26 September 2015

Astronaut Sally Ride's Mission to Mars (1987)

Astronaut Dr. Sally Ride on board the Space Shuttle Orbiter Challenger during STS-7 (June 1983), her first flight into space. Image credit: NASA
Dr. Sally Ride was a member of the 1978 astronaut class, the first selected for Space Shuttle flights. During mission STS-7 (18-24 June 1983), she became the first American woman in space. Ride flew one more Shuttle mission - STS-41G (5-13 October 1984) - and served on the Rogers Commission investigating the 28 January 1986 Shuttle Challenger accident before James Fletcher, in his second stint as NASA Administrator, made her his Special Assistant for Strategic Planning on 18 August 1986.

Fletcher charged Ride with drafting a new blueprint for NASA's future. She had help from a small staff, a 12-member advisory panel led by Apollo 11 astronaut Michael Collins, and a six-member space mission design team at Science Applications International Corporation (SAIC) in Schaumburg, Illinois. The result of her 11-month study was a slim report called Leadership and America's Future in Space.

On 22 July 1987, Ride testified before the U.S. House of Representatives Subcommittee on Space Science and Applications about her report. She told the Subcommittee that the "civilian space program faces a dilemma, aspiring toward the visions of the National Commission on Space, but faced with the realities of the Rogers Commission Report." The National Commission on Space (NCOS), mandated by Congress and launched by President Ronald Reagan on 29 March 1985, had been meant to blueprint NASA's future until about 2005. The NCOS counted among its members such luminaries as Neil Armstrong, Chuck Yeager, Gerard O'Neill, Kathryn Sullivan, physicist Luis Alvarez, planetary scientist Laurel Wilkening, and former U.S. Ambassador to the UN Jeane Kirkpatrick.

Headed by Thomas Paine, NASA Administrator from 1968 to 1970, the NCOS had exceeded its mandate. Its report, titled Pioneering the Space Frontier, was a wide-ranging 50-year master plan for "free societies on new worlds" that would have been dismissed as unrealistic even had it not been unveiled in the chaotic aftermath of Challenger. By some accounts, Paine dominated the NCOS process to such an extent that some of its less patient members - for example, Chuck Yeager - ceased to attend meetings.

The Ride Report. Image credit: NASA
Ride's study aimed to produce a more realistic blueprint of NASA's future. Whereas the NCOS report urged immediate adoption of its expansive (and expensive) "vision," Ride outlined four much more limited "Leadership Initiatives." They were, she explained, meant to serve "as a basis for discussion." These included a piloted Mars program; "Mission to Planet Earth," which aimed to study Earth from space using satellites; "Mission from Planet Earth" (exploration of the Solar System using robotic spacecraft); and construction and operation of a permanent outpost on the Moon. Each of Ride's proposals could occur in isolation; none necessarily depended on or followed from the others. By Fletcher's command all would rely to some degree on NASA's planned low-Earth orbit (LEO) Space Station.

SAIC began design of the Ride report's piloted Mars program in January 1987. The company presented its final report to the Office of Exploration (nicknamed "Code Z" for its NASA Headquarters mail code) in November of that year. James Fletcher created Code Z in June 1987 and placed Ride in charge as his Acting Assistant Administrator for Exploration. By then, Ride had announced that she would leave NASA in August. John Aaron, who replaced her as Code Z chief, made SAIC's report the basis for piloted Mars and Phobos mission "Case Studies" in Fiscal Year 1988.

SAIC employed a split/sprint Mars mission design. The company credited a 1985 joint University of Texas/Texas A & M student design project with originating the split/sprint concept, though similar concepts can be traced back to the 1950s. The split/sprint mission would use a pair of spacecraft: an automated one-way cargo spacecraft "slowboat" launched first followed by a piloted "sprint" spacecraft. Both would burn chemical propellants and aerobraking.

The cargo spacecraft would follow a propellant-saving low-energy path to Mars. It would transport to Mars orbit propellants for the piloted spacecraft's return to Earth. The piloted sprint spacecraft would leave LEO only after the cargo spacecraft had arrived safely in Mars orbit.

