NASA's Space Shuttle was conceived in the late 1960s as a fully reusable transport for reducing the cost of Earth-orbiting space station logistics resupply and crew rotation. In 1969, it came to be seen as an element in an expansive Integrated Program Plan that would also have included upgraded expendable Saturn V rockets, reusable manned Space Tugs and nuclear-propulsion cislunar Shuttles, Earth-orbital and lunar-orbital space stations, a lunar surface base, and manned Mars expeditions - all by the mid-1980s. This vision of America's future in space found little favor in the Nixon White House or in Congress, however. By 1973, only the Space Shuttle survived, and then only in a partially reusable form.
For a time the European Space Research Organization (ESRO) sought to provide NASA with a reusable Space Tug that would reach low-Earth orbit in the Shuttle Orbiter's payload bay and travel to orbits that the Shuttle could not reach. In August 1973, however, NASA and ESRO agreed that the latter should develop Spacelab, a system of segmented pressurized modules and unpressurized pallets that would operate in the Orbiter's payload bay to provide an interim sortie space station capability. ESRO joined with the European Launcher Development Organization to form the European Space Agency (ESA) in 1975.
When the semi-reusable Shuttle first reached space in April 1981, NASA anticipated launching Earth-orbiting satellites and planetary probes beyond the Orbiter's operational altitude using a modest flock of expendable auxiliary rocket stages. The largest and most powerful of these would be the Centaur G', a chemical-propulsion stage with a troubled development history. Centaur G' was tapped as NASA's main upper stage for boosting planetary probes - for example, the Galileo Jupiter Orbiter and Probe - onto interplanetary trajectories.
During Shuttle development in the 1970s, NASA budgets were tight, and planning for advanced missions - for example, humans on Mars - ceased within the U.S. civilian space agency. According to some within NASA, talk of moon bases and manned Mars missions was tantamount to professional suicide. When planning for NASA manned Mars missions resumed, it did so first outside of NASA. Mars exploration advocates outside the agency hoped that the Shuttle would inexpensively launch Mars spacecraft components, propellants, and crews, and also serve as a source of hardware that could be modified at modest cost to assemble manned Mars spacecraft.
Robert Parkinson, an engineer with the Propellants, Explosives, and Rocket Motor Establishment (PERME) in Great Britain, was among the first individuals to write about a NASA manned Mars mission based on Shuttle and Shuttle-related hardware. Inspired by the writings of Arthur C. Clarke and Wernher von Braun, Parkinson had joined the British Interplanetary Society in 1956. In a series of papers spanning 1980-1981, he wrote of a capable chemical-propulsion NASA Mars expedition which he dubbed "Mars in 1995!"
Parkinson inventoried Shuttle-derived hardware which he believed would become available by 1990 as part of NASA's planned Earth-orbital operations. His list included a powerful Heavy Lift Vehicle (HLV) capable of launching into low-Earth orbit payloads larger than the Shuttle Orbiter's payload bay could accommodate, drum-shaped high-performance OTVs with optional crew cabins, a Heavy Boost Stage (HBS) roughly the size of the Saturn S-IVB stage NASA used in the late 1960s/early 1970s to launch Apollo spacecraft out of Earth orbit toward the moon, an extendible solar array for generating up to 25 kilowatts of electricity, free-flying Spacelab modules, closed-cycle Space Station life support systems, and androgynous docking units. Development of such systems, Parkinson opined, "probably only awaits freeing of [NASA] funding currently tied up in [the development of] the Shuttle."
Because such systems would already be developed for Earth-orbital operations, Parkinson wrote, a NASA Mars expedition could be carried out in the 1990s with essentially no development cost, save for that of a manned Mars lander. In his first "Mars in 1995!" paper, he placed the cost of his expedition at just $3.3 billion, of which building and testing the manned Mars lander would account for about $740 million. He raised the total cost to $4.844 billion in a subsequent paper, of which $2.359 billion would be spent on the lander. Even this higher cost figure was, he noted, only five times the cost of the twin robotic Viking missions with landed on Mars in 1976. He added that "given the right circumstances, it is actually cheaper to send men [to Mars] than to try to do the same thing with dozens of robot expeditions."
