23 January 2016

Bridging the Gap Between Space Station and Mars: The IMUSE Strategy (1985)

NASA's sprawling Dual Keel space station design in 1986. Niehoff's Interplanetary Platform would have resembled the crew-tended freeflyer located at top left. Image credit: NASA
In common with many space advocates, I long for the day when humans set foot on Mars. In addition to being a fascinating place to explore, it is the world most like Earth in our planetary system (though it is still very alien).

We have a lot of work to do to get ready to go to Mars. Before we can plan long-term stays (the most economical kind), we need to determine whether Mars's gravity is adequate to halt (or at least dramatically curtail) bone loss and other afflictions of microgravity. We also need to determine as best we can whether life exists there.

The amount of effort we invest in seeking to ensure that we do not damage a martian biota through careless introduction of Earth microorganisms will say much about us as a species. Two salient facts should be kept in mind as we consider the question of how best to interact with life on Mars: first, Earth and Mars are probably very similar a few kilometers down, where we find abundant chemosynthetic life on Earth (that is, Mars is likely to be, like Earth, warm and wet below the surface); second, life formed early and rapidly on Earth, but it remained single-celled until just about 600 million years ago. Mars life, if it exists, might now be in a process of retreat, a rear-guard action leading to extinction as the planet cools and dries out; alternately, it might be biding its time.

That we know neither whether the human body can withstand Mars conditions for prolonged periods nor whether Mars life (if it exists) can withstand unharmed the microbiota the human body carries with it indicates that, for now, we should take a cautious approach to humans on Mars. That does not mean we should sit forever in low-Earth orbit. On the contrary, it means that we should seek to accomplish intermediate goals which themselves are important and exciting.

In the next few months, I plan several new posts that will describe some possible intermediate steps that could link where we are (a space station in low-Earth orbit and remote-controlled rovers, landers, and orbiters slowly exploring Mars) with where we logically should be headed (a science base at Mars with a long-term human population - think Antarctica - working closely with teleoperated machines). That could in turn lead where some of us want to be (a permanent, self-sustaining Mars colony serving as a jumping-off place for a new branch of humanity).

I like how John Niehoff's Integrated Mars Unmanned Surface Exploration (IMUSE) strategy logically ties together the NASA automated and piloted space programs. This has been attempted many times over the years - below I will mention one such attempt, the joint Jet Propulsion Laboratory (JPL)/NASA Johnson Space Center (JSC) Mars Sample Return (MSR) studies of the 1980s - but it has always run into institutional barriers or tripped over new, typically ill-considered, large-scale moon/Mars initiatives.

Niehoff was the manager of the Space Sciences Department at Science Applications International Corporation (SAIC) when, on 30 July 1985, he presented his IMUSE strategy to the National Academy of Science Space Science Board Major Directions Summer Study. He proposed employing reusable automated spacecraft with designs "deeply rooted" in planned U.S. space station technology to carry out a complex, evolving series of automated Mars Sample Return (MSR) missions between 1996 and 2016.

His work had its origins in the 1984 joint Jet Propulsion Laboratory/NASA Johnson Space Center MSR study and the work of the National Commission on Space (NCOS), a blue ribbon panel appointed by President Ronald Reagan at the insistence of Congress to chart a future for the U.S. in space. Former NASA boss Thomas Paine chaired the NCOS, which included such luminaries as Neil Armstrong, Sally Ride, and Chuck Yeager. Niehoff and SAIC provided both the JPL/JSC MSR study and the NCOS with planning and engineering support.

Niehoff explained that linking MSR with the Space Station Program would integrate it with "other capabilities and objectives of the larger space program." It would also create a bridge between early 1990s Earth-orbital station operations and a piloted Mars landing in the early 2020s.

At the time Niehoff made his presentation, the Space Station Program was just 18 months old. Reagan had used his January 1984 State of the Union Address to launch (in a bureaucratic sense, at least) the manned space laboratory. He gave NASA until 1994 to complete it.

NASA and its contractors studied a range of possible station configurations in 1984-1985. They had in fact begun concerted station planning before the first Space Shuttle launch in 1981. In early 1986, six months after Niehoff's presentation to the Major Directions Summer Study, NASA settled on the ambitious Dual Keel station design. The Dual Keel would provide ample facilities for space construction and satellite servicing and a home base for space tugs that could launch or retrieve spacecraft and satellites.

Niehoff's IMUSE spacecraft – which he dubbed an Interplanetary Platform (IP) – would transport smaller vehicles between Earth and Mars. It would provide them with "keep-alive" solar cell-generated electrical power, thermal control, course-correction propulsion, and other requirements typically provided by an expendable spacecraft bus.

The IP would cut costs over the course of the IMUSE program because it would need to be launched onto its interplanetary path only once. As the IP flew without stopping past Mars or Earth, the smaller vehicles it supported would separate to land on or go into orbit around the planet or would leave the planet to rendezvous and dock with the it.

Had Niehoff's IMUSE proposal gone ahead (and used his first scenario), the Interplanetary Platform would have been en route to its first Mars encounter at the time the Hubble Space Telescope captured these images. Image credit: NASA
Niehoff described a pair of IMUSE scenarios. In both, the IP would follow SAIC-developed Versatile International Station for Interplanetary Transport (VISIT) cycler orbits, which, he explained, would be "simultaneously resonant with both Earth and Mars." A spacecraft in a VISIT-1 orbit would circle the Sun in 1.25 Earth years, which meant that it would encounter Earth four times in five Earth years and Mars three times in two Mars years. A VISIT-2 orbit, on the other hand, would need 1.5 Earth years to complete. A spacecraft on a VISIT-2 path would encounter Earth twice in three Earth years and Mars five times in four Mars years.

Niehoff's first IMUSE scenario would begin with Earth-orbit departure of one 6340-kilogram IP – possibly pushed by a Space Station-based space tug – in May 1996. During its first Mars encounter (December 1997), the IP would drop off a 400-kilogram "smart rover" capable of complex autonomous operations and a 1110-kilogram communications orbiter for relaying radio signals between Mars and Earth. The rover and orbiter, packed separately in identical 2570-kilogram streamlined aerocapture vehicles, would skim the martian atmosphere to slow down so that Mars's gravity could capture them into orbit.

The rover would then descend to Mars's surface atop a 1170-kilogram "generic lander" capable of precision landing. After rolling off the lander onto the surface, it would employ a variety of scoops, picks, and drills to gather rock, sand, and dust samples.

In April 2001, a second rover and two 4300-kilogram Mars ascent vehicles would rendezvous and dock with the IP as its Sun-centered orbit carried it past Earth for the first time. This would demonstrate "hyperbolic rendezvous" ahead of its use in the piloted Mars program. Hyperbolic rendezvous would occur not in Mars or Earth orbit, but rather in the IP's orbit around the Sun. The technique would save propellants because the IP would not fire rocket motors to capture into and escape from Earth or Mars orbit.

Seven months later (November 2001), the IP would swing by Mars for the second time and drop off the 2001 rover, which would land at a new site on Mars. Ascent vehicle #1, meanwhile, would land near the 1996 rover and ascent vehicle #2 would set down near the 2001 rover.

Earth would not be positioned properly for the IP to make a direct return after the November 2001 Mars encounter, so the IP would orbit the Sun twice and return to Mars for the third time in July 2005. Ascent vehicle #1 would lift off from Mars bearing the 10 kilograms of samples the 1996 rover collected and ascent vehicle #2 would lift off bearing 2001 rover samples. The ascent vehicles would perform hyperbolic rendezvous and dock with the IP as Mars slowly shrank behind the three spacecraft.

