No Shortage of Dreams

It was the best of times. It was the worst of times. (With apologies to Charles Dickens.)

For NASA, the year 1967 began with the promise of a bold start for the Apollo Applications Program (AAP), the planned successor to the Apollo lunar program, which would see space station missions in low-Earth orbit and advanced lunar exploration missions. Top NASA officials briefed the press on their ambitious AAP plans on 26 January 1967 (see "More Information" below).

Barely a day later, fire raged through the crew cabin of the Apollo 1 Command and Service Module (CSM) spacecraft during a test on the launch pad, killing astronauts Gus Grissom, Ed White, and Roger Chaffee. The resulting investigation angered Congress — NASA had failed to report persistent problems in its relations with North American Aviation (NAA), the CSM prime contractor. Affronted legislators, already eager to cut government expenditures because of the soaring cost of U.S. military involvement in Indochina, responded in August-September 1967 by slashing President Lyndon Baines Johnson's Fiscal Year (FY) 1968 NASA budget request by nearly half a billion dollars.

The cuts mostly affected projects aimed at giving NASA a post-Apollo future; AAP, of course, but also the Voyager robotic Venus/Mars exploration program (see "More Information" below) and advance planning for piloted missions beyond the Moon, including piloted Mars/Venus flybys. Members of the NASA Office of Manned Space Flight (OMSF) Planetary Joint Action Group (JAG) had hoped that major funding for piloted flybys could begin in FY 1969, with the first in a series of piloted flybys — a Mars flyby with sample return — leaving Earth in late 1975 (see "More Information" below).

Even as OMSF had sought piloted flybys, the scientific community had continued its perennial quest for an expanded robotic program. In a February 1967 report to the Johnson White House, the President's Science Advisory Council (PSAC) disparaged piloted flybys and urged a 1970s program that would see robotic spacecraft begin a wide-ranging reconnaissance of the entire Solar System. Scientists were outraged when instead the FY 1968 budget cuts threatened to end U.S. robotic exploration entirely after the twin Mariner '69 Mars flybys.

In October and November 1967, NASA Administrator James Webb spoke out in favor of new robotic planetary missions in the 1970s. He urged members of Congress to take note of Soviet plans for robotic exploration beyond the Moon. Talks began with White House budget officials and Congressional leaders aimed at salvaging a 1970s planetary program from the wreckage of the FY 1968 budget process.

Meanwhile, in Florida, components of AS-501, the first flight-ready Saturn V rocket, came together with an Apollo CSM in the giant Vertical Assembly Building (VAB) at NASA Kennedy Space Center (KSC). Without the three-stage behemoth an Apollo Moon landing was impossible. The testing and assembly process had begun months before the Apollo 1 fire with the aim of a launch in the first quarter of 1967, but preparation for the automated test mission — which NASA designated Apollo 4 — hit one snag after another.

Following the fire, NASA subjected the CSM NAA had delivered to KSC for the Apollo 4 mission to enhanced scrutiny. The spacecraft, designated CSM-017, was found to contain more than 1400 wiring errors. Fixing them required months. Welding errors in the NAA-built Saturn V S-II second stage also needed correction.

The giant rocket was at last rolled out to Launch Pad 39A on 26 August 1967, but its troubles were not over, for Apollo 4 was also a test of launch pad hardware and pre-launch procedures. As the launch team struggled to make pad and rocket function together, the press, the public, and the Congress became increasingly impatient.

Apollo 4 lifted off at last on 9 November 1967. Rocket, spacecraft, launch facilities, and world-wide tracking & communications network operated together almost flawlessly.

About three hours after insertion into a 190-kilometer-high (118-mile-high) low-Earth orbit, the AS-501 Saturn V S-IVB third stage restarted to boost CSM-017 into an elliptical orbit. It was the first orbital restart of the stage, which would boost Apollo missions out of Earth orbit to the Moon.

The National Geographic Society-Palomar Observatory Sky Survey (NGS-POSS) imaged the sky from the North Celestial Pole to about 30° south declination between November 1949 and December 1958. The NGS-POSS was not conceived as a search for asteroids, but inevitably they appeared as streaks on many of its nearly 2000 glass photographic plates.

On 14 September 1951, for example, NGS-POSS astronomers Rudolph Minkowski and Albert George Wilson discovered asteroid 1951 RA. By noting its position on plates made as early as 31 August 1951, they were able to determine that it travels around the Sun in an inclined orbit that crosses the orbits of Earth and Mars. It completes an orbit every 508 days.

They determined that their new-found asteroid never comes very close to Mars — when it crosses the Red Planet's orbit about the Sun it is well above the orbital plane. When it crosses Earth's orbit, on the other hand, it is very near the orbital plane. As a result, it can pass very close to Earth. Soon after it was discovered, astronomers determined that 1951 RA would pass near Earth in 1969.

1951 RA was of sufficient interest to be made the 1620th named asteroid. In 1956, it was dubbed 1620 Geographos in honor of the National Geographic Society, which funded the NGS-POSS. The name Geographos means "geographer" in Greek.

1620 Geographos became a subject of special interest for University of California at Los Angeles astronomer Samuel Herrick. Following the 1969 close flyby, during which he refined knowledge of the parameters of its orbit, Herrick calculated that 1620 Geographos would pass close to Earth in 1994. He believed that its "ominous" orbit meant it stood a very good chance of striking Earth sometime during "the Third Millennium" (that is, in the interval between the years 2001 and 3001).

Herrick presented his results at the International Astronomical Union's Physical Studies of the Minor Planets colloquium held at Kitt Peak Observatory in March 1971. His contribution did not, however, appear in the colloquium proceedings NASA published later that year. Herrick subsequently passed away at age 62 on 24 March 1974.

According to Dutch-American astronomer Tom Gehrels, editor of the proceedings of the 1971 meeting, Herrick turned his contribution into a proposal to use 1620 Geographos as a planetary engineering tool that might infuse Earth's crust with new mineral wealth. This led Gehrels and the referees of the 1971 proceedings to declare Herrick's contribution to be "premature" and "outrageously innovative" and reject it.

Before the decade was out, Gehrels had an apparent change of heart. In 1979, he edited the first Asteroids compilation volume. Published by The University of Arizona Press, it included more than 50 papers summing up the field of asteroid studies. Among them was the review draft of Herrick's 1971 paper.

