A Long Way Home: Abort from Piloted Mars and Venus Missions (1970)

Cislunar abort: the crew of Apollo 13 on the deck of the aircraft carrier Iwo Jima after their safe return to Earth. Pictured are Lunar Module Pilot Fred Haise (left), Commander Jim Lovell, and Command Module Pilot Jack Swigert. Image credit: NASA.
On 13 April 1970, an oxygen tank exploded in the Apollo 13 Command and Service Module Odyssey, badly damaging the spacecraft 200,000 miles from Earth. NASA had no choice but to scrub the planned third Apollo lunar landing and return the Apollo 13 crew to Earth as quickly as possible. 

Astronauts Jim Lovell, Fred Haise, and Jack Swigert used the Lunar Module Aquarius as a backup propulsion system and lifeboat, swung around the Moon, and splashed down safely in Odyssey's Command Module on 17 April, about three and a half days after the explosion.

Amidst the drama of Apollo 13's mission abort, A. A. VanderVeen, a mathematician with NASA planning contractor Bellcomm, drafted a memorandum. In it, he pointed out that the time needed to return to Earth following a malfunction during the outbound leg of a Mars or Venus mission would nearly always be measured in months.

VanderVeen analyzed aborts for a piloted Mars orbiter ("capture") mission launched in 1981. An abort would begin with a rocket burn to slow the Mars spacecraft in its orbit around the Sun and cause it to fall back toward Earth. Because of the great cost of launching propellants off the Earth, he assumed that the spacecraft would carry no propellants dedicated entirely to an abort; it would perform its abort burn using only the propellants which, in a normal mission, would slow the spacecraft by 12,000 feet per second (3658 meters per second) at the end of its Earth-Mars transfer so that the gravity of Mars could capture it into orbit (that is, its Mars orbit insertion propellant).

A 270-day flight to Mars could be divided into three abort phases, VanderVeen found. Phase 1 would span from late in mission day 1 through mission day 60. During this period, the spacecraft would move slowly out from the Sun but remain relatively close to the Earth. A 12,000 feet per second (3658 meters per second) abort burn on mission day 60 would return the crew to Earth in 80 to 110 days.

Phase 2 would span mission days 60 through 180. Earth would pull ahead of the spacecraft during this period. Following the abort burn, the spacecraft would have to dip inside the orbit of Venus to gain speed and complete nearly one full orbit of the Sun in order to catch up with Earth from behind. An abort burn on mission day 180 would return the crew to Earth in 290 days, VanderVeen calculated.

Phase 3 would span mission days 180 through 270. The spacecraft would be playing catch up with Mars during this period. Aborts in Phase 3 would result in Earth returns longer than those in Phase 1 but shorter than those in Phase 2.

Increasing the quantity of abort propellant available would not meaningfully decrease Earth-return time, VanderVeen found. An abort on mission day 100 using only the spacecraft's Mars orbit insertion propellant would yield a 260-day Earth return. Adding enough propellant to change the spacecraft's speed by an additional 1000 feet per second (305 meters per second) would shave only 10 days off that return time. Providing enough propellant to change its speed by 24,000 feet per second (7315 meters per second) — that is, twice the velocity change needed for Mars orbit insertion in a normal mission — would yield a disappointingly lengthy 140-day Earth return.

Abort timing would also affect the speed at which the returning spacecraft would reach Earth. VanderVeen assumed that the Mars crew would reenter Earth's atmosphere directly in an Apollo-derived Earth entry module. The Apollo reentry system was designed to withstand reentry at up to 40,000 feet per second (12,192 meters per second). This would suffice for aborts initiated during the first 130 days of flight. 

For aborts initiated between 130 and 200 days after Earth departure, however, an improved Apollo heat shield or braking rockets designed to slow reentry would be required. Aborts during the remainder of the Earth-Mars transfer would demand "advanced [reentry] systems or a high retro-fire maneuver" requiring much additional propellant.

VanderVeen concluded that, all things considered, successfully aborting a Mars mission after departure from Earth orbit would be extremely challenging. His memorandum's chief recommendation reflected the essential hopelessness of an abort in interplanetary space: he wrote that "all major [spacecraft] systems should be thoroughly checked out very early in the mission while a short return abort opportunity exists."

Source

"Abort from Mars and Venus Missions - Case 103-8," A. A. VanderVeen, Bellcomm, Inc., 15 April 1970.

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North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit

A CSM-Only Back-Up Plan for the Apollo 13 Mission to the Moon (1970)

What if a Crew Became Stranded on Board the Skylab Space Station? (1972)

The Proper Course for Lunar Exploration (1965)

Image credit: NASA.

For a time in the early 1960s, Thomas Evans headed up the Advanced Lunar Missions Study Program in the NASA Headquarters Office of Manned Space Flight. By May 1965, when the 11th Annual Meeting of the American Astronautical Society (AAS) was held in Chicago, Illinois, he had retired from NASA to become a farmer in Iowa. This gave him the freedom to speak his mind about what he felt were the Apollo Program's shortcomings.
 
Evans told assembled members of the AAS that "the idea of a manned [landing] on the [M]oon was so spectacular. . . that [it] dominated most pronouncements and thoughts on the space program." He then declared that the objective had "too much the flavor of a stunt to be the final goal of a $20 billion national effort." Evans argued that 
[Our] situation today is comparable to one which might have occurred during the railroad building era in America a century ago. It is as if the federal government had invested vast sums in the construction of the first railroad spanning the North American continent, but had procurred only a single engine and caboose. . . The first crossing by that engine and caboose would have been a major milestone in man's progress and would have been greeted with enthusiasm and applause. But then those responsible for the program would have faced a major decision. . . Should the project be stopped? Should the engine-caboose be run repeatedly back and forth across the Continent to constantly remind the world of our great achievement? Or should a further modest investment be made in. . . some freight and passenger cars, to convert the system into something of practical value? Only the last solution would have been tenable then, and only a similar constructive approach would seem acceptable now. 
Evans was hopeful that good sense would prevail. He pointed to statements by President Lyndon Baines Johnson and Vice-President Hubert Humphrey (chair of the National Space Council) which he said made clear that "the United States fully intends to explore the [M]oon, not merely to visit it." He explained that the Saturn rockets and Apollo spacecraft NASA had under development would provide "an excellent base upon which to build a broad program of manned. . . lunar exploration beyond the first landing."

He noted that NASA expected to be able to launch six Saturn V rockets per year beginning in 1969. After explaining that "most Saturn Vs will be used for lunar operations since there are only a limited number of credible missions for this vehicle in earth orbital and planetary programs during the early 1970s," Evans outlined four candidate Saturn-Apollo-based lunar exploration programs. 

In the first, the baseline Apollo program, a single Saturn V rocket would launch a Apollo Command and Service Module (CSM) carrying three astronauts and the Lunar Excursion Module (LEM) (as the Apollo Lunar Module — LM — was known at this time). Two astronauts would land on the Moon in the LEM for a one-day stay. They would explore an area 0.2 miles in radius centered on their LEM. The crew would have at its disposal only 250 pounds of payload such as scientific instruments. 

The baseline Apollo Lunar Excursion Module (LEM) on the Moon as envisioned in 1964. Image credit: Grumman/NASA.

Evans' second candidate program would be based on the Apollo Extension System (AES) that NASA had begun to study as early as 1963. This option would, he explained, permit "sophisticated orbital survey. . . to gather data on the entire surface of the [M]oon," as well as lunar surface stays lasting up to 14 days. 

Two Saturn V rockets would be required for each AES lunar surface mission. The first would launch a piloted CSM and an automated cargo LEM loaded with 2500 pounds of supplies and equipment. The CSM would transport the cargo LEM (often called a LEM Shelter) to lunar orbit, then the LEM would separate and land automatically on the Moon. The CSM and its crew would then return to Earth. 

The second Saturn V would launch three astronauts and Apollo CSM and LEM spacecraft "improved" to enable long missions. Two astronauts would land in the improved LEM near the cargo LEM, which would serve as their shelter during their 14-day surface stay. They would use a small surface rover or a pair of flying vehicles to explore an area five miles in radius. 