In April 2006, the IP would swing by Earth for the second time to drop off the Mars samples it had collected 10 months earlier. A Space Station-based tug would rendezvous and retrieve the samples after they aerocaptured into Earth orbit. The IP would also pick up ascent vehicle #3 and two 2000-kilogram automated Mars surface stations.

It would release these during its fourth Mars encounter in April 2009. Ascent vehicle #3 would land close to the still-operational 1996 rover. The surface stations would land at separate sites, bringing to four the number of Mars landing sites explored in the IMUSE program. The stations would conduct life science experiments, test manufacture of propellants from martian resources, and study the effects on spacecraft materials of long exposure to martian surface conditions.

During its third Earth encounter (April 2011), the IP would pick up a "manned precursor payload" consisting of equipment and supplies for the first piloted Mars landing expedition. It would drop off the manned precursor payload in December 2013, during its fifth Mars encounter, and pick up samples from the 1996 rover launched from Mars by ascent vehicle #3. In April 2016, the IP would encounter Earth for the fourth and final time to drop off the samples.

Niehoff's second IMUSE scenario would employ two IPs. These would deliver the same payloads to Mars in the same manner as his first scenario, but would start later and then proceed at an accelerated rate. The first IP would leave Earth in July 1998 and fly past Mars in February 2000, November 2003, August 2007, and May 2011. It would encounter Earth in July 2003, July 2008, and July 2013. IP #2 would leave Earth in April 2001, fly past Mars in November 2001, July 2005, and April 2009, and encounter Earth in April 2006 and April 2011. IMUSE scenario #2 would return the first Mars samples to Earth in April 2006 and drop off the first piloted program precursor payload at Mars in May 2011.

The piloted program, which eventually might employ large cycling spacecraft based on Space Station modules and other hardware to rotate crews to and from a long-term Mars surface outpost, would commence shortly thereafter. Piloted cyclers might travel permanently in VISIT-type orbits, becoming in effect space stations in solar orbit. The NCOS timetable called for a Mars surface outpost to be in place by 2035, 50 years after Niehoff presented his study.

Source

"Integrated Mars Unmanned Surface Exploration (IMUSE), A New Strategy for the Intensive Science Exploration of Mars," J. Niehoff, Science Applications International Corporation; presentation to the Planetary Task Group, Major Directions Summer Study, Space Science Board, National Academy of Science, 30 July 1985

More Information

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

A Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)

Making Rocket Propellants from Martian Air (1978)

The Collins Task Force Says Aim for Mars (1987)

The 1991 Plan to Turn Space Shuttle Columbia Into a Low-Cost Space Station

18 January 2016

What If a Space Shuttle Orbiter Had to Ditch? (1975)

Final approach: the inner and outer wing flaps and body flap are visible at the aft end of the descending Orbiter. Image credit: NASA
High on any pilot's list of things not to do with an aircraft is to ditch - that is, to make an emergency landing in water. Planes that nimbly slip through air become about as graceful as a brick when they touch an ocean swell. Anyone who has flubbed a dive and belly-flopped knows how painfully hard water can be.

Aircraft ditching behavior became of great interest in the United States during the Second World War, when B-24 Liberator bombers damaged by enemy fighters and flak - or simply lost and low on fuel - ended otherwise successful bombing runs over Nazi Germany by ditching in the English Channel or North Sea. Even in calm seas, the B-24 did not fare well. More often than not the plane broke apart and sank within minutes.

The Arsenal of Democracy: Workers assemble B-24 Liberator aircraft in the Consolidated Vultee plant in Fort Worth, Texas. More than 18,000 B-24s flew a wide range of missions in all Second World War operational theaters. Image credit: Wikipedia
Because of this, on 20 September 1944, four months past the beginning of the D-Day invasion of Europe, a B-24 Liberator with two brave airmen on board intentionally ditched in the calm waters of Virginia's James River. Close by in a small boat was a team of engineers from the National Advisory Committee for Aeronautics (NACA) Langley Aeronautical Laboratory in nearby Hampton, Virginia. As the 44,100-pound, four-engine, straight-wing aircraft skimmed the water's surface at 97 miles per hour with its landing gear up, instruments inside the fuselage collected data on motion and deceleration.

The B-24's belly touched water at a point just behind the wing trailing edges. The plane began to skip, its nose rising and dipping to the left; then the water seemed to grab the bomber hard. Inside, the crew felt deceleration equal to 2.6 times the force of Earth's gravity. It threw them forward against their safety harnesses. Propellers still whirling, the plane nosed down and pieces flew out of an enormous cloud of spray that momentarily hid it from view. Rescuers moved in quickly; meanwhile, both pilots climbed atop the aircraft.

The men were in good shape, but their plane, a veteran of several European bombing missions, would never fly again. Even under the relatively benign conditions of the test, its fuselage had cracked, nearly breaking in two. The crack acted as a hinge, so the plane floated, rapidly filling with water, with both its tail and its nose in the air. The right inboard motor was gone, sheared away upon contact with the water.

When the NACA engineers lowered themselves inside to recover their instruments, they were in for a shock. Almost every piece of equipment bolted to the interior of the B-24 had torn loose and been flung forward, forming a nearly impassable heap just behind the cockpit. They found their instruments, secure in water-tight containers; meanwhile, a U.S. Navy salvage boat with a crane moved in fast to hoist the plane out of the water before it joined its missing engine 30 feet down on the muddy bottom of the James River. Smaller boats collected floating pieces.

On the salvage boat's deck, the plane looked even worse than it had in the river. A large dent marked where its belly first touched the water at a descent rate of 1.8 feet per second. Though they had been reinforced for the ditching test, the bomb bay doors had been pressed inward. The bomber's thin skin was rumpled over large areas; where it wasn't creased and puckered, it was ripped.

The 20 September 1944 ditching test became a pivotal event in aerospace history. It brought home to engineers as never before the powerful forces that ditching brought to bear on aircraft. It led NACA Langley to study ditching behavior in many types of aircraft. Because ditching full-size planes was both costly and dangerous, the lab developed techniques for testing scale-model airplanes in a water trough in what became known as the Langley Impacting Structures Facility (LISF). Above all, their experiments showed that ditching was actually crashing.

Fast forward 30 years to 1975. The era of scale-model experiments was gradually drawing to a close - computer models of complex phenomena, though still crude and costly, had made their debut in aviation and other fields. When NASA had formed in 1958, Langley had become one of its research centers. With the splashdown of the Apollo-Soyuz Test Project Apollo Command Module in the Pacific Ocean in July 1975, the era of U.S. space capsules was over. The era of wings in Earth orbit was about the begin.

The Space Shuttle stack as envisioned in 1975 with major components indicated. Image credit: NASA
NASA and its contractors envisioned several plausible scenarios which might lead a Space Shuttle Orbiter to ditch. The Orbiter was a glider, so it could not try again if it missed its runway at Kennedy Space Center (KSC), Florida. If the Orbiter crew realized the problem in time, they might ditch in the Banana or Indian Rivers or in the Atlantic Ocean off Cape Canaveral.

In the event that two of the Orbiter's three Space Shuttle Main Engines (SSMEs) failed early in its ascent to space, the Orbiter would need to return to KSC; however, depending upon when the engines failed, it might not have enough altitude and energy to turn around, line up with the Shuttle runway, and stretch out its descent. In that case, it would probably fall short of the coast.

In October 1975, William Thomas, a former Langley engineer who had taken a job with Grumman Aerospace Corporation in Bethpage, New York, published results of 67 tests of a 1/20-scale model of the Space Shuttle Orbiter. The tests occurred in the LISF starting in 1974. The actual Orbiter was planned to be 37.2 meters (122 feet) long, so the tests saw a 1.86-meter (6.1-foot) fiberglass and balsa-wood Orbiter launched into a broad trough of water using a ceiling-mounted "catapult" device. The trough could simulate smooth seas or seas with swells and waves.

