To Mars by Way of Eros (1966)

True-color image of Eros, the second-largest Near-Earth Asteroid, from the NEAR Shoemaker spacecraft. Image credit: NASA.

German astronomer Gustav Witt discovered the asteroid Eros on 13 August 1898. Eros was both the first asteroid found to orbit entirely outside of the Main Belt of asteroids between Mars and Jupiter and the first known planet-crosser; it crosses the orbit of Mars. Eros orbits the Sun in a little more than 643 days. Eros and Earth pass nearest each other — at a distance of about 14 million miles — every 81 years.

In March 1966, Eugene Smith, an engineer with Northrop Space Laboratories in Hawthorne, California, described a piloted Eros flyby mission. The mission would, he explained, help to prepare NASA for piloted missions to Mars. He wrote that "the value of the Eros mission to subsequent manned planetary flights having a higher level of difficulty and complexity is of no small consequence."

Eros exploration might also help scientists to understand Main Belt asteroids and small planetary moons (for example, the martian satellites Deimos and Phobos). Smith noted that Eros — which he described as "brick-shaped" — would pass within 14 million miles of Earth on 23 January 1975, its closest approach of the 20th century.

This proposal might seem prescient to readers familiar with current NASA Mars plans, which include a peculiar scheme to capture a boulder from the surface of a Near-Earth Asteroid using a robotic spacecraft and then send a crew to rendezvous with it in lunar orbit. The astronauts would perform spacewalks to sample the boulder. The mission, it is argued, would test a variety of technologies with potential piloted Mars mission and asteroid deflection applications.

Smith's mission was, however, part of a distinctly different piloted Mars program evolutionary strategy. At the time Smith presented his paper, NASA and its contractors devoted considerable effort to studies of piloted free-return Mars/Venus flyby missions based on Apollo technology. The first of these was expected to depart Earth for Mars in late 1975. Among other expected benefits, a piloted Mars flyby would provide interplanetary flight experience ahead of 1980s piloted Mars landings.

The Northrop engineer expected that a Mars flyby spacecraft would likely be so heavy that placing all of its components and propellants into space would need either a Saturn V rocket with a nuclear-thermal upper stage or multiple all-chemical Saturn V launches followed by assembly through multiple dockings in Earth orbit. He called instead for a 1975 piloted Eros flyby that would provide experience applicable to Mars landings, yet could depart Earth on a single uprated Saturn V rocket.

The 527-day Eros flyby mission would begin with launch from Cape Canaveral on 3 May 1974, at the opening of a 30-day launch window. The Eros Saturn V and its payload, the Eros Flyby Spacecraft Vehicle (EFSV), would stand 21 feet taller than the 363-foot-tall Apollo Saturn V.

Apollo (left) and Eros spacecraft configurations compared. With one exception (D is the Eros Mission Module while d is the Spacecraft Launch Adapter housing the Apollo Lunar Module), the lower-case and upper-case letters identify equivalent systems. a/A = Launch Escape System; b/B = Command Module; c/C = Service Module; e/E = Saturn V rocket Instrument Unit; f/F  = Saturn V S-IVB third stage; g/G = J-2 rocket motor. The Apollo configuration would measure 143 feet long; its Eros counterpart, 164 feet. Image credit: David S. F. Portree/Northrop Space Laboratories.

Eros Command Module/Eros Service Module. Image credit: Northrop Space Laboratories.

Smith's EFSV would comprise the conical Eros Command Module (ECM), outwardly a twin of the Apollo Command Module, but bearing a six-man crew; the Eros Service Module (ESM), a 21.5-foot-diameter, 34.3-foot-long substitute for the 12.8-foot-diameter, 25.7-foot-long Apollo Service Module; and the cylindrical, 21.5-foot-diameter, 30-foot-long Eros Mission Module (EMM). An S-IVB stage and Instrument Unit — respectively the third stage and the "electronic brain" of the Saturn V rocket — would inject the EFSV into 100-nautical-mile (n-mi) Earth orbit. Mass injected into orbit including the S-IVB and IU would total about 165 tons.

When Smith presented his paper, the Apollo Saturn V was still more than a year away from its maiden flight. NASA expected that it would be able to launch about 130 tons into 100-n-mi Earth orbit.

Smith suggested that NASA boost Saturn V capacity to 165 tons by uprating the five J-2 engines in its S-II second stage. Alternately, the rocket's S-IC first stage might be fitted with twin 260-inch-diameter solid-propellant strap-on rocket motors, increasing its capacity to a whopping 215 tons. The latter alternative, Smith wrote, would provide ample margin for EFSV weight growth during development. It would, of course, also constitute a more radical (and thus more costly) change in the basic Saturn V design than would S-II engine uprating.

During Apollo Moon missions, an S-IVB would ignite following S-II stage separation and burn for 2.5 minutes to place itself, the IU, a shroud housing the Apollo Lunar Module (LM), and the Apollo Command and Service Module (CSM) into 115-n-mi parking orbit about the Earth. About two hours and 44 minutes after launch, the S-IVB would ignite a second time and burn for six minutes to put the CSM and LM on course for the Moon. The stage and the IU would then separate.

When used as part of Smith's EFSV, the S-IVB would carry out its first burn much as in the Apollo Moon missions, but its second burn would be different. Upon arrival in parking orbit, the crew in the ECM would check out the EFSV's systems. Assuming that all appeared normal, they would then ignite the S-IVB engine at perigee (the low point in its Earth-centered orbit) to raise the ESFV's apogee (the high point in its Earth-centered orbit) and gain over 90% of the velocity needed to depart Earth orbit for Eros. At S-IVB burnout they would still orbit Earth, but in an elliptical "Intermediate Departure Orbit" with an orbital period of two days.

Eros flyby mission plan. Please click on image to enlarge. Image credit: Northrop Space Laboratories.

The astronauts would next separate the ECM/ESM from the EMM/spent S-IVB and turn it end for end so that it could link its nose-mounted probe docking unit with a drogue unit at the bottom of a conical recess in the top of the EMM. After casting off the spent S-IVB stage, the crew would transfer to the EMM, their main living and working space during the Eros flyby mission.

There they would deploy the EMM's eight solar panels, a steerable "sensor turret," a large dish antenna, and a "support structure" which, along with the conical recess in the top of the EMM, would shield the ECM from harsh sunlight and micrometeoroids. The disk-shaped solar panels would ride to Earth orbit folded and stacked under the aft end of the EMM. After linking the EMM and ECM/ESM electrical and control systems, they would check out all EFSV systems a second time.

The ESM would include two RL-10A-3 main engines that would burn high-performance cryogenic liquid hydrogen/liquid oxygen propellants. Smith calculated that the ESM would need only one engine to perform most Eros flyby mission maneuvers, but he included separate twin engines in his design for redundancy.

If the EFSV failed its second checkout, the astronauts could abort their mission by separating from the EMM in the ECM/ESM, pointing the ESM engines forward, and firing them at next perigee on 5 May 1974 to reduce speed. They would then separate from the ESM in the ECM and reenter Earth's atmosphere. If EFSV systems continued to function normally, however, the astronauts would fire the ESM engines at perigee to add enough velocity to place their spacecraft on course for Eros.

Eros Flyby Spacecraft Vehicle configured for Earth-orbit departure and interplanetary flight. A = twin RL-10A-3 engines; B = Eros Service Module; C = Eros Command Module; D = Eros Mission Module; E = high-gain antenna; F = sensor turret; G = four-panel solar array. The spacecraft would orbit the Sun with its twin solar arrays pointed Sunward and its high-gain antenna pointed toward Earth. Image credit: David S. F. Portree/Northrop Space Laboratories.

The EMM would contain near its center a spherical pressurized habitat module similar to the one in NASA Marshall Space Flight Center's February 1965 Mars/Venus piloted flyby study (see "More Information" below). In the event of a solar flare, the crew would retreat to a "storm cellar" with hatches at both ends. The forward hatch would lead to the ECM and the aft hatch to the habitat sphere.

A centrifuge would divide the sphere into forward (crew quarters) and aft ("mission task area") halves. Smith hoped that periodic "centrifugation" in the small centrifuge would be sufficient to maintain crew health during the 17.5-month Eros voyage, since spinning the entire EFSV to create acceleration which the crew would feel as gravity would create engineering challenges — for example, designing solar arrays that would track on the Sun as the spacecraft rotated. Smith wrote that meeting these challenges would increase the EFSV's mass so that it no longer could depart Earth on a single uprated Saturn V.

A hatch in the aft end of the habitat sphere would lead to a pressurized equipment room, which would in turn lead to a round "probe hatch" in the aft end of the EFSV. The probe hatch would open into space.

