1 Introduction

Large Deployable Reflectors (LDRs) willbe installed on the Engineering Test SatelliteVIII (ETS-VIII) scheduled to be launched in2004. To allow for mobile satellite communi-cations via small handheld terminals, the LDRmust be larger than any such reflector in exis-tence today (with a surface of approximately19 m×17 m), and to offer sufficiently highsurface accuracy of the reflector (2.4 mmRMS) to support S-band communications (2.5/ 2.6 GHz). To permit the construction of suchan LDR, we are currently working to establishthe following technologies:

(1) Engineering design of cable-mesh deploy-able antenna structure

The reflecting surface structure, consistingof metal mesh and cables, is supported by adeployable truss structure; this configurationprovides efficient folding operations and ahighly accurate reflection surface.

(2) Engineering design and verification testingof a modular deployable structure

The large-scale structure is to be con-structed using elements (modules) featuring adegree of dimensional accuracy that will allowprecise manufacture, adjustment, and verifica-tion testing. Linking multiple modules willprovide greater accuracy, reliability, andexpandability than available under conven-tional designs involving the manufacture andtesting of a large-scale integral structure.

(3) Coupled analysis of cable-mesh and trussstructures, and motion analysis of the flex-ible structure

The structural characteristics of the flexi-ble nonlinear deployable structure are precise-ly analyzed, ensuring high surface accuracyand reliable deployment.

This paper describes the design, develop-ment, and verification of the LDR.

2 Outline of LDR

2.1 Structure of LDRTwo LDRs are to be deployed on the ETS-

VIII. One LDR will serve as a transmissionreflector and the other will function as a

SHINTATE Kyoji et al. 33

3-3 Large Deployable Reflector (LDR)

SHINTATE Kyoji, TERADA Koji, USUI Motofumi, TSUJIHATA Akio, and

MIYASAKA Akihiro

Large Deployable Reflectors (LDRs) are carried on Engineering Test Satellite VIII (ETS-VIII), which is scheduled to be launched in 2004 (JFY) and demonstrates mobile communica-tions via geostationary satellite using cellular-phone-sized terminals. LDR is required tohave a tennis-court-sized reflector and high accuracy of its surface. To meet the require-ments, LDR is designed based on a modular-mesh concept in which the structure consistsof several basic modules. This paper describes concept of design and verification tests ofLDR.

Keywords Large Deployable Reflector, LDR, Engineering Test Satellite VIII, Deployable antenna

34

reception reflector. When both LDRs are fullydeployed, the reflector area of the LDR will beas broad as a tennis court (Fig.1). Whereasconventional large reflectors are designed,manufactured, and tested as integral struc-tures, the LDR features a modular design inwhich structural elements (modules) of highdimensional accuracy are combined to allowfor highly precise manufacture, adjustment,and verification ground testing. Fig.2 shows asingle module.

Each module features a reflector surfacemade of radio-reflective metal mesh (gold-plated molybdenum) and a cable network, allsupported by a truss structure. A parabolicsurface is formed by adjusting the lengths ofthe rod members (standoff) forming the trussstructure of each module and by extending therods from the vertexes of the hexagon formedperpendicular to the reflector surface. In orderto guarantee an orbital service life of 10 yearsfor the materials constituting these modules(e.g., cables, mesh, CFRP), various types ofservice tests (involving ultraviolet rays, radia-tion, etc.) were conducted, and the design wasmodified to reflect the results of these experi-ments.

2.2 LDR deployment The deployment mechanism is shown in

Fig.3. The principle behind the deployment ofthe LDR is the same as that of an automaticumbrella; a spring is attached to the center ofthe module. Additional springs are mountedon the structure to provide sufficient force forinitial deployment.

In order to ensure a controlled deploymentspeed for each module and to synchronizedeployment of the modules, the length ofwires extending from the deployment mecha-nism are controlled. These wires are gradual-ly extended by means of stepping motors, witha total of four such motors controlling thedeployment of the 14 modules of the LDR.Fig.4 shows the arrangement of the motors.

Fig.5 shows the configuration of the LDRat the time of launch. The LDR is designed towithstand the load at launch. When the LDRis within the stowing the reflector is held in

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Schematic diagram of deployed LDRFig.1

Single LDR moduleFig.2

LDR deployment mechanismFig.3

Arrangement of deployment motorsFig.4

place by two mechanical arms equipped withhold-on/release mechanisms (HRMs).

3 Outline of development of LDR

3.1 LDR development schedulePreliminary design of the LDR began in

1997. A basic design was completed in 1998,followed by critical design from 1999 to 2001and design follow-up currently underway in2003. Test breadboard model (BBM) includ-ing seven modules modified to reflect theresults of preliminary design was manufac-tured and was put through various tests, whichconfirmed the feasibility of the basic technolo-gies involved.

