In just about a year, the New Horizons spacecraft will begin daily observations of the dwarf planet Pluto. A month later, on 14 July 2015, the piano-sized 478-kilogram probe will fly by Pluto at a nominal distance of only 10,000 kilometers moving at a velocity of 14 kilometers per second. At that speed and distance, New Horizons will briefly return images of Pluto in which objects as small as 50 meters wide could be visible.

Pluto was discovered in 1930, during Lowell Observatory’s hunt for a planet beyond Neptune. The observatory, founded in 1894 by wealthy Bostonian Percival Lowell to find proof of intelligent life on Mars, had begun its search for a trans-Neptunian planet in 1906. The search for Planet X (as Percival Lowell dubbed his hypothetical world) was at least partly motivated by the growing disdain with which Lowell’s Mars theories were greeted by professional astronomers. Lowell was eager that his observatory should be seen to be credible; discovery of a new planet would, he felt, restore and cement its eroded credibility.

Lowell employed a bevy of young women as “computers” to attempt to determine the position of Planet X based on the motion of the planet Neptune, which did not orbit the Sun precisely as expected. By assuming that Pluto had a mass six times as great as Earth, Lowell and his assistants narrowed the region of the sky where they expected to find Planet X to a portion of the constellation Gemini.

Percival Lowell did not live to see a trans-Neptunian world found (he died in 1916). Following his death, the search for Planet X stalled while his observatory and his widow feuded over the money he had bequeathed to endow Lowell Observatory in perpetuity. The search did not resume in earnest until 1929. When it did, it was meant to survey the sky along the entire ecliptic, the line along which the planets move. The ecliptic corresponds to the plane of the Earth’s orbit about the Sun.

On 18 February 1930, 23-year-old Lowell Observatory astronomer Clyde Tombaugh discovered that a tiny dot of light on photographic plates he had made on 23 January and 29 January 1930 had changed position slightly against the background stars. The small movement signified that it was moving slowly, and thus was far from the Sun. The tiny dot in Gemini, near Lowell’s predicted position for Planet X, was subsequently found on plates dating back to before Lowell’s death.

Lowell Observatory revealed Tombaugh’s find to the world on 18 March 1930, on what would have been Percival Lowell’s 75th birthday. It named the object Pluto, in part because the first two letters in the name were Percival Lowell’s initials. Newspapers around the world hailed the discovery of the Solar System’s ninth planet.

Pluto was a puzzler, however. An object six times Earth’s mass was expected to show a disk when observed using large telescopes, but Pluto did not. Furthermore, the planet had a bizarre tilted orbit that partly overlapped that of Neptune.

As astronomers continued their observations of Pluto, they revised estimates of its size downward. By 1960, some astronomers thought that it was about the size of Earth; others thought it might be as small as Mercury. This only increased the mystery surrounding the planet, for if it was to account for the observed discrepancies in Neptune’s orbit, then it had to be several times as massive as Earth. Some astronomers proposed the existence of another, larger planet beyond Pluto. One scientist proposed a much more novel explanation.

George Peterson Field was the pen name of Dr. Robert Forward. Safely hidden behind the protective cloak of his nom de plume, the newly minted Ph.D. physicist speculated in a “science fact” article in the December 1962 issue of Galaxy science fiction magazine that Pluto was a gift from a “Galactic Federation.”

He began by calculating that a body about the size of Mercury but with six times the mass of Earth would be so dense that it would have to be made of the collapsed matter found only in certain dwarf stars. Such an object could not exist naturally; unrestrained by the massive gravity of a dwarf star, it should have exploded long ago. Therefore, Forward asserted, Pluto must be artificial.

He suggested that Pluto was in fact a “gravity catapult.” He wrote that “it would have to be whirling in space like a gigantic, fat smoke ring, constantly turning from inside out.” A spacecraft that approached the ring’s center moving in the direction of its spin would be dragged through “under terrific acceleration” and ejected from the other side.

If the acceleration the ultradense smoke ring gave the spacecraft were about 1000 times the acceleration Earth’s gravity imparts to falling objects, then the ring would boost the spacecraft to nearly the speed of light in about one minute. The passengers and crew would, however, feel nothing as their spacecraft accelerated, for the gravitational force from the roiling ring would act on every atom of it uniformly. The ring would slow by a small amount as it accelerated the spacecraft.

Forward wrote that a “network of these devices in orbit around interesting stars” would provide “an advanced race” with an “energetically economical” means of star travel. The rings in the network would “cartwheel slowly” so that over time they would point at many possible destination stars.

