Jumat, 03 Maret 2017

Robot rendezvous (1999)

As the year 1999 began, NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, was arguably closer to launching a Mars Sample Return (MSR) mission than ever before. About one martian year (roughly two Earth years) earlier, NASA had committed to the decade-long Mars Surveyor Program, the culminating mission of which was to be MSR.

By late 1998, JPL had settled on an MSR mission design based on the Mars Orbit Rendezvous (MOR) mode. This was not surprising, since the Pasadena laboratory had staunchly advocated MOR since the early 1970s. At that time, JPL was responsible for building the Viking Orbiter, and MSR missions in the late 1970s/early 1980s were expected to be based on Viking hardware. The MOR mode would require use of an Orbiter; MOR's chief rival, Direct-Ascent, would not because it would launch samples directly from the surface of Mars back to Earth. No Orbiter meant no role for JPL in Viking-based Direct-Ascent MSR; JPL thus supported MOR. This institutional preference became thoroughly ingrained by the early 1980s.

In MOR MSR's basic form, samples would reach Mars orbit in an ascent vehicle. An orbiter would perform rendezvous and collect the samples, then would depart Mars orbit for Earth. Splitting the Mars ascent and Earth return functions between ascent and orbiter vehicles would enable a smaller, lighter Mars lander than in Direct-Ascent, and thus would trim overall mission mass. The reduced mass of MOR MSR would mean that the mission could leave Earth on a smaller, cheaper launch vehicle or could include more science payload - for example, a rover for sample collection beyond the immediate landing site.

One can argue, however, that MOR increases mission complexity and thus risk. JPL's 1998-1999 MOR MSR plan aimed to reduce risk by collecting samples from two different martian sites using landers launched from Earth during two Earth-Mars transfer opportunities (specifically, in 2003 and 2005). After completing its 90-day sample collection mission, each lander would launch to Mars orbit a Mars Ascent Vehicle (MAV) bearing an Orbiting Sample (OS) canister. To help keep its MSR mission under a strict cost cap, NASA invited the French space agency, Centre National d'Etudes Spatiales (CNES), to provide the MSR orbiter.

At the August 1999 AAS/AIAA Astrodynamics Specialist Conference in Girdwood, Alaska, a team of engineers from JPL and another from JPL contractor Charles Stark Draper Laboratory (CSDL) presented papers in which they examined how the CNES orbiter might perform rendezvous with the 2003 and 2005 OSs. They proposed a complex three-phase MOR strategy for each OS consisting of preliminary, intermediate, and terminal rendezvous phases.

In 2003, OS preliminary rendezvous would begin with MAV liftoff. The 2003 MSR lander would be rated to function on Mars for 90 days, so its MAV would need to launch from Mars within 90 days of touchdown. The 2003 OS would thus reach Mars orbit no later than April 2004. To save money and ensure adequate development time, the JPL MSR mission would employ a simplified solid-propellant MAV with a spin-stabilized first stage and a second stage with only a simple guidance system.

In their paper, the JPL engineers noted that even small OS orbit dispersions could place significant rendezvous propulsion demands on the CNES orbiter. An OS dispersion of only 1° in inclination, for example, would require that the orbiter alter its velocity by an additional 60 meters per second to match orbits, which would require an additional 48 kilograms of propellants.

For their MOR calculations, they assumed that a MAV capable of reliably placing the OS into a circular orbit 600 kilometers above Mars (plus or minus 100 kilometers) and inclined 45° to the planet's equator (plus or minus 1°) could be developed. They assume that the OS would take the form of a 14-to-16-centimeter sphere covered with solar cells which would power a radio beacon. The OS power system would include no batteries, so the beacon would operate only when the cells were in sunlight.

Between July 24 and August 26, 2006, the CNES orbiter would arrive in 250-by-1400-kilometer Mars orbit inclined 45° to Mars's equator. Once there, it would activate its Radio Direction Finder (RDF) to begin a four-week hunt for the 2003 OS. The RDF, which would collect OS data for relay to controllers on Earth, would have a range of 3000 kilometers. The JPL engineers suggested that other spacecraft in Mars orbit (Europe's Mars Express, the U.S. Mars Surveyor 2001 orbiter, or a specialized U.S. navigation & communications orbiter proposed for launch in 2003) might augment data from the CNES orbiter's RDF.