The model included a replaceable balsa insert designed to give some sense of the belly damage a ditching Orbiter could expect. Weights enabled Thomas to simulate either 32,000-pound or 65,000-pound cargoes in its cargo bay. With the lighter cargo, the full-scale Orbiter would weigh 85,464 kilograms (188,247 pounds); with the heavier, 103,200 kilograms (227,313 pounds). The corresponding model weights were 10.68 kilograms (23.53 pounds) and 12.9 kilograms (28.41 pounds). Small lead weights permitted tests at intermediate Orbiter weights and allowed Thomas to trim the model so that it would, for example, dip one wing as it approached the water.

The model also included adjustable flaps and landing gear which could be installed to simulate gear-down ditching or left off to simulate ditching with landing gear doors closed. Flaps and landing gear were designed to break away at scale stresses - for example, on a full-sized Orbiter, the main landing gear would fail under a load of 356,270 pounds. The 1/20-scale landing gear would break if subjected to a torque of 6.41 pounds.

In the first of the 67 tests, the model Orbiter's nose was pitched up 16°, its aft-mounted body flap - located below the SSME engine bells - was tilted down 11.7°, and its wing flaps (inner and outer) were tilted up 4°. The water in the LISF trough was calm.

The 1/20-scale Orbiter, with a simulated mass of 93,000 kilograms and a simulated speed of 53.5 meters per second (just 120 miles per hour - slow for a Shuttle landing), contacted the water with its landing gear up. It skipped, then sank deeper on the next contact. The model decelerated very rapidly - it stopped four fuselage lengths from where it first touched the water. In the full-size Orbiter, this would have amounted to about 160 meters (490 feet).  It was, Thomas commented, a "very stable run."

Beginning with Test 4, the model Orbiter was fitted with instruments for recording normal (fore-aft) and longitudinal (left-right) deceleration. These revealed that even a perfect ditching would likely harm the Orbiter crew. Apart from the instrumentation, the Test 4 Orbiter model was configured exactly like the Test 1 model. It touched calm water with its nose pitched up 12° moving at a scale speed of 72 meters per second (161 miles per hour).

Had it been a full-scale Orbiter carrying a crew, they would, after the initial skip, have been thrown forward against their straps with a force equal to 8.3 times the pull of Earth's gravity. As the Orbiter swerved to a stop, they would have felt a longitudinal jolt of 4.5 gravities. Test 4 was, it would turn out, only a little more arduous than average.

For Test 5, conditions were virtually identical to those of Test 4. Landing speed was slightly higher at 75.1 meters per second (168 miles per hour). Yet had the model been a full-scale Orbiter, it would have subjected its crew to 19.4 gravities of deceleration when it made its second contact with the water. The model's inner wing flaps broke free; this hinted that structural damage on the full-scale Orbiter was likely.

The first test of an Orbiter model with a simulated 65,000-pound payload (Test 17) saw a scale deceleration of nearly 11 gravities. In all, 14 of the 67 tests subjected the model Orbiter to greater than 10 gravities of scale deceleration.

Tests 9 and 62 were without question the most dramatic. In both, the model Orbiter stalled following release and hit the water tail first.

Other tests saw the 1/20-scale Orbiter model skip along simulated 2.1-meter (seven-foot) wave crests, plow through waves with a series of sharp jolts, dive under the water and bob to the surface, and lose both its inner and outer wing flaps. Tests with landing gear down never went well; the gear always broke away. In a full-scale Orbiter, tearing away the landing gear would likely have permitted water to enter through the damaged wheel wells.

Thomas's interpretation of the results of the 67 tests was notable: "a fairly smooth runout is expected but considerable fuselage tearing and leaking or flooding will occur." He was confident, however, that a full-scale Orbiter would remain afloat if its wings, which contained hollow spaces, remained intact. The more damage the wings suffered, the faster the Orbiter would sink.

The LISF 1/20-scale Orbiter tests were, of course, simplistic. They did not reflect the fact that Space Shuttle Orbiters were not designed to withstand the deceleration loads most of the model tests indicated. The average ditching deceleration ranged between five and eight gravities; this would have been sufficient to cause significant structural damage. In other words, in almost all cases, the Orbiter would have snapped apart.

Moments before the end: the plume from the Solid Rocket Booster leak that doomed Challenger is clearly visible. Image credit: NASA
A little more than a decade later (28 January 1986), the Challenger accident made obvious the Space Shuttle Orbiter's fracture lines. The Orbiter Challenger did not explode; rather, the brown External Tank (ET) upon which it rode and from which it drew liquid hydrogen/liquid oxygen propellants for its SSMEs was destroyed by a malfunctioning Solid Rocket Booster (severe wind shear might also have played a role).

The fuel and oxidizer the ET contained came together and ignited, producing an explosion, but it was aerodynamic forces that tore the Orbiter apart. Basically, as its ET disintegrated, Challenger's nose stopped pointing the right way. This subjected it to drag and deceleration.

The crew compartment broke free, trailing behind it a comet's tail of cables. Some of the crew inside remained conscious long enough to take prescribed - though futile - emergency measures. The compartment remained mostly intact until it hit the water about two minutes later.

The Payload Bay disintegrated, but Challenger's main payload, a Tracking and Data Relay Satellite with an attached Inertial Upper Stage, remained more or less intact as it flew free of the fireball and fell toward the Atlantic. Challenger's wings separated, partly disintegrating. Each, however, remained recognizable in images and video captured from the ground. The aft compartment containing the SSMEs also emerged from the fireball mostly intact.

After Challenger, the Space Shuttle Program came under intense scrutiny. The Report to the President by the Presidential Commission on the Space Shuttle Challenger Accident cited Thomas's 1975 report when it stated that the probability was high that a Shuttle Orbiter would break up and sink after a ditching. Even if the Orbiter remained intact, the Commission report continued, cargoes mounted in the Payload Bay would break loose from their supports, slide forward, and smash into the back of the crew cabin. Though Thomas's report did not in fact say these things, they were logical conclusions based on the results of the 67 1/20-scale model Orbiter test runs.

Sources

YouTube - "Ditching of a B-24 Airplane into the James River" - https://youtu.be/WjadMxpXprk (uploaded by Jeff Quitney - accessed 16 January 2016)

YouTube - "Space Shuttle Orbiter Ditching Investigation of a 1/20-Scale Model" - https://www.youtube.com/watch?v=dlG-HcZIDl0 (uploaded by Jeff Quitney - accessed 16 January 2016)

Ditching Investigations of Dynamic Models and Effects of Design Parameters on Ditching Characteristics, Report 1347, L. Fisher and E. Hoffman, Langley Aeronautical Laboratory, National Advisory Committee for Aeronautics, 1958

Ditching Investigation of a 1/20-Scale Model of the Space Shuttle Orbiter, NASA Contractor Report 2593, W. Thomas, NASA, October 1975

Report to the President by the Presidential Commission on the Space Shuttle Challenger Accident, Presidential Commission on the Space Shuttle Challenger Accident, Volume I, pp. 182-183, June 1986

"A Plane Crash in 1944 Is Saving Lives Today," Peter Frost, Daily Press, 22 February 2009 - http://articles.dailypress.com/2009-02-22/news/0902210116_1_b-24-successful-emergency-landing-hudson-river (accessed 16 January 2016)

More Information

What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

What If a Lunar Module Ran Low on Fuel and Aborted Its Landing? (1966)

Where to Launch and Land the Space Shuttle? (1971-1972)

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)

10 January 2016

Starfish and Apollo (1962)

9 July 1962: An artificial aurora lights the sky over the Pacific Ocean following the Starfish Prime space nuclear explosion. Image credit: U.S. Air Force
Since I first posted a less detailed version of this post on my old Romance to Reality website (1996-2006), the Starfish Prime nuclear test has become a popular topic on the Internet. On 9 July 1962, the U.S. Air Force launched a 2200-pound W-49 nuclear warhead into space on a Thor rocket from Johnston Atoll in the Pacific Ocean. The warhead exploded with a yield of 1.44 megatons of TNT at an altitude of 248 miles above the Pacific.

