By today's standards, it was an unpretentious little satellite - 80.75 inches long, 6 inches in diameter, with a mass of 31 pounds. Most of this was the burned-out fourth stage of the Juno 1 launching rocket. The 18.13-pound payload was equipped to measure temperatures, micrometeoroid impacts, and cosmic rays. The designers, who produced this modest contraption in just under three months, would have considered a modern pocket calculator a marvel from another world.
Yet when Explorer 1 - the first US Earth satellite - went into orbit 25 years ago, it helped restore the confidence of a nation.
A few months earlier, the Soviet Union had electrified the world with the launch of two Sputniks, the second of which carried the dog Laika. Then the US Vanguard satellite earned the nickname ''Dudnik'' when its first rocket blew up on launching Dec. 6, l957. As though to rub in the failure, the Vanguard satellite itself, having been thrown clear, rolled across the ground with its radio beacon plaintively beeping its location.
There were humiliation, confusion, and self-doubt throughout the United States.
Then, at 10:45 p.m. Eastern standard time on Jan. 31, 1958, Wernher von Braun and his team of German rocket engineers did what they had for years been saying they could do. Adding an extra stage to an Army rocket, they launched a satellite into orbit. A decade and a half earlier, with their V-2 ''vengeance weapons'' pounding London, these men had been ''the enemy.'' Now they were national heroes.
There was wild celebration in the military and civilian communication centers that monitored the launching. Army Secretary Wilbur Brucker, in a giddy moment, established the Concatenated Fraternity of Master Missileers, Circa 1958, Pentagon Chapter. All involved received personalized, signed certificates of that order. Within a year, Dr. von Braun had also received the highest civil-service award, the Distinguished Federal Service Medal.
Thus, Explorer 1 was more than a technological triumph. It symbolized the emergence of a new determination in a country that, having been knocked off its feet, was picking itself up, preparing to run what it perceived to be a long-term race.
The US scientific and technological enterprise, suffering from neglect and niggardly funding, was about to undergo a renaissance. There was sudden recognition that poor high-school science and mathematics education undercut the fundamental strength of that enterprise. Here, too, vigorous remedial action would soon be taken at both the national and local levels.
In short, the US faced the fact that it had not been upstaged by ''superior'' Soviet technology so much as it had let itself down. With that recognition came the effort which later made the country preeminent in space.
The US had indeed been caught napping when the Soviet Sputnik 1 went into orbit Oct. 4, 1957. In spite of clear warnings, most government officials, much of the press, and almost all of the general public were genuinely astounded to learn that what they had ignorantly considered a technologically backward adversary had propelled the world into the space age.
Von Braun and his associates were neither astounded nor depressed. They were disappointed that the US was not the first into space, as they knew it could have been. Yet they recognized the event for what it was - the opening of a new dimension for human achievement. ''Today, man has taken his first step toward Mars,'' von Braun observed.
The news of Sputnik 1 came during a visit of Washington brass to the Army's Redstone Arsenal in Huntsville, Ala. (later the George C. Marshall Space Flight Center) where von Braun worked. Maj. Gen. John B. Medaris, commander of the US Army Ballistic Missile Agency, and von Braun immediately offered their unit's previously rejected services as satellite launchers. Von Braun told Secretary of Defense Neil McElroy, ''When you get back to Washington and all hell breaks loose, tell them we've got the hardware down here to put up a satellite anytime.''
This was no mere bravado. Von Braun based his confidence on thorough technical studies previously carried out and on rockets that, unlike the Vanguard vehicle, were already well tested.
One can only speculate as to when a satellite might first have orbited. Postwar studies by the Army and Navy had concluded this could probably be done in the late 1940s or early '50s.
For example, studies completed in 1946 by the group that later became the Rand Corporation considered a launch date as early as 1951 to be feasible. These foresaw communications, spy, and weather satellites. A Rand report noted prophetically that ''achievement of a satellite craft by the United States would inflame the imagination of mankind, and would probably produce repercussions in the world comparable to the explosion of the atomic bomb.''
Significantly, and largely ignored in the West, the Soviets appear to have been thinking along similar lines. Six years before Sputnik, on Oct. 4, 1951, rocket engineer M.K. Tikhonravov said publicly that the USSR was capable of launching satellites. Later, on Nov. 27, 1953, academician Alexander N. Nesmeyanov told a World Peace Council session in Vienna that ''science has reached such a stage that . . . the creation of an artificial satellite of the Earth is a real possibility.''
Meanwhile, in the US, the early satellite studies were shelved, partly because of cost. However, a little-known private study in Britain, published in 1951, would later help reopen US thinking. In this study, British Interplanetary Society members Alan Dixon, Kenneth Gatland, and Anthony Kunesch showed how to cut the scale and cost of satellite launching.