The third candidate program, based on Apollo Logistic Support System (ALSS) studies, would also use two Saturn Vs per 14-day surface expedition, but would differ from AES in that the LEM Truck, a beefed-up LEM descent stage capable of delivering four tons of payload to the lunar surface, would replace the cargo LEM. The LEM Truck's principal payload, Evans wrote, would be the Mobile Laboratory (MOLAB), a pressurized rover that would permit two astronauts to explore an area 50 miles in radius. 

The Northrup MOLAB pressurized lunar rover would have arrived on the Moon atop of modified LEM descent stage (LEM Truck). The cylinder on top of the tubby pressurized compartment is the docking unit for linking with the Apollo CSM that delivered the MOLAB/LEM Truck to lunar orbit. This was one of several pressurized rover designs put forward in the mid-1960s. Image credit: Northrup/NASA.

Evans noted that, in spite of their impressive capabilities, the AES and ALSS cargo delivery systems would be "inherently inefficient" because astronauts would need to travel to the Moon and back to deliver each automated cargo lander. This would mean that the mass of the CSM systems required for crew support and Earth-return (life support, lunar-orbit departure and course-correction propellants, reentry heat shield, and parachutes) would need to be subtracted from the mass of the payload that the AES and ALSS systems could deliver to the Moon's surface.

Lunar Exploration Systems for Apollo (LESA), the fourth program Evans described, would avoid this inefficiency. LESA, Evans explained, was "a family of shelters, vehicles, and other equipment. . . tailored to support not only short-term reconnaissance operations by two or three astronauts but also semi-permanent scientific stations manned by up to 12 or even 18 men." 

LESA 1 Shelter with rover. Image credit: Boeing/NASA.

The Saturn V-launched LESA Shelter lander would follow a direct-ascent trajectory from Earth to the Moon, so would need no CSM. This would enable delivery of up to 14 tons of payload. Crew delivery at first would be by improved Apollo CSM and an upgraded LEM capable of landing three men on the Moon. The CSM would remain in hibernation in lunar orbit while the crew was on the surface; the LEM would hibernate on the surface while its crew lived in the LESA Shelter.

A 90-day, three-man LESA 1 expedition would explore an area 80 miles in radius; a 365-day, 12-to-18-man LESA 3 outpost made up of additional Shelters and other specialized modules (for example, a nuclear power plant) and relying on advanced direct-ascent landers for crew rotation and resupply would survey an area 200 miles in radius. The former would require a total of three Saturn V launches; the latter, 10 to 17 Saturn V launches. 

Developing the AES would cost an additional $500 million over the $20 billion already committed to Apollo, Evans estimated, while ALSS development would cost $1 billion. Developing LESA 1 would cost $2 billion — just 10 percent of the amount already committed to Apollo. LESA 3 would evolve from LESA 1 for an additional $800 million.

Evans then proposed a two-phase post-Apollo lunar program. In Phase I, which would be based on AES, ALSS, or LESA 1, astronauts would explore three areas of the Moon judged to be of "major geoscientific interest" totaling up to 1800 square miles ("a meager sample," Evans noted, "of the total 10 million square miles of lunar surface"). In Phase II, which would be based on LESA 3 modified for six astronauts, NASA would maintain an outpost on the Moon for four years. 

Evans compared operations costs of the four programs. He determined that a combination of LESA 1 in Phase I and modified LESA 3 in Phase II would be most economical, with a total cost of less than $8 billion. ALSS/modified LESA 3, with an operations cost of $8.3 billion, would also be economically acceptable, while AES/modified LESA 3 would be "a disastrous selection" — together, the two phases would cost a total of about $20 billion. 

The retired NASA manager ended his paper by broadly assessing the state of NASA lunar planning. He noted that, of the $26 million allotted to planning for advanced piloted lunar systems in the Fiscal Year 1965 NASA budget, most was budgeted for examination of inefficient and limited systems such as AES. "Only a trickle," he wrote, was devoted to the study of "more sophisticated and efficient systems." 

NASA and its contractors continued studies of advanced lunar systems throughout the 1960s and into the early 1970s. Studies focused mainly on AES/ALSS-type missions. It was hoped these would fly during the 1970s as part of the Apollo Applications Program (AAP), which became AES's successor shortly after Evans' May 1965 presentation. At the same time, scientific advisory groups advocated for advanced lunar exploration.

Apollo did not, however, imply a long-term national commitment to lunar exploration. Between 1964 and 1968, President Lyndon Baines Johnson repeatedly signaled his support for an Apollo-derived post-Apollo NASA program; lack of support for the program in Congress, however, caused NASA Administrator James Webb to turn the agency's efforts increasingly away from post-Apollo lunar exploration. In addition, the Apollo 1 fire of 27 January 1967, which killed astronauts Gus Grissom, Ed White, and Roger Chaffee, did immeasurable damage to NASA's post-Apollo prospects.  

NASA Administrator James Webb (center) with Vice-President and National Space Council chair Hubert Humphrey (left) and President Lyndon Baines Johnson (right). Image credit: NASA.

In the 1969-1971 period, when NASA Administrator Thomas Paine's Integrated Program Plan (IPP) held sway, the space agency and its contractors studied complex and costly lunar transportation systems (such the Nuclear Shuttle), space stations in lunar orbit, and permanent lunar surface bases. Such plans received no support from the Administration of President Richard Nixon, however, and all IPP planning ceased soon after Paine's resignation in September 1970. 

Despite these setbacks, some features of AAP lunar advance planning found their way into the last three Apollo missions to the Moon (Apollos 15-17). Designated J-class, their technological improvements included heavier lunar surface payloads, enhanced lunar surface mobility, space suits with greater flexibility and endurance, longer lunar surface stay times (up to three days), added lunar surface scientific instruments, a bay full of Moon-pointing scientific sensors in the lunar-orbiting CSM, and a subsatellite ejected into lunar orbit from the CSM.

The image at the top of this post illustrates the course U.S. lunar exploration took after Evans presented his paper. It shows Apollo 17 Commander Eugene Cernan saluting Old Glory in the Taurus-Littrow valley in December 1972. 

Apollo 17 left Earth atop the penultimate Saturn V rocket to fly (the last to fly would launch the Skylab Orbital Workshop, the last vestige of AAP, into low-Earth orbit in May 1973, eight years after Evans' presentation). Apollo 17's jeep-like Lunar Roving Vehicle (just visible behind Cernan) ranged up to 7.6 kilometers from its home base, the LM Challenger (behind flag), during three traverses spanning three days. The only professional scientist to reach the Moon, geologist and Lunar Module Pilot Harrison Schmitt, snapped the picture. 

Source

"Lunar Exploration: What is the Proper Course?" Thomas Evans, Post Apollo Space Exploration, Francis Narin, editor, 1965, pp. 647-661; paper presented at the 11th Annual Meeting of the American Astronautical Society in Chicago, Illinois, May 3-6, 1965.

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Project Hyreus (1993)

The Project Hyreus mission emblem. Image credit: University of Washington Department of Aeronautics and Astronautics.

In Greek mythology Hyreus (pronounced "HY-ree-us") is Orion's father. Students in the University of Washington (UW) Department of Aeronautics and Astronautics had a different take on this obscure figure, however. The end of the Cold War and efforts to rein in a galloping U.S. Federal deficit yielded a decline in aerospace spending in the late 1980s/early 1990s. This led to "downsizing" and corporate mergers in aerospace industry. New hires slumped, confronting aerospace engineering students with an uncertain future.

According to the 28 UW students who contributed to the 1993 Project Hyreus report, Hyreus (pronounced "HIRE-us") was a mortal who succeeded in living off the land in the barren underworld, and for that achievement was made the God of Gainful Employment. The students performed the Project Hyreus Mars Sample Return (MSR) study in UW's Space Systems Design course as part of the NASA/Universities Space Research Association (USRA) Advanced Design Program (ADP). Dr. Adam Bruckner was their instructor. 

