Hydrogen is the most common kind of normal matter in the universe. Perhaps the universe is trying to tell us something, for the most common chemical element makes an excellent energetic rocket fuel. That does not mean, however, that it is easy to manage.
Odorless and colorless hydrogen gas becomes liquid, and thus dense enough to pour into rocket tanks, only by cooling it to a temperature of of minus 253° Celsius (C) or less. At that temperature, hydrogen causes almost any material to crack at a microscopic level; this means that liquid hydrogen can damage components in rocket engines, some of which – for example, spinning turbines – operate under great stress even at room temperature. Hydrogen also gradually escapes as a gas from almost any tank, potentially creating a fire and explosion hazard.
In the late 1950s, the U.S. Air Force and NASA contracted with the Convair Division of General Dynamics, makers of the Atlas missile, to build the Centaur, the world’s first hydrogen/oxygen rocket stage. By 1960, the dual-engine Centaur had become central to planned U.S. robotic lunar and planetary programs such as Mariner and Surveyor. It also became a propulsion development test-bed for large hydrogen-fueled Saturn and Nova rockets. After President John F. Kennedy’s 25 May 1961 “moon speech” before Congress, Centaur development became a pacing item in the U.S. piloted lunar program.
Development of Centaur did not, however, proceed as smoothly as was hoped. In January 1961, Pratt & Whitney, developers of Centaur’s twin RL-10 engines, stopped testing after repeated engine test-stand explosions. In early February 1961, NASA and contractor officials met at NASA Headquarters in an urgent effort to sort out Centaur’s problems.
On either side of the Centaur meeting, the Soviet Union launched Venus flyby probes from Baikonur Cosmodrome in Central Asia. The first, launched on 4 February 1961, was designated “Heavy Sputnik” to hide its true nature after its upper stage failed to boost it from low-Earth orbit. The second, designated Venera 1, lifted off and left Earth orbit as planned on 12 February 1961. The 644-kilogram probe subsequently failed to make a scheduled transmission to Earth; the precise date of the communication failure remains unclear, though in March 1961 the Soviet news service TASS dated it to February 27 and most sources now agree that it took place between 17 and 22 February. In May-June 1961, in collaboration with Soviet scientists, the Jodrell Bank radio observatory in Britain unsuccessfully sought signals from Venera 1 as it was due to fly by Venus.
Opportunities for Earth-Venus transfers occur every 19 months. Both U.S. and Soviet engineers meant to launch Venus probes during the next Earth-Venus opportunity, which would span from 18 July to 12 September 1962. In the U.S., the Jet Propulsion Laboratory (JPL) continued work on the roughly 500-kilogram Mariner-A flyby probe it hoped could be dispatched to Venus on an Atlas-Centaur rocket.
Centaur, meanwhile, suffered more setbacks. In August 1961, NASA tasked JPL with examining whether it could launch a Venus probe on an Atlas-Agena B rocket during the July-September Earth-Venus transfer opportunity. The Agena upper stage, which burned hypergolic (ignite-on-contact) propellants, had first flown successfully in May 1960. NASA had tapped Atlas-Agena B to launch the Ranger probes, the first of which – Ranger 1, a Block I design intended to gather data on cislunar space – left Earth on 23 August 1961.
The Atlas-Agena B was not as powerful as Atlas-Centaur was planned to be, so the 1962 Venus Mariners could weigh no more than about 200 kilograms each, or less than half as much as the Mariner-A design. Atlas-Agena B had its share of reliability problems: Ranger 1 became stranded in low-Earth orbit after its Agena B refused to ignite a second time.
After a study lasting barely three weeks, JPL engineers told NASA that a lightweight Venus probe could indeed be made ready for the July-September 1962 Earth-Venus transfer opportunity. To save time, they based their probe design on Block I Ranger. The Pasadena, California lab dubbed its makeshift interplanetary spacecraft Mariner-R. NASA approved JPL’s design and, on 28 September 1961, told the world that it would launch a flyby Mariner to Venus in the July-September 1962 period atop an Atlas-Agena B rocket.
The major goal of the Mariner-Venus 1962 mission would be to scan the planet using a a pair of radiometers to try to settle the contentious question of Venus’s surface and atmosphere temperatures. The spacecraft would include no camera; most scientists thought it unlikely that it could glimpse the planet’s surface through the thick Venusian clouds. At its extremely low transmission rate – just 8.3 bits per second – the spacecraft would need weeks to stream even a few images back to Earth.
JPL built the Mariner-R spacecraft against a backdrop of high-profile failures in the Ranger program. On 20 November 1961, in a near-repeat of the Ranger 1 experience, Ranger 2’s Agena B stranded it in low-Earth orbit. On 31 December 1961, NASA announced that it would launch twin Mariners to Venus to help to ensure mission success. On 26 January 1962, Ranger 3, a Block II design intended to deposit a spherical balsa-cushioned capsule on the lunar surface, missed the moon by about 37,000 kilometers after a series of malfunctions and errors during launch and Earth-orbit departure. Ranger 4 struck the moon on 26 April 1962, becoming the first U.S. spacecraft to touch another world; it returned no data, however, because it failed to deploy its electricity-generating solar arrays and ran down its batteries soon after launch.
