The Inflatable Satellite
nasa langley research center2007_1_38It looks like a party decoration gone wildly out of scale: A gigantic silver balloon towering over its creators and their Plymouth station wagon in the cavernous interior of an airship hangar. Yet it’s the prototype of a spacecraft, in an era when that term usually meant something the size of a washing machine. Beginning in August 1960, with the launch of Echo I , satellites like this one set the stage for the modern era of worldwide space-based telecommunications—using aviation technologies that dated back to the eighteenth century.
This 100-foot sphere is not an actual satellite but an experimental version of what would be called Echo I , undergoing an inflation test in 1959. Its volume exceeds half a million cubic feet; if laid flat, its surface would cover more than 30,000 square feet. The great balloon was designed to reflect radio signals from one place on earth to another, the first time that feat would be accomplished using an artificial satellite. Oddly enough, however, when this pioneering communications-satellite project was first conceived, it involved neither communications nor satellites.
In January 1956 William J. O’Sullivan, of the National Advisory Committee for Aeronautics (which would become NASA in October 1958), was asked to examine a number of proposed experiments for measuring the density of the rarefied upper atmosphere. The chosen experiment would be part of America’s contribution to the International Geophysical Year (July 1957 through December 1958). Every proposal presented to O’Sullivan’s committee proved unsatisfactory, so while musing about the problem in a hotel room one evening, he hatched his own solution: a kind of balloon buoy that would be inflated and then released in the high atmosphere. The balloon would be tracked by radar to measure the drag force upon it, which is proportional to the atmospheric density.
The drag measurements would become more sensitive as the ratio of the balloon’s mass to its cross-sectional area decreased. In the extremely low pressures of the upper atmosphere, this required making the balloon as big as possible, and its skin as thin and light as possible. At first O’Sullivan envisioned a balloon two and a half feet across, but a colleague showed that it would have to be bigger to yield useful data. The diameter finally chosen was 12 feet, because that was the height of the ceiling in the shop that would fabricate it.
The next development jumps directly from the pages of Astounding Science Fiction —specifically, from a nonfiction feature in March 1952 titled “Don’t Write, Telegraph,” by J. J. Coupling, a pseudonym used by John R. Pierce, who was Bell Telephone’s director of research in communications principles. Pierce’s article is a forecast of the coming world of communications satellites, and one technology it foresees is the use of huge reflective balloons for bouncing radio waves from one earth-based station to another.
In speeches and articles over the next few years, Pierce honed the theme, advocating balloon satellites about 100 feet across. Independently, O’Sullivan, who tried to launch a 12-foot atmospheric balloon in 1958 only to see the rocket malfunction, began to see his idea’s potential for communications. He even inflated a 12-foot balloon before a congressional committee to demonstrate how it would work. The two men’s initiatives came together in early 1959 under NASA’s sponsorship. Though their names were forever linked by this project, Pierce and O’Sullivan worked in different areas of the Echo program, and they never met.
The new space agency was desperately seeking ways to close the “satellite gap” after the Soviet success with Sputnik in October of 1957. The big, shiny sphere offered one solution—a temporary one, but it might lead to more robust replacements. High-performance “active” communications satellites, with power supplies and equipment to amplify and rebroadcast messages, were already in planning, and an active prototype had performed successfully in orbit in December 1958 (though with a delay of several hours between receiving and forwarding the signal). The silvery balloon’s simple passive reflection (hence the name Echo , coined by O’Sullivan) would bounce back far weaker signals, but the bandwidth would be larger, which would enable more information to be transmitted, including television images.
The new device was informally dubbed a “satelloon.” The project became a collaboration among NASA, the California Institute of Technology’s Jet Propulsion Laboratory (JPL), and the U.S. Naval Research Laboratory in Washington, with Pierce’s Bell Labs developing ground-based technologies to send and receive the signals. The two most important terrestrial installations were JPL’s pair of 85-foot parabolic dishes at Goldstone, California, and Bell’s 60-foot transmitter and steerable “horn” receiver at Holmdel, New Jersey. The prototype balloons, much bigger than O’Sullivan’s 12-foot version, quickly outgrew the largest quarters he could find, prompting a move to the U.S. Navy dirigible hangar at Weeksville, North Carolina, which is where this photo was taken. Airdock 2 was 1,058 feet long and 177 feet high at its peak.