The solar arrays and aft end of the EFSV would point toward toward the Sun during most of the mission. This would place the ECM/ESM in shadow, which, along with heavy insulation, would prevent the cryogenic propellants in the ESM from boiling away during the long voyage.

On 18 January 1975, the astronauts would begin tracking Eros using radar, a reflecting telescope with a 30-inch primary mirror, and other instruments mounted in the sensor turret. On 23 January 1975, they would adjust their course using the ESM engines to ensure an Eros close-approach distance of about 50 miles and would begin gathering Eros science data.

About eight hours before closest approach, the astronauts would "catapult" a 200-pound automated probe out of the probe hatch toward the asteroid. The probe would function much as the Block III Ranger lunar probes had been meant to do; that is, it would image Eros until it smashed into its surface and was destroyed, yielding detailed close-up images in its final seconds. The EMM's dish antenna would relay to Earth data from the probe's TV camera and other instruments.

Closest approach to Eros would occur about 14 million miles from Earth on 28 January, just five days after the Earth-Eros close approach. Close proximity would permit a higher rate of data transmission from the EFSV to Earth during the flyby than would otherwise be possible.

The piloted Eros flyby spacecraft would spend about 90 seconds within 200 miles of the asteroid's sunlit side and about 30 seconds within 100 miles. On 30 January 1975, the crew would end Eros tracking and fire the ESM engines to correct course deviations imparted by the 23 January maneuver, the automated probe launch, and the weak tug of the asteroid's gravity.

The astronauts would load the ECM with scientific data — mainly film — and check out its systems beginning on 10 October 1975. On 12 October, they would abandon the EMM and use the ESM engines to place the ECM on course for Earth atmosphere reentry. They would then jettison the ESM, reenter the atmosphere at about 40,000 feet per second — about 3500 feet per second faster than Apollo lunar-return speed — and descend to a landing on parachutes.

Image credit: NASA.

Congress killed NASA's plans for piloted Mars and Venus flyby missions in August 1967, in the aftermath of the January 1967 Apollo 1 fire. Smith's piloted Eros flyby proposal received little attention. The only U.S. piloted mission of 1975 was the Apollo-Soyuz Test Project, which saw the final Apollo CSM dock with the Soviet Soyuz 19 spacecraft in low-Earth orbit.

When NASA at last explored a near-Earth asteroid, it explored Eros. The $112-million Near-Earth Asteroid Rendezvous (NEAR) robotic mission — the first mission in NASA's low-cost Discovery Program — left Earth on 17 February 1996, 22 years after the planned launch date of Smith's piloted Eros flyby.

On 20 December 1998, NEAR failed to enter Eros orbit because its computer aborted a crucial engine burn. Three days later, after some quick reprogramming, NEAR flew past the 22-mile-long, 13-mile-wide asteroid at a distance of 2375 miles. It returned 222 images. They revealed that Eros is shaped like a ballet slipper or, as some would have it, a banana.

On 14 February 2000, after another revolution around the Sun, NEAR at last orbited its target. NASA renamed the spacecraft NEAR Shoemaker in March 2000 to commemorate renowned planetary geologist and asteroid and comet discoverer Eugene Shoemaker, who had died in a car crash in Western Australia in July 1997 while looking for ancient asteroid impact craters. During the year that followed, the spacecraft radioed to Earth more than 160,000 close-up images of Eros. New images revealed many odd smooth "ponds" made of dust.

Though designed as an orbiter, NEAR Shoemaker succeeded in landing on Eros on 12 February 2001. It may have landed in a dust pond, cushioning its impact. It returned gamma-ray spectrometer data from the asteroid's surface until 28 February 2001.

Eros flew past Earth at a distance of 16.6 million miles on 31 January 2012, its closest approach since 1975. The asteroid will pass slightly closer to Earth than it did in 1975 on 24 January 2056.

Sources

"A Manned Flyby Mission to Eros," Eugene A. Smith, Proceedings of the Third Space Congress, "The Challenge of Space,” pp. 137-155; paper presented at the Third Space Congress in Cocoa Beach, Florida, 7-10 March 1966.

The Near Earth Asteroid Rendezvous Mission: A Guide to the Mission, the Spacecraft, and the People, Johns Hopkins University Applied Physics Laboratory, December 1999.

NASA Press Release 01-29, "Asteroid Mission Not Yet 'NEAR' An End," D. Savage, NASA Headquarters, 14 February 2001.

"NEAR Shoemaker Weekly Report," Michelle Stevens (for Debra Fletcher), 2 March 2001.

More Information

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

Missions to Comet d'Arrest & Asteroid Eros in the 1970s (1966)

Earth-Approaching Asteroids as Targets for Exploration (1978)

Pluto: An Alternate History

New Horizons at a Pluto that never was. Image credit: NASA

Astronomical errors led to the discovery of Pluto in 1930. If those errors had been avoided, then it is likely that no one would have gone looking for a trans-Neptunian planet, and Pluto probably would not have been spotted until the 1970s or 1980s. The result: we would never have called Pluto a planet.

I will defend this bold assertion shortly; before that, however, an overview of planet-hunting history since the 18th century is in order. This will provide the context we need to understand why Pluto was found so soon and why it became included in the Sun's family of planets.

The Solar System known to humans ended at Saturn until 1781, the year comet-hunter William Herschel stumbled upon Uranus. After a time, astronomers noted that the seventh planet did not move quite as expected. They speculated about the existence of an eighth planet massive enough to tug on Uranus with its gravity.

Twenty years after Herschel found Uranus, Giuseppe Piazzi found Ceres in the space between Mars and Jupiter. In short order, other astronomers found Pallas, Juno, and Vesta. Until the early 1850s, these worlds were considered to be planets, bringing the total known to 11.

There the planet population stood until 1845, when K. L. Hencke stumbled on Astraea and then, in 1847, Hebe. Astraea was the 12th planet discovered, but Hebe was the 14th, for the search for a planet beyond Uranus had paid off in 1846 with the discovery of Neptune.

Neptune's gravity accounted for the irregularities in the orbit of Uranus. However, it soon became clear that Neptune did not move exactly as expected. This led some to propose the existence of yet another large planet in the outermost reaches of the Solar System.

Meanwhile, the number of worlds known between Mars and Jupiter took off like a rocket. In addition to Hebe, 1847 saw the discovery of Iris and Flora. In 1848, Metis joined the list of planets. Hygeia was found in 1849, and Parthenope, Victoria, and Egeria in 1850. Irene and Eunomia joined the list in 1851, bringing the total number of planets orbiting the Sun to 23.

By then, most astronomers had decided that enough was enough. Clearly, Ceres and her sisters had much in common. It seemed that they were representatives of a new class of small Solar System bodies. By 1854, a term that Herschel had coined after the discovery of Ceres, Pallas, Juno, and Vesta had gained widespread acceptance. The worlds between Jupiter and Mars became known as "asteroids" and the Solar System planet count shrank to eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. (The terms asteroid, minor planet, and planetoid have, historically, been used interchangeably.)

There things stood until the early years of the 20th century, when wealthy and eccentric American amateur astronomer Percival Lowell got into the act. Lowell had founded an observatory in 1894 in Flagstaff, Arizona, to seek evidence of intelligent life on Mars. He wrote a series of books in which he argued that fine lines some astronomers glimpsed on the disk of Mars were strips of vegetation growing beside canals dug by an ancient, dying martian civilization.

Though a hit with the public, Lowell's vision was greeted with derision by professional astronomers. By 1906, even he had begun to lose faith, so he gave his observatory a new mission: Lowell Observatory would search for the undiscovered planet beyond Neptune. Lowell called it Planet X. His calculations gave it six times the mass of Earth. Other astronomers, such as William Pickering, sought a trans-Neptunian planet, so the search became a race.

Clyde Tombaugh found Planet X at Lowell Observatory in 1930, 14 years after Percival Lowell's death. It was soon named Pluto for the Roman god of the cold, dark underworld. There was much rejoicing — at first.

Pluto was an odd customer from the get-go. Its orbit crosses Neptune's and is tilted 17° relative to the plane of the Solar System. It was also mysteriously faint. A world large enough to tug on Neptune should have been relatively big, hence relatively bright. Weird Pluto didn't even show a planet-like disk. This led to much puzzlement and at least one imaginative theory (see "Pluto, Doorway to the Stars" in the More Information section below).

Pluto's peculiarities also fueled detractors who believed that it did not qualify to be grouped with Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. I conducted a very cursory search — paging through a science textbook from 1933, just three years after Pluto was discovered — and found that Pluto's peculiar orbit had already led at least two geologists to call it a planetoid, not a planet.