A spacecraft accelerated by a ring could, upon arriving at another star in the network, enter that star’s ring moving against the ring’s spin. This would decelerate the spacecraft very rapidly and increase the ring’s spin by a tiny amount. In effect, the spacecraft would pay back the network for the acceleration it borrowed when it began its journey.

Forward ended his article by noting that such a device could be shot through space by a larger gravity catapult and braked “by pushing against a massive planet,” such as Neptune. This, he added, might account for Pluto’s odd orbit with respect to the eighth planet. He speculated that, at some time in the past, the Galactic Federation had noted the rise of humans and had launched Pluto toward Sol to serve as “a coming out present.”

Forward’s concept is so imaginative and appealing that it ought to be true. New data on Pluto soon ruled it out, however. In 1977, James Christy of the U.S. Naval Observatory Western Station, located just a few kilometers from Lowell Observatory in Flagstaff, Arizona, found Pluto’s moon Charon. The discovery of a body orbiting Pluto enabled astronomers to calculate its mass accurately for the first time. Pluto, as it turned out, has only one-quarter of 1% of Earth’s mass. Subsequently, it was found to have a diameter of only about 2350 kilometers, making it only two-thirds as large as Earth’s moon. After the turn of the 21st century, Pluto was found to have four more moons, all smaller than Charon.

Though Pluto did not turn out to be a link in a galactic transportation network, it did turn out to be a link to something big. Pluto was the first member of the Kuiper Belt to be found. The Kuiper Belt, a part of the Solar System long theorized but only confirmed beginning in 1992, is the “third realm” of bodies orbiting the Sun after the Sun-hugging realm of the rocky planets and the realm of the giant planets. It is far bigger than the first two realms combined. As New Horizons closes in on Pluto, we know of over 1000 bodies in trans-Neptunian space. Astronomers estimate that more than 100 times that number might exist. Assuming that New Horizons continues to operate as planned, mission planners expect to direct it past several more Kuiper Belt Objects after the Pluto flyby.

If Pluto is so small that it cannot account for the discrepancies in Neptune’s orbit, then what does? In August 1989, the Voyager 2 spacecraft flew past Neptune. By carefully tracking the robot spacecraft, celestial dynamicists refined their estimate of Neptune’s mass. When they did, the observed discrepancies in its orbital motion vanished. There was thus never a need to find a Planet X. Error had led to coincidence, and the result was mysterious Pluto.

Reference:

“Pluto, Doorway to the Stars,” George Peterson Field, Galaxy Magazine, December 1962, pp. 78-82.

Related Beyond Apollo Posts:

Galileo-style Uranus Tour (2003)

Beyond Cassini: Saturn Ring Observer (2006)

Throughout the Space Shuttle design process, NASA fought a rearguard action to preserve reusability. In 1969, the U.S. civilian space agency sought a fully reusable design with a piloted Booster and a piloted Orbiter, each carrying liquid propellants for placing the Orbiter into Earth orbit. Inadequate funding support from the Nixon White House and Congress coupled with a U.S. Air Force requirement that the Orbiter include a payload bay at least 60 feet long and 15 feet wide soon made that design untenable, however.

NASA and its contractor teams took a rapid series of cost-cutting steps during 1970-1972. The design process became messy and almost untrackable, with concepts proposed, abandoned, and proposed again in rapid succession or even simultaneously by different contractor and NASA teams.

The piloted Booster shrank after engineers tacked a pair of reusable solid-propellant rocket motors onto its tail. Then it ceased to be piloted, becoming part of what amounted to a three-stage rocket. Riding bolted to the top or side of the Booster’s expendable second stage, the piloted Orbiter became in effect a reusable third stage that would complete its climb to Earth orbit by burning liquid hydrogen (LH2) fuel and liquid oxygen (LOX) oxidizer carried in tanks inside its streamlined fuselage.

In part to prevent the Orbiter from growing out of all proportion as its payload bay grew, NASA moved low-density LH2 out of the Orbiter fuselage into cheap expendable drop tanks. The move also ended worries about safe containment within the Orbiter of volatile LH2, which is prone to slow seepage even through solid metal.

The Orbiter carried LOX for its ascent to orbit inside its fuselage for a little while longer. By August 1971, however, the delta-winged Orbiter contained only enough propellants to maneuver in orbit and to slow itself so that it could deorbit and reenter Earth’s atmosphere. At first, its orbital maneuvering engines were expected to burn LH2/LOX, but then NASA substituted hypergolic (ignite-on-contact) propellants.

During the same period, the preferred Shuttle stack design flip-flopped between two candidates. One (image at top of post) had two LH2/LOX stages stacked one atop the other. The first-stage engines were mounted directly beneath their stage, as on a conventional rocket. The engines for the second stage were built into the tail of the Orbiter mounted on its side. They would ignite at altitude after the first stage separated and, owing to their position on the side of the second stage, would thrust off center.

