AMONG THE CLASSICS Salient events, inventions, discoveries, successes, and triumphs of man over matter in this exciting quarter century

1969

MOON LANDER

'One small step for a man* was made possible by one giant step

for engineering

After the Apollo 11 mission landed two men on the moon , many in the United States hailed the event as victory in the space race over the Soviets. The 1969 land­ing meant something different, though, to one project leader involved in the construc­tion of the lunar landing craft. "The big­gest single thing that came out of build­ing the lunar vehicle was how to provide reliable design," said Joseph G. Gavin, for­merly program manager for the module at Grumman Corp. , in Bethpage, Long Is­land, N.Y., and now a senior management consultant there.

The lunar modules were the first craft in history destined to function only out­side the earth's gravity and atmosphere. The result of seven years of sometimes round-the-clock labors, the contraption looked like a metallurgist's conception of a four-legged ar thropod all of 22 feet (6.7 meters) high. The craft was even referred to as the " b u g . "

Through most of the 1960s, the lunar module, or LM, absorbed the waking lives

Gary Stix Associate Editor

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of some 7000 people, 3000 of them en- 6

gineers, at G r u m m a n Corp. Since then, and particularly in light of the Challenger accident, the lunar mission has come to seem a halcyon moment in the saga of U.S. engineering practice. "There was more spirit in that engineering group than any­thing that I have experienced before or after," said Benedict Gaylo, who managed the 250 G r u m m a n engineers charged with developing the LM's electronic systems and who has since worked on large military and nuclear plant engineering projects.

N o n e t h e l e s s , p r o b l e m s c o n t i n u e d throughout , with a fire killing three as­t ronauts in the Apollo 1 command mod­ule on a launch pad in 1967 and the explo­sion of an oxygen t a n k in t he service module in mid-flight during the Apollo 13 mission. The command module carried the three astronauts to lunar orbit and back and the service m o d u l e con ta ined the propulsion system.

Any further disasters may well have been prevented by the additional supervision of the National Aeronautics and Space Ad­ministration (NASA), instituted after the 1967 fire. Grumman, the LM's prime con-

During the Apollo 15 mission of July and August 1971, one man on the moon— James B. Irwin, pilot of LM-10—salutes another—-David R. Scott, mission com­mander, as Scott took the photograph. Be­hind Irwin, a lunar mountain called the Hadley Delta soars some 3400 meters. To the right of LM-10, also called Falcon, is the lunar roving vehicle with which Irwin and Scott explored the rim of the Hadley Rille, as well as the edges of craters and the slopes of the lunarApennine Mountains.

tractor, not only emerged unscathed from the many investigations into the Apollo 1 and 13 accidents—it even came out ahead, since the LM's propulsion and life support systems were what enabled the Apollo 13 crew to r e tu rn safely to ea r th . ( N o r t h American Aviation, in El Segundo, Calif., now part of Rockwell International Corp., was the prime contractor for the command and service modules.)

Even so, the LM's unknowns gave pause to even the most accomplished systems designers. So nerve-wracking were they, said Grumman ' s Gaylo, that one of his fondest memories of the entire program was watching the liftoff of the sixth and last lunar module to visit the moon's sur­face. Rober t Gi l ru th , w h o headed the J o h n s o n M a n n e d Spacecra f t Cente r , Houston, was also glad to see the program end. "You can't keep throwing sevens all

76 0018-9235/88/1100-0076$1.00©1988 IEEE IEEE SPECTRUM 25TH ANNIVERSARY

the t ime , " he said of the fact that no as­tronauts were killed in flight.

Green cheese or what? The moon itself was a good example of

what LM designers had to contend with. Theories about the lunar surface ranged far and wide. In Chariots for Apollo, (Atheneum, New York, 1985) a book about the making of the lunar module, Charles R. Pellegrino and Joshua Stoff wrote, "The planetary scientists u p at Cornel l were imagining all sorts of hostile things on the moon—traps in waiting—everything from molten lava to hidden ice, from deep dust to bug-infested craters (lunar ticks?), even ant imat ter ."

One imponderab le was whe ther the moon was firm enough to land on. Geo-physicist T h o m a s G o l d f rom C o r n e l l University, Ithaca, N.Y., deduced from the

polarization and direction of light reflected by the m o o n tha t virtually the entire sur­face was covered with dust. According to Gold, now a professor emeritus at Cornell, the press distorted his statements to sug­gest that the soft powder would engulf the a s t r o n a u t s — " . . . i t was d i s g u s t i n g , I couldn't get reporters to listen to what I sa id"—whereas his predict ions proved close to the reality: only a few inches of soft dust a top a sturdy, compacted layer of the same substance.