Hyreus was a follow-on to UW's 1992 Project Minerva NASA/USRA ADP study, which proposed a piloted Mars expedition based on the 1990 Martin Marietta Mars Direct plan. The Minerva study had found feasible Mars Direct's reliance on Earth-return rocket propellants manufactured from martian resources, a technique called In Situ Propellant Production (ISPP). In the Mars Direct, Minerva, and Hyreus plans, ISPP relied on carbon dioxide gas in the martian atmosphere because it is readily available all over the planet. Carbon dioxide makes up about 95 percent of the martian atmosphere, which is only about 1 percent as dense as Earth's atmosphere. 

The UW students emphasized a Sabatier/Reverse Water-Gas Shift (RWGS) ISPP system, which would produce liquid methane fuel and liquid oxygen oxidizer, though they also examined a carbon monoxide ISPP system. The UW students explained that Hyreus aimed to demonstrate ISPP technology in a critical mission role at a relatively low cost ahead of a piloted ISPP Mars mission. 

Assuming that Hyreus succeeded, the mission would exploit the mission-enhancement potential of ISPP by returning to Earth a Mars surface sample with a mass of from 25 to 30 kilograms — that is, one more than 10 times larger than in most other MSR proposals. Analysis of such a large sample would enable scientists to locate water deposits and seek life on Mars, the students contended.

Hyreus Sabatier/Reverse Water-Gas Shift (RWGS) In Situ Propellant Production (ISPP) system. Image credit: University of Washington Department of Aeronautics and Astronautics.

The 400-kilogram Sabatier/RWGS ISPP plant would need a total 122 kilograms of cryogenic liquid hydrogen feedstock brought from Earth. The hydrogen would gradually boil and escape, so Hyreus would depart Earth with an extra 88 kilograms on board to make up for losses. 

The Sabatier/RWGS plant would take in dust-laden martian air at a rate of 9.6 kilograms per day. The air would pass through a hydrocyclone dust filter to a compressor, then to a condenser that would liquify its carbon dioxide. Residual trace gases (nitrogen and argon) would be vented overboard, and the carbon dioxide would be pumped to the ISPP unit. There it would be combined with 0.24 kilograms of liquid hydrogen feedstock per day to produce carbon monoxide gas and water. 

The plant would vent the carbon monoxide overboard and pump the water to an electrolyzer, which would split it into gaseous hydrogen and oxygen. The oxygen, produced at a rate of 4.62 kilograms per day, would go to a liquifier, then to its final destination in the Earth Return Vehicle (ERV) oxidizer tank. 

The hydrogen, meanwhile, would go to the Sabatier reactor, where it would be joined with martian carbon dioxide in the presence of a nickel or ruthenium catalyst to yield water and methane gas at a rate of 1.15 kilograms per day. The methane would go to a liquifier, then to the ERV's twin fuel tanks. The water, meanwhile, would return to the electrolyzer. Over 1.4 years the Sabatier/RWGS ISPP system would produce 480 kilograms of methane and 1921 kilograms of oxygen for the ERV's single rocket engine. 

The students found that the carbon monoxide ISPP system had two advantages over the Sabatier/RWGS system: it would need no Earth-supplied feedstock and would be smaller, simpler, and less massive (just 300 kilograms). On the other hand, the carbon monoxide and oxygen it produced constituted a propellant combination less efficient than methane/oxygen. This meant that the carbon monoxide ISPP plant would need to manufacture 3440 kilograms of carbon monoxide and 1960 kilograms of oxygen to make up for the reduced performance.

Both ISPP systems would rely for electricity on a nuclear-fueled Dynamic Isotope Power System (DIPS) attached to the ERV. The DIPS would also power other MLV systems. The Sabatier/RWGS and carbon monoxide ISPP systems would draw from the DIPS 1.2 and 1.1 kilowatts of electricity, respectively. 

Landing its hydrogen feedstock and heavy ISPP unit on Mars would mean the Sabatier/RWGS Hyreus spacecraft would need a sturdier lander structure, a larger aerobrake, larger parachutes, and more landing propellant than the carbon monoxide Hyreus spacecraft. The carbon monoxide Hyreus would, on the other hand, need a larger ERV to enable it to hold enough carbon monoxide/oxygen propellants to reach Earth. The students calculated that the Sabatier/RWGS Hyreus would have a mass of 4495 kilograms at launch from Earth; the carbon monoxide Hyreus mass would total 4030 kilograms. 

Hyreus "raked sphere-cone" aerobrake. Image credit: University of Washington Department of Aeronautics and Astronautics.

At launch, the Hyreus spacecraft would comprise an aerobrake and a Mars Landing Vehicle (MLV) bearing the Satellite Observation and Communication at Mars (SOCM) orbiter, Special Planetary Observation Transport (SPOT) rover, and the ERV. Hyreus would leave Earth between 22 May and 20 June 2003 on a $400-million, 940-metric-ton Titan IV/Centaur rocket, the most powerful U.S. launcher expected to be available. 

Two solid-propellant rocket motors would boost the Titan IV off the launch pad, then the first stage would kick in a little more than two minutes after liftoff. During first-stage operation, the 7.5-meter-diameter launch shroud would split and fall away, exposing Hyreus atop the Centaur upper stage. After Titan IV second stage separation, the Centaur would fire to place itself and the Hyreus spacecraft into parking orbit 300 kilometers above Earth. 

The Hyreus aerobrake would include two folding "flaps" so that it could fit within the confines of the Titan IV launch shroud. After arrival in parking orbit, the flaps would hinge into place and lock to give the 11.3-meter-long aerobrake its full 9.4-meter width. The students chose a "raked sphere-cone" aerobrake over one with a biconic shape because it would be 20% lighter and have an open back that would offer more options for deploying the SOCM orbiter. 

A second Centaur burn would push Hyreus out of parking orbit toward Mars, then the Centaur would detach and fire its engine a final time to avoid striking and contaminating the planet. Depending on the exact Earth launch date, Earth-Mars transfer would last from 188 to 217 days. Hyreus would perform course corrections during the transfer using the MLV's four descent rocket motors. 

On 25 December 2003, Hyreus would enter the atmosphere of Mars traveling at 5.69 kilometers per second. Aerodynamic drag would slow the spacecraft so Mars's gravity could capture it into the desired near-polar orbit. Hyreus would descend to an altitude of 55 kilometers, then would skip out of the atmosphere and climb to apoapsis (the high point of its orbit) 2470 kilometers above Mars. There the MLV descent rockets would ignite briefly to lift the spacecraft's periapsis (the low point of its orbit) out of the atmosphere to an altitude of 250 kilometers. 

Mars would rotate beneath the orbiting Hyreus spacecraft, gradually positioning the selected landing site so that descent could begin. A second apoapsis burn would put Hyreus on course for its second aerobraking maneuver, which would place it into an orbit with a 580-kilometer-high apoapsis and a periapsis beneath the martian surface near the planned landing site. 

Following the second apoapsis burn, Hyreus would deploy the 282-kilogram SOCM orbiter. After deployment, SOCM would fire thrusters to raise its periapsis to 580 kilometers and circularize its orbit. The solar-powered SOCM would carry a Ground-Penetrating Radar to seek subsurface water and a wide-angle camera for monitoring weather at the MLV landing site. The orbiter would transmit its data to the MLV for relay to Earth. 

After the second apopasis burn, the Hyreus spacecraft would fall toward its landing site. The students proposed three candidate sites within 15° of the martian equator. Near-equatorial sites were preferred, they argued, because the planet's rotation would give the ERV an extra boost when the time came for it to lift off from the planet. All of the landing sites included smooth areas large enough to permit a safe off-target landing, as well as a variety of sampling sites within rover range (~20 kilometers) of the MLV. 

The UW students' prime Hyreus landing site was at 148.1° W, 13.8° S in Mangala Valles, a 350-kilometer-long outflow channel. In addition to the channel itself, Mangala included young volcanoes, ancient rocks, and young and old impact craters. The first backup Hyreus site was at 63° W, 16° N in Valles Marineris, a system of wide, deep canyons with horizontally layered walls. The second backup, at 45° W, 20° N, was in Chryse Planitia, an ancient flood plain near the site where Viking 1 set down on 20 July 1976. The students noted that a visit to the derelict Viking 1 lander "would offer the chance to get first hand analysis of the aeolian and other weather effects on the lander over the 20 years it has been there." 