Next, engineering model (EM) including14 modules was manufactured to reflect theresults of basic design and BBM testing, pro-viding subsequent confirmation of the overallfeasibility of the flight model. At the sametime, the deployment performance and relia-bility of the LDR were evaluated through cou-pled analysis of the cable-mesh and trussstructures using, among other means, theanalysis program “SPADE” (NTT NetworkInnovation Laboratories) for flexible struc-tures. Based on the results of these develop-ment tests, fully functional machines of a pro-totype flight model (or “PFM,” designed forreception) and a flight model (“FM,” for trans-mission) were manufactured and subject totesting (separately, each as a single LDR) inSeptember 2003. Testing of the flight modelintegrated with the satellite main body willbegin in early 2004.

3.2 Features of LDR development test-ing, in-orbit experimentation, andreflection

In conventional deployable structures(involving solar paddles, for example) accu-rate orbital deployment was ensured throughground deployment tests in which specimenswere suspended in order to counteract theeffects of gravity. However, deployment ofthe LDR is more complex than the single-stepdeployment of conventional structures. Thebehavior of the LDR is thus more difficult topredict using such suspension techniques.Consequently, we decided to add the follow-ing tests, based on the conclusion that groundexperimentation alone was insufficient toguarantee successful orbital deployment.

(1) Micro-gravity test using aircraft (usingBBM)

(2) Orbital experiment using a small model viathe rocket-borne “piggy-back” method

(3) Deployment test in a vacuum chamber

Among the above-described tests, (2) pro-vided the most useful results. In this orbitalexperiment, a small partial model (LDREX) ofthe large deployable reflector was chosen asthe test specimen, and was carried “piggy-back” on an Ariane 5 rocket. The LDREXwas half the size of the actual machine, with 7modules. Fig.6 shows the installation of theLDREX on the Ariane 5.

SHINTATE Kyoji et al. 35

Configuration of the LDR at the timeof launch

Fig.5

Diagram of LDREX orbital experimentFig.6

36

In an experiment conducted in December2000, an unexpectedly large amount of oscil-lation occurred in the initial stage of deploy-ment, immediately after the hold-on/releasemechanisms (HRMs) were disengaged. Thiscaused the reflector mesh to become caught inthe truss members, halting deploymenthalfway. However, since the LDR wasdeployed by about 10 degrees (0 degrees inthe stowed state and approximately 90 degreeswhen fully deployed), estimations of frictionalresistance and the like were able to be con-firmed, with successful comparison of experi-mental results in orbit with test data obtainedon the ground. On the other hand, to preventthe oscillation seen in the initial stage ofdeployment (and the resultant entanglement ofthe reflector mesh), the following design mod-ifications were incorporated into the LDR.

(1) Suppression of the oscillation of the reflec-tor upon disengagement of the HRM

- Modification of the disengagement sequencefor the HRM (previous method of simultane-ous release of the upper and lower elementsof the HRM is replaced by one in which thelower element is released after the upper ele-ment).

- Reduction of the speed of release (damper isattached to reduce shock when the HRM isdisengaged, coupled with regulation of themechanism’s deployment speed)

(2) Prevention of entanglement of reflectormesh

- Installation of a strip preventing extruding ofthe reflector mesh from the stowed position

- Installation of a standoff rod (preventing thereflector mesh from reaching the stand-offphysically even in cases in which the reflec-tor mesh does extrude)

Moreover, in order to ensure that the LDRcould provide reliable deployment, additionalsprings were incorporated into the design toincrease deployment force in the initial stage

of deployment. To verify the validity of these design

improvements, the following additional testswere conducted.

(1) Micro-gravity test with aircraft (usingEMs, for 7 modules and for 14 modules)

(2) Cup-up test (using EMs)(3) Deployment force check test (using EMs)

Fig.7 shows the configuration of themicro-gravity test using the EMs. This exper-iment was conducted in France in April 2002.Data was then recorded relating to the behav-ior of the reflector immediately followingrelease with renewed release sequence, inaddition to information on the behavior of thereflector in the initial stage of deployment.This experiment confirmed that even if accel-eration perturbation was greater than seen inorbit, the LDR reflector was sufficientlyrobust. Further, experimentation confirmedthat the redesigned reflector did not causeentanglement of the mesh or any similar prob-lem in a micro-gravity environment.

