Space verification of combined membrane structure (May 10, 2015)
The combined membrane strucrure is a structural concept that Prof. Natori in ISAS Japan proposed. The main idea of this concept is to construct a structure by combining many membrane structures. For example, the planar structure is made of membrane, and the support structure is made of inflatable tubes, and a structure is constructed by connecting both structures.
Membrane structure has excellent property of light-weight, deployment, and packaging, so that it is suitable for space structure. However, it needs compression member to support the tension of the membrane because the membrane can bear only tension and cannot bear compression. If it does not have compression member, some system is necessary to apply the tension to the membrane, e.g. the membrane itself is spinned so that the membrane is tensiled by the centrifugal force. In this case, the membrane should spin all the time, and the design of the configuration of the structure is limited.
In order to resolve this problem, it was proposed to emply inflatable tubes made of membrane as the compression member. In this case, the gas supply system is necessary so that the weight and volume of the system may increase. That's true, but the required gas is small because the gas have to be supplied only to assist the extension of the tube against the spring-back effect of the crease of the membrane and tubes. Therefore, the gas supply system will be small even though the system will be large. In addition, the time for the deployment will be short if we use inflatable structure (it is possible to deploy large structure quickly only by supplying the gas).
Thus the combined membrane structure will have more and more advantage ober other structure if the structure is larger and larger.
The nano-satellite SPROUT (right figure) that our laboratory launched in May 2014 will investigate the behavior of this combined membrane structure when it is deployed in space, which is the main mission of SPROUT. SPROUT has cubical shape with about 20cm in each side, and will deploy a triangular membrane with 1.5m in its side. Membrane is stored under Miura-folding, and will deploy when the nytrogen gas will be injected to two thin alminum laminate tube.
The shape of the membrane during the deplyoment and after the deployment will be digitized by the stereo vision of two cameras. We will evaluate how this combined membrane structure deploy in space and maintain its shape quantitatively using the shape data and the measured data of the attitude by gyros, the strain by the piezo-films on the tube, the pressure in the tube by pressure sensors.
You can see the detail of SPROUT in the web page of SPROUT!
We originally planed the deployment of the combined membrane structure of SPROUT between January and March in 2015. However, we changed the plan after we investigated the status of the satellite on orbit (the status of batteries, the temperature of the satellite, and so on). We thought we have to reset the parameter in the deployment mission based on the result of the deployment test of the experimental model on the ground in the similar condition as the orbit. Therefore, the deployment mission is delayed now.
May 24, 2015 is the first anniversary of the launch of SPROUT. So we hope we can conduct the deployment mission before that day. Please stay tuned!
P.S. (November 22, 2015)
THe deployment mission of SPROUT was conducted at 11 pm in June 23, 2015. We confirmed that all of the deployment mechanisms such as the release of the door of the storage, the supply of the gas using SMA actuator, and so on. However, the tubes did not extend straight but curved, so that the membrane did not deploy sufficiently. The right photos were taken on orbit and the membrane is captured. We have several possible reason of the failure of the deployment, and will determine the reason after the micro gravity experiment using airplane planned in January 2016. You can see the summary of the deployment mission in the "first report" posted at October 13, 2015 on the web page of SPROUT.
P.S.2 (March 31, 2017)
The deployment mission of the combined membrane structure of SPROUT was not successful, but we detected the reason of the failure and summarized the tips for the deployment of the combined membrane structure in the web page "Space Demonstration of Combined Membrane Structure".