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
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 to 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. Headed by Thomas Paine, NASA Administrator from 1968 to 1970, it had produced instead 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.

The Ride Report. Image credit: NASA
Whereas the NCOS report urged immediate adoption of its expansive (and expensive) "vision," Ride outlined four much more limited "Leadership Initiatives" "as a basis for discussion." These included the 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 lunar outpost. Each of Ride's proposals could occur in isolation; none necessarily depended on or followed from the others, though by Fletcher's command all would rely to some degree on NASA's planned low-Earth orbit (LEO) Space Station.

SAIC began to design 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. Fletcher created Code Z in June 1987 and placed Ride in charge as his Acting Assistant Administrator for Exploration. By that time, 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 Code Z's 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 in fact similar concepts date 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 rely on aerobraking at Earth and Mars.

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 was confirmed to have arrived safely in Mars orbit.

So that its six-person crew would be exposed to weightlessness, radiation, and isolation for as little 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 expenditure of large quantities of propellants - the SAIC split/sprint mission design offered 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.

A sprint-type mission using a single combined round-trip crew/cargo spacecraft would, SAIC calculated, need 25 heavy-lifters, while the 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 due to weather constraints or rocket malfunctions.

By the time the heavy-lifter attained its maximum capability in 2002, Phase I of SAIC's three-phase Mars program would be ended and Phase II would have just begun. Phase I, starting in 1992, would include 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 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 Space Station would retrieve the samples from HEO and deliver them for quarantine and initial study to an "isolation half-module" added to the Space Station in 1998. The samples would enable scientists to identify any hazards in Mars's 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, 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 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 sojourn 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 its 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 and 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 orbit after it aerobraked in Mars's atmosphere. A 9.1-metric-ton cooling 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 engines to push the cargo spacecraft out of LEO. After sending the cargo spacecraft on its way, the OTV would separate, fire its engines to slow itself, aerobrake in Earth's upper atmosphere, 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 apoapsis (orbit high point), then fire its rocket engines to raise its periapsis (orbit 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 Station-derived pressurized crew modules connected in "race track" formation; that is, in a square with each module linked by short tunnels at or near their ends. A pair of 4.4-meter-diameter, 12.2-meter-long habitat modules, each with a mass of 15.5 metric tons, would form two sides of the square; a 4.4-meter-diameter, 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 ERV/storm shelter would be mounted at the center of an 11.4-meter-diameter, one-metric-ton flattened conical aerobrake heat shield. ERV, ERV aerobrake, crew modules, tunnels, propellant tanks, and engines would nestle 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.

The assembly crew based at the Space Station would link a newly assembled smaller (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 one-year piloted 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.

Launching the piloted sprint spacecraft early would, however, add an abort option to the mission. If, for example, while the sprint spacecraft was en route to Mars the cargo spacecraft's propellant cooling system failed, allowing the Earth-return propellants it kept liquid to turn to gas and escape, then the crew could use the propellants that they would have used to circularize their orbit around Mars after aerobraking to ensure that their spacecraft would skim through Mars's uppermost atmosphere on 3 July 2005. The aeromaneuver, 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 surface stay lasting up to 20 days. Image credit: P. Hudson/NASA
SAIC explained that one goal of Phase II of the Mars program would be to seek out a site for a permanent Mars base. The company envisioned that NASA would launch a series of three split/sprint missions by the end of the first decade of the 21st century.

In fact, while the first crew explored Mars's surface 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 the 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 Mars samples. On 2 August 2006, shortly after casting off the spent ascent stage, the astronauts would fire the piloted spacecraft's twin engines to begin a 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 one of the early designs for 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, precursor missions, spacecraft components, or 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 the agency 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 Space Station 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 its Space Station.

Her matter-of-fact tone annoyed some within NASA. Ride, who by the time she completed her report was nearing the end of her nine-year NASA career, 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 Fletcher had committed only 0.03% of NASA's budget to funding the new Office of Exploration. This, Ride explained, 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.

Sources

"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)

Gumdrops on Mars (1966)

7 comments:

  1. Hello, David, I'm a reporter at Estadao, one of the main newspaper in Brazil. How can I reach you? I'm writing about Mars and, if you agree, I'd like to send you some questions. My e-mail is andre.oliveira@estadao.com or andreol88@gmail.com. Thank you very much. Regards!

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  2. Wow! Now I get it. I apologize for this very long comment, but your quite excellent post leads me to radically downgrade all my expectations for human exploration of space. I might as well express these here...

    So a very minimal mission to Mars (i.e. three astronauts in one lander for one month) would take at least 15 heavy-lifter launches!? And that would require a separate cargo trip with transfer of the return fuel in Mars orbit - i.e. a major risk with no back-up plan!? So the standard "sprint" single-spacecraft mission would take 25 launches!?

