled for the summer of 1980, but due to various Shuttle problems, the launch was postponed to the summer of 1983. NASA policy required all experiments to be delivered and accepted for the original launch date - with no major experiment changes or updates allowed in the long waiting period. This was the main reason why no FMC (Forward Motion Compensation) system could be added to the Metric Camera.
Also, since the Spacelab-1 launch, originally planned for the summer months, was delayed twice from September to October, and then finally to the end of November 1983, the lighting conditions over the higher latitudes of the northern hemisphere became increasingly unfavorable as the sun elevation for the camera operations never exceeded 30º.
NASA promised a reflight of the Metric Camera on the EOM -1/2 (Earth Observation Mission) of NASA scheduled for launch in the summer of 1986. For this Shuttle flight, the Metric Camera was equipped with a FMC system and with high-resolution films to improve the ground resolution considerably. The camera system was already integrated into the EOM-1/2 payload and waiting for launch - when the Challenger accident happened on January 28, 1986 (STS-51L). This catastrophic event revised all further Shuttle flights completely so that no more reflight for the Metric Camera could be realized.
Note: The only calibrated mapping film camera which has been flown after the Metric Camera was the Large Format Camera (LFC) of NASA, which was operated on Shuttle flight (STS-41G), Oct. 5-13, 1984, on the initiative of Fred Doyle. This camera was equipped with a FMC system and a large image size of 46 cm x 23 cm (with the long size of the film in the flight direction) to improve the stereoscopic effect. It could be shown, that from these images, location accuracies of better than 10 m could be obtained for all three coordinates of the target, and that compiling and revision of topographic maps at a scale of 1:50,000 and larger was possible.
Figure 8: Metric Camera image of the Mount Everest region with the summit at the center (image credit: DLR)
Figure 9: Metric Camera image of the White and Blue niles in Sudan, Africa (image credit: NASA)
MRSE (Microwave Remote Sensing Experiment):
• The main mode in X-band (9.6 GHz) featured a two-frequency scatterometer (2 FS) to measure backscatter from the ocean surface (both modes featured a low-noise amplifier)
• A high-resolution mode (25 m ground resolution) was to be used for SAR (Synthetic Aperture Radar) applications
• A passive mode for radiometer applications (measurement of ocean surface temperatures).
Originally, the objective of the radiometer was to support the active modes by measuring the influence of the atmosphere for calibration. Unfortunately, a malfunction of the MRSE instrument transmitter occurred during the mission which prevented the operation of the SAR and the scatterometer modes of the instrument. The failure was caused by arcs of the high-voltage cathode supply at the TWTA (Travelling Wave Tube Amplifier) connections in the low-pressure environment (vacuum) of the Shuttle orbit.
Pre-flight tests of the TWTA operation in a vacuum chamber provided correct results. The most probable causes of the malfunction onboard Spacelab-1 were seen in a seal ring leakage that resented a partial pressure for the TWTA. Note: the TWTA worked again perfectly after the return of the Spacelab-1 mission under atmospheric conditions. It was later used for many years in the airborne E-SAR instrument of DLR. 19)
Figure 10: Conceptual view of the MRSE antenna system (image credit: DLR)
The MRSE equipment had been installed in the Shuttle bay on the right side of the pallet, with an antenna pointing of about 34º to the rear and 35º upwards. The antenna was an offset Cassegrain system type with a parabolic main reflector, a hyperbolic subreflector, and a horn feed. Two linear polarizations (V, H) could be selected by a wave guide switch. The main parts of the antenna used carbon fiber on the basis of honeycomb structures. The two-axis antenna pedestal allowed depression angles from 25 to 55º, and azimuth angles from -35 to 40º relative to the pallet coordinate system.
Table 3: MRSE antenna characteristics
The MRSE microwave radiometer featured a Hach-type receiver and a modified Dicke radiometer with two reference temperatures for calibration. The “hot” reference temperature was 371 K, the “cold” reference was at 293 K which corresponded to the ambient temperature of 20ºC. The radiometer was operated throughout the mission covering 35 data takes in various flight paths.