The Echo balloon reflected telephone signals on two channels, 960 MHz and 2390 MHz. The strength of the broadcast signal was 10 kilowatts, which would typically be reduced by 180 decibels—that is, a factor of a billion billion—between sender and receiver. Despite this loss, communication was still possible because Bell Labs equipment, including masers cooled to 2 degrees Kelvin with liquid helium, could pick out signals as weak as 10-18 watts.
The balloon’s skin was made from dimensionally stable polyethylene terephthalate—better known as Mylar—.0005 inch thick (“half as thick as the cellophane from a cigarette pack,” as it was often described). In 1959 Mylar was most familiar to consumers for its use in frozen-food pouches that could be dropped into boiling water; it was also used for recording tape. NASA researchers tested dozens of materials, but only Mylar met the severe criteria, which included holding together at temperatures ranging from 300 degrees Fahrenheit in direct sunlight to -80 degrees in the earth’s shadow.
A radio-reflective aluminum coating was added on top of the Mylar. On Echo I this was vapor-deposited, using a technique developed by Reynolds Metals that created a film about one-thousandth as thick as the Mylar—so thin that just four pounds of it covered the entire surface. On Echo II it was aluminum foil .00018 inch thick, one-fourth the thickness of kitchen foil, with a second layer for strength laminated to the underside of the .00035-inch Mylar. All told, the skin on Echo II measured .0007 inches thick, about one-fifth as thick as the page you’re reading.
The satellite carried no instrumentation except for two 107.9 MHz beacon transmitters that were used in tracking it from earth. They are visible in this picture as white squares near the balloon’s equator. Each beacon was as big as a dinner plate and carried a half-ounce transmitting unit the size of a cigarette lighter. These units were powered with 70 solar cells and 5 storage batteries.
Like hot-air balloons, Echo satellites were assembled from “orange peel”–shaped sections, 82 of them in Echo I and 106 in Echo II . (The seams are visible as white ticking.) Each tapering section is more than 150 feet long. They were attached at the top and bottom of the sphere to circular sections known as pole caps. The pole caps were reinforced with an extra layer of Mylar, as were the sections to which the beacons were attached.
Joining these sections to form an airtight envelope proved a maddening chore. The General Mills Corporation (the cereal maker, which pursued a modestly successful aerospace sideline in the 1950s) attempted the first balloon, but its seams would not hold. Superior methods were devised by Gilmore T. Schjeldahl, a Minnesota polymer expert who had gotten his start manufacturing plastic pickle-barrel liners in his basement. In Schjeldahl’s version, shown here, the balloon’s joints were even made electrically conductive. That way all two-plus miles of seams could be tested for leaks by using a volt-ohm meter.
The sphere is undergoing test inflation (note the fans in the foreground and the filler tube beneath the balloon). It took 12 hours to pump in 40,000 pounds of air. With the addition of helium (note the pressure bottles in the foreground) the engineers were able to achieve neutral buoyancy, a first for large-scale inflation.
In space, things would be much easier. With no ambient pressure against the satellite, hardly any gas would be needed. In fact, air was now Echo ’s enemy, because traces of air trapped in the folds had caused a prototype balloon to explode during a suborbital test. In that test, engineers had intentionally left the air inside as a simple way to inflate the balloon, but in the vacuum of space it expanded all too suddenly and burst the fragile fabric. The accident created an unintentional light show along the Atlantic coast, with the aluminized shreds brilliantly reflecting the setting sun as they fell to earth.
From then on, space-based inflation would rely on sublimation, a phase change directly from solid to gas. Inside Echo ’s skin, porous bags held about 10 pounds of powdered benzoic acid and 20 pounds of powdered anthraquinone. In space, these powders would vaporize slowly as they absorbed the sun’s heat, gently inflating the envelope to full size.
The big balloon would be launched tightly folded inside a canister just 26 inches across. Workers spent weeks trying one pleating scheme after another. The solution came when an engineer noticed the efficient accordion-style folding scheme used in his wife’s plastic rain hat. Echo I ’s clamshell-shaped canister was designed with the same sort of practical thinking; its seal, which would be blown open with plastic explosives to release the satellite, was laced shut before launch with ordinary fishing line.
