An orbiter would comprehensively map and study the surface, while a lander would search for life on the surface. After Mariner 4 revealed the Martian atmosphere was much thinner than previously believed, the lander had to incorporate rocket braking, and grew beyond the capability of the Saturn IB. So the program was reconfigured in 1965 to launch two 11 metric ton Voyagers to Mars at once aboard a single Saturn V launch in 1973. Congress killed the program in 1967 before a full-scale development contractor could be selected. NASA managed to accomplish nearly the same mission in 1975 using two Viking spacecraft launched by Titan 3C-Centaur boosters.
Technical Description of Voyager
The final plans for Voyager prior to its cancellation in late 1967 were as follows:
The orbiter would conduct visual mapping and topography, map planetary temperature distribution, observe daily and seasonal changes on the surface, study the planet's geology, gravity, geodesy, large-scale atmospheric features - and biology. The orbiter would approach as low as 1150 km to the surface, in orbits with periods of from 6 to 12 hours. Its planned lifetime was six months on the early mission, extended to two years on later missions.
The lander weight included 20% contingency for growth during development. The 4000 kg design weight was allocated to three subsystems:
The lander could send data to earth at 600 bits per second directly, or 50,000 to 200,000 bps by relaying through the orbiter. The early missions would be battery-powered with 5 kW-hr batteries, and therefore limited to two days of operation . Later missions would allow use of robust landers powered by nuclear thermal generators, capable of six months to two years of operation, with deployable rovers.
History of Voyager
The origins of Voyager can be traced back to the earliest post-Sputnik US studies on the course of a future space program. At this time, rather than defining missions to be accomplished, the constraint was what launch vehicles would be available, and what payloads they could hurl to various destinations in the solar system. On 18 July 1958 NACA's National Integrated Missile and Space Vehicle Development Program considered that their 'Type IV' launch vehicle (equivalent to the later Saturn C-3) would be used to send a 2300 kg 'probe' to Mars in January 1967, followed by one to Venus four months later. NASA's December 1959 'Ten Year Plan of the National Aeronautics and Space Administration' concentrated on unmanned and manned exploration of the moon, however. Heavyweight 2300 kg Saturn-launched lander probes to the planets were not foreseen until the 1970's. Voyager was identified by name in the spring of 1960 in the NASA semi-annual report to Congress. Voyager was to be the second generation planetary spacecraft after Mariner, capable of orbiting and landing capsules on Mars or Venus. Preliminary studies were underway, it was reported, but final planning would have to await decisions and funding for development of the Saturn I launch vehicle (at that time planned to have a Centaur-derived third stage, the S-V). This version of Voyager would be limited to 1090 kg, including a small landing capsule of 100 to 150 kg.
JPL planners began to study Voyager-class missions in 1961, followed by a May 1962 study of advanced missions and spacecraft. These came to two conclusions -- that too little was known about the atmosphere of either planet to design a lander at that time, and the largest wish-list of instruments that would be the payload for an orbiter came to 230 kilograms. Neither of these conclusions pointed to a heavy spacecraft in the short-term. They also identified major areas of technical development needed for any such future missions - improvements in the deep-space tracking and control network, development of sterilization methods to ensure that earth spacecraft did not contaminate other potentially life-bearing planets, and improvements in solar and nuclear thermal power generation.
NASA's Donald Hearth found all of this too cautious. He required intrusive amounts of paperwork from JPL in order to know what they were up to, while informally asking several companies to study unmanned Mars landers at their own expense. These included the usual suspects - Avco, General Electric (ballistic missile re-entry vehicle specialists), Douglas, Convair, Lockheed, North American, and Space Technology Laboratories. Heath was hell-bent on achieving a landing on Venus by June 1967. NASA called for issued a request for proposal for Voyager Design Studies to 21 bidders on 5 March 1963. In those days things moved fast. The industrial briefing to 37 prospective contractors and subcontractors was held six days later. On 25 March, 13 companies submitted bids. These were examined by a selection board two days later, and by 4 April General Electric and Avco were informed they would be receiving modest $ 125,000 and $ 144,546 study contracts.
The concept was for a Voyager Venus launch in 1967, followed by one to Mars in 1969. Progress was dogged by continuing hostility between JPL and NASA headquarters. JPL felt that working on a lander was premature. Some JPL astronomers had concluded that the atmosphere of Mars might be much thinner than assumed. Values for the Martian surface-level atmosphere pressure as low as 1% that of earth were mentioned, compared to over ten times that estimated previously. As a result of this 'pessimism', NASA terminated JPL's Advanced Planetary Spacecraft Study on 1 September 1963 and gave Avco and General Electric an extra month to consider the impact of a lower surface pressure for the design of their landers.