So that its six-person crew would be exposed to weightlessness, radiation, and isolation for as short a time as possible, the piloted spacecraft would follow a roughly six-month path to Mars, remain at the planet for only one month, and then return to Earth in about six months. This would yield a piloted Mars mission duration of no more than 14 months.

Shuttle-derived heavy-lift launch vehicle. Image credit: M. Dowman/Eagle Engineering
In common with most other post-Challenger piloted Mars plans, the SAIC team abandoned the Space Shuttle as its primary means of launching spacecraft components and propellants to LEO. In the Shuttle's place, it proposed a heavy-lift rocket based in part on Shuttle hardware. The new rocket would debut in 1996 with a launch capability of 36 metric tons to LEO, then would evolve by 2002 to carry 91 metric tons to LEO.

Though it featured a piloted mission of short duration - which in most cases would imply large propellant expenditure - the SAIC split/sprint mission design provided substantial propellant savings by refueling the crew spacecraft in Mars orbit. This would in turn slash the number of costly heavy-lift rockets required to launch spacecraft components and propellants to the Space Station for assembly.

Launching a single round-trip combined crew/cargo sprint spacecraft would, SAIC calculated, need 25 heavy-lift rockets, while the two-spacecraft split/sprint design would need only 15. In addition, because the cargo and crew spacecraft would depart Earth more than a year apart, heavy-lift launches could be spread out over a longer period, making launch vehicle, payload, and launch pad preparations less sensitive to delays caused by weather or rocket malfunctions.

By the time the heavy-lifter attained its maximum launch capability in 2002, Phase I of SAIC's three-phase Mars program would be ended and Phase II would just have begun. Phase I, starting in 1992, would comprise a series of robotic precursor missions. Mars Observer, in 1987 already an approved NASA mission, would map Mars from orbit beginning in 1993; then, in 1995, Mars Observer 2 would establish and act as radio relay for a planet-wide network of hard-landed penetrator sensor stations. Orbital mapping and the seismic/meteorological net would help scientists and engineers to select landing sites for automated Mars Sample Return (MSR) and piloted Mars missions.

Mars Rover Sample Return concept. Image credit: NASA
A pair of MSR spacecraft would depart Earth in 1996 to collect Mars surface samples and return them to high-Earth orbit (HEO) in 1999. A reusable Orbital Maneuvering Vehicle (OMV) based at the LEO Space Station would retrieve the samples from HEO and deliver them for quarantine and initial study to an "isolation half-module" added to the Station in 1998. The samples would enable scientists to identify hazards in Mars surface materials and would aid engineers in the design of spacecraft, rovers, habitats, space suits, and tools.

Phase I would also include biomedical research on board the Space Station, which Ride assumed would reach Permanent Manned Configuration (PMC) in 1994. Almost immediately after it achieved PMC, NASA would add a Life Science Module. A six-person crew would then conduct a Mars mission simulation on board the Station that would last for the planned piloted sprint mission duration of 14 months.

If the astronauts remained healthy after the simulation, which would be conducted in weightlessness, then in 1996 NASA would begin development of a Mars sprint spacecraft lacking any provision for artificial gravity (that is, no part of it would rotate to create acceleration which the crew would feel as gravity). A module for housing Mars spacecraft assembly crews would join the Station in 2002, kicking off Phase II of SAIC's Mars program. The cargo spacecraft for the first split/sprint mission would depart LEO during the favorable 2003 low-energy Earth-Mars transfer opportunity.

If, on the other hand, biomedical researchers determined that the simulation crew had suffered harm from their long stay in weightlessness, then NASA would add a "variable-gravity module" to the Station in 2001. Crews would conduct simulations in the spinning module to determine the minimum level of artificial gravity required to safeguard astronaut health. Development of an artificial-gravity sprint spacecraft would not commence until after the simulations ended in 2004. If the artificial-gravity sprint spacecraft needed as much development time as its no-gravity counterpart, then the first piloted Mars mission might not leave Earth until 2013. SAIC largely ignored this possibility.

SAIC's automated cargo spacecraft (right) in Earth-orbit launch configuration with large Orbital Transfer Vehicle (OTV). The conical vehicle at the center of the cargo spacecraft's dish-shaped aeroshell is the piloted Mars Lander. Spherical tanks around the Mars Lander contain Earth-return propellants for the piloted sprint spacecraft. Image credit: Science Applications International Corporation
Launching parts and propellants from Earth's surface for the 238.5-metric-ton cargo spacecraft and a single 349.6-metric-ton reusable Orbital Transfer Vehicle (OTV) would require seven heavy-lift rocket launches. The cargo spacecraft would carry at the center of its 28-meter-diameter bowl-shaped Mars Orbit Insertion (MOI) aerobrake heat shield the mission's two-stage, 60-metric-ton Mars Lander.

Spherical tanks surrounding the Lander would hold the 82.5 tons of cryogenic liquid hydrogen/liquid oxygen propellants the piloted sprint spacecraft would need for return to Earth. The cargo spacecraft would also carry 4.2 metric tons of propellants for correcting its course during flight from Earth to Mars and 16.4 metric tons of propellants for circularizing its Mars-centered orbit after it aerobraked in Mars's atmosphere. A 9.1-metric-ton refrigeration system would prevent the propellants from boiling and escaping.

On 9 June 2003, the 30.5-meter-long cargo spacecraft/OTV stack would move away from the Space Station using small thrusters. The OTV would then ignite its main engines to push the cargo spacecraft out of LEO. After sending the cargo spacecraft on its way, the OTV would separate, turn end over end, fire its engines to slow itself, aerobrake in Earth's upper atmosphere, fire its engines to circularize its orbit, and return to the Station for refurbishment, refueling, and reuse.

The cargo spacecraft's course would intersect Mars on 29 December 2003. It would aerobrake in Mars's upper atmosphere to slow itself so that the planet's gravity could capture it into orbit. The cargo spacecraft would rise to its orbital apoapsis (high point), then fire its rocket engines to raise its orbit periapsis (low point) out of the martian atmosphere and circularize its orbit. Flight controllers would then begin careful checkout and monitoring of the cargo spacecraft and its cargo, paying special attention to the propellants the piloted sprint spacecraft would need for return to Earth.

Partial cutaway view of SAIC's piloted sprint Mars spacecraft. A = bowl-shaped Mars Orbit Insertion aerobrake heat shield; B = cylindrical habitat modules (2); C = cylindrical logistics module; D = cylindrical "bridge" tunnel; E = cylindrical tunnel linking docking unit (right), bridge tunnel, and Earth Recovery Vehicle; F = drum-shaped Earth Recovery Vehicle; G = flattened conical aerobrake heat shield; H = engines (2); I = spherical liquid hydrogen tank; J = spherical liquid oxygen tanks (2). Not shown: cylindrical command module, cylindrical airlock module, and one spherical liquid hydrogen tank. Image credit: Science Applications International Corporation/DSFPortree
SAIC offered a piloted spacecraft design with 4.4-meter-diameter Station-derived pressurized crew modules connected in a "race track" configuration; that is, in a square with each module linked by short tunnels at or near their ends. A pair of 12.2-meter-long habitat modules, each with a mass of 15.5 metric tons, would form two sides of the square; a 12.2-meter-long, 10.8-metric-ton logistics module would form the third side; and an 8.5-metric-ton command module and a 3.2-metric-ton airlock module would together make up the fourth.

A pressurized "bridge" tunnel would cross the inside of the square, linking directly the two habitat modules. Another tunnel would pierce the center of the bridge tunnel vertically. Its forward end would link with the top of the drum-shaped, 11.9-metric-ton Earth Recovery Vehicle (ERV), while its aft end would carry a docking unit. The ERV, situated deep within the spacecraft's structure, would double as the crew's solar flare "storm shelter." Four spherical tanks holding a total of 91.9 metric tons of cryogenic liquid hydrogen/liquid oxygen propellants and two rocket engines with a combined mass of 4.6 metric tons would be mounted atop the crew modules. The vertical tunnel's docking unit would protrude beyond the sprint spacecraft's twin engine bells.

The ERV/storm shelter would be mounted at the center of a one-metric-ton, 11.4-meter-diameter flattened conical aerobrake heat shield. ERV, ERV aerobrake, crew modules, tunnels, propellant tanks, and engines would nest within a bowl-shaped, 25-meter-diameter, 16.1-metric-ton MOI aerobrake. Except during propulsive maneuvers and aerobraking, four solar arrays capable of generating a total of 35 kilowatts of electricity at the piloted spacecraft's maximum distance from the Sun (that is, in Mars orbit) would extend beyond the edge of the MOI aerobrake. During maneuvers and aerobraking, the arrays would be folded out of harm's way atop the crew modules. Fully assembled and loaded with propellants, the piloted spacecraft's mass would total 193.7 metric tons.

An assembly crew at the Space Station would link a newly assembled small (197.4-metric-ton) OTV to the piloted spacecraft, then would attach the larger OTV used to launch the cargo spacecraft to the new OTV. This would create a 48-meter-long, 738.7-metric-ton Earth-departure stack.

SAIC's piloted sprint spacecraft (right) in Earth-orbit launch configuration with large and small reusable OTVs. Image credit: Science Applications International Corporation
The stack would move away from the Space Station on 21 November 2004. Shortly thereafter, the first OTV would ignite its engines to start the second OTV and the piloted sprint spacecraft on their way. Its work completed, it would then separate, aerobrake in Earth's atmosphere, and return to the Station for reuse. The second OTV would repeat this performance, then the piloted sprint spacecraft would burn nearly all of its propellants to place itself on course for Mars.

The piloted spacecraft would aerobrake in Mars's atmosphere and fire its engines to circularize its orbit on 3 June 2005. Almost immediately after MOI, the crew would rendezvous with the waiting cargo spacecraft. Three astronauts would board the Mars Lander, deorbit, and land at the pre-selected landing site. They would explore the site for from 10-to-20 days.

The other three astronauts, meanwhile, would transfer the Earth-return propellants stored on board the cargo spacecraft to the piloted spacecraft's empty tanks. They would also discard the piloted spacecraft's MOI aerobrake.

SAIC noted that the ideal trajectory for a sprint Mars mission launched as soon as possible after the cargo spacecraft arrived at Mars on 29 December 2003, would have the piloted spacecraft depart Earth on 8 January 2005, reach Mars on 2 August 2005, depart Mars on 1 September 2005, and return to Earth on 8 January 2006. SAIC's Earth-departure date, a little more than a month ahead of the ideal date, would increase the piloted mission's duration by almost two months (that is, to 14 months).

Launching the piloted sprint spacecraft early would, however, add an abort option to the mission. For example, if the sprint spacecraft were en route to Mars and the cargo spacecraft's propellant refrigeration system failed, allowing the sprint spacecraft Earth-return propellants it kept liquid to turn to gas and escape, then the crew could use the propellants they would have used to circularize their orbit around Mars after aerobraking to cause their spacecraft to skim through Mars's uppermost atmosphere on 3 July 2005. This aero-maneuver, if properly executed, would nudge the piloted spacecraft's course enough that it would intersect Earth on 15 January 2006.

SAIC's Mars crew lander would reach Mars orbit 18 months ahead of its three-person crew. It would become the astronauts' base of operations during a Mars surface stay lasting up to 20 days. Image credit: P. Hudson/NASA
SAIC envisioned that NASA would launch a series of three split/sprint missions by the end of the first decade of the 21st century. While the first crew explored the surface of Mars and worked in orbit to prepare their spacecraft for the trip home, the cargo spacecraft for the second Mars crew would depart LEO boosted by the same large aerobraking OTV the first mission's cargo and piloted spacecraft had used. The second crew would leave Earth orbit in early 2007 and return from Mars in early 2008. The final crew in the series would depart for Mars in early 2009 and return home in early 2010.

After the third Mars expedition, establishment of a Mars base - Phase III of SAIC's program - could begin. The company provided few details of Phase III.

