Astronaut Telescope Servicing at Earth-Sun L2 (1999)

Interplanetary space showing the positions of the Sun, Earth, Earth's orbit about the Sun, the Moon, the Moon's orbit about the Earth, and the five Earth-Sun Libration Points. Image credit: NASA.

The Earth-Moon and Sun-Earth Libration (L) points are not places in the sense that one can land on them and pick up rocks. Because of this, some space exploration planners perceive them to be unsatisfying destinations. The L points have, however, long been proposed as space transportation way stations and as radio relay and scientific instrument sites.

In 1999, the Decadal Planning Team (DPT), a secretive NASA-wide study group chartered by President William Clinton's Office of Management and Budget, identified astronomical observatories in "halo orbits" around the Sun-Earth L points as a key NASA goal for the early 21st century. These large and complex instruments would, among other tasks, seek to observe Earth-like worlds around other stars.

The NASA Exploration Team (NExT), the DPT's immediate successor, subsequently sought to incorporate the Sun-Earth L point emphasis into its piloted spaceflight planning. In a 20 December 1999 presentation to the NeXT, for example, NASA Johnson Space Center exploration planner Bret Drake examined ways that the Sun-Earth L points might aid future piloted Mars missions.

An automated solar observatory orbiting the Sun-Earth L1 point, 1.5 million kilometers from Earth, could provide Mars crews with early warning of solar flares, Drake explained. Radio relays in halo orbit about Sun-Earth L4, 60° ahead of the Earth along its Sun-centered orbit, and Sun-Earth L5, 60° behind the Earth along its orbit, could enable continuous radio communication between Earth and crews exploring Mars during superior conjunctions, when the Sun blocks line-of-sight radio contact between the two planets.

Drake hastened to add that the Sun-Earth L points would not be good staging places for piloted Mars missions. He explained that the trip to and from a Sun-Earth L point would add almost two months to the typical duration of a roundtrip Mars voyage that started from low-Earth orbit (LEO).

Piloted missions to Sun-Earth L points might, however, serve as experience-building intermediate steps between piloted LEO missions and piloted Mars missions. Drake suggested that L point missions could enable astronauts to experience interplanetary conditions (for example, solar radiation undiminished by Earth's magnetic field), yet would have one-way trip times as short as 25 days.

Drake proposed that NASA astronauts carry out a 100-day telescope-servicing mission to Sun-Earth L2, 1.5 million miles from Earth. The mission would employ Solar-Electric Propulsion (SEP) technologies and techniques first proposed in 1998 for NASA's Mars Design Reference Mission.

The mission would begin with the unmanned launch to LEO of a 32,975-kilogram telescope-servicing spacecraft comprising a 14,450-kilogram inflatable "mini-Transhab" crew module, a 4271-kilogram Apollo Command Module-shaped Earth Return Vehicle (ERV), and a 14,164-kilogram two-stage Chemical Propulsion Module. The spacecraft would reach LEO within the streamlined shroud of a next-generation expendable rocket called an Evolved Expendable Launch Vehicle-Heavy (EELV-H).

A Space Shuttle Orbiter would rendezvous with the telescope-servicing spacecraft in LEO so that astronauts could oversee inflation of the doughnut-shaped single-deck mini-Transhab and deployment of its twin electricity-generating solar arrays. They would install equipment and furnishings in the mini-Transhab and stock it with supplies, then would return to Earth.

A second EELV-H would place a 33,000-kilogram automated Solar-Electric Propulsion (SEP) Vehicle into LEO, where it would automatically deploy solar-array wings and dock with the telescope-servicing spacecraft. Over the next seven months, the SEP Vehicle would operate its electric-propulsion thrusters at perigee (the low point in its orbit about the Earth) to raise its apogee (the high point in its orbit).

The result of these SEP Boost Phase maneuvers would be a highly elliptical orbit loosely bound to the Earth. The SEP Vehicle would then detach from the telescope-servicing spacecraft and operate its thrusters at apogee to return to LEO for refurbishment and reuse.

Use of the SEP Vehicle to place the telescope-servicing spacecraft into a highly elliptical Earth orbit would dramatically reduce the quantity of chemical propellants required to leave LEO for Earth-Sun L2. SEP thrusters produce little thrust but can do so over long periods and expend little propellant. This approach would greatly reduce overall mission mass and the number of EELV-H and Shuttle Orbiter flights required to place the telescope-servicing spacecraft into LEO.

The telescope-servicing spacecraft would carry no crew during the SEP Boost Phase because it would pass through Earth's radiation belts repeatedly. Over time, this would subject the crew to an unacceptably high cumulative radiation dose.

Drake inserted into his telescope-servicing mission assembly-and-launch sequence an optional piloted mission that would fly only if the telescope-servicing spacecraft needed repairs following the SEP Boost Phase. A Shuttle Orbiter would deliver to LEO a maintenance crew, a small lifting-body Crew Taxi, and a chemical-propulsion rocket stage. The stage would rapidly boost the Taxi into a highly elliptical Earth orbit matching that of the telescope-servicing spacecraft.

The maintenance crew would rendezvous and dock with the telescope-servicing spacecraft. After completing the needed repairs, they would undock, fire the Crew Taxi's rocket motors at apogee to lower its perigee into Earth's atmosphere, perform reentry, and glide to a landing.

If, however, flight controllers on Earth determined that the telescope-servicing spacecraft in highly elliptical Earth orbit was healthy and that no repairs were needed, the Crew Taxi would deliver a four-person crew to the telescope-servicing spacecraft. After casting off the Taxi, they would ignite the telescope-servicing spacecraft's first chemical-propulsion stage at perigee to escape their loosely bound highly elliptical orbit and begin the 25-day voyage to Sun-Earth L2. They would then cast off the spent stage.

In the Sun-Earth L2 Operations Phase, the telescope-servicing spacecraft would enter a "halo parking orbit" centered on Sun-Earth L2. For 50 days the astronauts would service large next-generation telescopes in halo orbits around Sun-Earth L2, much as Space Shuttle crews in 1993, 1997, 1999, 2002, and 2009 serviced the Hubble Space Telescope in LEO. Drake suggested that during their down time between servicing calls they might conduct unspecified scientific research.

Their mission completed, the astronauts would ignite the second stage of the telescope-servicing spacecraft's Chemical Propulsion Module to begin return to Earth. About 25 days later, they would strap into the ERV capsule, undock from their home of the previous 100 days, reenter Earth's atmosphere, and parachute to a landing. The other components of the telescope-servicing spacecraft would burn up in Earth's atmosphere.

Even as Drake presented his Earth-Sun L2 servicing mission concept, NASA engineers conceived of a Gateway space station in halo orbit about Earth-Moon L1 as a base for observatory servicing and as a stepping stone to points all over the lunar surface. They envisioned that observatories needing servicing would ignite small thrusters to begin a slow transfer from their Earth-Sun L1 and L2 halo orbits to the vicinity of the Gateway. Once at Earth-Moon L1, they would be serviced by spacewalking astronauts, "cherry picker" booms, and teleoperated systems.

Flying formation with teleoperated systems, an advanced space telescope arrives in the vicinity of the Earth-Moon L1 Gateway. The twin red spheres carry imagers that supply information on the telescope to astronauts inside the Gateway. As they escort the telescope, a boxy teleoperated robot with several jointed appendages moves into the shadow cast by its multi-layer sunshield. Partially silhouetted against the Moon, the Gateway includes six solar arrays, a doughnut-shaped pressurized mini-Transhab habitat module, multiple docking ports, servicing equipment, and three rocket stages for unspecified missions. Please click on the image to enlarge. Image credit: NASA.

Cislunar space showing the positions of Earth, the Moon, the Moon's orbit about Earth, and the five Earth-Moon Libration Points. Image credit: NASA.

In January 2004, in the aftermath of the STS-107 Columbia Space Shuttle accident (1 February 2003) and at the start of the 2004 election cycle, President George W. Bush called for a new NASA program to take humans to the Moon and Mars. At first, the Vision for Space Exploration (VSE), as it became known, incorporated many elements of DPT/NExT.

Soon after Michael Griffin became NASA Administrator on 13 April 2005, however, the VSE veered away from DPT/NExT and toward the Constellation Program, which Griffin called "Apollo on steroids." Bush showed little interest in the VSE after he announced it, so did not intervene to keep his program on track.

Constellation and the VSE were mostly abandoned in 2009-2010 under President Barack Obama. The global economy was in crisis following the collapse of the U.S. housing market in 2008 and the near-collapse of the global financial system. Spaceflight, rarely a high priority, took a distant back seat to repairing the U.S. economy.