Hearth presented the case for Voyager to NASA Administrator James Webb in December 1963. The new uncertainty regarding atmospheric pressure had killed JPL's alternative, low-end Mariner B lander. To land in the lower pressure, the capsule for that concept would have to weigh more than the planned Atlas Centaur booster could handle. Therefore the only alternative, he said, to press on with Saturn-I launched Voyager. Both Avco and General Electric had come up with excellent lander designs, which would deliver 70 to 91 kg of instruments to the Martian surface. They would be targeted to the 'green' areas of Mars showing the greatest seasonal change and be equipped with miniature laboratories to determine the nature of life on Mars.
General Electric planned to carry 657 two landers on one 934 kg orbital bus. The orbital bus would include 939 kg of propellant, bringing the total spacecraft mass to 3187 kg. The landers would be shaped like GE's conical ICBM re-entry vehicles. They would use rockets for final braking and deploy tip bars to right themselves on the surface. Landing targets for 1969 were Syrtis Major (10 deg N, 285 deg longitude) and Pandorae Fretum (24 deg S, 310 deg longitude).
The Avco spacecraft had a total mass of 2961 kg, including 1361 of propellant, the 838 kg orbiter, and the single 762 kg lander. The latter consisted of a jettisonable aeroshell for re-entry and a spherical hard lander built to take a parachute-braked 12 m/s landing shock. After bouncing across the surface, it would unfurl itself on six petals (remarkably similar to the Soviet Luna E-6 lander which had begun its long series of attempts to reach the moon earlier that year). Nuclear thermal generators would provide power. Avco planned to land at no less than ten different locations on Mars during four launch campaigns in 1969-1975. These ranged from Syrtis Major to both polar caps.
But Webb refused to give the go-ahead. Apollo had the priority, and cutbacks to even Apollo were already coming. America's space program was heading toward its decline. So it was back to JPL's more modest plans for interim Mariner orbiter missions. Voyager could only be fully funded in the post-moon landing budgets. This would push the first launch back to 1971.
However Congressional unhappiness with the string of JPL Ranger failures and the waning support for the space program meant that NASA could not support funds for both JPL's Mariner-Mars 1969 and Heath's Voyager 1971. So NASA cancelled Mariner-Mars 69 in order to save the $1.25 billion Voyager project. Voyager was officially authorized to proceed on 16 December 1964. Requests for proposal for a prime contractor were issued on 15 January 1965. JPL's role was limited at that point to supervision of the preliminary design phase of the program. The 22 January bidder's conference was attended by 28 companies. By 3 May three down-selected companies began work on the 90-day preliminary design phase: Boeing, General Electric, and TRW. One would receive a final production contract.
On 15 July 1965 came the shocking findings of Mariner 4, the first spacecraft to flyby Mars and return data. The atmospheric pressure at the surface was as low as 0.4% of that of earth - essentially a vacuum, and under half that of even JPL's most pessimistic assumption. It would be impossible to land a significant payload on the surface without using a larger, heavier lander using rocket braking for touchdown. NASA bit the bullet and announced in mid-October 1965 that development of the Saturn IB-Centaur would be terminated and that Voyager would be launched by the Saturn V. However the existing production Saturn V's were allocated to the Apollo moon landings. This, together with funding limits and delays necessary to redesign the lander, meant that the first Voyager flight would have to be delayed to 1973. A single Saturn V launch would boost two Voyager probes to Mars.
The change took the sense of urgency out of the program, and JPL remained hostile to trying to build a spacecraft on such a grand, revolutionary scale. After a long series of failures in the first half of the 1960's, they had finally begun to achieve success through incremental changes to proven spacecraft designs. Voyager funding was drastically cut, but work on refining the spacecraft design and identifying missions in the 1973-1979 period continued. On 17 October 1966 the decision was taken to put Von Braun's Marshall Spaceflight Center in charge of development of both Voyager and its modified Saturn V launch vehicle. JPL's role would be limited to working with NASA Langley on lander subsystems. Voyager struggled on a bit longer, but Congress was now finding little favor with new high-cost space projects. On 22 August 1967, the House approved a NASA budget that totally eliminated all funds for Voyager. President Johnson did not fight the deletion.
Voyager was resurrected as the faster-better-cheaper Viking project. This developed a new Titan 3C-Centaur booster in replacement of the Saturn IB-Centaur cancelled by NASA and landed the two successful Viking landers on Mars in 1975, long after the last Saturn V had flown.
Gross mass: 11,700 kg (25,700 lb).
Unfuelled mass: 4,900 kg (10,800 lb).
Height: 7.20 m (23.60 ft).
Diameter: 6.10 m (20.00 ft).