We know now that the calculations that pointed to a big planet beyond Neptune — a planet with enough gravity to account for the discrepancies in Neptune's orbit — were flawed. The astronomers had got Neptune's mass wrong. Put the correct mass into the equations and the Neptune discrepancies vanish.

By the time we worked out that we had no need of a planet beyond Neptune, we knew that Pluto was too small to be that planet anyway. After we found its moon Charon in 1978 we could accurately calculate Pluto's mass. Its mass is about 0.0022 that of Earth (Earth = 1). Put another way, Pluto is about one-fifth of 1% as massive as Earth.

What if somehow we'd computed Neptune's orbital motion properly and never set out to find Planet X? If Lowell and others hadn't raced to find a trans-Neptunian planet in the 1906-1930 period, then it's quite possible — even likely — that we would not have stumbled upon Pluto until the 1970s or 1980s.

Let's say arbitrarily that we discovered Pluto and Charon together in 1978. Just as in our timeline, we would have used Charon's orbital motion to compute Pluto's tiny mass. Small mass combined with Pluto's weird orbit around the Sun would have meant that we would not have rushed to call Pluto a planet.

We probably would instead have rushed to seek other bodies like Pluto, and it is likely that with 1980s and 1990s technology we would have found several. That would have been the clincher. Pluto, we would have decided, was the first body to be found in a new population of bodies. We would have cited Ceres and the Main Belt asteroids as a precedent.

Would we then have called Pluto an asteroid? I suspect so. We might have called the Asteroid Belt between Mars and Jupiter the Inner Asteroid Belt and the one containing Pluto the Outer Asteroid Belt. No doubt some would have dubbed Pluto "the Ceres of trans-Neptunian space."

Perhaps we would have adopted a different name for the Outer Asteroid Belt: the name most astronomers have in fact adopted. In our timeline, David Jewitt and Jane Luu discovered the first trans-Neptunian body (other than Pluto) in 1992. Called 1992 QB1, it was the first recognized member of the long-hypothesized Kuiper Belt.

In our 2015, we know of more than a thousand Kuiper Belt Objects (KBOs) out of a population that might number in the billions. Most, like 1992 QB1, are quite small; perhaps a couple of dozen are similar to Pluto and Charon in terms of size and mass (Pluto is about 2370 kilometers wide, or about two-thirds the diameter of Earth's moon; Charon, 1200 kilometers across).

Had we found Pluto in 1978, we would still have sought to explore it, for it remains the nearest large trans-Neptunian body. Quite probably a space mission much like New Horizons would have been launched to asteroid Pluto, just as Dawn was launched to asteroids Ceres and Vesta. (Dawn, however, was able to orbit both bodies; New Horizons was a fast flyby.)

How might the world have changed if Pluto had not been found until 1978?

The discovery of Pluto in 1930 helped to repair Lowell Observatory's battered reputation, permitting it to grow into the respected institution it is today. Had it not found Pluto, its greatest claim to fame, it might not have survived. Perhaps it would have closed its doors in the 1930s.

Without Lowell Observatory, its home city, Flagstaff, Arizona, would have developed a different character. It would not have passed the world's first dark-skies ordinance in 1958 nor become world's first International Dark-Sky City in 2001.

My late wife and I would have had to find a different place to get married. We were wed in 1998 on the Lowell Observatory grounds, near the bucket-shaped dome housing the 24-inch Clark refractor Percival Lowell used to map canals on Mars (a telescope I learned to operate in 2001 and used to observe Mars in 2003).

Without Lowell Observatory, Flagstaff would probably not have become home to an unusually large number of scientific institutions for its size. For example, the U.S. Naval Observatory, where Charon was discovered, probably would not have set up shop west of town in the 1950s.

The Astrogeology Branch of the U.S. Geological Survey used Lowell Observatory telescopes for moon mapping starting in about 1960, then moved to Flagstaff in 1963. Had it not become based in Flagstaff, it would likely have been split between rival lunar geology groups in Menlo Park, California, and Washington, DC.

The Astrogeology Branch was largely responsible for astronaut geology training during Apollo. Much training took place near Flagstaff — at the Grand Canyon, on the Bonito Lava Flow and Cinder Lakes, in and around Meteor Crater. With no Astrogeology in Flagstaff, Apollo geology training would have followed a different course.

Those are mostly negative or neutral changes in the timeline. Would there have been any positive ones?

I suspect that, had we found Pluto in 1978, not 1930, we would have been spared the ego clashes and animosity generated when Pluto was "demoted" in 2006. No one could have exploited the hyped-up controversy over whether Pluto was a planet to gain fame and sell books and Internet content because there wouldn't have been any hyped-up controversy.

We also would have been spared the odd, unsatisfactory term "dwarf planet." A dwarf planet fails to "clear" its orbit but orbits the Sun and is round like a planet (or, to put it another way, it is in hydrostatic equilibrium — during formation its gravity was sufficient to pull the stuff it is made of into a spherical shape). Pluto orbits the Sun and is round, but has a resonating relationship with Neptune and has neighbors in similar orbits, so it has not cleared its orbit. Hence, Pluto is a dwarf planet. Ceres has earned the dwarf planet classification, too, as have three other bodies out past Pluto — including, oddly enough, Haumea, which is apparently oblong.

I should note here that asteroid Vesta would probably have been called a dwarf planet under the current definition if it hadn't had its south pole blown off by a collision with another, smaller asteroid after its gravity had finished pulling it into a spherical shape. If Haumea can be a dwarf planet, then why can't more nearly spherical Vesta?

The most embarrassing thing about the dwarf planet label is that bodies we call planets do not clear their orbits. Jupiter's Trojan asteroid swarms and Earth's Near-Earth Asteroid population attest to this. Even more bizarre, Neptune remains a planet even though the presence of Pluto means that it has not cleared its orbit. Its gravity has "managed" Pluto's orbit, but Pluto is still there. So, strictly speaking, most or all of the Solar System's planets are dwarf planets.

Note that the definitions say that planets and dwarf planets orbit the Sun. They thus manage to exclude the thousands of planets we have found orbiting other stars. Basically, they assume a Sun-centered universe. Those who proposed and supported the current definitions of planet and dwarf planet didn't have that in mind — in fact, according to at least one source, extrasolar planets were excluded because of concerns about accurately labeling planets and brown dwarfs. It's worth noting this peculiarity, however, because it points up the fact that the definitions need work.

It is possible that the non-discovery of Pluto in 1930 would have had other, unforeseeable effects outside the world of astronomy. In a world where a butterfly's flapping wings in New York City might produce a typhoon in Taiwan, anything seems possible. Perhaps the Cuban Missile Crisis would have gone hot — or not happened at all. Perhaps Steven Spielberg would have directed Star Wars. Perhaps Apple would have been named Radish. Who can say?

Sources

Historical Geology, R. Moore, McGraw-Hill Book Company, 1933, pp. 5-6, 651.

"The Asteroids: History, Surveys, Techniques, and Future Work," T. Gehrels; in Asteroids, T. Gehrels, editor, The University of Arizona Press, 1979, pp. 3-24.

Twitter correspondence with C. Lintott (https://www.zooniverse.org/), 16 May 2018.

More Information

Clyde Tombaugh's Vision of Mars (1959)

Pluto, Doorway to the Stars (1962)

New Horizons II (2004-2005)

Peeling Away the Layers of Mars (1966)

Craters inside craters inside craters: Hadley crater, Mars, in colors indicative of depth. Each new impact dug deeper, exposing more of Mars's complex history to exploration. Image credit: NASA.

Planning for piloted spaceflight typically emphasizes transportation; that is, it focuses on methods of traveling from Earth to some destination and back again. Other than landing and liftoff, astronaut activities on the surface of a target world normally receive little attention. This is not too surprising at the present stage of spaceflight development, given the many challenges inherent in moving humans between worlds.

What is more surprising is that, as early as 1965, NASA's Marshall Space Flight Center (MSFC) turned its attention to the scientific tasks astronaut-scientists might perform on Mars. In that year, as part of an ongoing series of Mars mission studies that began in 1962 with the EMPIRE piloted Mars/Venus flyby/orbiter study, the Huntsville, Alabama-based NASA center contracted with Avco/RAD to study piloted Mars surface operations. This truly was far-sighted thinking; when MSFC contracted with Avco/RAD, NASA, with President John F. Kennedy's end-of-decade deadline for a piloted lunar landing fast approaching, had barely begun to pay serious attention to the scientific tasks that Apollo astronauts would perform on the moon.