Fig.8 shows the configuration of the cup-up test. This test was conducted in the sum-mer of 2002. When the LDR is in the sus-pended state (cup-down), the reflector facesdownward. In this case, the oscillation of thereflector upon release of the HRM is sup-pressed by gravity; thus, this test is likely tounderestimate the effects of oscillation. To

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Configuration of micro-gravity test (14modules)

Fig.7

remedy this, we configured the experimentsuch that the reflector was made to faceupward (cup-up), and the boom was linked tothe reflector and tested, where the reflectorwould be linked to the main body of the satel-lite by the boom if the LDR is mounted on thesatellite structure. This experiment confirmedthat modification of the disengagementsequence of the HRM did not impair thestrength of the boom. Further, the perturba-tion exerted on the main body of the satelliteupon disengagement remained within inter-face spec.

These experiments have led to improvedaccuracy in analytical orbital models predict-ing the effects of deployment of the HRM onreflector motion. These tests also allow forrevision of the models of reflector behaviorbased on the results of micro-gravity experi-mentation. Fig.9 shows a comparisonbetween cup-up test results and analyticalresults.

The results of the micro-gravity and cup-up testing described above thus attest to thesufficiency of the countermeasures imple-mented to suppress the reflector oscillation

and mesh entanglement seen in the orbitalLDREX experiment.

On the other hand, in the deployment forcetest, a limit value was identified through theintentional addition of an anti-deploymentforce. Comparison of these test results withresults of analysis confirmed the validity ofthe analytical model, demonstrating thatattachment of an assisting spring will increasedeployment force in the initial stage of thedeployment by the required margin.

3.3 Test of standalone LDRBeginning in the latter half of fiscal 2002,

a proto-flight test (PFT) was conducted for thereception LDR, and an acceptance test (AT)was conducted for the transmission LDR. Themain test items are as follows.

(a) Boom deployment test(b) HRM deployment test(c) Reflector deployment test(d) Environmental tests (sinusoidal-wave

vibration test, acoustic test, and thermalvacuum test)

In order to confirm the stability of deploy-ment characteristics (i.e., to confirm satisfac-tory deployment in orbit) before and after theLDR is subject to environmental load, checkitems (a) to (c) were evaluated before andafter the environmental test. The boomdeployment test is outlined in Fig.10, thereflector deployment test is shown in Fig.11,and the vibration test is illustrated in Fig.12.

SHINTATE Kyoji et al. 37

Configuration of the cup-up testFig.8

Comparison between cup-up testresults and analytical results (acceler-ation at a given point on the installedmodule)

Fig.9

38

The PFT/AT results confirmed that the fin-ished design is of a quality satisfying therequirements for a standalone LDR. Accord-ingly, the LDR will soon be installed on themain body of the satellite for subsequent over-all prototype flight testing. Upon completionof these tests, the LDR is scheduled to beremoved from the satellite main body, as astandalone LDR to be subject to final testing

of items (a) to (c); we will then await launch.

4 Conclusions

This paper described the outline anddevelopment history of the LDR. Long yearsof development of the LDR has now broughtus to final testing of a completed flight modelincorporating numerous design improvements.Although the flight model is somewhat heav-ier due to these design improvements (reflect-ing the results of the orbital LDREX experi-ment), the overall design remains lightweight,satisfying the initial target value of 1 kg/m2,i.e., the reflector’s weight is now approximate-ly 143 kg (0.7 kg/m2).

The LDR has been developed with the aimof ensuring successful deployment in orbit,and we have conducted every feasible test toreduce the risks involved. Nevertheless, in thefuture development of similar large deploy-able structures, it is necessary to divide devel-opment items into two in order to increasedevelopment efficiency; (i) those requiringand permitting ground testing, and (ii) thosenot permitting ground testing and subject todesign assurance. Furthermore, it is a techni-cal challenge to establish innovative designand ground testing techniques. The test dataaccumulated in the course of development ofthe LDR to date, in addition to the orbital datafollowing launch, will prove to be valuableresources in resolving the technological chal-lenges of any such future development.

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Boom deployment testFig.10

Reflector deployment testInitial deployment (top)Full deployment (bottom)

Fig.11

Vibration testFig.12

SHINTATE Kyoji et al. 39

References1 A. Miyasaka, et al., "A Tennis-court-sized Reflector for Communication Satellites-Use for Engineering Test

Satellite VIII", JC-Sat 2002, 87-91.2002.

2 M. Homma, et al., "Experiment Plan of ETS-8 in Orbit: Mobile Communications and Navigation", IAC-02-

M.3.08, 2002.

SHINTATE Kyoji, Ph. D.

Japan Aerospace Exploration Agency

TERADA Koji

Japan Aerospace Exploration Agency

USUI Motofumi

Japan Aerospace Exploration Agency

MIYASAKA Akihiro, Dr. Eng.

NTT Network Innovation Laboratories

Study on Thermal Control and Distor-tion for Space Use

TSUJIHATA Akio

Japan Aerospace Exploration Agency

40 Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003