Gavin remembers th ings differently. From a corner office at G r u m m a n head­quarters, he gestured across the mammoth parking lot to Plant 5, where Gold told him over lunch that the module would sink 10 meters. He was reassured only when the unmanned Surveyor probe touched gently down without sinking.

Also on the project leaders' worry list

were fears that the module might land on a steep slope and tip over, stranding the as­t ronauts with no hope of rescue, and that dust stirred up by rocket exhausts might engulf the capsule. The L M never did keel over. But on one mission the astronauts could not see out of the LM windows for the last 50 feet before touchdown.

T h e G r u m m a n design t eam knew it could never answer many of its questions until the first mission. The LM, in fact, was a tall order for the then relatively minor player in the space industry. According to Gavin, what qualified Grumman to bid on the contract were the electronic systems at the heart of its A-6 attack plane and the E-2C early warning aircraft. The compa­ny had also been the main contractor for Orbiting Astronomical Observatories and canisters housing the balloons that were shot up in a rocket for the Echo II program.

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Stix—Moon lander 77

Radio waves were bounced off the reflect­ing balloons from one part of the earth to another.

Grumman did not get its first choice in the Apollo program. It lost out on a team bid for the command and service modules with General Electric Co. as the prime con­tractor. But in 1962, it won the $387 mil­lion L M contract, which brought it more than $2 billion by the program's end in the early 1970s—about a tenth of the total Apollo program cost. By then, 10 LMs had flown on Apollo missions, including six that set down on the moon.

In Grumman's favor was its advocacy of a plan first proposed by NASA engineer John C. Houbol t , in which a lunar lander would be launched from a craft circling the moon. Rejected approaches were clumsy, calling for a trajectory to the moon either directly from the earth, requiring an enor­mous rocket, or from earth orbit, with pay-loads launched by separate Saturn rock­ets for assembly on high.

The craft that won had three modules, the L M and the c o m m a n d and service modules, which split the design task into manageable units . NASA had only the sketchiest of ideas about what it wanted from Grumman , and most of them were set as ide . O n e ear ly p l a n h a d the as ­t ronauts , protected only by their space suits, descending to the moon on a flying platform. It was quickly discarded as in­compatible with an extended stay on the lunar surface.

A subsequent design proposal added a helicopter-like cockpit where astronauts would sit. This scheme, too, was rejected when Grumman and NASA engineers real­ized that seats were unnecessary with only one-sixth the earth's gravity.

In the end, two triangular windows were put in front of the astronauts ' faces to pro­vide them with a full field of vision. The design eventually consisted of a descent stage, used for descent propulsion from the command and service modules and as a launch platform from the moon's surface, plus an ascent stage, containing the crew compar tment and launch propulsion.

Systems engineering Getting from tha t preliminary agree­

ment to the moon in 1969 was a study in the principles of systems engineering, which "an awful lot of people talk about [but] no t many p r a c t i c e . . .wel l , " said Gavin.

To Grumman, systems engineering is the design of a design—a reversal of the natu­ral impulse to " run off and do things right away," said engineer Christopher (Chris) J. Witt , who led the team integrating the gu idance and con t ro l systems. Taking NASA-supplied data about the physical properties of the moon , the design team defined overall systems, subsystems, and test requirements and from this developed

actual design specifications. The direction of Grumman 's work flowed from a joint study defining the mission in which Grum­man, NASA, and Nor th American Avia­tion were participants.

Efficient management of the thousands of technical personnel involved was vital. Managers encouraged a team spirit by as­signing technicians and engineers to small groups. But "we didn't want any improvi­sa t ion ," said consultant Gavin. Any re­quest to deviate from a prescribed proce­dure had to be submitted in writing to a team of 20 project leaders, who approved it only after discussing how it might affect the system as a whole.

Clean-room conditions were strictly en­forced for fear that a human hair might clog the reaction control rockets that stabi­lized the craft or that dirt might fill the as­t ronauts ' compartment . Tools also were carefully checked lest any be left aboard to float about in flight.