Table 4: MRSE receiver characteristics
Grille (Infrared spectrometer):
Grille is a French/Belgian sensor with the objective to measure the chemical makeup of the middle and upper atmosphere 15-150 km altitude range - by observing how chemical species emit or absorb radiation. Grille provides a good resolution in the infrared region (2.5-10 µm) of the spectrum; it measures vertical profiles of: CO, CO2, NO, H2O, CH4, H2O and HCl.
The instrument name comes from a special “grille” (literally cricket) used as a window for one leg of its optical system and as a mirror for the other to overcome the limitations of many conventional instruments. Grille possesses the advantage of a luminosity approximately one hundred times better than the conventional slit spectrometer and, compared to the Fourier transform spectrometer, has the practical advantage of directly recording the spectral information in the very narrow spectral range where this information is relevant. The analysis of the Grille measurements lead to the discovery of methane in the mesosphere from 50 km upward, a higher altitude than previously observed or expected. 20) 21) 22) 23) 24) 25)
The Grille telescope has an aperture diameter of 30 cm and a focal length of 6 m. Two detectors are being used in parallel to cover the entire spectral range. The limb-viewing instrument is reprogrammable (use of a microprocessor) to allow interaction between the payload specialist on board and the groundbased investigators. A built-in calibration light source permits tests at any time before and during flight.
Grille performed 25 occultation scenes on Spacelab-1. Observations at sunset took place in the northern hemisphere at latitudes ranging from 56-30º. The sunrise observations took place at high southern latitudes, they provided pertinent information on interhemispheric seasonal variations of the observed atmospheric species, such as thermospheric CO.
The Grille instrumentation was mounted onto the unpressurized pallet, having a mass of 128 kg and a volume of 0.7 m2 x 1.8 m (height). The mass of the module equipment was 15 kg. The source data rate was 51.6 kbit/s.
Note: The Grille instrument was also flown on the ATLAS-1 mission of NASA on STS-45 (March 24-April 2, 1992)
Figure 11: Optical layout of the Grille spectrometer (image credit: NASA)
ISO (Imaging Spectrometric Observatory):
ISO is an echelle-cross disperser grating spectrograph of NASA/MSFC. The experiment objective was to obtain daytime and nighttime low light level spectroscopic measurements of atomic and molecular species in the middle and upper atmosphere from the extreme ultraviolet to the infrared (30 to 1300 nm). There were five spectral bands from 30-1300 nm. Some parameters of the ISO instrument were: 26) 27) 28)
- Instrument: Consists of an array of five imaging spectrometers ( 0.5 m, f/4.0)
- Imaging type: Spatially resolved spectral imaging (slice of 20 km atmosphere altitude range imaged on the limb at 90 km TRH)
- Other modes: Limb scanning with front mirror, shuttle roll scan
- Detector: Intensified solid-state array (CCD), 380 x 488 pixels
- Wavelength range: 30 to 835 nm, five simultaneous images
- Spectral resolution: 0.25 to 1.0 nm plus 0.01nm at 307 nm band
- Temporal Resolution: 4 second frame time with two 2 second sub frames.
The ISO instrument consists of five identical spectrometer modules each of which is restricted to a given spectral range in the 30-1300 nm region. Each module is an imaging spectrometer with a coincident FOV of 0.65º x 0.01º. Imaging is obtained along the length of the observational field by use of an intensified CCD array developed especially for the ISO. The wavelength resolution varies between 0.2 - 0.6 nm over the spectral range. A scan mirror is used to direct the spectrometer at selected regions of the atmosphere. The experiment also had a solar pointing mode in which observations of the extreme ultraviolet (30 - 125 nm) spectral region of the sun were made.
ISO obtained a wealth of information about emissions from the middle atmosphere (mesosphere) and the thermosphere extending above it. ISO also compiled the first comprehensive spectral atlas of the upper atmosphere, a data base rich in information on several chemical processes. Many unexpected effects were observed that may require years of analysis to be understood. In addition to surveying the natural atmosphere, ISO gathered data on the induced atmosphere around the Shuttle.
Figure 12: Illustration of the ISO instrument (image credit: NASA)
SOLSPEC (Solar Spectrum irradiation measurement):
SOLSPEC is provided by Service d' Aeronomie of CNRS, France. The objective is to detect solar irradiance variations. In particular, it is important to know whether variations in general climatological data are caused by increasing contamination of the atmosphere or by variations in solar radiation. The instrument measures the solar irradiance from 170 - 3200 nm (FUV to MWIR) using three double spectrometers and an on-board calibration device. Operating at or near its planned accuracy, SOLSPEC obtained 35 high-quality solar spectra sets.
