European Retrievable Carrier Research Articles

Development of in-situ Space Debris Detector

Due to high relative velocities, collisions of spacecraft in orbit with Space Debris (SD) or Micrometeoroids (MM) can lead to payload degradation, anomalies as well as failures in spacecraft operation, or even loss of mission. Flux models and impact risk assessment tools, such as MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) or ORDEM (Orbital Debris Engineering Model), and ESABASE2 or BUMPER II are used to analyse mission risk associated with these hazards. Validation of flux models is based on measured data. Currently, as most of the SD and MM objects are too small (millimeter down to micron sized) for ground-based observations (e.g. radar, optical), the only available data for model validation is based upon retrieved hardware investigations e.g. Long Duration Exposure Facility (LDEF), Hubble Space Telescope (HST), European Retrievable Carrier (EURECA). Since existing data sets are insufficient, further in-situ experimental investigation of the SD and MM populations are required. This paper provides an overview and assessment of existing and planned SD and MM impact detectors. The detection area of the described detectors is too small to adequately provide the missing data sets. Therefore an innovative detection concept is proposed that utilises existing spacecraft components for detection purposes. In general, solar panels of a spacecraft provide a large area that can be utilised for in-situ impact detection. By using this method on several spacecraft in different orbits the detection area can be increased significantly and allow the detection of SD and MM objects with diameters as low as 100μm. The design of the detector is based on damage equations from HST and EURECA solar panels. An extensive investigation of those panels was performed by ESA and is summarized within this paper. Furthermore, an estimate of the expected sensitivity of the patented detector concept as well as examples for its implementation into large and small spacecraft are presented.

Oblique hypervelocity impacts: Implication for the analysis of material retrieved after exposure to space

In the past few years, a wide variety of surfaces have been brought back to Earth after being exposed to the space particulate environment. The impact features found on this material can give clues to the characteristics of the impacting man-made debris and meteoroids. Many investigations have been carried out to deduce projectile parameters (size, shape, and velocity vector) from the morphology of impact features and their origin from the analysis of projectile remnants inside craters formed. However, there are still ambiguities in the interpretation of these results. Recently, the post-flight analysis of solar arrays retrieved from the hubble space telescope (HST) showed the lack of data concerning the interpretation of many impact features. In the present study, we have examined especially the distinctive features of craters caused by particles at oblique incidence. These craters represent more than one third of impacts with a size between 5 μm and 1 mm observed on the European Retrievable Carrier (EuReCa) and HST solar arrays. Interpretation difficulties of this kind of impacts on solar cells led to hypervelocity impacts test onto pure silica targets performed with iron projectiles at different incidence angles and different velocity ranges. They were made in order to find a possible link between the incidence angle of a projectile, the impact velocity, and the parameters, which could be deduced from the analysis of the crater and projectile remnants. A detailed survey of impacts features formed was done for each couple angle velocity. High-resolution observations show an evolution of the crater morphology and circularity with the increasing angles of incidence and velocity, and some changes in the projectile remnants amount, appearance, and position are also noted.

Derivation of stratospheric aerosol properties from the ORA experiment

The solar Occultation RAdiometer (ORA) is a seven broadband channel instrument working in the UV to near-IR range, that was launched in 1992 on board the EUropean REtrievable CArrier for a 1-year mission. About 7000 orbital occultations of the Sun have been recorded and processed through vertical and spectral inversions. Starting from the wavelength dependence of the retrieved aerosol extinction coefficient, properties of particle size distribution have been derived within the frame of the Mie theory, with a vertical regularization. The inversion algorithm will be presented as well as important results about the time evolution of stratospheric aerosols in the post-Pinatubo period. Global profiles of particle size distribution properties will be presented and interpreted.

Direct Simulation of Apex Enhancement on the Flux onto European Retrievable Carrier

The extended direct simulation Monte Carlo method is employed to model fluxes of meteoroid and space debris onto surfaces of the sun-pointing spacecraft European Retrievable Carrier. Apex enhancement of the Earth motion on flux is considered by including a parameter to describe the anisotropic velocity directionality in the meteoroid distribution. The anisotropy of the measured fluxes onto different surfaces is well explained by this approach, and results are consistent with measured data. Also, the effect of the apex enhancement of the Earth motion on the morphology of the impacts is analyzed, and a good agreement with measured data is achieved. Our simulation allows an estimation of the extent to which the directionality distribution of the meteoroid velocity unit vectors deviates from the isotropic distribution.

