Blueprint for 1970s planetary exploration (1968)

In August 1967, Congress refused to support NASA's plans for the 1970s. Citing fiscal restraint, it rejected piloted Mars/Venus flyby missions in 1975 and 1977 and canceled the Voyager Mars/Venus program, NASA's only robotic program planned for the decade. The Apollo Applications Program, which had been tapped as the agency's main 1970s piloted program, suffered a cut of half a billion dollars.

This assault on NASA's future was partly the result of the deadly Apollo 1 fire (January 1967), which undermined confidence in the U.S. civilian space agency. A growing Federal budget deficit fueled by the escalating war in Indochina also played a role.

NASA's detractors argued that piloted flybys, Voyager, and AAP were stealthy steps toward an early commitment to costly piloted Mars landing missions. Others complained that NASA's program lacked "balance." This criticism meant different things coming from different people. For some, it meant that NASA gave to astronauts tasks that robots could perform more cheaply and with less risk; for others, it meant that NASA placed too much emphasis on the moon and Mars and not enough on the rest of the Solar System.

NASA officials met with Congressional leaders in late September 1967 to try to negotiate a replacement for Voyager. NASA Administrator James Webb and others reminded them that, with Voyager gone, the U.S. would have no robotic planetary program after the Mariner 1969 Mars flyby missions, leaving to the Soviet Union the prestige benefits of Solar System exploration. Congress relented partially, agreeing to initiate funding in Fiscal Year 1969 for a pair of Mariner 1971 Mars orbiters and a pair of Mariner-based Mars orbiter/lander missions in 1973.

This concession, combined with the successful first unmanned flight of the Apollo Saturn V rocket (Apollo 4) in early November 1967, encouraged some within NASA to look for ways of accommodating the detractors while continuing planning for piloted Mars missions. In late November-early December 1967, NASA's Office of Manned Space Flight asked J. Downs and W. Thompson of Bellcomm, NASA's Apollo planning contractor, to develop a plan for a feasible "balanced manned and unmanned planetary program through 1980." Their blueprint, completed in late February 1968, included Mariner-based robotic Mars and Venus spacecraft as precursors to piloted Mars and Venus flybys and robotic pure science missions to Mercury, Jupiter, Saturn, and beyond.

Downs and Thompson kicked off their program with a Mariner Venus flyby in 1970. The spacecraft, which would be built from "spare parts" left over from Mariner Mars 1969, might use Venus's gravity to speed it toward a flyby of the planet Mercury. The next year, NASA would launch the Mariner Mars orbiters it had discussed with Congress. The Bellcomm engineers called for them to be launched on Titan III-C rockets (bottom image below) so that they could each carry to Mars a 350-pound rough-landing probe bearing 13 pounds of instrumentation. The probes would begin the in-situ search for life on Mars.

Next up, in 1972, a Titan III-C would launch a Venus orbiter with an atmosphere probe. In keeping with NASA's agreement with Congress, two more Titan III-C rockets would launch one Mars orbiter with probe each in 1973. Downs and Thompson expected that the 1971 landing probe would have found life on Mars, so the instruments on the twin 1973 probes could focus on learning about that life. In addition to Mars, the orbiters would image Phobos and Deimos, the two small martian moons.

The year 1973 would also see a Mariner spacecraft fly past Venus and release a 600-pound probe designed to survive landing on the cloudy planet's harsh surface. With help from Venus's gravity, the Mariner would then fly past Mercury. Downs and Thompson noted that placing a spacecraft into orbit around Mercury would demand a great deal of energy (hence propellant), and advised that the decision about whether to fly a Mercury orbiter should be postponed until after the 1973 flyby. They also noted that the next Venus-Mercury flyby opportunity would not occur until 1982.

In 1974, NASA would expand its horizons to the stars by launching a 600-pound "Galactic Jupiter Probe" on an Atlas rocket with a Centaur upper stage. As envisioned by engineers at NASA's Goddard Space Flight Center in Maryland, the Galactic Jupiter probe would explore Jupiter and use a gravity assist from that giant planet to gain speed and bend its course. The spacecraft would climb above the plane of the ecliptic to explore interplanetary particles and fields and, ultimately, escape the Solar System entirely to wander derelict among the stars.

In the Downs-Thompson blueprint, 1975 was a busy year. A Mars orbiter more sophisticated than any launched before would dispatch a heavy probe to a site scientists had identified as exobiologically interesting based on Mariner Mars 1971 and 1973 data. A second Galactic Jupiter Probe would begin its journey to Jupiter and beyond, and NASA would launch two Venus orbiters, each bearing two rough-landing probes.

The year 1976 would see the first of four NASA missions to non-planetary Solar System bodies: an Atlas-Centaur would launch a Mariner past short-period Comet d'Arrest. In 1978, a Mariner would fly past the asteroid Icarus, and asteroid Eros would receive a Mariner in 1979. Finally, a Mariner launched on a Titan III-C/Centaur would fly past Comet Encke in 1980.

In 1977, NASA would launch a Venus orbiter with a high-resolution cloud-piercing radar and multiple atmosphere probes. The new-design Venus orbiter used in 1975 and 1977 would need a launch vehicle more powerful than the Titan III-C - possibly a reduced-capability Saturn V, Downs and Thompson wrote. The 1975 and 1977 Mars missions would also need this powerful rocket.

The 1977 Mars flight would serve as a dedicated precursor for the piloted Mars/Venus flyby mission scheduled for launch in 1978. Its landing probe would, for example, provide data on the topography of a landing site chosen for one of the piloted flyby spacecraft's large Mars Surface Sample Return (MSSR) probes.

The year 1977 would also see the first "Grand Tour" spacecraft leave Earth on a Titan III-C with a Centaur upper stage. The new-design 1000-pound spacecraft would fly past Jupiter and receive a gravity-assist "kick" to Saturn. The gravity-assist it would receive while exploring Saturn would speed it onward to mysterious Uranus, where a third gravity-assist would send it on to Neptune. The spacecraft would fly past the Solar System's most distant gas giant planet nine years after departing Earth. A second Grand Tour spacecraft would leave Earth in 1978.

Also in 1978, NASA would launch the first of two piloted Mars/Venus flyby missions. Downs and Thompson wrote that the two piloted flyby missions would serve as precursors for a piloted Mars landing mission in 1984. The 1978 mission would fly past Venus in 1979, where the crew would release weather balloons and surface impactors. Later in the year, it would fly past Mars, releasing a small swarm of MSSR probes. These would land, collect Mars samples, and return them to the astronauts on the flyby spacecraft for immediate analysis. In 1981, the astronauts would fly past Venus a second time and return to Earth. The second piloted Venus/Mars/Venus flyby mission would depart Earth in 1981 and return home in 1983.

Minimum-energy launch opportunities are what they are, so it is not too surprising that NASA carried out missions resembling those in the Downs-Thompson blueprint. The 1971 Mariner Mars orbiters, for example, corresponded to the Mariner 9 mission, though the latter included no landing probe. (Mariner 8, the first of the intended pair of 1971 Mars orbiters, crashed in the Atlantic after its Atlas-Centaur launch vehicle failed.) The 1973 Mariner-based Mars orbiters and landers were named Viking, then funding cuts pushed their launch to 1975. NASA missed the 1970 Venus-Mercury opportunity, but launched Mariner 10 in 1973 (middle image above). It flew past Venus in February 1974, then past Mercury in March 1974, September 1974, and March 1975.

NASA launched its first Galactic Jupiter Probe two years early; Pioneer 10 left Earth in March 1972 and flew past Jupiter in December 1973 (bottom image above). Its twin, Pioneer 11, left Earth in April 1973, flew past Jupiter in December 1974, and flew past Saturn in September 1979. NASA cancelled the Grand Tour in 1972, but launched the Mariner-based Voyager 1 and 2 spacecraft in September 1977 and August 1977, respectively. Voyager 1 flew past Jupiter in March 1979 and Saturn in November 1979 (top image above). Voyager 2 flew past Jupiter in July 1979, Saturn in August 1981, Uranus in January 1986, and Neptune in August 1989.

