Form 9.B Project Summary

Chron:

971101

Proposal Number:

15.01-9991

Project Title:

Sputtering Silicon Coatings for Large

Aperture (2 meter) Silicon Carbide

Optical Segments

Technical Abstract (Limit 200 words)

Silicon Carbide (SiC) optics have been identified as

a key technology for several NASA missions

including Next Generation Space Telescope

(NGST). SiC has superior thermal stability and

excellent specific stiffness making it ideal for space

based optical systems. NGST requires SiC optical

segments which are both lightweighted and large

(1-2 meter segment sizes). Polishing these large SiC

segments pre- sents a number of problems; the

pieces are very thin and cannot with- stand large

polishing pressures. Flat or spherical optical

surfaces can be obtained directly on SiC materials

using conventional polishing systems. The problem

has been in obtaining non-symmetric aspheric

surface profiles in the hard SiC material. A common

solution has been to coat SiC optics with a thick

cladding (0.005") of silicon. The silicon can be

easily polished with moderate pressures and the

coefficient of thermal expansion (CTE) match

between SiC and silicon is very good. SSG has

extensive experience in the silicon coating of SiC

optics. In order to make the process feasible for a

program like NGST a number of technical issues

need to be addressed: (1) the sputtered silicon

coating process needs to be modified to eliminate

coating stresses and make silicon coatings suitable

for very thin, lightweighted SiC optical substrates;

(2) the metrology associated with the SiC substrate

machining needs to be improved to minimize the

amount of silicon needed in the cladding; (3) a

large-scale coating facility needs to be developed;

and (4) the current process needs to be modified to

address the uniformity requirements associated

with large scale optical segments. The proposed

Phase I work will address all these issues. During

Phase I a large sputtering chamber with a 2-meter

capacity will be brought on-line and the viability of

the processes proposed will be demonstrated with a

number of sub-scale empirical demonstrations.

Potential Commercial Applications (Limit 200 words)

The NGST application alone represents an

important Phase III application. The development

of the unique large-scale, sputtered coating

capability will also make the development of large

aperture (1-2 meter diameter), ultralightweighted

SiC optical systems viable for a number of NASA,

DoD, and commercial applications.

Name and Address of Principal Investigator (Name,

Organization Name, Mail Address, City/State/Zip)

Joe Robichaud

SSG, Inc.

65 Jonspin Road

Wilmington , MA 01887

Name and Address of Offeror (Firm Name, Mail Address,

City/State/Zip)

Alan McEacharn

SSG, Inc.

65 Jonspin Road

Wilmington , MA 01887