Abstract

Thin metal mirrors are prime candidates for space applications, because of their high thermal conductivity, low weight, and ability to withstand vibration during launch. Of all the fabrication processes, at the present state of the art, electroforming appears the most suitable for producing accurate, thin, metal mirrors with satisfactory mechanical and physical properties. Great strides were made over the past two years in precision electroforming. These are described along with General Electric’s spincasting process for the fabrication of masters.

© 1966 Optical Society of America

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References

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  1. F. A. Lowenheim, Ed. Modern Electroplating (John Wiley & Sons, Inc., New York, 1963).
  2. L. Roberts, Astronaut. Aeron. 3, 22 (Dec.1965).
  3. F. J. Schmidt, I. J. Hess, “Electroforming Aluminum for Solar Energy Concentrators,” NASA Contractor Rept. NASA CR–197 (1965).
  4. J. H. Connor, A. Brenner, J. Electrochem. Soc. 99, 234 (1952).
    [CrossRef]

1965 (1)

L. Roberts, Astronaut. Aeron. 3, 22 (Dec.1965).

1952 (1)

J. H. Connor, A. Brenner, J. Electrochem. Soc. 99, 234 (1952).
[CrossRef]

Brenner, A.

J. H. Connor, A. Brenner, J. Electrochem. Soc. 99, 234 (1952).
[CrossRef]

Connor, J. H.

J. H. Connor, A. Brenner, J. Electrochem. Soc. 99, 234 (1952).
[CrossRef]

Hess, I. J.

F. J. Schmidt, I. J. Hess, “Electroforming Aluminum for Solar Energy Concentrators,” NASA Contractor Rept. NASA CR–197 (1965).

Roberts, L.

L. Roberts, Astronaut. Aeron. 3, 22 (Dec.1965).

Schmidt, F. J.

F. J. Schmidt, I. J. Hess, “Electroforming Aluminum for Solar Energy Concentrators,” NASA Contractor Rept. NASA CR–197 (1965).

Astronaut. Aeron. (1)

L. Roberts, Astronaut. Aeron. 3, 22 (Dec.1965).

J. Electrochem. Soc. (1)

J. H. Connor, A. Brenner, J. Electrochem. Soc. 99, 234 (1952).
[CrossRef]

Other (2)

F. A. Lowenheim, Ed. Modern Electroplating (John Wiley & Sons, Inc., New York, 1963).

F. J. Schmidt, I. J. Hess, “Electroforming Aluminum for Solar Energy Concentrators,” NASA Contractor Rept. NASA CR–197 (1965).

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Figures (13)

Fig. 1
Fig. 1

Spincast mechanism in place with a 10-m spincast truss mounted thereon. This configuration is capable of spinning two parabolic quadrants with a total diameter of 10 m. Modification of the truss will enable the spincasting of a 10-m one piece parabola.

Fig. 2
Fig. 2

The spincasting machine is fundamentally a precision bearing system coupled to an accurate speed control. Photograph shows spincast bearing housing that will be mounted onto a seismatic shock isolated mass.

Fig. 3
Fig. 3

The 3-m spincast mold structure in this photograph has been turned upright and placed onto the spincast machine. The parabolic dish shown here has been roughened and is in the process of being cleaned.

Fig. 4
Fig. 4

3-m spincast structure is both statically and dynamically balanced and leveled, when mounted on the rotating machine.

Fig. 5
Fig. 5

The plastic has been poured into the sealed spinning structure and allowed to spin for several days to harden. The mold was then uncovered for inspection. Photograph shows a wood catwalk reflected in the spincasting.

Fig. 6
Fig. 6

An example of electrodeposition stress as a function of current density.

Fig. 7
Fig. 7

The 3 m rigid dish structure shown here upside down was used to spincast a 2.9 m Mirror Master.

Fig. 8
Fig. 8

After the spincasting has been completed and hardness checks indicated a successful casting, the surface of the casting is metallized by either chemical reduction or vacuum deposition of silver. The metallized spincasting is placed into an electroforming tank where a conforming anode passes current to the metallized plastic surface and deposits metal onto the surface of the spincasting. After the deposit is plated about 1 cm, the spincasting with the deposited metal is removed from the bath. A conforming plastic parabolic back-up structure is then bonded to the back-face of the nickel deposit, giving a uniform support to the deposit.

Fig. 9
Fig. 9

The spincast mold is removed from deposited nickel male parabola. The silver that was originally placed onto the plastic now acts as a separation media.

Fig. 10
Fig. 10

Male master in electroforming tank.

Fig. 11
Fig. 11

After the required nickel thickness is deposited from a rotating conforming anode onto the male master, the assembly with its thin skin is removed from the tank. At the outer edge a curved shaped gutter was placed prior to the electroforming operation so that a semi-torus would form around the periphery.

Fig. 12
Fig. 12

Handling torus in place ready for mirror master separation.

Fig. 13
Fig. 13

After successive heating-cooling cycles the handling torus is lifted, taking with it the thin-skin mirror. Picture shows the first male generation nickel master and the second-generation mirror immediately after separation.

Tables (1)

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Table I Nickel Electroforming Bafh

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