SOLSPEC consists of 3 separate spectrometers: the UV spectrometer covers the range 170-370 nm, the visible spectrometer covers the range 350-900 nm, and the infrared spectrometer covers the range from 800 to 3200 nm. The instrument consists of four parts: dispersive elements, an in-flight calibration device, detectors, and a counting system. SOLSPEC is a double monochromator using two holographic gratings as a dispersive element. The two gratings are mounted on the same mechanical axis to provide high accuracy for the bandpass. The input window is a grind which reduces the effect of an angular variation (±2.5º) between the optical axis and the sun. 29) 30)
For the three spectrometers, the rotation angle of the two gratings in cascade is 30º. The three sets of gratings rotate on the same axis. The detector for the ultraviolet and visible spectrometers is a photomultiplier tube. The infrared spectrometer uses a PbS cell as detector.
Calibration lamps are employed to monitor any change of the sensitivity of the instrument. During sun-oriented operation, calibration and solar measurements are being alternated at 15 minutes each. All the planned observations were accomplished by the instrument on Spacelab-1.
Figure 13: Schematic of the SOLSPEC instrument optical configuration (image credit: CNRS)
Aside from the Spacelab-1 mission on STS-9, the SOLSPEC instrument was flown on the following missions:
• The free-flying EURECA platform mission of ESA from Aug. 1992 to June 1993. Deployment on STS-46, retrieval of platform on STS-57.
• ATLAS-1 (Atmospheric Laboratory for Applications and Science) mission on STS-45 (March 24-April 2, 1992)
• ATLAS-2 mission on STS-56 (April 8-17, 1993)
• ATLAS-3 mission on STS-66 (Nov. 3-14, 1994)
SOLCON (Solar Constant radiometer):
SOLCON is of IRMB (Institut Royal de Météorologie Belgique - Royal Meteorological Institute of Belgium), Brussels, Belgium, (PI: R. Crommelynck). Measurement of the solar constant. The SOLCON instrument is a cooperative effort of IRMB, Space Science Dept. of ESA, and NASA/LaRC. Objective: Measurement of the absolute value of the total solar irradiance (and long-term variations). The absolute value of the solar constant is a critical term in the determination of the Earth' s radiation budget as well as for the studies of Earth albedo. In addition, it is one of the main components in the energy balance equation and is responsible for the dynamic behavior and circulation of the atmosphere and, thus, also of climate. 31) 32)
The SOLCON radiometer is the first differential absolute solar radiometer in space based on a full symmetrical metrological design (two side by side cavities) and operation (successive opened and closed state of the measurement cavity). SOLCON features two channels which enable any degradation of the black surfaces to be detected and compensated and the self-consistency of the radiometric system to be determined in space. The radiation measurement is being done by using a heat balance system driven automatically by a feedback system.
Each of the two radiation sensors has an independently controlled shutter. The radiometer is operated by using various combinations of open and closed shutters and a reference electrical power source which has a stable and known output.
At the beginning and the end of each measurement sequence, the correct behavior of the radiometer system is ascertained by having the shutter of both channels closed, applying the reference power source to one heater, and using the servo-system to adjust the power applied to the other until heat flux balance is achieved. The roles of the channels are then reversed and the same procedure followed. The measurement of the electrical power applied to each channel for the two cases gives a value for the precision of the servo-system. Because the power of the reference electrical source is already known, this is a simultaneous check of the data processing system.
Figure 14: Illustration of the SOLCON radiometer (image credit: IRMB)
The actual radiation flux measurements are made by pointing the radiometer to the sun's center and opening the shutter of the channel to which the servo-system power is attached. The servo-system compensates for the extra heat input until heat flux balance is achieved again. The shutter is then closed, and the servo-system should adjust the power back to its previous value. The difference in the power applied with the shutter opened and closed is a function of the incident radiation flux. The absolute total irradiance can be calculated from the known characteristics of the instruments. This sequence of opening and closing the shutter will be repeated several times, always using the same channel for the measurement.
