Novel Ultra-Lightweight Optics

Joe Ritter
Director of Optical Systems Research
SAIC Technology Research Group


The development of novel lightweight optics and support structures 
is of vital importance to the advancement of both ground and space-
based astronomy.  Primary mirrors are one of the main drivers of 
the mass of space based optical systems, as the other spacecraft 
masses are roughly proportional to the optical system mass.  
Therefore lightweight optics are an essential component of reducing 
launch costs while increasing payload utility.   An analogous 
relationship holds true for ground based observatories.
As an example, the Hubble space telescope has a 4.5 m2 primary 
mirror with an areal density of ~ 180kg/m2.  Its successor, 
the Next Generation Space Telescope will have 10 times the 
collecting area, and 10% of the areal density and active figure 
control to allow a robust response to slewing and changes in 
environment.  These 100-fold improvements are pushing the limits 
of current optical technologies, yet proposed future missions for 
imaging extrasolar planets 100 light-years from earth (e.g. the 
NASA Gossamer Terrestrial Planet Imager - planned 25 years from 
now) will require coordinated arrays of multiple space telescopes 
each having over 4000 m2 of collecting area!  In order to use a 
conventional (e.g. Delta or EELV) launch vehicle a large diameter 
primary active optic having areal density of <100 grams/m2 is 
required for these missions.  Clearly to achieve this million-fold 
improvement in area/density at reasonable cost, new directions for 
research outside of classical telescope design must be explored.  
Although such fantastic missions seem unrealistic, the road to 
these goals will lead to great advances in astronomical 
instrumentation, and to our knowledge of the universe.
The ability of photoactive isomers to change structure within 
a polymer matrix in response to light may have applications for 
large ultra-light-weight optics, as well as to mega-element 
adaptive optic correctors and other nano-machines.  The invention 
and development of the first ultra-light-weight (<200 grams/m2) 
optically active polymer optic (photonic muscle mirror) whose 
figure can be actively controlled using lasers will be described.  
Plans for an oscillating exciton based photocontractile polyer 
for use as an adaptive optic corrector will be discussed.
A brief overview of other technologies such as electroform 
replication of large optics, rapid replication and novel figure 
control of high modulus large area SiC-SiC optics, aerogel optics 
and other current interdisciplinary research interests will be discussed.