The first stage would be reusable; it would deploy parachutes and lower to a gentle landing at sea, then be recovered and towed to port for refurbishment. The second stage would reach orbit attached to the Orbiter, then would separate, reenter, and break up over the ocean.

The other candidate design (image below) featured a reusable Orbiter and a pair of reusable LH2/LOX boosters mounted on the sides of a single large expendable External Tank (ET). The lightweight ET’s interior would be split between a small tank for LOX and a large one for LH2. The twin side-mounted boosters would expend their propellants and fall away a couple of minutes after liftoff, deploy parachutes, and descend to a gentle ocean landing. Pipes leading from the ET tanks would feed propellants to the Orbiter’s engine cluster throughout ascent to orbit.

In a final cost-cutting move, NASA replaced the reusable liquid-propellant boosters with reusable solid-propellant boosters. The liquid-propellant boosters could be turned off in the event of a major malfunction; the solid-propellant boosters could not.

Mounting engines on the reusable Orbiter meant that they would be returned to Earth for refurbishment and reuse. The resulting off-center thrust troubled many engineers, however, because it meant that thrust forces would be transmitted through the Orbiter to the second stage (in the case of the first Shuttle design alternative) or the ET (in the case of the second). This would place added stress on the Orbiter, its links to the second stage or the ET, and the second stage or ET itself. Links between the second stage or ET and the Orbiter would include propellant pipe connections, which would be prone to leaks even without the added stress of off-center thrust.

Off-center thrust also meant that the LOX tank, when full the heaviest part of the second stage or ET, had to be situated atop the LH2 tank, the lightest part of the second stage or ET. Putting the dense LOX on top helped the Shuttle stack to remain stable in flight as the Orbiter’s engines rapidly emptied the second stage or ET and the stack’s center of gravity shifted, but it also placed added stress on the second stage or ET structure. Because the LOX at the top of the second stage/ET needed a long pipe to reach the engines on the Orbiter’s tail, the arrangement also increased the risk of propellant pipe rupture.

During the 1970-1972 Shuttle design evolution, several engineers proposed and re-proposed a novel alternative to off-center thrust: a cluster of reusable engines that would operate attached to the bottom of the expendable second stage or ET. After the Orbiter reached Earth orbit and its main engines shut down, the engine cluster would be detached from the second stage or ET and, using an armature system of booms or struts, be swung into a storage compartment inside the aft end of the Orbiter fuselage.

The second stage or ET would then be cast off. In the case of the ET, vented residual propellants would cause it to tumble, rapidly reenter the atmosphere, and break up. When the astronauts on board the Orbiter completed their mission in Earth orbit, the engine cluster would return to Earth with them, where it would be removed from the compartment, refurbished, and mounted on a new second stage or ET.

The NASA Manned Spacecraft Center – renamed the Lyndon B. Johnson Space Center (JSC) in February 1973 – managed Space Shuttle development. Shuttle engineers were quick to reject the swing-engine design. They did this mainly because its armature system seemed overly complex and thus prone to malfunctions.

The swing-engine concept would not die, however. In March 1974, in fact, JSC chief of engineering Maxime Faget (designer of the 1969 all-reusable Shuttle) and JSC engineers William Petynia and Willard Taub filed an application to patent the swing-engine design. By then, the decision to settle on the second stack configuration described above was two years old (NASA Administrator James Fletcher announced the choice on 16 March 1972).

The JSC engineers proposed three swing-engine design approaches. The U.S. Patent Office granted their patent on 30 December 1975.

All of their design approaches would, they argued, eliminate stress on the Shuttle stack caused by off-center thrust, enable transposition of the ET LOX and LH2 tanks, and improve stack flight characteristics during ascent through Earth’s atmosphere. The results would include a lighter Orbiter and ET, more payload, and greater safety.

As a bonus, the swing-engine system would enable the Orbiter to adjust its center of gravity after it released or took on an orbital payload, thus improving its reentry and atmospheric gliding flight characteristics. It would do this by shifting the engine cluster forward toward the back of the Orbiter payload bay using the same mechanical armature system that would swing the engines away from the bottom of the ET. The armature system would also serve to swivel (gimbal) the engines to steer the Orbiter/ET stack during ascent to orbit.

Other benefits would spring from the swing-engine design. The ET and engine cluster could be tested together without an Orbiter attached. All piping links between the Orbiter and the ET would be eliminated. Separable links between the ET and the engine cluster would be required, of course. Compared with the bulky Orbiter, however, the engine cluster would be small, easily handled, and easily mounted on the ET and tested for leaks.