Table 5: Chronology of Shuttle-based solar-constant measurements with absolute radiometers
ACRIM (Active Cavity Radiometer Irradiance Monitor):
ACRIM is provided by NASA/JPL. The objective is the measurement of the total solar Irradiance with state-of-the-art accuracy and precision. ACRIM is part of an on-going long-term program of extra-atmospheric observations to determine the magnitude and direction of possible variations in the total solar output of optical energy. The principal use of this information is in the study of the Earth' s climatology and the physical behavior of the sun.
ACR consists of three sensors as shown in Figure #. Two right, circular, conical cavity detectors are connected to the heatsink by two thermal impedances. All four parts are electro-deposited 99.99% pure silver. The interiors of the cavities are coated with a specular black paint. Resistance temperature sensors are bonded to the cavity apertures. The primary cavity is irradiated through a precisely machined and accurately measured aperture. The detector's FOV (Field of View) is defined by an extension of the heatsink. The heatsink assembly is insulated from the outer case. 33)
The dissipation of a fixed amount of power in each primary cavity produces a constant temperature drop across the thermal impedance. This drop, transduced by the resistance temperature sensors, is used by an electronic servo-system which automatically maintains constant cavity power dissipation by controlling the dc voltage supplied to the cavity heater. The primary cavity detector of the ACR is accurately maintained at a slightly higher temperature than the heatsink at all times.
The ACR operates in a differential mode. A shutter alternately blocks solar radiation from, and admits it to, the primary cavity. In the shutter-closed or reference phase of the measurement, the ACR views its own heatsink. Electrical heating provides the necessary power to balance the cavity' s conductive and radiative losses and maintains the constant cavity-heatsink temperature difference. When viewing the sun in the shutter-open or observation phase, the power supplied by the electronics automatically decreases by an amount proportional to the solar irradiance of the cavity aperture. Absolute irradiance measurements are derived from the difference in the electrical power supplied to maintain the constant cavity-heatsink temperature difference in the two phases of measurement.
The ACRIM detectors are independently shuttered. Channel A is being used routinely to monitor the total solar irradiance. The solar flux is defined in SI units with an absolute uncertainty of 0.1% and a precision of 0.02%. The shuttering cycles are 60 s open and 60 s closed.
The second detector (channel B) is intermittently compared with channel A to establish channel A's long-term stability or to calibrate any apparent degradation. The third detector (channel C) is being used, after initial comparison with A and B, to resolve the ambiguities arising from the operation of the first two.
Figure 15: Schematic view of the ACRIM detectors (image credit: JPL)
Figure 16: Illustration of the ACRIM instrument assembly (image credit: JPL)
ALAE (Atmospheric Lyman-Alpha Emissions):
The ALAE experiment is of CNRS (Centre National de Recherches Spatiales), France, and of IASB (Space Aeronomical Institute of Belgium), Brussels. Investigation of atmospheric hydrogen and deuterium through the measurement of Lyman-alpha emissions. The experiment objective was to study various sources of Lyman-alpha emissions in the atmosphere, in the interplanetary medium, and possibly in the galactic medium.
The equipment consisted of a spectrophotometer with an atomic hydrogen absorption cell and an atomic deuterium absorption cell, and a solar-blind photomultiplier for the detector. A major accomplishment of the ALAE experiment was the quantification (first ever) of the amount of deuterium in the thermosphere - and it saw the auroras in the Northern and Southern hemispheres. It also detected the glow of hydrogen atoms and free protons (hydrogen nuclei) colliding and exchanging electrical charges in the corona of hydrogen gas that envelops Earth. About 80% of the planned objectives were accomplished. 34) 35)
Astronomy payloads: (X-Ray Spectrometer, VWFC, FAUST)
Figure 17: Illustration of 3 astronomy instrument aboard SL-1 (image credit: NASA)
The X-Ray Spectrometer is an astronomy instrument of ESA/ESTEC which was part of the pallet payload on Spacelab-1 (Experiment No ES023). The objective was to observe the brighter cosmic X-ray sources and to study the spectral features and their associated temporal variations over a wide energy range from about 2 to 30 keV. This experiment aimed at obtaining spectra of cosmic X-ray sources with higher spectral resolution than any other non-dispersive spectrometer flown so far.
