Aerospace Materials: Chapter 5. High Performance Polymers And Advanced Composites For Space Application

Chapter 5

High performance polymers and advanced

composites for space application

Rikio Yokota

Introduction

The AIAA reported on the state of space technology in SPACE 2000–2020.New and more advanced polymer composites having lighter, stronger, moredimensionally stable, and stiffer properties were predicted as being needed todevelop space platforms to exploit the solar system [1]. Although internationalspace station programmes have been delayed due to worldwide economicproblems, there have been many technically notable successes, such as onboard satellite repair technology, planetary exploration using space vehiclessuch as the US Mars pathfinder, deployment of large space structures, andthe development of application satellites. During this period, graphite/epoxycarbon fibre reinforced polymer composite (CFRP), which is an advancedpolymer composite, has been developed actively and used in spacecraftprimary structures. It is still almost the only suitable material for these primarystructures. High temperature matrix resins such as addition-type polyimidesand high temperature thermoplastic resins are under development (seechapters 13 and 15), but are not yet familiar in space [2].

Aromatic polyimides are well known to have excellent thermal, mechan-ical, and electrical stability based on their hetero-aromatic structures, andvarious high performance polyimide films have been developed and nomi-nated as suitable materials for the membranes of flexible large structures,such as extendable solar arrays [3]. This chapter discusses the technologicaldevelopment of high performance polymers and advanced polymericcomposites for space applications in Japan, covering the following topics:

1. advanced composites for spacecraft primary structures;2. advanced composites for the newly developed three-stage M-V rocket;

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3. high performance polymeric materials and composites for flexible and/orrigid extendable structures; and

4. heat resistant matrix resins.

Advanced composites for spacecraft primary structures

In Japan, space activities that are conducted in various government minis-tries and agencies are coordinated by the Space Activities Commission.The Institute of Space and Astronautical Science (ISAS) is the centralinstitute for scientific research in space, and the National Space DevelopmentAgency (NASDA) is in charge of the development of application satellitesand their launchers. ISAS was founded in 1981 by reorganization of theInstitute of Space and Astronautical Science, University of Tokyo. Thepresent ISAS is a national research institute conducting inter-universityresearch in cooperation with researchers from universities in Japan andother countries.

Table 5.1. Summary of ISAS scientific satellites

Date Name Weight (kg) Application

1970.2 OHSUMI 24 test satellite

1971.9 SHINSEI 66 cosmic ray et al

1972.8 DENPA 75 plasma et al

1974.2 TANSEI-2 56 test satellite

1975.2 TAIYO 86 solar x-rays et al


1978.2 KYOKKO 126 auroral image et al

1978.9 JIKIKEN 90 plasma et al

1979.2 HAKUCHO 96 x-ray stars et al


1981.2 HINOTORI 188 solar flares et al

1982.2 TENMA 216 x-ray galaxies et al

1984.2 OHZORA 216 upper atmosphere

1985.1 SAKIGAKE 138 test spacecraft

1985.8 SUISEI 140 Halley’s comet

1987.2 GINGA 420 x-ray sources et al

1989.2 AKEBONO 295 auroral and plasma

1990.1 HITEN 140 lunar swingby

1991.8 YOHKOH 420 solar flares

1992.7 GEOTAIL 1008 ISAS and NASA

1993.2 ASCA 420 x-ray sources et al

1995.3 S.F.U. 4000 space experiments

1997.2 HALCA 830 space VLBI antenna

1998.7 NOZOMI 540 Mars exploration


ISAS succeeded in launching the first Japanese satellite OHSUMI intoorbit in 1970. Since then, 24 scientific and test satellites have been launched,including SUISEI and SAKIGAKE to explore Halley’s comet in 1986.To improve performance and increase payload capability, launchers andsatellites require the development of primary and secondary structures thatare much lighter than those produced from conventional metals. Since themain structural configuration of SUISEI was made of carbon fibre reinforcedepoxy, ISAS used advanced composites for the primary structures of all thesatellites.

