Self-deployable large space structure (December 27, 2016)
Huge space strcuture such as space solar power system (SSPS) has been proposed since more than 30 years ago, and the research has been still in progress.
For example, Mankins showed the design of SSPS that he calls "SPS-ALPHA" in his report. The right figure is the illustration of SPS-ALPHA. The size of the structure is not explicitly shown in the report, but it is supposed to be several km order. He proposed the operation of total system including the attitude control, and the construction method of this huge structure using space robots. The report gives various suggestions to realize SPS-ALPHA. In Japan, JAXA and J-Space Systems have proposed a SSPS different to each other. China has proposed a SSPS, too.
But unfortunately, even a small scale model of SSPS has not been launched yet. Currently, it seems that there is no space project on SSPS that includes the launch of spacecraft. The research on such a structure remains the numerical study and the grounnd experiment so far.
Recently, concept of statshade (external occulter) has been proposed for observation of planets nearby stars . In this concept, a large planar structure (starshade) such as thin membrane is placed between the star and the space-telescope so that the light from the star does not enter the telescope and high-contrast image can be obtained by the telescope. The appropriate shape of the starshade has been studied and the shape like a flower petal is proposed in the literature . In the proposal, the structure consists of a thin large membrane with a rigid frame at the external edge, and the diameter of the starshade is 50m. The folding/deployment method has been also proposed, but we think that the proposed method is a little complicated and that it is not easy to guarantee the relyable deployment of the folded structure.
These structures must be extremely light-weight, which can be satisfied by gossamer structure such as membranes , cables, and thin flexible beams.
Considering such background, we have been studying on the realization of these structures in space that is not only a paper work but more strategic research and development.
The key technologies to realize such structures in space are as follows:
As for point#1, we employ reliable deployment method. Generally, the deployment from the folded structure enforces the structural members compressive stress, which sometimes induces the structural instability or stick of the deployment. It is important to estimate the effect of external forces and the interaction between the structural members disturbing the deployment, and design the structure with sufficiently small disturbance .
- Folding, latching, unlatching, and deployment of ultra-light structure with large apparture planar/curved surface
- To ensure enough stiffness to achieve the mission
- To ensure enough shape accuracy to achieve the mission
- Assembling of structure elements (modules) to integrate huge structure
Ad for point#2, SSPS or starshade do not require high stiffness compared with high-frequency antenna or telescope, but still require a certain stiffness, which is larger than spinning solar sail such as IKAROS. We must determine the requirement of the stiffness and weight to achieve the mission, which includes the design of the whole spacecraft, or we must provide the typical design value of the proposed structure.
As for point#3, the solar reflector of SSPS and the starshde do not requre highly accurate surface compared with high-frequency antenna or telescope, but they must have appropriate shape accuracy, which is higher than solar sail.
As for point#4, we must consider the senario of the deployment of modules from the rocket, the deployment of each module on orbit, randez-vous, and the docking of modules. We may need autonomoous docking system or distributed (swarm) robot system at the docking phase.
Our laboratory is studying on self-deployable truss using bi-convex booms that consists of two tape springs contacting with each other at the edges. We expect the self-deployable truss is suitable for a structure element for large space structure, and are researching on the structure totally, i.e. the research includes the theory, numerical analysis, experiment, and space verification of the small devices, small scale structural models, and the application models as in the right figure.
For example, we are proceeding the research, development, and verification (RD&V) as follows in order to investigate the feasibility of the self-deployable truss using bi-convex booms:
- Estimation of bending and torsional properties of a bi-convex boom considering the contact problem of two tape springs [5, 9]
- Theoretical prediction of self-extending force and the undetachment condition of the boom wrapped around a hub during the deployment 
- Dynamic characteristics 
- Design of self-deployable truss, i.e., nodes and the booms considering the thickness of the boom
- Theory of folding of a membrane considering its thickness 
- Evaluation of the deployment and storage characteristics of the truss [6,7,8]
We conducted the deployment test to verify the design method by ensuring the success of the storage and the deployment. As in the following movies, our method is available for the design of such self-deployable truss.
||triangular truss in vacuum chamber
We conducted the deployment test under micro-gravity environment, too.
|7N12B truss with membrane||
Now, our concern is about the folding method of the membrane, and hold-release mechanism of the truss for the launch. The figure below illustrates the folding pattern of a membrane that takes into account the effect of the thickness of the membrane, the example of the mounting method of the truss to a micro-satellite, and a curved surface consisting of self-deployable 3D truss.
||micro-satellite with self-deployable truss
||Self-deployable curved surface
We will publish the papers about these topics in 2017 and 2018.
This research is a part of the research "Establishment of prediction method of dynamics of large gossamer multi-body space structures and understanding of their dynamics
" supporetd by JSPS KAKENHI.
John C. Mankins, SPS-ALPHA: The First Practical Soloar Power Satellite via Arbitrarily Large Phased Array, Final report of A 2011-2012 NASA NIAC Phase 1 Project, September 15, 2012.
Webstar Cash, et.al., Starshade Technology Development, 2010.|
Jeremy Kasdin, The flower-shaped starshade that might help us detect Earth-like planets", March 2014.|
Shoko Arita, Yasuyuki Miyazaki, A study of dynamic evaluation of structural buckling, Mechanical Engineering Journal, Vol.2, Paper No.15-00677, pp.1-8, March 31, 2016, DOI: 10.1299/mel.15-00677.
Yasuyuki Miyazaki, Shota Inoue, Akihiro Tamura, Analytical solution of the bending of a bi-convex boom , Mechanical Engineering Journal, Vol.2, No.6, Paper No.15-00465, December 15, 2015, DOI: 10.1299/mej.15-00465.
Shota Inoue, Akihiro Tamura, Daishi Kawarabayashi, Dan Hyodo, Yasuyuki Miyazaki, Report on Microgravity Experiments of Self-Deployable Truss Structure Consisting of BCON Booms, Digital Proceedings of the 8th Asian Conference on Multibody Dynamics, paper-1290215, pp.1-10, August 7-10, 2016, Kanazawa Miyako Hotel, Kanazawa, Japan.
Daishi Kawarabayashi, Yasuyuki Miyazaki, Concept of Three-Dimensional Self-Deployable Truss and Characteristics of Its Deployment in Micro-Gravity
Environment, The 60th JSASS Space Science and Technology Conference, HSASS-2017-4286, pp.1-6, September 6-9, 2016, Hakodate Arena, Hakodate City, Hokkaido.
Noboru Tada, Shota Inoue, Yasuyuki Miyazaki, Membrane Deployment Deorbit System by Convex Tapes, Deorbit Device Competition, October 17-23, 2016, Hotel Longoz, Varna, Bulgaria.
Yasuyuki Miyazaki, Mechanics of wrapping of convex tape around cylinder, The 32nd Space Structure and Materials Symposium, December 9, 2016, JAXA/ISAS, Sagamihara City, Kanagawa (to be appeared).
Momoko Fukunaga, Yasuyuki Miyazaki, Detachment Condition of a Tape-Spring Wrapped Around a Hub, The 25th Space Engineering Conference, December 21-22, 2016, Hotel Kamefuku, Yamaguchi City, Yamaguchi (to be appeared)．
M.C. Natori, Naoko Kishimoto, Ken Higuchi, and Hiroshi Yamakawa, Basic Geometrical Consideration on Deployable and Adaptive Structures for Efficient Spacecraft Systems, ISTS2008-c-05.