0G TESTING OF ALTERNATIVE BOOM ROOT INTERFACE CONCEPTS FOR ROLLABLE COMPOSITE BOOMS

In July 2021, DLR conducted a test campaign in artificial weightlessness to verify some of its concepts. During this dedicated flight day, the entire 20 m x 5 m test area of the special Airbus A310 was available for 5 experiments in the field of deployable high strain composite space structures. The results presented here originate from experiment No. 4 in which two different deployment mechanisms for DLR's deployable CFRP masts were tested. Both types of mechanisms use new interface concepts to attach the booms to the satellite structure with high stiffness during and after deployment. Both concepts were extensively evaluated in artificial weightlessness with respect to their safe deployment and stowage as well as their resulting interface stiffness. The test setup in the aircraft, the test plan and the test procedure are described hereunder. The results are discussed and recommendations are given for the further development of the boom and mechanisms as well as the testing of such structures in artificial weightlessness

CTM Boom Deployment Mechanism with Integrated Boom Root Deployment for Increased Stiffness of the Boom-to-Spacecraft Interface

CTMs (Collapsible Tube Masts) are well known for small and medium sized solar sails as they can create huge and stiff sail backbone structures out of a very small mass. But one key issue with those masts is the need for a full deployment of the booms cross section in order to generate the full stiffness. Close to the deployment mechanism the stiffness is significantly decreased. Usual mechanisms try to counteract this drawback by guiding rollers or surfaces that support the boom in this weak transition zone. The underlying paper will present a different approach: The boom spool of the novel deployment mechanism contains a simple but reliable mechanism that is triggered at the end of the longitudinal deployment. This inner mechanism deploys the booms cross section and locks the boom spool into the outer walls of the surrounding structure. The result is a boom deployment mechanism that supports the utilization of the full potential of the CTMs

Advanced Interface Concepts for Rollable Composite Space Booms under Test in Artificial Weightlessness

In July 2021, DLR conducted a test campaign in artificial weightlessness. During a dedicated flight day, the entire 20 m x 5 m test area of the special Airbus A310 was available for 5 experiments in the field of deployable high strain composite space structures. The results presented here originate from experiment No4 in which two different deployment mechanisms for DLR's deployable CFRP masts were tested. Both types of mechanisms use new interface concepts to attach the booms to the satellite structure with high stiffness during and after deployment. Both concepts were extensively evaluated in artificial weightlessness with respect to their safe deployment and stowage as well as their resulting interface stiffness. For this purpose, the test setup in the aircraft, the test plan and the test procedure are described. Finally, the results are discussed and recommendations are given for the further development of the boom and mechanisms as well as the testing of such structures in artificial weightlessness

Parabelflug mit aufrollbaren Raumfahrtstrukturen

Beim Transport von Satelliten ins All ist der begrenzte Platz an Bord der Rakete die größte Hürde. Durch dieses Nadelöhr muss alles hindurch, was in den Weltraum fliegen soll. Einige Komponenten, wie Solargeneratoren oder Antennen, müssen im All jedoch große Flächen aufspannen, um ihre Funktion zu erfüllen. Daher sind faltbare und aufrollbare Strukturen ein sehr wichtiger Entwicklungszweig in der Raumfahrt. Sollen diese Strukturen besonders leicht und kompakt sein, ergeben sich zwangsläufig Konzepte, die nur in der Schwerelosigkeit des Alls funktionieren. Entfalten sich diese Strukturen auf der Erde, brechen sie unter ihrem eigenen Gewicht zusammen. Zur Überwindung des daraus resultierenden Defizits an realistischen Tests und somit zur Erbringung des Funktionsnachweises führte das DLR – teils in Kooperation mit der NASA – im Juli 2021 fünf erfolgreiche Versuche zur Entfaltung großer Strukturen an Bord eines Spezialflugzeugs unter künstlicher Schwerelosigkeit durch

ZERO-G EXPERIMENTS OF THE BIONICWINGSAT - A 2U-CUBESAT WITH DEPLOYABLE, BIOLOGICALLY-INSPIRED WINGS

In this paper, recent testing of a novel deployable structure with several potential applications in space will be described, with the focus on performed deployment experiments in a DLR Zero-g flight campaign and in ground tests. Through a cooperative effort of the German Aerospace Center (DLR) and the National Aeronautics and Space Administration (NASA), a biologically-inspired structurally-integrated membrane featuring distributed functional elements has been developed and integrated into the 2U CubeSat called BionicWingSat. Such a membrane structure could be useful for all sorts of applications in which a relatively flat area is desirable such as solar sails, drag sails, or solar shades. For SmallSats and CubeSats, the design proposed also has the desirable property of being self-deploying without the need for powered deployment mechanisms. Building on previous work inspired by the wings of earwigs, the research presented in this paper focuses on testing of developed design concepts for such structural systems. To do so 24 fully integrated wings on two BionicWingSats in 2U Cubesat format were experimentally deployed in a microgravity environment during a dedicated DLR Zero-g flight campaign in 2021. The results of these experiments, the built hardware and test articles, the test arrangement, as well as a comparison to ground tests are discussed in this paper

Design and Testing of the BionicWingSat in a Zero-g Flight Campaign - A 2U-CubeSat with Deployable, BiologicallyInspired Wings