So, too, did a 1953 study by University of Maryland physicist S. Fred Singer. He explored the possibilities of a small, 100-pound satellite called MOUSE (Minimum Orbital Unmanned Satellite of the Earth). This prompted science-fiction writer Arthur C. Clarke to cable Dr. Singer: ''May the MOUSE become a mountain!''
Meanwhile, von Braun's team had begun to build the capacity for launching satellites as it developed Army missiles. The time seemed ripe to reopen the question.
So thought Frederick C. Durant III when he arranged a meeting of rocket experts, including von Braun, at the Office of Naval Research (ONR) in the summer of 1954. President of the International Astronautical Federation and a former American Rocket Society president, Mr. Durant had the wide-ranging influence that enabled him to be a catalyst at this critical juncture. He also kept the Monitor's science editor briefed on these developments to the extent that official secrecy, liberally interpreted, allowed.
The upshot was a detailed program called Project Orbiter, which eventually led to Explorer 1. Summarizing this in a secret memo Sept. 15, von Braun said a small satellite could be orbited ''within a few years'' using technology ''available now.'' He added, again prophetically, ''It would be a blow to US prestige if we did not do it first.''
Meanwhile, unaware of the secret Orbiter planning, a committee of the International Geophysical Year also was thinking satellites. IGY was to be a comprehensive study of the Earth carried out by many nations that would start in 1957. On Oct 4, 1954, three years before Sputnik, this committee asked ''that thought be given to the launching of small (scientific) satellites. . . .'' Both the US and the USSR, which were heavily committed to IGY, announced satellite programs.
Orbiter planners assumed their project would be the obvious US choice. But to their chagrin, the US picked Vanguard, a competing ONR project that would rely on technology less developed than that of von Braun.
Orbiter was canceled. To make matters worse, from von Braun's point of view, the Army was later restricted to develop only missiles with ranges under 200 miles. This grounded the longer-range rockets he had developed and which could have been the basis for satellite launchers.
Feelings ran high. Inspectors were sent to Cape Canaveral to make sure the Huntsville group didn't pull ''a fast one.'' They checked to see if a fourth stage had been added to two of the longer-range rockets stored at the cape - a stage that would have allowed an object ''accidentally'' to be put in orbit.
This is how matters stood as the IGY began. Sputnik should have been no surprise. Soviet experts publicly said a satellite would be launched soon. Privately, they emphasized this to experts such as Frederick Durant. But the US chose not to listen.
Backed by the Orbiter planning and with two rockets virtually at the ready, von Braun moved quickly when the (ultimately successful) Vanguard rocket failed. All that was needed was the Explorer 1 payload. William H. Pickering, director of the Jet Propulsion Laboratory in Pasadena, Calif., assembled a ''tiger team'' that worked around the clock to produce the satellite. State University of Iowa physicist James A. Van Allen and his graduate student Wei Ching Lin supplied cosmic ray counters that turned out to be crucially important.
Explorer 1 went into an elliptical orbit with a perigee 224 miles above Earth's surface and an apogee 1,575 miles high. As it went through the high point, the cosmic ray counters died. Dr. Van Allen concluded the sensors were saturated. He had discovered the now famous Van Allen radiation belts. These are regions high above the atmosphere filled with electrically charged particles trapped by Earth's magnetic field. Scientists had not suspected their existence. It was the first big scientific payoff of satellite research and one of the major discoveries of the IGY.
As the space age unfolded, the vision of that 1946 Rand study was rapidly fulfilled. TIROS 1, the first weather satellite, went into orbit April 1, 1960. Telstar 1, the first satellite to link two continents by television, was orbited July 10, 1962. The public, however, was far more conscious of its predecessor communications satellite: Echo 1. Orbited Aug. 12, 1960, Echo was a large, aluminized balloon that acted as a radio mirror and quickly became the brightest , most widely recognized satellite in the sky.
There were military satellites, too. The US Navy's first Transit navigation satellite went up April 13, 1960. The first Air Force Midas satellite reached orbit shortly afterward on May 24. It watched for the infrared (heat) signature of long-range missile launches.
As the US moved rapidly into the space age, its technological confidence returned. It went on to put men on the moon and bring closeup views of remote planets to millions of living rooms.
Now, a quarter century after Explorer 1, an American president again warns of technological lag. Again he decries a dangerous decline in high-school science and math teaching. And again, policymakers wonder what they should do to maintain the nation's strength.
If von Braun were still with us, he would have no doubt as to what course to recommend. He would be stalking the corridors of power asking insistently, ''When are we going to Mars?''