Hyreus Mars Landing Vehicle (MLV) entry, descent, and landing. Image credit: University of Washington Department of Aeronautics and Astronautics.
Hyreus MLV in Mars landing configuration. The drawing is somewhat inaccurate; by the time the MLV rested on its deployed landing gear on the surface of Mars the SOCM orbiter and parachute canister would be absent. Image credit: University of Washington Department of Aeronautics and Astronautics.

The aerobrake would slow the Hyreus MLV to a speed of 220 meters per second 10 kilometers above Mars, then a tractor rocket would deploy the lander's first parachute. As it unfurled, explosive bolts would fire to jettison the aerobrake. 

Two more parachutes would deploy eight kilometers above Mars. The parachute cluster would slow the MLV to 40 meters per second 500 meters above the landing site. Explosive bolts would then fire to jettison the MLV's upper structural frame and the attached parachute cluster, exposing the ERV. Four throttleable landing rockets would ignite a moment later. 

The MLV would feel a maximum deceleration of 6.5 times Earth's gravity as its four footpads contacted Mars. At touchdown, the MLV would have a mass of 2650 kilograms.

Mars surface operations would last from 547 to 574 days. The Hyreus mission would focus on the three Mars surface activities. The first, ERV propellant loading, would begin immediately after landing. Controllers on Earth would check out and activate the Sabatier/RWGS ISPP plant. Valves would open to admit martian air into the hydrocyclone filter and release hydrogen feedstock. The electrolyzer would switch on after it filled with water, then the Sabatier reactor would activate after it received sufficient hydrogen from the electrolyzer. Unless a malfunction occurred, the ISPP plant would fill the ERV's propellant tanks without human intervention after it was switched on.

The second major Mars surface activity, sample acquisition, would be the primary task of the 185-kilogram SPOT rover. SPOT would comprise three sections one meter wide by 0.44 meters long joined by ball-and-socket joints. Each section would include one pair of 0.5-meter-diameter wire wheels. Hub-mounted electric motors would independently power the wheels on the front and middle sections, while the wheels on the rear ("trailer") section would be passive rollers.

Hyreus Special Planetary Observation Transport (SPOT) rover. Image credit: University of Washington Department of Aeronautics and Astronautics.

SPOT's front section would carry a pair of cameras for science and navigation and a Remote Manipulator Arm (RMA) with four interchangeable sampling tools. These would include a scoop/grabber ("scoobber"). The trailer section would include a large drill for subsurface sampling. After SPOT collected a sample, it would seal it within a Cylindrical Sample Collection Cell (CSCC) and place it into a sample storage bay in its front section. 

Upon return to the MLV, the SPOT RMA would hand the CSCCs one at a time to an RMA on the MLV for transfer to the ERV. The ERV would maintain the samples at martian ambient temperature to help keep them pristine. 

The third area of Mars surface activity would be MLV science. The MLV would carry 57.1 kilograms of science equipment, including three exobiology experiments, a seismometer (to be deployed by SPOT at least 200 meters from the MLV so that vibration from the ISPP system would not interfere with it), a camera, a weather station, a mass spectrometer, and an RMA with 18 interchangeable tools.

After 1.4 years of operation, the Sabatier/RWGS ISPP plant would run out of hydrogen and shut down. Controllers on Earth would then prepare the ERV for liftoff. The primary launch window for Mars departure would span from 25 June to 21 July 2005. In the event of difficulties (for example, if ISPP needed more time than expected), then launch from Mars would be postponed until the 19 June-22 August 2007 launch window opened. 

Explosive bolts would sever connections linking the ERV to the MLV, then the ERV's RL-10-derived engine would ignite to launch it into a 300-kilometer circular parking orbit about Mars. The ERV would orbit Mars until it reached the correct point in its orbit for Mars-Earth transfer orbit injection, then would ignite its engine again to put itself on course for Earth. During Mars-Earth transfer, it would position itself so that the Apollo-style bowl-shaped aerobrake on its Earth Return Capsule (ERC) would shade the samples from the Sun. 

Assuming an on-time launch from Mars, the Hyreus ERV would reach Earth's vicinity on 31 March 2006. If launch were delayed to 2007, Earth arrival would occur on 29 April 2008. The battery-powered ERC would separate from the ERV, then the latter would fire its engine a final time to bend its course away from Earth. This Contamination and Collision Avoidance Maneuver would, the students wrote, prevent Mars dust and possible microbes on the ERV's exterior from reaching the homeworld. 

Shielded by its aerobrake, the Hyreus ERC would enter Earth's upper atmosphere at a speed of 11.2 kilometers per second. Atmospheric drag would slow it to 7.8 kilometers per second so that Earth's gravity could capture it, then a brief rocket burn would circularize its orbit at 340 kilometers of altitude for recovery by a Space Shuttle orbiter. 

The students acknowledged that direct ERC entry into Earth's atmosphere followed by a parachute descent to the surface would cost less than orbital recovery by a Shuttle, but opted for the latter because it would permit astronauts to safely study the Mars samples outside of Earth's biosphere. If their preliminary analysis indicated that the Mars samples posed a hazard to life on Earth, the Shuttle crew could attach the ERC to a Payload Assist Module solid-propellant rocket motor and dispose of it in deep space. 

The UW students presented their Hyreus study in July 1993 at the 8th NASA/USRA ADP summer conference near NASA's Johnson Space Center (JSC) in Houston, Texas. Not coincidentally, NASA JSC and contractor engineers were also studying ISPP MSR mission designs at this time. They found the UW students' work sufficiently impressive to ask for a briefing at NASA JSC. NASA engineers subsequently cited the Hyreus report in NASA ISPP MSR documents. The God of Gainful Employment smiled upon the Hyreus students; several subsequently found jobs at NASA centers and with aerospace contractors. 

Sources

"Mars Rover Sample Return Mission Utilizing In Situ Production of the Return Propellants," AIAA 93-2242, A. P. Bruckner, L. Nill, H. Schubert, B. Thill, and R. Warwick; paper presented at the AIAA/SAE/ASME/ASEE 29th Joint Propulsion Conference and Exhibit in Monterey, California, 28-30 June 1993. 

Project Hyreus: Mars Sample Return Mission Utilizing In Situ Propellant Production Final Report, NASA/USRA Advanced Design Program, Department of Aeronautics and Astronautics, University of Washington, 31 July 1993.

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Human Exploration Using Real-Time Robotic Operations (HERRO) (2009-2011)

26 November 2011: Mars Science Laboratory rover Curiosity lifts off from Space Launch Complex 41 at Cape Canaveral Air Force Station, Florida, atop an Atlas V 541 medium-lift expendable rocket. The first launches of the HERRO mission in late 2030-early 2031 would see three Atlas V or equivalent rockets each launch a Truck rover bearing two Rockhound rovers to Mars. The three Truck/Rockhound combinations would land in widely separated 100-kilometer-diameter exploration regions. A six-person HERRO crew would arrive in Mars orbit in 2033 to begin a 549-day stay, during which they would remotely operate (that is, teleoperate) the rovers to explore the three regions. Image credit: NASA.

This (long) post outlines the most recent (2009) high-level NASA plan for landing humans on Mars. Called Design Reference Architecture (DRA) 5.0, it embraces long-held expectations regarding the role of astronauts in Mars exploration; the most significant of these is that when astronauts are dispatched to Mars for the first time they will land on its surface. 

The post then describes an alternative piloted Mars mission concept, called Human Exploration Using Real-Time Robotic Operations (HERRO), which could serve as an interim step designed to place on firmer ground planning for a follow-on piloted Mars landing mission. The HERRO concept could in fact provide data that would enable us to make an essential determination; that is, whether the traditional goal of humans on Mars remains a desirable one. 

In January 2007, NASA began efforts to update Design Reference Mission (DRM) 4.0, its plan for a piloted Mars landing mission. DRM 4.0 was based mostly on work performed in the 1998-2001 period. The updated DRM, the aforementioned DRA 5.0, was developed by the Mars Architecture Working Group (MAWG), which drew its more than 100 members from across NASA. The MAWG worked under the guidance of the Mars Architecture Steering Group (MASG). DRA 5.0 was formally published in July 2009. 