Parkinson's 1995 NASA Mars expedition would begin with eight Space Shuttle launches in September-October 1994. Reflecting early Shuttle-era optimism, Parkinson estimated that each Shuttle launch would cost just $28.75 million. Assembly of the expedition's three unique Orbital Assembly (OA) spacecraft would take place in a 400-kilometer circular Earth orbit. The eighth Shuttle Orbiter would deliver the five-person Mars crew and stand by to observe the beginning of their departure from Earth orbit. In the event of trouble before the beginning of Earth-orbit departure, the Shuttle could recover the crew for return to Earth.
Two OAs, designated Orbiters, would at launch from Earth orbit each comprise an HBS, a pair of 30-ton OTVs (one for Mars orbit capture and one for Mars orbit departure & Earth-orbit capture), a Spacelab-derived pressurized module with an unpressurized pallet, and an androgynous docking unit. The Spacelab-derived module would provide living and working space for the crew, as well as protection from the six solar flares Parkinson said the crew could expect during their 18-month expedition.
Orbiter 1, with a mass at launch from Earth orbit of 211,312 kilograms and a crew of three, would also include a six-meter-diameter high-gain radio dish antenna for high-data-rate communication with Earth and two 2.5-meter-diameter Venus atmosphere entry probes. Orbiter 2, with a mass of 210,947 kilograms and a crew of two, would include a 1750-kilogram cylindrical docking module with four androgynous docking ports and two extendible solar arrays. Either Orbiter could support the entire crew in an emergency.
The third OA, the unmanned Lander Assembly (LA), would have a mass at launch of only 193,482 kilograms. In addition to an HBS, it would comprise one OTV with a three-meter-diameter crew cabin and an androgynous docking unit, a drum-shaped stores module with supplies for the expedition's outbound leg and androgynous docking units at both ends, three 1225-kilogram automated Mars sample return landers, a 938-kilogram propulsion package that would enable one of the Mars sample returners to reach and return from a martian polar cap, six 31-kilogram penetrator Mars hard-landers, a 473-kilogram Mars-orbiting radio relay satellite to enable Mission Control on Earth to remain in continuous contact with the crew on the surface of Mars, and the 7.6-meter-diameter, 15,983-kilogram Lander Module.
On 8 November 1994, the three OAs would ignite their HBS engines to begin Earth-orbit departure. Over the course of several revolutions about the Earth, they would fire the HBS rocket motors at their periapsis (orbit low point) to raise their apoapsis (orbit high point). In the image at the top of this post, OA 2, with its docking module and folded solar arrays, and unmanned OA 3, with the Lander Module, are viewed through a porthole on OA 1 as the three spacecraft ignite their engines. A maneuver at final apoapsis would adjust the plane of the expedition's path to Mars relative to the Sun, then a final periapsis burn would push the three OAs out of Earth's gravitational grip.
After escape from Earth, the three OAs would cast off their spent HBSs and dock to form their cruise configuration. Orbiter 1 and Orbiter 2 would dock nose-to-nose with the docking module between them. The LA OTV/crew cabin would undock from the stores module/Lander Module, then the former would dock at one lateral docking module port and the latter would dock at the other. Following the last docking, the five astronauts would have available 1125 cubic meters of living space. They would then extend the twin solar arrays on the docking module.
The OAs would reach Mars on 10 June 1995. Shortly before arrival, the crew would retract the solar arrays to protect them from deceleration stress during the Mars capture maneuver. Orbiter 1 would undock from the Orbiter 2 docking module, and the LA OTV/crew cabin and stores module/Lander Module would both undock from the Orbiter 2 docking module and redock with each other. The three OAs would then ignite their OTV engines to slow down so that Mars's gravity could capture them into a 23,678-by-3748-kilometer orbit with a period of 13.5 hours. The high elliptical orbit was a propellant-saving measure; relatively loosely bound to Mars, it would enable an economical Mars escape when time came to return to Earth.