Herrick proposed a two-phase plan spanning about five years which would, he declared, generate much greater public enthusiasm than the Apollo lunar landings. In the first phase, engineers would used unspecified propulsive means to push 1620 Geographos into a safer orbit and "explosive cleaving" to separate a portion of the asteroid and push it toward Earth.

The second phase would see the separated portion guided toward an impact on the Isthmus of Panama. Herrick painted a target on the Atrato River in Colombia, which, he explained, had been proposed in the year 1540 as the site for a canal linking the Caribbean Sea and the Pacific Ocean.

On 25 March 1994, the impactor would streak through midnight skies over the cities of Quito, Bogota, and Medellin on its way to a "rendezvous" with the "jungle wasteland of northwestern Colombia." The resultant impact crater would form a "new canal from sea to sea." The "interocean Crater-Canal" would include no locks — it would be a sea-level passage through the isthmus that would permit the mixing of Caribbean and Pacific waters.

Herrick assumed that 1620 Geographos would be made of "nickel and the heavier elements that are mostly locked in the earth's core: rhenium, osmium, iridium, platinum, gold, etc." The impact would, he estimated, deposit on Earth extraterrestrial minerals worth 900ドル billion. They would be collected from the water-filled crater as Earth's supply of these valuable minerals became depleted.

Herrick acknowledged that potential regional and global ecological effects of the 1994 impact would have to be carefully studied. He also acknowledged that 1620 Geographos might not be made of useful metals. He suggested that the techniques developed to deflect most of the asteroid away from Earth and excavate the canal in 1994 could, if necessary, be applied to another, more mineralogically suitable Earth-approaching asteroid. Searching for a new candidate impactor could also reveal future threats to Earth.

In 1994, 20 years after Herrick's passing, 1620 Geographos orbited nearer Earth than it had in two centuries. It did not, however, pose a threat — at its closest approach it passed about five million kilometers away (about 12 times the distance between the Earth and the Moon). The asteroid will not pass as close again until the 26th century. Earth is safe from 1620 Geographos on a time-scale of millions of years.

On 25 January 1994, the Clementine spacecraft lifted off from Vandenberg Air Force Base, California, bound for the Moon and 1620 Geographos. The spacecraft was intended to collect scientific data while demonstrating sensor and miniaturized spacecraft technologies that could be applied to ballistic missile defense systems. After a leisurely one-month transfer, Clementine orbited over the poles of the Moon for about two months (it was the first lunar polar orbiter).

On 3 May 1994, Clementine began a circuitous transfer to 1620 Geographos. Had it succeeded, it would have become the first spacecraft to fly by a near-Earth asteroid. Unfortunately, a computer malfunction on 7 May caused Clementine to fire one of its thrusters continuously, expending most of its remaining propellant supply and imparting a spin rate sufficient to render most of its instruments ineffective.

During the 1994 close approach Earth-based radar studies showed that 1620 Geographos is five kilometers long by about two kilometers wide. It is probably a "rubble pile" made up of many small asteroids loosely bound by mutual gravitational attraction. Earth-based studies have also revealed that it is a mainly stony asteroid not especially rich in metals.

Sources

"Voyage to the Planets," Kenneth F. Weaver, National Geographic, Volume 138, Number 2, August 1970, pp. 174-178.

"Exploration and 1994 Exploitation of Geographos," Samuel Herrick, Asteroids, Tom Gehrels, editor, The University of Arizona Press, 1979, pp. 222-226.

Dictionary of Minor Planet Names, Lutz D. Schmadel, Springer-Verlag, 1992, p. 211.

More Information

To Mars By Way of Eros (1966)

MIT Saves the World: Project Icarus (1967)

Multiple Asteroid Flyby Missions (1971)

Earth-Approaching Asteroids as Targets for Exploration (1978)

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

There's no award for "Most Imaginative Space Engineer," but if there were, Geoffrey Landis would certainly be a top contender. In fact, if such an award is ever created, it should perhaps be named the Geoffrey, in parallel with science fiction's Hugo Award, which owes its name to pioneering author, editor, and publisher Hugo Gernsback. Not incidentally, Landis owns a pair of Hugos; he received his first in 1992 for "A Walk in the Sun," a short story set on the Moon, and his second in 2003 for his story "Falling Onto Mars."

Landis is an engineer at NASA's Glenn Research Center (GRC) in Cleveland, Ohio. Much of his NASA work has centered on energy systems, with an emphasis on solar photovoltaic power.

In a brief paper prepared for the February 2003 Space Technology and Applications International Forum in Albuquerque, New Mexico, Landis made a compelling case for Venus, not the Moon, nor Mars, nor a twirling sphere, torus, or tube in open space, as the ideal place to establish an off-Earth human settlement. Specifically, he set his sights on the Venusian atmosphere just above the dense sulfuric-acid clouds. Landis called it "the most earth-like environment (other than the Earth itself) in the Solar System."

Most people think of Venus as a hell planet because they think only of its surface. By about 1960, scientists using Earth-based instruments had determined that Venus had a temperature of 342° C (648° F). Many, however, refused to believe that Venus could be so hot. Some tried to find a loophole: they hypothesized that the Venusian atmosphere was hot while its surface was cool enough for liquid water and life.

Mariner 2, the first successful interplanetary spacecraft, flew past Venus in December 1962. Its crude scanning radiometer found a lower temperature — around 230° C (450° F) — though one still much higher than most planetary scientists expected. Mariner 2 also determined that air pressure at the Venusian surface was at least 20 times Earth sea-level pressure.

For more than two decades, Venus was the Soviet Union's favorite Solar System exploration target. The Venera landers determined that its surface is made of basalt, a volcanic rock. They also found that the mean atmospheric pressure at the surface is 96 times Earth sea-level pressure and that the surface temperature averages about 462° C (863° F) with relatively modest day/night, latitude, and altitude variations.

The Venusian atmospheric temperature, on the other hand, was found to vary significantly with altitude, a fact that the Soviet Union would put to good use. In June 1985, the Vega 1 and Vega 2 spacecraft released armored landers and lightly constructed rubber balloons as they flew past Venus on their way to Comet Halley. The Vega 1 lander touched down but returned minimal data. Vega 2 landed successfully and survived the hellish surface conditions for 56 minutes.