On September 24, 2006, controllers on Earth would begin the intermediate rendezvous phase by commanding the CNES orbiter to perform the Nodal Phasing Initiation (NPI) maneuver, the first in a series of maneuvers over 19 weeks designed to nearly match orbits with the 2003 OS. Radio signal roundtrip travel time would gradually increase from 23 to 43 minutes over the 19 weeks as Mars and Earth moved apart in their Sun-centered orbits.

At the start of this phase, both OS and orbiter would be in orbits inclined about 45° to Mars's equator; however, their orbits would have different ascending and descending nodes (that is, they would cross the equator at different places) and thus different orbital planes. In the planned 2003 OS orbit, the nodes would shift along the equator at the rate of 6.09° per day. This shifting, called regression of the nodes, would occur because of irregularities in the martian gravity field. The NPI would adjust the CNES orbiter's orbit so that its nodes would shift at a slightly different rate, enabling it to gradually match nodes with the 2003 OS.

Between October 8 and November 5, 2006, Mars would be behind the Sun as viewed from Earth and largely out of radio contact. No maneuvers would occur during this solar conjunction period, though nodal phasing would continue.

The Nodal Phasing Termination maneuver on January 7, 2007, would see the 2003 OS and CNES orbiter in nearly the same orbital plane. At the end of the intermediate rendezvous phase (February 4, 2007), the orbiter would be two kilometers below and 400 kilometers behind the OS. In its slightly lower (thus slightly faster) orbit, the orbiter would close with the OS at a rate of 200 kilometers per day (about 8.3 kilometers per hour).

In their paper, the CSDL engineers proposed a "double coelliptic" rendezvous strategy for the week-long terminal rendezvous phase. The CNES orbiter would fire its rocket motor about two days before planned OS capture to place itself in an orbit only 0.2 kilometers lower than that of the OS. This would slows the closing rate to about 20 kilometers per day (about 0.8 kilometers per hour).

The orbiter would acquire the OS with its twin Light Detection and Ranging (LIDAR) lasers as it closed to within five kilometers. At a distance of 0.4 kilometers, the orbiter would perform several maneuvers to intersect the OS's orbit 80 meters ahead of the OS. As it crossed the OS's path, it would fire its motor again to precisely match orbits.

The orbiter would then keep station with the OS for four hours. During this period, controllers on the ground would check the orbiter's systems. If everything checked out as normal, they would then give it the go-ahead to perform OS capture. If all went as planned, the CNES orbiter would automatically capture the 2003 OS on February 11, 2007.

The 2005 OS preliminary rendezvous would overlap the 2003 OS intermediate rendezvous. For purposes of their study, the JPL engineers assumed that the 2005 MAV would deliver its OS to Mars orbit on October 8, 2006, the last possible day before the start of solar conjunction. The 2005 OS would be targeted to an orbit matching as closely as possible that planned for the CNES orbiter at the time it captured the 2003 OS.

Intermediate rendezvous in 2005 would begin immediately after 2003 OS capture (that is, at the end of the 2003 OS Terminal Rendezvous phase) on February 11, 2007. Nodal phasing would end after 13 weeks, on May 13, 2007, and the 2005 OS Intermediate Rendezvous phase would end on June 10, 2007.

The 2005 OS terminal rendezvous would resemble its 2003 counterpart. The CNES orbiter would capture the 2005 OS on June 17, 2007, then would begin a series of maneuvers over four weeks to place itself into the proper orbital plane for departure for Earth on July 21, 2007.

The JPL engineers calculated that each 10-meter-per-second velocity change during intermediate rendezvous would require about 8 additional kilograms of orbiter propellant and subsystem mass at launch from Earth, and that the orbiter would need to make velocity changes totaling 478 meters per second during intermediate rendezvous if it were to have a 99% probability of successfully capturing both the 2003 and 2005 OSs. This would imply a rendezvous propellant mass of 382.4 kilograms. They noted that the MSR Project required only a 99% probability of retrieving one OS, and that this level of reliability could be achieved with an orbiter capable of velocity changes totaling 349 meters per second (which implied a propellant mass of 279.2 kilograms).

The CSDL engineers added that a 99% probability of successfully retrieving one OS meant a 60% probability of retrieving both. They calculated that terminal rendezvous using the propellant-saving double coelliptic rendezvous strategy would require velocity changes totaling only a little more than one meter per second up to the 80-meter stationkeeping point, and no more than 4.6 meters per second from the 80-meter point up to capture.

Paraterraforming (1992)

In traditional terraforming, humans alter an uninhabitable world until higher plants and animals adapted to Earth conditions can survive unprotected on its surface. In an August 1992 paper in the Journal of the British Interplanetary Society, Richard L. S. Taylor argued that terraforming would require labor over many millennia to reach its goal. He proposed instead a technique he dubbed "paraterraforming," which would see relatively rapid construction of a "worldhouse" that would cover most of a world's surface with an air-tight "roof" between one and three kilometers high (image above).

Paraterraforming would offer other important advantages over traditional terraforming besides speed. A worldhouse could be constructed using technologies known since the 1960s, Lewis estimated. Terraforming, on the other hand, would demand technological breakthroughs. Initial investors in the paraterraforming project could live to see at least a small part of the uninhabitable world's surface roofed over and made to resemble Earth. The long timescale inherent in most traditional terraforming proposals, on the other hand, would mean that initial investors could expect to receive no gratification in return for their investment. Finally, paraterraforming's modular approach would allow "staged pay-as-you-go funding," so could proceed in fits and starts. Terraforming would require sustained high funding levels.

In his paper, Taylor emphasized Mars paraterraforming. He pointed out that Mars's gravity is only one-third as strong as Earth gravity, so terraformers would need to pile on an atmosphere 75% as massive as Earth's to give it an earthlike surface pressure. With only 28% of Earth's surface area, Mars might not contain enough gas in its crust and polar ice caps to create such an atmosphere, and importing gas from elsewhere in the Solar System might prove to be impractical. Taylor estimated that providing an earthlike surface pressure inside a two-kilometer-tall Martian Worldhouse (MWH) would require less than one-tenth as much gas as a terraformed Mars atmosphere.

Taylor proposed that MWH construction begin in a seismically stable area with little subsurface ice. The MWH roof would comprise inner and outer layers held in place by cables. Atmospheric pressure within the MWH would push its roof upwards, so supports within it would serve primarily to hold it down.

Taylor envisioned three types of MWH support towers. Inhabited Mars Support Towers (IMASTs) would resemble the 3.25-kilometer-high "vertical super-city" designed by the British architect W. W. Frischmann in 1965. Each would measure 110 meters across its foundation and consist of six load-bearing masts clustered around a hollow core outfitted to house 500,000 settlers. Mars Support Towers (MASTs), uninhabited IMASTs, could be converted into full-fledged IMASTs as martian population grew. IMASTs and MASTs would be spaced equidistantly six kilometers apart. Compression-Tension Towers (CTTs), uninhabited 30-meter-diameter tubes with tension cables running through their cores, would be spaced equidistantly two kilometers apart.

The first IMAST would provide a manufacturing and construction facility for MWH components. Six MASTs and 30 CTTs would be erected around it, yielding a habitable MWH "cell" 30 kilometers wide. Taylor envisioned adding MWH cells until eventually about 84% of Mars was roofed over.

The unroofed 16% of the planet would include Valles Marineris, a tectonic rift system with crustal layers. Taylor wrote that the abundance of mineral deposits found in Earth's rift zones suggested that Valles Marineris might provide materials for manufacturing MWH structures. Other unroofed areas would include the poles, which would provide ices and gases and serve as "dumping zones," and volcanoes taller than seven kilometers. The calderas of such volcanoes rise above most of the thin martian atmosphere; Taylor maintained that this would make them ideal locations for solar power generators.

He wrote that settlers might choose to flood with water areas of low elevation within the MWH to create lakes and seas. The towers standing in them would, he noted, need to be specially braced to stand against currents and waves.

Taylor then threw cold water on his paraterraforming concept and on the concept of planetary settlement in general, arguing that

An Ideal Home in orbit (1959-1960)

As Beyond Apollo readers in the United Kingdom may know, this weekend the 103rd Ideal Home Show draws to a close at Earls Court in London. Typically, the Ideal Home Show has had little to do with spaceflight. This has not, however, always been true. The Ideal Home Show in March 1960 had the theme of "A Home in Space." With help from Douglas Aircraft Company, the show's organizers built a life-size mockup of a plausible four-man Astronomical Space Observatory (ASO). W. Nissim, an engineer in the company's Advance Design Section, designed the ASO and wrote a report describing it to guide the builders. As many as 200,000 people toured the mockup, which stood more than three stories tall.

The ASO was envisioned as a spent-tank space station; that is, it would start out as a rocket stage filled with liquid propellants and would be converted into a pressurized habitat for astronauts after it expended its propellants by placing itself into low-Earth orbit. The spent-tank station concept may have originated with Wernher von Braun in the 1940s. In the late 1950s, several space engineers, including Krafft Ehricke of General Dynamics and Kurt Strauss and Caldwell Johnson of NASA's Manned Spacecraft Center, developed spent-tank station designs. Beginning in late 1964, von Braun urged that the concept be made part of NASA's proposed Apollo-based post-Apollo space program. By 1966, the Saturn S-IVB stage-based "wet workshop" (images at top) had become a key element of the Apollo Applications Program (AAP).
Nissim proposed that the ASO be built into the second stage of a 107-foot-tall, 17-foot-diameter chemical-propellant rocket. He envisioned launching the ASO from near-equatorial Christmas Island, located in the Indian Ocean northwest of Australia. The rocket's first stage, with three engines generating 150,000 pounds of thrust each, would expend 154,266 pounds of liquid hydrogen fuel and liquid oxygen oxidizer during 145 seconds of operation, boosting the second stage to a velocity of 9800 miles per hour.

The second stage would separate from the spent first stage, coast for eight seconds, then ignite its single 150,000-pound-thrust engine to boost itself to a velocity of 16,300 miles per hour. Following engine shutdown, the second stage would coast to an apogee (highest point above the Earth) of 300 nautical miles. At apogee, the engine would ignite a second time to boost the second stage to an orbital velocity of 17,000 miles per hour and circularize its orbit, which would be inclined 40° relative to Earth's equator. The second stage would burn a total of 86,788 pounds of liquid hydrogen and liquid oxygen to achieve its operational orbit.

A = second-stage rocket engine; B = tanks holding gaseous oxygen and nitrogen for liquid hydrogen tank purging and pressurization; C = streamlined launch shroud segment with solar cells on concave inner surface (one of four); D = Schmidt telescope; E = star tracker for accurate telescope pointing; F = Cassegrain telescope; G = loop antenna for radio astronomy; H = emergency reentry vehicle; I = airlock hatch for spacewalks; J = emergency reentry vehicle launch escape/deorbit rocket motor (in airlock); K = relaxation area restraint positions (one of two); L = hatch from central column to interior of liquid hydrogen tank; M = central column; N = common bulkhead separating liquid hydrogen and liquid oxygen tanks; O = food lockers; P = life support equipment; Q = sleep area; R = radiation-shielded compartment; S = space suit storage.
During launch and ascent to orbit, the initial four-man crew would ride in a conical emergency reentry vehicle with a dome-shaped nose, three fins, and a single solid-propellant motor. The emergency reentry vehicle would be mounted atop a six-foot-diameter cylindrical central column embedded in and protruding from the top of the second-stage hydrogen tank.

In the event of launch vehicle trouble during launch and ascent, the solid-propellant motor would ignite, blasting the emergency reentry vehicle to safety. The spent motor would then separate and the vehicle would descend to Earth nose first. During ascent, the astronauts would face forward in the direction of the vehicle's nose; during descent, their couches would pivot so that they would face in the direction of its tail. Shortly before landing, the emergency reentry vehicle would deploy a parachute to slow its descent.

Assuming, however, that they arrived safely in orbit, the astronauts would immediately begin to prepare the second stage for occupancy. First, they would turn it to maximize the amount of sunlight striking it and open valves in the second-stage engine. Solar heating would speed escape of any residual hydrogen through the engine nozzle into space.

Next, a space-suited astronaut would open a hatch in the emergency reentry vehicle leading into the airlock at the top of the central column. After sealing the hatch behind him, he would open a hatch into the radiation shelter, a section of the central column embedded within the hydrogen tank. There he would open a valve that would release into the hydrogen tank nitrogen gas stored in spherical tanks at the bottom of the second stage. The nitrogen would escape through the engine nozzle, purging the tank of any remaining hydrogen. The engine valves would then be closed.

A = second-stage rocket engine; B = tanks holding gaseous oxygen and nitrogen for liquid hydrogen tank purging and pressurization (five clusters); C = lower liquid oxygen tank bulkhead; D = liquid oxygen tank; E = common bulkhead separating liquid oxygen and liquid hydrogen tanks; F = bottom of central column; G = central column; H = sleep area; I = space suit storage; J = life support equipment access panel; K = lavatory; L = crew personal lockers; M = ventilation duct.
The astronaut would next open a hatch leading from the central column into the hydrogen tank and move to the tank's bottom end. There he would permanently seal the hydrogen outlet port leading to the engine by welding a cover over it or by injecting a plastic sealant. He would then return to the central column, seal the hatch behind him, and release nitrogen into the hydrogen tank to check for leaks. While his shipmates monitored the tank's internal pressure, he would return to the emergency reentry vehicle.

Assuming that pressure in the tank remained steady, a space-suited astronaut would enter the central column to release oxygen into the hydrogen tank. According to Nissim, the pressure in the tank would equal the atmospheric pressure on Earth at 10,000 feet of altitude. The atmosphere in the tank would, however, contain as much oxygen as occurs at Earth's sea level. Located in the same area as the nitrogen tanks, the spherical oxygen tanks would contain enough gas to supply the ASO crew for 45 days.

The three astronauts waiting in the emergency reentry vehicle would then enter the hydrogen tank and doff their space suits. They would cut away metal covers welded over pre-installed equipment and openings (for example, air ducts), then would remove equipment and furnishings stowed in the central column and install them in the tank.

The crew would also point the emergency reentry vehicle's nose at the Sun and open four petal-like streamlined launch shroud segments located between the top of the second stage and the bottom of the emergency reentry vehicle. Besides revealing a "storage area" containing folded astronomical instruments, this would expose to the Sun electricity-generating solar cells covering the concave inner surfaces of the shroud segments. Attitude control thrusters and gyroscopes would keep the station properly oriented as it revolved around the Earth. (Nissim, by the way, proposed fueling the attitude control thrusters with crew urine.)

Pointing the emergency rentry vehicle at the Sun would also help to regulate temperature on board the ASO. The open shroud segments, telescopes, and emergency reentry vehicle would partially shade the spent stage part of the station. Alternating blue and white stripes of equal area would cover its hull. The blue stripes would absorb sunlight while the white stripes would reflect it. Most heating in the converted hydrogen tank would come from on-board equipment and the astronauts' bodies. Nissim estimated that the interior of the spent stage would maintain a temperature of 72° Fahrenheit.

The emergency reentry vehicle would be powered down, so would lack a significant internal heat source. It would, however, be in direct sunlight whenever the ASO was over the Earth's day side, so would be colored white with thin blue stripes so that it would reflect most of the sunlight striking it.

With ASO electricity, life support, and thermal control up and running, an astronaut would don a space suit, enter the central column airlock, pump the air it contained into the converted hydrogen tank, and open a hatch leading to the station's exterior. Linked to the airlock by a thin cable, he would deploy astronomical instruments from the storage area between the top of the stage and the bottom of the emergency reentry vehicle. By operating above Earth's obscuring atmosphere, Nissim explained, the ASO's instruments would for the first time in history permit astronomical observations of the entire electromagnetic spectrum from gamma rays to very long radio waves.

After deploying and checking the instruments, the spacewalker would return to and repressurize the airlock, then rejoin his colleagues in the tank. After doffing his space suit, he would settle into a routine that would see two crew members on duty, one asleep, and one off duty at all times.

In their explanatory text for the mockup, the Ideal Home Show organizers wrote that the initial crew would return to Earth in the emergency reentry vehicle, which they called the "reentry Vehicle (nosecone)." This would mean that only the initial crew could reside in the station before it was abandoned. According to its designer, however, the ASO would operate "forever," with new four-man crews and supplies arriving by ferry spacecraft every 30 days.

Nissim did not specify how astronauts would transfer between ferry and ASO. His design lacked docking ports, so he might have meant for astronauts to spacewalk between the two vehicles. Ferry spacecraft would remain at the ASO only long enough to rotate crews and drop off supplies. The emergency reentry vehicle, on the other hand, would remain part of the ASO throughout its career, enabling crews to evacuate immediately in the event of catastrophic meteoroid puncture, fire, or massive life support failure.

International Lunar Resources Exploration Concept (1993)

By the end of 1992, the handwriting had been on the wall for the Space Exploration Initiative (SEI) for some time. President George H. W. Bush had launched the moon and Mars initiative on the 20th anniversary of the Apollo 11 lunar landing (July 20, 1989), but it had almost immediately run headlong into fiscal and political realities. The change of Presidential Administration in January 1993 was the final nail in SEI's coffin. Nevertheless, exploration planners across NASA continued to work toward SEI goals until mid-1993.

In February 1993, Kent Joosten, an engineer in the Exploration Program Office (ExPO) at NASA’s Johnson Space Center in Houston, Texas, proposed a plan for lunar exploration which, he hoped, would take into account the emerging realities of space exploration in the 1990s. His International Lunar Resources Exploration Concept would, he wrote, reduce "development and recurring costs of human exploration beyond low-Earth orbit" and "enable lunar surface exploration capabilities significantly exceeding those of Apollo." It would do these things by exploiting lunar oxygen as oxidizer for burning liquid hydrogen fuel brought from Earth, shipping most cargo to the moon separate from the crew, and relying on cooperation with Russia.

According to Joosten, a lunar lander making a direct flight from Earth's surface to the lunar surface that would arrive on the moon with empty oxidizer tanks and then reload with liquid oxygen mined and refined from lunar regolith (that is, surface material) would have half the mass of a lander that performed an Apollo-style Lunar-Orbit Rendezvous mission (itself a mass-saver) and brought to the moon oxidizer for the return trip from Earth. This would in turn permit a smaller launch vehicle, slashing costs.

One-way automated cargo landers, each rectangular in shape and capable of delivering 11 tons of payload to the moon's surface, would be assembled and packed in the U.S. and shipped to Russia in C-5 Galaxy or Antonov-124/225 transport planes, then launched on Russian Energia rockets from Baikonur Cosmodrome in Kazakstan. Joosten noted that launch teams at Baikonur could service two Energia rockets at the same time and that three Energia launch pads existed. An Energia would place a cargo lander into Earth orbit attached to a Russian "Block 14C40" upper stage that would then boost the lander toward the moon.

Shuttle-derived heavy-lift boosters would launch the piloted landers from Kennedy Space Center's twin Complex 39 Shuttle pads. The pads, monolithic Vehicle Assembly Building, and other KSC facilities would require modifications to support the new piloted lunar effort, but no wholly new facilities would need to be constructed, Joosten explained. The piloted lander, carrying an international crew and about two metric tons of cargo, would be placed into Earth orbit, then a new-design Trans-Lunar Injection Stage would put it on a direct trajectory to land near the pre-established automated oxygen production facilities.

Joosten's crew lander design outwardly resembled the "Eagle" transport in the 1970s TV series Space: 1999 (image at top of post). The crew compartment, a conical capsule modeled on the Apollo Command Module (but lacking a nose-mounted docking unit), would be mounted on the front of a horizontal, three-legged lander. At launch, the capsule would sit on top of the stack surmounted by a solid-propellant launch escape system. The three legs would fold against the lander's belly beneath a streamlined shroud during ascent from Earth. On the moon, the crew hatch would face downward, providing ready access to the surface via a ladder on the lander's single forward leg; on the launch pad, the hatch would permit horizontal access to the capsule interior much as did the Apollo Command Module hatch. The crew compartment windows would be inset into the hull and oriented to enable the pilot to view the landing site during descent.

The crew lander would land on and launch from the moon using four belly-mounted throttleable rocket motors. Soon after lunar touchdown, the lander would be reloaded with liquid oxygen from the automated oxygen plant. The entire lander would lift off the lunar surface for flight to Earth; no expendable descent stages would be left behind to clutter up the moon. Nearing Earth, the crew capsule would separate and orient itself for reentry by turning its Apollo-style bowl-shaped heat shield toward the atmosphere. The lander section, meanwhile, would steer toward a reentry point away from populated areas. The crew capsule would use a steerable parasail-type parachute. Joosten recommended recovering the crew capsule on land - perhaps at Kennedy Space Center - to avoid the greater cost of Apollo-style water recovery.

Joosten envisioned a three-phase lunar program, but provided details for only Phases 1 and 2. In Phase 1, three cargo landers would deliver to the target landing site a nuclear power system, an automated liquid oxygen production facility, robotic diggers, loaders, power supply, and propellant transport "carts," and a pressurized exploration rover and science equipment. The first piloted lander carrying two astronauts would then arrive for a two-week stay, during which they would check out the automated systems and explore using the pressurized rover. Several Phase 1 piloted missions to the same site would be possible.

In Phase 2, three cargo flights would deliver a second pressurized rover, an airlock module, consumables on a cart, and science equipment. A fourth cargo flight would deliver a four-person crew for a six-week stay. The crew would divide up two to a pressurized rover. The airlock module would include docking units so that the two rovers and the consumables cart could link to it, forming a small outpost. Phase 3 might see larger crew sizes and longer stay times; alternately, NASA might change direction and use technology developed for the lunar program (for example, the crew capsule and Shuttle-derived heavy-lifter) to send humans to Mars.