The JSC engineers’ first swing-engine design, illustrated above, assumed a quartet of Shuttle engines, a single vertical stabilizer, and a door-shaped aft fuselage opening. The armature system would swing the engines into the fuselage so that their engine bells pointed aft.

The second design, illustrated below, assumed three Space Shuttle engines in a vertical row and an Orbiter with twin out-splayed vertical stabilizer fins. The armature system would swing the engines up and over the aft end of the Orbiter fuselage and lower them into a rectangular slot between the fins. After a horizontal landing on Earth, their engine bells would point skyward.

The JSC engineers’ third swing-engine design also assumed three engines arranged in a vertical row, but could be used with either single or double vertical stabilizer Orbiter configurations. The armature system would tilt the engine cluster 45° and slide it on rails into a rear-facing opening in the aft fuselage. As with their second design, the engine bells would point upward after the Orbiter glided to a landing.

The swing-engine concept had, of course, become a mere curiosity well before the U.S. Patent Office granted Faget, Petynia, and Taub their December 1975 patent. Following the March 1972 selection of the Shuttle stack configuration, NASA awarded Rockwell International the contract to build Space Shuttle Orbiters on 26 July 1972. The company built a total of five space-worthy Orbiters, each with three Space Shuttle Main Engines mounted in a triangle on their aft fuselages, over a span of more than 20 years.

The Orbiters functioned admirably, though they needed far more costly refurbishment and maintenance than NASA had envisioned when it proposed its all-reusable Space Shuttle design in 1969. Booster system malfunctions claimed two Orbiters and their seven-person crews, however. Challenger was destroyed on 28 January 1986 when a solid-propellant booster joint burned through, leading to ET structural failure and Orbiter break-up 73 seconds after launch. Columbia, the first Orbiter to fly (12-14 April 1981), was lost after foam insulation on the ET it rode broke loose during ascent and struck and damaged its wing leading edge. This led to wing structural failure and Orbiter breakup during reentry on 1 February 2003, at the end of a 16-day mission.

References:

Patent No. 3,929,306. Space Vehicle System, Maxime A. Faget, William W. Petynia, and Willard M. Taub, NASA Johnson Space Center, 5 March 1974 (filed), 30 December 1975 (granted).

Space Shuttle: The History of the National Space Transportation System, the First 100 Missions, Dennis R. Jenkins, 3rd Edition, 2008.

Related Beyond Apollo Posts

A Stronger, Safer, Better Space Shuttle (1982)

Shuttle With Aft Cargo Carrier (1982)

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

Fixing the NASA Piloted Program after Challenger: Views from 1989 and 1993

In mid-1964, only three years after President John F. Kennedy put the U.S. on course for the moon, a team of engineers at Marshall Space Flight Center (MSFC) in Huntsville, Alabama, became the first NASA group to study piloted Mars/Venus flyby missions based on Apollo Program hardware. They conducted their in-house study because they wanted to see humans voyage to other planets and because President Lyndon B. Johnson had made it clear that, to reduce spaceflight costs, the U.S. civilian space program after Apollo should be based on spacecraft and rockets developed for the moon landing.

In its public statements about its future, NASA emphasized that President Johnson supported Earth-orbiting space stations. Modified Apollo Command and Service Module (CSM) spacecraft would ferry scientist-astronauts, supplies, and experiment apparatus to the low-cost stations, which, it was hoped, would provide concrete benefits to American taxpayers through research in medicine, manufacturing processes, Earth resources exploration, agricultural monitoring, and advanced technology. Johnson also supported continued lunar exploration.

LBJ’s vision of NASA’s future made no mention of piloted Mars/Venus flybys based on Apollo’s technological legacy. On the other hand, neither did it specifically forbid them.

Even before the MSFC engineers completed their study in February 1965, other NASA centers sensed that they might be left behind and began their own piloted flyby studies based on Apollo technology. On 1 October 1964, North American Aviation (NAA), the Apollo CSM prime contractor, began such a study for NASA’s Manned Spacecraft Center (MSC) in Houston, Texas. The company presented results of its nine-month study at MSC on 18 June 1965.

NAA proposed to exploit three major Apollo Program hardware elements: the Block II Apollo CSM (the design variant intended for lunar missions); two-stage and three-stage Saturn V rockets; and the Spacecraft-LEM Adapter (SLA), which in Apollo lunar landing missions housed the Lunar Excursion Module (LEM) moon lander and the CSM’s Service Propulsion System (SPS) engine bell during ascent through Earth’s atmosphere. (The LEM was subsequently renamed the Lunar Module and abbreviated LM.) The SLA linked the bottom of the CSM with the top of the three-stage Saturn V’s S-IVB third stage. NAA was the SLA prime contractor.

The photo of the Apollo 11 spacecraft on the launch pad at the top of this post zeroes in on its conical Command Module (CM) under the white Boost Protective Cover, its drum-shaped silver-and-white Service Module (SM), and, below that, its tapered, segmented white SLA. The CM and SM together formed the CSM. Workers on the launch pad gantry provide a sense of scale.

The bottom photo above, a striking view of the Apollo 15 CSM in lunar orbit, displays Block II Apollo CSM features obscured in the Apollo 11 launch pad image. These include the large Service Propulsion System (SPS) engine bell (left), the slightly discolored housing for umbilicals linking the SM with the silvery, conical CM, and the extended probe docking unit on the spacecraft’s nose (right).

The most obvious change in the Block II Apollo CSM for NAA’s piloted Mars/Venus flyby missions would be the replacement of the single SPS main engine with three LEM descent engines. The throttleable LEM engines, each with independent propellant tanks and plumbing, would provide propulsion redundancy during long voyages between planets.

Any single engine could perform all necessary maneuvers, NAA declared. Under normal circumstances, however, the middle engine would perform course corrections and the two outboard engines would perform a retro burn beginning not more than two hours before Earth-atmosphere reentry at the end of the Mars or Venus flyby mission.

NAA calculated that its flyby CMs would usually return to Earth traveling faster than the planned maximum Apollo lunar-return velocity of about 36,000 feet per second. Flyby mission reentry speed would depend on many factors; for example, a close Mars flyby typically meant a fast Earth-atmosphere reentry. The company calculated that 47,500 feet per second was a typical Mars flyby Earth approach velocity, while 44,000 feet per second was typical for a Venus flyby.

NAA told MSC that the CM’s bowl-shaped heat shield (A in the drawing above) could, in theory, be beefed up to withstand reentry at a blistering 52,000 feet per second. The company argued, however, that “engineering conservatism” made high-speed reentries unattractive. Hence the retro burn, which would slash reentry velocity to no greater than 45,000 feet per second. NAA told MSC that the Block II Apollo CSM heat shield would need only modest modifications to withstand reentry at that velocity.

NAA reported that the Block II Apollo CSM would have a total mass of 57,690 pounds. Hydrazine/nitrogen tetroxide propellants would account for 37,360 pounds of that total. The Venus flyby CSM would have a mass of 34,840 pounds with 16,000 pounds of propellants on board and the Mars flyby CSM would have a mass of 73,080 pounds with 44,770 pounds of propellants. The Mars flyby CSM would thus have more than twice the mass of the Venus flyby CSM, while the Venus flyby CSM would have a little more than half the mass of the Block II Apollo lunar CSM.

During the Mars flyby Earth reentry retro burn, the more extreme of the two, the outboard engines could fire for up to 29 minutes to slow the flyby CSM by up to 12,400 feet per second. The flyby SM would then separate, exposing the CM’s modestly beefed-up heat shield. During passage through Earth’s atmosphere, the heat shield might attain a temperature of 5000° Fahrenheit.

NAA recommended a crew of four for most of the piloted flyby mission scenarios it studied, though it conceded that a Venus flyby mission might get by with only three astronauts. To make room for a fourth crewmember in the flyby CM, the center launch-and-reentry couch (B1) would be relocated forward of its Apollo CM position, placing it closer to the main display and control console.

The new fourth couch (B3) would be mounted on the aft interior bulkhead about two feet behind and slightly above the relocated center couch. Some equipment would be moved to accommodate the new couch. The left-hand couch (not shown) and the right-hand couch (B2) would remain in their Apollo CM positions.

The remaining labeled systems on the drawing above were designed to link to other flyby spacecraft modules. The Apollo-type probe docking unit (C), for example, would link the CSM with a modified Apollo-type drogue docking unit on top of the flyby spacecraft’s main living and working volume, the three-deck Mission Module (MM).

As noted above, the Block II Apollo CSM included a single housing for umbilicals and cables that linked the SM and the CM. These carried water and electricity from fuel cells and gaseous oxygen from cryogenic tanks in the SM to the CM. Data, including voice signals transmitted through the CSM’s SM-mounted high-gain antenna, traveled in both directions. They also linked the CM Environmental Control System (ECS) to radiators on the SM hull. The umbilicals were severed and the housing hinged out of the way as the SM was cast off just before CM reentry.

