Introduction

Aircraft parabolic flights are a useful tool for performing short duration scientific and technological experiments in reduced gravity. Together with drop towers, sounding rockets, the International Space Station (ISS) and other manned and unmanned spacecraft, aircraft parabolic flights with the Airbus A310 ZERO-G completes the set of flight research opportunities for European scientists (see Fig. 1).

Fig. 1
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Reduced gravity platforms accessible to European scientists (Credit: DLR)

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The principal value of parabolic flights is twofold: firstly, in conducting verification tests prior to space experiments in order to improve their quality and success rate, and after a space mission to confirm or invalidate (sometimes conflicting) results obtained from space experiments; and secondly, in providing a flying laboratory in which the gravity level can be modified, producing, at a relatively low cost, scientific results for experiments operated by the scientists themselves and for which the microgravity duration and levels are adequate. Aircraft parabolic flights are the only flight opportunity beside ISS and Chinese spacecraft where medical research on human test subjects can be performed in weightlessness.

For these purposes, ESA has organised 62 parabolic flight campaigns (Pletser et al. 2015) since 1984 in the frame of its Microgravity Programme, CNES has organised 47 campaigns since 1989, and DLR has organised 35 campaigns since 1987, with several airplanes: NASA’s KC-135, CNES’ Caravelle, the Russian CTC Ilyushin IL-76-MDK, and the Airbus A300 ZERO-G. In addition, two Joint European Partial-g Parabolic Flight Campaigns were jointly organised by ESA, CNES and DLR using the Airbus A300 ZERO-G for experiments at reduced gravity levels, typically at Moon and Mars g-levels (Pletser et al. 2012). In parallel, nine ESA Student campaigns were organised by ESA’s Education Office for experiments proposed by European university students with NASA’s KC-135, CNES’ Caravelle and the Airbus A300 ZERO-G (Callens et al. 2011; Pletser et al. 2005).

The main advantages of parabolic flights for microgravity investigations are: the short turn-around time (typically about 8 months between the experiment proposal and its performance), the reliability of the campaign dates, the relatively low cost involved (ESA, CNES and DLR provides the flight opportunity free of charge to investigators), the flexibility of experimental approach (laboratory type instrumentation is most commonly used), the possibility of direct intervention by investigators on board the aircraft during and between parabolas, and the possibility of modifying the experiment set-up between flights. Other more detailed objectives are presented in Pletser et al. (2015).

Parabolic Flight Campaigns

The microgravity environment is created in the Airbus A310 ZERO-G flying the following manoeuvres (see Fig. 2):

  • from steady horizontal flight, the aircraft climbs at 50°(pull-up, see Fig. 3) for about 20 s with accelerations between 1.8 and 2 g;

  • all aircraft engines thrust is then strongly reduced for about 20 to 25 s, compensating the effect of air drag (parabolic free fall);

  • the aircraft dives at 42 ∘ (pull-out), accelerating at about 1.8 to 2 g for approximately 20 s, to come back to a steady horizontal flight.

Fig. 2
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The parabolic flight manoeuvre of the Airbus A310 (Credit: Novespace)

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Fig. 3
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The Airbus A310 in pull-up (Photo: Novespace - Eric Magnan / Airborne Films)

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These manoeuvres are flown separated by intervals of several minutes. Duration of intervals between parabolas can be arranged prior to the flight such as to give enough time to investigators to change an experimental set-up. A typical flight duration is between two and half and three hours, allowing for 30 parabolas to be flown per flight, in sets of five, with approximately two minutes intervals between parabolas and with four to six minutes between sets of parabolas. During the reduced gravity period, after a transitory phase of a few seconds, the residual accelerations sensed by experimental set-ups attached to the aircraft floor structure are typically in the order of 10 −2g, while for an experiment left free floating in the cabin, the levels can be improved to typically 10 −3g.

Take-offs and landings are made at the Bordeaux airport, although other airports have been used in the past in Köln, Brussels and Berlin. Parabolas are flown in dedicated air zones over the Gulf of Biscaye, the Mediterranean Sea, or Germany respectively.

The majority of the experiments conducted on microgravity research campaigns are proposed in answer to International Announcement of Opportunities and selected after Peer reviewing (Pletser et al. 2008). ESA’s Announcement of Opportunity is permanently open for microgravity experiments to be conducted during parabolic flights. Proposals can therefore be sent to ESA at any time. Proposals are sent to selected external peers for reviewing from a scientific standpoint. After peer recommendation the technical feasibility of the proposal is assessed and, upon positive assessment an experiment proposal is manifested for a specific campaign. DLR is also prepared to receive proposals at any time. The proposals will be selected for flight after external evaluation. ESA, CNES and DLR offer the opportunity of participating in the parabolic flights to selected investigators free of charge.