As a result, with almost no exceptions, "those things we worried about didn't give us a problem," Gavin said. "The places we didn't worry about is where we ran into problems. " One example: there was no evi­dence in early tests of a potentially clog­ging residue in the liquid-glycol cooling system, so when the residue showed up, it seemed to appear out of nowhere.

The LM itself had to be treated with ex­traordinary care. Because it would be used in a vacuum and at low gravity, its struc­tural support could be, and in fact had to be, quite flimsy to meet NASA's weight res­trictions. The module's skin, only a few thousandths of an inch thick, had to be protected from accidental damage. "If you h a d a b o o t o n , you cou ld k ick r i g h t through i t , " said Thomas (Tom) J. Kelly, the L M program engineering manager. An outer guard protected the module from micrometeoroids whizzing through space.

Also, astronauts came visiting Grum­man as much as possible, said Gavin, to remind the G r u m m a n crew "whose neck we were protect ing."

No stone unturned Every conceivable problem had to be

considered, and even so, it was impossible to foresee every eventuality. Grumman pre­pared as best it could by simulating some 500 types of landing. The severest case postulated the craft landing on an icy hill, sliding down and hitting a surface like a curbstone.

Several kinds of simulation were tried. A free-flying platform that simulated the one-sixth gravity of the lunar surface was built and tested by NASA. Kelly described it as a bedstead with turbojets, which often flew around crazily and once almost in­jured someone.

A more successful simulator, built by G r u m m a n to teach manual landing tech­niques, was based on an infinity-optics sys­

tem. It allowed the astronauts to watch a television picture of a three-dimensional papier-maché model of the moon's surface a n d obse rve how it c h a n g e d as they manipula ted simulated LM controls— actually a scanning optical head moving on Χ-, Y-, and Z-axes over the model.

Worries about the lunar surface turned out to be groundless but led to overdesign of the landing gear. It included pads 37 inches (94 centimeters) in diameter and legs flexible enough to "give" up to 30 in. on impact. The craft could land on a surface with 24-in. depressions or protruberances. As planned, the Apollo II LM landed at a vertical velocity of less than 2 feet (60 cm) per second. "The astronauts set down like a crate of eggs ," said Kelly.

The care taken in designing the LM was also due to the 1967 death of three as­tronauts trapped in the Apollo 1 command modu le while per forming tests on the launch pad . After a NASA-supervised board concluded that Nor th American Aviation's program was deficient in "de­sign and engineering, manufacture and qual i ty c o n t r o l , " every contractor was forced to revamp its electric systems, ad­ding considerably to its costs and 12 to 18 months to its manufacturing time, though the t ab was picked up by N A S A . For Grumman, the $25 million extra covered, a m o n g o ther th ings , equipping circuit breakers with flame-proof bags or coating them with " m u d , " a kind of fire-resistant synthetic rubber. Much of the wiring had to be ripped out because it was not self-extinguishing in pure oxygen. To test the new measures, a mock-up of the module was set on fire.

Grumman had its share of difficulties. The first manned earth orbital mission to include a LM had to be replaced by another Apollo orbital mission, because the first module delivered to Cape Kennedy had leaks in the propulsion system, which had to be rectified with new seals. "The equip­ment had not matured," said Rocco A. Pé­trone, then NASA's director of launch operations at Cape Kennedy and now at Rockwell International as vice president, systems safety. Also, Pétrone termed the Grumman engineers who accompanied the modu les " r o o k i e s , " unaccus tomed to working in the team setting of manned space projects, though they quickly adapt­ed. Moreover, the LM adapter, the section of the boost vehicle that encapsulated the LM, left "very little room in which people could work , " said Pétrone.

Gaylo and his engineers had to jettison their knowledge of conventional aircraft design. At the time, most aircraft electronic systems were an afterthought, stuffed in among preexisting structures. The L M re­quired a different approach. There was no air to cool electrical and electronic sub­systems, and a liquid-glycol loop was used instead. Since conventional aircraft design

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considerations were not of concern, most L M electronic systems were designed to fit into an equipment rack, cutting down on weight, volume, and cable lengths needed because packaging was centralized [Fig. 1].

Each electronic unit, including commu­nicat ions , caut ion and warning instru­ments, and batteries, was lined up vertical­ly like a slice of bread in a loaf and attached on either side to a cold plate that circulat­ed the glycol. "The standardized electron­ics packag ing was car r ied back to the G r u m m a n aircraft p rog rams after the Apollo program ended ," said Gaylo.