On 22 July 1962, Mariner 1 stood ready in pre-dawn darkness atop its Atlas-Agena B launcher at Launch Complex 12 on Florida’s Cape Canaveral. The Atlas lit up its engines and began to climb. The rocket soon began to maneuver strangely. A little less than five minutes into the Mariner 1 mission, with just six seconds to go before the spacecraft would separate from the Atlas atop its Agena B stage, the Range Safety Officer pressed the destruct button. Mariner 1 emerged from the explosion fireball largely intact and transmitted until it splashed into the Atlantic Ocean 64 seconds later. The malfunction was quickly traced to a self-reinforcing combination of a single missed symbol in the rocket’s guidance computer code and poor communication between rocket and ground.
Mariner 2 lifted off from Pad 12 on 27 August 1962. Its Atlas-Agena B rocket performed as planned. Immediately after the Agena B stage shut down for the second time, 211-kilogram Mariner 2 separated, hinged open its twin solar arrays, and, using 10 nitrogen-propellant attitude-control thrusters, pointed them at the Sun. The Agena B, meanwhile, turned 140° and slowed itself by venting unused propellant so that it would not follow Mariner 2 to Venus. A week later, the spacecraft pointed its dish-shaped high-gain antenna at Earth.
Meanwhile, in Central Asia, Soviet engineers readied three 1962 Venus probes. The first, launched 25 August, and the second, launched 1 September, were designed to release spherical capsules that would enter the Venusian atmosphere and, it was hoped, survive to touch down on the planet’s surface. Upper-stage failures meant that neither left low-Earth orbit. The first burned up in Earth’s atmosphere the day after Mariner 2 left Earth; the second met the same fate on 5 September, two days after Mariner 2’s high-gain antenna locked on Earth. The third, a flyby Venera, was launched on 12 September at the close of the 1962 Earth-Venus transfer opportunity. Its launch vehicle exploded, destroying it.
Mariner 2 thus became the only survivor of five Venus mission attempts of 1962. As the 4.9-meter-wide, 3.7-meter-tall spacecraft fell Sunward toward its rendezvous with Venus, it alternated between sending to Earth engineering data describing its state of health and science data describing conditions in the interplanetary void. For example, a dust detector registered a single impact during the Mariner 2 mission; engineers planning future interplanetary missions breathed a sigh of relief, for this indicated that spacecraft could expect fewer potentially damaging micrometeoroid strikes than previously calculated.
Mariner 2 also encountered a solar flare on 23 October 1962. An ionization chamber and a Geiger counter monitored the flare’s onset, peak, and gradual decline over a period of days. Though scientists admitted that they would need much more data in order to determine the effects of solar flares on piloted interplanetary vessels, their initial assessment was that solar activity would be less of a threat than had been anticipated.
With the voyage of Mariner 2 well underway, the scientific debate over what it might find at Venus reached a new intensity. Measurements made from Earth had indicated that its surface temperature reached at least 342° C, yet the temperature in its atmosphere was a frosty minus 39° C. The atmosphere almost certainly contained carbon dioxide; the jury was still out with regards to the presence of Venusian oxygen and water vapor.
Young professor Carl Sagan, a member of the atmosphere radiometer instrument team, contended that Venus was an inferno, with carbon dioxide gas in its atmosphere acting like the glass of a greenhouse. Others explained away the temperature measurements by invoking a Venusian ionosphere dense with electrons.
Some scientists expected that data from Mariner 2 would indicate that Venus’s clouds were made of dust tossed aloft by violent winds; friction between dust grains, they argued, would heat the planet. Others opted for more traditional Venusian hypotheses: they believed that Venus was covered by a carbonated water ocean, that it was a swamp world like Earth in the Carboniferous era, or that it had seas of bubbling petroleum.
Mariner 2 was a very short mission by modern standards; it encountered Venus after a flight of only 109 days. That 109 days was, however, replete with heart-stopping glitches. For example, a mid-course correction on 4 September, when Mariner 2 was 1.5 million kilometers from Earth, added about four kilometers per hour more than planned to Mariner 2’s speed; this meant that its Venus flyby would occur at a distance of nearly 33,800 kilometers, more than double the hoped-for 14,500 kilometers. This raised fears – happily soon allayed – that the spacecraft might pass too far from Venus to accomplish useful science. The mid-course correction was the first-ever rocket maneuver in interplanetary space.
One of Mariner 2’s twin solar arrays short-circuited and stopped producing electricity, cured itself, then failed for good. Fortunately, the arrays produced more electricity than expected and Mariner 2 was close enough to the Sun that a single array was enough by the time the final failure occurred.
Despite automatic cooling louvers and careful placement of heat-reflective insulation and coatings, Mariner 2 soon began to overheat. Many of Mariner 2’s systems were rated for a temperature no greater than 54° C, but by mid-November had exceeded their maximum by up to 22° C. The spacecraft’s simple onboard computer remained mostly reliable despite the heat until five days before the planned encounter, when it failed to transmit an “update pulse.” Controllers on Earth opted to send Mariner 2 the command that would begin its Venus flyby science program rather than rely on the onboard computer.