The Starfish Prime nuclear blast produced a flash of light visible over much of the Pacific basin. For seven minutes after the explosion, an artificial red aurora danced in the skies over island groups as widely separated as Hawaii, Tonga, and Samoa. The blast's electromagnetic pulse damaged electrical systems on the Hawaiian island of Oahu, 800 miles away from the explosion.

Starfish Prime, a follow-on to U.S. high-altitude nuclear tests conducted in 1958, was publicized in advance. Many widely scattered aircraft and naval vessels, as well as sounding rockets, were used to observe its effects.

Though it sought answers to scientific questions, it was intended also to test whether nuclear explosions in low-Earth orbit (LEO) could augment and expand the Earth-girdling Van Allen radiation belts to create a barrier that would incapacitate Soviet intercontinental missiles launched against the United States. The test series of which it was part, Operation Dominic, was partly a response to the Soviet Union's August 1961 decision to end a three-year nuclear testing moratorium.

Schematic cross-section of the inner and outer Van Allen Belts based on James Van Allen's 1958 model. In February 2013, NASA announced that data from the two Van Allen Probes indicated that a third radiation belt can sometimes form beyond the outer belt. Image credit: Wikipedia
High-energy particles Starfish Prime pumped into the belts probably contributed to the failure of Telstar 1 just four months after its 10 July 1962 launch. Telstar 1 was the first active communications satellite, meaning that it received and re-transmitted incoming radio signals. The satellite was reacquired in January 1963, but failed permanently on 21 February. Six other satellite failures have been traced to Starfish Prime.

No one knew how long the beefed-up radiation belts might persist. Some feared that the increased radiation might last until 1967-1968, when NASA hoped to carry out the first Apollo expedition to the moon. The Apollo spacecraft, launched from Cape Canaveral on Florida's east coast, would have to traverse the augmented Van Allen Belts, and no one could say what effect their radiation would have on Apollo crews.

A Bell Labs technician puts the finishing touches on the experimental multi-national Telstar 1, the world's first privately sponsored satellite. A Thor-Delta rocket boosted the 170-pound satellite into a 592-by-3687-mile Earth orbit the day after the Starfish Prime nuclear explosion. Image credit: Bell Laboratories 
D. James and H. Schulte, researchers with NASA's newly created advance planning contractor, Bellcomm, analyzed the effects of Starfish Prime on NASA moon plans in a memorandum they sent to NASA Headquarters on 5 October 1962. It was among the first of many memos and reports Bellcomm would supply to NASA over the decade that followed.

James and Schulte based their analysis of the LEO radiation environment during the first Apollo mission on a model of the post-Starfish Prime Van Allen belts developed by NASA Goddard Space Flight Center scientist Wilmot Hess. His model placed the lower limit of the expanded inner Van Allen belt at an altitude of about 600 miles.

Just two days after Starfish Prime, NASA announced that, after more than a year of sometimes heated discussion, it had selected the Lunar-Orbit Rendezvous (LOR) mission mode for accomplishing Apollo moon landings. LOR would see lunar mission functions split between two manned spacecraft – a large command ship and a small moon lander. The command ship would come no closer to the moon than lunar orbit. The lander would operate independently only during descent to the moon's surface, on the surface, and during ascent to lunar orbit.

LOR mission plan. Please click to enlarge. Step 10 shows the lunar lander separating from the command ship; 11 and 12 show the lander descending and on the surface; 13 and 14 show the lander ascent stage climbing to lunar orbit and docking with the command ship; and 15 shows the ascent stage being cast off and the command ship firing its engine to leave lunar orbit and fall back to Earth. Image credit: NASA
LOR had won out over Earth-Orbit Rendezvous (EOR) because it promised to reduce the mass of the lunar spacecraft, enabling launch on a single Saturn C-5 rocket (as the Saturn V was known in 1962), and because it would make the moon lander small compared to the EOR lander and thus safer to land. EOR needed multiple Earth launches and landed the entire piloted lunar spacecraft on the moon.

Despite NASA's decision, James and Schulte examined the radiation environment for both LOR and EOR Apollo missions. This reflected lingering anxiety both inside and outside NASA concerning LOR.

Many worried that the LOR mission mode's namesake maneuver, the post-lunar landing rendezvous and docking between the command ship and the moon lander in lunar orbit, might prove too challenging. They worried in particular that, with Earth's ground-based tracking stations too far away to be of use, the spacecraft in lunar orbit would have difficulty finding each other. If, during Apollo development, this were found to be so, then an EOR backup plan would become necessary.

In James and Schulte's EOR scenario, NASA would launch a single large piloted lunar spacecraft with mostly empty propellant tanks into LEO. There it would rendezvous and dock with a separately launched automated tanker containing its LEO departure propellants.

James and Schulte assumed that, before an EOR Apollo spacecraft could set out for the moon, it would need to orbit the Earth at least six times in a 252-mile-high parking orbit inclined 28.5° to Earth's equator (28.5° is the latitude of launch facilities at Cape Canaveral). During its first orbit after launch, controllers on the ground would track the piloted EOR spacecraft to determine its precise path.

Rendezvous and docking with the tanker would need up to 2.5 orbits, then propellant transfer and final orbit determination/spacecraft checkout would require two more. After a final half-orbit, the EOR Apollo spacecraft's orbital motion would have caused its orbital plane to become aligned for launch to near-equatorial landing sites on the moon. It would then ignite its engines to depart LEO.

The Bellcomm planners determined that, based on the Hess model, the EOR Apollo astronauts would receive a radiation dose of four rad in LEO before setting out for the moon. They would experience most of their LEO radiation exposure during orbits five and six, when they would begin to pass through a magnetic field anomaly that spans the Atlantic from Brazil to South Africa.

NASA Goddard Space Flight Center illustration of the South Atlantic Anomaly.
Within the South Atlantic Anomaly, as it is known today, the Van Allen belts dip to within 100 miles of Earth's surface. If the EOR Apollo astronauts could not depart LEO on schedule, then they would pass through the widest part of the South Atlantic Anomaly during orbits seven, eight, nine, and 10, and would receive up to six rads per orbit.

LOR Apollo would, by contrast, not linger in LEO. James and Schulte assumed that the LOR Apollo spacecraft/LEO-departure booster combination would circle Earth once in 252-mile-high LEO while controllers precisely tracked it to determine its orbit. It would complete half an orbit more so that its orbital plane would align for departure to near-equatorial landing sites on the moon.

The LOR Apollo crew would stay far from the South Atlantic Anomaly during their one and a half orbits of the Earth. Because of this, their radiation dose in LEO from the augmented Van Allen belts would amount to only 0.02 rad.

In both the LOR and EOR modes, the astronauts would receive a dose of 16 rad while crossing the augmented Van Allen belts en route to the moon. Thus, the minimum dose the EOR astronauts would receive would be 20 rad, while LOR astronauts would receive 16.02 rad.

The Bellcomm planners noted that future nuclear explosions in LEO could dramatically boost the dose moon-bound astronauts would receive during Van Allen belt passage. They added that a nuclear bomb packed with Uranium-238 could increase the radiation in the belts "a hundredfold."