A plethora of subcontractors Grumman contracted out more than 100

of the vehicle's subsystems, so "we got into all kinds of things an aerospace company normally doesn't get involved with ," Kelly said. Grumman project engineers would probe into why something malfunctioned until they reached the limits of a subcon­tractor's knowledge. For instance, it was feared that the liquid-glycol cooling sys­tem's residue could eventually block cool­ing passages. "We got into chemical analy­sis of the antifreeze and chemicals used, and we were asking questions they couldn't a n s w e r , " said Kelly. The invest igat ion eventually found that the problem result­ed from substituting one rust-inhibiting additive for another.

G r u m m a n also leaned on electronics subcontractors to discover a cure for the "purple p lague , " a blackish-purplish in-termetalhc compound that formed where gold leads were attached to a silicon tran­sistor when pressure or temperature was ex­cessive. It made contacts brittle but proved eradicable when the amoun t of each ele­m e n t was precisely con t ro l l ed d u r i n g manufacture. To engineer Witt , a signifi­cant spinoff from the entire program was the understanding gained of the chemis­try of different materials ' interactions.

Some subcontractors took quality goals really to heart , Kelly said. A case in point was the t i tanium fuel tanks for the ascent stage manufactured by Aerojet General Corp. , Sacramento, Calif. Heat-treating one tank gave it an unexpectedly bluish tinge, for no discoverable reason. Other­wise the tanks functioned according to specification. But Kelly remembers a top c o m p a n y official tell ing h im: " I f th is thing's going to the moon, I don't want my name on i t , " and a new set of tanks that did not change color was manufactured.

The LM project emphasized redundan­cy. Every subsystem possible had a back­up, often a complete system that was never used—or not for its original purpose. For instance, the secondary guidance system for getting the L M back to the command modu le was used only on the abort ive Apol lo 13 mission.

In some cases, backups were not possi­ble. To keep weight down, the modu le

could have only one ascent engine. "A seri­ous [fuel] leak, and the astronauts wouldn't have been able to get off the m o o n , " said Kelly. Said NASA's Pétrone, "If it didn't light it would have been all over. " For that reason, the ascent batteries were checked periodically during descent. Any failure would have meant aborting the descent and returning the LM to the command mod­ule using power from the descent batter­ies [Fig. 2]. The G r u m m a n project team accordingly decided that they had to un­derstand everything about the ascent en­gine. There was to be no experimenting with new system designs, complexity was to be avoided to ease testing, and engine components such as fuel valves were made redundant wherever possible.

Anxiety over the ascent engine was so acute that Grumman added a subcontrac­tor in mid-design. The prototype from Bell Aerosystems Co., Buffalo, N.Y., the origi­nal subcontractor, failed a key test. Known as the bomb test, it checked on a source of combust ion instability great enough to have exploded some early Titan rockets on ignition tests. The b o m b test injected a pressure pulse into the engine's combustion chamber while it was operat ing. If the pulse disappeared after a given number of engine cycles, the pressure spikes tha t might cause the engine to explode would be avoided.

The Bell engine never malfunctioned, but the threatening pulse remained, and "we s tar ted to get concerned t h a t the schedule might be affected," said Kelly. An alternate design competition was held and Nor th American's Rocketdyne Division, Canoga Park, Calif., won the contract for an alternate fuel injector, though Bell con­t inued as contractor for the rest of the rocket engine. " I don' t think the Bell peo­ple ever felt satisfied with the way things came o u t , " Kelly added.

The LM saves lives One backup measure ended up saving

the lives of the three Apollo 13 astronauts in April 1970. NASA had the original LM design modified in the early 1960s to func­t ion as a backup for a disabled command module. The modifications gave the LM slightly more electrical capacity, water, and oxygen. When an electrical short caused the explosion of an oxygen tank in the ser­vice module early in the Apollo 13 mission, the astronauts took refuge in the L M and used its propulsion system to push them around the m o o n and back to the borders of the earth's atmosphere. The three then recharged the command module's entry batteries from the LM's power before jet­tisoning the L M and returning to the com­mand module for the trip home through t h e a t m o s p h e r e . Jok ing ly , G r u m m a n presented North American with an invoice for a towing charge. " I 'm not sure it's ever been p a i d , " said Pétrone, who went to

work for Rockwell International after leav­ing NASA.

