EURECA (European Retrievable Carrier)
EURECA was an ESA space environment exploration mission designed and developed to be recovered from orbit after completion of the mission and returned to Earth. The main objective of the recovery mission was the post-flight study of environmental effects (meteoroids and space debris impact) and wear-out mechanisms to the spacecraft and its payload.
• Launch of EURECA by Shuttle (Atlantis, STS-46, EURECA was part of the payload in the cargo bay) from KSC, Cape Canaveral, FLA, on July 31, 1992 (8 day mission).
The EURECA payload was deployed from the Shuttle on Aug. 2, 1992 using the RMS (Remote Manipulator System). Then EURECA performed a burn raising its orbit from 420 km to an operational altitude of 508 km. It began its scientific mission on August 7, 1992.
• Retrieval of EURECA by Shuttle (Endeavour) during the STS-57 mission (June 21 - July 1, 1993) using the Shuttle's RMS , also referred to as Canadarm. EURECA spent 11 months (336 days) in a sun-pointing orbit.
Figure 1: Artist's view of the EURECA platform (image credit: ESA, NASA)
The EURECA spacecraft bus structure had dimensions of 4.6 m x 2.6 m. The bus structure consisted of carbon fiber struts connected by titanium nodal joints. A grapple fixture permitted deployment/retrieval by the Shuttle Remote Manipulator System (RMS). EURECA was three-axis stabilized by magnetorquers, supported by a reaction control assembly of 6 x 21 mN nitrogen thrusters. Orbit transfers between altitudes of 400-500 km were performed by the orbit transfer assembly of redundant 4 x 21 N hydrazine thrusters (the propellant volume was sized for two transfers and 9 months on-orbit stay). The attitude rate was measured by an accelerometer package, gyros and IR Earth and sun sensors. Power was provided by twin deployable/retractable panels of silicon solar cells, generating 1.5 kW at 28 VDC (providing 1 kW average for payload operations). In addition, 4 NiCd batteries provided energy of 40 Ah each.
The launch mass of EURECA was 4490 kg (payload capacity of up to 1000 kg). At the time, EURECA was the largest spacecraft so far built and flown by ESA. When deployed, EURECA measured 20 m across from wing tip to wing tip. 1) 2) 3) 4) 5)
Table 1: EURECA spacecraft parameters
Figure 2: Alternate illustration of the EURECA spacecraft (image credit: ESA)
The external surface of the spacecraft was almost entirely covered by thermal Multi-Layer Insulation (MLI) blankets. The only exceptions were the radiators and some boxes mounted on the bottom of the spacecraft, which were painted, and the solar-array wings. The total area of the exposed external surface was about 140 m2 , including 99 m2 of solar arrays (front and back surfaces), with a deployed span of 20 m tip-to-tip.
Orbit: Low Earth Orbit (LEO) circular; altitude = 508 km, inclination = 28.45º, retrieval altitude of 476 km.
RF communications: Data was transmitted via S-band downlink at rates up to 256 kbit/s.
The mission's output was composed of space science and experiment data sent to the ground regularly for scientific and engineering analysis, materials processes in the environment of very low residual acceleration that was offered by the EURECA mission, sample exposure to the space environment, surface forces research, space particle collection and new technology applications. While a significant portion of the mission's yield was contained in its abundant and continuous data generation, the primary mission objective was the analysis in ground based laboratories of the biological and material-samples after their return to Earth and the ability, in principle, to the spacecraft and payloads again in a later flight. 6) 7)
Mission operations of EURECA-1 was provided by ESOC in Darmstadt; some payload operations were provided by MUSC (Microgravity User Support Center) of DLR in Cologne, Germany.
Figure 3: Release photo of the EURECA spacecraft from the Space Shuttle on 2 August 1992 (image credit: NASA, ESA)
Background: The spacecraft was developed and integrated at EADS (formerly DASA/ERNO), Bremen, Germany under ESA contract as a re-usable, multi-disciplinary platform for microgravity, science and technology missions. Its design life was based on at least five flights, each lasting from several months to nearly one year, and an on-ground turn-around time of maximum two years. - However, only a single mission was conducted with the EURECA spacecraft.