The two Orbiters would cast off their spent Mars orbit insertion OTVs and redock to form their Mars orbital configuration. The LA would split as before so that its components could resume their places on the docking module. Because the LA would be less massive than the two Orbiters, its OTV would retain about 7000 kilograms of nitrogen tetroxide/hydrazine propellants after its Mars orbit insertion burn and would not be cast off.
After surveying prospective landing sites from orbit at periapsis over several days, the conical Lander Module would be readied for descent to Mars's surface. Three astronauts would strap into couches in its cramped ascent module capsule and undock from the stores module. At apoapsis, they would fire the Lander Module's Reaction Control System thrusters to lower its periapsis to 50 kilometers, where Mars atmosphere entry would begin. A bowl-shaped heat shield modeled on the Viking lander aeroshell heat shield design would protect the Lander Module during its fiery descent through the thin martian atmosphere.
The Lander Module would slow to Mach 2.5 by the time it fell to an altitude of 10 kilometers, then a 20-meter-diameter ballute ("balloon-parachute") would deploy to slow it to subsonic speed. Five kilometers above Mars the ballute would separate and a parachute would deploy. At the same time, the Lander Module heat shield would fall away, exposing its four landing engine clusters and three landing legs. A downward-pointing camera would enable the Lander Module pilot to observe the planned landing site for the first time since leaving Mars orbit. The landing engines would ignite 800 meters above Mars; then, moments later, the parachute would separate. The pilot would then guide his craft to a safe landing.
Parkinson's Lander Module design, which resembled conical lander designs put forward in the 1960s, included in its lower section a two-by-three-meter crew cabin. Soon after landing, the crew would climb down through a tunnel into the cabin and don Mars surface suits. After depressurizing the crew cabin, they would open a door-like hatch, walk down a short ramp, and put the first human bootprints on another planet.
Parkinson called for a 20-day Mars surface stay, during which the three astronauts would explore using 500 kilograms of science equipment and a 500-kilogram unpressurized rover more capable than the Lunar Roving Vehicle used during the last three Apollo missions. As they explored, they would collect up to 350 kilograms of Mars rocks and dirt for return to laboratories on Earth.
The two astronauts on board the orbiting docked OAs, meanwhile, would deploy the mission's cargo of automated Mars probes. The 2.5-meter-diameter automated sample returners would each collect and launch up to a kilogram of rock and soil (or ice, in the case of the polar sample returner) into a 350-kilometer circular Mars orbit.
When the time came to leave Mars's surface, the three astronauts would board the Lander Module ascent capsule and ignite three engines similar to the Apollo Lunar Module ascent-stage engine. The ascent capsule would blast free of the Lander's lower section, leaving behind the crew cabin. During the first-stage burn, four strap-on propellant tanks would feed the three engines. After first-stage shutdown, the tanks and two outer engines would detach; then, after a brief coast, the remaining engine would reignite to place the ascent capsule into a 350-kilometer circular Mars orbit.
As the docked OAs neared apoapsis, one astronaut would board the LA OTV/crew cabin and undock from the docking module, then ignite the LA OTV rocket engine to descend to a rendezvous with the Lander Module ascent capsule. The ascent capsule would include a low-mass ("skeleton") version of the expedition's standard androgynous docking unit. The LA OTV/crew cabin would dock with the ascent capsule, then the surface crew would transfer to it with their Mars samples. After the ascent capsule was cast off, the LA OTV/crew cabin would rendezvous with and recover the three sample returner sample capsules. The LA OTV/crew cabin pilot would then fire its engine to return to the OAs. Parkinson calculated that, even after this series of maneuvers, the LA OTV/crew cabin would retain enough propellants for two astronauts to carry out a 10-day sortie to Phobos, Mars's innermost and largest moon.
On 25 July 1995, the expedition would depart Mars orbit. Before departure, the astronauts would cast off the LA OTV/crew cabin and depleted stores module, retract the twin solar arrays, and undock Orbiter 1 from Orbiter 2. Each would then ignite its remaining OTV engine at periapsis to escape Mars orbit and begin a five-month journey to Venus. After OTV shutdown, the crew would redock the two Orbiters and extend the solar arrays.