The term "Architecture" replaced the term "Mission" when referring to DRA 5.0 in part to signal a shift in NASA's plans for an evolutionary program of scientific space exploration. In addition to multiple piloted Mars landing missions, DRA 5.0 sought to include International Space Station (ISS) missions, piloted lunar exploration in the Constellation Program, and robotic Mars missions including Mars Sample Return (MSR) missions. 

DRA 5.0 scheduled its first piloted Mars landing for the late 2030s. Taking into account plans to cancel the Space Shuttle in 2010 that were hatched in the aftermath of the February 2003 Columbia accident, it replaced NASA's venerable semi-reusable winged crew and cargo spacecraft with the Ares I rocket for launching Orion crew vehicles and the Ares V heavy-lift rocket for launching cargo. The rockets, both under development in 2007, were to be derived from Shuttle hardware. Though named for the Greek god the Romans renamed Mars, the Ares rockets were primarily designed with Constellation Moon missions in mind. 

In documents used as sources for this post there occur discrepancies in spacecraft designs, weights, sizes, and other particulars. For example, a document will on one page display a spacecraft assembly sequence that requires three Ares V launches; on another page of the same document, the text will then describe an assembly sequence that requires four Ares Vs. 

These discrepancies are not explained, though they might reflect changing energy requirements for Earth-Mars and Mars-Earth minimum-energy transfers. Mars has a decidedly elliptical orbit about the Sun, so the energy required to visit and return from it changes markedly from one minimum-energy Earth-Mars transfer opportunity to the next; such opportunities occur every 26 months. To avoid confusion, in most cases in this post the DRA 5.0 and HERRO spacecraft appear in the forms that occur most often in their respective study documents.

The Shuttle-derived Ares I crew rocket (left) and Ares V cargo rocket as envisioned in 2009. Mars DRA 5.0 would require a minimum of three Ares I rockets and 21 Ares V rockets launched over a period of about eight years to explore three 100-kilometer-diameter exploration regions on Mars. In addition to the three medium-lift rockets described in the image at the top of this post, the HERRO mission would need one Ares I rocket and four Ares Vs to explore three 100-kilometer-diameter regions. Twenty-six months would separate the medium-lift rocket launches from the HERRO Ares I and Ares V launches; the Ares Vs would be launched and their payloads joined in Earth orbit over a period of about five days. Image credit: NASA.

A DRA 5.0 mission would begin with four Ares V launches from NASA Kennedy Space Center (KSC) in Florida. Two Ares Vs would each boost into low-Earth orbit a 28.8-meter-long, 96.6-ton Nuclear-Thermal Rocket (NTR) core stage. The NTR stage would contain liquid hydrogen actively cooled to prevent boiloff. Two more Ares Vs would each place into orbit an approximately 64-ton payload packaged inside a 30-meter-long Mars aeroshell with a mass of about 43 tons. In addition to enabling aerocapture and atmosphere entry at Mars, the bullet-shaped "triconic" aeroshells would serve as streamlined Earth launch shrouds. 

The stages and aeroshells would rendezvous and dock autonomously in low-Earth orbit to form an outwardly identical pair of cargo spacecraft. Neither spacecraft would carry a crew as it ignited its three 25,000-pound-thrust NTR engines to begin a minimum-energy Earth-Mars transfer lasting about 350 days.

Near Mars, the two cargo spacecraft would cast off their NTR core stages. One aeroshell, containing a 63.7-ton Mars Descent/Ascent Vehicle (MDAV) lander, would perform an aerocapture maneuver in the thin martian atmosphere to slow itself so that the planet's gravity could capture it using minimal propellants; then, after rising to apoapsis (orbit high point), it would reenter the atmosphere.

After any aeromaneuvers required to reach its preselected landing site, the MDAV would discard its two-part aeroshell, ignite descent rockets, and land in a level area near the center of a 100-kilometer-diameter exploration region. Orbital mechanics and aeromaneuvering limitations would mean that DRA 5.0 landers could not land at high-latitude and polar sites.

Following touchdown, the MDAV would deploy a nuclear power system on a robotic cart. Trailing cables, it would move a safe distance away from the landing site before power system activation. The MDAV would then begin splitting carbon dioxide drawn from the atmosphere to fill its empty oxidizer tanks with liquid oxygen. The first Mars mission crew would not leave Earth if the MDAV failed to fill its tanks.

The other aeroshell, containing a 64.3-ton Surface Habitat (SHAB) lander, would not land immediately. Instead, it would ignite rocket motors at apoapsis to raise its periapsis (orbit low point) out of the martian atmosphere and achieve a stable orbit. There it would remain awaiting arrival of the first six-person DRA 5.0 Mars landing crew in about 18 months.

The spacecraft at the top in the illustration above is the DRA 5.0 Mars Transfer Vehicle (MTV) for carrying the crew to and from Mars orbit; the spacecraft at the bottom could be either of the two cargo spacecraft. They are shown as they would appear in Earth orbit just before departure for Mars. Image credit: NASA.

The Mars Transfer Vehicle (MTV) bearing the first crew would leave Earth orbit 26 months after the first two cargo spacecraft. In the months prior to departure, three Ares V rockets would place into low-Earth orbit an NTR core stage, a "saddle-shaped" truss structure containing a drop tank, and a "supporting payload." They would rendezvous and dock autonomously. The completed MTV would measure 96.7 meters in length and have a mass of 356.4 tons. 

The supporting payload, located at the front of the newly assembled MTV, would include four solar arrays and an inflatable Transhab crew module with a docking port at its front. Within a short saddle truss mounted behind the Transhab the supporting payload would include a cylindrical contingency food container and a backup docking port. 

The food container would be called into play if the astronauts could not land on Mars; in that event, they would be required to remain on board the MTV in Mars orbit long enough for Earth and Mars to align to permit a minimum-energy Mars-Earth transfer, a period of about 500 days. Its contents might also be put to use if, after landing successfully on Mars, the crew had to evacuate the surface early.

The food container was not the only contingency hardware included in DRA 5.0. At the time NASA launched the first MTV, it would also launch four more Ares V rockets carrying two NTR core stages and two aeroshells containing MDAV and SHAB landers. The latter would be virtually identical to the first pair launched 26 months earlier. The NTR stages and aeroshell/lander combinations would autonomously dock in orbit to form two more cargo spacecraft. 

The second set of cargo spacecraft would be intended to serve the crew of the second Mars landing mission, which would leave Earth orbit in the second MTV 26 months after the first. They could, however, also serve as backups for the first Mars landing crew's MDAV and SHAB landers. They would reach Mars about 170 days after the first crew. If the first crew were required to use them, the second crew's departure from Earth would be delayed until a third set of cargo spacecraft could reach Mars.

With the MTV assembled in Earth orbit, the first Mars landing crew would lift off in an uprated Orion spacecraft atop an Ares I rocket. They would dock their nine-meter-long crew transport, developed for the Constellation lunar program, with the MTV front docking port on the inflated Transhab, then would enter the MTV and check out its systems. A standard Orion atop an Ares I and a repair crew would stand by at NASA KSC, ready to provide assistance if the MTV failed its orbital checkout. 

An alternate launch configuration would see the uprated long-lived Orion boosted to Earth orbit on an Ares V rocket as part of the supporting payload. In that case, the crew, launched separately in a standard Orion on an Ares I, would dock with the MTV's backup docking port. The standard Orion used for crew delivery would be cast off before the MTV left Earth orbit for Mars.

Assuming the MTV passed orbital checkout, its three NTR engines would ignite to perform a 57.8-minute Trans-Mars Injection (TMI) burn. The crew would then settle in for a weightless Earth-Mars transfer lasting about 180 days.