The instrument, based on the gas scintillation proportional counter (GSPC), had an effective detector area of some 180 cm2 with an energy resolution of about 9% at 7 keV. The detector was collimated to a 4.5º (FWHM) field of view. There were 512 energy channels. 38) 39) 40) 41)
Figure 18: Schematic view of the GSPC instrument (image credit: ESA)
Data were accumulated for all intended targets. These included: Cyg X-2, 4U1636-53, Her X-1, Coma, Cyg X-3, Perseus, Cyg X-1, Cas A, Crab, Cen X-3, Cen X-2, and Vela X-1. The excellent energy resolution of the instrument permitted line features to be identified in these sources with unprecedented quality.
VWFC (Very Wide-Field Camera):
VWFC is an experiment developed by the Laboratoire d' Astronomie Spatiale of CNRS, France. VWFC was used by the crew to take wide-angle ultraviolet-light photographs of vast regions of sky not observable from Earth (general sky survey). Very little large scale ultraviolet mapping of the sky had been accomplished to date. The instrument was mounted in the Spacelab scientific airlock. It was operated during the night phase of the orbits 84 to 91, 94 to 96, and 98. 42) 43)
Figure 19: Schematic illustration of the VWFC (image credit: CNRS)
The VWFC was operated in two UV modes: “photometric“ and “spectrometric.”
1) The photometric mode (FOV of 54º) was direct photography through filters for observation of the following sources:
- Large-scale distribution of ultraviolet radiation in the Milky Way. Study of the stellar clouds as a whole for their geometrical extension and their energetic spectral distribution.
- Diffusion of the galactic light above the galactic plane and in front of the large absorbing clouds. Observation of this source permits the detection of large extensions of the galactic material and studies of possible connections with the local group of galaxies. A general study of the sky background allowed discrimination off the galactic and extragalactic light from sunlight scattered by interplanetary dust (Zodiacal light and Gegenschein)
- Study of the optical emission of the interstellar matter
- Study of stars, especially the peculiar ultraviolet objects.
2) In the spectrometric mode (nebular spectrograph), the light from the center of the photometric field was concentrated on a slit covering 10º x 10 arcminutes on the sky. The wavelength range detected in this mode was 130 to 270 nm, with the most sensitive range being 155 to 192 nm. In the latter wavelength region the resolution was 0.5 to 0.8 nm.
VWFC is a Schmidt-type camera placed at the long focal length of the hyperbolic mirror. With its hyperbolic primary mirror, an image of the sky could be obtained at f/13 and a large object field. The small convergence of the beam ahead of the Schmidt camera allowed placement of various devices (interference filters, gratings, etc.) into the beam - which did not impose a high positional accuracy for the optical elements. The filters centered at 1650, 1930, and 2530 A.
The data was recorded on photographic film. An image intensifier was used in both modes to shorten integration time. Once a sequence was initiated, it was completed automatically by computer control; provisions were made for manual operations. Pointing was accomplished with the Orbiter since the camera was rigidly mounted in the Spacelab scientific airlock.
FAUST (Far Ultraviolet Space Telescope):
FAUST was developed at NASA and UCB. The objective was to observe faint astronomical sources with sensitivities higher than previously available. FAUST covered the spectral range of 130-180 nm, inaccessible by observers on Earth. The experiment covered the following functions: 44)
- Search for a class of sources known as ultraviolet stars which are predicted to exist at the stage of evolution prior to the final death of a star
- Observations of galaxies and quasars to study the the activity at the cores of galaxies and in providing the data necessary for interpretation of observations of galaxies at very high redshifts.
- A secondary experiment objective was to verify the suitability of the Spacelab as a platform for far ultraviolet astronomy.
The instrument consisted of a far ultraviolet space telescope (FAUST) and an electronic interface module. The instrument employed an f/1.12 Wynne camera configuration with an effective collecting area of 150 cm2 and a field of view of 7.5º. The imaging capability was better than 2 arcmin in the entire field of view. The detector system used a microchannel plate image intensifier in conjunction with a 60-exposure, 35 mm film pack of Kodak IIA0.
FAUST observed a total of 22 separate targets on 21 nighttime passes. An observation consisted of one, two, or three separate exposures from 1 to 15 minutes in duration. Approximately 95% of the planned objectives were accomplished. During the mission, the instrument was located on the Spacelab-1 pallet in the cargo bay of the Shuttle.