The Venus detour, Parkinson explained, would accelerate the docked Orbiters toward Earth. Without the gravity-assist from Venus, the round-trip Mars voyage would need three years; with it, the Mars expedition could be completed in 18 months. During the Venus swingby, the crew would deploy the twin Venus probes housed in Orbiter 1. These would be modeled on the Large Probe from the 1978 Pioneer Venus Multiprobe mission.
NASA's first Mars expedition would return to Earth 10 months after departing Mars, on 16 May 1996. The astronauts would again undock the OAs and retract Orbiter 2's twin solar arrays. They would ignite the OTV engines for the final time to capture into a 77,687-by-6800-kilometer Earth orbit with a period of 24 hours, then would redock for the final time and extend the solar arrays to await retrieval.
A Space Shuttle Orbiter, meanwhile, would transport into low-Earth orbit an OTV/crew cabin, which would climb to a rendezvous with the waiting OAs and dock with the docking module. The Mars crew would board with their samples, then the OTV/crew cabin pilot would undock and fire its motor to return to the waiting Shuttle Orbiter. The abandoned docked OAs would remain in Earth orbit as a long-lived monument to the early days of U.S. piloted Solar System exploration. The Shuttle Orbiter would deorbit to deliver the Mars astronauts, physically weakened by nearly 18 months in weightlessness, to a hero's welcome on Earth.
NASA human spaceflight would follow a path very different from those Parkinson and other optimistic early 1980s space planners anticipated, though until early 1986 they had some justification for holding onto their dreams. In July 1982, President Ronald Reagan declared the Shuttle operational. The first Spacelab flight, STS-9/Spacelab-1 in late 1983, saw an ESA astronaut join American astronauts in Earth orbit for the first time. In his January 1984 State of the Union speech, Reagan declared for a Space Station and invited European, Canadian, and Japanese participation. The Shuttle-launched station was to be completed by 1994.
Reagan's station was, however, meant to be a relatively low-cost laboratory. Such an orbital facility would have no need of the heavy-lift rockets, large in-space stages, and OTVs Parkinson had assumed would become available by 1990. NASA hoped that the lab station might be designed as a foot in the door leading eventually to a more ambitious and costly shipyard station, but the January 1986 Challenger accident meant that such schemes came under close scrutiny and were found wanting. At the same time, systems such as the Centaur-G' stage were judged to be too volatile to carry on board a piloted spacecraft, reducing planned Shuttle utility.
The cost of Shuttle operations was also a major factor in the death of early 1980s Mars plans. The Nixon Administration had made decisions that ensured a low Shuttle development cost and high operations costs. NASA, a part of the Executive Branch, felt obligated despite this to continue to tout Shuttle economy. The U.S. space agency was cagey about how much it spent on Shuttle missions; for a time, a figure of $110 million per flight was used in Shuttle payload cost calculations. Independent cost estimates placed the per-flight cost of the Shuttle at up to $1.5 billion; even assuming that the true cost was "only" $1 billion per flight, the Earth-to-orbit transportation cost of Parkinson's Mars expedition alone would have reached $9 billion, or about double the highest cost estimate for his entire expedition.
Images in this post are © David A. Hardy/www.astroart.org. Used by permission.
References:
"Is Nuclear Propulsion Necessary? (or Mars in 1995!)," AIAA-80-1234, R. Parkinson; paper presented at the AIAA/SAE/ASME 16th Joint Propulsion Conference in Hartford, Connecticut, 30 June-2 July 1980.
"Mars in 1995!" R. Parkinson, Analog Science Fiction/Science Fact, June 1981, pp. 38-49.
"A Manned Mars Mission for 1995," R. Parkinson, Journal of the British Interplanetary Society, October 1981, pp. 411-424.
"Mars in 1995!" R. Parkinson, Spaceflight, November 1981, pp. 307-312.