NAA’s Mars flyby CSM would include two umbilical housings. The larger of these (D), present also on the Venus flyby CSM, would cover hoses for supplying the CM with water, oxygen, and nitrogen from tanks in the SM and cables for data transfer between the SM and the CM. Oxygen and nitrogen would be stored in separate tanks as high-pressure gas. Addition of nitrogen to the flyby CM’s breathing mix reflected NAA’s decision to abandon the Apollo CM’s pure oxygen atmosphere; the company made this choice in large part because data on the health effects of long-term exposure to a pure oxygen atmosphere were lacking.

Nitrogen would slowly seep into the flyby CM while it was unoccupied – that is, while the crew was in the MM – to make up for inevitable slow cabin leakage. To cool the flyby CM while a crew was on board, water would vent into space through an evaporative cooling chamber. Replacing the ECS radiators on the flyby SM hull with the evaporative system would not only simplify the flyby CSM ECS design, it would also largely eliminate the risk of ECS meteoroid damage. NAA considered this especially important for the Mars flyby CSM, which would skirt the inner edge of the Asteroid Belt after its Mars flyby.

NAA reminded its MSC audience that the flyby CSM would support its crew for a much shorter period of time than would the Block II Apollo CSM. The flyby crew would reach and depart Earth-orbit in the flyby CSM, return to Earth in the flyby CM in the event of an abort immediately after Earth-orbit departure, briefly power up the flyby CSM and fire its center engine during course corrections, and return to Earth’s surface in the flyby CM at the end of their mission. The company estimated that the flyby astronauts would live inside the flyby CM cabin for no longer than 72 hours at a stretch, not the 10 or more days of a lunar mission.

The smaller of the two umbilical housings (F) on the Mars flyby CSM would cover umbilicals forming part of its electrical power system. These would circulate coolant from a compact plutonium-fueled mercury-rankine isotopic system (E) in the flyby CM to redundant curved radiator panels on the flyby SM’s hull and back again in a continuous loop.

The 1370-pound isotopic system would generate four kilowatts of electricity for the flyby CSM, the MM, and the Probe Compartment attached to the MM. Shielding, water, and equipment would protect the flyby astronauts from the power system’s low-level radiation during the brief time they would ride in the CM.

The chief justification for an isotopic source on the Mars flyby CSM was the Mars flyby mission’s maximum distance from the Sun (about 2.2 times the Earth-Sun distance), which would render electricity-generating solar cells largely ineffective. The Venus flyby, on the other hand, could depend on an ample solar energy supply. NAA assumed when making its Venus flyby CSM mass estimate that a 525-pound solar-cell power system would be mounted on the Venus flyby spacecraft’s Probe Compartment.

If, however, NASA chose to make the piloted flyby CSM designs for Mars and Venus more or less the same (to reduce development costs, for example), it might choose to use an isotopic system in both the Mars and Venus spacecraft. In that case, the Venus flyby CSM would also include two umbilical housings and would have a correspondingly greater mass.

This post is the first in a series describing the piloted Mars/Venus flyby mission concept NAA developed for NASA MSC in 1964-1965. Other posts in the series will examine in detail the piloted flyby spacecraft’s 5600-cubic-foot MM, its Probe Compartment and cargo of automated probes, its artificial-gravity system, piloted flyby Earth-launch methods, and piloted flyby mission profiles.

References:

“An Evolutionary Program for Manned Interplanetary Exploration,” M. W. Jack Bell; paper presented at the AIAA/AAS Stepping Stones to Mars Meeting in Baltimore, Maryland, 28-30 March 1966.

Manned Mars and/or Venus Flyby Vehicles Systems Study Final Briefing Brochure, SID 65-761-6, North American Aviation, Inc., 18 June 1965.

“Future Effort to Stress Apollo Hardware,” Aviation Week & Space Technology, 16 November 1964, pp. 48-51.

Related Beyond Apollo Posts:

After EMPIRE: Using Apollo Hardware to Explore Venus and Mars (1965)

EMPIRE Building: Ford Aeronutronic’s Mars/Venus Piloted Flyby Study (1962)

Manned Asteroid Flyby Mission (1966)

Since I relaunched Beyond Apollo as a WIRED Science Blog in March 2012, I have sought to post at least weekly. There are, after all, so many aspects of space history to write about, so many tales to tell, that I could write something new every day for a decade and only just get started.

I’ve often fallen short of my goal. Were it not for a backlog of posts from Beyond Apollo before it came to WIRED and from my old Romance to Reality website, I probably would have managed at most three posts per month. At least one in three of those would probably have constituted what I term “piffle.” I don’t much care for piffle-y posts.

Then, starting in March, WIRED underwent upgrades and cleanup and a snag or two, with the result that I found myself not posting for a couple of weeks. I spent that time writing and massaging images for my recent Solar Power Satellite post, which, it turns out, has generated plenty of comment and earned some praise.

All of which leads me to think carefully about my old ambition of a post per week. I came to the realization that my meatiest (and perhaps best) posts are often as substantial as the articles I used to write for print magazines. I never turned out a 2500-word magazine article in a week; why should I expect to turn out a 2500-word blog post in a week and repeat the feat every week indefinitely?

As an aside, I learned early on that, word for word, shorter pieces take more time than longer pieces. A 2500-word article might need two weeks of earnest effort, not counting research, travel, and pitching the article in the first place. My NASA-published book Mir Hardware Heritage, on the other hand, I wrote in six months, and it has more than 200 pages. Humans to Mars, another NASA book, needed about eight months, but I was at work on several other projects, doing a summer fellowship in Washington, DC, and moving from Texas to Arizona at the same time.

So, getting back to the point of this post – henceforth, I plan to write a new post every two weeks. That’s 26 meaty posts per year, probably with a few “from the author” comments (like the one you are reading now) thrown in.

My next post will be about a 1965 North American Aviation piloted Mars/Venus flyby study performed for NASA’s Manned Spacecraft Center in Houston. It is part of a series of Beyond Apollo posts on the largely forgotten piloted flyby mission plans of the 1960s. I had thought that I had completed the images for the new post; adding an extra week to my production time means, however, that I have enough time to scan and polish up more cool images.

Thank you for reading Beyond Apollo.

Of all the many spaceflight concepts NASA has studied, the most enormous was the Solar Power Satellite (SPS) fleet. Czech-born physicist/engineer Peter Glaser outlined the concept in a brief article in the esteemed journal Science in November 1968, and was awarded a patent for his invention on Christmas Day 1973. In October 1976, the U.S. Department of Energy (DOE) and NASA began a three-phase, four-year joint study of the SPS concept. Total study cost was $19.6 million, of which DOE paid 60%.

Glaser had noticed that a satellite in geosynchronous Earth orbit (GEO), 35,786 kilometers above the equator, would pass through Earth’s shadow for only a few minutes each year. It was well known that a satellite in equatorial GEO moves at the same speed the Earth rotates at the equator (1609 kilometer per hour). This means that, for people on Earth’s surface, the satellite appears to hang motionless over one spot on the equator. Glaser also understood that electricity did not have to travel through wires; it could be beamed from a transmitter to a receiver.

Glaser mixed these three ingredients and came up with a satellite in equatorial GEO that would use solar cells to convert sunlight into electricity, convert the electricity into microwaves, and beam the microwaves at a receiving antenna (rectenna) on Earth. The rectenna would turn the microwaves back into electricity, then wires would carry it to the electric utility grid.

The great advantage an SPS enjoyed over a solar array on Earth’s surface was, as mentioned, that it would spend almost no time in Earth’s shadow. Earth’s rotation meant that an Earth-surface solar array could make electricity at most about half the time. The rest of the time it would sit dormant under the night sky.

The problem with the SPS concept was that, if a solar satellite was to contribute a meaningful amount of electricity to the interlinked U.S. utility grids – and, by DOE’s reckoning, “meaningful” meant gigawatts – then it would have to be colossal by normal aerospace engineering standards. The SPS silhouetted against the Sun in the NASA artwork at the top of this post is typical: it would have measured 10.5 kilometers long by 5.2 kilometers wide and had a mass of 50,000 tons.

Paired with a rectenna a couple of kilometers across, such an SPS would contribute five gigawatts to the U.S. electricity supply. DOE estimated that 60 such satellites with a total generating capacity of 300 gigawatts could contribute meaningfully to satisfying projected U.S. electricity demand in the 2000-2030 period.

There was, of course, no way that NASA could launch such huge satellites intact, or even in a few modular parts. It would need to construct the SPS fleet in space, most likely in GEO, from many parts. This called for an armada of highly capable space transport vehicles and an army of astronauts and automated assembly machines.

The “Space Freighter” pictured in the Boeing painting above was, as its name implies, meant to serve as the main cargo launcher for SPS construction. Fully reusable to cut costs, it would have comprised at launch a delta-winged, unmanned Booster with a piloted, delta-winged Orbiter on its nose. After separating from the Orbiter, the Booster would have deployed turbofan jet engines and flown to a runway at its launch site.

Had it been built, the Space Freighter would have utterly outclassed all other launchers. Its Orbiter would have delivered 420 metric tons of cargo to a staging base in low-Earth orbit (LEO). For comparison, the largest single-launch U.S. payload ever put into LEO, the Skylab Orbital Workshop, weighed 77 metric tons. Skylab was launched on a two-stage Saturn V rocket.