James and Schulte noted that the Van Allen belts are inclined relative to Earth's equator and do not cover its poles. If the belts became impassable, they wrote, NASA would have little choice but to launch Apollo astronauts through the Van Allen belt gaps over Earth's poles.

Unfortunately, Cape Canaveral was poorly placed for polar launches because rockets launched due south or north would pass over populated areas. These included Cuba and Brazil to the south and the major cities of the U.S. eastern seaboard to the north.

James and Schulte wrote that a country with polar launch capability might explode nuclear weapons in space to bar a nation without such capability from launching men to the moon. They did not mention the Soviet Union specifically, nor did they point out that the Soviet Union, with its extensive Arctic Ocean coastline, was well placed to carry out polar launches.

The Van Allen radiation belts returned to normal a few years after Starfish Prime. Nuclear explosions in space never menaced Apollo astronauts, in large part because on 5 August 1963, representatives of the U.S., Great Britain, and the Soviet Union met in Moscow to sign the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water. Conclusion of the treaty, which needed more than eight years to negotiate, very likely received some impetus from Starfish Prime. The treaty, which permitted only underground nuclear tests on Earth and curtailed spread of nuclear test fallout, entered into force on 10 October 1963, and has subsequently been signed by nearly all United Nations member countries.

Sources

Memorandum, D. James and H. Schulte, Bellcomm, to W. Lee, NASA Headquarters, "Radiation environment of EOR and LOR," Bellcomm, October 5, 1962

"The Artificial Radiation Belt Made on July 9, 1962," W. Hess, Journal of Geophysical Research, Volume 68, Number 3, 1 February 1963, pp. 667-683

Wikipedia - "Starfish Prime" (https://en.wikipedia.org/wiki/Starfish_Prime - accessed 9 January 2016)

Wikipedia - "Telstar" (https://en.wikipedia.org/wiki/Telstar - accessed 12 January 2016)

U.S. Department of State - "Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water" (http://www.state.gov/t/isn/4797.htm - accessed 12 January 2016)

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

Space Race: The Notorious 1962 Plan to Launch an Astronaut on a One-Way Trip to the Moon

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

He Who Controls the Moon Controls the Earth (1958)

01 January 2016

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

 24 July 1969: Richard Nixon and Thomas Paine (left), NASA's third Administrator, wait on board the aircraft carrier Hornet for splashdown of the Command Module Columbia at the end of the Apollo 11, the first mission to land men on the moon. At the time, Paine was lobbying hard for Nixon's acceptance of the IPP. Image credit: NASA
When one reads of NASA's 1969 Integrated Program Plan (IPP), it is often difficult to know whether to laugh or cry. The IPP, a product of George Mueller's NASA Headquarters Office of Manned Space Flight, began to evolve as early as 1965, but not until May 1969 did it take on the grandiose form NASA Administrator Thomas Paine stubbornly advocated to President Richard Nixon.

Paine, a Washington neophyte who had replaced the politically wily James Webb in late 1968, expected that the IPP would be NASA's reward for winning the race to the moon. Having vanquished the Soviet Union, Paine urged his NASA Center directors across the country to "think big" in their plans for post-Apollo space projects.

Had NASA gained approval for its Integrated Program Plan in 1969, a vast network of space transportation systems, space stations, and surface bases might have been in place by 1984. Image credit: NASA

In its various versions, the IPP included space stations in low-Earth orbit (LEO), geosynchronous orbit (GEO), and near-polar lunar orbit; Saturn V and Saturn V-derived rockets for launching them; a fully reusable Earth-to-LEO Space Shuttle for launching astronauts, cargo, and propellants; a reusable modular Space Tug that could operate manned or unmanned and do double-duty as a "Lunar Module-B" (LM-B) moon lander; a reusable Nuclear Shuttle for LEO-GEO and LEO-lunar orbit transportation; and lunar and Mars surface bases. All of this complex and expensive infrastructure was meant to become operational by the mid-1980s at the latest.

The IPP is sometimes wrongly attributed to Wernher von Braun, director of NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Von Braun was in fact skeptical about the IPP. He did not expect an Apollo-level commitment to spaceflight following Apollo's culmination, let alone one several times larger. He had spent the 1960s seeking opportunities to expand U.S. manned spaceflight using his Saturn rocket family. By the time Neil Armstrong set foot on the moon during Apollo 11, however, it was abundantly clear to the pragmatic German-born rocketeer that this would not happen.

Nevertheless, with his position rapidly eroding in the new political climate, von Braun at Paine's request tasked MSFC's artists with pumping out IPP illustrations and its advance planners with grafting a manned Mars mission onto the up-to-then cislunar IPP. He then touted the Mars plan to Nixon's high-level Space Task Group (STG) on 4 August 1969. Paine called von Braun NASA's "Big Gun" and expected the STG to be bowled over by anything he put before them. The first NASA manned Mars mission could occur as early as 1981, von Braun told the STG in a 30-minute presentation.

Nixon had appointed the STG in February 1969 to provide him with alternatives for NASA's future. Paine, a member of the STG, had won over Vice President Spiro Agnew, the STG's chairman, enabling him to put forward the IPP as the only choice for NASA's future. The STG's September 1969 report offered Nixon three schedules for accomplishing the IPP, but that was not the same as providing three program alternatives. Paine might have offered Nixon a choice between an LEO space station, a moon base, or a man on Mars. Instead, he insisted on a package containing all three.

This was, of course, an ill-considered move. Nixon's Office of Management and Budget had made it clear that NASA should expect rapidly declining annual budgets, not rapidly increasing ones. Nixon interpreted Paine's stubborn advocacy of the ambitious IPP as a clumsy effort at bureaucratic empire-building, not as a sincere proposal for a bold ("swashbuckling" was a term Paine used) American space program.

Paine's inflexibility created a vacuum that the Nixon Administration filled. NASA had supplied a single plan for its future that was unacceptable, so the Nixon White House made its own plan that served the President's political ends.

First, before accepting the STG report in September 1969, the White House added a fourth IPP schedule with no fixed dates. Nixon then adopted the line that IPP development would proceed as funding became available with the goal of a man on Mars by the year 2000, a date so far in the future as to be meaningless.

Next, in July 1970, a year after Apollo 11, Nixon accepted Paine's resignation, effective on the first anniversary of the STG report's public release (15 September 1970), and replaced him with the much more pliant James Fletcher. Finally, on 5 January 1972, at the start of the 1972 election year, Nixon made the Space Shuttle the sum total of NASA's post-Apollo piloted program. He touted the jobs it would create in California, a state undergoing an "aerospace depression" and one that was vital to his 1972 re-election bid.

5 January 1972: President Richard Nixon and NASA's fourth Administrator, James Fletcher, in California with a model of the Space Shuttle. The Space Shuttle was the only element of the IPP to fly, and then only in a partially reusable form. It first reached orbit on 12 April 1981. Image credit: NASA
Before that fateful announcement, however, NASA expended considerable effort on planning the IPP's execution. Paine's resignation did not stop the study efforts immediately. The LEO Station and Shuttle received more attention than the other elements because they were viewed together as the IPP's first step, but planners continued to look at all elements of the IPP well into 1971.

In June 1970, E. Grenning, an engineer with Bellcomm, NASA's Washington, DC-based advance planning contractor, developed a "traffic model" (basically a flight schedule) based on a modified version of Paine's IPP Option I (the so-called "Maximum Program"). Grenning's model spanned the years 1970 through 1984.

Grenning explained that the IPP was based on two fundamental principles. These were "the systematic establishment of semi-permanent manned bases in various locations in cislunar space and eventually in interplanetary space" and the "parallel introduction of low cost transportation systems. . . for the purpose of economically moving cargo and personnel to and from the bases."