Echo I was launched from Cape Canaveral atop the third stage of a Thor-Delta booster rocket on August 12, 1960. (Strictly speaking, this satellite was Echo 1A ; the first attempted Echo launch, in March 1960, was aborted when its Delta rocket failed.) Thirty-three minutes later, after reaching a 1,000-mile altitude and achieving successful separation, the balloon inflated and assumed a nearly circular orbit, 48.6 degrees off equatorial.
Then it spoke. “It is a great personal satisfaction to participate in this first experiment in communications,” said the voice of President Dwight D. Eisenhower, in a prerecorded message that was beamed from the Goldstone receiving station, bounced off Echo , and received at Holmdel. “This is one more significant step in the United States program.” A peaceful promise followed: “The satellite balloon which has reflected these words may be used freely by any nation for similar experiments.” Echo I was the world’s thirty-first artificial satellite overall (25 launched by the United States, 6 by the U.S.S.R.) and by far the largest object ever sent into space from earth.
The next important message came the following day: “Hello, this is Bill Jakes, calling Phil Tardoni at Jet Propulsion Laboratory.” Just an ordinary phone call, except that its transcontinental live transmission from Bell Labs had caromed off a balloon hurtling through space. Since Echo moved so quickly across the horizon, aiming both antennas to bounce the message perfectly required enormous precision. Nonetheless, real-time space-based communications had begun.
On August 19 a portrait of Eisenhower became the first “outer space wire photo,” or fax. That same day, a Holmdel signal reached France in the first transatlantic satellite radio transmission. “The future might see a televiewer in Cincinnati, for example, flicking on his set and catching the Olympic games in Europe … [or] picking up his phone, asking for a friend in Russia, Japan, or South Africa and hearing him loud and clear almost immediately,” suggested a visionary science writer for the Wisconsin Rapids Daily Tribune .
The triumph made good politics, international and domestic. Radio Free Europe broadcasts were transmitted via Echo . During a campaign swing, the Democratic vice-presidential candidate, Sen. Lyndon B. Johnson, a longtime space booster, fingered a swatch of the satellite’s skin. On election night CBS trumpeted its use of the IBM 70-90, “the same [computer] used to track the Echo satellite,” to tally the returns. Two days after John F. Kennedy’s victory, the first “space letter” was faxed. Postmaster General Arthur E. Summerfield used it to extend his office’s traditional holiday request, “Shop and Mail Early.”
E cho watching became the new American pastime. In the night sky, it was easily visible to the naked eye. At 16,000 miles per hour, it required just two hours to circle the globe. You could watch it disappear, then see it return. Daily newspapers printed timetables showing when the satellite would pass over their cities. People gathered nightly, on street corners and in cornfields, heads craned skyward to follow its travels. Life magazine joined ham radio operators in their basements as they strained to track its signals.
The first Montgolfier balloons had inspired similar awe as they floated over the French countryside in the 1780s; here was their space-age equivalent. Many of today’s space scientists can recall begging their parents to let them stay up late to watch Echo . It flew over the world’s biggest cities and its most primitive hinterlands. It was like-wise visible across the Soviet Union, which offered no official explanation to its citizens. The Soviet space program remained ahead of America’s (its Lunik probes had already orbited the moon, and Sputnik IV was equipped to carry a man), but still, you could actually see Echo every night.
Even in the near-emptiness of outer space, the fragile ball faced dangers. On August 14 it survived a meteor shower. The orbit had been chosen so that the balloon would spend its first week and a half in constant sunlight, and when it passed into the earth’s shadow for the first time, observers held their breath. Robbed of the sun’s heat, the balloon’s gas might resolidify, and it was an open question whether the balloon might grow misshapen or even burst on subsequent reinflation. These fears proved groundless.
collection of richard f. snow.2007_1_41The seemingly frail balloon proved remarkably durable. Though “wrinkled like a prune” (according to press reports) by the tons of micrometeorites that hit, and eventually punctured, its thin skin, the weary traveler kept flying, broadcasting the first television pictures by satellite (images of a rodeo cowboy and a trained seal) in April 1962.
