Akio Tsujihata

Technology status of the 13 m aperture deployment antenna reflectors for Engineering Test Satellite VIII

Abstract Large deployable antenna reflectors for Engineering Test Satellite VIII (ETS-VIII) are now stated in the critical design phase. The Fourteen 4.8m modules, which construct a 19.2 m × 16.7 m (13m aperture) antenna reflector, have been fabricated as Engineering Models. Ground testing for the fourteen modules will be performed until next spring. This paper describes results of critical design for the antenna reflectors and their validation plans. Each module consists of a gold-plated molybdenum mesh surface, spacially determined cable network, and a deployable truss structure as a supporting structure. Stowed size is 1 m (diameter) × 4 m (height). In stowed configuration, the lowest eigen frequencies of the antenna reflector are 47 Hz (longitudinal) and 69 Hz (lateral) respectively. The lowest eigen frequency is 0.14 Hz. Solar ray transparency of the reflector structure is designed to be more than 85% to avoid excessive solar pressure torque. Weight of each reflector is expected to be less than 100 kg. In addition, we will perform a piggyback deployment experiment in transfer orbit using the second stage of the first flight H-II A vehicle in 2000. Half scale seven modules antenna reflector will be used to validate its deployment reliability. Design, analysis and test results of LDR-P are also introduced in this paper.

Study on Ground Verification for Large Deployable Modular Structures

A quantitative assessment is provided of the difficulty of ground deployment tests and evaluates the validity of modularized deployment testing for large space structures. An index that well shows the difficulty of ground deployment tests is the ratio of gravity force to deployment force. The relationship between this index and the accuracy of deployment tests is calculated using an analysis model of the large deployable antenna reflectors onboard Engineering Test Satellite VIII (ETS-VIII). The index showed that a deployment structure whose diameter is more than 10 m has insufficient evaluation accuracy; thus the structure should be divided into modules. The index also showed that the single module of the large deployable antenna onboard ETS-VIII is of the appropriate size to evaluate deployment reliability. The influence of module connection on the deployment motion is also examined. The cross correlation between the changes in strain energy profile during deployment in a single module and those in combined modules is calculated to show how many modules should be connected and tested. The resistance force that arose due to the module connection is also calculated using the beam strain energy. It is clarified that ground deployment testing for four combined modules should be conducted in addition to the ground deployment testing for a single module when the deployment force margin is not large enough.

LARGE DEPLORABLE REFLECTOR ON ETS-VIII

Engineering Test Satellite-VIII (ETS-VIII) is a three-axis-stabilized geostationary satellite intended to develop the advanced technologies for a large-scale spacecraft bus. Some of the objectives are development, test, and verification of Large Deployable Reflector (LDR). A large- scale reflector is one of key technologies for geostationary satellite communication using handheld size terminals. The reflector functions and performances will be confirmed by S-band frequency mobile communication experiments using the reflectors and active phased array feeds. The most distinctive feature of the reflector is an adoption of the module structure. The reflector is an assembly of 14 independent hexagonal modules. For this concept, technologies to estimate multi- module performance from single-module performance are important. The estimating technologies are deployment analysis, structural analysis, thermal analysis, and so on. Some of these analyses were conducted and the results confirmed adequacy of the design.

ANALYSIS AND TEST METHODS FOR LARGE DEPLOYABLE SPACE STRUCTURES

This paper describes deployment analysis, test methods and results for a large aperture modular mesh deployable antenna reflector. The reflector will be installed on the Engineering Test Satellite VIII, which will be launched in 2003. Two kinds of development models are considered in this paper. One is a full-scale, fourteen modules engineering model, the other is a half-scale, seven modules flight model for in-orbit experiments by ARIANE 5. Some important items to be considered for the design and evaluation of large deployable reflectors are described. Typical results gained with our analysis tool SPADE for large deployable space structures are discussed. They include redundant constraints, ground testing contingency mode, and mesh behavior. Essential items in the design and evaluation of LDR for ETS-VIII were considered. Resultant deployment characteristics obtained by deployment analysis are correlated to the results of ground deployment testing. Micro-gravity experiments in a jet-airplane were performed to eliminate the ambiguity discovered in a deployment analysis. We proposed a modularized test method for large deployable space structures. Limitation of the analysis are clarified.

Tri-Fold Deployable Reflector for Communication Satellites

JAXA, Japan Aerospace Exploration Agency, is now developing tri-fold deployable reflectors. The reflector can be made to be up to 28m in diameter. The weight density is less than half its predecessor, the large deployable reflector mounted on the Engineering Test Satellite VIII. This concept can be applied to realize an over 50m reflector by constructing modular reflector in which the tri-fold reflector is one of the segmented modules. The trifold reflector is made from the tri-fold deployable truss and the reflector surface. The trifold deployable truss is composed of three four-sided links with joints and can be stowed as a collapsible umbrella. As a stand-alone, the reflector can take on an octagonal shape. For the modular reflector, the segmented module is hexagonal. The feasibility and design of tri-fold deployable reflectors have been confirmed and improved through structural analyses. The analyses are performed with JAXA’s FEM analyzer “Origami/ETS.” The prototype of trifold reflector has been developed and is now undergoing testing. From the result of tri-fold truss deployment test it is confirmed that JAXA’s FEM Analyzer can estimate the mechanical behavior of hardware within 10% error. Afterwards the reflector will be tested and evaluated in the deployment, hold and release, vibration, and surface accuracy measurement tests.

A Study on the Accuracy of Deployment Testing for Large Deployable Structures

This paper examines the difficulty of ground deployment tests quantitatively. An index that well shows the difficulty of ground deployment test is the ratio of gravity torque to deployment torque. The relationship between this index and the accuracy of deployment test is developed. We perform deployment tests using a simple planar truss under micro gravity and gravity environments. Ground tests in which the index value of the truss is incremented several times are also performed. Comparing these test results, we find that the estimation error of the deployment force is 10%, even for the simplest structure whose difficult index value = 1. We introduce an empirical equation that sets a linear relationship between the difficulty index value and the evaluation accuracy. We can conclude that that it is infeasible to test the ground deployment of structures whose difficulty index value exceeds 1000. The difficulty index of the modularized large deployable reflectors for ETS-VIII is calculated. We find that the single module of the LDR was designed to be appropriate size to evaluate the deployment reliability, however, evaluation accuracy would be insufficient if ground deployment testing is performed only on more than seven combined modules.