A major change from the IPP as submitted to Nixon was that the manned Mars program, which would span seven years, was not tied to any specific dates. Grenning explained, however, that, when the decision was taken to proceed with the manned Mars program, its seven-year schedule would need to be tied to existing Earth-Mars minimum-energy transfer opportunities, which occur every 26 months.

Another change was that Grenning listed proposed automated planetary exploration missions. This was a response to protests from scientists, who were understandably eager to explore the many types of worlds in the Solar System. The "Balanced Base" planetary program would include 21 missions, all of which would leave Earth between 1976 and 1984.

In addition, Grenning stretched the pre-Mars IPP over a slightly longer period, so that its elements would not all be in place until 1984. Combined with not providing a specific date for its man-on-Mars program, this made Grenning's traffic model for Option I somewhat more conservative than the one in the STG report. It was, however, more conservative only relative to the grandiose Option I Paine championed.

Until 1975, Grenning's model was based wholly on Apollo spacecraft and Saturn rockets, none of which were reusable. Because it used no reusable vehicles and established no permanent bases, it was simple in execution compared with the traffic model that began to take hold in 1975.

The year 1970 would see three Apollo moon-landing missions, Grenning wrote, each with three astronauts, a Command and Service Module (CSM), and a Lunar Module (LM) launched on a three-stage Saturn V rocket. They would constitute the continuation of the Apollo lunar landing missions that had begun with Apollo 11. It is interesting to note here that Grenning's model, dated June 1970, seemed to exist in a parallel universe; after the Apollo 13 accident in April 1970, Apollo was grounded until January 1971.

The year 1971 would see the first two Extended Apollo missions. An uprated Saturn VB rocket would launch three astronauts, an Extended CSM (XCSM) capable of 16 days of flight, and an Extended LM (XLM) capable supporting two astronauts for three days. The XLM would have a landed payload capacity of 1000 pounds. NASA would fly two Extended Apollo missions per year from 1971 through 1974, plus one in 1975, for a total of nine missions and 54 man-days on the moon.

Once again, Grenning's model did not match up with reality. In January 1970, Paine had announced that, far from being uprated, Saturn V would cease production. He had also cancelled Apollo 20, at the time the last planned moon-landing mission, leaving at most seven landings after Apollo 12. The Apollo 13 near-disaster subsequently trimmed the number of piloted lunar landings to six.

The IPP would have seen two-stage Saturn V rockets (designated Int-21) launch many payloads. Int-21 would have remained operational as late as the mid-1980s. This image shows the only two-stage Saturn V; it launched the Skylab space station in May 1973. Image credit: NASA
In Grenning's traffic model, 1972 would see the first two-stage Int-21 Saturn V derivative launch the first Apollo Applications Program (AAP) Orbital Workshop (OWS). The AAP OWS was a 22-foot-diameter Saturn V S-IVB third stage converted into a temporary space station. The Int-21, of which a whopping total of 41 were meant to fly between 1972 and 1984, would be capable of placing up to 250,000 pounds into LEO.

Saturn IB rockets would launch three CSMs, each bearing a three-man crew, to the first AAP OWS between mid-1972 and early 1973. NASA would launch a second AAP OWS at the beginning of 1974. A total of nine CSMs would deliver crews to the the second AAP OWS by early 1976.

Paine had cancelled Apollo 20 so that its Saturn V could be used to launch the first AAP OWS. In February 1970, NASA announced that the AAP OWS program would be called the Skylab Program, a name that Grenning did not use in his June 1970 traffic model document.

Reusable IPP spacecraft and semi-permanent bases would make their debut in 1975, overlapping with missions using Apollo-Saturn systems and helping to ensure that there would be no gap in U.S. manned spaceflight. As already indicated, these would increase the complexity of NASA manned space operations. Spacecraft and bases would need to be assembled, refueled, and resupplied using other spacecraft and bases that would themselves need to be assembled, refueled, and resupplied.

Cutaway of a Saturn Int-21-launched Space Station Module with docked and docking research modules and, at its far end, a transfer module for transporting Station crews and supplies from a Space Shuttle Orbiter payload bay to the Station. Image credit: NASA
In 1975, NASA would launch on an Int-21 its first LEO Space Station Module (SSM), the prototype for all subsequent SSMs. Grenning wrote that the LEO SSM, which would orbit between 200 and 300 nautical miles above the Earth, would be used to conduct science, applications, and technology research. It would also serve as a depot for cargo bound for GEO and the moon, a satellite repair base, and an assembly and launch control center for automated and piloted planetary missions.

Soon after the LEO SSM reached space, the fully reusable Space Shuttle would take wing for the first time. In the LEO SSM's first year, winged Shuttle Orbiters would visit it three times. The 12-man Shuttle Orbiter would lift off vertically on the back of a winged, manned booster larger than a 707 airliner, then would separate and ignite its own cluster of engines to complete the climb to LEO. It would carry up to 50,000 pounds of payload in its 15-by-60-foot payload bay. A Shuttle Orbiter would be good for 100 flights before it could no longer be adequately refurbished and would need to be replaced.

The cislunar portion of the IPP architecture. Space Station Modules, colored-coded blue, appear in low-Earth orbit, in synchronous Earth orbit, in lunar orbit, and on the lunar surface. The Shuttle is depicted as the only Earth-to-orbit transportation system, though the Saturn V would have remained in service into the 1980s. Image credit: NASA
In 1975, NASA would also conduct a test flight of the Saturn VC, a beefed-up three-stage Saturn V with a Space Tug/LM-B fourth stage. The Saturn VC, an "interim system" for bridging the gap between Apollo and more advanced IPP lunar systems, would be capable of placing 100,000 pounds into lunar orbit. The LM-B, a Space Tug with landing legs, could operate on the lunar surface for 14 days at a stretch.

Early in 1976, a Saturn VC would launch a 50,000-pound SSM and a fully fueled Space Tug/LM-B to near-polar lunar orbit. During 1976, 1977, and 1978, nine Saturn VCs would launch four Space Tug/LM-Bs and five four-man "QCSMs" to the lunar-orbit SSM, enabling a continuous lunar population of four astronauts. The QCSM, which Grenning did not describe, would be an interim system like the Saturn VC. Two-man crews would land on the moon in Space Tug/LM-Bs four times in 1976, five times in 1977, and four times in 1978. Each trip to the lunar surface and back would expend 50,000 pounds of liquid hydrogen/liquid oxygen (LH2/LOX) propellants.

One design concept for the Space Tug/LM-B. Image credit: NASA
A slightly different design concept for the Space Tug/LM-B. Both the Tug/LM-B in this illustration and the one shown above it would have had similar capabilities. Image credit: NASA
The Space Tug would have an important "Space Shuttle Augmentation" function. Among augmentation missions considered was piloted satellite servicing beyond Space Shuttle/Space Station operational altitude. Image credit: NASA
The American Bicentennial year of 1976 would see an Int-21 boost a stack of five fully fueled Space Tug/LM-Bs into LEO. With a full load of LH2 fuel and LOX oxidizer, each Tug/LM-B would have a mass of about 50,000 pounds. Space Tug/LM-Bs would be designed for a one-year in-space lifetime. Beginning in 1976, one Space Tug/LM-B would be based at the LEO SSM at all times for use in satellite servicing, spacecraft assembly, Earth-orbital rescue, and other missions.

The lunar-orbit SSM would have on hand two fully fueled Space Tug/LM-Bs at all times. One would land on the moon and the other would stand by to rescue the surface astronauts in the event that their Space Tug/LM-B malfunctioned. After a year of operations, Space Tug/LM-Bs based at the lunar-orbit SSM would be stripped down and turned into tankage for a propellant depot in lunar orbit.