FAUST was re-flown on the ATLAS-1 mission on STS-45 (March 24 - April 2, 1992).
Figure 20: Schematic view of the FAUST instrument (image credit: NASA)
Background of the Spacelab Program
During the NASA Skylab missions in 1973-74, and in the development phase of the Space Shuttle program, NASA/MSFC (NASA/Marshall Space Flight Center) was already studying possible ways to use the proposed new vehicle's capabilities for scientific research - resulting in the idea and concept of a laboratory in space which was later called “Spacelab”. 45) 46) 47) 48) 49) 50)
In the same time frame, NASA wanted to internationalize the Space Shuttle program, approved by President Richard Nixon in early 1972, to share the burden of development costs. This resulted in negotiations with ESRO (European Space Research Organization), the predecessor agency of ESA (European Space Agency), and later with young ESA (created in 1975) and in an agreement, under which ESA assumed responsibility for funding, developing, and building of the Spacelab facility. Europe wanted to get involved in space research with NASA as its strong partner in this cooperative venture. At the time, the Spacelab development was guided by two major considerations:
1) To make the capabilities of the Shuttle system immediately available to the user (research community)
2) To undertake a first step in the direction of “space station” development and operation. In comparison with conventional free-flying spacecraft, the Spacelab idea presented for the first time an environment of an orbiting laboratory in which men could work and support a great variety of research experiments. The concept promised to offer a great potential for all parties involved.
A meeting of European ministers in Brussels in July 1973 officially launched the Spacelab project (providing funding). On Sept. 24, 1973, a memorandum of understanding was signed between ESRO (European Space Research Organization) and NASA (Note: ESA was created in 1975 as the successor to ESRO and ELDO). - Hence, a Spacelab research facility was developed using the MSFC requirements. MSFC also retained responsibility for technical and programmatic monitoring of Spacelab development activities in Europe, which involved some 50 manufacturing firms in 10 European countries. Additional duties of MSFC included the establishment of a new Spacelab POCC (Payload Operations Control Center) facility.
The Spacelab-1 mission was conceived in 1975 when an Announcement of Opportunity was issued. In 1976, the experiments were selected and in 1977, the selected investigators met for the first time at MSFC in Huntsville, ALA. In this first mission it was to be shown that that the Spacelab-Shuttle combination could be used for scientific research, not only in the traditional space science disciplines, but in such disciplines as the life sciences and materials research. NASA and ESA had selected 73 individual investigations for Spacelab-1. About half of these investigations could be technically combined into integrated facilities in the materials science and life science area. The investigators for the various experiments came from the USA, Canada, 11 European countries, and Japan. Half of the payload was selected by NASA and half by ESA. The total payload mass of Spacelab-1 was close to 3,000 kg. 51)
The scientists on Spacelab-1 organized themselves into the IWG (Investigator's Working Group), a body which represented the scientific interests of the mission and which was given unprecedented responsibilities in the definition of the mission. The main duties of the IWG members were to work with the project in allocating Shuttle and Spacelab resources to different disciplines and investigations, to organize the inflight science operations, and to nominate and select four payload specialists, two for flight and two for critical roles in the ground-based activities.
An industrial consortium, headed by MBB/ERNO-VFW Fokker (now EADS Space Transportation), was named by ESA in June 1974 to build the pressurized modules. In addition, 5 unpressurized pallet segments (each about 2.8 m in length) were built by BAC (British Aerospace Corporation) under contract to MBB/ERNO-VFW Fokker. The first Spacelab was completed and delivered in early 1982 (LM1), a second Spacelab (LM2) was purchased by NASA in the mid-1980s. Each Spacelab was designed for a service life of 50 missions.
Figure 21: Conceptual configuration of the Spacelab elements (image credit: NASA)
In retrospect, Spacelab heralded a new approach to the utilization of space. The Spacelab program encouraged international participation during the development phase and during the 15 years of operation that followed (1983-1998) with a total of over 25 Spacelab flights (Table 6). That spirit of international cooperation gave investigators from all corners of the globe the opportunity to conduct science experiments aboard the Shuttle.