Paul Swan, who had worked with Cornell astronomer Carl Sagan in 1964 to identify landing sites for automated Voyager Mars landers, was Avco/RAD's study leader. In a summary paper presented at the March 1966 Stepping Stones to Mars meeting (the last major Mars-focused engineering meeting until the 1980s), Swan and three of his Avco/RAD colleagues explained that an "understanding of the possibilities and limitations of [human explorers on Mars] should serve both to keep our eyes on a far horizon, and to guide our footsteps on the early stepping stones which must be negotiated."

The first successful robotic Mars probe, 261-kilogram Mariner IV, had flown past the planet on 14-15 July 1965, while the Avco/RAD engineers performed their study, and they included in their report references to its findings. They noted, for example, that Mariner IV had imaged overlapping craters (implying a lack of erosion, hence little water) and had found no evidence of a martian magnetosphere (implying that solar flare radiation could reach its surface mostly unchecked). In general, however, the Avco/RAD team adhered to the optimistic pre-Mariner IV view of Mars, which was based on a century of Earth-based telescopic observations. Their Mars was, for example, etched by a mysterious network of slender, linear canals, though no such features appeared in Mariner IV images.

First look: one of the best of the 21 images of Mars the Mariner IV flyby spacecraft beamed to Earth in July-August 1965. Image credit: NASA.

Despite this apparent flaw, Avco/RAD's planning methodology remains relevant today. In fact, it can be argued that, by planning the scientific exploration of a "fictional" Mars, Swan and his colleagues demonstrated that their methodology could be applied to any world humans might choose to explore.

Swan's team acknowledged that the decision to send humans to Mars might be taken "for reasons of international competition, for domestic political considerations, or to stimulate the economy," but hastened to add that such justifications should not be permitted to dictate the science activities that would take place during piloted Mars exploration. They assumed that science would dictate engineering requirements for Mars spacecraft, space suits, and rovers, and not the reverse. Though necessarily simplistic, this approach put aside uncertainty about Mars exploration objectives.

The Avco/RAD team identified three potential overarching scientific programs for the first piloted Mars mission: these were exobiology, planetology, and exploitation. The first of these was, they wrote, "basic and compelling," and might in fact provide a justification for a piloted Mars mission that could stand on its own (that is, in the absence of underlying political and economic motives). Planetology would focus on the history and present state of Mars as a planet. Exploitation would entail prospecting for resources and determining hazards ahead of a follow-on long stay-time piloted Mars mission.

Mars, the team told the Stepping Stones conference, would not be explored as Earth has been explored. On Earth, scientists can usually visit a field site, gather data, return to the lab to study the data and formulate new questions, and then return to the field site to perform new investigations. Because the cost of exploring Earth is small compared to that of exploring Mars, terrestrial exploration can, in other words, be iterative and open-ended.

Mars astronaut-scientists, on the other hand, would need to gather rapidly as much data at their landing site as possible, because the large number of interesting potential landing sites and the difficulty and cost of reaching Mars would make unlikely an early return to any one site that was visited. To accommodate this fundamental constraint, Avco/RAD called for every piloted Mars mission to conduct a range of experiments that would metaphorically cast a fine-meshed net over its landing site with the aim of capturing "variable amounts of different kinds of information over wide dynamic ranges."

The team noted that the likely existence of "totally . . . unanticipated phenomena" would complicate data gathering. To illustrate this, Swan and his colleagues asked their audience to consider "the plight of the Martian astronaut-scientist who finally manage[d] to reach Earth, but completely failed to anticipate magnetic fields greater than a few gammas, and therefore also magnetospheres, Van Allen belts . . . and all other phenomena associated with the mere existence of the Earth's magnetic dipole."

The Avco/RAD team then metaphorically peeled Mars like an onion; that is, they divided the planet and its surroundings into concentric spheres of scientific interest. Innermost was the endosphere, the molten spherical body of the planet bounded by its lithosphere (the crust, including the solid surface). Next was the hydrosphere, which included all water within and on the lithosphere, in the atmosphere, and in the biosphere. The biosphere would comprise the living things of Mars, which, the team explained, would probably have "an intimate relationship to the lithosphere, the hydrosphere, and the atmosphere."

Deimos, outermost of Mars's two small satellites, remains enigmatic. Image credit: NASA.

The atmosphere, next out from the planet's center, would include "all the neutral, gaseous molecules out to the shock wave in the solar wind," while the electro/magnetosphere would include the ionosphere, radiation belts, and any magnetic field that might have eluded Mariner IV's magnetometer. Last and farthest from the center of Mars was the gravisphere, which would contain the moons Phobos and Deimos and any dust belts that might encircle the planet. Avco/RAD also listed solar physics as an area of scientific interest for piloted Mars missions; that is, any "solar phenomena observed while using the planet as a base of operations."

Swan's team proposed two piloted Mars mission scenarios designed to explore these spheres of scientific interest. The first, the "minimal" missions, would occur between 1976 and 1986 and would use Apollo-level (that is, 1970) technology. The second, the "extended" mission, was tentatively scheduled to occur in the 1982-1986 time period. It would require technologies beyond the Apollo state of the art.

The four minimal-mission surface crew members would explore a landing site within 30° of the martian equator for 21 days during a period when the biosphere at the site was at "peak growth." While the four surface astronaut-scientists did their best to keep up with "a very active schedule" of wide-ranging data-gathering, two astronauts would orbit Mars on board the mission "mothership," the command module. Among other tasks, they would deploy automated probes to investigate the martian moons and any dust belts. Time near Mars would total 40 days.

The Avco/RAD team expected that, in addition to the Mars-orbiting command module, the minimal mission would need three landed modules. These would reach the landing site on common-design landers. The modules would include a drum-shaped, 9500-pound "main shelter" where the four surface astronauts would live and work; a two-person, 8700-pound, 20-foot-long pressurized Molab rover capable of three five-day, 500-mile surface traverses over the course of a 21-day surface mission; and a 1550-pound "garage" module for storing the Molab, 2050 pounds of Molab expendables, and 3000 pounds of science equipment.

The surface crew would remain sequestered from all martian life throughout their stay. After every Mars walk, space-suited astronaut-scientists would undergo decontamination, and samples they gathered would remain sealed in quarantine until they were returned to Earth laboratories and found to be safe.

This degree of caution would be necessary, the Avco/RAD team wrote, because determining conclusively the degree of pathogenicity of martian life would probably not be possible during a three-week surface stay. If the surface crew became exposed to a virulent martian bacterium, its effects would probably not have time to become readily apparent before they returned to the orbiting command module. The crew in orbit would then become exposed, and the infection might be transmitted to Earth.

Avco/RAD's second type of piloted Mars mission, the extended mission, would see 42 astronauts occupy three 14-person surface bases for 300 days while four astronauts remained on board a command module in Mars orbit. Because the surface crews would remain on Mars for 300 days, they might witness most of the seasonal life cycles of native organisms at the base sites. While the small army of surface explorers ranged over the regions surrounding their base sites, the astronaut-scientists in Mars orbit would rendezvous with and explore Phobos and Deimos.

The south polar ice cap of Mars. Image credit: ESA.

The three bases would be "so situated as to provide access to all major features of interest," Swan's team explained. Northern Syrtis Major Base would support Molab traverses to Libya and Aeria ("two northern desert regions"), while a base in Hellas (an "unusually bright and somewhat anomalously colored desert region") would enable access to Zea Lacus, where five canals intersected. The third base would be sited among the south pole's snowy Mitchell Mountains. (It should be noted that neither the canals of Zea Lacus nor the Mitchell Mountains actually exist.)

At least six common-design landers would deliver eight modules to each base site, for a total of eighteen landers and 24 modules on Mars. For redundancy, two 80-kilowatt nuclear reactors would supply each base with electricity and two main shelters with regenerative life support would house each base crew. A pair of "storage and maintenance shelters" at each base site would house two 22,000-pound, two-man Molabs capable of 30-day, 1500-mile traverses, plus a total of 34,000 pounds of Molab expendables and science equipment.

Sources

"Martian Landing Sites for the Voyager Mission," P. Swan and C. Sagan, Journal of Spacecraft and Rockets, January-February 1965, pp. 18-25.

NASA Facts: A Report from Mariner IV, NASA Facts, Vol. III, No. 3, 1966.

"Manned Mars Surface Operations," P. Swan, R. Hanselman, R. Ryan, and R. Suitor, A Volume of Technical Papers Presented at the AIAA/AAS Stepping Stones to Mars Meeting, pp. 69-86; paper presented in Baltimore, Maryland, 28-30 March 1966.

More Information

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

Gumdrops on Mars (1966)

A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

Dyna-Soar's Martian Cousin (1960)

Re-Purposing Mercury: Recoverable Space Observatory (1964)

Launch of astronaut John Glenn on board Friendship 7. Image credit: NASA.