As aircraft parabolic flights are considered to be test flights, particular precautions are taken to ensure that all operations during flights are conducted safely and that flying participants are adequately prepared for the repeated high and low gravity environments. Prior to a campaign, ESA, CNES and DLR, with the help of their Contractor Novespace, provide support in the experiment equipment design and in all related safety aspects. All experiments to be performed and all equipment to be installed on board the aircraft are reviewed from a structural, mechanical, electrical, safety and operational points of view by experts several months before a campaign. Technical visits are made to the experimenters’ institutions to review equipment. A safety review is held one month before the campaign. During this review, the integration of all equipment is discussed and the overall safety aspect of the campaign is assessed.

The campaign itself takes place over two weeks. The first week is devoted to the experiment preparation and loading into the aircraft. During the second week, usually on the Monday, a final safety review visit is conducted on board the aircraft to verify that the experiments are ready for flight and that all safety recommendations have been implemented. A flight briefing is organised on the Monday afternoon to present the flight manoeuvres, the emergency procedures and medical recommendations, and all experiments are briefly presented by the investigators. Typically, three flights of 30 parabolas each take place each morning on the Tuesday, Wednesday and Thursday, followed each time by a debriefing during which the needs and requests of investigators are reviewed and discussed. On request, one or two flight days can be added.

All experimenters invited to participate in parabolic flights must pass a medical examination. During the flights, specialised personnel supervise and support the in-flight experiment operations. In addition, a Flight Surgeon participates in all flights to supervise the medical aspect of in-flight operations and to assist participants in case of sickness. Due to the alternation of flight phases of low and high gravity, parabolic flight participants might suffer from motion sickness. Therefore, prior to the flights, anti-motion sickness medication is made available on request to flying participants.

After the campaign, parabolic flight investigators are requested to send a report with results of their experiments to the agencies. Results of ESA experiments are placed in the ESA’s Erasmus Experiment Archive (EEA) database (http://eea.spaceflight.esa.int/portal/).

The Airbus A310 Zero-G

The former ‘Chancellor Airbus’ A310-304 ‘10 + 21’ was delivered from aircraft manufacturer Airbus to East German airline Interflug on 24 June 1989 and was used by Interflug for East German government leaders and normal flight business until 1991. On 27 August 1991, the aircraft became the property of the German Air Force and, with the name ‘Konrad Adenauer’, the VIP aircraft was used for journeys and state visits by German Federal Chancellors and government ministers between 1993 and 2014. The A310 ‘10 + 21’ was stationed at the Cologne Bonn airport during its mission for the German Federal Ministry of Defence. Exactly 25 years after the initial handover, the ‘Konrad Adenauer’ was handed over to its new owner, Novespace, on 24 June 2014, after which a series of qualification flights took place in the Summer of 2014 from the airport of Bordeaux-Mérignac (see Fig. 4). From 3 September 2014 until 18 March 2015, Lufthansa Technik in Hamburg overhauled the aircraft and converted it for use in parabolic flights. The certification process took place from July 2014 until Spring 2015 in agreement with the regulations of the European Aviation Safety Agency (EASA) and the French Direction Générale de l’Aviation Civile (DGAC).

Fig. 4
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Both Airbus ZERO-G side by side in Bordeaux: the future A310 ZERO-G in the foreground (left) and the A300 ZERO-G in the background (right) (Photo: Novespace)

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The Airbus A310 has approximately the same dimensions as the Airbus A300, except that it is shorter in length by about 5m. However, as the seating accommodation in the Airbus A310 is slightly different from that of the Airbus A300 after modifications for parabolic flights, the cabin area and the interfaces for experiments are similar: approximately 20 m long by 5 m wide and 2.25 m high (see Fig. 5). This makes the Airbus A310 ZERO-G the world largest airplane for parabolic flights. Table 1 shows some technical characteristics of the Airbus A310 ZERO-G aircraft. More details can be found in Novespace (2014, 2015a, 2015b).

Fig. 5
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The 100 m 2 experiment area of the Airbus A310 ZERO-G, the world largest parabolic flight aircraft (Photo: Novespace)

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Table 1 Characteristics of the Airbus A310 Zero-G
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The first scientific campaign took place in the April-May 2015 timeframe. The three main European space agencies CNES, ESA and DLR, which are the regular users of parabolic flights, decided to organise jointly a cooperative microgravity parabolic flight campaign to mark this beginning of a new era in microgravity and reduced gravity research (see Fig. 6). Twelve experiments, representing a mixed payload of physical and life sciences, have been conducted by investigators invited by the three agencies.