Although the LM never experienced any disaster as large, the existence of a back­up team of experts in Hous ton and Beth-page helped solve some minor in-flight p rob l ems . O n one miss ion , the a b o r t switch started making contacts randomly. G r u m m a n engineers surmised that a sol­der ball had come loose and might cut the mission short if it hit the proper contacts. They cal led engineers f rom the M a s ­sachusetts Institute of Technology in Cam­bridge with whom they had worked, and devised a software fix allowing the switch inputs to be ignored. The astronauts then keyed the data in manually on the craft, finishing just minutes before the module vanished behind the m o o n , cutt ing off communications.

There were comic moments , too. LM water levels dropped more than expected, and it took several missions to discover why. The command module used chlorine to eliminate bacteria in its water supply, the LM used iodine. Said Gaylo, "One of the astronauts casually commented that the LM water tasted much better than the com­mand module water. Because of the iodine, it tasted like a little scotch was added . "

O n one mission, the LM, left in lunar orbit once the astronauts returned to the command module, failed to respond to a radioed command to descend to the moon said Gaylo. A seismic transducer left by the astronauts was to measure the LM's im­pac t on landing to help de te rmine the structure of moon rocks. Later, Grumman learned that one of the astronauts had un­screwed a hand controller as a souvenir, deactivating the circuitry involved.

Television was key to the space program's popularity, then and now. On one mission, astronauts were unable to unfold an anten­n a tha t sent television pictures back to earth. The event was viewed as so serious that after the mission, Gaylo, as manager of G r u m m a n ' s electronic systems, was given a "one-way ticket" to fly to the Bel­mont , Calif., manufacturing facility of an­tenna maker Dalmo Victor, and told to stay there until the system was fixed.

Spinoffs The attention to detail that marked the

lunar module's construction led to testing measures that Grumman was later to apply to flight-testing airplanes and to the qual­ity control of airplane design and subcom­ponents . These included real-time testing of airplanes in the form of an automated telemetry station that allowed the test team to see what was happening during a test flight. The use of this station shortened the flight-test development of Grumman's F-14 fighter by a year, said Kelly.

Some of the design procedures then de­veloped were adopted by private industry or have been incorporated into Depart-

80 IEEE SPECTRUM 25TH ANNIVERSARY

ment of Defense specifications, and the program also influenced the development of better computer programming and fly-by-wire technology.

Asked if he would do things differently today, Kelly said today's computer technol­ogy would have made it easier to meet NASA weight specifications. "We could have made out like a bandi t with fiber op­tics and a data-bus system architecture," he sa id . M i c r o p r o c e s s o r s c o u l d have processed the da ta in subsystems and sta­tus information, and a few flat-panel dis­plays wi th co lo r g raph ic s cou ld have replaced the multitude of gauges, warning lines, and tape displays. Moreover, the 160 circuit breakers could have been simplified with a multiplexed, solid-state switched electric power distr ibution system. One m a j o r difference today, sa id Pé t rone , would be backup propulsion systems for the ascent engine.

Nonetheless, " the basic L M configura­tion and general arrangement was primar­ily mission dependent, rather than state-of-the-art dependent, and therefore would remain essentially unchanged," comment­ed Kelly in a 1981 presentation before the American Institute of Aeronautics and As­tronautics, New York City.

Following the L M project, Grumman ' s star plummeted when it lost ou t as the shuttle's prime contractor to Rockwell and o t h e r s . T h e event was p r o f o u n d l y demoralizing for the company, and en­gineer Wi t t still l aments t he 100-hour weeks leading u p to the submission of the proposal.

Apollo vs. the Shuttle Seven days a week, 12 to 13 hours a day

and sometimes more was the normal work­ing pace during the L M development. All the while, a sense of mission prevailed. Yet, says Gavin in looking back, the United States failed to build on its achievements in going to the moon . "The Apol lo pro­gram had far more impact overseas than it did at h o m e , " Gavin said. " U p until five or six years ago, there was a feeling of tech­nological inferiority in Europe and Japan. That has been evaporating. I don' t think America understands t h a t . "

The contrast between the NASA of the mid-1960s and today's agency proved dis­turbing to some G r u m m a n veterans, who remember when NASA demanded detailed explanations for such trifles as a capaci­tor put in backwards. They also question NASA's decision-making these days. Of the chill temperatures on the day of the Challenger flight, Gavin said, "If we had been concerned about the temperature at the t ime of launch, I can ' t imagine we would have l aunched . " Kelly, however, viewed the Challenger catastrophe more philosophically. These were ambitious mis­sions, he said, and " I 'm not surprised they finally had a disaster.. . .We were fortunate

we didn ' t . . . " Apollo never felt routine, as the shuttle program began to. Pétrone said that one of his chief tasks as manager of the Apollo program, a title he took on after serving as Cape Kennedy launch director, was to ensure that workers did not become complacent. "This bird doesn't know that the other one flew," is what he told his subordinates on later Apol lo missions.

