Ab8tmct-Projections of the growth of earth-sehg systems for the htter half of the 1980's show I data tmnanision requirement of 300 Mbit/s md &ow. Mission umstdnta md objectives led to the condusion that the most efficient technique to ntum the data h m 8 ensingsatellitetoagroundstrtionisthroughageosynrbronousdrtareky satellite. Of the two finlcs that are involved ( -sateIlite to relay satellite and relay satellite to grourrd), a laser system is most attractive for the sprce-tosprce link. A five-ym program was conducted which has &own the bmic technial feia'bitity of wmptishing thig link with a C02 laser system operaat a wavelength near 10 pm. The system wes a rnercury-cadmbm-telluride infraed mixer cooled to approxk m8tely 100 K by 8 ndi8tive cooler. The h r loal osciil8tor md couphgmoduhted I.ser tnnanittez use conductive& coded beryllium oxide construction. The optical 811-8 wed for t & r e -ceptionhasa~ofwminrlly92dBwitha3~bermwidthof80rru. T r r c~j i t t e r b l e s s t h . a t e n r r m d~P c q p h i t i o n o c c u r s m l~t h n n Manuscript received April 22, 1976; revised July 6, 1976. The submission of this paper was encouraged after review of an advanced proposal. are with the Space and Communication Group, Hughes Aircraft Company, El Segundo, CA 90245. Hammer, Inc., Melville, NY 11746. B. J . Peyton and T. Flattau are with AIL, a division of Cutler-PROCEEDINGS OF THE IEEE, FEBRUARY 1977 e LANDSAT-1 e TIROS-N e ITOS 0.001 O.O1 1960 i 1970 1980 Fa. 1. Space data transmission requirements. tions satellite. All intersatellite links are assumed to use laser communication systems, while all satellite-ground links use RF systems. The advantages provided by laser systems are compactness, freedom from frequency allbcation limits (which, for example, limit a &-bandlink to about 300 Mbit/s), and freedom from interference due to terrestrial RFI.Although the discussion has concentrated on a particular requirement which leads to the desirability of intersatellite links, such links have obvious utility in other applications. In domestic satellite systems, an intersatellite link would permit two satellites to serve essentially as a single system. By eliminating the transfer of data between satellites through a ground station, frequency allocations for ground-satellite links are conserved [ 181 . Similar considerations apply to international communication satellite systems [ 191 , where interregional telephony without intersatellite connections can require as many a s ' three hops-with an attendant excessive one-way propagation time.

This paper presents the results of an experimental evaluation of a new type of piezoelectric ceramic device designed for use as a laser mirror tuner. Thin plates made from various materials were assembled into a circular bimorph configuration and tested for linearity of movement, maximum travel, and resonant frequency for varying conditions of clamping torque and mirror loading values. Most of the devices tested could accept mirror diameters up to approximately 1.3 cm and maintain a resonant frequency above 2 KHz. Typical mirror translation without measurable tilt was +/-20 microm or greater for applied voltages of less than +/-300 V.

An infrared heterodyne radiometer has sufficient sensitivity for application to high resolution spectrometric studies of the sun and the absorption of sunlight in the atmosphere. In the 10-microm region, the resolution can typically range from less than 6.7 x 10(-3)cm(-1) to 6.7 x 10(-2) cm(-1). The minimum detectable signal can approach 10(-24) W/Hz. The infrared heterodyne radiometer (IHR) can also be used for atmospheric propagation studies at the emission frequencies of the CO(2) laser for the examination of the feasibility of space-to-ground laser communication links.

The first weather satellite was launched on 1 April 1960. In the 25 years since, weather satellites have contributed to improved weather analyses and forecasts worldwide. As a maturing component of a global observing system, the meteorological satellite promises even greater financial benefits and a higher quality of life to mankind.

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