In this paper, recent developments in the design, manufacturing, and testing of a novel deployable structure with several potential applications in space will be described. Through a cooperative effort of the German Aerospace Center (DLR) and the National Aeronautics and Space Administration (NASA), a biologically inspired structurally integrated membrane featuring distributed functional elements has been developed and tested in a 2U CubeSat called BionicWingSat. Such a membrane structure could be useful for several applications in which a relatively flat area is desirable such as solar sails, drag sails, or solar shades. For SmallSats and CubeSats, the design proposed also has the desirable property of being self-deploying without the need for powered deployment mechanisms. Building on previous work inspired by the wings of earwigs, the research presented in this paper includes structural design of self-deploying hinges, a survey of various advanced additive layer manufacturing (ALM) methods for making hinges, mechanical characterization of the hinges, and finite element analysis (FEA) of the hinges. In this work, the conflicting goals of maximizing deployed structural stiffness, maximizing deployed area, maximizing stowed packaging efficiency, and maximizing resistance to creep when stowed must be considered. The resulting design concept is a gossamer structure that cannot support its own weight in gravity. For this reason, a focus in this paper is on a parabolic flight test campaign in which 24 fully integrated wings on two BionicWingSats were tested in a microgravity environment. From this test campaign, several lessons were learned regarding the wing design and procedures for carrying out microgravity tests of this manner

Experimental methods using force application of a single boom for a 500-m²-class solar sail

Solar sailing missions rely on deployable systems for large area-to-mass ratios once in space, while still being small enough for launcher envelopes in the stowed configuration. Many of these deployable systems feature booms that are flattened and subsequently coiled onto a spool / hub. As part of a collaborative deployable space structures research effort between the National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR), a boom deployment system for a future 500 m² solar sail has been developed. To achieve the respective solar sail size goal, 16.5-m-long booms produced by NASA were integrated into a DLR-designed deployer mechanism. This considerable size, as well as the lightweight construction of the booms and respective deployable systems makes testing on the ground a significant challenge. Some systems for gravity compensation as well as vertical testing to minimize the influence of gravity have been used in the past. However, an uncertainty factor remains towards the behaviour in the space environment. The focus of this paper is the load application testing of the integrated boomdeployment mechanism system under microgravity condition, as well as a comparison to vertical testing under gravity. Testing in microgravity was performed during a parabolic flight test inside an aircraft and it included stowage and full deployment of a single boom along the longitudinal axis of the aircraft. The load application was split into two categories: static testing, which induced a linear force ramp to the static boom for either compression or compression-bending; and dynamic testing, which applied a constant force to a boom during extension provided by the deployer mechanism. Both types of tests were performed multiple times at two distinct lengths of the boom, fully deployed (12.76 m) and ~28.6 % deployed (3.65 m). More parameters that are vital to the test philosophy are the angles of attack in the force application and the highest force applied. The data acquisition used for the applied load and deflection measurements of the boom is also presented

Design and Sizing Method for Deployable Space Antennas

The dimensions of space borne instrument-, antenna- and solar array structures do often exceed the available envelope of common launch vehicles. To realize such systems anyhow the structures are provided with folding mechanisms that allow a space saving orbit transfer. A side effect from this deployment concept is the fact that a structure which provides a sufficient deployed stiffness for space environment can also fulfil the stiffness requirements for launcher payload in stowed configuration. Consequently, the sizing of such structures demands the consideration of different configurations that are composed out of the same essential structural parts. The thesis, thereby, illustrates how the roles of the single components change for the different configurations. For instance, a component that carries a major part of the load in a first configuration can be nearly offloaded in a second one. Moreover, this component can load another part with its own mass, whereas, this other component is passive in the first configuration and needs to be carried. Thus, the core of this thesis contains the introduction into an exemplary antenna structure design as well as a method for an adequate sizing of all relevant structural parts. The developed method is then integrated in a Finite Element Analysis (FEA) aided, closed loop sizing chain. The used automated close loop sizing helps to rapidly react on changed requirements and generates the possibility of performing fast parameter studies to improve the understanding of such a sophisticated structure. The validity of these approaches is finally proven by presenting a re-sized antenna configuration after the parameter study and its evaluation. This final configuration more than meets the previously defined requirements for the exemplary antenna structure

Trade-Off on Large Deployable Membrane Antennas

As the current discussions on climate changes suggest, the need for understanding the occurrences on our planet is given. To monitor indicators of global change like glaciers, polar caps, ocean currents or vegetation distribution, space-borne low frequency SAR (Synthetic Aperture Radar) satellites are feasible tools to realize such monitoring. For low frequency antennas, apertures of high area are necessary to guaranty a sufficient antenna gain. Using traditional mani-fold structures, the over all weight and packed size of such antenna becomes very high and, therefore, the orbit transfer will increase the mission costs markedly. To provide a very light antenna that needs a minimum of cargo volume in packed configuration, the DLR in coopera-tion with ESA is elaborating a study on VERY LARGE STABLE MEMBRANE ANTENNA ARCHITECTURES. Beside these simple physical requirements, objectives regarding out of plane accuracy and dynamic performance shall be design driving items. The following pages draw first considerations on possible mission scenarios, present the so far developed designs and show results of membrane wrinkling analysis and tests