Hermann Potočnik, an Austrian Army officer writing under the pseudonym Hermann Noordung, described the benefits of telescopes in space in his seminal 1929 book Das Problem der Befahrung des Weltraums: der Raketen-Motor. The 1995 NASA-sponsored English translation of Noordung's work includes a brief section titled "Unlimited Visibility." It describes how,

beyond Earth’s blanket of air, nothing weakens the luminosity of the stars; the fixed stars no longer flicker; and the blue of the sky no longer interferes with the observations. At any time, the same favorable, almost unlimited possibilities exist, [and] telescopes of any arbitrary size, even very large ones, could be used.

In 1946, Princeton University astronomer Lyman Spitzer also wrote about the possibilities of space-based astronomy, and it was with him that U.S. efforts to place telescopes into space originated. In 1960, NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, began work on the Orbiting Astronomical Observatory (OAO) series of space telescopes. The Grumman-built satellites would image the cosmos in wavelengths that could not easily penetrate Earth's atmosphere and radio the images they captured to receiving stations on Earth.

Astronomers eagerly anticipated the OAOs, but for the general public NASA in 1960 was all about Project Mercury. The first manned Mercury orbital flight, designated MA-6, took place on 20 February 1962. A modified Atlas missile propelled astronaut John Glenn into space on board the Friendship 7 spacecraft. Glenn orbited Earth three times and, despite a sensor fault which made it appear that his spacecraft's heat shield had come loose in orbit, splashed down safely in the Atlantic Ocean a little less than five hours after launch.

Three more astronauts rode Mercury capsules into orbit. The last Mercury mission, MA-9, saw Gordon Cooper orbit Earth 22.5 times in the Faith 7 capsule. His 34-hour mission spanned 15-16 May 1963.

Final Mercury: Technicians hoist Gordon Cooper's Faith 7 Mercury spacecraft on Launch Complex 14 at Cape Canaveral, Florida. Image credit: NASA.

If Windsor Sherman, an engineer at NASA's Langley Research Center (LaRC) in Hampton, Virginia, had had his way, then Mercury would have found a new role as part of NASA's space astronomy program. In a NASA Technical Note published a year and a half after MA-9, Sherman proposed that NASA modify manned Mercury capsules to serve as recoverable unmanned Earth-orbiting observatories.

Sherman's Mercury-derived observatory would weigh more than the manned Mercury (2150 kilograms versus 1660 kilograms) and would require a higher orbit (at least 500 kilometers) to ensure that it would operate above Earth's atmospheric "airglow." The manned Mercury's Atlas booster would not be up to the task, so the recoverable observatory would launch on an Atlas with an Agena B upper stage. A similar booster-upper stage combination launched Ranger robot explorers to the moon.

Cutaway drawing of a Mercury-derived recoverable space observatory. Image credit: NASA.

Upon attaining orbit, the Mercury-derived observatory's nose would split down the middle and hinge open like a clam shell to clear the light path for a reflecting telescope with a curved primary mirror 76 centimeters in diameter. The telescope would occupy an inverted mushroom-shaped volume one meter wide at its widest point and 2.81 meters long. It would collect the light of astronomical targets such as comets, stars, nebulae, and galaxies, and, using a rotating tilted mirror, direct it by turns to six cameras mounted between the underside of the primary mirror and the Mercury heat shield. The cameras would record images in the gamma-ray, infrared, visible, and ultraviolet (UV) parts of the spectrum on up to 6000 frames (1000 frames per camera) of 70-millimeter photographic film.

Sherman called photographic film "one of the best information storage devices yet devised." A good photographic image of a celestial object would, he wrote, contain 10 times as much information as a good television image of the same object. On the down side, photographic film would require shielding against space radiation lest it become clouded and its information storage capacity degraded.

He acknowledged that, as an alternative to film recovery, exposed film might be developed in space automatically and scanned using a television camera. This technique would be used on board the automated Lunar Orbiter spacecraft. Sherman noted, however, that scanning an photographic image, transmitting it to Earth, and reassembling it would inevitably cause data loss. He estimated that images from scanning would contain half as much information as the exposed film the Mercury-derived observatory would return to Earth.

Sherman estimated that, unless GSFC and Grumman upgraded its systems, OAO would need about 860 days to transmit to Earth the 6000 image frames his Mercury-derived recoverable observatory could collect and return to Earth in 200 days. Upgrades to improve image transmission rate would increase OAO complexity, power consumption, and mass, so that the non-recoverable observatory could not be launched as planned on an Atlas rocket with an Agena upper stage.

As Sherman's Mercury-derived recoverable observatory orbited the Earth, it would rely for stability and pointing on a modified OAO guidance system. Sherman expected, however, that it would be unable to track astronomical targets with sufficient precision for film photography. He offered a preliminary design for a "fine-image stabilization system" meant to compensate for image smear by automatically adjusting the focus of the six cameras. He acknowledged, however, that designing a sufficiently stable pointing system for the recoverable observatory remained an important "problem area."

Sherman only briefly discussed the Mercury observatory's electrical power needs. He noted that non-rechargeable batteries sufficient to power the spacecraft for 200 days could not fit within the tight confines of the Mercury capsule, and would in any case be far too heavy. The LaRC engineer suggested that a deployable solar array might instead be used to recharge batteries, but gave no hint as to its likely dimensions, design, or location.

The Langley engineer also did not contend with the thorny issues of the Mercury spacecraft's demonstrated poor longevity. By the time Cooper manually guided Faith 7 to a splashdown in the Pacific Ocean, all of his spacecraft's automatic piloting systems had failed. He was reduced to timing his retrorocket burn using his wristwatch. Any similar malfunction would have doomed the wholly automated Mercury observatory.

Assuming that its endurance could be extended, at the end of its 200-day mission the Mercury-derived observatory would close its clam-shell nose, orient itself with its broad heat shield pointed approximately in the direction of its orbital motion, ignite its solid-propellant retrorocket pack, and reenter Earth's atmosphere. The Mercury-derived observatory's bifurcated nose would mean that it would deploy two separate main parachutes, each smaller than manned Mercury’s single parachute. Splashdown and recovery would otherwise occur as in manned Mercury missions.

In addition to its superior information capture potential, advantages of the recoverable Mercury-derived observatory would include cost-saving reuse of instruments and spacecraft components during subsequent missions. The Mercury observatory would also permit an ancillary scientific/engineering experiment; because it would return to Earth, any signs of long-term exposure to the space environment that it carried (for example, micrometeoroid pitting) could be subjected to analysis.

Sherman's plan for giving Mercury a new lease on life generated scant enthusiasm. OAO-1 reached orbit on an Atlas-Agena D rocket on 8 April 1966, 15 months after Sherman completed his paper. It carried UV, X-ray, and gamma-ray instruments. Unfortunately, its electrical system overheated, developed arcing, and failed, so that OAO-1's mission ended after only three days. The satellite returned no astronomical data.

Pre-flight artist concept of OAO-1 in Earth orbit. Image credit: Grumman/NASA.

OAO-2, with a suite of 11 UV astronomy instruments, abandoned the Atlas-Agena rocket. It reached orbit atop a more powerful Atlas-Centaur on 7 December 1968. OAO-2 operated for a little more than four years. It revealed, among other things, that enormous haloes of hydrogen gas surround comets and that young stars burn very hot.

The third OAO, launched on 3 November 1970 and retroactively dubbed OAO-B, included a 38-inch UV telescope. Unfortunately, the Centaur upper stage meant to push the satellite into orbit malfunctioned, so that it crashed into the Atlantic minutes after launch.

OAO-3, the last in the series, bore the name "Copernicus" to commemorate the 500th anniversary of the birth of the great Polish natural philosopher. Launched on 21 August 1972, it carried the heaviest NASA scientific payload up to that time (2220 kilograms). This included a Princeton University-built UV telescope and a British X-ray telescope. The non-recoverable observatory explored the cosmos until February 1981.

Sources

Conversion of a Spacecraft Designed for Manned Space Flight to a Recoverable Orbiting Astronomical Observatory, NASA Technical Note D-2535, Windsor L. Sherman, NASA Langley Research Center, December 1964.

The Problem of Space Travel: The Rocket Motor, Hermann Noordung, NASA SP-4026, 1995.

Encyclopedia of Satellites and Sounding Rockets of Goddard Space Flight Center 1959-1969, NASA Goddard Space Flight Center, no date (1970?).

More Information

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L1

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

Cometary Explorer (1973)

Gumdrops on Mars (1966)

Exploring Mars in the happy days before Mariner IV. Image credit: Philco Aeronutronic.