A great variety of Spacelab mission configurations were flown involving pressurized and/or unpressurized (pallet) Spacelab module combinations (Figure 21). At times, the payload service devices like power supply, command and data handling system, and temperature control system, were housed in a pressurized container called the igloo (also standard Spacelab equipment) located somewhere in the payload bay of the Shuttle. In addition, free-flyer platforms (ASTRO-SPAS, SPARTAN, etc.) were deployed, carrying a variety of instruments for dedicated observations.
The results from the Spacelab science missions testify to the value of the Shuttle and Spacelab concepts for manned space science. The great variety of experiments flown in Spacelab and other Shuttle-attached payloads is impressive. More significant, however, is the tangible gain from space science research. The story of Spacelab and other Shuttle attached payloads is one of opportunity and discovery.
Table 6: Chronology of Shuttle missions with Spacelab modules/elements
The Spacelab logistics pallet (unpressurized carrier) was reused for the ISS (International Space Station) assembly flights (ISS-7A) even after the two Spacelabs (LM1 and LM2) were retired in 1998. One such flight was STS-104 (July 12-25, 2001) where the pallet was used to carry a new air resupply system to the ISS inside the Shuttle's cargo bay.
A brief overview of some Spacelab mission achievements:
The Spacelab missions flown have had widely different configurations and objectives. Some of the missions have conducted investigations from many different scientific disciplines. A good example of such a mission is Spacelab-1 which flew experiments in the fields of: atmospheric science, solar science, materials science, space plasma physics, the life sciences and astrophysics. In fact, Spacelab-1 represented all of the scientific disciplines that have been addressed by the Spacelab missions as a whole. Some of the missions conducted a set of investigations with a focus in one discipline. A good example of the latter category is ASTRO-1 which carried 4 telescopes, 3 of which were co-aligned on a common pointing system to conduct studies of a large number of astrophysics targets. 52)
The Spacelab-1 mission was preceded by so-called OSTA-1 and -2 (Office of Space and Terrestrial Applications) and OSS-1 (NASA's Office of Space Science) precursor missions, a designation that was given to the early payloads in the Shuttle program. Three precursor Shuttle flights were conducted to test smaller elements of the Spacelab system. The OSTA-3 precursor demonstration mission was actually flown after the Spacelab-1 mission.
Some representative achievements are listed here giving an indication of the Spacelab research topics.
The Spacelab missions that have focussed most on astrophysics are Spacelab-2 and Astro-1 with important contributions coming from missions such as ATLAS-1. Both Spacelab-2 and ASTRO-1 flew large telescopes, most of which were mounted on the IPS (Instrument Pointing System). The Spacelab-2 experience indicated that the environment of a large manned spacecraft in LEO, together with the operation of thrusters and pointing system which can generate light scattering particulates, results in an induced radiative emission level that is not suitable for infrared observations. - The major contribution have been in the UV and X-ray spectral ranges, due largely to the fact that Spacelab flight opportunities emerged just as the technology in these wavelength regions was coming into its own.
The main contributions in this area have come from the Spacelab-1 and -3 missions nd in particular from the ATLAS-1 and -2 missions. These missions have taken advantage of the ability to fly very comprehensive and highly calibrated instruments. Efforts were made to coordinate observations of the ATLAS missions with other important spacecraft such as UARS and the POES series of NOAA, allowing valuable supplementing of the longer duration datasets of the unmanned missions. The Spacelab missions provided the capability to calibrate an instrument, operate it in space and to view the same target as instruments on other spacecraft, and then return it to the laboratory for post-flight recalibration. - The largest group of atmospheric instruments was flown on the ATLAS-1 mission. These instruments were able to measure a larger number of atmospheric species over a larger range in altitude than has been done for any other mission (important baseline for global change studies).
Each Spacelab mission, and in fact each Shuttle mission, has carried an impressive complement of cameras ranging from standard held-held cameras to large format precision-mapping cameras. The MOMS (Modular Optoelectronic Multispectral Scanner) instruments on STS-7 (OSTA-2), STS-41B (OSTA-3), and STS-55 (Spacelab-D2) pioneered new observation techniques. MOMS-01 introduced the CCD pushbroom line-scanning detector technology on a spaceborne platform. MOMS-02 introduced stereoscopic along-track pushbroom imaging with a three-line imaging system (the first spaceborne multi-line stereo imager anywhere).