NASA launched no piloted flyby in 1978; in fact, when that launch opportunity came and went no American astronauts had reached space since July 1975 (and none would again until April 1981). Instead, it launched the first U.S. Venus orbiter, Pioneer Venus 1 (May 1978), and Pioneer Venus 2 (August 1978), which carried a cluster of four Venus atmosphere entry probes (top image below). Budget cuts and Space Shuttle problems meant that Pioneer Venus 2 was the last U.S. planetary probe to leave Earth for nearly 11 years.

A Feasible Planetary Exploration Program Through 1980 - Case 710, J. P. Downs and W. B. Thompson, Bellcomm, February 29, 1968.

Mars Sample Return quarantine & recovery (1985)

Beginning in late 1983, a team of engineers and scientists from NASA's Johnson Space Center (JSC), the Jet Propulsion Laboratory, and Science Applications Incorporated jointly defined a Mars Sample Return (MSR) spacecraft and mission plan (top link below). Among their proposed follow-on study objectives for Fiscal Year 1985 was to better define Mars sample quarantine protocols and associated risks. In addition, the team recognized the need to rapidly recover the Mars sample after its arrival at Earth.

JSC's Solar System Exploration Division contracted with Houston-based Eagle Engineering to examine these issues and provide "rough" cost estimates. In its study, performed between May and September 1985, Eagle explored 10 options for retrieving a Mars sample following its return to Earth.

Eagle found that Direct Entry into Earth's atmosphere, with an estimated price tag of from $5.2 million to $9.8 million, would be the simplest and cheapest Mars sample recovery option, but would also carry the greatest risk (one chance in 600,000) of contaminating the terrestrial environment with potentially "malignant" martian microbes. Eagle acknowledged, however, that its contamination risk estimates (which, it explained, were based on "limited data") were arbitrary.

In Direct Entry, a reentry capsule carrying the sealed Mars sample canister would intersect Earth's atmosphere over the Pacific Ocean near Hawaii traveling at upwards of 11 kilometers per second. An ablative coating would protect the capsule from reentry heating. Eagle noted that a shallow atmosphere-entry angle would subject the sample canister to a long heat pulse, a low deceleration load, and imprecise landing site targeting (and, therefore, possible delayed recovery), while a steep angle would yield a short heat pulse, a high deceleration load, and more precise targeting.

After slowing to subsonic speed, the capsule would deploy a 5.5-meter-diameter parachute. A Defense Department transport aircraft - probably a C-130 - would snatch the descending capsule by the parachute in midair and winch it into its cargo hold, then would fly directly to the Centers for Disease Control (CDC) in Atlanta, Georgia, or to a newly constructed Planetary Sample Receiving Laboratory (PSRL) in a remote location. Eagle did not include the $14-million cost of the new lab in its cost estimates. The company assumed that the C-130 would be one of three similarly configured air-snatch planes in the recovery area, each of which would carry 11 aircrew on board.

Eagle's second option was Shuttle Recovery, which, the company estimated, would have only one chance in 100 million of releasing potentially harmful martian microbes into the terrestrial environment. A delta-winged Space Shuttle Orbiter would be prepositioned in Earth orbit in anticipation of the arrival of an Earth Return Vehicle (ERV) bearing the sample canister. The ERV would skim through Earth's upper atmosphere to use drag to slow down (that is, it would aerobrake) and enter an elliptical Earth orbit. It would then discard its protective aeroshell and fire a rocket motor at the apoapsis (high point) of its orbit to raise the periapsis (low point) of its orbit above the atmosphere and circularize its path around the Earth.

Eagle noted that the Shuttle Orbiter was incapable of climbing higher than about 500 kilometers above the Earth (in fact, it reached about 610 kilometers during STS-31, the Hubble Space Telescope deployment mission, in April 1990). If the ERV's orbit following the apoapsis burn was above the Shuttle altitude limit, then the Orbiter would need to deploy a teleoperated Orbital Maneuvering Vehicle (OMV). The OMV would match orbits with the ERV, dock with it, lower its orbit, and then separate.

After the Shuttle Orbiter rendezvoused with the ERV, the astronauts would capture it using their spacecraft's robot arm and place it inside a seven-ton biological containment/sample cooling container in the Orbiter's payload bay for return to Earth. The container would, Eagle wrote, be designed to survive intact a Shuttle accident during reentry and landing. A slightly cheaper but "significantly" more risk-fraught alternative would be for a spacewalking astronaut to extract the sample canister from the ERV and carry it into the two-deck Orbiter crew cabin for return to Earth.

Eagle placed the cost of the Shuttle return option at between $150 million and $173 million, of which $120 million would, in theory, pay for the Space Shuttle flight (in practice, Space Shuttle flights were considerable more expensive than this). The company also examined recovery of the sample from a high elliptical Earth orbit (the 1984 JSC/JPL/SAI design study proposed that the ERV capture into such an orbit). Eagle found that the Orbital Transfer Vehicle (OTV) required to reach such an orbit would boost their estimated cost by from $50 million to $100 million.

Eagle's third recovery option was Recovery to Space Station Structure. The company estimated that for this and all subsequent recovery options, the likelihood that harmful martian microbes could escape into Earth's environment would be less than one chance in 100 million. A Shuttle Orbiter would deliver to NASA's Space Station in 500-kilometer-high Earth orbit a biological containment/sample cooling container and three tons of propellants for a Station-based OMV. This would, the company noted, make use of about half the Shuttle's payload capacity, leaving the other half for additional Station-bound cargo unrelated to the sample recovery operation.

Spacewalking astronauts would attach the containment/cooling container to the Station's exterior. Some time after that, the ERV would aerobrake and maneuver into a circular orbit. The Station crew would then dispatch an OMV to recover it and bring it to the Station.

The Station's robot arm would transfer the ERV from the OMV to the containment/cooling container. A Shuttle mission to the Station would then collect the container for return to Earth, along with about half a payload bay of Earth-bound cargo unrelated to the sample recovery operation. Eagle placed the cost of this option at between $167 million and $193 million.

Option 4, Space Station Sample Repackaging, would see a Shuttle Orbiter deliver parts for modifying the Life Sciences Module (LSM) airlock that was expected to be part of the Space Station along with propellants for a Station-based OMV. Alternately, a Shuttle mission would detach the LSM from the Station and transport it to Earth for modification, after which a second Shuttle mission would return it to the Station.

The OMV would capture the ERV and deliver it to the LSM airlock, where astronauts would extract the sample canister and repackage it within a small biological containment/sample cooling container. The container would then be returned to Earth inside a Shuttle Orbiter crew cabin. The ERV would remain in quarantine inside the LSM airlock until scientists in the PRSL on Earth had analyzed the returned Mars sample and determined that it posed no threat. Eagle estimated that this option would cost between $302 million and $714 million.

Option 5, for which Eagle had little enthusiasm, was dubbed Minimal Sample Analysis at Space Station. It would closely resemble Option 4, except that a small sub-sample would removed from the sample canister in the LSM for "minimal" biological analysis. "There is some question," the company noted, "as to how much use a minimal analysis would be." Eagle placed the cost of this option at between $316 million and $749 million.

Eagle's Option 6, Small Sample Sterilized at Station and Sent to Earth, was also derived from its Option 4. Astronauts would remove a sub-sample and heat it enough to kill martian microbes while preserving evidence of their existence. A Shuttle Orbiter would then transport the sub-sample to Earth. The remainder of the sample (and, possibly, the Station crew) would remain in quarantine until scientists in the PSRL had checked out the sub-sample. Eagle placed this option's cost at between $316 million and $927 million.

After Option 6, Eagle's proposed sample-handling options became much more complex and expensive, adding significantly to the cost of returning a sample from Mars. Option 7, Separate Quarantine Module Attached to Station, would see a Shuttle Orbiter dock a specialized LSM-derived Quarantine Module (QM) to the Station. Eagle noted that the cost of "[d]edicated facilities. . .will seem more reasonable if a number of sample return missions are envisioned," and added that "[m]anned Mars missions might. . .use the [QM]" for quarantine of astronauts returning from Mars.