When Obama unveiled a new space plan in 2010, it resembled DPT/NExT more than Constellation. The Bush Administration's decision to cancel the Space Shuttle led to the most significant deviation from the DPT/NExT architecture: retention of Constellation's large rocket under the name Space Launch System. Resembling an oversized EELV-H, SLS replaced the Shuttle Orbiter and the solar-electric tug of the DPT/NExT plan. The Orion Crew Exploration Vehicle (CEV) replaced the lifting-body taxi.

Meanwhile, China launched a program to explore the Moon using robots. Chang'e 1 orbited the Moon in 2007-2009; Chang'e 2 orbited the Moon in 2010-2012 before leaving lunar orbit for a flyby of the Near-Earth Asteroid 4179 Toutatis; and Chang'e 3 landed on the Moon in late 2013.

Chang'e 4, targeted for the lunar farside hemisphere, landed successfully in January 2019. It transmits radio signals to Earth via the Queqiao satellite, which reached a halo orbit around Earth-Moon L2 in June 2018. In addition to relaying signals from Chang'e 4 and its rover to Earth, Queqiao also serves as a radio observatory remote from the radio noise of Earth.

A radio-relay satellite in Earth-Moon L2 halo orbit enables communication with spacecraft out of line-of-sight radio contact on the hidden farside hemisphere of the Moon. Image credit: NASA.

Sources

"Future Missions for Libration-point Satellites," R. Farquhar, Astronautics & Aeronautics, May 1969, pp. 52-56.

"Strategic Considerations for Cislunar Space Infrastructure," IAF-93-Q.5.416, W. Mendell and S. Hoffman; paper presented at the 44th Congress of the International Astronautical Federation, 16-22 October 1993.

"Representative Human Missions to the Sun-Earth Libration Point (L2) '100' Day Class Mission," SEL2 Ver. R, Bret G. Drake, NASA Johnson Space Center, presentation materials, 20 December 1999.

"'Invisible Planets' Gain Favor as Real Estate in Space," L. David, Space.com, 19 January 2000.

More Information

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L4

Lunar GAS (1987)

Riccioli Outpost (1990)

The red oval at left marks Riccioli crater, Paul Lowman's candidate site for a lunar geology/astronomy outpost. The crater is approximately round, but appears foreshortened because it is near the lunar limb. Image credit: NASA.

NASA held a workshop in August 1990 to examine candidate lunar base sites as part of the Space Exploration Initiative (SEI). U.S. President George H. W. Bush had announced SEI on 20 July 1989, the 20th anniversary of the Apollo 11 Moon landing. SEI aimed to return American astronauts to the Moon to stay and to carry out the first piloted Mars expedition. For most of its first year, SEI lacked a timetable, though in November 1989, The 90-Day Study, NASA's initial SEI blueprint, scheduled the return to the Moon for as early as 2001. On 11 May 1990, Bush called for American astronauts on Mars by 2019.

One candidate lunar base site was 156-kilometer-wide Riccioli crater. Riccioli is located southwest of Oceanus Procellarum, near the edge of the Moon's disk as viewed from Earth, just west of prominent dark-floored Grimaldi basin. Named by 17th-century astronomer-priest Giovanni Battista Riccioli for himself, the crater includes slumped crust blocks (graben) overlain with ejecta from the impact that blasted out the nearby multi-ringed Orientale basin, the youngest large basin on the Moon.

Heavily degraded Riccioli crater. The red oval marks a possible outpost site on the interior uplift. Light-colored ejecta from Mare Orientale (out of shot to the lower left) is discernible over much of the crater. Image credit: NASA.

Riccioli's ancient, complex geology and its position near the Moon's equator and western limb had drawn the gaze of geologist Paul Lowman. At the August 1990 workshop, he advocated for the crater's irregular interior uplift as the site for a geoscience outpost and astronomical observatory. In places, the interior uplift stands more than 800 meters above the crater floor.

Paul Lowman. Image credit: NASA

NASA put Lowman on its payroll in 1959. By some accounts, he was the agency's first geologist. He worked at NASA Headquarters in Washington, DC, then moved to the newly built NASA Goddard Space Flight Center in Greenbelt, Maryland, a Washington suburb. He trained Mercury, Gemini, and Apollo astronauts to identify and photograph Earth's geologic features from Earth orbit and participated in the development of Apollo lunar geology experiments. He wrote about future lunar mining as a member of the interagency Working Group on Extraterrestrial Resources; he also took part in an internal NASA study of a temporary lunar outpost based on Lunar Module spacecraft and other Apollo technology (please see "More Information" below).

After Apollo, Lowman participated in Skylab Earth observation experiments and the Landsat Program. The Earth-orbiting Landsat automated satellites sought resources and monitored the environment on Earth.

Lowman assumed that geologist-astronauts at Riccioli outpost would have at their disposal several rovers equipped as campers. He planned three traverses within Riccioli, each about 100 kilometers long with multiple stops. The traverses would each last several days.

Traverse 1 would begin with a sample stop just outside the outpost's front door. Lowman believed that the Riccioli interior uplift might include some of the oldest lunar crust. From there, the geologist-astronauts would drive across the dark mare to sample light plains material — probable ejecta from the Orientale basin — on Riccioli's northeast rim. The Orientale ejecta, he asserted, could contain pieces of mantle material from deep within the Moon.

Lowman's Traverse 2 would explore criss-cross grabens and rilles (canyons) in search of recent volcanism. Lowman hoped that the explorers might uncover water-rich minerals they could mine.

During Traverse 3, they would sample craters with dark haloes along the Riccioli southeast rim about 50 kilometers from the outpost. Lowman believed that the dark haloes could be signs of relatively recent volcanism; that the craters they surround could be volcanic vents and the haloes erupted volcanic material. Alternately, the impacts that blasted out the craters might have exposed ancient dark deposits buried beneath Orientale basin ejecta.

Lowman expected that geologist-astronauts would build on the exploration experience they gained in Riccioli crater to rove beyond its degraded walls. Riccioli is located in the Moon's "wild west," a region of complex geology that even today is in many ways mysterious. Lowman named as geologic exploration targets within a few hundred kilometers of Riccioli the ring mountains and small mare plains of Mare Orientale; the Reiner Gamma swirls, a prominent magnetic anomaly; the Marius Hills volcanic complex, a highly ranked Apollo candidate landing site; and bright Aristarchus crater.

Astronomers based at near-equatorial Riccioli outpost could, Lowman added, observe nearly the entire celestial sphere every month. He suggested that the generally level Riccioli crater floor could provide a stable platform for groups of sensitive astronomical instruments that needed to be kept carefully aligned to function properly. A cluster of carefully aligned small telescopes could, he noted, act as a single large telescope.

Riccioli crater's near-limb location meant that Earth would stand low in the eastern sky; low enough that at some locations the crater rim and central uplift could hide the home planet from view. Radio telescopes built out of sight of Earth could, he explained, operate without interference from terrestrial artificial and natural radio sources.

Lowman revealed a playful side when he proposed that Riccioli outpost might include a bright strobe light. This could be activated when the Moon was at first-quarter phase, when it stands high and half-lit immediately after sunset for observers on Earth. The Sun would not yet have risen at Riccioli crater, so the blinking strobe would stand out against the dark part of the first-quarter lunar disk.

SEI excited many space scientists, engineers, and enthusiasts, though neither the public nor the Congress supported it. The U.S. economy fell into recession in 1990; set against a backdrop of economic hardship, the Moon and Mars program appeared frivolous. SEI ended soon after President Bush left the Oval Office in January 1993. NASA, meanwhile, redoubled its efforts toward building the International Space Station in low-Earth orbit in cooperation with its long-time International Partners Europe, Canada, and Japan and with its old rival Russia.

Lowman, for his part, never stopped advocating for a lunar outpost, and Riccioli crater remained his favorite candidate outpost site. In 1996, taking into account new miniaturized space technology and capable robots, he proposed a mostly automated astronomy outpost in Riccioli crater built up using small, cheap automated landers. Lowman passed away a week after his 80th birthday on 29 September 2011.

Sources

A Site Selection Strategy for a Lunar Outpost — Science and Operational Parameters: Determining the Impact of Science and Operational Parameters for Six Sites on the Moon by Simulating the Selection Process, Conclusions of a Workshop, 13-14 August 1990, Solar System Exploration Division, NASA Johnson Space Center, Houston, Texas, pp. 31-36.

"Remembering Paul Lowman," Landsat Science (https://landsat.gsfc.nasa.gov/remembering-paul-lowman/ — accessed 30 December 2019).

"Paul Lowman: NASA's 76-Year-Old Maverick," NASA Goddard Space Flight Center, 11 September 2007 (https://www.nasa.gov/centers/goddard/news/series/moon/lowman_intro.html — accessed 30 December 2019).

More Information

As Gemini Was to an Apollo Lunar Landing by 1970, So Apollo Would Be to a Lunar Base By 1980 (1968)

Harold Urey and the Moon (1961)

Mission to the Mantle: Michael Duke's Moonrise

High Noon on the Moon (1991)

Apollo 16 Commander John Young leaps in the Moon's low gravity and salutes Old Glory. The bright morning Sun shines from the left (east) in this image, causing the Lunar Module Orion in the background to cast a west-pointing shadow. All Apollo landings took place during lunar morning. Image credit: NASA.

"Why does the Moon change shape?" It's a question astronomy educators hear often. The answer is that our planet's natural satellite does not change shape; it is, of course, always spherical. What changes is how the Sun illuminates the side of the Moon we can see.

The Moon, like most other Solar System moons, is a synchronous rotator; that is, the period of time it needs to rotate on its axis once is essentially equal to the period of time it needs to orbit its primary once. For the Moon, the time required for both one rotation about its axis and one revolution about the Earth is about 28 days.

That is why humans on Earth see only the Moon's Nearside hemisphere. The Farside hemisphere, always turned away from Earth, remained mysterious until 1959, when humans glimpsed it for the first time courtesy of the Soviet Union's Luna III spacecraft.

This adaptation of a NASA diagram by Bill Dunford displays the parts of the Moon that are lit by the Sun as viewed from a vantage point above the terrestrial and lunar north poles. Nothing about it is to scale. The Sun is out of frame to the right. Numbers are called out in the text below. 

We call the shape of the lighted part of the Moon as viewed from Earth its "phase." Traditionally, however, the first phase of the lunar day/night cycle is new Moon (1 on the lunar phase diagram), when Nearside has no lighted part. When new, the Moon is situated between the Earth and the Sun. In addition to being unlit, the Nearside is lost in the Sun's glare.

Occasionally the Moon crosses over the Sun; new Moon is the time of partial, annular, and total solar eclipses. An eclipse does not occur every time the Moon is new because the Moon's orbit about the Earth is inclined slightly (about 5.1°) relative to Earth's orbit about the Sun.

The disc of the Moon is about 0.5° wide as viewed from Earth. The Sun, though 400 times farther away than the Moon (about 149,600,000 kilometers versus 363,100 kilometers) is also 400 times bigger than the Moon (about 1,392,000 kilometers versus 3475 kilometers), so it appears to be the same size as the Moon (0.5° wide) in Earth's sky. This means that, during total eclipses, the Sun's ghostly corona becomes visible as the Moon blocks the bright disk of the Sun.

The Moon is, however, moving away from Earth at a rate of about four meters per century. In just a few million years, it will no longer be wide enough in Earth's sky to cause total solar eclipses. All eclipses after that will be either partial or annular.

About two days past new Moon, people on Earth can look west in evening twilight and glimpse a slender crescent Moon (2 on the lunar phase diagram). It is called a waxing ("growing") crescent. The horns of the waxing crescent point toward the east, away from the setting Sun. If one looks carefully, one might observe that the part of the Nearside that is not yet lit by the Sun is visible.

This is probably a good place to mention that the Earth seems to change shape as viewed from the Nearside hemisphere. When the Moon is new, the Earth is full. In fact, Earth phases are always the opposite of Nearside phases.

As seen from the Nearside, the full Earth is about four times larger than the full Moon (2° wide in the black lunar sky) and reflects about 75 times as much light. When the Moon is a waxing crescent, Earth is mostly full. This means that sunlight reflected off Earth can light the part of the Nearside that direct sunlight does not yet reach.

As on Earth, the Sun rises in the east on the Moon. The line between light and darkness — the terminator — advances westward a little faster than a typical human can comfortably jog. High mountains and crater rims catch the morning Sun's bright rays first. Viewed through even a modest-size telescope, they appear as isolated islands of light. As the Sun climbs higher, light fills in the plains, lowlands, and crater floors.

Seven days past new, the Nearside is half lit for observers on Earth (3 on the lunar phase diagram). This phase is called first quarter. The first-quarter Moon rises in the east as the Sun stands at noon, reaches its highest point at sunset, and sets in the west at midnight.

About 10 days past new, the Nearside is halfway between first quarter and full (4 on the lunar phase diagram). We call this phase waxing gibbous ("gibbous" means convex — the term refers to the shape of the advancing dawn terminator).

Fourteen days past new, the Nearside is fully lit by the Sun as viewed from Earth (5 on the lunar phase diagram). The full Moon is visible all night; it rises in the east as the Sun sets in the west, stands highest at midnight, and sets in the west as the Sun rises in the east. When the nearside is full, the Earth is new as viewed from the Moon.

When the Moon is full, the Earth stands between it and the Sun. For this reason, full Moon is when partial and total lunar eclipses — during which the shadow of the Earth falls on the Moon — can occur. As with solar eclipses, lunar eclipses do not occur at every full Moon because the Moon's orbit is tilted relative to Earth's orbit about the Sun.

Newcomers to the pleasures of amateur astronomy often turn their first telescope toward the Moon for the first time at full Moon. If one can stand the bright glare from the fully lit Nearside, one can examine many contrasting light and dark areas through a small telescope; many such albedo features (as they are known) are, in fact, best seen when the Nearside is fully lit. Of particular interest are the Nearside-spanning whitish-gray rays of the large impact crater Tycho.

All things considered, however, the fully lit Nearside appears bland; crater rims and mountains cast no shadows, so all sense of surface relief is absent. The Moon might as well be a painted billiard ball. Viewing the Moon when it is less than full — and focusing on the terminator — is, in my opinion, much more rewarding.

About 18 days past new, the Moon has reached waning (shrinking) gibbous phase (6 on the lunar phase diagram). It rises between dusk and midnight and is visible in clear skies in the west until mid-morning the next day. The terminator line, formerly the line of lunar dawn, becomes the line of lunar dusk. Darkness advances from east to west as light advanced two weeks before.

Twenty-one days past new, night reclaims the Nearside's eastern half. This phase is called last quarter (7 on the lunar phase diagram). For people on Earth, the Moon rises at midnight, stands highest at dawn, and sets at noon.

About 25 days past new, the crescent Moon — called the waning ("shrinking") crescent — rises in the east just before the Sun (8 on the lunar phase diagram). Its horns point westward, away from the Sun. The dark part of the Nearside is again lit by sunlight reflected off a nearly full Earth. A relatively small telescope reveals the advance of the sunset terminator; crater bottoms, lowlands, and plains grow dark, then mountains and crater rims slowly shrink and finally vanish in darkness.

If you look through a telescope at the crescent Moon before dawn, take care not to look at the Sun when it peeks above the horizon; eye damage will result. Instead, attempt to keep sight of the crescent Moon as fades into the blue sky of earthly day.

The end of Day 28 sees a new lunar day-night cycle begin (1 on the lunar phase diagram). The Moon stands between the Sun and Earth, lost in the Sun's glare, and it is again midnight at the center of the Nearside hemisphere.

The small basaltic plain Sinus Medii — Latin for "Central Bay" — marks the Nearside's center. Equatorial Sinus Medii was an early Apollo Program landing site candidate, but no Lunar Module (LM) spacecraft landed there. When it is midnight in Sinus Medii, it is high noon at the center of the rugged Farside hemisphere. The Farside's center is located on the lunar equator north of the impact crater Daedalus.

Changes in orbital geometry and lighting angles in the Earth-Moon system are today mainly of interest to stargazers amateur and professional, but a half-century ago it was different. Apollo missions were leaving Cape Kennedy, Florida, every few months bound for the Moon, and lighting conditions were a critical part of landing site selection and mission timing.

Conservative Apollo mission rules dictated that the LM should land only between 12 and 48 hours after sunrise at its target landing site, when the Sun would stand between 5° and 20° above the eastern horizon. At the appointed time, the Apollo mission Commander (CDR) and Lunar Module Pilot (LMP) would ignite the descent engine of their spindly-legged spacecraft over the Farside to slow it so that its orbit would intersect the lunar surface at its Nearside landing site.

As it approached its pre-planned landing site from the east, the LM would pitch up to point its descent engine and four round foot pads at the lunar surface. As the landing site became visible outside the twin triangular LM windows, the Sun would shine from behind the spacecraft. This would prevent it from shining into the astronauts' eyes. The shadow of the LM would then become visible on the surface, enabling the astronauts to gauge the size of lunar surface features to help them pick out a spot for a safe landing.

Because of limited supplies of avionics cooling water, battery power, and breathing oxygen, the longest an Apollo lunar surface mission could last was about 72 hours. The period during which Apollo explorers could gain experience working in lunar lighting conditions thus only spanned from 12 hours (the earliest permitted landing time) to five days (the latest permitted landing time of two days plus the maximum stay-time of three days) after dawn at the landing site.

In 1991, Dean Eppler, a geologist in the NASA Johnson Space Center (JSC) Lunar & Mars Exploration Program Office (LMEPO) with an interest in lunar geologic fieldwork, conducted a study of the effects on lunar surface operations of the whole range of lunar lighting conditions in support of Space Exploration Initiative (SEI) planning. SEI, launched amid great fanfare by President George H. W. Bush on 20 July 1989, aimed to complete Space Station Freedom, return American astronauts to the Moon to stay, and then launch humans to Mars. "To stay" implied that astronauts would need to land, drive, walk, and work on the Moon throughout its day-night cycle at multiple locations all over the Moon.

Eppler had help from a spaceflight legend. John Young (1930-2018) joined NASA in 1962 as a member of the second Astronaut Class ("the New Nine") and was a veteran of six space missions (Gemini III, Gemini X, Apollo 10, Apollo 16, STS-1, and STS-9), four of which he commanded. He was Chief of the Astronaut Office at JSC from 1974 until 5 May 1987, when he was made JSC Director Aaron Cohen's Special Assistant for Engineering, Operations, and Safety.

Apollo 16 Commander John Young (left) with Command Module Pilot Kenneth Mattingly (center) and Lunar Module Pilot Charles Duke (right). Image credit: NASA.

Though his new job was widely seen as punishment for candid views he expressed in the aftermath of the 28 January 1986 Challenger accident, Young tackled it with gusto. He delved into a wide range of technical and safety issues and distributed throughout NASA hundreds of memoranda offering advice. Young also made himself available to people such as Eppler (and, incidentally, to this author); that is, to individuals eager to learn from and commit to record Young's unique body of experience and knowledge.

Young first had an opportunity to observe the Moon's surface from lunar orbit when he served as Apollo 10 Command Module Pilot (CMP) in May 1969. He told Eppler that, viewed from a spacecraft in lunar orbit, the transition from the sunlit part of the Moon to the earth-lit part was sudden and that the eye adjusted almost immediately to the reduced light level. Features on the lunar surface remained almost as visible as they had been under direct sunlight, and it was even possible to pick out features within shadows in earth-lit areas.

Young reported that the change from the earth-lit part of the Moon to unlit portions of the Farside, out of reach of light from both Sun and Earth, was "dramatic." Nothing could be seen of the Moon's surface even at an orbital altitude of only a few tens of kilometers. The horizon was discernible only because stars were visible above it but not below it.

As Apollo 16 CDR in April 1972, Young piloted the LM Orion to a landing at Descartes, the only Apollo site entirely within the lunar highlands. The highlands, which cover about 80% of the Moon's surface, are lighter in hue than basaltic plains like Sinus Medii.

Young told Eppler that, in his opinion, landing a spacecraft equivalent to the Apollo LM would be possible at a site lit only by light reflected off the Earth. Landing in earthlight at a prepared site — that is, one with flashing strobes and electronic landing aids — would be easier than landing a helicopter at night on Earth, he added.

Young experienced the challenges of getting about on the lunar surface under low-angle sunlight soon after climbing down Orion's ladder at Descartes. Moving toward the Sun (eastward) was difficult because of its fierce glare, and moving away from the Sun (westward) was treacherous because shadows disappeared behind the rocks and crater rims that cast them. This created a washed-out landscape where obstacles were hard to see and avoid.

Moving north or south meant reduced glare and visible shadows. This is one reason why the first two Apollo flights that included a Lunar Roving Vehicle (LRV), Apollo 15 and Apollo 16, had pre-planned lunar traverses that were oriented generally toward north and south.

Image credit: NASA.

Image credit: NASA.

Image credit: NASA.

The photographs above, taken from the same location within the space of a few minutes by Apollo 16 LMP Charles Duke, give some sense of the difficulties posed by these lunar-surface lighting phenomena. The reader should bear in mind that early 1970s photographic film was less capable of capturing surface topography in challenging circumstances than were astronaut eyes.

The top image shows the view toward the glaring low-angle Sun. The middle image shows John Young at work near the Apollo 16 LRV. He is facing north. As the orientation of the shadows indicates, the Sun is located to the right of the field of view, so surface feature visibility is near optimum. Rocks, footprints, and LRV tracks are obvious.

The bottom image, taken facing west directly away from the low Sun, looks very different, but in reality displays a rocky landscape similar to that shown in the top and middle images. Apart from rocks close to Duke (and Duke's own helmet), however, surface features obscure their own shadows and thus are almost invisible.

Based on Young's observations and his own calculations, Eppler proposed schedules for operations at various lunar surface locations. He determined that in Sinus Medii the period from local dawn until 5.5 days after local sunrise would be optimal for walking, driving, and landing.

From 5.5 days to nine days after sunrise at Sinus Medii the Sun would hang within 20° of local vertical, with noon taking place on day seven. The near-vertical lighting angle would mean that terrain features would cast no shadows, making walking and driving difficult. A descending lander would cast a shadow, but only directly beneath the lander, where it would most likely not be visible to the pilot. Eppler advised that only "restricted surface operations" should occur during the near-noon period. Landings should take place only at prepared sites.

The period from nine to 28 days after sunrise at Sinus Medii would be optimal for surface activity, Eppler found, though lighting conditions would vary greatly over that span of time. Between nine and 14 days after sunrise, the Sun would lower toward the west and would again cast visible shadows (except toward the east, away from the Sun). A lunar lander approaching an outpost landing field from the east would have to contend with both direct solar glare and absence of a handy lander shadow. Sunset would occur on day 14, with a half-lit Earth shining high in the sky.

On day 21 — midnight at Sinus Medii — full Earth would light the landscape. Seven days later, with a half-Earth high in the sky, the Sun would rise again in the east. Surface activity could thus take place at Sinus Medii without break or restrictions for 24.5 days of the 28-day lunar day/night cycle; that is, from day nine after sunrise to day 5.5 after sunrise.

At the center of the Farside, the lighting situation would be very different. Starting 14 days after local dawn, the Sun would set and — with no Earth in the sky — the landscape would become lost in darkness. Only by using artificial lighting could astronauts find their way. Landings would be prohibited throughout Farside night except at prepared sites.

Eppler also examined lighting on the east and west lunar limbs (that is, on the edges of the Nearside hemisphere near the equator) and at the Moon's poles. The western limb would see the Sun set in the west 14 days after local sunrise with a full Earth on the eastern horizon. The lighted fraction of the Earth would decrease as night progressed.

Between day 23 and day 28 after sunrise at the western limb site, Earth would provide too little light for surface operations without artificial lights. It would become completely invisible at western limb sunrise — which would, of course, occur in the east.

The eastern limb would experience sunset while Earth was new, so would become very dark immediately. Eppler expected that a fat crescent Earth, located just above the western horizon, would provide adequate lighting for surface operations starting on day 19 after local sunrise. On day 21, Earth would be half lit, and it would be full on day 28, when the Sun would once again rise in the east.

The lunar poles would see Earth phases like those at Sinus Medii. Earth would hover, bobbing and tilting slightly, near the Nearside southern horizon for north pole sites and near the Nearside northern horizon for south pole sites.

The Sun would circle the horizon at a polar site, never setting. Astronauts would need to note its position on the horizon and take care not to turn directly toward it without adequate eye protection. In addition, local mountains and crater rims would occasionally block the Sun or Earth and some areas — mainly deep crater bottoms — would forever lie in cold shadow.

Sources

Lighting Constraints on Lunar Surface Operations, NASA Technical Memorandum 4271, Dean B. Eppler, NASA Johnson Space Center, May 1991.

Forever Young: A Life of Adventure in Air and Space, John W. Young with James R. Hansen, University Press of Florida, 2012.

More Information

What If an Apollo Lunar Module Ran Low on Fuel and Aborted its Landing? (1966)

Keep My Memory Green: Skill Retention During Long-Duration Spaceflight (1968)

Log of a Moon Expedition (1969)

Exploring Mars from Pole to Pole: MESUR Network (1991)

Pioneer Venus 2 releases its three small Venus atmosphere entry probes. Through artist license, the large probe is visible against the clouds of Venus; it would not in fact have been visible at the time the small probes were released. Image credit: NASA.

On 8 August 1978, NASA launched Pioneer Venus 2 (PV2) on an Atlas-Centaur rocket. The 904-kilogram spacecraft, known also as Pioneer Venus Multiprobe, released a 1.5-meter-diameter battery-powered atmosphere entry probe on 16 November and three 76-centimeter-diameter probes on 20 November.

On 9 December 1978, the five parts of PV2 entered the thick, hot Venusian atmosphere. The drum-shaped probe carrier burned up as planned at an altitude of 110 kilometers. Sturdy conical heat shields protected the spherical instrumented probes from aerodynamic heating. As drag slowed it, the large probe deployed a parachute.

Two of the small probes, which did not include parachutes, exceeded all expectations by surviving landing and transmitting data from the hellish Venusian surface. One, the Day Probe, transmitted for 67.5 minutes before succumbing to heat, pressure, and battery failure, setting a new world record for spacecraft endurance on Venus.

PV2 was the last U.S. planetary mission launched until 1989. NASA Ames Research Center (ARC), located near San Francisco, California, managed PV2 and its sister spacecraft, PV1 (the Pioneer Venus Orbiter).

In July 1991, ARC proposed a multiprobe system outwardly not too different from PV2, but intended to create a long-lived network of low-cost science stations on Mars. According to ARC's report on the concept, its network would reflect a design philosophy with "unique characteristics . . . derived from the Pioneer Project corporate memory."

Mars networks were first proposed in the early 1970s. Scientific advisory groups endorsed the network concept repeatedly in the following two decades as the best way to obtain global-scale weather and seismic data. In the late 1980s, at the behest of the NASA Headquarters Solar System Exploration Division (SSED), the Jet Propulsion Laboratory (JPL) Precursor Task Team included a network in its program of precursor robotic missions for paving the way for astronauts on Mars. In common with previous Mars network plans, the 1989 plan invoked spear-shaped penetrators to hard-land stations at low cost.

NASA ARC's Mars Environment Survey (MESUR - pronounced "measure"), on the other hand, invoked cheap rough-landing landers, or "stations," that would deploy protective airbags seconds before landing. MESUR would build up a "pole-to-pole" network of 16 stations during the 1999, 2001, and 2003 minimum-energy Mars launch opportunities.

Each 158.5-kilogram MESUR lander would leave Earth attached toa Mars atmosphere entry deceleration system and a simple cruise stage. Upon arrival at Mars, each would cast off its cruise stage and enter the atmosphere directly from its Earth-Mars trajectory at up to seven kilometers per second. The ARC report compared this with the Viking landers, which entered from Mars orbit at only 4.4 kilometers per second. The lander's heat shield, a two-meter-diameter flattened cone, would be designed to withstand atmosphere entry during planet-wide dust storms, when suspended dust particles might exacerbate shield erosion.

Partial cutaway of a MESUR station on the surface of Mars. Image credit: NASA Ames Research Center.

The ARC report acknowledged that the disk-shaped lander might bounce to rest on Mars in either "heads" or "tails" orientation, but rejected as costly and risky a mechanical system for tipping it upright. The ARC engineers opted instead for circular ports that would enable controllers to deploy instruments from either side of the station. Instruments might include imagers, an atmospheric structure experiment, gas analyzers, a weather station, a spectrometer, and a seismometer.

The report explained that solar cells were initially ARC's preferred MESUR power system, but analysis had shown that the number of cells that could be mounted on the lander's small surface would not generate enough electricity to drive its science instruments unless landings were limited to sites within 30° of the martian equator. This limitation was deemed unacceptable by the MESUR Science Definition Team, so engineers opted for a small (nine-kilogram) General Purpose Heat Source (GPHS) Radioisotope Thermal Generator (RTG) "brick" based on Ulysses solar polar orbiter/Galileo Jupiter orbiter RTG technology.

Sixteen MESUR landers would need 16 GPHS bricks over six years. The report noted that the entire MESUR Network would need less than half as much plutonium as the Cassini Saturn orbiter, which would carry two RTGs with 18 GPHS bricks each.

Cutaway of the MESUR Network launch shroud showing four MESUR landers (one is mostly obscured behind the lander support structure) and the solid-propellant Mars transfer orbit injection stage. Image: NASA Ames Research Center.

The MESUR mission would begin in 1999 with the launch of a single Delta II 7925 rocket from Cape Canaveral, Florida, with four MESUR landers mounted on a framework within its 9.5-foot-diameter streamlined launch shroud. After a solid-propellant upper stage placed them on course for Mars, the landers would separate from the framework to travel on "independent free-flyer trajectories" that would permit precise Mars landing site targeting. Three side-mounted landers would tumble after separation, but sloshing propellants in their cruise stages would gradually damp their gyrations.

The landers would discard their cruise stages 125 kilometers above Mars. Ten kilometers above the planet, each would deploy a pilot parachute, then cast off its heat shield and open its single main parachute. The landers would image the surface and collect atmospheric structure data during the final eight kilometers of descent.

Just two meters above the landing site, each lander would release its main parachute and inflate its airbags. A small rocket on the parachute would ignite to prevent it from settling over the lander.

The MESUR lander design would permit landings at sites up to six kilometers above the base datum, the martian equivalent of Earth's sea level. The base datum, referenced to the minimum Mars atmospheric pressure required for liquid water to exist on the surface, was established after Mariner 9 mapped the planet from orbit in 1971-1972. (In 2001, a new system referenced to the mean radius of Mars as measured by Mars Global Surveyor's MOLA instrument replaced the base datum.)

Though all 16 MESUR landers would carry the same suite of instruments, their individual landing sites would be selected to cater to different science requirements. The report advised that weather stations should be spaced widely over the planet, while seismic stations should form closely spaced "triads." These conflicting requirements forced a "compromise network design."

MESUR Network Stations 1 and 2 would land near each other on the north rim of Valles Marineris to form a "seismic pair." Station 3, at the foot of Olympus Mons in Tharsis, would also emphasize seismic research. Station 4 would aim to extend the weather record for Chryse Planitia, where Viking 1 accumulated data from 1976 to 1983.

The Tharsis hemisphere of Mars showing proposed positions of MESUR stations. See text for explanation. Image credit: NASA.

In 2001, two Delta II 7925s would launch 20 days apart bearing four more MESUR landers and a communications relay orbiter, respectively. The latter payload, based on an existing Earth-orbital comsat design, would serve as radio relay for the expanding network, enabling MESUR stations to return data from sites all over the martian surface.

It would reach Mars in 10 months on a slow "Type II" trajectory to reduce the amount of propellant it would need to slow down so that the planet's gravity could capture it. Launch of the communications orbiter would be delayed until 2001 in order to spread its cost over a longer period.

With the successful arrival of the four 2001 stations, a "minimal network" would be in place on Mars. Station 5, on the Marineris north rim, would create a "seismic triad" with Stations 1 and 2, while Station 6, northwest of Olympus Mons, would create a seismic pair with Station 3. Station 7, east of Solis Planum ("a region of known dust storm activity"), and Station 8, in western Acidalia Planum, would expand martian meteorological coverage.

The final two MESUR Delta II 7925 launches in 2003 would boost four landers each on course for Mars. Stations 9 and 10 would be located near the north and south poles, respectively, while Station 11 would report weather conditions in Aonia Terra, southwest of the great Argyre basin. Stations 12 (northwest Hellas), 13 (Elysium Planitia), and 14 (Deuteronilus Mensae) would further extend martian meteorological coverage.

Station 15 (Sirenum Terra) would form a Tharsis seismic triad with Stations 3 and 6. Station 16, in Syrtis Major on the side of Mars opposite Olympus Mons, would create a seismic pair with Station 13 and, with the Tharsis triad, enable the size of Mars's core to be determined.

The Syrtis Major hemisphere of Mars showing proposed positions of MESUR stations. See text for explanation. Image credit: NASA.

The entire 16-station network and its communications orbiter would function for at least a martian year (a little more than two Earth years). This would mean that the 1999 stations would have to endure for three martian years (6.5 Earth years), while the 2001 stations and communications orbiter would need to function for two martian years (4.3 Earth years).

In its 1991 strategic plan, published the same month as ARC's MESUR report, the SSED dubbed MESUR its "baseline plan" for a Mars network mission. In November 1991, NASA elected to move MESUR Phase A development to JPL, where the project was split into two parts.

MESUR Network would be preceded by MESUR Pathfinder, a single-spacecraft mission for technology testing. Pathfinder was built larger than the the planned MESUR landers so that it could deliver to Mars a six-wheeled "microrover." JPL also opted for solar power in place of NASA ARC's RTG bricks and a petal system to permit it to flip itself upright and release the rover instead of small instrument deployment ports.

In 1994, in the wake of the Mars Observer failure, NASA funded the Mars Surveyor Program in place of MESUR Network. Work continued on Pathfinder under the auspices of NASA's low-cost Discovery Program, however, and it landed successfully on Mars on 4 July 1997.

Mars Pathfinder Lander (background) and Sojourner rover. Image credit: NASA.

Sources

Mars Environmental Survey (MESUR) Science Objectives and Mission Description, NASA Ames Research Center, 19 July 1991.

Solar System Exploration Division Strategic Plan: Preparing the Way to the New Frontier of the 21st Century, Special Studies Office, Space Telescope Science Institute, July 1991.

More Information

Pioneer Mars Orbiter with Penetrators (1974)

Prelude to Mars Sample Return: The Mars 1984 Mission (1977)

Mission to the Mantle: Michael Duke's Moonrise (1999-2009)

This NASA image of the gibbous Moon by photographer Lauren Harnett includes an intruder — the International Space Station (ISS) (lower right). The Moon, last visited by humans in December 1972, is about 384,400 kilometers away; ISS, permanently occupied since November 2000, is about 1000 times nearer Earth.

A casual glance at the Moon's disk reveals signs of ancient violence. Nearside, the lunar hemisphere we can see from Earth, is marked by gray areas set against white. Some are noticeably circular. The Apollo expeditions revealed that these relatively smooth basalt plains are scars left by large impactors — comets or asteroids — that pummeled the Moon more than 3.5 billion years ago. These gray areas cover about 20% of the lunar surface. They are concentrated on the nearside, the lunar hemisphere that faces the Earth.

An Earth-based observer cannot view the largest and oldest giant impact basin because it is out of view on the Moon's hidden farside. South Pole-Aitken (SPA) Basin is about 2500 kilometers wide, making it perhaps the largest impact scar in the Solar System. Lunar Orbiter data revealed its existence in the 1960s, though little was known of it until the 1990s, when the U.S. Clementine and Lunar Prospector polar orbiters mapped surface chemistry over the entire Moon. Their data showed that the basin floor probably includes material excavated from the Moon's lower crust and upper mantle. In the first decades of the 21st century, laser altimeters on the U.S. Lunar Reconnaissance Orbiter (LRO) and Japanese Kaguya spacecraft confirmed that SPA includes the lowest places on the Moon.

Lunar hemispheres centered on the Moon's highest point (left) and lowest point (right). Both occur in the Moon's Farside hemisphere and are believed to be associated with the excavation of the South Pole-Aitken Basin perhaps 4 billion years ago. On this U.S. Geologic Survey topographic map, blue indicates low areas and gray and black indicate high areas. 

South Pole-Aitken (SPA) Basin with major features labeled. The 140-kilometer-wide crater Antoniadi includes a 12-kilometer-wide unnamed crater, the floor of which is more than nine kilometers below the mean lunar radius (the lunar equivalent of Earth's sea level). It is the lowest point on the Moon. Image credit: NASA/DSFPortree.

Michael Duke, a retired NASA Johnson Space Center geologist with the Colorado School of Mines, participated in both Apollo and 1990s lunar explorations. In 1999, Duke was Principal Investigator (PI) leading a team that proposed a robotic SPA sample-return mission in NASA's low-cost Discovery Program. To fit under Discovery's mission cost cap of $150 million (in Fiscal Year 1992 dollars), Duke's team proposed "the simplest-possible mission" — a single lander with no sample-collecting rover, a lunar-surface stay-time of just 24 hours, and a low-capability lunar-orbiting radio-relay satellite (needed because farside is not in line-of-sight radio contact with Earth). Believing that these limitations added up to a high risk of mission failure, NASA rejected the 1999 Discovery proposal.

In 2002, however, the National Research Council's planetary science Decadal Survey declared SPA sample return to be a high scientific priority and, at the same time, proposed a new class of competitively selected medium-cost missions. The latter marked the genesis of NASA's New Frontiers Program, which originally had a cost cap per mission of $700 million.

The New Horizons Kuiper Belt Object (KBO) flyby mission was already under development when NASA created the New Frontiers Program. NASA gave New Frontiers a highly visible first mission by adopting New Horizons into the program. Selection of the KBO mission came to be regarded as the first New Frontiers proposal cycle, though it included no competition. NASA had taken a similar approach when it made Mars Pathfinder its first Discovery Program mission in 1992.

Geologist Michael Duke in 2004. Image credit: NASA.

Duke's team immediately began to upgrade its SPA proposal for the second New Frontiers proposal cycle. In October 2002, Duke described the new SPA mission design at the 53rd International Astronautical Federation Congress (the Second World Space Congress) in Houston, Texas. To avoid tipping off competing New Frontiers proposers, his paper provided only limited technical details.

Duke argued that the SPA sample-return mission could collect ancient deep crust and mantle rocks without a costly rover. Clementine and Lunar Prospector had shown that at least half of the surface material in the central part of SPA was native to the basin, so stood a good chance of having originated deep within the Moon.

Furthermore, Apollo demonstrated that any lunar site is likely to yield a wide assortment of samples because the Moon's low gravity and surface vacuum enable asteroid impacts to widely scatter rock fragments. The Apollo 11 mission to Mare Tranquillitatis, for example, found and returned to Earth rocks blasted from the Moon's light-hued Highlands. Duke proposed that the SPA sample-return lander sift about 100 kilograms of lunar dirt to gather a one-kilogram sample consisting of thousands of small rock fragments. These would have many origins, but a large percentage would be likely to have originated in the Moon's deep crust and mantle.

A SPA sample-return lander sifts lunar dust in quest of small fragments of lower crust and upper mantle material. The gray dome mounted sideways on the right side of the lander, above the sample arm attachment point, is the sample-return capsule for carrying a one-kilogram sample through Earth's atmosphere. Image credit: NASA.

NASA rejected the Discovery SPA mission in part out of concern for lander safety. Duke noted that, with the New Frontiers Program's $700-million cost cap, the SPA sample-return mission could include two landers. This would provide a backup in case one crashed. He pointed out, however, that automated Surveyor spacecraft of the 1960s had found the Moon to be a relatively easy place on which to land even without the benefits of 21st-century hazard-avoidance technology. Two landers would also increase the already good chance that the mission could collect samples representative of the basin's earliest history.

A $700-million budget would also enable a relay satellite "more competent" than its bare-bones Discovery predecessor. It might be placed in a halo orbit around the Earth-Moon L2 point, 64,500 kilometers behind the Moon as viewed from Earth. From that position, the satellite would permit continuous radio contact between Earth and the landers. A satellite in lunar orbit could remain in line-of-sight contact with both the landers and Earth for only brief periods.

NASA had argued that a single day on the Moon provided too little time to modify the SPA Discovery mission if it suffered difficulties. The SPA New Frontiers mission would, therefore, remain on the Moon for longer. Duke noted, however, that stay-time would probably be limited to the length of the lunar daylight period (14 Earth days) because designing the twin landers to withstand the frigid lunar night would boost their cost.

In February 2004, Duke's mission — christened Moonrise — became one of two SPA sample-return missions proposed in the second New Frontiers proposal cycle. In July 2004, NASA awarded Moonrise and a Jupiter polar orbiter called Juno $1.2 million each for additional study. In May 2005, the space agency selected Juno for full development.

Juno's selection did not end proposals for SPA Basin sample-return, though it did mark the beginning of the end of Duke's involvement. In the third New Frontiers proposal cycle, which began in 2009, a Jet Propulsion Laboratory/Lockheed Martin/Washington University in St. Louis team led by Brad Jolliff, Duke's deputy PI in the 2003-2004 cycle, proposed a SPA Basin mission called MoonRise. In 2011, the SPA sample-return mission was again selected as a New Frontiers finalist, but it lost out in the final selection to the OSIRIS-Rex asteroid sample-return mission. MoonRise was not selected as a finalist in the 2017 New Frontiers cycle.

Sources

"Sample Return from the Lunar South Pole-Aitken Basin," M. Duke, Advances in Space Research, Volume 31, Number 11, June 2003, pp. 2347-2352.

"NASA Selects Two 'New Frontiers' Mission Concepts for Further Study," D. Savage, NASA Press Release 04-222, NASA Headquarters, 16 July 2004.

NASA Facts: MoonRise - A Sample-Return Mission From the Moon's South Pole-Aitken Basin, NASA Facts, JPL 400-1408, June 2010.

"MoonRise: Sample Return from the South Pole-Aitken Basin," L. Akalai, B. Jolliff, and D. Papanastassiou; presentation to the International Planetary Probe Workshop, Barcelona, Spain, 17 June 2010.

Personal communication, B. Jolliff to D. Portree, 3 March 2018.

More Information

Peeling Away the Layers of Mars (1966)

An Apollo Landing Near the Great Ray Crater Tycho (1969)

Catching Some Comet Dust: Giotto II (1985)

Lunar GAS (1987)

SEI Swan Song: International Lunar Resources Exploration Concept (1993)

In the top image, the Soviet Union's two-stage Energia heavy-lift rocket and Buran reusable shuttle orbiter ride a transporter to a launch pad at Baikonur Cosmodrome in Kazakhstan. A sturdy armature designed to hoist the combination upright on the pad obscures Energia's lower half. In the bottom image, 59-meter-tall Energia stands on a launch pad bearing Polyus, an experimental military payload developed in response to the U.S. Strategic Defense Initiative. After the Soviet Union crumbled and Russia became a potential international supplier of rockets and spacecraft, hopeful NASA advance planners tentatively tapped Energia to launch hardware for piloted Moon and Mars missions. Image credit: NPO Energia.

By the close of 1992, the handwriting had been on the wall for the Space Exploration Initiative (SEI) for more than two years. President George H. W. Bush had launched his Moon and Mars exploration initiative on the 20th anniversary of the Apollo 11 lunar landing (20 July 1989), but it had almost immediately run headlong into a minefield of fiscal and political difficulties. 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 into early 1994.

In the same period, the Soviet Union was falling apart. Even as Bush called on NASA to return astronauts to the Moon and launch them onward to Mars, Soviet domination in eastern Europe collapsed, then the Soviet Union itself began to disintegrate. A bungled coup d'etat in August 1991 undercut the authority of Soviet President Mikhail Gorbachev and led to the official demise of the Soviet Union on 26 December 1991. The largest state on Earth divided into more than a dozen countries, with the Russian Federation under President Boris Yeltsin emerging as the most significant.

The end of the U.S.-Soviet Cold War created dangers and opportunities. Some feared that, impelled by economic chaos in the former Soviet Union, scientists and engineers would sell their skills and knowledge abroad, leading to unprecedented global nuclear proliferation.

Others noted that high-level Soviet space officials had begun to peddle their space hardware at important aerospace meetings in the late 1980s. They saw an opportunity to, among other things, save the U.S./European/Japanese/Canadian Freedom Space Station from cancellation. Yeltsin and Bush agreed to wide-ranging space cooperation in June 1992, partly in the hope that NASA money might help to forestall an exodus of Russian aerospace talent.

In February 1993, Kent Joosten, an engineer in the Exploration Program Office (ExPO) at NASA's Johnson Space Center (JSC) in Houston, Texas, proposed a plan for lunar exploration which, he hoped, would take into account the emerging realities of post-Cold War space exploration. His International Lunar Resources Exploration Concept (ILREC) 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 the abundant oxygen in the lunar regolith (that is, surface material) as oxidizer for burning liquid hydrogen fuel brought from Earth, shipping most cargo to the Moon separate from crews, employing Earth-based and Moon-based teleoperations, and cooperating with the Russian Federation.

Joosten's concept was a variant of the Lunar Surface Rendezvous (LSR) mission mode. The Jet Propulsion Laboratory (JPL) in Pasadena, California, put forward LSR in 1961 as a candidate mode for achieving President John F. Kennedy's goal of a man on the Moon by the end of the 1970s. In 1962, after NASA selected Lunar Orbit Rendezvous (LOR) as its Apollo lunar mission mode, the LSR scheme faded into obscurity. Joosten's concept was not inspired by the early 1960s scenario; instead, his work drew upon contemporary In-Situ Resource Utilization (ISRU) and Mars surface rendezvous techniques proposed for use in NASA's Mars Design Reference Mission 1.0 and Martin Marietta's Mars Direct scenario.

The Apollo LOR mode was designed to permit the U.S. to reach the Moon quickly and relatively cheaply, not to support a sustained lunar presence. It split lunar mission functions between two piloted spacecraft, each of which comprised two modules. Modules were discarded after they fulfilled their functions.

Joosten's ILREC piloted moonship would be roughly intermediate in size between the Apollo Lunar Module (LM) (left) and the Apollo Command and Service Module (CSM) (right). This NASA artwork from 1966 is a partial cutaway showing two blue-clad astronauts moving from the CSM to the LM in preparation for undocking and landing on the Moon. A third astronaut, who will remain in lunar orbit, awaits LM undocking strapped into his CSM couch.

At the start of an Apollo lunar mission, a Saturn V rocket launched a Command and Service Module (CSM) mothership and a Lunar Module (LM) Moon lander. The mighty rocket's S-IVB third stage boosted the CSM and LM into a parking orbit about the Earth; then, about 90 minutes later, reignited to push itself, the CSM, and the LM out of Earth orbit toward the Moon. This maneuver, called Trans-Lunar Injection (TLI), marked the real start of the lunar voyage.

After TLI, the CSM separated from the spent S-IVB, turned end-for-end, docked with the LM, and extracted it from the S-IVB. The S-IVB then vented propellants to change its course so that it would not interfere with CSM/LM navigation. Beginning with Apollo 13, the S-IVB was intentionally crashed on the Moon to trigger seismometers left behind by previous Apollo expeditions.

As they neared the Moon, the Apollo crew fired the CSM engine to slow down so that the Moon's gravity could capture the joined Apollo spacecraft into lunar orbit. The LM then separated from the CSM bearing two of the astronauts and descended to the lunar surface using the engine in its Descent Stage.

After a maximum of three days on the Moon, the Apollo lunar crew lifted off in the LM Ascent Stage using the Descent Stage as a launch pad. The astronaut in the CSM performed a rendezvous and docking with the Ascent Stage in lunar orbit to recover the moonwalkers — hence the name Lunar Orbit Rendezvous — then the crew discarded the LM Ascent Stage and fired the CSM engine to depart lunar orbit for Earth. Nearing Earth, they cast off the CSM's drum-shaped Service Module and reentered Earth's atmosphere in its conical Command Module (CM).

According to Joosten, a spacecraft that flew from Earth to the lunar surface, arrived on the Moon with empty oxidizer tanks, and reloaded them for the trip home with liquid oxygen mined and refined from lunar regolith, could have about half the TLI mass of an equivalent LOR spacecraft. The Apollo 11 CSM, LM, and spent S-IVB stage had a combined mass at TLI of about 63 metric tons; the ILREC spacecraft and its spent TLI stage would have a mass of about 34 metric tons. This substantial mass reduction would permit use of a launch vehicle smaller than the Apollo Saturn V, potentially slashing lunar mission cost.

Lunar regolith is on average about 45% oxygen by weight. According to Joosten, literally dozens of lunar oxygen (LUNOX) extraction methods are known. He listed 14 as examples, including one, Hydrogen Ilmenite Reduction, for which the U.S. Patent Office had issued a patent to the U.S.-Japanese Carbotek/Shimizu consortium.

Joosten assumed that an automated LUNOX extraction process involving "solid-state high-temperature electrolysis" could produce 24 metric tons of LUNOX in cryogenic liquid form per year. He estimated that the process would need between 40 and 80 kilowatts of continuous electricity, and suggested that a nuclear reactor would be the best power-supply option. Such a reactor would have ample reserve power for charging electrically powered teleoperated mining vehicles and could supply crew electricity needs when astronauts were present.

Joosten acknowledged that ILREC emphasized technologies "in somewhat different areas than most exploration scenarios." Among these were teleoperated surface vehicles and surface mining and processing. On the other hand, the technological areas it emphasized had a "high degree of terrestrial relevance," a fact which, he argued, might prove to be a selling point for the new piloted lunar program.

Automated exploration missions would precede the new piloted lunar program. These might take the form of Lunar Scout orbiters and Artemis Common Lunar Landers, both JSC-proposed projects. The automated missions would have some "science linkages," Joosten explained, but would serve mainly to locate landing sites with abundant oxygen-rich regolith, perform ISRU experiments under real lunar conditions using real lunar materials, and map candidate landing sites to enable mission planners to certify them as safe for landings and rover traverses.

The NASA JSC engineer envisioned a three-phase piloted lunar program, though he provided details only for Phases 1 and 2. In Phase 1, three cargo landers would deliver equipment to the target landing site ahead of the first piloted mission. Flight 1 of Phase 1 would deliver the nuclear reactor on a teleoperated cart and the automated liquid oxygen production facility (the latter would remain attached to its lander); flight 2 would deliver teleoperated diggers, regolith haulers, oxygen tankers, and carts for auxiliary fuel-cell power and consumables resupply; and flight 3 would deliver a pressurized Moon bus exploration rover and science equipment for the astronauts who would reach the Moon on flight 4.

Following launch on an Energia rocket, translunar injection, and an Earth-moon voyage lasting up to about a week, a U.S.-built cargo lander bearing a self-deploying LUNOX regolith processing payload descends toward the lunar surface on a direct-descent trajectory. The lander is arranged horizontally, not vertically, to reduce the risk of tipping and, as important, to provide the astronauts who will follow it to the Moon with easy access to its cargo. Image credit: NASA.

After touchdown, the LUNOX regolith processing payload pivots into vertical operational position and deploys ramps so that teleoperated regolith hauler rovers (two are shown on the left side of the image) can reach its screen-covered input hopper. Meanwhile, a teleoperated tanker rover (right) collects and stores LUNOX in preparation for the arrival of a piloted ILREC spacecraft. Image credit: NASA.

An Energia-launched cargo lander slowly lowers a U.S.-built pressurized Moon bus lunar rover to the surface ahead of the arrival of the first two-person ILREC crew. Image credit: NASA.

The one-way automated cargo landers, each rectangular in shape and capable of delivering 11 metric 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 Energia rockets from Baikonur Cosmodrome, a Russian enclave in independent Kazakhstan. The Soviet Union's Energia heavy-lift rocket and Buran reusable shuttle were developed beginning in 1976 in response to the planned U.S. Space Shuttle. Energia replaced the Soviet answer to the U.S. Saturn V rocket, the N-1, which was cancelled in 1974 after four failed test flights. 

In contrast to the N-1, Energia flew successfully both times it was launched. Energia payloads were required to perform a short burn after they separated from the rocket so that they could achieve a stable orbit about the Earth. Polyus, launched 15 May 1987, did not orient itself properly ahead of the burn and did not reach orbit, while the unpiloted Buran completed a single orbit as planned and landed on a Baikonur runway on 15 November 1988. 

Based on data Russia provided to NASA, launch teams at Baikonur could prepare two Energia rockets for launch simultaneously. Three Energia launch pads were available — two originally built for the Soviet N-1 Moon rocket and an all-new pad. Energia could launch a 5.5-meter-diameter canister containing a U.S.-built cargo lander attached to a Russian "Block 14C40" upper stage. Following an Earth-orbit insertion burn, the upper stage would perform a TLI burn, boosting the cargo lander toward the Moon.

Shuttle-derived heavy-lift boosters would launch Joosten's piloted landers from the twin Kennedy Space Center (KSC) Complex 39 pads. The pads, monolithic Vehicle Assembly Building, and other KSC facilities, most of which were originally constructed in the 1960s for the Apollo Moon program, were modified in the 1970s to serve the Space Shuttle. They would require new modifications to support the ILREC program; Joosten assured his readers, however, that no wholly new facilities would need to be constructed at the Florida spaceport.

Joosten considered both Shuttle-C and in-line Shuttle-derived launchers. The Shuttle-C design had a cargo module with attached Space Shuttle Main Engines (SSMEs) mounted on the side of a Shuttle External Tank (ET) in place of the delta-winged Shuttle Orbiter. The in-line design, a conceptual ancestor of the Space Launch System, would place the cargo module on top of a modified ET and three SSMEs underneath. The tank would have attached to its sides twin Advanced Solid Rocket Motors more powerful than their Space Shuttle counterparts. Joosten appears to have favored the Shuttle-C design.

The image above is slightly confusing: it displays a piloted ILREC lander and, below that, a conical TLI stage with three engines, but does not make clear that, except for the white, black, and gray conical crew capsule at the top, both lander and stage would be hidden from view under a streamlined white launch shroud. Missing from this illustration is the solid-propellant launch-escape system tower mounted on the crew capsule's nose. Image credit: NASA.

A piloted ILREC lander descends toward a landing near the regolith processing lander and the teleoperated tanker rover. The aft compartment, located between the two rear landing gear, holds up to two tons of cargo. Image credit: NASA.

Shortly after touchdown, the teleoperated tanker rover moves into position beside the ILREC crew lander and extends an umbilical so that it can refill the lander's empty liquid oxygen tanks with LUNOX for the trip home to Earth. Note the position of the crew hatch and two of the lander's four engines. Image credit: NASA.

The Shuttle-derived heavy-lift rocket would launch the piloted lander, bearing an international crew and about two tons of cargo, into Earth orbit. About 4.5 hours after liftoff, following a systems checkout period, the TLI stage would place the piloted lander on a direct trajectory to the Moon. The stage would then be cast off.

Joosten's crew lander design outwardly resembled the fictional "Eagle" transport spacecraft from the 1970s Gerry Anderson TV series Space: 1999. 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 horizontally oriented three-legged lander. The three landing legs would fold against the lander's belly beneath a streamlined shroud during ascent through Earth's lower atmosphere.

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 CM 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 spacecraft would land on and launch from the Moon using the same set of four belly-mounted throttleable rocket engines.

During descent to the lunar surface, the engines would burn Earth oxygen and hydrogen. Soon after lunar touchdown, the lander would be reloaded with liquid oxygen from the automated lunar oxygen plant.

During return to Earth, Joosten's spacecraft would burn Earth hydrogen and lunar oxygen. The entire crew lander would lift off from the Moon; only descent stages that delivered automated payloads would remain on the Moon to clutter up the site. After a brief period in lunar parking orbit, the ILREC lander would ignite its four engines again to place itself on course for Earth.

Nearing Earth, the crew capsule would separate from the lander section 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 well away from populated areas. The crew capsule would deploy a steerable parasail-type parachute. Joosten recommended that NASA recover the capsule on land — perhaps at Kennedy Space Center — to avoid the greater cost of an Apollo-style CM splashdown and water recovery. Most of the lander section would burn up during reentry.

The first piloted ILREC lander, with a U.S.-Russian crew of two on board, would spend two weeks on the Moon. The crew would inspect the automated mining and oxygen production systems and explore using the Moon bus rover. In Phase 1, the Moon bus would be capable of traveling away from the crew lander landing site for two or three days at a time.

Several Phase 1 piloted missions to the site would be possible; alternately, NASA and Russia could skip immediately to Phase 2 — establishment of a temporary lunar outpost — after only a single Phase 1 piloted flight. In ILREC Phase 2, three more cargo flights would deliver to the same site a second Moon bus rover, a rover support module with an attached airlock derived from Space Station hardware designs, consumables in a cart-mounted pressurizable Space Station-derived module, and science equipment.

An Energia-launched cargo lander would deliver the U.S.-built airlock/rover support node to the outpost site and lower it to the lunar surface. Astronauts in the pressurized Moon bus rovers would drive it to a flat area using teleoperations techniques, then would use robot arms on their rovers to lower stilt-like supports. These would level and raise the airlock/node. After the airlock/node's wheels became raised off the ground, they would be removed, clearing the way for the twin rovers to "dock" with the node's two round side ports (one port is visible below the observation cupola just right of center). Image credit: NASA.

Phase 2 ILREC temporary lunar outpost. Two pressurized rovers are docked tail-first to the support node, as is a pressurized consumables cart (at the end of the node opposite the airlock). Hanging regolith-filled bags on the node provide added protection from ionizing radiation. Wheels removed from the airlock/node are stacked to the left of the surface access gangway; they serve as spares for the pressurized Moon bus rovers. A buried electrical cable (visible as a curved line in the lunar dirt running from center to lower right) leads toward a nuclear reactor (out of view). Image credit: NASA.

Phase 2 outpost with components identified. The lower image is turned 90 degrees relative to the top image. Image credit: NASA.

A piloted flight would then deliver a four-person crew for a six-week lunar surface stay. The crew would divide up into pairs, with each pair living in and operating a Moon bus rover. The support module/airlock would include docking ports so that the two Moon buses and the consumables module cart could link to it, forming a small outpost.

The Moon buses would tow auxiliary power carts in Phase 2 to enable longer traverses across the lunar surface. The Moon bus/cart combinations might travel in pairs along parallel routes or one Moon bus might remain at the outpost while the other Moon bus and its power cart ventured far afield. In the event that a Moon bus rover failed beyond walking distance from the outpost and could not be repaired, the other Moon bus could rescue its crew.

ILREC Phase 3 was poorly defined: it might see larger lunar crews venturing further afield, or NASA might change direction and use technology developed for the lunar program to put humans on Mars (perhaps still in partnership with Russia). Joosten identified the piloted Moon lander crew capsule, Shuttle-derived heavy-lift rocket, pressurized Moon bus rovers, and Energia as candidate Mars mission hardware. Both Energia and the Shuttle-derived rocket might be upgraded for piloted Mars missions; they might even be merged to create a single international heavy-lift rocket more powerful than either Energia or the Shuttle derivative.

Joosten envisioned that in Phases 1 and 2 Russia would pay for Energia and the Block 14C40 TLI stage, while NASA would pay for the Shuttle-derived rocket and its TLI stage, the crew and cargo landers, Moon bus rovers and teleoperated carts, and lunar oxygen production systems. In exchange for Russia's participation, its cosmonauts would walk on the Moon in the early years of the 21st century. If U.S.-Russia space cooperation were for any reason curtailed, NASA could continue the Moon program by using Shuttle-derived launchers to launch Moon-bound cargo — provided, of course, that U.S. policy makers determined that an all-U.S. Moon program was worth the added cost.

Sources

Mir Hardware Heritage, NASA Reference Publication 1357, NASA Johnson Space Center Reference Series No. 3, David S. F. Portree, March 1995, pp. 168-170.

"International Lunar Resources Exploration Concept," Kent Joosten, Low Cost Lunar Access Conference Proceedings, 1993, pp. 25-61; paper presented at the AIAA Low Cost Lunar Access conference, Arlington, Virginia, 7 May 1993.

International Lunar Resources Exploration Concept, Presentation Materials, Kent Joosten, Exploration Programs Office, NASA Johnson Space Center, February 1993.

Press Kit: Apollo 11 Lunar Landing Mission, NASA, 6 July 1969.

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