Bringing EURECA back to Earth following its first mission proved to be an invaluable contribution not only to payload and mission product owners, but also to technical areas dealing with in-orbit performance validation and, in particular, with the identification of the causes of in-orbit anomalies.
Figure 4: EURECA flight scenario involving Shuttle deployment and retrieval of the spacecraft (image credit: ESA)
The Eureca payload included a total of 16 active instruments/experiments (six for microgravity research, two for space radiation research, five for space science research, three for technology demonstrations) and a number of entirely passive payloads. - Only those sensors are described and indexed that fit into the scope of the book, namely: “Observation of the Earth and its Environment.” The other sensors (in the life and material sciences) are simply listed with a short commentary.
ERA (Exobiology and Radiation Assembly). A multiuser life science facility for experiments on the biological effects of space radiation. PI: H. Bücker, DLR, Germany. 8)
AMF (Automatic Mirror Furnace). Optical radiation furnace for growing single, uniform crystals from the liquid or vapor phases, using the travelling heater or Bridgman methods. PI: K. W. Benz, Universität Freiburg, Germany.
SGF (Solution Growth Facility). A multiuser facility for growing monocrystals from solution. PI: J. C. Legros, Université Libre de Bruxelles, Belgium.
PCF (Protein Crystallisation Facility). A multiuser solution growth facility for protein crystallisation in space. PI: W. Littke, Universität Freiburg, Germany.
MFA (Multi-Furnace Assembly). A multiuser facility dedicated to material science experiments. PI: A. Passerone, National Research Council, Genoa, Italy
HPT (High Precision Thermostat). An instrument for long-term experiments requiring microgravity conditions and high precision temperature measurement and control (typical experiments are: `caloric', `critical point', and `phase transitions'). PI: G. Findenegg, Ruhr Universität, Bochum, Germany.
SFA (Surface Forces Adhesion). Study of the dependence of surface forces and interface energies on physical and chemical-physical parameters such as surface topography, surface cleanliness, temperature, and the deformation properties of the contacting bodies. PI: G. Poletti, Università di Milano, Italy.
IOC (Inter-Orbit Communication Instrument):
A technological experiment to provide a pre-operational in-flight test and demonstration of all required instrument functions and services. PI: R. Tribes, CNES, France. The instrument utilized the 20/30 GHz band for transmission between the user satellite, ground station, and relay satellite. The ESA communications satellite, Olympus, was used as the relay satellite between EURECA and the ground station. 9)
Table 2: IOC instrument characteristics
During the EURECA 11 month mission, the IOC payload was configured in dormant mode for about 18 weeks. During the remaining time it was used for its commissioning, measurement and assessment of its 20/30 GHz Radio Frequency link behavior and quality, its exploitation in providing transmissions to users and its support to EURECA operations.
ASGA (Advanced Solar Gallium Arsenide Array):
ASGA was sponsored by ASI. A technological experiment for the performance testing of future solar arrays. PI: C. Flores, CISE SPA, Segrate, Italy. These solar cells (GaAs), already being used in a trial form to power the Soviet MIR space station, are expected to form the backbone of the next generation of compact, high power-to-weight ratio European solar energy generators. 10)
RITA (Radio-Frequency Ion Thruster Assembly):
Study of the use of ion electric propulsion in space. PI: H. Bassner, DASA-MBB, Munich, Germany. European research into radio-frequency ion propulsion was initially conducted in the 1960's by the University of Giessen, Germany. EADS's predecessor, MBB, then joined the development team in 1970 and undertook the industrial leadership. The first RITA instrument was successfully demonstrated in space aboard ESA's EURECA. At that time, the RIT-10 system aboard EURECA provided a nominal specific impulse of 3,058 seconds. It featured a beam diameter of 87 mm and provided flawless operation demonstrations of 240 hours in total. Measurements confirmed there was no EMC (Electromagnetic Compatibility) interference between the satellite, payload or electronics. 11) 12) 13)
Figure 5: RITA-10 on EURECA (image credit: EADS Space Transportation)
WATCH (Wide Angle Telescope):
PI: N. Lund, Danish Space Research Institute, Lyngby, Denmark. Objective: detection of celestial gamma-ray burst sources and X-ray sources with photon energies in the range of 6 - 150 keV, measurement of source direction. The total field of view (FOV) covered 1/4 of the celestial sphere. WATCH gradually scanned across the entire sky during the 11 month mission.