No pressurized passageway would link the Station to the QM while it held a Mars sample. If the QM was a permanent module of the Space Station, then it might be connected to it by a pressurized tunnel when no Mars sample was present and put to non-sample-related uses.

Alternately, the QM might be attached to the Station only when a sample was due to arrive from Mars. After the sample was placed in the QM, a Shuttle Orbiter would detach the module and transport it to Earth. Another Orbiter would return the empty QM to the Station when the next Mars sample was due to arrive in Earth orbit. Eagle estimated that Option 7 would cost between $605 million and $1.04 billion.

Antaeus Lab Module Attached to Station, Eagle's Option 8, took its name from the 1981 Antaeus report (bottom link below), which described a purpose-built Orbital Quarantine Facility (OQF) space station. The Antaeus module, which would be capable of supporting long-term detailed sample analysis on much the same scale as the Earth-based PRSL, would replace or augment the Station's LSM.

If researchers working in the Antaeus module found that the Mars sample was safe, then it would be transported to Earth. If, on the other hand, the sample were found to contain harmful martian microbes, then the Antaeus module would be detached and boosted into a 1270-kilometer-high long-term orbit using an OMV. In the event that harmful microbes escaped from the Antaeus module and contaminated the Space Station, then an OMV could boost the entire Station into a 650-kilometer-high orbit. Eagle estimated that orbit-raising maneuvers could extend the orbital lifetime of the Antaeus module or Station for long enough to permit NASA to develop a large rocket stage that could boost the contaminated Antaeus module or Station into interplanetary space.

Augmenting the Space Station with the Antaeus module would require perhaps eight Shuttle flights at an estimated cost of $120 million each, for a total of $960 million. The company placed the total cost of Option 8 at between $1.863 billion and $2.456 billion.

Eagle's Option 9, the 1/2 Quarantined Space Station, would be nearly identical to its Option 8, except that the Station modules that would support the scientists analyzing the sample in the Antaeus module would be isolated from the rest of the Station. This would be achieved by closing pressure hatches between the two halves of the Station and slightly reducing air pressure in the quarantined modules. Eagle expected that this option would cost the same as Option 8, though it added that "detailed study may show this option to have a somewhat higher cost."

Option 10, a Dedicated Antaeus Space Station identical to that described in the Antaeus report, would constitute a new (albeit small) independent space station in Earth orbit, making it the costliest of the 10 options. Eagle estimated that the Antaeus station would cost between $5.101 billion and $7.107 billion. This option would make unnecessary the PSRL on Earth since all quarantine and analysis would take place in Earth orbit. The company declared that Option 10 was "without a doubt the safest, biologically, of all the options," but added that "the price paid for this additional safety seems unreasonably high."

Having examined the 10 options, each more complex than the last, Eagle judged that Options 1, 2, and 3 would be adequate for Mars sample quarantine. The probability of a biological accident involving a Mars sample was simply too minute to justify the greater cost of Options 4 through 10.

The company then examined methods of Earth-orbital sample recovery. It assumed that, during Mars-Earth transfer, the sample would be preserved at cold Mars-like temperatures to maintain its scientific integrity. Earth orbit is, however, warmer than interplanetary space because Earth radiates heat. This would make difficult keeping the Mars sample cold for long periods in Earth orbit, so rapid recovery would be desirable.

Eagle also assumed that an ERV that employed rocket motors to slow itself so that Earth's gravity could capture it would end up in a high elliptical Earth orbit (700 kilometers by 40,000 kilometers or 700 kilometers by 70,000 kilometers, with orbital periods of 12 or 24 hours, respectively). This would have the advantage of placing it well away from the Earth's radiated heat through most of its orbit, but would also delay sample recovery.

For recovery from elliptical orbit, the planned OMV design would be inadequate, so Eagle invoked a new-design Orbital Transfer Vehicle (OTV) based on the Centaur upper stage. Recovery using an OTV based at the Station would be problematic because the Station's orbital plane would shift 6° per day relative to the ERV, forcing the OTV to burn a considerable quantity of propellant to match orbits with the ERV and return with it to the Station. Eagle found that the best-case recovery time for a sample in elliptical orbit would be equal to one orbital period (12 or 24 hours) plus about four hours, leading to totals of 16 or 28 hours.

A sample in a 500-kilometer circular orbit, on the other hand, would be subjected to more Earth-radiated heat, but could be recovered by a Shuttle Orbiter or an Orbiter- or Station-based OMV in as little as six hours. Providing the ERV with enough propellant to circularize its orbit at 500-kilometer altitude would, however, increase its mass by 2.5 times over the elliptical-orbit ERV. This would constitute "an unacceptable penalty," Eagle judged.

Planetary Sample Rapid Recovery and Handling, Report No. 85-105, Eagle Engineering, September 20, 1985.

http://beyondapollo.blogspot.com/2010/09/jpljsc-mars-sample-return-study-i-1984.html

http://beyondapollo.blogspot.com/2009/09/antaeus-report-1978.html

BNTR DRM 3.0 (2001)

In October 2001, nuclear engineers at NASA's Glenn Research Center (GRC) in Cleveland, Ohio, led by Stanley K. Borowski, Advanced Concepts Manager in GRC's Space Transportation Project Office, described a variant of NASA's 1998 Mars Design Reference Mission (DRM) 3.0 based on Bimodal Nuclear Thermal Rocket (BNTR) propulsion. The BNTR DRM concept, first described publicly in 1998, evolved from nuclear-thermal rocket mission designs Borowski and his colleagues developed during the abortive Space Exploration Initiative (1989-1993).

NASA's first Mars DRM, designated DRM 1.0 in 1997, was developed in 1992-1993 (link below). It was based on Martin Marietta's 1990 Mars Direct mission plan. The demise of President George H. W. Bush's Space Exploration initiative temporarily halted DRM work in 1993. NASA resumed its DRM studies after the discovery in 1996 of possible microfossils in martian meteorite ALH 84001, and released its baseline chemical-propulsion DRM 3.0 in 1998. There was no official DRM 2.0, though a "scrubbed" (that is, mass-reduced) DRM 1.0 bears that designation in at least one NASA document.

Shortly thereafter, NASA Johnson Space Center (JSC) in Houston, Texas, which led the DRM study effort, was diverted from DRM work by the in-house COMBO lander study. In the absence of guidance from Houston, NASA GRC developed a pair of DRM 3.0 variants: a solar-electric propulsion (SEP) DRM 3.0 and the BNTR DRM 3.0 considered here.

In BNTR DRM 3.0, two unpiloted spacecraft would leave Earth for Mars during the 2011 low-energy Mars-Earth transfer opportunity, and a third, bearing the crew, would depart for Mars in 2014. Components for the three spacecraft would reach Earth orbit on six Shuttle-Derived Heavy-Lift Launch Vehicles (SDHLVs), each capable of launching 80 tons into 220-mile-high assembly orbit, and in the payload bay of a Space Shuttle orbiter which would also deliver the Mars crew.

SDHLV 1 would launch Bimodal Nuclear Thermal Rocket (BNTR) stage 1. Each BNTR DRM mission would need three 28-meter-long, 7.4-meter-diameter BNTR stages. BNTR stage 1 would carry 47 tons of liquid hydrogen (LH2) propellant. The BNTR stages would each include three 15,000-pound-thrust BNTR engines developed as part of a joint U.S./Russian project in 1992-1993.

SDHLV 2 would boost the unpiloted 62.2-ton cargo lander into assembly orbit. The lander would include a Mars aerobrake and entry shield, landing parachutes, a descent stage, a 25.8-ton Mars surface payload including an in-situ resource utilization (ISRU) propellant plant, and an unfueled Mars Ascent Vehicle (MAV) made up of a conical Earth Crew Return Vehicle (ECRV) capsule and an ascent stage.

SDHLV launch 3, identical to SDHLV launch 1, would place into assembly orbit BNTR stage 2 containing 46 tons of LH2 propellant. SDHLV launch 4 would place the unpiloted 60.5-ton Habitat lander into assembly orbit. It would include a Mars aerobrake/entry shield identical to that of the cargo lander, parachutes, a descent stage, and a 32.7-ton payload including the crew's Mars surface living quarters.