Updating the NASA debris engineering model: a review of source data and analytical techniques

Orbital debris engineering models present a comprehensive view of the space environment to spacecraft designers and owners/operators. NASA is revising its orbital debris engineering model, ORDEM96, to incorporate approximately four years of new observations of the low Earth orbit (LEO) environment and new analytical methodologies. Since its last revision, significant measurements of the LEO environment have been made using radar and optical sensors ( e.g. the Haystack and Haystack Auxiliary Radars and the Liquid Mirror Telescope) and returned surfaces (the Space Shuttle, the Hubble Space Telescope solar arrays, and the European Retrievable Carrier). This paper reviews the data sources and outlines analytical techniques used to reduce data to engineering quantities such as flux and directionality. Also, this paper describes one of the new analytical techniques - a method of building statistical distributions of orbit families. We use a Maximum Likelihood Estimator to take a given set of data and estimate the orbit populations that created that particular data set. This method precludes the ability to say whether a particular detected object is in a particular orbit, but it gives an overall picture of the debris families in orbit within the limits of the sampling error.

Meteoroids and small sized debris in low earth orbit and at 1 AU: Results of recent modelling

We present consolidated flux data from the Long Duration Exposure Facility (LDEF) and develop an isotropic meteoroid model applicable to predicting damage to the LDEF surfaces. The model is shown to work well, and is used to derive the resultant component of orbital debris incident on the LDEF east (ram) and west (wake) faces. Overall, orbital debris dominates the measured fluxes at small sizes (aluminium penetration depth F max < 30 μm) whereas meteoroids dominate above this size (see also McDonnell et al., 1997). The east and west face comparison shows that at least 2 distinct populations of debris exist with different size distributions. Analysis of data from the European Retrievable Carrier (EuReCa) shows the interplanetary meteoroid flux to be biased towards the Earth-apex direction (in the measured size regime). An enhanced meteoroid model is derived which is consistent with both EuReCa and LDEF data, and which does not affect the debris fluxes derived from LDEF data.

Meteroid and debris micro-impacts on space-exposed solar arrays

The recent recovery of the Hubble Space Telescope (HST) Solar-Array-1 and the European Retrievable Carrier (EURECA) spacecraft offers an opportunity to widen our database on the low Earth particle environment. This paper describes investigations into impacts observed on the array surfaces after retrieval, and into calibration impact tests carried out using a plasma drag accelerator at the Fachgebiet Raumfahrttechnik, TU München. We have concentrated on examining ‘microimpacts’ (less than 500 μm in diameter). These small impacts form a consistent data set, as they are almost all craters in the cover glass of the solar cells. The size distribution and different morphologies of the impacts were established during optical and scanning electron microscope examinations. The results from a series of shots using the plasma drag accelerator are combined with experiments performed during the Apollo programme to give a scaling law for particle parameters and impact crater dimensions. This can then be used to convert the observed crater size distribution on the solar arrays to flux distributions, which can then be compared with results from models and from other satellites.

Paramagnetic centers in glasses induced by low earth orbit space radiation

After having been exposed to space radiation on the experimental platform Eureca (European Retrievable Carrier) for almost eleven months, different optical glasses were examined to determine radiation effects. For the 500 km high orbit with low inclination a radiation dose of 10 3 Gy is assumed. Using electron paramagnetic resonance (EPR) spectroscopy spectral components due to radiation effects were detected at room temperature. Oxygen hole centers (OHCs) were indicated in borosilicate glass, soda lime glass, phosphate crown glass, fluor crown glass and lanthanum crown glass, Ti 3+ was found in borosilicate glass. All investigated materials — excluding fused silica and fluoride glass — had differing intensities of Fe 3+ components caused by iron impurities in the samples. Comparing these results to earth specimen used in a simulation program, specially developed in preparation for the Eureca mission, the same type of radiation induced defects were identified. This confirms the validity of the simulation program as an appropriate tool to predict the performance of glass materials before space missions.