Mariner 2 approached Venus from its night side on 14 December 1962 after a voyage of 293 million kilometers. A little more than an hour before closest approach, at a distance of about 40,700 kilometers from the planet and 58 million kilometers from Earth, the atmosphere and surface radiometers detected Venus for the first time. A 42-minute radiometer scanning period then began on the planet’s night side. Forty-four minutes before closest approach, Venus’s dayside came into view of the scanning radiometers.
Mariner 2’s closest approach to Venus – at a distance of 34,773 kilometers – took place over its dayside in the early afternoon on 14 December 1962. The spacecraft reached its closest approach to the Sun – its perihelion – on 27 December at a distance of 105,465,000 kilometers. A week later, on 3 January 1963, Mariner 2 went silent, never to be heard from again.
The mission was judged to be an outstanding success, and went a long way toward settling debates about Venusian surface and atmosphere conditions. If anything, it hinted that Venus was more harsh than had been supposed. Some scientists remained reluctant to embrace the new data; in the Soviet Union in particular, the concept of a more or less clement Venus held on for several more years.
JPL hoped that, following the great success of Mariner 2, it would receive more support for its future plans, which included the advanced Mariner-B landing probe carrier and Voyager, a family of flyby, orbiter, and lander vehicles for exploring Mars and Venus. Unfortunately, the Pasadena lab – and, in particular, its leader, William Pickering – misjudged Mariner 2’s role in the NASA program. Mariner 2 was the first significant U.S. “first” in the space race with the Soviet Union. That first thus accomplished, attention shifted back to Ranger lunar program and Centaur upper stage problems.
On 18 October 1962, as Mariner 2 closed on its target, the Block II Ranger V failed mysteriously after an apparently flawless launch toward the moon. Congress soon grilled NASA officials over weaknesses in the Ranger program, and JPL was soon tasked with preparing Block III Rangers, which would include a completely rebuilt electronics systems. The Block III Rangers represented a climb-down in NASA and JPL aspirations; instead of delivering a package to the moon, they would seek to image the lunar surface close-up using six telescopic cameras as they plummeted toward intentional destruction.
With the race to the moon still NASA’s central focus, Voyager and Mariner B were judged to be of lower priority than fixing Ranger and Centaur and preparing the Surveyor lunar soft-landers. NASA opted to postpone Voyager and Mariner B. This brought to a head growing tensions between JPL and NASA over future lunar and planetary exploration. In such a battle, there could be only one victor.
After a period during which it considered moving Mariner B and Voyager to NASA Goddard Space Flight Center or NASA Ames Research Center, NASA opted to task a somewhat chastened JPL with a pair of upgraded Mariner-R-type Mars flyby spacecraft in 1964-1965. Mariner 3 failed, but Mariner 4 carried out world’s first successful Mars flyby in July 1965. NASA did not explore Venus again with spacecraft until the Mariner 5 flyby of 14 June 1967; when it did, it again judged that an upgraded Mariner-R design could do the job. Soon after Mariner 5, Congress opted to scrap JPL’s Voyager Mars/Venus program entirely. Planetary exploration using robots would not come into its own until after Apollo achieved its goal of beating the Soviets to the moon.
Aeronautical and Astronautical Events of 1961, Report of the National Aeronautics and Space Administration to the Committee on Science and Astronautics, U.S. House of Representatives, 87th Congress, 7 June 1962, pp. 4, 5, 6, 9, 10, 26, 50.
“Centaur Slippage Drag on Apollo,” H. Taylor, Missiles & Rocket, 12 February 1962, pp. 13-14.
“Centaur Faces Probe by House Group,” H. Taylor, Missiles & Rockets, 14 May 1962, pp. 13, 38.
“Centaur Troubles Explained,” Missiles & Rocket, 21 May 1962, p. 7.
Press release, “Mariner Spacecraft,” Jet Propulsion Laboratory, 19 July 1962.
Press release, “Mariner Scientific Experiments,” Jet Propulsion Laboratory, 19 July 1962.
“Mariner I Poised for Venus Shot,” Missiles & Rockets, 23 July 1962, pp. 32-33.
“Mercury, Jupiter Probes Planned If Funds Permit,” Missiles & Rockets, 26 November 1962, pp. 122-129.
Press release, “Venus Encounter,” Jet Propulsion Laboratory, 14 December 1962.
Press release, “Mariner Radiation Experiments,” Jet Propulsion Laboratory, 28 December 1962.
“JPL faces Mission Curtailment,” H. Taylor, Missiles & Rockets, 7 January 1963, p. 14.
“Mariner Unlocks Venusian Mysteries,” Missiles & Rockets, 7 January 1963, p. 16.
“After Venus Report. . .New Mariner Planning Pushed,” H. Taylor, Missiles & Rockets, 4 March 1963, pp. 12-13.
Aeronautical and Astronautical Events of 1962, Report of the National Aeronautics and Space Administration to the Committee on Science and Astronautics, U.S. House of Representatives, 88th Congress, pp. 78, 108.
Venus Space Probes, Novosti Press Agency Publishing House, 1979, pp. 1-12.