The BNTR stage forward section would include chemical thrusters for attitude control and for maneuvering capability for docking the stages with the Habitat and cargo landers in assembly orbit. The BNTR 1/cargo lander combination would have a mass of 133.7 tons, while the BNTR 2/Habitat lander combination would have a mass of 131 tons. Both combinations would measure 57.5 meters long. As the launch window for Mars opened, the BNTR stages would fire their engines to depart assembly orbit for Mars.

Following Earth-orbit departure, the BNTR engine nuclear reactors would switch to electricity-generation mode. They would heat a working fluid to drive three turbine generators providing a total of 50 kilowatts of electricity. Fifteen kilowatts of this would power a refrigeration system in the BNTR stage for minimizing LH2 boil-off.

As Mars loomed large ahead, the power generators would charge the lander batteries. The BNTR stages would then separate and fire their engines to miss Mars and enter disposal orbit around the Sun. The landers would aerobrake in Mars's upper atmosphere. The Habitat lander would capture into Mars orbit and extend twin solar arrays to generate electricity. The cargo lander would capture into orbit, then fire its deorbit engines to enter the atmosphere a second time. After casting off its heatshield, it would deploy three parachutes. Descent engines would fire, then landing legs would deploy just before touchdown. The GRC engineers opted for a horizontal landing configuration; this would, they explained, prevent tipping and provide the astronauts with easy access to the lander's cargo.

After cargo lander touchdown, a teleoperated cart bearing a nuclear power source would lower to the ground and trundle away to a safe distance trailing a power cable. This would power the lander's ISRU propellant plant, which over several months would react four tons of "seed" hydrogen brought from Earth with martian atmospheric carbon dioxide to produce 39.5 tons of liquid methane and liquid oxygen propellants for the MAV's ascent engines.

SDHLV launch 5, identical to SDHLV launches 1 and 3, would mark the start of launches for the 2014 Earth-Mars transfer opportunity. It would place BNTR stage 3 into assembly orbit. Because it would propel a piloted spacecraft, it would include three 3.24-ton radiation shields (one per engine). BNTR stage 3 would carry about 48 tons of LH2.

Thirty days after SDHLV launch 5, SDHLV launch 6 would place into assembly orbit a 5.1-ton spare Earth Crew Return Vehicle (ECRV) attached to the front of an 11.6-ton truss. A 17-meter-long tank with 43 tons of LH2 and a two-meter-long drum-shaped logistics module containing 6.9 tons of contingency supplies would nest along the truss's length. BNTR stage 3 and the truss assembly would rendezvous and dock, then propellant lines would automatically link the truss tank to BNTR stage 3.

A Shuttle orbiter carrying the Mars crew and a 20.5-ton deflated Transhab module would rendezvous with the BNTR stage 3/truss combination one week before the crew's planned departure for Mars. After rendezvous, the spare ECRV would undock from the truss and fly automatically to a docking port in the Space Shuttle payload bay. Astronauts would use the Shuttle's robot arm to hoist the Transhab from the payload bay and dock it to the front of the truss in the spare ECRV's place.

The Mars astronauts would enter the spare ECRV and pilot it to a docking at a port on the Transhab's front, then enter the cylindrical Transhab's solid core and inflate its fabric-walled outer volume. The inflated Transhab would measure 9.4 meters in diameter. Unstowing floor panels and furnishings from the core and installing them in the inflated volume would complete assembly. Transhab, truss, and BNTR stage 3 would make up the 64.2-meter-long, 166.4-ton Crew Transfer Vehicle (CTV).

The truss-mounted tank and BNTR stage 3 would hold 90.8 tons of LH2 at the start of CTV Earth departure on January 21, 2014. The truss tank would provide 70% of the propellant needed for departure. In the most demanding scenario, the BNTR engines would fire twice for 22.7 minutes each time to push the CTV out of Earth orbit toward Mars.

Following Earth-orbit departure, the crew would jettison the empty truss tank and use small chemical-propellant thrusters to start the CTV rotating end over end at a rate of 3.7 rotations per minute. This would create acceleration equal to one Mars gravity (38% of Earth gravity) in the Transhab module. Artificial gravity was a late addition to BNTR DRM 3.0; it made its first appearance in a 1999 paper. In artificial gravity mode, "down" would be toward the spare ECRV on the CTV's nose; this would make the Transhab's forward half its lower deck. Halfway to Mars, about 105 days out from Earth, the astronauts would stop rotation and perform a course correction burn using the thrusters. They would then resume rotation for the remainder of the trans-Mars trip.

The CTV would arrive in Mars orbit on August 19, 2014. The three BNTR engines would fire for 12.3 minutes to slow the spacecraft for Mars orbit capture. The spacecraft would complete one Mars orbit each 24.6-hour martian day.

The crew would pilot the CTV to rendezvous with the Habitat lander in Mars orbit. If the Habitat lander proved unable to land on Mars, the crew would remain in the CTV in Mars orbit until Mars and Earth aligned for the flight home (a wait time of about 500 days). They would survive by drawing upon the contingency supplies in the drum-shaped logistics module attached to the truss. If the Habitat checked out as healthy, however, the crew would fly the spare ECRV to a docking port on its side. After discarding the spare ECRV and Habitat solar arrays, they would fire the Habitat's deorbit engines, enter Mars's atmosphere, and land near the cargo lander.

The Habitat lander's horizontal configuration would provide the astronauts on board with easy access to the martian surface. After the historic first footsteps on Mars, the astronauts would inflate a Transhab surface habitat and commence a program of exploration lasting about 500 days.

The CTV would briefly fire its engines to align its orbit for the crew's return. The MAV bearing the crew and about 90 kilograms of Mars samples would then lift off burning methane and oxygen propellants made from martian air. It would dock at the front of the Transhab, then the astronauts would transfer to the CTV. They would cast off the spent MAV ascent stage, but would retain the MAV ECRV for Earth reentry.

The CTV would leave Mars orbit on January 3, 2016, after 502 days at Mars. The astronauts would first abandon the contingency supply module to reduce their spacecraft's mass so that the propellant remaining in BNTR stage 3 would be sufficient to launch them home to Earth. They would then fire the NTR engines for 2.9 minutes to change the CTV's orbital plane, then fire them again for 5.2 minutes to place it on course for Earth. The crew would spin the CTV end over end to create acceleration equal to one Mars gravity in the Transhab. The authors advocated increasing the spin rate gradually during the flight home to prepare the crew for return to Earth's gravity. About halfway home they would stop rotation, perform a course correction, then resume rotation. Flight to Earth would last 190 days.

Near Earth, the crew would stop CTV rotation for the final time, enter the MAV ECRV with their Mars samples, and undock from the CTV. The abandoned CTV would fly past Earth and enter solar orbit. The MAV ECRV would reenter Earth's atmosphere on July 11, 2016.

The authors compared their Mars plan with the baseline chemical-propulsion DRM 3.0 and with the NASA GRC SEP DRM 3.0. They found that their plan would need eight vehicle elements, of which four would be designs unique to the BNTR DRM 3.0. The baseline DRM 3.0, by contrast, would need 14 vehicle elements, 10 of which would be unique, and the SEP DRM would need 13.5 vehicle elements, 9.5 of which would be unique. BNTR DRM 3.0 would require that 431 tons of hardware and propellants be placed into Earth orbit; the baseline DRM 3.0 would need 657 tons and SEP DRM 3.0, 478 tons. Borowski and his colleagues argued that fewer vehicle designs and reduced mass would add up to reduced cost and mission complexity.

The BNTR DRM 3.0 variant became the basis for DRM 4.0, which was developed during NASA-wide studies in 2001-2002 (though NASA documents occasionally back-date DRM 4.0 to 1998, when BNTR DRM 3.0 was first proposed). DRM 4.0 differed from BNTR DRM 3.0 mainly in that it adopted a "Dual Lander" design concept developed in response to JSC's 1998-1999 COMBO lander study. In 2008, a decade after BNTR DRM 3.0 first became public, NASA released a version of DRM 4.0 modified to use planned Constellation Program hardware (for example, the Ares V heavy-lift rocket and the Orion Crew Exploration Vehicle). It dubbed the new DRM Design Reference Architecture (DRA) 5.0.