The twin three-meter-diameter, helium-filled balloons deployed between 50 and 55 kilometers (31 and 34 miles) above the Venusian surface — that is, just above the cloud-tops, in the zone Landis saw as promising for human settlement. Their small instrument payloads transmitted data for approximately two days — until they exhausted their chemical batteries.

In that time, the balloons rode the carbon dioxide winds from their deployment points over the nightside into bright Venusian daylight. The Vega 2 balloon travelled about 11,100 kilometers (6900 miles) and the Vega 1 balloon travelled 11,600 kilometers (7210 miles). When their instrument payloads exhausted their batteries, the balloons carrying them showed no sign of imminent failure. They might have lasted for months or even years.

The fragile balloons could last so long because 50 kilometers above Venus, just above the cloud tops, the temperature ranges from between 0° C to 50° C (32° F to 122° F) and the atmospheric pressure approximates Earth sea-level pressure. A thin fabric cover was sufficient to shield each balloon from sulfuric acid droplets drifting up from the cloud layer.

Venus settlers would float where Vega 1 and Vega 2 floated, but Landis rejected helium balloons. He noted that, on Venus, a human-breathable nitrogen/oxygen air mix is a lifting gas. A balloon containing a cubic meter of breathable air would be capable of hoisting about half a kilogram, or about half as much weight as a balloon containing a cubic meter of helium. A kilometer-wide spherical balloon filled only with breathable air could in the Venusian atmosphere lift 700,000 tons, or roughly the weight of 230 fully-fueled Saturn V rockets. Settlers could build and live inside the air envelope.

The air envelope supporting a settlement would not necessarily maintain a spherical form. Lack of any pressure differential would allow the gas envelope to change shape fluidly over time. It would also limit the danger should the envelope tear. The internal and external atmospheres would mix slowly, so the settlement atmosphere would not suddenly turn poisonous, nor would the settlement rapidly lose altitude.

A repair crew would not require pressure suits, Landis explained. They would, of course, need air-tight face masks to provide them with oxygen and keep out carbon dioxide; adding goggles and unpressurized protective garments would keep them safe from acid droplets.

Acid droplets in the Venusian atmosphere would no doubt be annoying, but Venus would lack the frequent toxic dust storms of Mars. Orbiting nearly twice as close to the Sun as does Mars, a Venusian solar farm would have available four times as much solar energy at all times — and with no dust storms to get in the way. Landis noted that solar panels could collect almost as much sunlight reflected off the bright Venusian clouds as they could from the Sun itself.

Mars, the Moon, and free-space habitats all must contend with solar and galactic-cosmic ionizing radiation. A settlement 50 kilometers above Venus, by contrast, could rely on the Venusian atmosphere to ward off dangerous radiation. Radiation exposure would be virtually identical to that experienced at sea level on Earth.

Many aspiring space settlers assume that humans and the plants and animals they rely on (or simply like to have around) will be able to live in one-sixth or one-third Earth gravity — the gravitational pull felt on the Moon and on Mars, respectively — with no ill effects. The hard reality, however, is that no one knows if this is true. It is possible that astronauts living in hypogravity — that is, gravity less than one Earth gravity — will experience health effects similar to those they experience during long stays in microgravity (for example, on board the International Space Station).

Venus is nearly as dense and as large as Earth, so its gravitational pull is about 90% that of humankind's homeworld. The likelihood that hypogravity will make long-term occupancy unhealthful might thus be reduced.

The Venusian atmosphere is rich in resources needed for life and the Venusian surface, while hellish, would lay only 50 kilometers away from the settlement at all times. Landis suggested that Venus settlers might use a suspended super-strong cable to lift silicon, iron, aluminum, magnesium, potassium, calcium, and other essential chemical elements to the floating settlement. He noted that laboratory experiments aimed at producing robots hardy enough to function on Venus for long periods had already begun; operators might use such rovers to remotely mine the surface from the comfort of the floating settlement.

Landis pointed to the Main Asteroid Belt between Mars and Jupiter as a potential source of resources for Venus. He noted that any given asteroid in the Main Belt is easier to reach from Venus than from the Earth or Mars. A spacecraft launched from Venus on a minimum-energy trajectory can, for example, reach resource-rich 1 Ceres, the largest asteroid, in a little less than an Earth year; a minimum-energy trip from Earth to 1 Ceres would need a little more than an Earth year.

The large Main Belt asteroids are in fact generally located farther away from each other than they are from Venus. They also orbit the Sun much more slowly: 3 Vesta needs 1325 Earth days to circle the Sun once; 1 Ceres needs 1682 Earth days; 2 Pallas, 1686 Earth days; and 10 Hygeia, in the outer part of the Main Belt, 2035 Earth days. This means that minimum-energy transfer opportunities between Main Belt asteroids occur years or even decades apart. Opportunities for minimum-energy transfers between Venus and any Main Belt asteroid, on the other hand, occur about once per Venus year (that is, about once every 225 Earth days).

As the journeys of the twin Vega balloons illustrate, Venus atmosphere settlements would ride fast winds. Those near the equator would circle the planet every four days. This would mean, Landis explained, that they would experience a day/night pattern of two days of darkness followed by two days of light. He expected that settlements eager for a more Earth-like lighting pattern could migrate to the Venusian circumpolar regions, where a circuit around the planet would be shorter.

If many "cloud cities" were eventually established in the atmosphere of Venus, then a preference for the poles might lead to crowding. If, on the other hand, any latitude were fair game, then Venus would offer for settlement a total area 3.1 times Earth's land area — that is, more than three times greater than the surface area of Mars. Landis wrote that, eventually, a "billion habitats, each one with a population of hundreds of thousands of humans, could. . . float in the Venus atmosphere."

Sources

Mariner Venus 1962 — Final Project Report, NASA SP-59, NASA Jet Propulsion Laboratory, 1965.

Soviet Space Programs 1980-1985, Nicholas L. Johnson, Volume 66, Science and Technology Series, American Astronautical Society, 1987, pp. 186-188.

"Colonization of Venus," Geoffrey A. Landis, Space Technology and Applications International Forum (STAIF) 2003, Albuquerque, New Mexico, 2-5 February 2003; American Institute of Physics Proceedings 654, Mohamed S. El-Genk, editor, 2003, pp. 1193-1198.