A total of 19 cosmic GBR (Gamma-Ray Bursts) were detected by the WATCH X-ray monitor during the 11 months flight of EURECA.
Figure 6: Illustration of the WATCH instrument (image credit: Danish Space Research Institute)
TICCE (Timeband Capture Cell Experiment):
Study of microparticle population distributions in near-Earth space, typically Earth debris, meteoroids, and cosmic dust. TICCE captures micron-dimensional particles with velocities in excess of 3 km/s and stores the debris for retrieval and post-mission analysis. PI: J. A. M. McDonnell, University of Kent, UK.
Particles detected by the instrument pass through a front foil and into a debris collection substrate positioned 100 nm behind the foil. Each perforation in the foil has a corresponding debris site on the substrate. The foil is moved during the mission in 50 discrete steps. The phase shift between the debris site and the perforation enables a determination of the impact time. Instrument mass = 8 kg, dimensions: 690 x 690 x 80 mm.
ORA (Occultation Radiometer Instrument):
Objective: measurement of aerosols and trace gas densities in the Earth's mesosphere and stratosphere (vertical profiles between 20 - 100 km of: ozone, nitrogen dioxide, water vapor, carbon dioxide, and background and volcanic aerosols) . PI: E. Arijs, BIRA (Belgisch Instituut voor Ruimte Aeronomie), Brussels, Belgium. 16) 17)
ORA measures the intensity of solar radiation during the sunrise and sunset phases of each orbit. It uses the sun pointing capabilities of EURECA and makes measurements in ten narrow wavelength bands (UV/VIS, NIR) in the spectral region 250 - 1100 nm. ORA consists of a UV/VIS unit, an NIR unit and a control/electronics unit. The UV/VIS unit has 8 similar modules which measure the relative solar irradiance in narrow bands. Each module contains a quartz window, an interference window to select the appropriate wavelength, optics to limit the detector viewing angle, and a photodiode.
The ORA instrument was mounted on the “science panel” of the carrier. It consists of a mechanical structure containing the UV-visible module (for the measurement of 03, NO2, H20 and aerosols in the stratosphere), the infrared unit (for the measurement of water in the mesosphere) and an electronics unit (for instrument control and interface with the satellite data handling system). EURECA being designed for micro gravity, moving parts in the instrument had to be limited to a minimum. Therefore, in view of the weight and power budget and considering that the carrier is sun pointing by itself, the ORA instrument has no sun tracking device. Instead, the field of view of the optical modules was chosen to be large enough to assure a full view of the sun.
SOVA (Solar Variability Experiment):
SOVA is a radiometer, a copy of SOLCON. Objective: measurement of the solar constant, its variability and its spectral distribution. PIs: D. Crommelynck, IRMB, Brussels, Belgium; C. Fröhlich, PMOD/WRC Davos, Switzerland. 18) 19)
The instrument is composed of three boxes, two of which (SOVA1 and SOVA2) house the various devices dedicated to functions such as sun-pointing, sun photometers, and two different types of absolute radiometers. The absolute radiometers are very accurate instruments for the measurement of total irradiance. They are essentially cavities, in which the solar radiation is trapped and absorbed. Heat flux transducers convert the radiative power into electrical power and return a calibrated measurement of the sun's radiation. The high precision radiometer (RELOS) is used to measure solar oscillations in total irradiance. The sun-pointing resolution of SOVA2 is 2 arc seconds. The sun photometers use interference filters to select the wavelength band and silicon diode devices to measure the radiation. The complete set of photometers covers the spectrum from 303 nm to 865 nm. 20) 21)
SOSP (Solar Spectrum Instrument):
Objective: study of solar physics and solar-terrestrial relationships in aeronomy and climatology. Measurement of absolute solar irradiance and its variations in the spectral range 170 - 3200 nm (accuracy of 1% in VIS/IR and 5% in UV). PI: G. Thullier, CNRS, Verriers le Buisson, France. 22)
SOSP has three spectrometers, one for each spectral domain (UV/VIS/IR). The spectrometers select the spectral range using a double monochromator; irradiance measurement with a photomultiplier in UV and VIS, in IR with a cooled lead sulfide cell. Spectral resolution: 1 nm in UV/VIS, 20 nm in IR. In-flight calibration is provided.
