NASA Technical Reports Server (NTRS) 20100014089: Manufacturing Precise, Lightweight Paraboloidal Mirrors

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by  NASA Technical Reports Server (NTRS)

Manufacturing
Automated Solvent Seaming of Large Polyimide Membranes
Success depends on precise control of all relevant process details.
Marshall Space Flight Center, Alabama
A solvent-based welding process en- The process is applicable to cast mem- dition, the formation of reliable seams
ables the joining of precise, cast polyimide branes made of CP1 (or equivalent) poly- depends on the deposition of a precise
membranes at their edges to form larger imide. The process begins with the pre- amount of the seaming solution along
precise membranes. The process creates a cise fitting together and fixturing of two the seam line. To ensure the required
homogeneous, optical-quality seam be- membrane segments. The seam is precision, deposition is performed by
tween abutting membranes, with no over- formed by applying a metered amount of use of an automated apparatus compris-
lap and with only a very localized area of a doped solution of the same polyimide ing a modified commercially available,
figure disturbance. The seam retains 90 along the abutting edges of the mem- large-format, ink-jet print head on an au-
percent of the strength of the parent ma- brane segments. After the solution has tomated positioning table. The printing
terial. The process was developed for orig- been applied, the fixtured films are al- head jets the seaming solution into the
inal use in the fabrication of wide-aper- lowed to dry and are then cured by con- seam area at a rate controlled in coordi-
ture membrane optics, with areal vective heating. The weld material is the nation with the movement of the posi-
densities of less than 1 kg/m2, for light- same as the parent material, so that what tioning table.
weight telescopes, solar concentrators, an- is formed is a homogeneous, strong joint This work was done by Robert Rood of
tennas, and the like to be deployed in that is almost indistinguishable from the Marshall Space Flight Center and
outer space. The process is just as well ap- parent material. James D. Moore, Chris Talley, and Paul A.
plicable to the fabrication of large precise The success of the process is highly de- Gierow of SRS Technologies, Inc. Further
polyimide membranes for flat or inflat- pendent on formulation of the seaming information is contained in a TSP (see
able solar concentrators and antenna re- solution from the correct proportion of page 1).
flectors for terrestrial applications. the polyimide in a suitable solvent. In ad- MFS-32129
Manufacturing Precise, Lightweight Paraboloidal Mirrors
Success depends on the proper selection of materials and process conditions.
Marshall Space Flight Center, Alabama
A process for fabricating a precise, dif- The process consists mainly of the fol- niques while the speed of rotation and
fraction-limited, ultra-lightweight, compos- lowing steps: the temperature are adjusted to obtain
ite-material (matrix/fiber) paraboloidal 1. A precise glass mandrel is fabricated the desired figure. The proper selec-
telescope mirror has been devised. Unlike by conventional optical grinding and tion of surfactant, speed or rotation,
the traditional process of fabrication of polishing. viscosity of the epoxy, and temperature
heavier glass-based mirrors, this process in- 2. The mandrel is coated with a release make it possible to obtain the desired
volves a minimum of manual steps and agent and covered with layers of a car- diffraction-limited, smooth (1/50th
subjective judgment. Instead, this process bon-fiber composite material. wave) parabolic outer surface, suitable
involves objectively controllable, repeat- 3. The outer surface of the outer layer of for reflective coating.
able steps; hence, this process is better the carbon-fiber composite material is 7. A reflective coat is applied by use of
suited for mass production. coated with a surfactant chosen to pro- conventional coating techniques.
Other processes that have been investi- vide for the proper flow of an epoxy 8. Once the final figure is set, a light-
gated for fabrication of precise composite- resin to be applied subsequently. weight structural foam is applied to the
material lightweight mirrors have resulted 4. The mandrel as thus covered is rear of the optic to ensure stability of
in “print-through” of fiber patterns onto mounted on a temperature-con- the figure.
reflecting surfaces, and have not provided trolled spin table. This work was done by Frederick Thomas
adequate structural support for mainte- 5. The table is heated to a suitable tem- Herrmann of Marshall Space Flight Cen-
nance of stable, diffraction-limited surface perature and spun at a suitable speed ter. Further information is contained in a
figures. In contrast, this process does not as the epoxy resin is poured onto the TSP (see page 1).
result in “print-through” of the fiber pat- coated carbon-fiber composite mate- This invention is owned by NASA, and a
tern onto the reflecting surface and does rial. patent application has been filed. For further
provide a lightweight, rigid structure capa- 6. The surface figure of the optic is mon- information, contact Sammy Nabors, MSFC
ble of maintaining a diffraction-limited itored and adjusted by use of tradi- Commercialization Assistance Lead, at
surface figure in the face of changing tem- tional Ronchi, Focault, and interfero- [email protected]. Refer to MFS-
perature, humidity, and air pressure. metric optical measurement tech- 31595-1.
NASA Tech Briefs, January 2006 21