Table 5.l shows the list of all the satellites and spacecraft launched byISAS. ASCA, launched in 1993, is a structurally advanced spacecraft toinvestigate solar sources. Because the focal length of ASCA’s ray mirror isso long, a high-precision Extendable Optical Bench (EOB) construction,made from carbon fibre reinforced polymer, was developed for the primarystructure as shown in figure 5.l [4]. All the tubes of the EOB are made ofcarbon fibre composite, using high modulus type fibres. The tubes arelaminated so that the longitudinal thermal expansion coefficient of the

Figure 5.1. Extendable optical bench (EOB) structure of x-ray telescope satellite ASCA.


Figure 5.2. Outline of M-V rocket and M-34 filament wound carbon fibre reinforced polymer motor casing.


tubes can be made zero or even negative. The lamination configurationis designed such that the negative expansion of the tubes compensates thepositive expansion of the metal top plates.

Advanced composites for the M-V rocket

M-V is the new generation satellite launcher of ISAS [5]. The first flight of M-V-1 was successfully completed in February 1997. M-V is a 30m long, 2.5mdiameter, 130 ton, three-stage solid propellant rocket, with a 2 ton launchcapability to low earth orbit (LEO). As shown in figure 5.2, the third stageM-34 rocket motor casing is made of filament wound carbon fibre reinforcedepoxy. A filament wound motor casing was selected not only because of itspotential high performance but also because of its cost advantage over a tita-nium alloy casing. To accommodate more than 10 tons ofM-34 rocket motorsolid propellant, the interior volume of the casing is 6.0m3. The maximumoperating pressure is more than 6.0MPa. The large nose faring is made ofan aluminium honeycomb sandwich shell with carbon fibre composite facesheets. The M-34 nozzle introduced a deployment system of tapereddouble reverse helical spring extensors, made of glass fibre reinforced compo-sites (GFRP).

High performance composites for flexible structures

A flexible solar array is an attractive example of applying a flexible andextendable advanced composite with aromatic polyimide film. Japan’s space-craft SFU retrieved by the Space Shuttle in January 1995, deployed two largeflexible solar arrays in low earth orbit. Because of a high glass transitiontemperature Tg and outstanding mechanical properties even at very lowtemperatures, aromatic polyimide is the most successful, widely used poly-meric material in space [6]. Until ten years ago, spacecraft were equippedwith rigid power generators of the solar paddle type. As spacecraft becamelarger they required much more electric power, and flexible solar arraysare the most attractive way for power generation. Figure 5.3 illustrates theSFU spacecraft and the solar array configuration with extendable mast.The deployed wing is 2.4m wide and 9.7m long. The solar array is composedof two boards and the mast canister. The extendable/retractable mast iscontinually coilable, consisting of three glass fibre reinforced polymerspring rods (longerons) and radial spacers. The main source of the springforce is generated by the bending strain energy of the glass fibre reinforcedpolymer longerons. The radial spacers were made of moulded UPILEX-R.No mechanical backlash exists, because there are no pin-joint hinges, result-ing in high dimensional stability. Each array blanket consists of 48 hinged


polyimide panels (films), 202mmwide and 2400mm long. About 27 000 solarcells are mounted on the two array blankets and generate 3.0 kW power. Thesilicon cells are 100 mm thick with 100 mm cover glass bonded by S-691-RTVsilicon type adhesive on to the polyimide panels [3].

Development of a large deployable antenna in Muses-B is anotheradvanced technology in space [7]. Figure 5.4 illustrates the Muses-B antennalaunched in 1997 to be used aboard the satellite for Space-VLBI (Very LongBaseline Interferometry).A 10mdiameter parabolic antennawithmesh surfacewas successfully deployed with steps extending the six extendable masts in lowearth orbit. Figure 5.5 shows a deployment test of the MUSES-B flight modelantenna. This incredibly complicated system consists of 6000 fine cables of highmodulus Kevlar 149 aramid covered by a CONEX aramid net. Because of therequirement for high surface accuracy, each cablemust keep precisely its lengthwithout creep under tension in space. It is known that a high strength Kevlar

Figure 5.3. Illustrated SFU spacecraft and deployed configuration of its solar array with

the extendable mast.


Figure 5.4. Configuration of MUSES-B antenna: (1) stowed in the nose faring, (2) deployed.