As Mars loomed large ahead, the MTV's NTR engines would fire for 16 minutes to slow it so the planet's gravity could capture it into orbit. Following the Mars Orbit Insertion (MOI) burn, the crew would mothball the MTV and transfer in the Orion spacecraft to the orbiting SHAB. After a successful SHAB checkout, the astronauts would command the Orion to undock, then would fire the SHAB's deorbit engines. Following reentry, aeromaneuvers, aeroshell separation, and descent, the SHAB bearing the crew would land near the MDAV. The Orion, meanwhile, would return to the MTV, dock, and shut itself down.

After six weightless months in interplanetary space, the crew would need to adapt to life in Mars surface gravity, which is a little more than a third as strong as Earth surface gravity. Drawing on advice from a 13-member Human Health and Performance Team, the MAWG/MASG opted for a one-month acclimatization period after landing, during which the astronauts would inflate the SHAB habitat and perform other "initial setup" activities, such as deploying crew rovers. The MAWG/MASG assumed that Mars gravity — possibly in combination with an exercise regimen — would be sufficient to maintain astronaut health. This would not, however, have been shown to be correct before the first Mars landing mission.

A Mars DRA 5.0 landing site. At left, in the middle distance, stands the MDAV beside an unpressurized crew rover. In the foreground at right, a small pressurized crew rover stirs up dust as it crawls over the surface. Behind it stands the SHAB lander, the six-person crew's home on Mars for about 500 days, with a second pressurized crew rover to its right and an unpressurized (possibly robotic) rover nearby. Image credit: NASA.

The overriding objective of the DRA 5.0 surface missions would be acquisition of scientific knowledge. This would take in goals which have historically been among the most significant justifications of space exploration. All would be related through the science of geology since rocks can serve as recording devices for those who can read them. Goal I would focus on whether life ever arose on Mars, while Goal II would emphasize Mars climate history and processes. The most overtly geological would be Goal III, which would focus on the evolution of the surface and interior of Mars. 

The MAWG/MASG examined three candidate Mars surface mission strategies. The Mobile Home strategy assumed the presence of large robust pressurized crew rovers towing trains of trailers bearing exploration equipment, including a drill rig for sampling the subsurface to a depth of hundreds of meters. The astronauts in the rovers would range for hundreds of kilometers over the martian surface. 

The less-ambitious Commuter strategy — the strategy the MAWG/MASG selected for DRA 5.0 Mars surface missions — would see reliance on a pair of "modest" pressurized rovers, two unpressurized rovers, and a trailer-mounted drill rig for sampling tens of meters beneath the martian surface. Prior to carrying out a series of monthly 100-kilometer traverses, each lasting up to two weeks, supply caches would be placed along prospective exploration traverse routes. How this would be accomplished was not explained in detail.

The Commuter pressurized rovers would be designed to carry two astronauts under normal operating conditions or four astronauts if a rover broke down far from the SHAB and its crew needed rescue. The "nimble" rovers would place astronauts in bulky Mars surface space suits within reach of diverse surface features of geologic interest, thus satisfying science requirements while limiting risk to Mars-walking astronauts.  

Both the Mobile Home and Commuter strategies would collect large quantities of samples which would be returned to the SHAB for analysis. About 250 kilograms of the most scientifically important samples would be retained for return to Earth; the remainder would be discarded. The MAWG/MASG expressed concern that 250 kilograms of samples might not fit readily into the MDAV ascent stage or the Orion capsule used to reenter Earth's atmosphere at the end of the mission.

The Mobile Home and Commuter strategies would face other operational challenges. Crews would not be able to rove far afield at times of heightened solar activity lest they suffer excessive radiation exposure. Even assuming advanced technology for generating and storing electricity, roving was not likely to occur every day during a traverse. The MAWG/MASG determined that, even if the pressurized rover moved as slowly as half a kilometer per hour, it might need to park every other day and deploy solar arrays with 400 square meters of area — which would extend for 40 meters in all directions from the rover — to make enough electricity to recharge its batteries after a day of driving. 

Possibly the most significant challenge from a scientific standpoint for DRA 5.0 astronauts would be observance of planetary protection protocols. The MAWG/MASG assumed that "Special Regions" on Mars where organisms might reside could be identified in advance of the piloted Mars landing missions based on data from robotic precursor missions. Such regions would only be explored using sterilized rovers remotely operated in real time (that is, teleoperated) by astronauts in the SHAB.

The third candidate surface exploration strategy, dubbed Telecommuter, received the least attention of the three described in the DRA 5.0 report. It would see astronauts in shirtsleeves in the SHAB rely mostly on teleoperated rovers to explore Mars; in-person astronaut exploration would be limited to places accessible from the SHAB on foot or using unpressurized rovers that might travel at most 20 kilometers during a traverse. 

The MAWG/MASG expected that deep drilling and extensive surface sampling would be extremely difficult within the confines of the Telecommuter strategy. On the plus side, the sterilized teleoperated rovers could venture with impunity anywhere on the surface of Mars without violating planetary protection rules.

Regardless of which surface strategy was used, after about 500 days on Mars the first DRA 5.0 astronauts would enter the MDAV ascent stage and ignite its engines to begin ascent to the MTV waiting in Mars orbit. The ascent engines would use the oxygen the MDAV collected from the martian atmosphere to burn methane it had brought from Earth. After docking and transfer to the MTV, the astronauts would cast off the MDAV ascent stage. They would also discard the contingency food canister after filling it with waste. 

The crew would then fire the NTR core stage engines for 10.7 minutes to perform Trans-Earth Injection (TEI). Following a six-month Mars-Earth transfer, the astronauts would board the uprated Orion, undock, and perform a burn that would bend its course to intersect Earth's atmosphere. They would then cast off the Orion service module. As the crew reentered the atmosphere and descended to a landing, the vacant MTV would swing past Earth and enter a graveyard orbit about the Sun.

Before the first DRA 5.0 crew returned to Earth, the second crew would set out for Mars. They would land in a new 100-kilometer-diameter exploration region in the equatorial or mid-latitudes. The third crew would depart Earth to visit a third such region before the second crew left Mars. The third crew's return to Earth, about eight years after the first DRA 5.0 mission began, would complete the initial scientific exploration of Mars by astronauts. 

The MAWG/MASG anticipated that the first three DRA 5.0 missions would together serve as a prudent stepping stone to Mars missions four through 10. These follow-on missions would, the DRA 5.0 report explained, see a "sustained human presence" on Mars, but they were otherwise undefined.

While the MAWG/MASG put the finishing touches on DRA 5.0, engineers and scientists at NASA Glenn Research Center (GRC), Case Western Reserve University, and Carnegie Mellon University prepared a preliminary plan for a piloted Mars mission that would carry the Telecommuter strategy to its logical conclusion. HERRO — which, it will be recalled, stands for Human Exploration Using Real-Time Robotic Operations — would see six astronauts on board a Crew Telerobotic Control Vehicle (CTCV) in elliptical Mars orbit explore three widely separated 100-kilometer-diameter regions on Mars using teleoperated Truck and Rockhound rovers. The CTCV would operate much as does an ocean research ship on Earth and the Trucks and Rockhounds would explore Mars's surface much as Remotely Operated Vehicles deployed from a research ship explore the ocean depths.

HERRO — it might be called "DRA 5.0 Telecommuter on steroids" — was intended as a prudent step toward Mars DRA 5.0, not a substitute. The HERRO study team argued that NASA needed to add interim steps to gain experience and knowledge ahead of piloted Mars landings. They noted, for example, that in 2009 no data existed on whether humans could remain healthy in Mars gravity for 500 days (this remains true at this writing). Assuming that they could without supporting data could make investment in piloted Mars landers, crew rovers, and surface suits a costly gamble.

Several of the NASA GRC engineers who participated in the MAWG also took part in the three-month HERRO study, which was performed under the auspices NASA's 2009 Innovative Partnerships Program. In fact, their participation in the DRA 5.0 and HERRO studies overlapped in time. They were thus well positioned to integrate HERRO and DRA 5.0. 

As described in the picture caption at the top of this post, a HERRO Mars mission would begin with launch of three medium-lift rockets. Each would carry an aeroshell containing a Truck rover bearing two Rockhound rovers. The three launches might occur in late 2030.