Also in 1976, the Space Shuttle would fly eight times. Six Shuttle missions would deliver astronauts, supplies, and cargoes, including two automated planetary spacecraft, to the LEO SSM. The remaining two missions would see the Shuttle orbiter serve in a "tanker" role. Each Shuttle Orbiterwould carry 50,000 pounds of LH2/LOX propellants, enough to refuel one Space Tug/LM-B.

The Space Shuttle Orbiter in one of its chief IPP roles: that of tanker supplying propellants to other IPP spacecraft. Image credit: NASA
A piloted Space Tug removes a cargo module from the Shuttle payload bay using robot arms, stacks it on its top (center left), performs rendezvous with a waiting moon-bound Nuclear Shuttle (upper right), and transfers the cargo module. Image credit: NASA
The first two missions of the Balanced Base planetary program, the Venus Explorer Orbiter and the Comet d'Arrest flyby, would depart Earth in 1976. Automated planetary missions would each need two fully-fueled Space Tug/LM-Bs. When the planetary launch window opened, Space Tug/LM-B #1 would ignite its rocket engines to accelerate Space Tug/LM-B #2 and the planetary probe, then would shut down its engines, undock from Space Tug/LM-B #2, turn end for end, and fire its engines again to return to LEO for refueling and reuse.

Space Tug/LM-B #2 would fire its engines to further accelerate the planetary probe, then would shut down its engines and release the probe onto its interplanetary trajectory. Space Tug/LM-B #2 would then turn end for end and fire its engines to slow itself and return to LEO.

Grenning's IPP included many Space Tug-launched robotic probes. The probe above resembles the Voyager Mars/Venus orbiter/lander design cancelled in 1967. Image credit: NASA
In 1977, the Space Shuttle would fly 10 times and the Int-21 would fly twice. The Space Tug/LM-B could not carry enough propellants to change from near-equatorial LEO SSM orbit to polar Earth orbit, so two Shuttle Orbiters would launch directly from Earth's surface into polar orbit to perform sortie (non-Space Station) missions. Polar sorties would occur at a rate of two per year through 1984.

Eight Shuttle missions would transport crews and cargoes bound for the LEO SSM. One of those would deliver to 50,000 pounds of LH2 propellant for the first NERVA nuclear-thermal rocket engine-equipped Nuclear Shuttle, and four would deliver 50,000 pounds of Space Tug/LM-B propellants each.

The Nuclear Shuttle would extend the IPP's reach to the moon and Mars, enabling establishment of moon and Mars bases. Note the crew cabin (upper right). Image credit: NASA
One Int-21 would launch the first Nuclear Shuttle and another would launch five fully fueled Space Tug/LM-Bs (four for the robotic planetary program and one for the LEO SSM). The Int-21 would not have the lift capacity to launch the Nuclear Shuttle to LEO fully fueled, so it would reach space with room in its tank for an additional 50,000 pounds of LH2. Before a newly launched Nuclear Shuttle departed LEO for the first time, a Shuttle Orbiter tanker would rendezvous with it to top off its tank.

Nuclear Shuttles would each be good for 10 missions from LEO to GEO or lunar orbit and back, then would be launched into disposal orbit around the Sun. Some would carry a cargo of worn-out Space Tug/LM-Bs into solar orbit with them.

Each Nuclear Shuttle mission would expend 240,000 pounds of LH2. Six Space Shuttle tanker flights would be required to refuel the Nuclear Shuttle once. The Nuclear Shuttle would transport to the lunar-orbit SSM six astronauts and 90,000 pounds of cargo, or 100,000 pounds of cargo in unmanned mode. It could return 10,000 pounds of cargo and six astronauts from the moon to the LEO SSM.

The Nuclear Shuttle could deliver 90,000 pounds of cargo and six astronauts to GEO and return six astronauts from GEO to the LEO SSM. After the GEO SSM was established in 1980, all Nuclear Shuttles would perform a shakedown cruise to GEO before traveling to lunar orbit for the first time. If it malfunctioned during its maiden flight to GEO, a Space Tug/LM-B could rendezvous with it to make repairs or return it to the LEO SSM.

The first Nuclear Shuttle would operate only in unmanned mode; its 10 missions would serve as an extended flight test. The first manned Nuclear Shuttle, the second launched, would reach LEO on an Int-21 in early 1979. Four manned and six unmanned Nuclear Shuttle flights would occur each year beginning in 1981, by which time one new Nuclear Shuttle would reach LEO and one old Nuclear Shuttle would be disposed of in solar orbit each year.

In 1977, four Tug/LM-B pairs would launch the Mars Explorer Orbiter, the Mars High Data Orbiter, and two Jupiter-Saturn-Pluto Mariner-class flyby spacecraft. The Tug/LM-Bs would burn the propellants with which they were launched to send the two Mars missions on their way, then would be refueled to launch the twin Jupiter-Saturn-Pluto missions. Grenning noted that dispatching automated spacecraft to destinations beyond the Main Asteroid Belt would need so much energy that the second Tug/LM-B could spare no propellants to return to LEO. It would, therefore, be expended.

The year 1978 would see a Mercury-Venus Mariner flyby, a Venus Mariner Orbiter, and a Solar-Electric Asteroid Belt Survey depart the LEO SSM. All Space Tug/LM-Bs used to launch these missions would be recovered. In 1979, NASA would launch the 6,000-pound Mars Soft Lander/Rover and two more Jupiter-Saturn-Pluto Mariner-class flybys, expending two Tug/LM-Bs.

In 1980, a second Venus Explorer Orbiter would leave Earth, as would two Jupiter Flyby/Atmosphere Probe spacecraft. The latter would expend two Tug/LM-Bs. The year 1981 would see a second Mars Explorer Orbiter, two Saturn Mariner-class Orbiter/Atmosphere Probes, and two more expended Tug/LM-Bs.

NASA would launch only one automated planetary mission, the 8,000-pound Mercury Solar Electric Orbiter, in 1982. Venus would get another Venus Explorer Orbiter and a Venus Mariner Orbiter/Rough Lander in 1983. NASA would also launch its second comet mission, this time a Mariner rendezvous with Comet Kopff. With a mass of 8500 pounds, it would be the heaviest of the 21 automated probes in the Balanced Base program. Mars would get a second High Data Orbiter and a second Soft Lander/Rover in 1984.

Back in NASA's piloted program, between 1979 and 1981 Int-21s would launch three more LEO SSMs. These would be combined with the first LEO SSM to form a "Space Base" with a permanent crew of from 50 to 100 astronauts. In 1980, an Int-21 would launch into LEO an SSM that would be mated to a Nuclear Shuttle and boosted to GEO. Early in 1979, Space Shuttle missions would begin to fly at a rate of 30 per year; by mid-1980, Grenning had the number of flights ramping up to 90 per year.

One proposed Space Base configuration. This three-armed design, which would have a permanent crew complement of 50 astronauts and scientists, would spin about its axis to produce acceleration in the habitat arm (left) which the crew would feel as gravity. The other two arms would each hold a nuclear reactor at a safe distance from the crew in the habitat module and core section. Also visible to the right of the Space Base is a small free-flying science module; these would dock with the non-spinning core section for servicing. Image credit: NASA
As indicated earlier, Grenning tied manned Mars missions to no particular year. Probably the manned Mars program would not begin until NASA had ample experience with long-duration spaceflight, orbital assembly, and Nuclear Shuttle operations. The Bellcomm planner did, however, lay out a seven-year plan encompassing two complete manned Mars missions and the first half of a third. The first and second missions and second and third missions would overlap.