"Bimodal Nuclear Thermal Rocket (NTR) Propulsion for Power-Rich, Artificial Gravity Human Exploration Missions to Mars," IAA-01-IAA.13.3.05, Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 52nd International Astronautical Congress in Toulouse, France, October 1-5, 2001.

"Artificial Gravity Vehicle design Option for NASA's Human Mars Mission Using 'Bimodal' NTR Propulsion," AIAA-99-2545,Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit in Los Angeles, California, June 20-24, 1999.

"Vehicle and Mission Design Options for the Human Exploration of Mars/Phobos Using 'Bimodal' NTR and LANTR Propulsion," AIAA-98-3883, Stanley K. Borowski, Leonard A. Dudzinski, and Melissa L. McGuire; paper presented at the 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit in Cleveland, Ohio, July 13-15, 1998.

http://beyondapollo.blogspot.com/2011/09/design-reference-mission-10-1993.html

Design Reference Mission 1.0 (1993)

The NASA Exploration Program Office (ExPO) at Johnson Space Center in Houston, Texas, commenced the Mars Exploration Study Project in the summer of 1992. Its aim was to determine how its First Lunar Outpost (FLO) plan (top link below) might find hardware commonality with a follow-on Mars program, thereby reducing the costs of both programs. Mars Exploration Study Team (MEST) workshops held in August 1992 and May 1993 produced a Mars Design Reference Mission (DRM) with little overt FLO commonality beyond outwardly similar conical capsules for lunar and Mars ascent/Earth reentry and an uprated variant of the FLO heavy-lift rocket. In fact, NASA's 1993 Mars DRM owed much to the 1989-1990 Martin Marietta Mars Direct mission plan championed by engineer Robert Zubrin, which bypassed the moon entirely.

As the MEST began its study, the Space Exploration Initiative (SEI) that spawned it was drawing to a close. The MEST's labors spanned the 1992 election, in which Republican incumbent George H. W. Bush lost to Democratic challenger William J. Clinton. Many space initiatives begun under Bush would continue and expand under Clinton - for example, U.S.-Russian space cooperation and the Discovery Program of low-cost robot explorers - but SEI, never popular, was not one of them.

NASA halted almost all DRM work by the summer of 1993, and would not begin again to study how human explorers might reach Mars until after the 1996 announcement that possible microfossils had been found in martian meteorite ALH 84001. In 1997, NASA designated its 1993 DRM "DRM 1.0" when it published a new DRM that it designated DRM 3.0. Odd as it may seem, there was no official DRM 2.0, though in at least one NASA document a "scrubbed" (mass-reduced) version of DRM 1.0 bears that designation.

The 1993 DRM's "FLO-class" heavy-lift rocket would be capable of boosting about 240 tons into a 500-kilometer circular low-Earth orbit (LEO). This would make the giant rocket more than twice as powerful as the Apollo-era Saturn V and nearly a quarter again as powerful as the booster used to launch FLO payloads.

NASA's first manned Mars expedition would need four flights of the uprated FLO-class heavy-lift rocket. Three heavy-lifter flights would suffice for each subsequent Mars expedition.

The MEST selected the September 2007 Earth-Mars transfer opportunity to begin its first manned Mars mission because it would be challenging in terms of the amount of propulsive energy required to launch payloads toward Mars. Three unmanned uprated FLO-class rocket launches in rapid succession would begin the mission. All payloads would have a mass at launch from Earth of between 60 and 75 tons.

The MEST decided that its Trans-Mars Injection (TMI) rocket stage, which would launch all DRM payloads out of Earth orbit toward Mars, should employ a nuclear-thermal rocket engine. The liquid hydrogen-fueled stage would be capable of boosting about 100 tons to Mars orbit and about 60 tons to Mars's surface.

The first uprated FLO-class rocket would launch an unmanned Earth-Return Vehicle (ERV) Mars orbiter. The ERV would include a cylindrical, two-deck habitat (hab) module similar to the one on the hab lander that would transport the first crew to Mars in 2009, a Trans-Earth Injection (TEI) stage, and solar arrays for generating electricity. Its TEI stage would carry liquid oxygen and liquid methane propellants for two modified RL-10 rocket engines that would launch the crew home to Earth after their Mars surface mission.

The second giant rocket would launch an unmanned fuel factory/Mars Ascent Vehicle (MAV) lander. The lander, which would carry liquid hydrogen feedstock and a nuclear reactor for MAV propellant manufacture, would deliver about 40 tons of cargo to the landing site on Mars, including a large pressurized rover for long (1000-kilometer) Mars surface traverses.

The third uprated FLO-class rocket launched in the September 2007 opportunity would place into Earth orbit an unmanned hab lander. A twin of the lander that would transport the first crew to Mars in 2009, it would include a regenerable (recycling) life support system and would rely for electricity on a small nuclear power source.

All three payloads would include bowl-shaped aerobraking heat shields (near the end of the 1993 DRM design process, the MEST adopted a bullet-shaped biconic heat shield design). The payloads would reach Mars in August-September 2008 and aerobrake in its atmosphere to shed speed and capture into orbit. The ERV orbiter would then discard its heat shield. The fuel factory/MAV and hab lander would ignite rocket motors to slow themselves and fall into Mars's atmosphere. Following a fiery descent toward their target landing site, they would each discard their heat shield, ignite landing rocket motors, and extend landing legs.

After the fuel factory/MAV lander touched down, a nuclear reactor would lower to Mars's surface on a small rover and trundle away trailing power cables under telerobotic guidance from controllers on Earth. The rover would place the reactor in a crater about 500 meters from the lander. The crater's upraised rim and distance would protect the landing site from radiation the reactor would produce after start-up.

Electricity from the reactor would power the fuel factory, where liquid hydrogen would be exposed to martian atmospheric carbon dioxide in the presence of a nickel or ruthenium catalyst, yielding liquid methane and water (bottom link below). The methane would be stored and the water electrolyzed to yield oxygen and hydrogen. The oxygen would be stored and the hydrogen recycled to manufacture more water and methane.

In one year, the fuel factory would produce and store 5.7 tons of liquid methane and 20.8 tons of liquid oxygen. The MAV would burn these during its ascent to the orbiting ERV at the end of the first Mars crew's surface mission. As a safety measure, the crew would not leave Earth until after the 2007 fuel factory finished making their ascent propellants. The fuel factory would then manufacture a 600-day supply of life support consumables (14.4 tons of water, two tons of nitrogen/argon, and three tons of breathing oxygen).

Meanwhile, the unmanned hab lander would set down nearby. Controllers on Earth would activate and monitor its systems to ensure its readiness for the first Mars crew.

Assuming that the 2007 payloads remained healthy, three more heavy-lift rocket launches would occur during the October-November 2009 Earth-Mars transfer opportunity. One would place into Earth orbit the habitat lander carrying the first six-person Mars expedition crew. The other two would launch an unmanned Earth-return vehicle (ERV) orbiter to serve as a backup for the 2009 first Mars crew or as the primary ERV for the 2012 second Mars crew and an unmanned fuel factory/MAV lander that would provide a backup for the 2009 crew or serve as the primary fuel factory/MAV for the 2012 crew. Following insertion into Earth orbit, TMI stages would boost the three payloads toward Mars.

The crew would reach Mars in about 180 days and aerobrake into a 250-by-34,000-kilometer orbit, then descend to a landing near the 2007 habitat and fuel factory/MAV. Soon after the crew landed, the 2009 fuel factory/MAV and ERV would aerobrake into Mars orbit. The 2009 fuel factory/MAV could be directed to land near the crew if they determined that its 2007 counterpart would be incapable of launching them into Mars orbit at the end of their surface stay. Otherwise, it would land at a new landing site within range of the 2007 pressurized long-traverse rover (that is, no more than 1000 kilometers away) and begin making propellants and life support consumables.