More Information

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

Venus as Proving Ground: A 1967 Proposal for a Piloted Venus Orbiter

Floaters, Armored Landers, Radar Orbiters, and Drop Sondes: Automated Probes for Piloted Venus Flybys (1967-1968)

Two for the Price of One: 1980s Piloted Missions with Stopovers at Mars and Venus (1968)

Multiple Asteroid Flyby Missions (1971)

Footsteps to Mars (1993)

The year 1984 was nearly equidistant between the first Moon landing of 1969 and the evocative year 2001. The Space Shuttle, flown into orbit for the first time on 12 April 1981, had been declared operational by President Ronald Reagan at the end of its fourth mission on 4 July 1982. In his 25 January 1984 State of the Union Address, Reagan gave NASA leave to use the Shuttle to launch and assemble its long-sought, long-postponed low-Earth-orbit (LEO) Space Station.

Space supporters could be forgiven for believing that, after a gap in U.S. piloted space missions that spanned from Apollo-Soyuz in July 1975 to the first Shuttle mission, a new day was dawning: that Shuttle and Station would lead in the 1990s to piloted flights beyond LEO. Surely, Americans would walk on the Moon again by 2001, and would put boot prints on Mars not long after.

There were, of course, some problems: despite being declared operational, Shuttle operations had yet to become routine. Despite some high-flown rhetoric at the time it was announced — President Reagan spoke of following "our dreams to distant stars" — the Station the White House agreed to fund was meant to serve as a microgravity laboratory, not a jumping-off place for voyages beyond LEO. Hardware for any "spaceport" function it might eventually have would need to be bolted on later, after some future President gave the word.

In addition, NASA's robotic exploration program remained a shadow of its former self. There would, for example, be no U.S. robotic probe in the international armada to Halley's Comet in 1985-1986.

Nevertheless, with American astronauts in space again and concept artists hard at work on tantalizing visions of sprawling space stations, very few foresaw rough waters ahead. It seemed the perfect time to revive advance planning for missions to the Moon and beyond, which had been virtually moribund in the U.S. since the early 1970s.

Advance planning revived first outside of NASA. Participants in the 1981 and 1984 The Case for Mars conferences, mindful of how Apollo had left no long-term foothold on the Moon, developed a plan for establishing and maintaining a permanent Mars base. The Planetary Society, with 120,000 members the largest spaceflight advocacy group on Earth, helped support the conferences.

The Planetary Society had grown rapidly following its founding in 1980 in large part because its President was planetary scientist Carl Sagan. His 1980 PBS television series Cosmos had done more to popularize space exploration than any public outreach effort since Wernher von Braun's 1950s collaborations with Walt Disney and Collier's weekly magazine.

In 1984, The Planetary Society asked the Space Science Department of Science Applications International Corporation (SAIC) in suburban Chicago, Illinois, to outline three piloted space projects for the first decade of the 21st century. These were: an expedition to scout out a site for a permanent lunar base; a two-year journey to a near-Earth asteroid; and, most ambitious, a three-year mission to land three astronauts on Mars.

The three projects were not meant to occur in the order in which they were presented, and any one of them could stand alone. In its report to The Planetary Society, the six-man SAIC study team declared that "any. . .would be a commanding goal for future U.S. space exploration."

The Planetary Society paid SAIC a modest fee. In their foreword to the SAIC report, Sagan and his lieutenant, Jet Propulsion Laboratory engineer Louis Friedman, called the team's work "a labor of love."

Space missions of an international character were of interest to The Planetary Society; it saw in them a means of reducing geopolitical tension on Earth and of dividing the cost of exploration among the space-faring nations. In their foreword, Sagan and Friedman wrote of their hope that the study would "stimulate renewed interest in major international initiatives for the exploration of nearby worlds in space." The SAIC team did not, however, emphasize this; apart from the European Space Agency-provided Spacelab modules from which the pressurized modules of its spacecraft would be derived, there was little evidence of international involvement in its proposed projects.

The SAIC team assumed that NASA would convert the Space Station into an LEO spaceport at the turn of the 21st century. The U.S. civilian space agency would use the Space Shuttle fleet to launch to the Station hangars, living accommodations for crews in transit to destinations beyond LEO, remote manipulators, propellant storage tanks, and auxiliary spacecraft such as Orbital Transfer Vehicles (OTVs). Parts and propellants for the team's piloted Moon, asteroid, and Mars spaceships would also reach the Station on board Shuttle Orbiters.

For its lunar base site survey mission, the SAIC team assumed no Space Shuttle upgrades. The standard Shuttle Orbiter could in theory carry up to 60,000 pounds (27,270 kilograms) to LEO in its 15-by-60-foot (4.6-by-18.5-meter) payload bay. Of this, 5000 pounds (2268 kilograms) would comprise Airborne Support Equipment (ASE) — that is, hardware for mounting payloads in the payload bay, providing them with electricity, thermal control, and other required services, and deploying them in LEO.

SAIC's lunar mission closely resembled the one it had presented in its December 1983 report to the National Science Foundation (please see "More Information" below). The mission — for which SAIC gave no start date — would need a total of 12 Shuttle launches and four piloted and automated "sorties" to the Moon.

SAIC planners assumed that the beefed-up LEO Station would normally include in its fleet of auxiliary vehicles two reusable OTVs, each with a fully fueled mass of about 70,400 pounds (32,000 kilograms). These would suffice for the lunar project, but more OTVs — including some considered expendable — would be needed for the asteroid and Mars missions.

At the start of each lunar sortie, a "stack" comprising OTV #1, OTV #2, and a lunar payload would move away from the Station. OTV #1 would fire its twin RL-10-derived engines at perigee (the low point in its Earth-centered orbit) to push OTV #2 and the lunar payload into an elliptical orbit. OTV #1 would then separate and fire its engines at next perigee to lower its apogee (the high point in its orbit) and return to the Space Station for refurbishment and refueling. OTV #1 would burn 59,870 pounds (27,215 kilograms) of propellants.

OTV #2 would fire its engines at next perigee to place the lunar payload on course for the Moon. Depending on the nature of the payload, OTV #2 would then either fire its engines to slow down and allow the Moon's gravity to capture it into lunar orbit or would separate from the lunar payload and adjust its course so that it would swing around the Moon and fall back to Earth.