Fig. 6
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The Technical Officers of the three European space agencies, respectively S. Rouquette for CNES, U. Friedrich for DLR, and V. Pletser for ESA during the first Cooperative European campaign (Photo: DLR)

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From May to November 2015 five further microgravity research campaigns were performed with the new Airbus A310 ZERO-G: two campaigns each for ESA and CNES, and one for DLR. Research campaigns are foreseen to continue at a rate of two campaigns for each of ESA and CNES per year, and one or two campaigns for DLR per year.

First Cooperative ESA-CNES-DLR Campaign COPF

The 1st cooperative parabolic flight (CoPF) campaign has been conducted from Bordeaux-Merignac airport from April 27th to May 8th, 2015. Three flights have been performed with 12 experiments on board, selected by CNES, DLR and ESA scientific committees.

ESA Experiments

  1. 1)

    Dual atom interferometer for Quantum Weak Equivalence Principle (QWEP) Prof. P. Bouyer (Laboratoire Photonique, Numérique, Nanosciences, Université Bordeaux 1, F)

    This experiment aims to test the Weak Equivalence Principle, which states that two different masses in a gravitational field fall with the same acceleration. To verify this statement at a microscopic and quantum level, a dual atomic species interferometer was developed to measure a differential acceleration between two atoms of different mass and structure.

    At low temperature, atoms behave like waves so that it is possible to manipulate these matter waves and make them interfere. Since atoms have a mass, the relative phase between their paths is sensitive to inertial effects. As in optics where large interferometers are used for accurate measurement, the sensitivity of the measure with a cold atom interferometer increases with the duration of the experimental sequence. On Earth, atoms fall under gravity and can’t be used at some point because they go out the experiment cell. In microgravity, the atoms stay in the experiment chamber and longer durations can be obtained, yielding much higher sensitivity. This experiment is preparatory for space applications on a satellite where a sensitivity of 10 −15 can be expected.

    As vibrations level is higher on board the Airbus A310 than in a ground laboratory, new technology has been developed with new, compact and robust set-up and laser sources, insensitive to thermal and mechanical fluctuations. A complex laser system (Ménoret et al. 2011) is used to trap and cool the two atomic species (rubidium and potassium). It is mainly based on telecom components, two 10 W optical amplifiers and a free space doubling stage to get light at 780 nm starting from 1560 nm (see Fig. 7). The frequency is very accurately locked on the atomic transition thanks to a femto second laser which generates a frequency comb. With this technique, the atoms can be cooled down to 2 μK. This low temperature gives a high coherence to the source of the atomic interferometer, so it increases the high signal to noise ratio. The atoms are contained into a science cell (see Fig. 7) where ultra-high vacuum is reached (10 −9 Torr) with passive (getters) and active pumps (ion pump).

    A frequency chain generates RF signals which allow to control the internal states of the atoms. A quartz oscillator is used as a frequency reference for the frequency comb and the RF signals. The whole system is controlled by a computer and cards generating very accurate analogue and digital signals with a high sample rate (1 million of points per second). This experiment requires three operators for its performance on the A310 ZERO-G (see Fig. 8).

    Transportable cold atom inertial sensors could be used in different domains, where their accuracy and long term stability constitute strong advantages. On Earth, atomic gravimeter or gyroscope can be used for inertial navigation, geophysics or metrology. Similarly, an atom interferometer working in an aircraft can be used for these purposes as it was demonstrated by measuring the residual accelerations. Connected to a classical accelerometer which is used for the coarse part of the measure, our fine measuring sensor can detect inertial effects more than 300 times weaker than the typical acceleration fluctuations of the aircraft (Geiger et al. 2011). This is an important step towards a full on board navigation station with cold atoms.

    In space, atom interferometers could be used for testing the General Relativity theory, like the atomic clock Pharao on ISS. This experiment is an important step in the frame of the space project STE-Quest, which aims at putting an atomic clock and a double species interferometer on a satellite to test the weak equivalence principle and gravitational redshifts. Last but not least, the field of space and on board gradiometry (measurement of gravity gradients) is growing quickly and cold atoms instruments start to be considered as the future technology breakthrough for these applications.

  2. 2)

    Is muscle force generation capacity impeded in microgravity? Prof. K. Albracht (German Sports University Cologne, D), Dr D. Belavy (Charité Campus B. Franklin, Zentrum für Muskel- und Knochenforschung, Berlin, D)

    The goal of the project is to perform a deeper examination of muscle force and function during high-load resistive exercise in microgravity. Available data suggest that high-load, muscle-specific exercise is necessary to maintain muscle mass and function during prolonged spaceflight. However, based upon existing literature, it can be postulated that individuals may not be able to reach as high muscle forces at all lower-limb joints during voluntary contraction in microgravity. This hypothesis has, however, not been tested and parabolic flight offers an ideal environment to test it. If the hypothesis would be true, this would limit our ability to perform exercise to maintain the musculature in microgravity. One possible mechanism is that, based upon neurophysiological studies, reduced muscle spindle afference in microgravity reduces the peak drive voluntarily attainable for muscle activation.

    This experiment aimed at examining whether there are indeed alterations of peak force generation characteristics in microgravity in the lower-limb, more specifically, whether maximum voluntary capacity and rate of force development of plantar flexion and leg press are impeded in microgravity. Maximal hand-grip force was measured as a control condition. As secondary outcome measures, muscle electromyographic activity, superimposed twitches and ultrasound parameters of musculotendinious loading were assessed.

    In order to investigate muscle force and function, muscle strength was tested during three different tasks: (1) grip strength, (2) leg press and (3) plantar flexion. The grip strength was tested with a hand-dynamometer. The maximum voluntary contraction of knee extensors and plantar flexors were carried out on a self-made dynamometer (see Fig. 9), which enables both isometric plantar flexion and isometric leg extension.

    To measure the force exerted during the maximum voluntary contractions, two force plates were implemented. For the plantar flexion, the subject’s leg was extended and the foot was attached to the small force plate on the bottom. For the knee extension the subject’s foot was attached to the large force plate on top. The dynamometer is specifically designed for parabolic flights. Muscle activity was measured using electromyography. The position of the ankle and knee joints were measured with a camera and muscle behaviour was visualized with an ultrasound probe (see Fig. 10).

    Lastly, the ability to fully activate the calf muscles during a volitional effort and some of the neuromuscular properties were studied by applying a brief electrical stimulation to the nerve commanding the calf muscle both during a maximum voluntary contraction and during rest.

    The outcomes of this experiment are to be applied to countermeasure against muscle atrophy in manned spaceflight. The importance of this issue for spaceflight is that if it is not possible to attain high load levels during microgravity, or if the force generation profile is impeded, then it might not be possible to exercise the musculature at the load levels that are better suited for maintaining muscle mass. This may be one explanation for the only moderate effect of exercise countermeasures in prolonged spaceflight against (calf) muscle atrophy.

    More generally, the results contribute to the basic understanding of human neurophysiology and biomechanics, in particular the influence of gravity on voluntary and involuntary force-generating capabilities.

  3. 3)

    2-D/3-D Analysis of root development in microgravity studied on parabolic flights Dr F. Ditengou, Prof. K. Palme (Institute of Biology, Universität Freiburg, D)

    Gravistimulated plants roots bend downwards (positive gravitropic response) while shoots bend upwards (negative gravitropic response). Although it is well accepted that the asymmetric auxin distribution during root gravitropic response facilitated by the coordinate activity of auxin influx and efflux carriers within the root apex is the central component of root graviresponse, however the mechanisms of gravitropic curvature establishment are still poorly understood. Specifically, precise timings of auxin distribution, root-growth reorientation and how growth is impacted at the cellular level are not known. To shed light on these points, auxin distribution and root growth at both tissue and cellular resolution were both simultaneously monitored in 3-dimensions in normal (1-g) and in altered gravity (parabolic flight).

    The growth of wild-type Arabidopsis thaliana, auxin-gravitropic mutant and the auxin reporter were recorded in flight during parabolic flights. Growing seedlings were fixed at different moments during the flights. Post-flight, using a recent root coordinate system combining advanced imaging techniques with pattern analysis, subtle changes of cell geometry and growth of Arabidopsis roots were quantitatively revealed in 3D, hence resulting in a cell atlas of the graviresponsive Arabidopsis root tip (see Fig. 11).

    The knowledge gained from this experiment allows to understand how plants perceive and respond to hyper- or micro-g. It can be used for predicting the behaviour of potential targets plant genotypes prior to spaceflight missions.

  4. 4)

    Collisional evolution of mm to cm size dust aggregates , Medea2 Prof. J. Blum (Institute for Geophysics und Extraterrestrial Physics, Technische Universität Braunschweig, D)

    This experiment investigates the initial phase of planet formation. It is known that particle growth starts with collisions of small, micrometre sized dust grains in circumstellar gas disks around young stars. While the formation of bodies up to a size of about one millimetre is well understood, the collision physics of millimetre sized dust aggregates and their further growth is still an active field of research. Recent simulations showed that particle growth stops at a size of ˜1 cm due to bouncing collisions. On the contrary, experiments have shown that further growth of these particles is still possible in individual collisions when one of the collision partners fragments while the other one gains mass. The aim of these experiments is to study firstly, the role of this growth effect on an ensemble of dust agglomerates stored in a quasi-two-dimensional particle container; and secondly, whether the fragments of the destroyed agglomerate stick to the surviving agglomerates and start a fragmentation-growth cycle.

    Two separate but similar experiments were performed simultaneously.

    The first experiment aimed at generating and observing collisions between cm-sized dust agglomerates, to gain new information about the early phase of planet formation (Kothe 2016). The instrumentation included an evacuated, vibrated particle container and a high-speed camera system to observe the experiment.

    The second, self-contained experiment was a prototype to fly on a sounding rocket. It used as particle container a small exchangeable evacuated (˜10 −3 mbar) glass tube which contains dozens of mm-sized dust particles. This container (see Fig. 12) was mounted on a shaking mechanism to induce small relative velocities, in the range mm/s to cm/s, among the particles as well as between container and particles to avoid sticking to the walls. The particle ensemble is observed by a high-speed camera through a prism, using LED backlight illumination in order to obtain 3D information on the particle trajectories (Kothe et al. 2013; Weidling et al. 2012).

  5. 5)

    Parabolic flight induced neuroplasticity studied with advanced magnetic resonance imaging methods Prof. F. Wuyts, Drs A. Van Ombergen, B. Jeurissen, P.M. Parizel (University of Antwerpen, B)

    The hypothesis of this experiment is that short duration microgravity and gravity transitions, experienced during parabolic flights, induce neuroplasticity in different regions of interest in the brain that are involved in the integration of neurosensory information, provided by the vestibular organs, vision and proprioception. Additionally, these results are to be compared with data to be collected on twelve cosmonauts flying on the International Space Station. Comparison between effects of short and long duration microgravity respectively in parabolic flights and during space flights could elucidate group differences in certain brain regions and tracts (Van Ombergen et al. 2013; Demertzi et al. 2015). Finally, the identification of sites of neuroplasticity related to adaptation to microgravity, g-level transitions, and ‘coping with motion sickness’ are used to verify these regions of interest in patients that suffer from continuous vertigo or instability, due to inappropriate adaptation after lesions, or patients with ‘mal de débarquement’ syndrome.

    By means of advanced Magnetic Resonance Imaging (MRI) methods, it is hypothesized that biomarkers for neuroplasticity can be identified when MRI images of the same subject, acquired 10 and 2 days before (L-10, L-2) and on the same day, 3, 7, 45 and 90 days after parabolic flight (R + 0, R + 3, R + 7, R + 45, R + 90), are compared with each other. Consequently, this will allow for the identification of specific regions of interest (see Fig. 13) and fibre tracts that are involved in neuro-vestibular processes. The L-2 and R + 0 scans were conducted in Bordeaux, close to the campaign site, to minimize the interval between the landing of the parabolic flight and the actual scan. The other scans are conducted at the University of Antwerp.

    Knowledge obtained from this study could improve the understanding on how neuroplasticity takes place and explain what happens in microgravity at the central level. Furthermore, it could also pinpoint towards the development of adequate countermeasures for space motion sickness as well as vestibular symptoms.

  6. 6)

    Microthrust by Thermal Creep Gas Flow through Porous Bodies Prof. G. Wurm, Dr J. Teiser (Faculty of Physics, University Duisburg-Essen, D)Recent experimental studies showed that porous materials as e.g. dust beds can act as an efficient gas pump due to thermal creep within the pores. The process of thermal creep is driven by temperature gradients and leads to gas flow within pores from the cold to the warmer part. This is most efficient in the pressure range around 1 mbar, depending on the kind of gas and the pore sizes. The goal of this project is to investigate the gas flow and especially the resulting gas velocities. A potential application of this mechanism is a thermally driven pump, which could be used as a thrust module for airborne systems in the Martian atmosphere. In laboratory experiments, convection prevents the detection of gas flow driven by thermal creep. Microgravity experiments are therefore necessary (see Fig. 14).

    The experiment was carried out in a vacuum chamber at pressures between 0.1 Pa and 1000 Pa with air as well as helium. The central part of the experimental setup is shown schematically in Fig. 15 and consists of a Peltier element with a central drilling, which develops a hot and a cold surface, when a voltage is applied. The central drilling contains a porous sample. A temperature gradient within the pores leads to thermal creep and therefore to a gas flow from the cold to the warm part. The temperature gradient is induced by copper meshes, which encase the porous sample and are coupled to the two different surfaces of the Peltier-element. The gas flowing through the pores is directed through a channel, in which tracer particles are kept. The tracer particles couple to the gas flow, so the gas velocity can be measured with a camera (same view as in Fig. 15). The tracer particles are confined to the test volume by the copper mesh on one side and a sieve on the other side. Due to the gas flow, the tracer particles are collected at the sieve. They are re-ejected with a small solenoid knocking on the sieve surface. One side of the Peltier element is coupled to a large thermal reservoir and to a cooling element on the outside of the vacuum chamber.