(a) (b)

(c)

(d)

Figure 5.5. Sequential deployment test of MUSES-B flight antenna: (a) stowed; (d) after

deployment.


149 cable exhibits very little elongation as stressed and has negative expansionover a wide range of temperatures. The tension of each cable and each extend-able mast was controlled strictly, using tensioners on the top of eachmast. Thisis the first application of high performance organic fibres for a large deployableparabolic antenna surface in space.

Heat resistant matrix resins

Aromatic polyimides are used widely in industry, because they possess highthermal stability, good mechanical properties, excellent electrical propertiesand excellent environmental stability [8]. Figure 5.6 shows the chemical struc-tures of commercially available, space application, polyimide films. Metal-lized polyimide films, called flexible multi-layer thermal insulations (MLI),are now indispensable for passive thermal control systems of spacecraft aswell as for flexible solar arrays. However, polyimides with these outstandingproperties often give poor processability even in the addition-type oligoimidesuch as BMI and PMR-15. Because of their intermolecular ordered structure,aromatic polyimides have poor molecular mobility beyond the glass

Figure 5.6. Chemical structures of commercially available, space application polyimide

films.


transition temperature Tg, resulting in extremely severe processing condi-tions for structural applications [9]. Figure 5.7 shows the temperature depen-dence of storage and loss moduli for isomeric biphenyl polyimide films.

The asymmetric biphenyl polyimide, a-BPDA/PDA has a very inflectedchain structure compared with the semi-rod s-BPDA/PDA polyimide, asshown in figure 5.7. The a-BPDA/PDA annealed at 400 8 C shows a higherTg than the s-BPDA/PDA treated under the same conditions [10]. Thedifference in the extent of the storage modulus decrease at Tg for the twopolyimides in figure 5.7 is attributed to the difference in the intensity ofintermolecular interactions, suggesting an improvement in the processabilityof a-BPDA derived polyimide resins.

Figure 5.8 shows thermogravimetric results under nitrogen for thenovel poly{(phenylsilylene) ethynylene1,3-phenyleneethynylene} (MSP-1),polyimide PI(BPDA/PDA), and their 1/1 blended films. Inorganic/organic

Figure 5.7. Temperature dependence of storage and loss moduli for isomeric biphenyl-type

polyimide films.


polymer blends of this type can be expected to form a class of new thermallystable, toughened matrix resins [11].

Summary

Advanced polymer matrix composites are important in a range of spaceapplications, notably in primary satellite structures, rocket casings, flex-ible/extendable structures such as antennae and as thermal insulators.

References

[1] Brodsky R F and Morais B G 1982 Aeronautics & Astronautics May pp 54–65

[2] Yokota R 1995 Proceedings of 1st China–Japan Seminar on Advanced Engineering of

Plastics, Polymer Alloys and Composites (Society of Polymer Science, Japan) p 100

[3] Shibayama Y et al 1991 Proceedings of the European Space Power Conference,

Florence, Italy p 735

[4] Onoda J et al 1994 IAF-94-1.1.174, Israel

[5] Onoda J et al 1994 ISTS-94-b-19, Japan

Figure 5.8. Thermogravimetric data in N2 flow of the novel poly {(phenylsilylene) ethyny-

lene-1,3-phenyleneethynylene} (MSP-1), PI(BPDA/PDA), and their 1/1 blend films.


[6] Yokota R et al 1997 Proceedings of 7th Symposium on Materials in a Space Environ-

ment, Toulouse, France (ESA/ONERA)

[7] Takano T et al 1996 ISTS-96-e-18, Japan

[8] Yokota R 1996 Structure and Design of Photosensitive Polyimides ed K Hone and T

Yamashita (TECHNOMIC) chapter 3

[9] Serafini T T 1984 Polyimides: Synthesis, Characterization and Applications ed K L

Mittal (New York: Plenum) vol 2 p 957

[10] Hasegawa M, Yokota R, Sensui N and Shindo Y Macromolecules in press

[11] Yokota R, Ikeda A and Itho M 1998 Polymer Prep. Japan 47 643


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Aerospace Materials: Chapter 5. High Performance Polymers And Advanced Composites For Space Application