If America's passive communication satellite program does nothing else, it will have brought the realities of the space age closer to more people than any other single project. Although the manned orbital flights captured the attention of the civilized world, they lacked the endurance of the giant Echo balloon satellites which in their lifetimes can be seen from any spot on the globe. Echo I, launched in August, 1960, and Echo II, placed in orbit in January, are man-made “stars,” visible at regular intervals, bringing to every observer an awareness of the nearness of space.

 The Echo program has brought the glamour of the space age to the layman in a real sense. Notwithstanding, there are far-reaching objectives planned by the National Aeronautics and Space Administration. Ultimately, they are expected to prove the feasibility of passive satellite communications in various modes including radio, Teletype and facsimile. On Jan. 25, Echo II joined a network of seven U.S. communication satellites, including a sister satellite, Echo I.

 The new balloon satellite will be seen by more persons than any other man-made object. It is by far the largest, but not the heaviest, satellite ever put in orbit. With a 135-foot diameter, compared with the 100-foot-diameter Echo I, Echo II is on an 800-mile-high circular, near-polar orbit. Weighing only 535 pounds, it is virtually all plastic and aluminum. A few pounds of radio equipment are aboard to aid tracking stations follow the balloon during its two-hour earth orbits around the poles.

 Designed as a perfect sphere, Echo II is expected to show whether such a satellite will stay spherical as long as it is in orbit, which is expected to be at least three years.

 Carried aloft folded in a 30-by-40-inch pod, Echo II achieved an apogee (high point in orbit) of 816 statute miles, a perigee (low point) of 642 miles, and an orbital period of 109 minutes for each complete trip around the globe.

 If the satellite does retain its shape, it will provide a large and unchanging reflecting surface, long lifetime, and access for transmissions from different ground stations at the same time. Unlike active communication satellites which require specific ground equipment to correlate with equipment aboard the satellite, passive satellite ground communication technology may improve radically without requiring changes in the orbiting spacecraft.

 Early radar reports indicated variations in the reflectivity characteristics of the balloon which may mean it has not retained its desired spherical shape. These reports are not conclusive, however, Optical trackers have not reported any such abnormalities and NASA offers several possible explanations for these radar observations: inaccuracy in measurement; interference with the radar beam caused by the launch vehicle and other objects which went into orbit with the spacecraft; or interference due to electrical gas used to inflate the satellite; or a distorted balloon due to a short pressurized period.

 Distortion of the balloon sphere does not necessarily mean a full loss of communication capabilities. Collins Radio illustrated this in a series of experiments with Echo I lasting more than three years. Utilizing transmitting and receiving facilities at Cedar Rapids, Iowa and Dallas, Tex., Collins pioneered in passive satellite communications. On Aug. 13, 1960, engineers at the two locations used Echo I for the first two-way voice radio transmission via a man-made satellite. A week later, engineers bounced a picture of then President Eisenhower off the big balloon for the first facsimile transmission in space.

 Continuing experiments show that Echo I, although wrinkled and battered and only about half its original size, still retains propagation characteristics. With a predicted lifetime of only a few weeks, Echo I is still in orbit.

 Experience with Echo I was instrumental recently in Collins being selected by NASA as one of the communication experimenters in the Echo II project. Partially financed by a $250,000 NASA contract, the Collins deep space tracking station at Richardson, Tex., is conducting experiments for a six-month period in cooperation with the Naval Research Laboratory at Stump Neck, Md., and the Naval Electronics Laboratory at San Diego, Calif.

 Utilizing its modified 28-foot parabolic antenna first built for the Echo I experiments, Dallas engineers successfully transmitted signals from the Dallas station to the Stump Neck facility January 25, on Echo II's first visible pass.

 In the six-week period following launch, Collins continued to illuminate the satellite at 2380 me with the 28-foot antenna. In March, Collins began utilizing its 60-foot-diameter parabolic antenna as the prime transmitting antenna at 2380 me. Various phases of the planned experiments call for transmission from the Collins site to each of the Navy sites via Echo II; simultaneous transmissions between the three sites including a two-way bounce from Collins to balloon to Collins; and a transcontinental bounce between the two Navy facilities.

 The primary objective of the Collins experimental program is to determine the communication capability of the Echo II satellite. The experiments also are designed to provide information concerning Echo II's shape and surface characteristics. Bandwidth experiments will be conducted up to 12 mes and possibly greater. Usable bandwidth measurements made by Collins on Echo I showed a balloon bandwidth capability in excess of 1.5 mes.

 Another important objective of the current tracking program is the collection of data which allows correlation of information collected from the inflight balloon with data gathered during pre-launch laboratory experiments by NASA.

 The Collins system is a transmitting-receiving-tracking facility employing two azimuth/elevation-mounted paraboloid antennas. The 28-foot antenna is equipped with a 10-kilowatt transmitter capable of operation at either 2380 mes or 2190 mes. The 60-foot antenna is equipped with a 10-kw transmitter. In normal operation, the 28-foot antenna illuminates the satellite with a radar signal at 2190 me while the 60-foot antenna serves as a monopulse tracking antenna and simultaneously illuminates the satellite at 2380 me.

 When visibility permits, an optical tracker on either antenna can be used to position either or both antennas for acquisition or can manually follow the path of the satellite. Normally, the system is capable of self-acquisition and self-tracking.

 As scientists discover more about the characteristics of Echo II, more sophisticated experiments are planned. The transmission of television is included in future experiments as more data is accumulated.

 The USSR, through its Academy of Sciences, has agreed with NASA to try to bounce radio signals off Echo II's reflective skin in the first joint experiment in communications via space between the two countries. The agreement calls for voice, facsimile pictures and code signals to be relayed by use of giant antennas at the Zemenky Observatory near Moscow and the Jodrell Bank Observatory in England. NASA received data from Soviet optical observations within a few hours after launch and noted that the information is of particular interest since it was obtained during the period shortly after the satellite was placed into orbit.

 Aside from knowledge gained during the early phases of the Echo II experiments, NASA expects to gather information which ultimately may lead to a world-wide passive satellite communication network. The agency has long been interested in controlled inflation systems for erecting large platforms in space without the tremendous weight drawbacks entailed by present mechanical systems. Inflatable devices could be used to deploy huge airborne antennas or Earth-orientation devices which use the Earth's gravity gradient, to name two possibilities.

 Thus, the inflation technique of balloon-type satellites poses an interesting problem. The inflation system tested by Echo II utilized a slower, more controlled inflating method which took about 90 minutes to complete. This allowed the satellite to hold much higher pressures minimizing the chance of placing stresses on the .00035-inch-thick skin which would cause it to burst.

 To effect proper inflation, small plastic bags were fastened to the inside skin of the balloon in a definite pattern. When the sphere was injected into orbit, solar heat began its work. It first melted a wax sealant on the outer edge of each plastic bag causing it to expand and unfold inside the satellite. This in tum exposed thousands of tiny perforated holes on the inner folds of the small bags allowing a chemical to escape in the form of gas.

 Because the chemical envelopes were positioned in such a way that each released gas at a different time, a gradual pressure build-up was achieved. The final result created a stronger space structure and better reflectivity.