One of the major distinctions between t h e t w o p r o g r a m s was t h e a m o u n t of money available. "Apollo had the luxury of almost a blank check. The space shut­tle was underbudgeted from the start and

stayed that way ," said John M. Logsdon, director of the Space Policy Institute at George Washington University, in Wash­ington , D.C. Logsdon also said N A S A supervision of Apol lo contractors was much closer.

Those who work at Grumman , which is still a NASA contractor, continue to de­fend a role for manned space flight for such missions as low-gravity materials manufacturing, which will need to con­tinue to be resupplied by manned missions. Fred W. Haise, one of the ill-starred Apollo 13's as t ronauts and now president of a

Electric-control

[2] The lunar module's electrical power subsystem consisted of four silver-zinc descent batteries, which supplied power to the LMfrom 30 minutes before separation from the command module until ascent from the moon; two electric control assemblies for the descent that regulated voltage; a scientific-equipment power outlet for connection of such gear as seis­mic measuring devices; two silver-zinc ascent batteries, which were used from ascent to docking and, if a mission had been aborted before the moon landing, would have been used to separate the descent stage, Fail­ure of an ascent battery would have required the mission to be aborted during descent. Also shown are two electric control assemblies for the ascent; a lighting control assembly; a dead-face relay, which removed power from any wires Unking the ascent with the descent stage before liftoff; buses that channeled power for the system electronics; two in­verters for dc-to-ac conversion; umbilical connectors to the command module and descent stage; and a cabin-lighting control assembly

Stix—Moon lander 81

Grumman division that is managing the systems engineering and integration for a U.S. space station for NASA, says that ac­cidents can occur with any type of tech­nology from cars to airplanes. " N o one is

1972

DIGITAL SCOPES

Analog-to-digital converters and memories turned a venerable instru­

ment into a remarkable new tool

out to shut down the airlines," he quipped. Despite recent setbacks, some of those

involved in Apollo believe that continuing manned spaceflight is essential for the United States. It lets us "dream that God

Precursors to the analog-to-digital con­version technology in digital scopes ap­peared in the transient recorders of the late 1960s. They were the only instruments able to store permanently a nonrepetitive sig­nal, such as a pressure wave following an explosion, but they were expensive, had low bandwidths (a few kilohertz), and were harder to use than oscilloscopes.

A transient recorder stored a signal with great precision, then recorded it on an x-y plotter or, if hooked up to a cathode-ray tube, displayed it on the screen. But the in­strument lacked the scope's most useful feature—the ability to display a signal as it occurs.

I t was n o t l o n g be fo re i n s t r u m e n t designers had the idea of combining tran­sient recorders and scopes. In 1970, Bio-mation Inc., now a division of Gould Elec­tronics Inc., Cupertino, Calif., introduced its 610 transient recorder, which is consid­ered by some to be the first digital scope, even though it lacked a CRT. When the in­strument 's output was fed to the input of an ordinary analog scope, the combination pe r fo rmed jus t like an ana log storage scope. The analog-to-digital converter al­lowed digitizing at an impressive 10 mil­lion samples a second (10 Msamples/s), al­though it converted voltages to only 6 bits, resolving to one par t in 64 or less than 2 percent of full scale.

Besides not having an integral CRT, the 610 lacked the feature that helped digital scopes revolutionize instrumentation: an operator can watch the live signal on a dig­ital scope and save any port ion of it, in­cluding that preceding the display, at the push of a but ton.

Why not digital? Until Schumann's development, Nico-

let had never marketed an oscilloscope, confining itself to biomedical and chemi­cal instrumentation. Schumann hoped to learn something himself from helping out with Jole's project. A n experienced ana­log circuit designer, he decided to tackle building an analog scope. But he soon be­came disheartened, realizing just how dif­ficult it was to design triggered sweep cir­cuits for horizontal deflection on the CRT.