Figure 7: Eureca - with its solar wings already folded against its sides - was recaptured in June/July 1993 after almost a year in orbit (image credit: NASA, ESA)
Inspection of retrieved spacecraft:
The retrieval of EURECA has given ESA a rare opportunity to study the fluxes and resulting effects of meteoroid and space-debris impacts on exposed spacecraft surfaces in LEO (Low Earth Orbit). With its fixed sun-pointing attitude, large areas of identical surface materials, and 1992-1993 exposure period, EURECA has provided impact data that are complementary to those from LDEF (Long Duration Exposure Facility) of NASA. Note: LDEF was deployed on April 7, 1984 on Shuttle flight STS-41C. LDEF was recovered 69 months after launch on January 12, 1990 (STS-32).
After the return of the Shuttle to KSC (Kennedy Space Center) on July 1, 1993, the EURECA spacecraft received a full inspection of the platform's upper surface in the Orbiter Processing Facility. The general impression was that there had been a significant change in the colors of the exposed surfaces, where outgassing products had been deposited on the thermal blankets. Areas of paint de-lamination and many micro-meteoroid impacts were clearly visible. 23) 24)
Figure 8: Illustration of scanned surfaces of the EURECA spacecraft (image credit: ESA)
Later on, a wide-ranging set of investigations was undertaken to identify and characterize all impact features on the surfaces. Many groups participated in these investigations. The impact features were used to deduce properties of the impacting population and thereby to contribute to the validation of space debris and meteoroid environment and damage models. MLI thermal blankets, solar cells and other surfaces were examined and the investigations included residue analysis.
The main findings of the detailed visual survey of Eureca's external surfaces can be summarized as follows:
• There was no functional failure on Eureca that could be related to an impact
• On the front sides of the solar arrays, more than 1000 impact features can be seen with the naked eye
• 71 impact punctures in the outer layer of the thermal blankets were detected on the main spacecraft body (non-penetrating impacts Three impacts were found on the ESA logo plate and 11 more on the scuff plates
• The impact features identified range in size from 100 microns to several millimeters. The largest crater diameter on the solar arrays is 6.4 mm. The largest feature on the main body is a 2 mm hole in the ESA/ERNO logo plate
• A surprisingly high proportion of the impacts on the solar-cell cover glasses - about 30% - show signs of directionality by having a non-spherical crater shape.
Figure 9: Impact events recorded on the EURECA spacecraft (image credit: ESA)
Figure 10: Impact craters on solar cells of EURECA spacecraft (the bright lines are spaced by 1.25 mm), image credit: ESA
Figure 11: Typical thermal-blanket puncture hole (image credit: ESA)
Figure 12: A 2 mm impact hole in one of the aluminum ESA logo plates (image credit: ESA)
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23) .G. Drolshagen, J. A. M. McDonnell, T. J. Stevenson, S. Deshpande, L. Kay, W. G. Tanner, J. C. Mandeville, W. C. Carey, C. R. Maag, A. D. Griffiths, N. G. Shrine, R. Acetia, “Optical survey of micrometeoroid and space debris impact features on EURECA,” Planetary and Space Science, Vol. 44, Issue 4, April 1996, pp 317-340
24) R. Aceti, G. Drolshagen, J. A. M. McDonnell, T. Stevenson, “Micrometeoroids and Space Debris - The Eureca Post-Flight Analysis,” ESA Bulletin No 80, Nov. 1994, pp. 21-26, URL: http://www.esa.int/esapub/bulletin/bullet80/ace80.htm
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.