The OSTA-1 and OSTA-3 precursor missions flew the imaging radar systems SIR-A (Shuttle Imaging Radar) and SIR-B, respectively. These were SAR (Synthetic Aperture Radar) instruments in L-band. SIR-B provided for the first time the ability to mechanically tilt the SAR antenna over a range of 15 - 55º so that radar imagery from multiple angles of incidence could be obtained. The SIR-C/X-SAR (Shuttle Imaging Radar with Payload C / X-SAR payload was a cooperative NASA/JPL, DARA/DLR, and ASI (Agenzia Spaziale Italiana) project flown on Space Shuttle Endeavour (STS-59 and STS-68). The distributed C- and L-band SIR-C radars allowed electronic beam steering in the range direction (123º) from a fixed antenna position of 38º (look angle), thus making it possible to acquire multi-incidence angle data without tilting the entire antenna. The SIR-C/X-SAR payload was the first spaceborne radar system capable of obtaining simultaneously multifrequency (3) and multipolarization radar imagery.
SRTM (Shuttle Radar Topography Mission) was flown on STS-99 (Feb. 11-22, 2000) providing the first fixed baseline single-pass spaceborne InSAR technology system with wide-swath ScanSAR and dual-frequency (C-band and X-band) coverage as well as with dual-polarization capability. As such, the mission represents one of the most significant mapping surveys from space of our planet ever undertaken.
Building mainly on Skylab experiences, the Spacelab and Shuttle program addressed such questions as to how well and for how long humans could function in the space environment. During the early days of Spacelab, a major problem facing manned spaceflight was the issue of space sickness. Significant progress has been made in understanding and in treating this problem, and a wealth of information on human performance in space has been gathered. A key result from the Spacelab-1 mission was evidence that lymphocytes are suppressed both in number and effectiveness, indicating a decrease in the performance of the immune system.
The studies with animals parallel to those with humans, using the more rapid development in Spacelab flights, has dealt with questions of human physiology in space, what remedial or countermeasures are needed and what environmental factors are important.
The field of material science experienced a great boost and some pioneering research on inhomogeneities on various Spacelab missions. Material science was not one of the traditional space science prior to the SS-7 (OSTA-2) mission in June 1983. Subsequently, a major effort of the Spacelab-1 mission, followed by STS-61A (Spacelab-D1), STS-42 (IML-1), STS-50 (USML-1), STS-47 (Spacelab-J), and STS-55 (Spacelab-D2), have brought about a rapid evolution in the microgravity related aspects of crystal growth, combustion science, and fluid physics. In microgravity physics, Spacelab-1 provided exciting results that have served as input for major studies.
The solar science investigations on Spacelab missions have addressed the sun from two perspectives. The first of these is the study of the sun as a star with a view of understanding its behavior. The second aspect is the sun as a source of energy to the Earth system. Solar instruments have been flown on STS-3 (OSS-1), Spacelab-1 and -2, and on STS-45 (ATLAS-1) and STS-56 (ATLAS-2). Instruments operating in the UV and visible spectral range have been used to study processes on the sun's surface and its corona. Several of these instruments have been mounted on the IPS (Instrument Pointing System) of Spacelab.
The solar analysis from Spacelab-2 observations permitted to determine the ratio of the abundance of helium to hydrogen in the sun's atmosphere to be 10%, and also found that the abundance of solar elements is different from solar flare to another. The sun's radiative variability is due to the highly variable magnetic field of the sun. It was also shown that the bubble-like convection cells, known as granules, behave differently in magnetically active regions (such as sunspots) than they do in magnetically quiet regions.
The second category of solar observations has taken good advantage of the fact that Spacelab instruments are retrieved after each mission. To monitor the solar irradiation, and to relate these measurements over the course of time to global change issues, very precise measurements are needed over a period of time commensurate with the principal solar changes (11 year solar cycle). In the UV range that affect the formation of the Earth's ozone layer, for example, it is important to measure the solar irradiation to an accuracy of 1 part in a hundred. Global change studies require measurements of the entire spectral range to accuracies of 1 part in a thousand for purposes of verifying global climate change models. The solar irradiance observations made during the ATLAS-2 mission have provided a benchmark reference for solar irradiance as the sun was in a very quiet condition (no sunspots) and a sister instrument on another spacecraft, observing the sun at the same time, yielded essentially identical results.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.