If their hab lander suffered damage during landing, the first crew would abandon it and move into the waiting 2007 hab. If it landed safely, however, the explorers would lower wheels and raise landing gear on the 2009 and 2007 habs and tow them together using an unpressurized rover. They would then link the twin habs with a pressurized tunnel, lower the landing gear and raise the wheels, and set up a greenhouse for growing vegetables to supplement their 800-day supply of dry food.

The first Mars outpost thus established, the astronauts would unpack the pressurized rover from the 2007 MAV lander. The nuclear- or methane/oxygen-powered rover would include a rear-facing docking port for linking to the habs, providing the explorers with additional pressurized living volume while the rover was docked and allowing easy movement between habs and rover. During their planned 600-day stay on Mars, the crew would carry out several 10-day rover traverses ranging up to 500 kilometers from the outpost (image at top of post).

After the first expedition, crews would no longer have at their disposal a pre-landed backup hab. The first manned Mars mission was expected to demonstrate hab reliability and landing safety, permitting NASA to do away with the backup hab and the heavy-lift rocket and TMI stage that would launch it.

If the lone hab lander crashed during landing, surviving crewmembers would use the MAV to evacuate to the orbiting ERV, where they would wait about 600 days for the beginning of the next minimum-energy Mars-Earth transfer opportunity. Similarly, in the unlikely event of a catastrophe that rendered the hab unlivable during the 600-day surface mission, surviving crewmembers could shelter temporarily in the pressurized rover, if it were available, then transfer to the MAV and evacuate to the ERV. There they would stay until the beginning of the next minimum-energy Mars-Earth transfer opportunity.

Assuming that the surface mission came off as planned, however, in October 2011 the first Mars crew would pack samples into the 2007 MAV and lift off. If the 2007 MAV failed pre-launch checks, the astronauts would drive their pressurized rover to the 2009 MAV. They would dock in Mars orbit with the 2007 ERV (or the 2009 ERV if the 2007 ERV were no longer operational), then would ignite the ERV's liquid oxygen/liquid methane TEI stage to leave Mars orbit. In the unlikely event that both MAVs or both ERVs failed, the 2009 crew could survive at their outpost until replacement payloads launched in early 2012 arrived at Mars in 2013.

As Earth grew large in their viewports, the first Mars explorers would enter the MAV capsule and undock from the ERV. They would then reenter Earth's atmosphere directly and descend to a landing using a steerable parachute. The ERV, meanwhile, would swing past Earth and enter solar orbit.

Assuming that the first crew did not need to use the 2009 MAV or ERV, the second Mars expedition crew would depart Earth in the first quarter of 2012, while the first crew was on its way home. In addition to the hab bearing the second crew, an ERV orbiter and a fuel factory/MAV lander would be launched during the 2012 Earth-Mars transfer opportunity for the 2015 third Mars expedition crew or to serve as backups for the 2012 crew. This pattern of launches could continue indefinitely, enabling intensive exploration of large areas of Mars.

Alternately - and this emerged as the MEST's preferred approach - at least three manned landings at a single site could build up a Mars base. The base approach would compensate for the lack of pre-landed backup hab landers after the first expedition; if a crew's hab became damaged during landing, they could transfer to the hab or habs already at the base site.

Multiple expeditions to a single site would also permit build-up of surface assets, potentially creating new Mars exploration capabilities. If all three expeditions occurred as planned, then by the time the third left Mars, the base would comprise four habs, three disused fuel factories lacking cargo or MAVs, three remotely placed reactors, and 120 tons of cargo including up to three pressurized and three unpressurized rovers.

"Mars Exploration Strategies: A Reference Program and Comparison of Alternative Architectures," AIAA 93-4212, David Weaver and Michael Duke; presented at the AIAA Space Program and Technologies Conference and Exhibit, September 21-23, 1993, Huntsville, Alabama.

Mars Exploration Study Workshop II, NASA CP-3243, Michael Duke and Nancy Anne Budden, editors, November 1993; report on a workshop "sponsored by NASA. . . Johnson Space Center and Held at NASA Ames, May 24-25, 1993."

http://beyondapollo.blogspot.com/2010/10/first-lunar-outpost-flight-plan-1992.html

http://beyondapollo.blogspot.com/2009/09/propellant-production-on-mars-1978.html

RAND and Mars resources (1962-1963)

Most early Mars expedition plans made little mention of potential martian resources. Apart from using the martian atmosphere to slow the crew lander for landing, Mars spacecraft generally depended little on materials or conditions peculiar to the planet. This was because so little was known of Mars (top image above).

The potential benefits of using martian resources for propellants, building materials, and life support consumables were so compelling, however, that some planners chose to incorporate them into their mission designs anyway. Chief among these benefits was a dramatic reduction in mission mass if Earth-return rocket propellants could be found at Mars.

The Working Group on Extraterrestrial Resources (WGER) formed in early 1962. Besides NASA, the group included representatives from the U.S. Air Force, the Army, the Bureau of Mines, aerospace corporations, and academe. The group, which met throughout the 1960s, focused mainly on lunar resources. A few researchers, however, treated the WGER as a forum for discussing eventual exploitation of Mars resources.

One of these forward-thinkers was Ernst Steinhoff (middle image above), representing the RAND Corporation, a think tank created in 1946 to provide advice to the U.S. military services. RAND had performed Mars studies for the Air Force as early as 1960. Steinhoff, whose specialty was rocket guidance, came to the U.S. in 1945 with Wernher von Braun, Ernst Stuhlinger, Krafft Ehricke, and the other members of the Peenemünde rocket team. After working to launch captured V-2 missiles for the Army (bottom image above), he went to work for U.S. industry in 1956. Steinhoff joined RAND in 1961, and was instrumental in the formation of the WGER the following year. He became the WGER's first chairman.

Steinhoff summed up his Mars work in papers presented at a March 1962 meeting at NASA's Marshall Space Flight Center in Huntsville, Alabama, and at the June 1963 American Astronautical Society Symposium on the Manned Exploration of Mars in Denver. George Morgenthaler of Martin Marietta Corporation organized the Denver symposium, the first non-NASA meeting devoted to piloted Mars travel. As many as 800 engineers and scientists heard Steinhoff's paper and 25 others. It was the first time so many people from Mars-related disciplines had come together in one place, and the last Mars meeting as large until the 1980s. Sky & Telescope magazine reported that the "Denver symposium. . . helped narrow the gaps between engineer, biologist, and astronomer."

Soon after the Denver symposium, Steinhoff became Chief Scientist at the Air Force Missile Development Center at Holloman Air Force Base, New Mexico, after which he continued his involvement with the WGER and his work on Mars subjects at a reduced level. This is unfortunate, because in his two papers he anticipated several Mars mission concepts that would, in time, emerge as significant in Mars exploration planning.

Steinhoff's work focused on "autarchic" - that is, self-sufficient - bases on Mars and Phobos. Self-sufficiency would be achieved through mining and processing local materials, and by equipping the base with regenerable (recycling) life support systems. The Phobos and Mars bases would support scientific research and serve as "terminals" for spacecraft.

Steinhoff estimated that extraterrestrial water could supply over 90% of the logistical needs of space-faring humans. He wrote that the moon's gravity - nearly 20% as powerful as Earth's - would make it an inefficient "interim space base" for fueling Mars-bound ships. Citing Clyde Tombaugh, who had written that Mars's moons were probably made of the same water-rich materials as Mars itself, Steinhoff proposed that Phobos supplant the moon as a stepping stone to Mars. Nuclear systems could cook water out of Phobos rocks, then split it into hydrogen and oxygen rocket propellants.

Steinhoff's early Mars expedition would comprise 18 astronauts in a convoy of three crew and six cargo spacecraft. They would use a conjunction-class profile, traveling to Mars in 256 days, remaining in the Mars system for 485 days, and then returning to Earth in 256 days.

Two chemists and two geologists would prospect Phobos for water-rich rocks. The little moon's weak gravity would enable space-suited astronauts to easily assemble "ready-to-operate" base modules shipped from Earth. Space construction workers, Steinhoff wrote, would be able to carry and connect 50-ton modules by hand.

Winged three-man shuttles based at the Phobos terminal would provide access to the Mars base, which would be built within 25º of the equator for easy access from Phobos's equatorial orbit. Steinhoff assumed that the martian atmosphere would be thick enough to support gliding shuttles requiring minimal landing propellant. He proposed that early shuttles drop cargoes and astronauts by parachute, then blast back to orbit without landing.

Among the early air-dropped cargoes would be a radio-controlled bulldozer, which astronauts on Phobos would use to prepare a safe runway ahead of the first shuttle landing. After the Mars base was established, the shuttles would rely on propellants manufactured on Mars to return to the Phobos base.

The Mars base would use vehicles and building techniques Steinhoff's RAND colleagues proposed in their Air Force studies. Rocket turbine engines tailored to the martian atmosphere would power surface rovers, airplanes, and helicopters with low-mass inflatable parts. Inflatable modules would provide living space for the earliest Mars explorers. Later astronauts would manufacture cement from martian materials, construct masonry and cinderblock buildings, and inhabit martian caves.

After the propellant needs of the Mars system were met, Phobos would become a fueling station for interplanetary spacecraft. Steinhoff estimated that enough propellant could be manufactured in just 100 days to launch a spacecraft from Phobos to 300-mile-high Earth orbit, and that Phobos propellants could cut the time required for transfer between the two worlds in half. He added that "use of indigenous resources, combined with more advanced nuclear ferry systems, may. . . pave the way to intensive interplanetary exploration within the limitations of our national resources." Phobos could, for example, serve as a refueling stop for Jupiter-bound piloted spacecraft.

"Use of Extraterrestrial Resources for Mars Basing," Ernst A. Steinhoff, Exploration of Mars, George Morgenthaler, editor, pp. 468-500; proceedings of the American Astronautical Society Symposium on the Exploration of Mars, Denver, Colorado, June 6-7, 1963.

"A Possible Approach to Scientific Exploration of the Planet Mars," Paper #38, Ernst A. Steinhoff, From Peenemunde to Outer Space, "A Volume of Papers Commemorating the Fiftieth Birthday of Werner von Braun," NASA Marshall Space Flight Center Technical Report, 1962, pp. 803-836.

"Manned Exploration of Mars?" Raymond Watts, Sky & Telescope, August 1963, pp. 63-67, 84.

Cycling NEP Mars spacecraft and Earth-moon/Sun-Mars L points (1991)

In February 1991, six engineers with McDonnell Douglas Space Systems Company in Houston, Texas, unveiled a Mars transportation scenario which, they explained, was "driven by the desire to explore Mars in a continuous fashion rather than designing a series of independent, Apollo-style missions. . .then phasing out the program." Specifically, they proposed using the Cislunar Libration Point (CLP) and the Cismartian Libration Point (CMP) as "parking orbit transportation nodes" for a pair of Nuclear-Electric Propulsion (NEP) Mars spacecraft.



The CLP, better known as Earth-moon L1, is situated about 70,000 kilometers from the center of the moon's Earth-facing Nearside hemisphere (that is, about 327,000 kilometers from Earth). The CMP, better known as Sun-Mars L1, is located 1.083 million kilometers Sunward of Mars. The McDonnell Douglas team assumed that, by the time their Mars program began, piloted Lunar Transfer Vehicles (LTVs) would already be using the CLP as a staging area for lunar landing missions.



The McDonnell Douglas engineers based their proposed NEP spacecraft design on one developed at NASA's Lewis Research Center in Cleveland, Ohio (image above). A 10-megawatt nuclear reactor on the spacecraft's nose would power its tail-mounted electric thruster clusters, which would ionize and expel xenon atoms to generate thrust. Electric propulsion spacecraft accelerate slowly but continuously and use much less propellant than equivalent chemical-propulsion and nuclear-thermal-propulsion spacecraft. The McDonnell Douglas engineers calculated that their reusable NEP Mars spacecraft could haul double the payload of an equivalent expendable chemical-propulsion Mars spacecraft while using 42% less propellant.



They based their Mars mission program schedule on the timeline for the Space Exploration Initiative (SEI) President George H. W. Bush had announced on May 11, 1990, as part of his commencement address at Texas A & M University. When Bush first unveiled SEI on July 20, 1989, the 20th anniversary of the Apollo 11 moon landing, he called for a return to the moon followed by an expedition to Mars, but he established no deadlines for accomplishing these feats. Bush's May 1990 timeline had the first Americans setting foot on Mars ahead of the 50th anniversary of Apollo 11 in 2019.



In late 2015 or early 2016, NEP Spacecraft 1 would transfer from 1000-kilometer-high Low-Earth Orbit (LEO) to its parking place at the CLP. It would have a mass of 455 metric tons when it started its five-month "maiden spiral" outward from Earth. During its slow voyage outward, Spacecraft 1 would orbit the Earth many times, gradually gaining altitude, and would pass repeatedly through the Earth-girdling Van Allen Radiation Belts. The repeated slow Van Allen Belt crossings would expose any astronauts on board to a lethal dose of radiation. Because of this, Spacecraft 1 would travel from LEO to CLP without a crew. It would expend 43 metric tons of propellant, reducing its mass to 412 metric tons.



Making the CLP and CMP destinations for the NEP spacecraft would eliminate the need for long spirals in and out of low planetary orbits at the start of each transfer between the Red and Blue planets. Spacecraft 1 and its sister ship Spacecraft 2 would each depart LEO once for the CLP and would never approach nearer to Mars than the CMP.



In early 2016, about a month after Spacecraft 1 reached the CLP, astronauts would arrive from LEO in a fast chemical-propulsion LTV. Rapid transfer from LEO to CLP would limit crew radiation exposure to levels similar to those experienced by Apollo crews.



The astronauts would perform exhaustive checks of Spacecraft 1's systems; then, if all checked out as normal, they would activate Spacecraft 1's NEP thrusters to take advantage of the 2016 minimum-energy Earth-Mars transfer opportunity. Such opportunities occur every 26 months. Spacecraft 1 would need 18 days to escape the Earth-moon system, then about 220 days to reach the CMP. This transfer duration would compare favorably with those of chemical-propulsion or nuclear-thermal-propulsion Mars spacecraft.



The transfer would include a coast period during which the electric thrusters would be switched off. The longer the coast period, the less propellant the spacecraft would need (but the longer the overall trip duration). Conversely, a shorter coast period would mean a shorter trip time (but greater propellant expenditure). After the coast period, Spacecraft 1 would point its thrusters in its direction of motion to slow itself. The McDonnell Douglas team assumed that Spacecraft 1 would arrive at the CMP with a mass of 350 metric tons.



Spacecraft 1 would park at the CMP for from 500 to 600 days to await the next minimum-energy Mars-Earth transfer opportunity, which would occur in mid 2018. During the wait period, the crew would separate from Spacecraft 1 in a two-stage expendable Mars lander. The journey from the CMP to the martian surface would require from 15 to 30 days, the McDonnell Douglas engineers estimated. They calculated that a Mars lander that needed 15 days to reach Mars from the CMP and could deliver 50 tons of payload to Mars's surface would have a mass of 150 tons.



After a surface stay of unspecified duration, the astronauts would lift off in the lander's ascent stage, leaving its expended descent stage and its payload behind on Mars. The journey from Mars back to the CMP would last from 15 to 30 days. The crew would dock with Spacecraft 1, transfer their Mars samples and data from the ascent stage, then cast off the ascent stage.



Meanwhile, back in the Earth-moon system, Spacecraft 2 would perform its unmanned maiden spiral from LEO to the CLP. It would park at the CLP until a crew arrived in an LTV. In mid 2018, about 26 months after Spacecraft 1 left the CLP, Spacecraft 2 would set out on a near-copy of Spacecraft 1's Mars voyage. Because the 2018 Earth-Mars transfer opportunity would be more favorable (that is, it would need less energy) than its 2016 counterpart, Spacecraft 2 would arrive at the CMP with slightly more mass (356 metric tons) than had Spacecraft 1. Its crew would then separate in a lander to explore a new landing site on Mars.