The SAIC team envisioned that OTV #2 would be fitted with a reusable aerobrake heat shield. After returning from the Moon, it would skim through Earth's upper atmosphere to slow itself, then would adjust its attitude using small thrusters so that it would gain lift and skip up out of the atmosphere. At apogee, it would fire its twin engines briefly to raise its perigee out of the atmosphere. OTV #2 would then rendezvous with the Station, where it would be refurbished and refueled for a new mission.

The SAIC team's lunar base survey mission would begin with Sortie #1, which would include no crew. OTV #2 would swing around the Moon after releasing a payload comprising a one-way lander bearing a pair of nearly identical 15,830-pound (7195-kilogram) lunar surface vehicles. Each vehicle would comprise a pressurized rover and a trailer. The lander would descend directly to a soft landing in the proposed lunar base region.

Like Sortie #1, Sortie #2 would include no crew. Unlike Sortie #1, Sortie #2 would see OTV #2 capture into a 30-mile-high (50-kilometer-high) lunar orbit. There it would deploy an unfueled single-stage Lunar Excursion Module (LEM) lander. OTV #2 would then fire its twin engines to depart lunar orbit for Earth. After aerobraking in Earth's atmosphere, it would return to the Station.

The first piloted sortie, Sortie #3, would see OTV #2 deliver to lunar orbit four astronauts in a pressurized crew module. They would pilot the OTV #2/crew module combination to a docking with the waiting LEM. The crew would board the LEM, load it with propellants from OTV #2, then undock. OTV #2 would fire its engines to depart lunar orbit, fall back to Earth, aerobrake in the atmosphere, and return to the Station.

The astronauts, meanwhile, would descend in the LEM to a landing near the one-way lander. After unloading the twin rover-trailers, the four-person crew would split into two two-person crews and begin a 30-day survey of candidate base sites within the 30-mile-wide (50-kilometer-wide) proposed lunar base region.

In addition to providing living quarters, the rover-trailers would each carry 2640 pounds (1200 kilograms) of science instruments for determining surface composition, seismicity, and stratigraphy at candidate base sites, plus a scoop or blade for moving large quantities of lunar dirt. They would rely on liquid oxygen-liquid methane fuel cells for electricity to power their drive motors.

The rover-trailers would travel together for safety; if one broke down and could not be repaired, the other could return all four astronauts to the waiting LEM.

Travel in harsh sunlight would be avoided. SAIC assumed that the rover-trailer combinations would spend most of the two-week lunar daylight period parked at a "base camp" under reflective thermal shields, venturing out for only a few 24-hour excursions. They would travel continuously during the two-week lunar night, however, their way lit by headlights and sunlight reflected off the Earth.

Sortie #4 would see OTV #2 and the crew module return without a crew to lunar orbit. The crew, meanwhile, would park the rover-trailers under the base camp thermal shields, load the LEM with samples, photographic film, and other souvenirs of their rover-trailer traverses, and ascend in the LEM to lunar orbit to rendezvous and dock with the OTV #2/crew module combination. They would then undock from the LEM, depart lunar orbit, aerobrake in Earth's atmosphere, and rendezvous with the Station. The SAIC planners proposed that the orbiting LEM and parked rover-trailers be put to use again during the initial phase of lunar base buildup.

For its piloted asteroid mission, SAIC considered eight mission plans taking in two asteroids in the Main Belt between Mars and Jupiter and four Earth-approaching asteroids. Three of the Earth-approaching asteroids were hypothetical — asteroid hunting was ramping up in the early 1980s, so the SAIC team sought to anticipate new discoveries. The team settled on a two-year voyage that would include a wide swing out into the Main Belt. There the spacecraft would fly past asteroid 1577 Reiss.

The main target of the mission would, however, be the Earth-approaching asteroid 1982DB, in 1984 the most easily accessible Earth-approaching asteroid known. Now named 4660 Nereus, nearly 40 years after its discovery it remains among the most accessible known asteroids.

Nine upgraded Shuttle Orbiters would launch parts and propellants for the asteroid mission spacecraft and the OTVs necessary to launch it from Earth orbit. The "65K" Shuttles SAIC invoked would be capable of launching 65,000 pounds (29,545 kilograms) to the Space Station. As with the lunar base survey mission, ASE would make up 5000 pounds (2268 kilograms) of the total. Following assembly and checkout, the piloted asteroid mission spacecraft/OTV stack would move away from the Station.

A total of five OTVs would be needed to launch the asteroid mission spacecraft out of Earth orbit. OTV #1 would ignite at the stack's perigee to raise its apogee. It would then separate and fire its engines at next perigee to lower its apogee, re-circularizing its orbit so it could return to the Station. OTV #2 would ignite at next perigee to boost the stack's apogee higher, then would detach and aerobrake in Earth's atmosphere to return to the Station. OTV #3 and OTV #4 would do the same.

The time between perigees would increase with each burn: the five-burn sequence would need about 48 hours, with nearly 24 hours separating the OTV #4 and OTV #5 perigee burns. On 5 January 2000, OTV #5 would fire its twin engines at perigee, launching SAIC's asteroid mission spacecraft onto a Sun-centered path toward 1577 Reiss and 1982DB. OTV #5, its propellant tanks empty, would then be cast off.

With the Earth-Moon system shrinking behind them, the three-person crew would spin up their spacecraft. Twin 81.25-foot-long (25-meter-long) hollow arms, each carrying a solar array and a radiator panel, would link twin habitat modules to a cylindrical central hub. Habitats, booms, and hub would spin three times per minute to create acceleration in the habitats, which the crew would feel as a continuous pull of 0.25 Earth gravities.

SAIC lacked data on whether 0.25 gravities would be sufficient to mitigate the deleterious effects of weightlessness (indeed, such data do not exist at this writing). The team explained that its choice of 0.25 gravities constituted "a compromise between the desire to have a near normal gravity, a short habitat arm length, and a slow spin rate."

A logistics supply module and two propulsion systems would be linked to the central hub's aft end. The main propulsion system, which would burn liquid methane and liquid oxygen, would be used for course corrections during the long trip from Earth to 1982DB and for departure from 1982DB. The storable-bipropellant secondary system would be used to perform 1982DB station-keeping maneuvers and course corrections during the short trip from 1982DB to Earth.