With their surface mission completed, the first Mars explorers would lift off in their Mars Lander's ascent stage. SAIC calculated that the ascent stage would make up about half the mass of the Lander. The piloted spacecraft would rendezvous and dock with the ascent stage in Mars orbit to collect the surface crew and their samples of Mars rocks, sand, and dust. On 2 August 2006, shortly after casting off the spent ascent stage, the astronauts would fire the piloted spacecraft's twin engines to begin their five-month return to Earth.

As Earth loomed large ahead of what remained of the sprint spacecraft, the astronauts would enter the ERV capsule with their samples. The ERV, which would resemble the early "hat box" design of NASA's planned Space Station lifeboat, would slide out of a radiation shield housing that would remain behind on the crew spacecraft. The abandoned sprint spacecraft would then fire its engines a final time to miss Earth and enter orbit about the Sun.

SAIC based its ERV configuration on this NASA design for a Space Station lifeboat. Image credit: NASA
The ERV would aerobrake in Earth's atmosphere, then an automated OMV from the Space Station would retrieve it. After physical examinations and a period of quarantine on board the Station, the first Mars crew would return to Earth on board a Space Shuttle.

SAIC wrote that its piloted split/sprint Mars mission could support international space cooperation. Other countries, both allies and rivals, could contribute money, services such as propellant delivery, crew members, robotic precursor missions, spacecraft components, and even entire spacecraft. For all the countries involved, piloted Mars missions would "provide an effective catalyst for significant advances in automation, robotics, life sciences[,] and space technologies. . .[and], through direct experience, address and answer key questions about long-duration human space flight and the role of human beings in space exploration."

NASA did not much care for the Ride Report; in fact, the agency at first refused to publish it. Ultimately NASA printed about 2000 copies - an unusually small number for such a high-level report. Perhaps this was because Ride acknowledged that NASA could not hope to lead in all areas of space endeavor. In addition, Ride proposed a manned Mars program after the Space Station was built with no intervening manned Moon program, placed robotic programs on a par with their piloted counterparts, and implied that NASA might not need a new piloted space initiative after it finished building the Space Station.

Her matter-of-fact tone seems also to have annoyed some within NASA. Ride was nearing the end of her nine-year NASA career, so felt free to express herself. She was quick to point out when NASA's actions apparently belied its enthusiasm for piloted missions beyond LEO; for example, when she noted the uncomfortable fact that NASA boss Fletcher had committed only 0.03% of the agency's budget to funding the new Office of Exploration. This, Ride noted, gave the appearance that Code Z had been established merely to quell critics who complained that NASA had no long-term goals.

Following her departure from NASA, Ride worked briefly at Stanford University, her alma mater. In 1989, she became a physics professor at the University of California-San Diego. She led space public outreach projects for NASA, co-founded the Sally Ride Science education company in 2001, participated in the Columbia Accident Investigation Board in 2003, and co-authored several science books for children. In early 2011, she was diagnosed with pancreatic cancer. She died at age 61 on 23 July 2012.


"Piloted Sprint Missions to Mars," AAS 87-202, J. Niehoff and S. Hoffman, The Case for Mars III: Strategies for Exploration - General Interest and Overview, Carol Stoker, editor, 1989, pp. 309-324; paper presented at the Case for Mars III conference in Boulder, Colorado, 18-22 July 1987

Leadership and America's Future in Space, Sally K. Ride, NASA, August 1987

Piloted Sprint Missions to Mars, Report No. SAIC-87/1908, Study No. 1-120-449-M26, Science Applications International Corporation, November 1987

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, David S. F. Portree, Monographs in Aerospace History #21, NASA SP-2001-4521, NASA History Division, February 2001

More Information

The Collins Task Force Says Aim for Mars (1987)

McDonnell Douglas Phase B Space Station (1970)

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

Gumdrops on Mars (1966)

24 September 2015

The Collins Task Force Says Aim for Mars (1987)

The Apollo 11 crew of Neil Armstrong (left), Michael Collins, and Edwin Aldrin. Image credit: NASA
The January 1986 Challenger Space Shuttle accident laid bare many shortcomings of the U.S. space program. NASA, which only 14 years before had soared to the moon, had suffered chronic underfunding since the truncated Administration of President Richard Nixon (1969-1974). At the same time, expectations for the Shuttle grew, until, in January 1984, President Ronald Reagan called upon NASA to use its Shuttle fleet to build an Earth-orbiting Space Station within a decade.

NASA had eagerly encouraged such expectations. The Shuttle, it promised, would fly cheaply and often, permitting it to replace all U.S. expendable rockets and fly commercial payloads for domestic and foreign customers. It would fly so inexpensively that Shuttle astronauts would economically service Earth-orbiting satellites. The Shuttle would reliably launch all U.S. robotic planetary missions, saving so much money that a new era of planetary exploration could begin. By conducting secret military missions - many launched from California into near-polar orbits - it would help to ensure U.S. national security. It would be safe enough that it would carry non-astronaut passengers - researchers, teachers, journalists, and others - and its crews would fly without pressure suits.

The Space Shuttle would also open the door to new space programs. The Space Station, NASA declared, was "the next logical step" after the Shuttle. That implied other, unspecified steps after the Space Station, in the 1990s and beyond.

Even before the Challenger accident called many of NASA's promises into question, Reagan had come under pressure to give the space agency a long-term goal that would provide a clear rationale and context for the Shuttle and Station programs. In late 1984, in fact, Congress mandated that the White House appoint an independent commission to study NASA's long-term options and offer recommendations for its future direction.

The Space Shuttle was developed in a dangerously constrained funding environment. Despite this, NASA sought to promote a bold vision of a Shuttle-launched future. Image credit: NASA
The National Commission on Space (NCOS) began its planned year-long study on 29 March 1985. Reagan tapped Apollo-era NASA Administrator Thomas Paine to head up the Commission. Among its commissioners were such aviation and spaceflight luminaries as first moonwalker Neil Armstrong, Chuck Yeager, the first person to fly faster than sound, and Kathryn Sullivan, the first U.S. woman to walk in space.

The NCOS report, titled Pioneering the Space Frontier, reached the news media in March 1986. Paine formally presented it to the White House and Congress on 22 July 1986. It called for a 50-year program that included fully reusable shuttles, heavy-lift rockets, an Earth-orbiting spaceport, a variable-gravity space station for biomedical research, lunar oxygen mines, cycling Mars liners, an outpost on inner martian moon Phobos, and a science base on Mars. It touched on topics as wide-ranging as self-replicating space factories, submersibles for the hypothetical world-ocean of Uranus, and U.S. involvement in the International Space Year of 1992.

Set against the backdrop of the Challenger accident and NASA's revealed weaknesses, the NCOS program appeared at best grandiose. The Reagan Administration quietly shelved the NCOS report.

Concern over NASA's long-term direction had, however, not abated. If anything, it had increased, in part because the Soviet Union had launched its long-awaited Mir core space station (20 February 1986). Many feared that the U.S. civilian space agency had lost not only its sense of direction, but also its place as the world leader in spaceflight.

On 18 August 1986, less than a month after the NCOS report reached Congress and the White House, NASA Administrator James Fletcher appointed Sally Ride, the first U.S. woman in space, as his Special Assistant for Strategic Planning. He charged her with preparing a new blueprint for NASA's future - one more focused and readily achievable than the NCOS blueprint - that would emphasize specific ways that NASA could demonstrate U.S. leadership in space.

Robotic Mars missions would have played significant roles in both the Collins Task Force piloted Mars program and Sally Ride's robotic Solar System exploration "leadership initiative." Image credit: NASA
While drafting her report, Ride received input in the form of a three-and-a-half-page paper from the NASA Space Goals Task Force, a 12-member group appointed by NASA Advisory Council chairman Daniel Fink and chaired by Apollo 11 Command Module Pilot Michael Collins. The Council gave the Collins Task Force final report its blessing during its 3-4 March 1987 meeting, and Fink submitted the report to Fletcher to pass on to Ride on 16 March.

The Space Goals Task Force declared that a "bold goal, clearly stated" would help the space agency to "focus and clarify" its long-term objectives. Mars, the Task Force declared, stood out as "the one entity most likely to capture widespread enthusiasm and support, while pulling considerable scientific and technical capability in its wake." It called for a public declaration that astronauts "exploring and prospecting on Mars" would henceforth become NASA's "primary goal."

The Task Force then outlined "preliminary steps" that the U.S. would need to take before Americans could take steps on Mars. First, the Space Shuttle would need to resume operations and new expendable rockets would need to be developed to supplement it. This would help to ensure uninterrupted U.S. space access. Funding for space technology research would need to be increased to reverse the "serious erosion of our technology base" that began during the Nixon Administration. In addition, an "aggressive" program of robotic Mars missions would be required.

NASA would also need to complete the Space Station as soon as possible so that it could serve as a test-bed for the development of Mars Program technologies and a laboratory for studying long-duration spaceflight effects on human physiology. "The Space Station is an element of human expansion [into space] in its own right," the Task Force declared, "but it is far more important because of its essential role in building the capability to conduct programs that achieve and demonstrate [space] leadership."

One of many piloted Mars lander designs proposed in the mid-to-late 1980s - the "molly bolt" configuration. Image credit: Eagle Engineering/NASA
When Americans set foot on Mars, the Task Force continued, it should be as part of a "peaceful enterprise done in the name of all humankind." It asserted, in fact, that American Mars explorers should, "[u]nder appropriate conditions," be accompanied by astronauts of other "qualified nations," including the Soviet Union.

The Task Force called for "a realistic schedule" for its Mars Program that would ensure "stable planning and execution of a studied, orderly, progressive series of events." As part of the effort to develop a schedule, NASA, the President, and the Congress would need to decide "whether the moon should be used as stepping stone to Mars, or should be bypassed."

It concluded by considering commercial opportunities that the Mars Program might create. NASA would "pull" commercial space ventures into existence through its revitalized research programs, the Collins Task Group report argued, adding that the "history of this Nation is replete with examples of successful commercial activity stimulated by the technologies resulting from the exploration of new frontiers." "The technical challenges associated with a program of human exploration of Mars are of such a magnitude," it continued, that they would "certainly provide many direct and indirect stimuli to American industry."

The Space Goals Task Force report influenced Sally Ride's August 1987 report Leadership and America's Future in Space, though she gave equal emphasis to four leadership initiatives (Earth studies, robotic Solar System exploration, an outpost on the moon, and humans to Mars). She believed that the U.S. could not demonstrate space leadership in all areas of spaceflight endeavor, so should choose one or two and excel in them. She also believed that NASA should return astronauts to the moon before accepting the greater challenge of astronauts on Mars.

Collins, probably the most articulate of the astronaut writers, subsequently sought to build support for the Mars-centered Space Goals Task Force program. In a prominent article in the November 1988 issue of the widely circulated National Geographic magazine and in his 1990 book Mission to Mars, he called upon NASA to bypass the moon and launch humans to Mars as early as 2004.


Letter with enclosure, Daniel J. Fink to James C. Fletcher, "NASA Space Goals Task Force Final Report," 16 March 1987

"Mission to Mars," Michael Collins, National Geographic, Volume 174, November 1988, pp. 732-764

Mission to Mars: An Astronaut's Vision of Our Future in Space, Michael Collins, Grove Press, 1990

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, David S. F. Portree, Monographs in Aerospace History #21, NASA SP-2001-4521, February 2001, pp. 68-69

More Information

Sally Ride's Mission to Mars (1987)

Evolution vs. Revolution: The 1970s Battle for NASA's Future

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

Where to Launch and Land the Space Shuttle? (1971-1972)

18 September 2015

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-rocket 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 "After EMPIRE" in the Related Posts listed 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.


"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

Dyna-Soar's Martian Cousin (1960)

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

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)

15 September 2015

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 crossed Neptune's and was 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?


Historical Geology, Raymond C. 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 Chris 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)

11 September 2015

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, for example, 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.


"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)

08 September 2015

Re-Purposing Mercury: Recoverable Space Observatory (1964)

Launch of astronaut John Glenn on board Friendship 7. Image credit: NASA
Hermann Poto─Źnik, 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 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. Similar malfunctions would doom 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.


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?)

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