Solar total irradiance observations from spacecraft: 1992–1993

A brief review of the simultaneous observations of solar total irradiance performed by the UARS ACRIM II (upper atmosphere research satellite active cavity radiometer irradiance monitor), EURECA SOVA 1 and SOVA 2 (European retrievable carrier platform solar variability experiments), ERBS ERBE (Earth Radiation Budget Satellite Earth Radiation Budget Experiment), Nimbus 7 ERB, and Atlas 1 and 2 in 1992–1993 (a period characterized as the declining phase of solar cycle 22), is presented in this paper. Statistical comparison of the irradiance values and the linear relationships among the time series are examined for the overlap period August 1992 to May 1993. The mean irradiance at 1 astronomical unit (AU) observed by the UARS ACRIM II, EURECA SOVA 1, EURECA SOVA 2, and ERBS ERBE is within the range of 1365.5–1366.9 W m−2, and high correlation (r2 = 0.94) exists among the time series. Linear regression models based on the measurements are used in estimating the observed irradiance and predicting the missing values. The challenge in establishing a homogeneous long‐term database from the independent observations of shorter duration requires a clear understanding of the compatibility of the data sets and any instrument‐related drift or degradation.

Optical survey of micrometeoroid and space debris impact features on EURECA

The results of an optical survey of impact features from micrometeoroids and space debris on the EUropean REtrievable CArrier (EURECA) are presented. EURECA was returned from space in June 1993 after almost 11 months in Low Earth Orbit. Impact features on all outer surfaces (mainly Multi Layer Insulation blankets and front and rear sides of solar arrays) were systematically recorded and measured. The size of recorded impact features ranges from about 30 μm to 6.5 mm. High resolution microphotographs were taken from 932 of the larger impact sites. The visibility of impacts differs largely for the different surfaces. Impacts are most easily detected on the cover glass of the solar cells. On these surfaces the measured cumulative flux of impact craters with a central pit diameter of 50 μm or larger is ≈1.5×10 −6/m 2s −1. On these glass surfaces, 225 out of 703 impacta which were measured in detail showed signs of directionality. The measurements, derived impact fluxes and a first evaluation of more detailed impact feature parameters and correlations are presented.

Empirical Scaling Laws for Crater Dimensions for Impacts into Solar Cells

The returned solar cells from the European Retrievable Carrier (EURECA) satellite and one Hubble Space Telescope Solar Array (HST-SA) acted as collector surfaces for microparticles in the vicinity of the Earth. Because only limited information on cratering formulae for solar cells was available from the literature, hypervelocity impact experiments on such samples were performed at the plasma drag accelerator facility of the Fachgebiet Raumfahrttechnik (LRT), TU München. The results from these experiments were combined with data from experiments performed during the Apollo program into a new scaling law relating particle parameters and impact crater dimensions on solar cell targets.

Microscopic and chemical analyses of major impact sites on timeband capture cell experiment of the eureca spacecraft

Extensive studies of over 100 impact sites on aluminium foils and mesh supports of the Timeband Capture Cell Experiment (TiCCE) on the European Retrievable Carrier (EuReCa) spacecraft were conducted with scanning electron microscope and energy dispersive X-ray spectrum analyser. Chemical elements of residues in and around the perforations and craters were examined to identify the origin of impactors. 73% of the impacts were classified: the minimum of 15% was due to natural particle impacts and the rest indicated high silicon presence. Possible origins of these silicon profiles were discussed. For micrometeoroid craters, the depths to diameter ratios were compared with those of meteoroid and orbital debris impacts on the Solar Maximum Mission satellite.

Space degradation of SOVA sunphotometers on EURECA

Two sunphotometers with three channels at 862 nm, 500 nm and 335 nm were operated in space for eleven months on board the European Retrievable Carrier (EURECA). Both instruments experienced substantial losses of sensitivity, although the second instrument was exposed 100 times less than the first one. After retrieval of EURECA, the instruments were examined and optically tested. Contamination and degradation of optical components were found, but only small changes in spectral bandpasses.

Post-flight measurements of meteoroid/debris impact features on EURECA and the Hubble solar array

The EUropean REtrievable CArrier (EURECA) and one of the Hubble Space Telescope (HST) solar arrays were returned from space in 1993 after, respectively, 11 months and 3.62 years in Earth orbit. ESA has initiated post-flight investigation programmes which include recording and analysis of impact features on all exposed EURECA surfaces (total area ≈ 140 m 2) and on the Hubble solar array (total area ≈ 60 m 2). The impact analysis plan, measurements for EURECA and model predictions for the Hubble array are presented.