All three would follow a conjunction-class mission profile; that is, they would reach Mars in about six months, remain there for about 18 months, and return to Earth in about six months. For safety, two identical six-man Mars spacecraft would travel as a convoy. At launch from the Space Base, each would comprise three Nuclear Shuttles, a mission module housing the crew, a payload module bearing unmanned probes and supplies, and a two-stage manned Mars Excursion Module (MEM) lander. Both Mars spacecraft would be capable of supporting the entire 12-man mission complement in case one failed catastrophically.

Nuclear Shuttle IPP mission applications would culminate with Mars missions in the 1980s. Each Mars expedition would include two piloted Mars spacecraft and each piloted Mars spacecraft would include one Nuclear Shuttle with strap-on tanks (as shown here) or a cluster of three Nuclear Shuttles (as shown in the next image). Image credit: NASA
The IPP Mars mission would have seen two Nuclear Shuttles used as interplanetary boosters. After they set a third Nuclear Shuttle, a Space Station Module-based crew module, and a piloted Mars Excursion Module lander on their way, each would have separated, turned end-for-end, and fired its NERVA engine to slow down and return to low-Earth orbit for reuse. Image credit: NASA
A pair of IPP interplanetary spacecraft en route to Mars. The bulbous forward section (right) would have housed sample-returner probes and the Mars Excursion Module piloted Mars lander. Image credit: NASA
Eighteen months before the first mission was set to depart the Space Base, NASA would launch four Nuclear Shuttles on Int-21 rockets and then launch four Space Shuttles to top off their tanks. The following year, the space agency would launch two more Nuclear Shuttles. These would each have a half-load of LH2 propellant because the Int-21s that launched them would also carry one MEM each. Topping off the Nuclear Shuttles' tanks would need three Space Shuttle flights. Six Shuttle flights would fuel Space Tug/LM-Bs used for Mars spacecraft assembly. A final pair of Int-21s would launch the twin SSM-derived Mars spacecraft mission modules; a final Space Shuttle would launch the Mars spacecraft crews.

As the countdown clock reached zero, the NERVA engines in the two outboard Nuclear Shuttles on each spacecraft would fire to place the third Nuclear Shuttle, mission module, payload module, and MEM on course for Mars. They would then shut down, separate, turn end for end, and fire their engines again to slow themselves and return to LEO. The center Nuclear Shuttle on each spacecraft would perform course corrections and slow the spacecraft so that Mars's gravity could capture them into orbit.

The Apollo Command Module-shaped MEM was designed to descend through the thin martian atmosphere found by the 1960s flyby Mars Mariners. It would have comprised two main parts: the descent module with Mars surface living accommodations and an airlock/garage with Mars surface rover; and the cramped ascent module, where the crew would ride during descent, landing, and ascent after the surface mission was complete. Image credit: NASA
MEM ascent stage liftoff. The ascent stage was meant to be a stage-and-a-half design with a cluster of approximately conical propellant tanks which would have been cast off during ascent and integral tanks in its cylindrical core stage. Image credit: NASA
After 18 months at Mars, during which at least one MEM would land on Mars for about a month (the second might be held in reserve in Mars orbit as a rescue vehicle), the twin center Nuclear Shuttles would fire again to put the mission modules on course for Earth. They would be used to perform course corrections; then, as they neared Earth, they would fire for the last time to slow the mission modules for capture into Earth orbit. Space Tug/LM-Bs would retrieve the Mars crews and the center Nuclear Shuttles.

The second and third Mars missions would be carried out in much the same way. The four outboard Nuclear Shuttles from the first mission would be reused for the second and third missions and the two center Nuclear Shuttles from the first mission would be reused for the third mission. The second mission would leave LEO before the first mission returned, so would need two new center Nuclear Shuttles. Grenning wrote that the third mission, preparations for which would begin in the fifth year of the seven-year program, might establish the first semi-permanent Mars surface base.

Grenning forecast that the seven-year manned Mars program would need four Space Shuttle flights and four Int-21 flights in its first year to place Mars spacecraft components and (especially) propellants into LEO. Year 2, toward the end of which the first two manned Mars spacecraft would depart from Earth orbit, would need four Int-21s and 13 Shuttles.

Year 3, during which preparation for the second Mars expedition would begin, would need just one Int-21 and 13 Shuttle flights. NASA would launch 20 Space Shuttle flights and three Int-21s in the Mars program's fourth year, 10 Shuttle flights and no Int-21s in its fifth, and 24 Shuttle flights and four Int-21s in its sixth. The final year of the program would see no Int-21s and 13 Shuttle flights.

Grenning also summed up the number of flights required to carry out the Maximum Rate cislunar program from 1975, when IPP stations and spacecraft began to replace Apollo-based stations and spacecraft, to 1984. The Space Shuttle fleet would accomplish 518 missions to LEO. The Saturn VC would fly 11 times between 1975 and 1979, when it would be phased out in favor of manned lunar flights via the Space Shuttle, LEO SSM, Nuclear Shuttle, lunar-orbit SSM, and LM-B. The Int-21 would fly 25 times, with a peak annual launch rate of five in 1981.

Was the Mueller/Paine IPP in any sense realistic? It depends on the judgement criteria one uses. Certainly, it was not a realistic option for 1970 America due to domestic political and economic considerations, the opposition of the Nixon White House and the Congress, and public disinterest.

In addition, one might take issue with its confident assertion that its network of reusable space systems and permanent and semi-permanent bases would save money. Complex reusable space systems require either costly development or costly maintenance and refurbishment. A single failure can take down an entire network of interdependent complex systems, and pioneering systems are more prone to failure than well-established ones. If, for example, a Space Shuttle had exploded, then crew and propellant transport would have ground to a halt throughout the IPP infrastructure for an indeterminate period of time.

One might, on the other hand, argue that the IPP's scale was not adequate for the challenges of piloted space exploration. Even the grand-scale IPP would have permitted astronaut access only to cislunar space and Mars. Perhaps we find the IPP grandiose in part because we have been conditioned to "think small" about space exploration. If our plans took in our entire local neighborhood - the Solar System - and sought to be realistic, then they would of necessity demand a scale orders of magnitude beyond that of the IPP.

Sources

"Integrated Manned Space Flight Program Traffic Model Case 105-4," E. M. Grenning, Bellcomm, Inc., 4 June 1970

The Next Decade in Space: A Report of the Space Science and Technology Panel of the President's Science Advisory Committee, Executive Office of the President, Office of Science and Technology, March 1970

"Statement About the Future of the United States Space Program," Richard M. Nixon, 7 March 1970

"An Integrated Space Program for the Next Generation," George Mueller, Astronautics &  Aeronautics, January 1970, pp. 30-51

"Integrated Space Program - 1970-1990," Internal Note-PD-SA-69-4, Terry Sharpe & Georg von Tiesenhausen, Advanced Systems Analysis Office, Program Development, NASA Marshall Space Flight Center, 10 December 1969

America's Next Decades in Space: A Report for the Space Task Group, NASA, September 1969

The Post-Apollo Space Program: Directions for the Future, Space Task Group Report to the President, September 1969

"Manned Mars Landing Presentation to the Space Task Group," Wernher von Braun, 4 August 1969

"Integrated Manned Space Flight Program: 1970-1980," NASA Office of Manned Space Flight, NASA Headquarters, 12 May 1969

Astronautics and Aeronautics, 1970, NASA SP-4015, 1972, pp. 77-79, 82-84

Astronautics and Aeronautics, 1969, NASA SP-4014, 1970, pp. 266-269, 304-305, 308

After Apollo? Richard Nixon and the American Space Program, John M. Logsdon, Palgrave MacMillan, 2015

More Information

Triple-Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

An Alternate Station/Shuttle Evolution: The Spirit of '76 (1970)

McDonnell-Douglas Phase B Space Station (1970)

Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter