Experimental Characterization of Weightlessness During Glider Parabolic Flights

Microgravity Science and Technology https://doi.org/10.1007/s12217-020-09836-6 ORIGINAL ARTICLE Experimental Characterization of Weightlessness During Glider Parabolic Flights Denis-Gabriel Caprace1,2 · Camille Gontier1,3 · Mohammad Iranmanesh1 · Mehdi Scoubeau1 · Vladimir Pletser4 Received: 16 April 2020 / Accepted: 24 September 2020 © The Author(s) 2020 Abstract Access to earthbound weightlessness is critical to many branches of applied sciences. Besides, several space systems require microgravity testing before their launch. Existing solutions (drop towers, parabolic flights, sounding rockets) offer variable durations and qualities of microgravity environment, but their cost and lead times make them unpractical for small actors such as universities or start-up companies. This leads to a growing interest for alternative microgravity platforms. Here, we study the use of gliders to perform parabolic flights at a lower cost, and we propose a systematic quantification of glider’s 0-g flight capabilities. Results of our flight test campaign show that gliders offer up to 5.5s of weightlessness, with excursions below 0.1g, and a satisfactory level of repeatability. Besides, the recordings do not suffer from the increased level of vibrations generated by piston engines, typical of light-aircraft-based alternatives. Operational considerations associated with glider parabolic flights are also discussed. Finally, we conclude that a microgravity platform based on gliders would be suitable especially for compact experiments and equipment in order to support accelerated design and development, or to produce preliminary experimental results. Keywords Microgravity experiments · Gliders · Parabolic flights Introduction Experiments in a reduced-weight environment are a fundamental part of many branches of applied sciences, such as material science, fundamental physics, fluid dynamics, physiology and space medicine, plant and cellular biology, combustion physics. All require conducting experiments in weightlessness (Seibert et al. 2001; Beysens and van Loon 2015; Pletser 2018). Additionally, the current trend of space commercialization (de Crombrugghe and Pletser 2017) induces a growing interest for weightlessness facilities. Yet, the number of solutions able to reproduce microgravity on Earth is limited and they all have their limitations (Herranz  Camille Gontier 1 LIDE Space, Louvain-la-Neuve, Belgium 2 Institutes of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium 3 Department of Physiology, University of Bern, Bühlplatz 5, 3012 Bern, Switzerland 4 Blue Abyss, Liverpool, United Kingdom et al. 2013; de Crombrugghe and Pletser 2017). Sounding rockets, aircraft parabolic flights and drop towers are today’s most valued microgravity platforms. However, their cost and lead times make them unaffordable or unpractical for many space actors, such as small start-ups, universities, or student projects (Council 2011). In particular, parabolic flights performed with aircraft were introduced in the 50’s, namely to study the effect of reduced-gravity environments on the human body (Haber and Haber 1950). They then developed as an easy-to-access and muti-purpose microgravity platform, which however has become more and more expensive and which nowadays also suffers from long lead times. There have been some recent interests in alternative, less costly solutions for microgravity testing. For instance, parabolic flights can be performed with light single-engine piston aircraft (de Crombrugghe and Pletser 2017), as was demonstrated by flight test campaigns operated with a Cessna 206 (Selig et al. 2016, 2017, 2018, 2019) and a CAP 10 (Perez-Poch et al. 2016a; Brigos et al. 2014). Microgravity was achieved for approximately 8 seconds during each parabola, with great operational flexibility. Sailplanes are also potentially favourable platforms for reaching weightlessness. A first quantification of gliders Microgravity Sci. Technol. 0-g flight capabilities has been realized (Pletser et al. 2017a, b) using a Grob G-103 Twin II. The results showed that: • • • Weightlessness can be achieved continuously for up to 6 seconds per parabola; A 20 to 25-minute flight allows performing up to 21 parabolas; The estimated order of magnitude of the average parasitic acceleration in weightlessness ranges between 10−2 and 10−1 g. The goal of the present study is to refine these results and to provide a more complete and systematic quantification of gliders 0-g flight capabilities. We present the results of a flight test campaign of parabolic flights realized with an Alexander Schleicher ASK-21 (which has similar characteristics to the G-103). Data were collected using custom-made recorders and accelerometers which allow us to precisely identify the level of 0-g achieved during parabolas, and their duration. In this article, we first expose in Section Context and Motivations the context of research and tests in microgravity, and we elaborate on the potential benefits of the development of low-cost sailplane-based microgravity platforms. In Section Description of the Experiments and Collection Of Data, we introduce the flight test campaign that aimed to better quantify the capabilities of sailplane-operated parabolic flights. We describe the sensors that are used to collect data, and the additional systems involved. Section Systematic Quantification of Gliders 0-g Flight Capabilities is dedicated to an analysis of the flight test results, with a specific focus on the microgravity phase. A comparison between the vibration levels measured in a glider and in a light motorized airplane is also presented. Finally, in Section Discussions, we discuss some operational considerations specific to glider flights, and we put in perspective the associated advantages and limitations with existing solutions. Context and Motivations Applications of 0-g Environments on Earth The range of scientific fields that are related to reducedweight environments is extremely large. Their thorough enumeration would be quite tedious. We refer to the reviews by Seibert et al. (2001) and Pletser and Harrod (2014) and Pletser (2016b) for a mere overview. Additionally, we here also provide three major examples of experiments that illustrate how access to weightlessness is fundamental to modern science. Fluid dynamics are notoriously difficult to model in weightlessness, which is a major impediment to spacecraft control efficiency. Indeed, sloshing in tanks of liquid propellants rockets or satellites leads to disturbing torques that are hardly predictable and controllable. The FLUIDICS (Fluid Dynamics in Space) experiment, run on board the International Space Station (ISS), is an attempt to better understand liquid sloshing and wave turbulence phenomena (Dalmon et al. 2019). The equivalence principle can be measured by comparing the accelerations of two atoms having diff (...truncated)