Results of solar spectral irradiance measurements by SOVA2 on EURECA

The solar irradiance has been measured at 3 wavelengths (335, 500 and 862nm) by the experiment SOVA2 from the European Retrievable Carrier (EURECA). The dataset, corrected for instrumental effects and degradation, is examined for solar variability on timescales from minutes to days.

Biological responses to space: Results of the experiment “Exobiological Unit” of ERA on EURECA I

Spores of different strains of Bacillus subtilis and the Escherichia coli plasmid pUC19 were exposed to selected conditions of space (space vacuum and/or defined wavebands and intensities of solar ultraviolet radiation) in the experiment ER 161 “Exobiological Unit” of the Exobiology Radiation Assembly (ERA) on board of the European Retrievable Carrier (EURECA). After the approximately 11 months lasting mission, their responses were studied in terms of survival, mutagenesis in the his (B. subtilis) or lac locus (pUC19), induction of DNA strand breaks, efficiency of DNA repair systems, and the role of external protective agents. The data were compared with those of a simultaneously running ground control experiment. The survival of spores treated with the vacuum of space, however shielded against solar radiation, is substantially increased, if they are exposed in multilayers and/or in the presence of glucose as protective, whereas all spores in “artificial meteorites”, i.e. embedded in clays or simulated Martian soil, are killed. Vacuum treatment leads to an increase of mutation frequency in spores, but not in plasmid DNA. Extraterrestrial solar ultraviolet radiation is mutagenic, induces strand breaks in the DNA and reduces survival substantially; however, even at the highest fluences, i.e. 3 × 10 8 Jm −2, a small but significant fraction of spores survives the insolation. Action spectroscopy confirms results of previous space experiments of a synergistic action of space vacuum and solar UV radiation with DNA being the critical target.

The European Retrievable Carrier (EURECA) as an observing platform from a user's point of view

The operational environment of EURECA as experienced by the SOVA2 experiment is presented. This experiment has independently measured the solar pointing with a high resolution sun sensor and monitored several temperatures as ancillary parameters to be used in evaluation of the scientific measurements. Results of these measurements are presented and experience with the novel telemetry / telecommand and data retrieval system is commented.

Solar total irradiance variability measured by SOVA-2 on board EURECA

During its 9 months of operation, the experiment SOVA-2 (Solar Constant and Variability) on board the European Retrievable Carrier (EURECA) has measured the total solar irradiance with two radiometers of the type PMO6-R. The solar variability has been investigated by bivariate spectral analysis of the irradiance and the Photometric Sunspot Index (PSI) to account for the sunspot blocking and after removal of the spot influence with the MgII-Index as proxy for the contribution of faculae and other bright magnetic elements.

Growth of calcium carbonate crystals on the European Retrievable Carrier flight

On the Solution Growth Facility (SGF) of the European Retrievable Carrier (EURECA), clear, colorless crystals of calcium carbonate up to 3 mm long have been grown from aqueous solution without the use of a gel. This is a much improved result compared with previous solution growth of CaCO 3.

In-Orbit Performance of the EURECA AOCS

The EURECA (European Retrievable Carrier) is a μ-gravity platform for multi-disciplinary space science missions and was developed by Deutsche Aerospace (DASA) under contract to the European Space Agency (ESA). On the 31st of July 92 it was launched on-board the US shuttle into a near Earth orbit and was retrieved on the 24th of June 93 in the course of the STS 57 shuttle mission. EURECA was controlled by ESA's Space Operations Centre in Germany. The attitude and orbit control subsystem (AOCS) of EURECA was developed and tested by DASA and MATRA.This paper reports about the in-orbit experience with the AOCS, which provided 3-axis stabilization for the different mission phases, including orbit transfer manoeuvres. It operated with three types of actuators (hydrazine, cold gas, magnetic torquers) and also several types of sensors (coarse and fine sun sensors, earth sensor, gyros). Examples from the Shuttle deployment, the payload operations phase under μ-gravity and the retrieval phase will be used to demonstrate the good overall AOCS performance. Special attention will be devoted to the complex, autonomous on-board failure detection which successfully mastered most of the encountered anomalies. In particular, problems relating to the tuning of the failure management system will be discussed and recommendations for potential improvements given for the benefit of other projects.