The hub's front end would have linked to it an experiment module, an "EVA station" airlock module for spacewalks, and a conical Earth-return capsule with a 37.4-foot (11.5-meter) flattened cone ("coolie hat") aerobrake. The experiment module would carry attached to its side a 16.25-foot (five-meter) radio dish antenna for high-data-rate communications.

The modules and propulsion systems on either end of the hub would spin as a unit in the direction opposite the hub, arms, and habitats, so would appear to remain motionless. Astronauts inside the hub-attached parts of the asteroid mission spacecraft would experience weightlessness.

The crew would point the Earth-return capsule aerobrake and the asteroid spacecraft's twin solar arrays toward the Sun, placing radiators, propulsion systems, logistics module, hub, hollow arms, experiment module, EVA station, and Earth-return capsule in protective shadow. In the event of a solar flare, the crew would use the spacecraft's structure as radiation shielding: they would retreat to the logistics module, placing aerobrake, Earth-return capsule, EVA station, experiment module, hub, and logistics module between themselves and the active Sun.

During their two-year mission, the asteroid mission crew would spend about 23 months carrying out "cruise science." Four hundred and forty pounds (200 kilograms) of the spacecraft's 1650-pound (750-kilogram) cruise science payload would be devoted to studies of human physiology in space, and 375 pounds (170 kilograms) would be used to perform solar observations and other astronomy and astrophysics studies. In addition, the spacecraft would carry 55 pounds (25 kilograms) of long-duration exposure samples on its exterior. These swatches of spacecraft metals, foils, paints, ceramics, plastics, fabrics, and glasses would be retrieved by spacewalking astronauts before the end of the mission.

SAIC's asteroid mission spacecraft would fly past 4.2-kilometer-wide 1577 Reiss at a speed of 2.8 miles (4.7 kilometers) per second 14 months into the mission (2 March 2001) and would intercept 1982DB just over six months later, on 12 September 2001. The 1577 Reiss flyby would occur while asteroid and spacecraft were 216.7 million miles (348.7 million kilometers) from the Sun. The spacecraft would spend 30 days near 1982DB, during which time Earth would range from 55 million miles (90 million kilometers) distant on 12 September 2001 to 30 million miles (50 million kilometers) away on 12 October 2001.

While close to 1577 Reiss, the crew would for the first time activate the "asteroid science" equipment packed in the experiment module. They would bring to bear on the Main Belt asteroid a 220-pound (100-kilogram) package of remote-sensing instruments, including a mapping radar and instruments for determining surface composition. They would also image 1577 Reiss using high-resolution cameras with a total mass of 110 pounds (50 kilograms).

The asteroid science instruments would be put to use again as the spacecraft closed on 1982DB. During approach, the crew would locate the asteroid precisely in space, determine its rotational axis and rate, and perform long-range mapping. They would then despin the spun parts of their spacecraft and, using the secondary propulsion system, halt a few hundred miles/kilometers from 1982DB to perform detailed global mapping. This would enable selection of sites for in-depth investigations.

The astronauts would then use the secondary propulsion system to place the spacecraft in a "stationkeeping" position a few tens of miles/kilometers away from 1982DB. Every three days they would move even closer — to within a few miles/kilometers — so that a pair of space-suited astronauts could leave the EVA station module airlock to explore the asteroid's surface.

The astronauts would each use a Manned Maneuvering Unit (MMU) to transfer from the spacecraft to 1982DB. The asteroid mission MMUs, modeled on the MMU first tested during Space Shuttle mission STS-41B (3-11 February 1984), would use gaseous nitrogen as propellant.

The SAIC team noted that 1982DB would have "negligible gravitational attraction," so the asteroid mission spacecraft would be unable to orbit it in a conventional sense. Spacecraft and asteroid would instead share nearly the same orbit around the Sun. 1982DB would, meanwhile, rotate at some unknown rate. The asteroid's rotation would mean that astronauts at a site of interest on its surface would tend to be move away from their spacecraft. In fact, if 1982DB rotated quickly enough, astronauts on its surface might pass out of sight of the spacecraft during their four-hour "asteroid-walks."

The SAIC team judged that loss of radio and visual contact with the surface crew would be undesirable, so proposed that the astronaut left behind on the spacecraft perform station-keeping maneuvers to match 1982DB's rotation; that is, that the astronaut keep his or her shipmates in sight by maintaining a "forced circular orbit" around 1982DB. The team budgeted enough secondary propulsion system storable propellants for a velocity change of 32.5 feet (10 meters) per second per surface visit.

If 1982DB were found to rotate slowly, then the velocity change needed to maintain the spacecraft in its forced orbit would be reduced. In that case, only astronaut stamina, the supply of MMU propellant, and the mission's planned 30-day stay-time near 1982DB would limit the number of surface visits. The SAIC team envisioned that the astronauts might explore as many as 10 sites. After each surface excursion, the spacecraft would resume stationkeeping several tens of miles/kilometers away from 1982DB.

The SAIC team assumed that 1982DB would measure 0.62 miles (one kilometer) in diameter. They noted that an asteroid of that size would have roughly the same area as New York City's Central Park (1.32 square miles/3.41 square kilometers). Based on this comparison, they judged that "a 30-day stay time should provide ample time to complete a thorough investigation of the object." (I would argue that 10 four-hour visits to Central Park would be nowhere near sufficient to characterize it, but presumably 1982DB would lack the many unique amenities and diverse population of that iconic urban oasis.)

During their surface visits, the astronauts would deploy four small and three large experiment packages on 1982DB and would collect a total of 330 pounds (150 kilograms) of samples. The 110-pound (50-kilogram) small experiment packages would each include a seismometer and instruments for measuring temperature and determining surface composition. The 220-pound (100-kilogram) large packages would include a "deep core drill," a sensor package for insertion into the core hole, and a mortar.

After the spacecraft resumed station-keeping for the last time, the crew would remotely fire the mortars in succession to send shockwaves through 1982DB. The seismometers would register the shockwaves, enabling scientists to chart the asteroid's interior structure.

On 12 October 2001, the asteroid mission spacecraft would use the primary propulsion system for the last time to depart 1982DB. Using the secondary propulsion system, the crew would bend its trajectory so that it would almost intersect Earth. They would then spin up the spacecraft to restore artificial gravity in the hollow arms and habitats.

