The first Kiwi-B nuclear-thermal engine ground test using liquid hydrogen (December 1961) ended early after the engine began to blast sparkling, melting bits of uranium fuel rods from its reactor core out of its nozzle. Though the cause of this alarming failure remained unknown, Lockheed Missiles and Space Company was made RIFT contractor in May 1962. In early summer 1962 the Marshall Future Projects Office launched the EMPIRE study, motivated in part by a desire to develop missions suitable for nuclear propulsion. Hence, early on NERVA became closely identified with Mars.
The second and third Kiwi-B ground tests (September 1962 and November 1962) failed in the same manner as the first. Failure cause remained uncertain, but vibration produced as the liquid hydrogen propellant flowed through the reactor fuel elements was suspected.
The PSAC and the White House Budget Bureau allied against the nuclear rocket program following the third Kiwi-B failure. They opposed funding for an early RIFT flight test because they saw it as a foot in the door leading to a costly piloted Mars mission, and because they believed the technology to be insufficiently developed, something the Kiwi-B failures seemed to prove. Kennedy himself intervened in the AEC-NASA/Budget Bureau-PSAC deadlock, visiting Los Alamos and the NRDS in December 1962.
On 12 December 1962, Kennedy decided to postpone RIFT until after additional Kiwi-B ground tests had occurred, explaining that "the nuclear rocket . . . would be useful for further trips to the Moon or trips to Mars. But we have a good many areas competing for our available space dollars, and we have to channel it into those programs which will bring a result—first, our Moon landing, and then consider Mars." Kennedy's decision marked the beginning of annual battles to secure continued nuclear rocket funding. 7
At the May 1963 AAS Mars symposium in Denver, SNPO director Harold Finger pessimistically reported that nuclear rockets were not likely to fly until the mid-1970s. 8 However, the fourth Kiwi-B test, in August 1963, revealed that vibration had indeed produced the earlier core failures. The problem had a relatively easy solution, so NASA, AEC, and nuclear engine supporters in Congress became emboldened. They pressed Kennedy to reverse his December 1962 decision.
William House, Aerojet-General's Vice President for Nuclear Rocket Engine Operations, felt sufficiently optimistic in October 1963 to tell the British Interplanetary Society's Symposium on Advanced Propulsion Systems that a Saturn V would launch a 33-foot-diameter RIFT test vehicle to orbit in 1967. He predicted that one NERVA stage would eventually be able to inject 15 tons on direct course to Mars, or 3 tons on a three-year flight to distant Pluto. 9
Kennedy never had the opportunity to reconsider his RIFT decision. Following the young President's November 1963 assassination, President Johnson took up the question. With an eye to containing government expenditures, he canceled RIFT in December 1963 and made NERVA a ground-based research and technology effort.
The year 1964 saw the successful first ground test of the redesigned Kiwi-B engine and the first NERVA start-up tests. It also marked the nuclear rocket program's peak funding year, with a joint AEC-NASA budget of $181.1 million. Though NERVA was grounded, work proceeded under the assumption that success would eventually lead to clearance for flight.
The nuclear rocket program budget gradually declined, dropping to $140.3 million in FY 1967. NERVA did not come under concerted attack, however, until the bitter battle over the FY 1968 budget. In August 1967, Congress deleted all advanced planning and Mars Voyager funds from NASA's FY 1968 budget because it saw them as lead-ins to a costly piloted Mars program, and Johnson refused to save them (see chapter 4). NERVA funding was eliminated at the same time.
Voyager had to wait until FY 1969 to be resurrected as Viking. Through Anderson's influence, however, NERVA did better—the nuclear rocket program was restored with a combined AEC-NASA budget of $127.2 million for FY 1968. As if to celebrate Anderson's intervention, the NRX-A6 ground test in December 1967 saw a NERVA engine operate for 60 minutes without a hitch.
Boeing’s Behemoth
In January 1968, the Boeing Company published the final report of a 14-month nuclear spacecraft study conducted under contract to NASA Langley. The study was the most detailed description of an interplanetary ship ever undertaken. 10 As shown by the EMPIRE studies, the propellant weight minimization promised by nuclear rockets tended to encourage big spacecraft designs. In fact, Boeing's 582-foot long Mars cruiser marked the apogee of Mars ship design grandiosity.
At Earth-orbital departure, Boeing's behemoth would include a 108-foot-long, 140.5-ton piloted spacecraft and a 474-foot-long propulsion section made up of five Primary Propulsion Modules (PPMs). The entire spacecraft would weigh between 1,000 and 2,000 tons, the exact weight being dependent upon the launch opportunity used. Each 33-foot-diameter, 158-foot-long PPM would hold 192.5 tons of liquid hydrogen. A 195,000-pound-thrust NERVA engine with an engine bell 13.5 feet in diameter would form the aft 40 feet of each PPM. The six-person piloted spacecraft would consist of a MEM lander, a four-deck Mission Module, and an Earth Entry Module.
Three PPMs would constitute Propulsion Module-1 (PM-1); two would constitute PM-2 and PM-3, respectively. PM-1 would push the ship out of Earth orbit toward Mars, then detach; PM-2 would slow the ship so that Mars' gravity could capture it into orbit, then it would detach; and PM-3 would push the ship out of Mars orbit toward Earth. At Earth, the crew would separate in the Apollo CM-based Earth Entry Module, reenter Earth's atmosphere, and splash down at sea.