The HERRO team sought to employ technology under development for NASA robotic Mars missions in their mission design. The Truck/Rockhound combinations would each ride to Mars in an aeroshell similar to that designed for Mars Science Laboratory Curiosity, which at the time of the HERRO study in 2009 was scheduled to launch to Mars in 2011. They would land using skycrane systems similar to the one expected to gently lower Curiosity to Mars's surface in 2012. 

Two Truck/Rockhound combinations would land on opposite sides of Mars at sites near the center of their assigned exploration regions. The third would land in a  south polar region. 

Truck rover with Rockhound rovers packed within an aeroshell derived from that of the Mars Science Laboratory Curiosity rover. The skycrane landing system, which would ride atop the Truck, is not shown. Image credit: NASA.

If the three Truck/Rockhound combinations left Earth in 2030, the CTCV bearing the crew would depart for Mars in early 2033. The HERRO study team described a CTCV resembling the DRA 5.0 MTV that would require four Ares V launches. The first would place into low-Earth orbit a 24.8-meter-long, 51.6-ton supporting payload outwardly similar to that of the DRA 5.0 MTV apart from the addition of two large dish antennas for transmitting large quantities of data to Earth. The antennas would need to be deployed before the Transhab could be inflated. 

The second Ares V would place in orbit a 26.1-meter-long, 135.8-ton saddle truss and drop tank. Again, it would differ from its DRA 5.0 counterpart mainly by the presence of two antennas, this time for transmitting to and receiving from the Trucks and Rockhounds on Mars large quantities of real-time data. 

The third Ares V rocket would launch into Earth orbit a 26.6-meter-long, 136-ton in-line propellant tank and the fourth a 29.9-meter-long, 132-ton NTR core stage outwardly identical to the one on the DRA 5.0 MTV. Supporting payload, saddle truss and drop tank, in-line tank, and NTR core stage would then rendezvous and dock autonomously in low-Earth orbit to form the 106.9-meter-long, 455.4-ton CTCV.

CTCV supporting payload. The deflated Transhab with docking port and large antennas is at right; the small saddle truss with food canister, docking port, and twin solar arrays (shown here folded) is at left. Image credit: NASA.
Saddle truss with drop tank. The twin dish antennas for transmitting to and from the Truck and Rockhound rovers on Mars are stowed on the disc-shaped docking structure at left. Image credit: NASA.
CTCV in-line propellant tank. Image credit: NASA.
Nuclear-Thermal Rocket core stage with three engines. The CTCV could complete its mission with only two functioning engines. Image credit: NASA.
Fully assembled HERRO CTCV with deployed antennas, inflated Transhab, and docked long-lived Orion (right). Image credit: NASA.

The HERRO crew, which would comprise four geologists and two pilots, would lift off from Earth atop an Ares I rocket in an uprated, long-lived Orion spacecraft and rendezvous and dock with the CTCV front docking port on the Transhab. After CTCV checkout they would ignite the three NTR core stage engines to begin the TMI maneuver; unlike DRA 5.0, the HERRO TMI burn would be split into two parts to reduce propellant consumption. TMI Burn 1, which would place the CTCV into an elliptical orbit about Earth, would expend all of the liquid hydrogen in the saddle truss drop tank; the tank would be discarded before TMI Burn 2, which would occur at next perigee. 

Shortly after TMI Burn 2, the crew would set the CTCV spinning end-over-end at a rate of 2.7 rotations per minute. This would produce acceleration in the Transhab equal to the pull of gravity on Mars's surface, thus providing an opportunity to confirm that Mars gravity would be sufficient to keep future landing crews healthy. The astronauts would then settle in for a six-month Earth-Mars transfer. 

The HERRO team proposed that the crew sleep and work in the Transhab's central core, which would be surrounded by tanks holding about 14 tons of water. By spending 16 hours of every day in the water-lined Transhab core, the astronauts would greatly reduce their exposure to Galactic Cosmic Radiation. 

The crew would despin the CTCV as they approached Mars, then would ignite the NTR core stage engines to perform MOI. The planet's gravity would capture the spacecraft into an elliptical, steeply inclined orbit with a period of 12.3 hours, or half a 24.6-hour martian day (known as a sol). The CTCV would reach apoapsis over the sunlit hemisphere of Mars twice per sol, with periapsis occurring twice per sol low over the nightside equator. The crew would then spin up the CTCV to restore Mars-level artificial gravity in the Transhab. 

The CTCV in artificial-gravity configuration. Red arrows indicate the spacecraft's end-over-end rotation. During flight to and from Mars and in Mars orbit the twin solar arrays and large antennas would respectively point continuously toward Sun and Earth. The small antennas would point toward the Truck and Rockhound rovers on Mars. Image credit: NASA.

As might be expected, the CTCV's orbital parameters were chosen to place it in line-of-sight radio contact at apoapsis with the Trucks and Rockhounds at their landing sites on opposite sides of Mars. This would enable two two-person geologist teams to take turns teleoperating the Trucks and Rockhounds in two work shifts, each lasting up to eight hours per sol, yielding a total teleoperations time per sol of up to 16 hours. 

Over the course of the 549-day CTCV stay in Mars orbit, lighting conditions at the Truck/Rockhound sites during the teleoperations shifts would change. At the non-polar sites shifts would start in early morning during the first third of the mission, around noon during the middle third, and in early evening during the final third. The south polar site would be in radio contact for two periods per sol totaling up to 10.6 hours during the first two-thirds of the mission.

The exploration regions centered on the Truck/Rockhound landing sites would each contain several one-kilometer-diameter areas of interest up to 20 kilometers apart. Within these the teleoperators would seek to identify 10-meter-diameter science sites. The rovers would spend up to two weeks within an area of interest and about a sol at each science site. 

Truck rover bearing two Rockhound rovers. The image shows the articulated control arms attached to each wheel, twin stowed Rockhounds, the 10-sided solar array, and twin boom-mounted high-gain antennas. Image credit: NASA.
Rockhound rover. The light blue boxes at the corners of its two-part body are navigation cameras and laser terrain mappers. Note the six "whegs," the mid-body hinge, hands with fingers and thumbs, and a very normal-appearing geology hammer. Image credit: NASA.

The HERRO team described their teleoperated Trucks and Rockhounds in considerable detail. The 800-kilogram Trucks, which could travel at up to 3.6 kilometers per hour, would each have four large independently motorized wheels mounted on "articulated control arms." The arms would permit the Truck to lower its two-meter-square chassis to the surface. This would enable two Rockhounds to disembark for exploration or board for long-range transport or battery charging. 

A box on the Truck located behind the Rockhound charging stations would support two low-gain antennas for relaying transmissions to and from the Rockhounds, a mast bearing a vertical four-meter-diameter solar array, and two boom-mounted high-gain antennas for relaying transmissions to and from the CTCV. In addition to batteries, the box would house a drill for sampling tens of meters below the surface and a lab for analyzing samples the drill and Rockhounds collected. 

The 145-kilogram Rockhound rover would resemble a mythical centaur. At the front of its horizontal aluminum-frame body would be mounted a vertical robotic torso with shoulders, two arms with elbows and hands, and three cameras in place of a head. It would stand a little more than a meter tall on a level surface. 

A motorized "hinge" would divide the rectangular Rockhound body into two 0.5-meter-square parts and a single motor drawing power from batteries would drive six wheel-legs ("whegs") arrayed along its sides. A low-gain antenna for transmissions to and from the Truck, navigation cameras, a small "arsenal" of science instruments, and a rack of tools including a geology hammer would round out its description.

The HERRO team explained that the Rockhound mobility system was based on a "biologically inspired" design developed, built, and tested by Case Western Reserve University. Its movement scheme was modeled on that of the lowly cockroach, which can flex its body and alter its six-legged gait to climb over obstacles taller than it is. 

The agile little rover would move at a top speed of about 10 centimeters per second and would be able to climb and descend 45° slopes of loose rocky material. By raising the front half of its body and tilting forward its humanoid torso, it would be able to "rear up" against rock walls to examine and sample features more than two meters above the ground. It would turn its torso 180° to drive backwards and to reach the tools stored on its aft section. 

The Rockhound would employ four teleoperational modes. Mode 1, called Traverse to New Location, would see it leave the Truck and move over easy terrain for about an hour at a time. No science would be performed and the rover and its teleoperator on board the CTCV would rely on low-resolution navigation cameras and laser terrain mappers to avoid obstacles. Mode 2, Visual Imagery, would see the Rockhound park in one location while its teleoperator put to use hand tools and microscopic, multispectral, high-resolution visual, and other imaging and sensing systems. 

Quiescent/Operator Off Duty, the third teleoperational mode, would see the Rockhound resting in its charging station on board the parked Truck. Charging the Rockhound's batteries would require about 16 hours using an induction charging system that would need no physical contact. The HERRO study team expected that induction might avoid problems created by ever-present airborne Mars dust that could plague a system reliant on a plug and socket. Mode 4, Rockhound Scout Mode, would see the rover move over the surface under teleoperator control for up to eight hours at a time in search of scientifically interesting sites. 

In some HERRO documents, the study team suggested that the HERRO mission might include an MSR option. This could take either of two forms: an independent robotic MSR mission or an MSR mission that would rely on the Truck/Rockhound rovers for sample collection. 

In the second instance, three MSR lander/ascent vehicles would launch to Mars at the same time as the Truck/Rockhounds. This would add three medium-lift rocket launches to the three slated to occur 26 months ahead of the CTCV launch in the baseline HERRO mission. In both cases, the MSR vehicles would land in the same three regions as the Truck/Rockhound combinations.

In both HERRO MSR scenarios, an independently launched teleoperated sample retrieval vehicle, based possibly on the Orion service module, would collect the sample canisters launched to Mars orbit by the three MSR ascent vehicles and deliver them to the CTCV. Sample retrieval in Mars orbit would, the HERRO team estimated, require retrieval vehicle maneuvers spanning about four months.

As their mission in Mars orbit reached its end, the HERRO mission crew would stop the CTCV's spin, recover the MSR sample canisters, discard the waste-filled food canister, and ignite the three NTR engines to perform TEI. As Mars shrank behind them, they would spin up the CTCV again. About six months later, they would stop the CTCV's spin for the final time, take their places in the uprated Orion, and undock. A short Orion burn would place them on course for Earth-atmosphere reentry. 

Meanwhile, the CTCV would swing past Earth. The HERRO study team suggested that it might adjust its course so that it would travel to the Earth-Moon L1 point, where it would park pending possible refurbishment and reuse.

The DRA 5.0 study was completed in 2009 in part to support the activities of the Review of U.S. Human Spaceflight Plans Committee chaired by former aerospace executive Norman Augustine. The Augustine Committee was appointed to advise the new Administration of President Barack Obama concerning NASA's path forward in the 21st century. 

The Augustine Committee requested a briefing on the HERRO study. The briefing helped to inform an approach to NASA's future that the Augustine Committee dubbed the "Flexible Path."
 
As stated at the beginning of this post, the MAWG/MASG envisioned that DRA 5.0 missions would be reached through interim missions — specifically, astronaut stays on board ISS and robotic Mars and piloted Moon missions. The Flexible Path called for new interim missions to be added to this sequence. Although HERRO is not referred to by name in the Augustine Committee's October 2009 final report, among the missions on the Flexible Path was a Mars orbital mission including "joint robotic/human exploration and surface operations [with] sample return."

Adding interim steps to existing U.S. space programs is nothing new. The most obvious example is the addition of Gemini to the NASA piloted program in 1962, a step made necessary when Apollo, which had been conceived initially as mainly an Earth-orbital program, became the U.S. lunar program. Gemini provided opportunities for astronauts, flight controllers, and others to develop new spaceflight skills and for life scientists to determine whether humans could survive in space long enough to reach and return from the Moon.

View of the Gemini VII spacecraft from the cockpit of Gemini VI-A in Earth orbit, 15 December 1965. Gemini VII and Gemini VI-A performed the first close rendezvous between two piloted spacecraft. Image credit: NASA.
Thumbs up: Robonaut II, a humanoid robotic torso developed by NASA Johnson Space Center (JSC) and General Motors, participates in a 2011 field exercise among the volcanic landscapes near Flagstaff, Arizona. Robonaut II's predecessor, the NASA JSC/Defense Advanced Research Projects Agency Robonaut robotic torso, was the inspiration for the HERRO Rockhound torso. Robonaut II is shown here attached to the front of a small remotely operated rover. Image credit: NASA.

Spaceflight planners suggested interim steps toward humans on Mars long before HERRO. In the 1960s, for example, they proposed piloted Mars and Venus flyby and orbiter missions. In 1993, in the waning days of the abortive Space Exploration Initiative, NASA GRC's Geoffrey Landis, a HERRO study participant, proposed a scenario he dubbed "Footsteps to Mars." These and other proposed interim missions leading toward humans on Mars can be explored by following the links in the "More Information" section below.

In the years since the 2009 DRA 5.0 and HERRO studies, NASA robotic Mars missions have displayed both the capabilities and limitations of robotic landers and rovers on Mars that are remotely operated from distant Earth. The Curiosity lander, which reached Mars on 6 August 2012, proved the capabilities of its aeroshell and skycrane systems. As of July 2022, after nearly a decade on Mars, the Curiosity rover had traversed only 28.15 kilometers. 

Lunar and planetary surface teleoperations remain of interest both inside and outside NASA. In the years since the HERRO study, astronauts on board the ISS in Earth orbit have teleoperated robots on Earth. The lunar-orbiting Gateway station, now under development in NASA's Artemis lunar program, is intended to support teleoperation of exploring robots on the Moon. 

Sources

Human Exploration of Mars Design Reference Architecture 5.0, NASA-SP-2009-556, Mars Architecture Steering Group, B. Drake, editor, July 2009.

COMPASS Final Report: Human Exploration Using Real-Time Robotic Operations (HERRO) — Rockhound Design, CD-2009-34, NASA Glenn Research Center/Case Western Reserve University/Carnegie Mellon University, August 2009.

COMPASS Final Report: Human Exploration Using Real-Time Robotic Operations (HERRO) — Truck Design, CD-2009-35, NASA Glenn Research Center/Case Western Reserve University/Carnegie Mellon University, August 2009.

COMPASS Final Report: Human Exploration Using Real-Time Robotic Operations (HERRO) — Crew Telerobotic Control Vehicle (CTCV) Design, CD-2009-36, NASA Glenn Research Center/Case Western Reserve University, September 2009.

Seeking a Human Spaceflight Program Worthy of a Great Nation, Review of U.S. Human Spaceflight Plans Committee, October 2009.

"HERRO (Human Exploration Using Real-Time Robotic Operations): A Robotically Intensive Strategy for Human Exploration," G. Schmidt and Steve Oleson, NASA Glenn Research Center, presentation materials, 28 October 2009.

"HERRO: A Science-Oriented Strategy for Crewed Missions Beyond LEO," AIAA-2010-69, G. Schmidt, G. Landis, S. Oleson, S. Borowski, and M. Krasowski; paper presented at the 48th AIAA Aerospace Sciences Meeting in Orlando, Florida, 4-7 January 2010.

"Human Exploration of Mars Design Reference Architecture 5.0," JSC-CN-19120, B. Drake, S. Hoffman, and D. Beaty; paper presented at the IEEE Aerospace Conference in Big Sky, Montana, 6-13 March 2010. 

"Human Exploration Using Real-Time Robotic Operations (HERRO) — Crew Control Vehicle (CTCV) Design," AIAA-2010-6817, S. Oleson, M. McGuire, L. Burke, D. Chato, J. Fincannon, G. Landis, C. Sandifer, J. Warner, G. Williams, T. Colozza, J. Fittje, M. Martini, T. Packard, D. McCurdy, and J. Gyekenyesi; paper presented at the 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exposition in Nashville, Tennessee, 25-28 July 2010.

"HERRO Missions to Mars and Venus using Telerobotic Surface Exploration from Orbit," G. Schmidt, G. Landis, and S. Oleson; paper presented at the AIAA Space 2011 Conference & Exposition in Long Beach, California, 26-29 September 2011.

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