In mid 2018, at about the time Spacecraft 2 departed the CLP, Spacecraft 1 would leave the CMP. Having left behind its lander and payload, Spacecraft 1 would have a mass of 173 metric tons when it departed the CMP and 138 metric tons when it returned to the CLP. Travel from the CMP to the CLP would need less time than from the CLP to the CMP because the NEP spacecraft would have less mass during the CMP-CLP transfer.



Upon arrival at the CLP in late 2018, Spacecraft 1's crew would board a waiting LTV and return to the LEO space station. In the from 500 to 600 days that followed, automated cislunar NEP freighters would deliver to unmanned Spacecraft 1 xenon propellant, life support supplies, spare parts, and an expendable lander for its next Mars voyage.



The McDonnell Douglas engineers noted that the CLP is an unstable libration point, so any spacecraft parked there would need to hold position using thrusters or risk ejection from the Earth-moon system. Fortunately, the occasional stationkeeping maneuvers would be small.



In mid 2020, near the end of its nearly two-year parked period, Spacecraft 1 would receive an LTV bearing the Mars program's third crew. The authors noted as an aside that cargo and astronauts bound for Mars could originate on the moon. After system checks, Spacecraft 1 would depart the CLP with a mass of 412 metric tons.



Spacecraft 2 would park at the CMP until mid 2020, then would begin its first transfer back to the CLP. It would depart the CMP with a mass of 173 metric tons and arrive at the CLP in late 2020 with a mass of 137 metric tons. Spacecraft 1, meanwhile, would arrive at the CMP for the second time in early 2021 with a mass of 366 metric tons. The twin NEP spacecraft could trade CLP and CMP parking places indefinitely, never meeting, the McDonnell Douglas team wrote.

"Optimal Cycling Between Cislunar and Cismartian Libration Points With Reusable Nuclear Electric Transfer Vehicles," Steven J. Sponaugle, Brian H. Rishikof, Steven F. Davis, Douglas A. Pesek, Diane R. Walyus, and Victor R. Bond, AAS 91-104; paper presented at the AAS/AIAA Spaceflight Mechanics Meeting held in Houston, Texas, February 11-13, 1991.

Optical astronomy from a manned planetary flyby spacecraft (1968)

Hubble Space Telescope/Spitzer Space Telescope composite image of the Sombrero Galaxy in visible and infrared light.

Hubble Space Telescope image of the Whirlpool Galaxy, a face-on spiral similar to our own Milky Way.

One criticism often leveled against the manned Mars/Venus flyby mission concepts NASA studied in the 1960s was that the flyby astronauts would be inactive during most of their mission. They would, the argument ran, justify their presence on board only during the planetary flyby or flybys, which would account for only a small portion of the total mission duration. The 1975 Mars flyby mission the NASA Planetary Joint Action Group proposed in 1966, for example, would last for 667 days, but the flyby spacecraft would spend only about 20 days within two million kilometers of Mars (top link below).



This argument could only be persuasive, however, if one assumed that the sole purpose of a manned flyby mission was to accomplish its flyby or flybys. In fact, NASA planners expected that the flyby astronauts would perform a wide range of experiments and observations throughout their mission. A manned flyby spacecraft would amount to a multi-purpose space station in orbit about the Sun instead of the Earth. Manned Mars/Venus flybys would also serve as experience-building steps toward manned Mars landing missions, much as Project Gemini had been for the Apollo Program.



In August 1966, H. London, an engineer with Bellcomm, NASA's advanced planning contractor, described how the 1975 manned Mars flyby spacecraft could explore asteroids in the Main Belt between Mars and Jupiter (middle link below). Its crew would, he explained, have at their disposal a 40-inch reflecting telescope intended primarily for high-resolution Mars photography during the flyby. Following its Mars flyby, the spacecraft would reach aphelion (its farthest point from the Sun) within the Main Belt. This would bring it to within 20 million miles of at least two major Main Belt asteroids.

Piloted flyby spacecraft over Venus with one-meter telescope in action.

In a February 1968 follow-on to the 1966 memorandum, Bellcomm engineer W. Grobman estimated that a one-meter (39.6-inch) reflecting telescope on board a flyby spacecraft would be capable of photographing objects as faint as 27.4 magnitude. For comparison, the 200-inch reflector on southern California's Mt. Palomar could photograph no object fainter than about 23.5 magnitude.



Grobman cited two factors that accounted for the flyby spacecraft telescope's superlative performance. First, the instrument would operate beyond Earth's obscuring atmosphere, well away from moonlight, aurorae, humidity, clouds, and city lights. Second, it would be capable of very long exposures.



A telescope in low-Earth orbit would circle the planet in about 90 minutes, so even with carefully controlled slewing could in most cases observe an astronomical target for no more than 45 minutes before losing sight of it behind the Earth. The flyby spacecraft telescope, on the other hand, would not follow a fast planet-centered orbit, and would spend most of its time far from any object that could block its view of the universe.



According to Grobman, the only obvious limit on exposure duration would be the ability of astronomical film to record arriving photons. He calculated that scientifically useful exposures lasting as long as 40 hours might be possible with existing films. He noted in passing, however, that radiation in interplanetary space might darken film. One solution, he wrote, would be to replace film with an unspecified electronic imaging system.

Spitzer Space Telescope infrared image of Messier 78, a nebula in the constellation Orion.

Hubble Space Telescope deep-field image of distant galaxies.

The flyby spacecraft telescope would be capable of recording spectra of very faint objects. Recording the spectra of distant galaxies would, Grobman explained, help to improve understanding of the relationship between galactic distance and speed of recession first noted by Edwin Hubble in 1929. Because the flyby spacecraft telescope would operate outside of Earth's atmosphere, the spectra it recorded could include regions of the electromagnetic spectrum invisible to Earth-bound telescopes, he added.



Grobman cited as another class of potential targets objects that change brightness over periods of an hour or less, such as the mysterious distant quasars (now known to be giant black holes in galaxy centers). The flyby spacecraft telescope, he wrote, would be capable of detecting subtle and rapid variations in the brightness of even very faint objects.



"Targets of opportunity" - that is, objects that appeared unexpectedly during the manned flyby mission - would be fair game for observation, Grobman added. Such targets might include supernovae and novae within or beyond our Milky Way Galaxy and comets newly arrived in the inner Solar System.

Hubble Space Telescope image of a Supernova 1994D (lower left) in Galaxy NGC 4526.

Spitzer Space Telescope infrared image of Comet Encke.

Grobman completed his memorandum after August 1967, when the U.S. Congress specifically forbade further NASA work on manned planetary flybys. Though no manned Mars/Venus flyby astronauts ever pointed a telescope at a distant galaxy or nearby asteroid, the Hubble Space Telescope in low-Earth orbit, the Spitzer Space Telescope in Earth-trailing solar orbit, and other automated instruments have decisively demonstrated the capabilities of space-based telescopes.



In the past decade and a half, NASA has worked toward placing large automated observatories into halo orbits around the Sun-Earth libration (L) points. Astronauts might voyage to the Sun-Earth L points to assist in deployment of new observatories and to upgrade and perform repairs on existing ones. Manned telescope servicing missions to the Sun-Earth L points could also serve as experience-building steps toward manned Mars missions (bottom link below).

Hubble Space Telescope image of red supergiant star V838 Moncerotis and "light echoes" on nearby gas and dust.

Hubble Space Telescope image of stars and planetary systems forming in the Carina Nebula.

Optical Astronomy on a Manned Planetary Flyby Mission - Case 710, W. D. Grobman, Bellcomm, Inc., February 8, 1968.



http://beyondapollo.blogspot.com/2010/03/planetary-jag-manned-mars-flyby-1966.html



http://beyondapollo.blogspot.com/2009/03/astronomy-from-piloted-mars-flyby-1966.html



http://beyondapollo.blogspot.com/2011/07/100-day-mission-to-sun-earth-l2-1999.html