The challenge lay in keeping the circuits linear over a wide range of sweep speeds. "It probably would have taken a month of experimenting to come up with something reasonable ," he says. Good analog sweep circuits were developed by other compa­nies, principally Tektronix, over 40 years. Schumann did not even consider copying circuits from a Tektronix manual. He want-

didn't intend us to be locked into this one p lace ," said Pétrone. And Kelly believes that scrapping manned flights would be "like asking Co lumbus : 'Wha t do you want to go over there for? ' " •

ed more of a challenge. Nicolet's digital signal averagers inspired

Schumann to use digital rather than ana­log sweep circuits and to add digital mem­ory. Signal averagers store a number of passes of a repetitive signal, as specified by the user, and average them to cancel noise. Having noticed that some Nicolet cus tomers want ing to view single-pass waveforms of nonrepetitive signals set the number of averages to one, Schumann saw the market potential of a digital scope.

There were other compelling reasons to go digital. The precision of analog scopes depends on the operator pinpointing vol­tages and time intervals by eyeballing a relatively fat trace on the tube's grid. The screen's height is typically 200 times the trace thickness, which translates to a max­imum resolut ion of 1/200, or only 0.5 percent.

Moreover, analog scopes with storage capability were awkward to use. Some tech­niques held the trace on the CRT for only seconds or minutes; others stored one sig­nal indefinitely. But a permanent , off­screen record was to be had only by pho­tographing the screen—an unreliable and expensive practice.

While digital scopes could conceivably eliminate many of the shortcomings of their analog counterparts, there seemed lit­tle chance they would ever match their speed. Analog scope bandwidths were sel­dom less than 1 megahertz , with some going to 200 M H z or beyond.

In theory, a digital instrument can pick up at most the Nyquist frequency, equal to half its sample rate. In practice, the sig­nal 's bandwid th may have to be much lower than the Nyquist frequency, but in the 1970s manufacturers usually specified bandwidth at half the sample rate.

Inexpensive, low-precision digital sweep circuits, consisting of a counter and an analog-to-digital converter, were respect­ably fast, sampling data points at about 1 Msamples/s for a bandwidth of 500 kilo-hertz. Higher-end converters with 12-bit resolution, however, cost about $1000 and had a bandwidth of only 50 kHz.

But Schumann was encouraged by ever faster analog-to-digital converters, with speeds doubling roughly every two years. He figured that for a competitive product, he would need a digitizing rate of at least 200 000 samples per second (200 ksam-ples/s) in a 12-bit converter in the $300 price range.

He broached the idea of a digital scope to Donald Haselhorst, Nicolet's president and other founder, who immediately en-

The genesis of what many consider the first true digital oscilloscope was a high-school electronics project assigned to Jole Shack-leford in 1970. Joie, a 15-year-old electron­ics enthusiast, wanted a challenge, and sug­gested collaborating with his stepfather, Robert Schumann, cofounder and then vice pres ident of Nicolet I n s t rumen t s Corp. , Madison, Wis. Schumann agreed, never dreaming that the project would lead to a revolutionary new product for Nicolet.

So revolutionary, that Nicolet at first had a hard time getting customers to see its advantages. Even the leading instru­ment makers—Tektronix Inc., Beaverton, Ore., and Hewlett-Packard Co., Palo Alto, Calif.—took a while to come around to digital technology.

But today, while analog scope sales are slightly declining, digital sales are overtak­ing them and are expected to be double the analog rate by 1992, according to Pr ime Data , a San Jose, Calif., market ing re­search firm. In 1983, H P gave up its ana­log line entirely to concentrate on digital scopes. It is now recognized that for many applications digital scopes are easier to use and more precise than the analog kind; of prime benefit is an ability to store data in memory for later viewing or analysis.

But pinpointing the first digital scope is no easy task, and a mild controversy still smolders over the issue. "I t is a little bit like trying to find the missing l ink," says Luis Navarro, engineering manager of Tek-t r o n i x ' s m e a s u r e m e n t a n d a c c e s s o r y products division. The bulk of the evidence points to the Nicolet product, al though other companies had pieces of the puzzle. With ease of use heading its priorities, Nicolet made breakthroughs that in retro­spect seem obvious, but in the early 1970s, the innovations worked synergistically to hatch a new species of instrument.

Karen Fitzgerald Associate Editor

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