The Mariner IV Mars flyby of 14-15 July 1965, marked a watershed in Mars exploration planning. Prior to Mariner IV, engineers and scientists could legitimately propose lifting-body and winged gliding Mars landers that could set down on the planet using almost no propellants. This was because the prevailing scientific opinion gave Mars an atmosphere roughly 10% as dense as Earth's. After data from doughty 261-kilogram Mariner IV finished trickling back to Earth – a process that lasted until 3 August 1965 – such designs were relegated to the dust-bin.

Mars, it turned out, has an atmosphere less than 1% as dense as Earth's. In such an atmosphere, gliders and lifting bodies might still be used – however, they would reach the martian surface traveling at supersonic speeds, not the easily managed subsonic speeds pre-Mariner IV mission planners had assumed. The Philco Aeronutronic Mars Excursion Module (MEM) pictured at the top of this post, for example, would slow only to Mach 2 (twice the speed of sound) before it reached the surface of Mars.

At such a speed, parachute deployment would be problematic, forcing reliance on rockets to slow the MEM below the speed of sound. This would in turn demand substantial quantities of propellants, greatly increasing the MEM's mass, which would generate knock-on mass increases throughout the Mars expedition design.

Less than a year after Mariner IV, Gordon Woodcock, a young engineer in the Advanced Systems Office at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, proposed what would become the new standard design for MEMs. His four-man MEM was based on the squat conical Apollo Command Module (CM) shape. Two and a half years after Woodcock published his paper, the crew of the Apollo 9 mission (3-13 March 1969), which tested the Apollo Lunar Module in Earth orbit, would name their Command and Service Module spacecraft Gumdrop with good reason.

The Command Module Gumdrop is hoisted aboard the U.S.S. Guadalcanal after the 10-day Apollo 9 mission in Earth orbit, 13 March 1969. Image credit: NASA.

For his Mars atmosphere entry simulations, Woodcock assumed a surface air pressure of 5.69 millibars – that is, a little more than 0.5% of Earth sea-level pressure. He noted that his independently developed Mars atmosphere model compared well with two models the Jet Propulsion Laboratory published just before his paper went to print.

The "semi-ballistic" Apollo CM shape, the MSFC engineer wrote, would have several advantages over lifting-body and delta-winged glider designs. It would, for example, have a low center of gravity and a "wide footprint," making tipping unlikely. The squat shape would enable installation of propellant tanks and payloads with very little wasted internal space.

Furthermore, the Apollo CM-shaped MEM would descend through the martian atmosphere not nose-first, like lifting bodies and gliders, but rather tail-first. This meant that it would not need to accomplish a problematic 180° turn or "flip" at supersonic speeds to point its braking and landing engines toward the ground.

Perhaps best of all, the Apollo Program would generate a large body of experience with use of the CM shape in Earth's upper atmosphere. Much of this experience could be applied to development of the CM-shaped MEM.

Woodcock's 56.1-ton MEM would comprise a descent stage roughly 33 feet across (the diameter of a two-stage Saturn V rocket) and, hidden beneath a protective nose-cone ("separable cap"), a 27.3-ton ascent stage. The ascent stage mass, determined largely by the amount of energy needed to climb to Mars orbit, would size the descent stage, he explained. His MEM would separate from its mother ship in Mars orbit at an altitude of 1000 kilometers, then would fire a retrorocket package to slow down and begin its fall toward the martian atmosphere.

Gordon Woodcock's Mars Excursion Module (MEM) design. Image credit: NASA.

Woodcock advised against MEM separation from the mothership prior to Mars orbit capture. It would relieve the mothership of the MEM's mass, reducing the quantity of propellants it would need to slow itself so that the gravity of Mars could capture it into orbit – thus reducing the overall mass of the expedition – but it would also introduce unacceptable risk. He noted that 10,000 simulations run on an IBM 7094 computer had shown that the safe Mars atmosphere entry corridor for the MEM would be very narrow and thus hard to target during a high-speed entry from an interplanetary trajectory.

The crew would ride in a spherical capsule atop the ascent stage during descent and landing. MEM atmospheric deceleration would cease at a velocity of 0.5 kilometers per second. The MEM's bowl-shaped heat shield would then detach, landing legs would extend, and four landing engines would ignite. Woodcock's MEM design did not include parachutes.

As the landing engines ignited, solid-propellant rockets would blast the separable cap away from the MEM ascent stage. With the conical cover gone, the MEM pilot would see his prospective landing site for the first time.

He would then have 100 seconds of maneuvering time to steer the MEM to a safe touchdown. If rugged terrain made this too short a time to find a safe spot or if a malfunction occurred, the pilot could abort the landing by blasting the ascent stage free of the descent stage and returning to Mars orbit.

MEM mass at touchdown would total 40.9 tons. Following a safe touchdown, the crew would exit an airlock adjacent to the ascent stage cabin and transfer to a Mars surface crew quarters module in the descent stage. The latter would take the form of a segment of a torus with a rectangular cross section.

The MEM descent stage engines would burn non-cryogenic storable propellants drawn from tanks positioned within the MEM to offset its center of gravity, enabling the spacecraft to generate a modest amount of lift during descent. A similar approach would enhance Apollo CM lift characteristics during Earth atmosphere reentry.

By revolving around its offset center of gravity using small thrusters, the CM could halt its descent and climb before descending again. This technique was used during Apollo missions to reduce the deceleration felt by astronauts during reentry at lunar-return speed (39,000 kilometers per hour).

Following the successful completion of their surface mission, the MEM crew would return to the ascent stage cabin and blast off for Mars orbit. The performance advantages of cryogenic propellants led Woodcock to opt for liquid oxygen oxidizer and liquid methane fuel in his ascent stage.

He envisioned a common propellant tank lined with "superinsulation" with a barrier separating the methane and oxygen. Helium stored under pressure in spherical tanks would drive propellants into the three ascent stage engines, any two of which would be sufficient to launch the MEM to Mars orbit.

Logistics MEM. Image credit: NASA.

Shelter MEM. Image credit: NASA.

Much as Apollo engineers envisioned that the basic Lunar Module design would be modified to give it new capabilities (for example, unmanned delivery of cargo to the lunar surface) as the Apollo Program evolved from initial brief sorties to in-depth lunar exploration, Woodcock envisioned that his MEM would form the basis of a long-term, increasingly capable and complex Mars exploration program.

He proposed a design for a one-way logistics MEM in which cargo and a "camper-type" pressurized rover would replace the MEM ascent stage and the surface operations shelter. A crew would arrive separately in a conventional MEM to unpack the cargo and explore widely in the rover.

Woodcock also offered a design for a one-way nuclear-powered MEM that would provide electricity to a long-term Mars surface base built up from one-way shelter MEMs. The nuclear-power MEM would include a shielded reactor, a reactor control room, and a skin-mounted radiator for discarding reactor waste heat.

Each shelter MEM would house five or six astronauts on three levels: communications & control on top; living quarters in the middle; and a laboratory at the bottom. The lab would connect to a "sortie room/decontamination airlock" that would enable access to the surface.

Woodcock calculated that 10.6 tons of water, food, and oxygen with a four-ton reserve could sustain a five-man crew in the MEM on Mars for 500 days. Like the logistics MEM, the power and shelter MEMs would land on Mars unmanned.

The Apollo CM-shaped MEM design became closely identified with piloted Mars missions after NASA MSFC director Wernher von Braun, famous for his 1950s Mars glider lander designs, presented a variation on Woodcock's Apollo-shaped lander theme to President Richard Nixon's Space Task Group in early August 1969. Image credit: NASA.

Sources

"Summary Presentation: Study of a Manned Mars Excursion Module," F. Dixon, Aeronutronic Division, Philco Corporation; paper presented at the Symposium on Manned Planetary Missions, 1963/1964 Status, NASA George C. Marshall Space Flight Center, Huntsville, Alabama, 12 June 1964.

An Initial Concept for a Manned Mars Excursion Vehicle for a Tenuous Mars Atmosphere, NASA TM X-53475, G. Woodcock, NASA Marshall Space Flight Center, 7 June 1966.

More Information

Dyna-Soar's Martian Cousin (1960)

A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

Dyna-Soar's Martian Cousin (1960)

Dyna-Soar spaceplane. Image credit: U.S. Air Force.

In 1960, Philip Bono, a Space Vehicle Design Specialist with the Boeing Airplane Company, envisioned a manned Mars spacecraft which outwardly resembled the X-20A Dyna-Soar single-seat orbital glider his company was at the time developing for the U.S. Air Force. Bono's Mars glider was, however, much larger than Dyna-Soar — large enough, in fact, to hold an eight-man "expeditionary force" and nearly 40 tons of supplies and equipment. The flat-bellied Mars glider measured a whopping 125 feet long and 95 feet across its delta wings.