Six uprated Saturn V rockets would place parts for Boeing's Mars ship in Earth orbit for assembly. Assembly crews and the flight crew would reach the spacecraft in Apollo CSMs launched on Saturn IB rockets. The 470-foot-tall uprated Saturn V, which would include four solid-fueled strap-on rockets, would be capable of delivering 274 tons to a 262-mile circular Earth orbit. Boeing envisioned modifying KSC Saturn V launch pads 39A and 39B to launch the uprated Saturn V, and building a new Pad 39C north of the existing pads.
Figure 12—In January 1968, Boeing proposed this complex Mars expedition plan using nuclear rockets and an opposition-class trajectory. The company's Mars ship would measure nearly 200 meters long and support a crew of six. (Integrated Manned Interplanetary Spacecraft Concept Definition, Vol. 1, Summary, D2-113544-1, Boeing Company, Aerospace Group, Space Division, Seattle, Washington, p. 7.)
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The company's report listed opportunities for nine Venus-swingby, one conjunction-class, and five opposition-class Mars expeditions between November 1978 and January 1998. The conjunction-class mission would last 900 days, while the Venus-swingby and opposition-class missions would last from 460 to 680 days.
Boeing envisioned using the MOR mission plan NASA Lewis used in its 1959-1961 studies. The MEM for descending to Mars from Boeing's orbiting Mars ship was designed for MSC between October 1966 and August 1967 by North American Rockwell (NAR), the Apollo CSM prime contractor. 11 NAR's MEM report, published the same month as the Boeing report, was the first detailed MEM study to incorporate the Mariner 4 results. Cost minimization was a factor in NAR's MEM design. The company proposed a 30-foot-diameter lander shaped like the conical Apollo CM. The Apollo shape, it argued, was well understood and thus would require less costly development than a novel design.
The lightest NAR MEM (33 tons) would carry only enough life support consumables to support two people on Mars for four days, while the heaviest (54.5 tons) was a four-person, 30-day lander. Like the Apollo Lunar Module (and many previous MEM designs), NAR's MEM design included a descent stage and an ascent stage. The MEM would contain two habitable areas—the ascent capsule and the descent stage lab compartment. The ascent capsule would include an Apollo docking unit for linking the MEM to the mothership, and the lab compartment would include an airlock for reaching the Martian surface.
Figure 13—Cutaway of North American Rockwell's 1968 Mars lander. Based on the Apollo Command Module shape, its design incorporated new Mars atmosphere data gathered during the 1965 Mariner 4 automated Mars flyby. (Manned Exploration Requirements and Considerations, Advanced Studies Office, Engineering and Development Directorate, NASA Manned Spacecraft Center, Houston, Texas, February 1971, p. 5-3.)
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The MEM's Apollo-style bowl-shaped heat shield would protect it from friction heating during Mars atmosphere entry. To reduce cost, NAR proposed to develop a single heat shield design for both flight tests in Earth's atmosphere and Mars atmosphere entry. This meant, of course, that the shield would be more robust, and thus heavier, than one designed specifically for Mars atmosphere entry. During Mars atmosphere entry the crew would feel seven Earth gravities of deceleration.
After atmospheric entry, the MEM would slow its descent using a drogue parachute followed by a larger ballute (balloon-parachute). At an altitude of 10,000 feet the ballute would detach. The MEM's descent engine would fire; then two of the astronauts would climb from their couches to stand at controls and pilot the MEM to touchdown. The company proposed using liquid methane/liquid oxygen propellants that would offer high performance but not readily boil off or decompose. The MEM would carry enough propellants for two minutes of hover. Its six landing legs would enable it to set down safely on a 15-degree slope.
Figure 14—North American Rockwell's plan for landing on Mars and returning to Mars orbit. The company's lander, a two-stage design, would support up to four astronauts on Mars for up to 30 days and return to the orbiting mothership with up to 300 pounds of rocks. (Integrated Manned Interplanetary Spacecraft Concept Definition, Vol. 4, System Definition, D2-113544-4, Boeing Company, Aerospace Group, Space Division, Seattle, Washington, January 1968, p. 145.)
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For return to the mothership in Mars orbit, the crew would strap into the ascent capsule with their Mars samples and data. The ascent stage engine would ignite, burning methane/oxygen propellants from eight strap-on tanks. The ascent stage would blast away from the descent stage, climb vertically for five seconds, then pitch over to steer toward orbit. Once empty, the strap-on tanks would fall away; the ascent engine would then draw on internal tanks to complete Mars orbit insertion and rendezvous and docking with the mothership.
NAR had MEM development commencing in 1971 to support a 1982 Mars landing. The company envisioned a MEM flight test program using six MEM test articles and a range of rockets, including three two-stage Saturn Vs. The 1979 piloted MEM entry and landing test, for example, would have a fully configured MEM launched into Earth orbit on a two-stage Saturn V with a piloted CSM on top. In orbit the CSM would detach, turn, and dock with the MEM for crew transfer. The crew would then cast off the CSM and fly the MEM to landing on Earth.
Boeing scheduled the first Mars expedition for 1985-1986, with Mars expedition contract awards in 1976, and Mars hardware tests in low-Earth orbit beginning in 1978. NAR estimated development cost of its MEM at $4.1 billion, while Boeing's study placed total Mars program cost at $29 billion.