While John Pierce preferred to garner acclaim in professional circles, William O’Sullivan became telecommunications’ first pop star, demonstrating Echo I ’s science to President Eisenhower in front of photographers. The father of the Echo satellite was also the father of a large, photogenic family, and their portrait was part of many early NASA briefing packages. Perhaps it comes as no surprise that when O’Sullivan appeared on “I’ve Got a Secret,” a popular television game show of the era, its celebrity panel all guessed him correctly as “the father of the Echo satellite.”
Nasa had big plans for the technology. it envisioned a necklace of Echo -type spheres in orbit around the earth, providing continuous communication as successive satellites passed over a target. In fact, just one more was sent into space: Echo II , in January 1964. A backup version of Echo II and its booster rocket awed crowds at the 1964 New York World’s Fair, and in a way, the Echo satellite remains at the fair today. A square of its shiny skin was included in the fair’s official time capsule, to be opened in 5,000 years. This collection lies buried near the Unisphere, a 140-foot stainless-steel globe that is ringed by orbits marking early space shots. A second, folded Echo satellite is on display at the National Air & Space Museum.
Echo II assumed a polar orbit, making it less useful for communication, but broke ground with its improved structural integrity. Instead of relying on internal pressure, this satellite was designed to deform its foil coating permanently during inflation, locking the balloon into its spherical shape. Thus Echo II would remain “inflated” even after its sublimating charge escaped (not owing to meteor puncture; this time releasing vents were built in).
Sunshine imparted momentum to Echo II , as it did with Echo I , tending to push it out of orbit. Measurements of this process provided some of the first quantitative evidence of solar pressure (which is also why comets’ tails swing away from the sun). Echo II even paid off diplomatically, as the world traveler became a world ambassador. After declining Eisenhower’s 1960 invitation to broadcast via Echo I , the Soviet Union signed the Dryden-Blagonravov agreement in 1962, the first cooperation between the superpowers in space. In that spirit, Echo II was used to bounce signals between the Jodrell Bank radiotelescope in Manchester, England, and Zimenki Observatory near Gorky, Russia.
For all its accomplishments, the Echo project was never more than an experiment. Its bounce transmission, with the attendant massive loss of signal strength, and its low, moving orbit, which made getting a fix difficult, were quickly outmoded by active relay systems in geostationary orbits. Yet the program had many positive spinoffs. The balloons’ reflective surfaces created a new industry in metallized foil deposition (the silvery “space blankets” used to drape marathoners are very similar to Echo ’s skin). More important, space balloons demonstrated that signals reflected from space could be received and understood on earth, despite fears of electrical interference from the ionosphere. That made the prospect of commercial satellite communication look much more plausible.
Although their use in communications was over, the launching of inflatable satellites did not end with Echo II . Four more went aloft during the 1960s to take readings of atmospheric conditions, and Pageos (Passive Geodetic Earth Orbiting Satellite), launched in 1966, helped the U.S. Coastal and Geodetic Survey to precisely fix the location of reference points around the world. These points were used to compile extremely accurate maps, take exact measurements of the earth’s dimensions, and verify the theory of continental drift. And inflatable satellites are still being launched today, from space stations to telescopes. Whenever a big thing needs to be launched in a small package, an inflatable is a strong candidate.
But the biggest scientific payoff from the Echo project was purely accidental. Even when adjusted to extreme sensitivity to capture Echo ’s feeble signals, Holmdel’s antenna was continually plagued by faint static. The radio astronomers Arno Penzias and Robert Wilson investigated every possible cause for this interference, right down to pigeon droppings soiling the reflector. Their analysis revealed that this unprecedented “ear,” sharp enough to hear into space, was detecting blackbody emissions, evidence of the primordial birth of the universe. Echo had inadvertently helped verify the Big Bang.
On May 24, 1968, Echo I performed William O’Sullivan’s original drag experiment one last time, when the sunshine that had given it inflation and fame finally pushed the sagging sphere back into the earth’s atmosphere, where it burned up. Backyard stargazers lamented the loss of an old friend (though they could hardly complain; on its launch in 1960, NASA had projected a life span of about a year). All told, Echo I had circled the earth 35,600 times, traveling more than a billion miles. Echo II followed on June 7, 1969, leaving the earth just one shining moon, which was reached six weeks later by Apollo 11 . Coverage of the landing was live, via satellite.