    The Martian surface is in the focus of many scientific studies and currently explored by remote sensing from orbiters and by ground based laboratory rovers. Airborne instruments can close the gap between those two different platforms, as they are still close to the surface, but potentially can cover more terrain than rovers. Additionally, airborne systems are ideal platforms to study atmospheric processes. However, the Martian atmosphere is rather thin (few mbar), so classical aircrafts do not work efficiently. Thermally induced gas flow can therefore provide a propulsion method for thin atmospheres. The advantage of thermally induced thrust is the capability of creating thrust without moving parts, so that this mechanism might offer a highly reliable system.

    More distant but of immediate importance is the application to porous bodies in protoplanetary disks. Temperature gradients might transform these bodies into self-propelled objects which can influence the transport of matter in early phases of planet formation (Teiser et al. 2015).

Fig. 7
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Laser system to cool and trap the atoms (left); Science chamber with an ultra-high vacuum apparatus including Rubidium and Potassium atoms for the experimental sequence (right) (Photos: LPNN, Univ. Bordeaux)

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Fig. 8
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The set-up of the Dual atom interferometer experiment during the CoPF campaign (Phots: DLR)

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Fig. 9
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A subject performs the leg press task in a sitting position on the dynamometer during the CoPF campaign (Photo: DLR)

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Fig. 10
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Ultrasound recording of muscle fibres (Credit: German Sport University Koln, D)

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Fig. 11
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Graviresponsive of the Arabidopsis thaliana root tip obtained by combining advanced imaging techniques with pattern analysis (Credit Univ. Freiburg)

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Fig. 12
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An operator observes the movement of particles in a shaken container cell during the CoPF campaign (Photo: DLR)

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Fig. 13
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Reconstructed regions of interest in the brain of a subject after comparison of MRI images taken prior to and after a microgravity exposure (Credit: Univ. of Antwerpen)

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Fig. 14
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Experiment set-up on board the A310 ZERO-G during the CoPF campaign (Photo: DLR)

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Fig. 15
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Schematic sketch of the experimental setup (the surrounding vacuum chamber is not shown for simplicity). (Credit: Univ. Duisburg-Essen)

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DLR Experiments

  1. 1)

    Interactions of the human heart and the aorta in parabolic flights Dr U. Limper (Space Physiology Institute, DLR, Cologne, D), Prof. J. Tank (Clinical Pharmacology Institute, Hannover Medical School, D)

    This experiment had three objectives. The first objective was to test the modified Mobil-O-Graph device that underwent technical modifications for its application aboard the International Space Station for the experiment called “Cardiovector”. The Mobil-O-Graph device determines the central aortic pressure and the aortic pulse wave velocity via an oscillometric technique at the upper arm of the subject. The second objective of the experiment was to compare the Mobil-O-Graph estimates of the aortic pressure to the central aortic pressure estimates based on peripheral finger blood pressure measurements. The third objective was to measure cardiac performance by an inert gas rebreathing technique and by the analysis of systolic time intervals during gravity transitions. It is hypothesized that the central aortic pressure is lower in microgravity compared to 1 g although the cardiac output is higher in microgravity with respect to 1 g. This could cause hyperperfusion of organs that might be of importance for the astronaut health monitoring on long duration space flights.

    Simultaneous measurements were performed on two subjects in standing (see Fig. 16) and supine position in 1.0, 1.8 and 0 g. Mobil-O-Graph and inert gas rebreathings were performed intermittently during several parabolas. ECG, impedance cardiography, phono cardiography plethysmography of the carotid artery and finger blood pressure measurements were performed continuously (Fig. 17).

    The physiological results of this experiment increase the understanding of the human cardiovascular system in space related environments. Experiment results can be found in Hametner et al. (2016) and Moestl (2016).

  2. 8)

    Technical validation of a neurocognitive test battery for implementation on the Russian segment of the ISS Prof. S. Schneider, Dr T. Vogt (German University of Sport, Cologne, D)

    Living in extreme environments is accompanied by a number of stressors, which can be classified either as physiological (e.g. microgravity, missing sunlight) or psychological stressors (e.g. confinement). From a multitude of studies, it is well known that stress has a negative impact on mental health and cognitive performance and both factors might impair mission success and safety during longer space missions (Schneider et al., 2008a, 2008b).

    Based on this consideration, a first set of experiments is proposed for embedded neurocognitive testing within the restrictions on board the International Space Station (ISS). Using the existing Soyuz docking manoeuvre training, which is currently performed on board the ISS, and integrating an active EEG system to allow for localisation of brain cortical activity using source localisation algorithms, this experiment (see Fig. 17) aims are (1) to assess mental load and cognitive performance by using neurocognitive markers (P300) and to correlate these with docking performance, (2) to explore how these markers are influenced by stress, and (3) to assess whether exercise could act as a “neuro-enhancer” and an adequate countermeasure to stress as currently discussed in the literature. Experiment results can be found in Wollseiffen et al. (2016).

  3. 9)

    Parabolic flight testing of separation mechanisms for pico- and nano-satellites Dr N. Pilz (Aerospace Institute Berlin, D), Drs H. Adirim, F. Baumann (Technical University Berlin, D)

    This test of separation mechanisms in microgravity included the test two different systems, namely SEMENA 2 and TUPEX-5.SEMENA 2 - Enhanced separation mechanism for Nano-Satellites

    Considering the increasing number of small satellite launches, satellite separation systems are of special importance, as they constitute the actual mechanical interface between the satellite and the launch vehicle. Moreover, small satellite separation systems have to ensure a reliable fixation of the satellite to the launch vehicle structure until the moment of separation, while at the moment of the desired release they have to guarantee the controlled separation of the satellite from the launch vehicle with a defined separation velocity. For several years, an increasing trend can be observed at numerous institutions to develop, build and having launched nano- and micro-satellites with a launch mass of between 20 to 150 kg.

    Different test model configurations of an advanced version of a mechanically released Separation Mechanism for Nano-Satellites (SEMENA-2, see Fig. 18 left) were tested in microgravity. The objective of the experiment was to observe the successful separation of a 20 kg dummy satellite of defined dimensions (see Fig. 18 right), which was ejected successively and repeatedly by all SEMENA-2 test model configurations into a safety net cage. The separation process was filmed by several camcorders from different perspectives (see Fig. 19) in order to draw conclusions as regards the quality of separation with respect to the velocity and rotational speed of the dummy satellite.

    TUPEX-5 - Examination of the separation behaviour of a picosatellite swarm With the progressive miniaturization of satellites, these can be brought as swarm into Earth orbit and share tasks at low cost. A major technical challenge of these so-called picosatellites is to deploy them simultaneously from the upper stage of the rocket without collision. In project TUPEX-5, the simultaneous separation of four 330-gram picosatellites (see Fig. 20), developed at the Technical University of Berlin, is investigated. The separation and activation of these picosatellites in microgravity are recorded by several cameras for post-flight image analysis of accelerations and rotational rates of the dummy satellites.

  4. 10)

    Gravity dependence of receptor-ligand interactions Prof. W. Hanke (University of Hohenheim, Stuttgart, D)

    The question, whether pharmacological substance might depend on gravity in their action is of importance for the pharmacological welfare of astronauts during long lasting space missions, but it might also deliver important information for ground based pharmacology. Looking at targets of presently used pharmacons, two groups of substance are of high interest. These are ligands binding to GPCRs (G-Protein Coupled Receptors) or to ion channels. Consequently, as both targets are classical receptors, ligand-receptor interaction should be investigated under different gravity conditions. Such ligands can be agonists, antagonists, or of more complex action. This experiment investigated the gravity dependence of ligand-receptor interactions of pharmacologically interesting substances.

    The experiment (see Fig. 21) is designed as a modified stopped-flow apparatus using fluorescent dyes to measure ligand binding (receptor-ligand interaction) and substance incorporation into membranes. Among others, classical fluorescent dyes for membrane potential and intracellular ion concentrations (i.e. pH and Ca ++), as well as for membrane fluidity were used, as they are well established to investigate the action of drugs on membranes and cells. Some more detailed information was obtained also about the incorporation of lipophilic and amphiphilic substances into membranes (Sieber et al. 2016).

    CNES Experiments

  5. 11)

    Microgravity effect on the haptic perception of geometric shapes Drs M. Tagliabue, J. McIntyre, G. Clement, M Beraneck (Université Paris Descartes, CNRS, F)

    The aim of the experiment is to understand how gravitational signals, such as vestibular information, affect the haptic perception of shapes and dimensions. In particular, the effect of the perceptive distortions observed for the visual perception of 3D objects in microgravity on the perception of 3D objects through haptic (tactile) system was investigated. If similar distortions occur for both visual and haptic perceptions, this would mean that the visual distortions previously observed might not be due to a direct effect of the gravitational signals on the visual system, but more likely to an interaction between gravity and the brain areas involved in the elaboration of the spatial information independently from the sensory modality through which they have been acquired.

    Practically, subjects have to estimate then adjust dimensions of rectangles in different directions, in order to make them square, with the help of a haptic device connected to a computer (see Figs. 22 and 23). At first, an audio signal indicates which plane and direction the subject will have to deal with. Planes can be vertical, sagittal or horizontal. Direction might be length, width or height. Then, the subject has to estimate the specific dimensions of the corresponding rectangle. You could experience the same kind of perception on ground when you touch an empty box with your finger while your eyes are closed. Then, the subject has to adjust the given direction in order to make it square. After he validates the dimension change, another task is given. After few campaigns, several subjects have been measured.

  6. 12)

    PROGRA 2 - Light diffusion and polarization of terrestrial and extra-terrestrial dusts Dr J.B. Renard (LPC2E-CNRS, Orléans, F)

    Clouds of solid particles are present in many regions of the Solar System. Most dust clouds are not characterized by a high density but they might be remotely detected by the light they scatter. In-situ observation, remote observations or direct investigation of interplanetary dust are common practice for the research on light scattered by clouds of solid particles. This light scattering can be studied using different techniques. Reduced gravity can be used to recreate conditions close to those existing in space. Such a set-up allows laboratory experiment measurements which can serve for relating remote or in-situ observations to physical parameters (size, porosity, nature). Parabolic flights are used for that purpose because light scattering measurements can be made within seconds for any kind of particles without discrimination by weight or composition.

    The PROGRA2 project was set-up to provide key scientific results in terms of astrophysics (e.g. agglomeration processes in proto-stellar clouds, evolution of dust particles in cometary comae) and physics of the atmospheres (e.g. Titan, Earth). The PROGRA2 experiment allows measurements under microgravity conditions of polarization phase curves for clouds of dust particles. The sizes that can be used range from a few to hundreds of micrometres; regular or irregular particles can be tested (Renard et al. 2014).

    PROGRA2 is an imaging polarimeter with a rotating arm to change the phase angle (angle between direction of illumination and direction observation). It allows retrieving the complete polarization phase function between 10 ∘ and 165 ∘ . The light sources are between 540 and 1500 nm. The detectors are cameras, with a spatial resolution of approx. 20 μm per pixel. The microgravity conditions are suitable for levitating compact particles with diameters greater than 20 μm. For smaller and/or lighter particles, the microgravity produces agglomerates of particles.During this campaign (see Fig. 24), carbon particles produced in laboratory and that simulate carbonaceous particles found on comets and asteroids were investigated. In particular, the effect of the particles porosity on the scattering phase functions was studied. Three samples of volcanic ashes from Etna have been used, with mean size distribution centred on 50 μm, 100 μm, and 200 μm, and one basalt sample having a size distribution between 100 and 200 μm.

    The light scattering researches of PROGRA 2 were used to develop a new concept of light aerosols counter. This instrument is used now routinely for the monitoring of air quality and for the study of aerosols from ground up to the middle stratosphere.

Fig. 16
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Two subjects being measured simultaneously for the experiment ‘Interactions of the human heart and the aorta’ during the CoPF campaign (Photo: DLR)

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Fig. 17
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Two subjects wearing EEG caps perform the neurocognitive test battery experiment during the CoPF campaign (Photo: DLR)

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Fig. 18
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SEMENA-2 Test model configuration mounted on Base Plate of Experiment Rack (left) and together with mounted 20 kg dummy satellite (right) (Photos: Aerospace Institute Berlin)

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Fig. 19
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Test of the SEMENA-2 separation mechanism: view of the dummy satellite after release in the safety net cage during the CoPF Campaign (Photo: DLR)

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Fig. 20
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Dummy satellite (right) and CAD model of satellite separation (left) (Credit: Technical University Berlin)

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Fig. 21
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Prof. Hanke and Dr Sieber performing the ‘Gravity dependence of receptor-ligand interactions’ experiment during the CoPF Campaign (Photo: DLR)

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Fig. 22
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Haptic device used for the ‘haptic perception of geometric shapes’ experiment (Credit: Université Paris Descartes)

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Fig. 23
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A subject preforms the ‘haptic perception of geometric shapes’ experiment during the CoPF Campaign (Photo: DLR)

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Fig. 24
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The PROGRA 2 experiment set-up in flight during the CoPF Campaign (Photo: DLR)

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Conclusions

Since April 2015, the Airbus A310 ZERO-G, the world largest airplane for reduced gravity research, is used in Europe for short duration microgravity investigations mainly by ESA, the French space agency CNES and the German Space Agency DLR. The first campaign was a Cooperative campaign shared by the three agencies with twelve experiment reported above. Following this initial campaign, a CNES, an ESA and a DLR campaign were conducted successfully respectively in May, June and September 2015. Parabolic flight campaigns are foreseen to continue at a rate of two campaigns per year for CNES and ESA and one to two campaigns per year for DLR.

With this unique programme, developed within an excellent cooperation between space agencies and Novespace, parabolic flights will continue to provide scientific and technical knowledge in the various scientific disciplines and technology fields that take advantage of the microgravity or reduced gravity. Together with drop towers, sounding rockets, the ISS and other manned and unmanned spacecraft, parabolic flights with the Airbus A310 ZERO-G complete the set of flight research opportunities in reduced gravity for European scientists and researchers of other countries.