    Thanks for bringing to light these simple figures David. I find them extremely significant because rocket technology has actually not changed during the 28 years (!) since this Sally Ride report. Indeed the artist image of a "Shuttle-derived heavy-lift launch vehicle" looks extremely similar to the currently developed SLS - down to the 4 SSME engines on the first stage. And the second stage of the SLS will get the good old LH2/LOX RL10 engine, whose development began in 1959 and which has been used already on Centaur, Saturn I and Delta...

    Can you confirm that even today, it would still take at least 15 to 25 SLS launches for one single mission to Mars? It is obvious to me that this is simply not going to happen. During the golden sixties, at the zenith of its power and motivated by the space race, the U.S. built no more than 17 Saturn V. While each of them could land a crew on the moon (and 6 actually did), production stopped in 1968. So what are the chances that your government decides to spend a roughly similar amount of money for one single Mars mission?

    I suspect now that NASA has reached the same conclusions quite some time ago. This would explain their inability to deliver a convincing plan. I hoped that a Chinese repetition of the 1957-1961 "humiliation" could kick-start a new Space Race, but even that can not justify 20 heavy launches per mission.

    I guess that our only hopes to see humans on Mars (probably not in our lifetimes) are either a huge scientific discovery, or a major technological breakthrough in space propulsion. The discovery would take more than briny water or even microscopic life, rather something like underground ecosystems of macroscopic organisms... And the breakthrough can not use nuclear fission which is now unacceptable. I am not even sure that a fully re-usable launcher would qualify: what would be its payload to LEO?

    I wonder if someone has evaluated (for intercomparison purposes) the LEO payloads necessary for the classical deep space mission. How many SLS would be required to get back to scientifically interesting lunar places, e.g. the poles for water exploration or the far side to set up an automatic astronomical observatory? How many SLS to get in orbit around Mars, e.g. on Phobos, and teleoperate robots on the surface as you advocated several times?

    I have access to insider opinions about the usefulness of the ISS: quite limited technologically speaking, and actually nil from a science point of view. So if this is the best we can do with human spaceflight, why do we keep doing it? Let's rather invest all this money in robotic exploration and in fundamental research for gound-breaking space propulsion technologies. By the time this research bears fruit, we will know exactly where to go to see with our own eyes the wonders of the Solar System.

    With this, I rest my case...

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    1. Very good. I mean, there are some things you write with which I disagree. Nevertheless, I think you are the first person ever who has put their finger on the main reason why I like this mission plan. It is honest.

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    2. The study completely ignores the ideas of Robert Zubrin; his book "The Case for Mars" outlines a different (and much cheaper) plan.

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    3. That could be because Zubrin & Baker's Mars Direct plan had not yet been invented. It came along in 1990. This is one reason why spaceflight history is important - it permits people to place specific mission concepts in proper context. You will note that the SAIC plan proposes arriving at Mars with empty tanks, just as did Zubrin & Baker. Mars Direct is an interest synthesis of concepts.

      dsfp

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  3. Thanks for the compliment. It is new for me to write on this topic, while you are a specialist. So I would be happy to learn about the things with which you disagree :-)

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  4. Just a couple of things. First, I don't see the automated cargo ship as a single point failure waiting to happen. The piloted sprint spacecraft is launched on a trajectory that enables a powered flyby and return to Earth to avoid that eventuality. There would, of course, be a brief period in Mars orbit when something might go wrong - after sprint spacecraft MOI - something that might prevent the piloted spacecraft from refueling. The likelihood of that happening is, however, small.

    I hope that discovery of life on Mars in any form does not lead to humans on Mars. Humans cannot help but contaminate the planet. This could be a catastrophe from a science standpoint and I believe from an ethical standpoint, too. We will need to learn to leave biospheres the hell alone - at least until we can be certain we can interact with them without messing them up.

    I suspect that a piloted Mars mission could be accomplished with fewer SLS launches even if it followed this mission plan to the letter. This Shuttle-derived heavy-lifter is not all that powerful. SLS would launch something like 130 metric tons, so in theory would reduce the number of launches proportionately. In addition, very soon after this was published Code Z began to look at ways of reducing mass. Probably the best way to cut mass would be to drop most chemical propulsion from the cargo spacecraft. Replacing the cargo spacecraft with a solar-electric system might be best all around. One might also replace the chemical OTVs with a solar-electric system that would put both the cargo and crew spacecraft into elliptical Earth orbits. The crew would join their spacecraft at apogee so they wouldn't have to endure repeated Van Allen Belt passages over months and would ignite a small chemical stage at perigee to perform TMI. There are other concepts as well, such as inflatables and tightly closed life support systems, than can trim mass.

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