Though Bono's Mars glider was impressively large, it was part of a Mars expedition plan that was stripped-down and bare-bones by early 1960s standards. It lacked redundancy and provided few abort modes. For those familiar with Wernher von Braun's 1950s plans for Mars expeditions, some of which included 10 or more cargo and crew spacecraft, Bono's plan must have seemed daring, even reckless.

Bono himself acknowledged that his study did not "present the solution to many major problem areas." He nevertheless assured his readers that it was "restricted to the realm of practicality and reflect[ed] a moderate degree of conservatism."

A large crane hoists into place the forward section of Bono's Mars glider. Final assembly occurs on the launch pad. Image credit: Boeing Airplane Company via San Diego Air & Space Museum.

Prior to launch, the forward section of Bono's glider would be lowered into place atop its aft section on the launch pad. All assembly would take place on Earth. In the event of trouble during ascent, the crew would blast free in the glider's forward section. The glider aft section would be mounted atop a living module with an attached small rocket stage which in turn would rest upon a short central booster rocket.

Six tall outboard booster rockets would surround and hide the short booster, living module/rocket stage, and most of the aft section of the glider. Fully assembled, loaded with liquid hydrogen and liquid oxygen propellants, and ready for launch, Bono's massive Mars stack would stand 248 feet tall and weigh in at 4150 tons.

Abort: the forward section of the Mars glider (upper right) blasts free of a malfunctioning booster rocket during first-stage ascent. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Bono, in common with many Mars exploration enthusiasts of the early 1960s, optimistically targeted his expedition for the favorable 1971 Earth-Mars transfer opportunity, when the energy required to reach Mars would be at a minimum. On 3 May 1971, seven plug-nozzle engines — one per booster — would ignite and power up to generate a total of 10 million pounds of thrust. The advanced plug-nozzle engine design would do without large engine bells, in theory largely eliminating engine cooling requirements and reducing engine mass. The crew would feel a maximum acceleration equal to 5.6 times the pull of Earth's gravity during ascent.

During first-stage operation, four of the outboard boosters would supply propellants to all seven engines. The rocket would climb to an altitude of 200,000 feet, where it would cast off the four expended boosters. These would fall to Earth 60 nautical miles downrange of the launch site.

Bono's Mars spacecraft begins second-stage flight by casting off four outer boosters (lower left). Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The three remaining engines would continue firing with the two remaining outboard boosters supplying all of their propellants. At 352,000 feet, the two boosters would expend their propellants and detach. The short central booster would continue firing until it placed the glider, living module, and small rocket stage on a trans-Mars trajectory, then would expend its propellants and detach. The Mars spacecraft — two-part glider, living module, and small rocket stage — would have a mass of nearly 138 tons following Earth escape.

Safely on course for Mars, the astronauts would crawl through a tunnel in the glider's aft section to reach the 45-foot-long, 18-foot-diameter living module. They would deploy an inflatable 50-foot dish-shaped antenna for radio communication with Earth (the dish might have been a late addition to Bono's plan, for it is not depicted in any of the illustrations for this post). During the 259-day voyage to Mars, the crew would breathe a 40% oxygen/60% helium air mix, so in their radio reports to Earth they would sound like Donald Duck.

The end of second-stage operation: the remaining pair of outboard boosters exhaust their propellants and separate, leaving to the short central booster the task of placing the glider, living module, and small rocket stage on course for Mars. This image displays the plug-nozzle engines unobscured by exhaust — they are the cones at the bottoms of the two boosters (lower left and lower center). Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Its job done, the short central booster stage shuts down and fires thrusters to separate from the Mars spacecraft. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

On 17 January 1972, at the end of a 259-day Earth-Mars transfer, the crew would strap into the glider and separate it from the living module. They would discard a 10.4-ton capsule containing human waste accumulated during the voyage to Mars. The small rocket stage, meanwhile, would ignite its four 20,000-pound-thrust Pratt & Whitney-built Centaur engines to slow itself and the living module so that Mars's gravity could capture them into orbit.

After deploying the antenna, the crew would point the glider's nose — which would contain a nuclear reactor for generating the Mars expedition's electricity — at the Sun. This would place the living module in shadow, and would shield the liquid hydrogen/liquid oxygen propellants in the small rocket stage from solar heating. Bono assumed that no course corrections would be necessary so that his spacecraft could maintain its nose-toward-Sun attitude throughout the journey to Mars.

17 January 1972: Arrival at Mars. The unpiloted living module (left) ignites its small rocket stage to slow down so that the planet's gravity can capture it into orbit while the glider bearing the crew enters the martian atmosphere directly. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The waste capsule — the skinny conical object between the living module and the glider in the image directly above — would strike Mars. Needless to say, this peculiar concept would likely have had few fans among scientists; it would certainly have introduced massive amounts of Earth bacteria into the martian environment, greatly complicating studies of any native martian biosphere that might exist.

The glider, meanwhile, would carry the eight-man crew directly into the martian atmosphere with no stop in orbit. If conditions on Mars were not suitable for an immediate landing — for example, if a planet-wide dust storm were raging — then the crew would have no way of aborting atmosphere entry and descent to the surface. (Such a storm did in fact occur in late 1971, though by January 1972 it had mostly abated.)

The Mars glider casts off its drag parachute as it steers toward a smooth area of martian desert. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Vertical descent and touchdown. The artist depicts Mars as smooth and dusty, with no obvious rocks on its surface. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

As it descended past 3000 feet of altitude, the glider would deploy a 42-foot-diameter drag parachute to reduce speed. The Mars glider pilot would steer his craft toward a level stretch of ochre desert. At an altitude of 2000 feet — which Bono declared (wrongly, as it turns out) was "adequate to clear the highest mountain of Mars" — three landing engines with a combined thrust of 60,000 pounds would ignite to slow it to a hover. The glider would then lower vertically to the surface in a billowing cloud of yellow dust and sand and touch down on skids with its nose aimed 15° above the horizon. At touchdown, the Mars glider would have a mass of 70.4 tons.

Bono's description of the glider's aerodynamic performance was based on an estimated martian surface air pressure equal to about 8% of Earth's. The true value is, however, less than 1% of Earth's surface pressure. In the actual martian atmosphere, a single 42-foot parachute would not be adequate to slow the heavy glider's descent. In addition, the glider's wing design would not produce sufficient lift to enable effective gliding. In short, Bono's glider would reach the surface while still moving at supersonic speed. Some call this "lithobraking."

Mars Outpost: members of the eight-man crew lower the glider's nose-mounted nuclear reactor onto the expedition truck. In the background (right) stand radio antenna masts and the inflatable dome-shaped shelter. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

During the 479-day "Mars Operational Phase," the eight Mars explorers would set up a 20-foot-diameter, 2000-pound inflatable living dome and relocate the glider's nuclear reactor several thousand feet away so that it could safely generate electricity for their encampment. The crew would have at their disposal about 4.2 tons of scientific gear. They would explore and move equipment using a truck-like two-ton rover.

Near the end of their stay on Mars, the astronauts would reconfigure their glider for launch by moving its landing engines so that they could serve as ascent engines and by returning the reactor to its place on its nose. They would also anchor the aft section of the glider to the surface using stakes and cables. The glider's forward section would then blast off at a 15° angle using the aft portion as its launch pad.

Liftoff from Mars: the forward part of Bono's Mars glider begins the climb to Mars orbit. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Bono wrote that his Mars glider's delta wings would provide lift, greatly reducing the quantity of propellant and the size of the engines it would need to attain Mars orbit. In the actual martian atmosphere, however, the glider he described would not reach orbit before it expended its propellants.

The crew would dock the glider forward section tail-first with the waiting living module which would have loitered in Mars orbit throughout their surface stay. Several astronauts would spacewalk to join together the glider and living module and detach the empty torus-shaped propellant tanks on the living module's small rocket stage. The tanks would have been retained after the Mars orbit capture maneuver emptied them so that they could protect the small rocket stage and the precious Earth-return propellants it contained from meteoroid punctures.

Members of Bono's Mars crew cast off empty torus-shaped propellant tanks on the small rocket stage (upper right) attached to the aft end of the living module (center) in preparation for Mars orbit departure. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The forward section of Bono's Mars glider separates from the living module ahead of Earth atmosphere reentry. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

24 January 1974: the forward section of Bono's Mars glider returns to Earth. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The crew would use the living module rocket stage to depart Mars orbit on 21 October 1973, then would discard it. Four months later (24 January 1974), as the home planet shimmered invitingly ahead, the crew would board the glider forward section once more and cast off the nuclear reactor and living module (they would burn up in Earth's atmosphere). Bono's glider, its weight reduced to just 15 tons, would then reenter Earth's atmosphere directly 997 days after launch and glide to a triumphant desert landing on skids.