Three months later, they would load their samples, film, and other data products into the Earth-return capsule and undock from the spacecraft. On 13 January 2002, almost exactly two years after Earth departure, the crew would aerobrake their capsule in Earth's atmosphere and pilot it to a rendezvous with the Space Station. Meanwhile, the abandoned asteroid mission spacecraft would swing by Earth and enter a disposal orbit around the Sun.

SAIC's third proposed project, the first piloted Mars landing, would employ a four astronauts and six spacecraft (not counting OTVs). The largest spacecraft combination, the 265,880-pound (120,600-kilogram) Mars Outbound Vehicle (MOV), would comprise the 43,870-pound (19,600-kilogram) Interplanetary Vehicle (spacecraft 1), the 25,130-pound (11,400-kilogram) Mars Orbiter (spacecraft 2), and the conical 83,555-pound (37,900-kilogram) Mars Lander (spacecraft 3). The Mars Orbiter and Mars Lander together would comprise the Mars Exploration Vehicle.

The Interplanetary Vehicle would resemble the SAIC team's asteroid mission spacecraft, though it would lack an Earth-return capsule and would move through space with its logistics module pointed toward the Sun. The Interplanetary Vehicle's hub, twin hollow arms, and twin habitats would revolve three times per minute.

The Interplanetary Vehicle's EVA station would link it to the Mars Orbiter, a bare-bones, non-rotating vehicle made up of a single habitat module and hollow arm, a solar array, a radiator, a radio dish antenna, an EVA station, an unspecified propulsion system, and the conical Mars Departure Vehicle (spacecraft 4). The Mars Orbiter EVA station would link it to the Mars Lander ascent stage. The Mars Lander would include a 175.5-foot-diameter (54-meter-diameter) flattened-cone aerobrake.

SAIC's second, smaller Mars mission spacecraft combination, the 94,600-pound (43,000-kilogram) Earth Return Vehicle (ERV) (spacecraft 5), would resemble the asteroid mission spacecraft even more closely than would the Mars mission Interplanetary Vehicle. The ERV, which would include the 9750-pound (4430-kilogram) Earth Return Capsule (spacecraft 6), would depart Earth ahead of the MOV, on 5 June 2003, but would follow a Sun-centered path that would cause it to reach Mars after the MOV, on 23 January 2004. It would leave LEO with no crew on board.

A total of five Shuttle launches, each capable of putting into LEO 60,000 pounds (27,270 kilograms), would launch ERV and OTV parts and propellants to the Station. ASE would make up 5000 pounds (2268 kilograms) of each Shuttle Orbiter payload.

Three OTVs (two based permanently at the Station plus one assembled specifically for the Mars mission) would then launch the ERV toward Mars. Each OTV would in succession ignite its engines at perigee to increase the ERV's apogee, then would separate. OTV #1 would use its twin engines to return to the Station after separation, OTV #2 would rely on its aerobrake heat shield, and OTV #3 would expend all of its propellants to place the ERV on course for Mars and be discarded. The ERV's three-orbit Earth-departure sequence would last about six hours.

The MOV with four astronauts on board would leave Earth orbit 10 days later, on 15 June 2003. Thirteen Space Shuttle launches would place MOV and OTV parts and propellants into Earth orbit. Seven OTVs would perform perigee burns over the space of a little more than two days to boost the 265,300-pound (120,600-kilogram) MOV toward Mars. Following separation, OTV #1 would ignite its engines at perigee to return to the Station; OTVs #2 through #6 would return to the Station after aerobraking; and OTV #7 would burn all of its propellants and be discarded.

The MOV would arrive at Mars on 24 December 2003, 30 days ahead of the ERV. Assuming that telemetry from the ERV indicated that it remained able to support a crew, the MOV crew would cast off the Interplanetary Vehicle (this is depicted in the image at the top of this post), strap into the Mars Lander ascent capsule, and aerobrake in the martian atmosphere. The abandoned Interplanetary Vehicle would swing past Mars and enter solar orbit.

Following aerobraking, the two-part Mars Exploration Vehicle would climb to an apoapsis (orbit high point) of 600 miles (1000 kilometers). The Mars Orbiter and Mars Lander would then separate. One astronaut would remain on board the Mars Orbiter. He or she would ignite its propulsion system at apoapsis to raise its periapsis (orbit low point) to 600 miles (1000 kilometers), giving it a circular orbit about the red planet. The three astronauts in the Mars Lander, meanwhile, would fire its engine briefly at apoapsis to raise its periapsis to an altitude just above the martian atmosphere.

As the planet rotated beneath the Mars Lander, the three astronauts would prepare for atmosphere entry and landing. As the target Mars landing site came into range, they would ignite the Mars Lander engine at apoapsis, lowering their periapsis into the atmosphere. They would cast off the aerobrake after atmosphere entry and lower to a soft landing using the Mars Lander descent engine.

Immediately after touchdown, the crew would deploy a teleoperated rover. Trailing power cables, the rover would carry a small nuclear reactor a safe distance away from the Mars Lander and bury it. The crew would then remotely activate the reactor to supply their encampment with electricity.

SAIC's Mars mission would, of course, have a range of cruise, Mars orbital, and Mars surface science objectives. The study team explained that, during the six-month Earth-Mars cruise, the astronauts on board the Interplanetary Vehicle would have at their disposal a cruise science payload identical to that carried on board the asteroid mission spacecraft.

Human physiology studies during the trip to Mars would, in addition to any scientific objectives, have a prosaic operational goal: they would emphasize keeping the Mars landing crew in good shape for strenuous activity on the planet. The astronauts would also observe the Sun for science and to detect solar flares that might cause them harm.

The one-person Mars Orbiter and three-person Mars Lander crews would have many objectives at Mars, some primarily scientific and others primarily operational. The "primary duty" of the lone astronaut on board the Mars Orbiter would be to support the surface crew, the SAIC team explained. Four hundred and forty pounds (200 kilograms) of remote sensors would enable her or him to spot threatening weather conditions near the landing site and generate detailed maps of landing site terrain and surface composition for both the crew on Mars and scientists and mission controllers on Earth.

The surface crew would have as "a major goal" the selection of a future Mars base site, the SAIC team explained. They would have at their disposal 1980 pounds (900 kilograms) of science equipment, including a 220-pound (100-kilogram) Mobile Geophysics Lab rover, 110 pounds (50 kilograms) of high-resolution cameras, four small deployable science packages with a mass of 110 pounds (50 kilograms) each, and three large deployable science packages with a total mass of 880 pounds (400 kilograms) each.

The small packages would measure temperature, detect Marsquakes, and determine surface composition, while the large packages would include a 440-pound (200-kilogram) deep-core drill, a 220-pound (100-kilogram) sensor package for insertion down core holes, and a mortar for generating shock waves that the seismometers in the small packages would register, permitting scientists on Earth to understand the subsurface structure of the landing site. The surface crew would also set up an inflatable "tent" in which they would begin examination of the 550 pounds (250 kilograms) of Mars samples they would collect for return to Earth.

As their stay on Mars reached its end, the surface crew would load their samples, film, and other data products into the Mars Lander ascent stage and blast off to rendezvous and dock with the Mars Orbiter. The nuclear reactor they left behind would power equipment long after they departed. The SAIC team suggested, for example, that it could provide electricity to a device that would extract oxygen from the martian atmosphere and cache it for future Mars base builders.

The ERV, meanwhile, would close in on Mars. Like the asteroid spacecraft, it would move through space with its Earth-return aerobrake pointed toward the Sun.

After docking with the Mars Orbiter, the reunited crew would transfer their surface and orbital Mars data products to the Mars Departure Vehicle, then would undock from the Mars Orbiter and set out in earnest pursuit of their ride home. Because launching it back onto an interplanetary path after crew recovery in Mars orbit would demand considerable quantities of propellants, the ERV would not enter Mars orbit.

Instead, to reduce overall Mars mission mass (and thus the number of Shuttle launches needed to launch it into LEO and and the number of OTVs needed to place it on course for Mars), the crew would rendezvous with the ERV as it raced past the planet on a free-return trajectory that would take it back to Earth after 1.5 orbits around the Sun and 2.5 years of flight time. This approach, which SAIC termed Mars Hyperbolic Rendezvous (MHR), resembled the Flyby Landing Excursion Mode put forward by Republic Aviation engineer R. Titus in 1966. SAIC did not reference his pioneering work.

As might be expected, the SAIC team felt it necessary to study possible contingency modes for crew recovery in the event that MHR failed. If, for example, the unmanned ERV malfunctioned en route to Mars before the crew discarded the Interplanetary Vehicle and aerobraked the Mars Exploration Vehicle into Mars orbit, the astronauts could perform a powered Mars swingby maneuver using the Mars Lander and Mars Orbiter propulsion systems, bending their course so that they would intercept Earth 2.5 years later. The crew would separate in the Mars Lander near Earth and use its aerobrake to capture into Earth orbit.

Assuming, however, that all occurred as planned, the Mars Departure Vehicle would dock with the ERV a few hours after leaving Mars orbit. As Mars shrank behind them, the astronauts would transfer to the ERV with their samples and other data products, cast off the spent Mars Departure Vehicle, and spin the ERV's arms and habitats to create acceleration.

During the 2.5-year cruise home to Earth, the astronauts would study human physiology, the Sun, and astrophysics using a science payload identical to that carried on board the Mars mission Interplanetary Vehicle and the asteroid mission spacecraft. The SAIC team suggested that they might also continue study of the samples they had collected on Mars, though they did not indicate how this would be accomplished in the absence of a sample isolation lab, instruments, and tools.

On 5 June 2006, three years to the day after they left Earth, the crew would undock in the Earth Return Capsule, aerobrake in Earth's atmosphere, and rendezvous with the Space Station. The abandoned ERV, meanwhile, would swing past Earth and enter solar orbit.

SAIC offered preliminary cost estimates for its three projects and compared them with the cost of the Apollo Program, which encompassed 11 piloted missions, six of which landed two-man crews on the Moon. A dispassionate observer might be forgiven for believing that SAIC's cost estimates were unrealistically low. Partly this was the result of Shuttle cost accounting. Taking its lead from NASA, the SAIC team calculated that the 18 Shuttle flights needed for its Mars mission would cost only 2ドル billion, or about 110ドル million per flight.

The lunar base site survey would, the SAIC planners calculated, cost only 16ドル.5 billion, or about a quarter of the Apollo Program's 75ドル billion cost in 1984 dollars. The asteroid mission would be slightly cheaper, coming in at 16ドル.3 billion. The Mars mission, not surprisingly, would be the most costly of the three. Even so, it would only cost about half as much as Apollo; SAIC estimated that it would cost just 38ドル.5 billion.

Just 15 months after SAIC turned over its study to The Planetary Society, the optimistic era of piloted mission planning that had begun with the first Space Shuttle launch drew to a close. Following the loss of the Shuttle Orbiter Challenger on 28 January 1986, at the start of the 25th Shuttle mission, advance planning did not stop; in fact, it expanded as NASA sought to demonstrate that the Shuttle and Station Programs had worthwhile long-term objectives, and thus should continue in spite of Challenger.

The rules, however, had changed. After Challenger, few planners assumed that the Space Station President Reagan had called for in January 1984 would ever become an LEO spaceport, and even fewer assumed that Shuttle Orbiters alone would suffice to launch the components and propellants needed for piloted missions beyond LEO.

Post-Challenger plans would call for a purpose-built LEO spaceport to augment the Station and Shuttle-derived heavy-lift rockets to augment the Shuttle. Both of these would increase the estimated cost of piloted exploration beyond LEO.

Color artwork in this post is Copyright © Michael Carroll (http://stock-space-images.com/) and is used by kind permission of the artist.

Sources

Manned Lunar, Asteroid, and Mars Missions - Visions of Space Flight: Circa 2001, A Conceptual Study of Manned Mission Initiatives, Space Sciences Department, Science Applications International Corporation, September 1984.

"Visions of 2010 - Human Missions to Mars, the Moon and the Asteroids," Louis D. Friedman, The Planetary Report, March/April 1985, pp. 4-6, 22.

More Information

NASA Glenn Research Center's 2001 Plan to Land Humans on Mars Three Years Ago

High Noon on the Moon (1991)

Near-Term and Long-Term Goals: Space Station and Lunar Base (1983-1984)

A New Step in Spaceflight Evolution: To Mars by Flyby-Landing Excursion Mode (1966)