Sources

"A Conceptual Design for a Manned Mars Vehicle," Philip Bono, Advances in the Astronautical Sciences, Vol. 7, pp. 25-42; paper presented at the Third Annual West Coast Meeting of the American Astronautical Society, Seattle, Washington, 4-5 August 1960.

San Diego Air & Space Museum Image Collection (http://sandiegoairandspace.org/collection/image-collection — accessed 23 November 2017).

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What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Image credit: NASA.

On 28 July 1973, the Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off from Launch Pad 39B at Kennedy Space Center, Florida, bound for the Skylab Orbital Workshop in low-Earth orbit. Despite their mission's numerical designation, they were the second crew to visit Skylab; in a move guaranteed to generate confusion for decades to come, NASA had designated as Skylab 1 the unmanned Workshop launched on 14 May 1973, and had dubbed the first crew to visit it Skylab 2.

The Skylab 3 Apollo Command and Service Module (CSM) separated from the S-IVB second stage of its Saturn IB launch vehicle and began maneuvering to catch up with Skylab. During final approach to the Workshop, one of the four steering thruster quads on the CSM began to leak nitrogen tetroxide oxidizer from its forward-firing engine. The crew dutifully shut off the quad and used the three quads remaining to complete docking without further incident.

On 2 August, a second thruster quad began to leak, raising fears that tainted nitrogen tetroxide might have damaged both quads. If this were the case, then the Skylab 3 CSM's remaining two quads and Service Propulsion System (SPS) main engine might also have been compromised; though the individual quads and the SPS had independent plumbing, all contained oxidizer from the same batch. If the leaks continued and spread, moreover, nitrogen tetroxide might contaminate the inside of the CSM's drum-shaped Service Module, potentially damaging other spacecraft systems.

The leaks did not catch NASA off guard. As was common in the 1960s and early 1970s, NASA had considered potential Apollo and Skylab failures - however unlikely - and had planned ahead. Within hours of the second leak, The U.S. civilian space agency put into motion a variant of a plan Kenneth Kleinknecht, Skylab Program Manager, and Lawrence Williams, Apollo Spacecraft Program Office, had described less than a year earlier at the Fifth Annual Space Rescue Symposium in Vienna, Austria.

In their paper, Kleinknecht and Williams explained that Skylab would provide the first true opportunity for space rescue in the U.S. space program. One-seat Mercury and two-seat Gemini spacecraft had been too small and limited in capability to serve as rescue spacecraft. Apollo lunar CSMs were much more capable; even so, they each carried only a little more breathing oxygen, fuel cell reactants, and food than were needed to support a three-man crew for the duration of a lunar mission (about 10 days). If an Apollo CSM had become stranded in lunar orbit — by an SPS failure, say — then its crew would have perished long before NASA could have attempted a rescue.

The Skylab Orbital Workshop. The red arrow points to the Multiple Docking Adapter's radial port. Image credit: NASA.

If astronauts needed to evacuate Skylab, they could board their CSM docked at Skylab's front port, undock from the Workshop, and splash down in the ocean in less than a day. If, on the other hand, a crew's CSM became unusable while they lived and worked on board Skylab, then the astronauts could await rescue.

Stranded astronauts were unlikely to run out of supplies. Kleinknecht and Williams noted that the Orbital Workshop would be launched with enough oxygen, food, water, and other supplies on board to support three men for eight months. At the time they presented their paper, NASA planned three three-man Skylab visits lasting 28, 56, and 56 days — that is, a total of a little less than five months.

NASA, meanwhile, would prepare and launch a rescue CSM with a crew of two. Skylab, Kleinknecht and Williams explained, had a second, radial docking port on its Multiple Docking Adapter. The rescue CSM would dock at the radial port to pick up the stranded crew.

They proposed that the CSM intended for the next Skylab crew should become the rescue CSM. This would presumably reduce by one the number of long-duration Skylab missions that could be flown. A fourth CSM, which would serve as the backup CSM throughout the Skylab program, would serve as the rescue CSM for Skylab 4, the third and final planned Skylab crew.

Image credit: NASA.

Kleinknecht and Williams estimated that stripping out the rescue CSM's aft bulkhead lockers to make room for a "rescue kit" would require about a day. The rescue kit would include a pair of special astronaut couches, connectors and hoses for linking two additional space-suited astronauts to the rescue CSM's life support and communications systems, and an experiment-return pallet for bringing home a select few of the stranded crew's science results. The rescue CSM's two-man crew would recline in the left and right CSM couches; the three rescued Skylab crewmen would return to Earth in the center couch and in the two special couches mounted below the others in place of the lockers.

The rescue CSM would bring along a special Apollo probe-and-drogue docking unit that would enable astronauts inside Skylab to manually undock and cast off the crippled CSM. This would clear the Workshop's front port for any future CSM dockings. Kleinknecht and Williams did not explain what would happen to the unmanned CSM after it was discarded.

Though the time needed to install the rescue kit was minimal, the time needed to refurbish Pad 39B and prepare the rescue CSM and Saturn IB rocket for launch would depend upon when NASA declared that a rescue was necessary. After each Skylab Saturn IB launch, ground crews would need about 48 days to refurbish Pad 39B and prepare the next Skylab CSM and Saturn IB.

If a rescue were judged to be necessary at the beginning of the 28-day first manned Skylab mission (Skylab 2), then the mission would be extended by 20 days, making the total duration about 48 days. If a rescue were declared to be necessary late in Skylab 2 — say at the time of planned return to Earth — then preparations for the next Skylab CSM launch would be farther along, but would have started later. The rescue CSM and Saturn IB would thus need 28 days before they could lift off, bringing the total Skylab 2 mission duration to about 56 days, or double the duration planned at launch.

Activation of the Skylab rescue capability early in the Skylab 3 or Skylab 4 mission might permit a rescue before the return time planned when the stranded crew left Earth, Kleinknecht and Williams found. A failure near the planned conclusion of Skylab 3 or Skylab 4 would see a rescue CSM launched as little as 10 days after the rescue plan was activated.

Skylab rescue crewmen Vance Brand (left) and Don Lind. Though he never flew to Skylab, Brand would reach space as part of the Apollo-Soyuz Test Project mission in July 1975 and as Commander of Space Shuttle missions STS-5 (November 1982), STS-41-B (February 1984), and STS-35 (December 1990). Lind would reach space as a Mission Specialist on Shuttle mission STS-51-B (April-May 1985). Image credit: NASA.

The 2 August 1973 failure of the second Skylab 3 CSM thruster quad unleashed a storm of activity. NASA prepared the backup Skylab CSM, not the Skylab 4 CSM, as its rescue vehicle, and tapped Skylab 3 backup crewmen Vance Brand and Don Lind to pilot it.

NASA had made other changes to Kleinknecht and Williams' rescue plan. The special probe-and-drogue docking unit for casting off the malfunctioning CSM had become a concave drogue unit that would be installed over the front port. It was launched with Skylab, not in the rescue CSM. After they installed it, the stranded astronauts would "trigger" the drogue to manually release their balky CSM. The rescue CSM would then dock at the front port, not the radial port.

Almost as soon as NASA activated the rescue plan, laboratory analysis on Earth showed that the batch from which the nitrogen tetroxide in the Skylab 3 CSM's propulsion systems had been taken was not tainted. As unlikely as it might seem, the two thruster quad malfunctions lacked a common cause.

Working in the CSM simulator in Houston, astronaut Brand demonstrated that the Skylab 3 crew could maneuver their spacecraft adequately even if they lost a third thruster quad. That is, if they were left with only one functioning quad when time came for them to return home, they could still safely deorbit their CSM.

Though rescue preparations continued as a precaution, by 10 August NASA managers had cleared the Skylab 3 crew for the full duration of their planned 59-day mission on board the Workshop. On 25 September 1973, Bean, Lousma, and Garriott returned to Earth as originally planned, in the CSM that had launched them to Skylab.

Sources

"Skylab Rescue Capability," Kenneth S. Kleinknecht and Lawrence G. Williams; paper presented at the Fifth Annual Space Rescue Symposium Organized by the Space Rescue Studies Committee of the International Academy of Astronautics, 23rd Congress of the International Astronautical Federation, Vienna, Austria, 9-12 October 1972.

Skylab News Reference, NASA Office of Public Affairs, March 1973, pp. IV-6 - IV-8.

"Skylab: Outpost on the Frontier of Space," T. Canby, National Geographic, October 1974, p. 460.

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What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)