Engineers speak of “gross liftoff weight” (GLOW) when they describe large launchers. The Space Shuttle had a GLOW of about 2040 metric tons and the three-stage Apollo Saturn V, about 3000 metric tons. Estimated GLOW for the Space Freighter was a whopping 11,000 metric tons.

Alert readers will notice discrepancies in the paintings that illustrate this post. These occur because the images are based on design concepts developed by different engineers in different phases of the multi-year SPS study. The Boeing Space Freighter Orbiter design is different from the Space Freighter Orbiter design depicted above. This Orbiter, probably a NASA design, has skinny main wings, forward canard fins, and a payload bay near its front; not, as in the Boeing design, at mid-fuselage. It would, however, have had the same capabilities as the Boeing Space Freighter.

The NASA painting above depicts a hexagonal LEO staging base with a central “control tower.” Access tubes link the control tower to docking modules at the hexagon’s six vertices. Between the access tubes are color-coded triangular “marshaling yards” with socket-like bays for storing standardized Space Freighter cargo containers.

The staging base control tower has mounted on its roof a “space crane” descended from the much smaller Space Shuttle Canadarm, which was under development at the time DOE and NASA conducted their joint SPS study. The control tower space crane is positioning a cargo container so that an automated chemical-propulsion Orbital Transfer Vehicle (OTV) can dock with it. After docking and space crane release, the OTV would automatically transport the container to a construction base in GEO.

Another, smaller space crane rides a track around the edge of the hexagon. It is shown unloading a cargo container from the newly docked Space Freighter Orbiter.

The painting includes many other details. It shows, for example, what appears to be a conventional Space Shuttle Orbiter approaching the staging base in the background. Rockwell, prime contractor for the Space Shuttle, proposed that second-generation Space Shuttle Orbiters serve as dedicated crew transports for the SPS program. The company envisioned that replacing the Orbiter’s payload bay with a pressurized crew module would enable it to transport up to 75 astronauts at a time.

Next to the crew transport is a cluster of cylindrical modules for housing the staging base crew and astronauts in transit between Earth and GEO. A piloted OTV for transporting astronauts to and from the GEO SPS work-site – identical to the automated OTV, except for the presence of a pressurized crew module – is shown docked with the LEO staging base at lower right.

In the SPS study, NASA sought to balance automation and astronauts. Automation was, its engineers noted, good for repetitive actions such as fabricating the tens of kilometers of trusses needed to support SPS solar cell blankets.

The basic “beambuilder” depicted in the upper image above would turn tight rolls of thin aluminum sheeting into sturdy single trusses. The more complex multiple beambuilder system in the lower image would combine and link together single trusses to make the major structural members of the satellite.

Astronauts would supervise and maintain the beambuilder robots and join together the trusses they fabricated. Automated OTVs would deliver thousands of aluminum rolls to the GEO work-site, which the astronauts would then load into the beambuilders.

DOE and NASA expected to added two SPSs to the “fleet” in GEO each year starting in 2000. Each SPS would need about 200 Space Freighter launches and hundreds of OTV transfers between the LEO staging base and GEO. Propellants for the OTVs, as well as 50 metric tons of orbit trim propellants for each SPS per year, would demand even more Space Freighter launches.

Despite extensive reliance on automation, the 30-year SPS project would require the presence of nearly 1000 astronauts in space at all times. Most would be based in GEO.

In addition to construction workers, personnel needed in space would include physicians, administrators, OTV pilots, life support engineers, general maintenance workers (“janitors”), cooks, space suit tailors, and computer technicians. Personnel needed on the ground – at the launch/landing site, at the rectennas, and at widely scattered factories for manufacturing SPS parts, OTVs, spares, foodstuffs, and propellants – would outnumber astronauts by at least 10 to 1, NASA and DOE estimated. Building and operating the SPSs could become a major new U.S. industry.

As beambuilders and astronauts completed trusswork sections, automated OTVs would begin to deliver rolls of solar cell “blankets” to the SPS work-site. The NASA painting above shows in the background an automated OTV laden with bluish rolls of solar cell blankets (upper right).

Meanwhile, an automated system feeds blanket sections to a piloted “cherry picker” at the end of a small space crane. The cherry picker’s “pilot” – who wears only shirt-sleeves in his pressurized cab – uses manipulator arms to link one end of a solar cell blanket to a truss.

More than 50 square kilometers of solar cell blankets would be spread over the trusswork of each SPS in this way. The end result of this intensive human and machine labor is depicted in idealized form immediately below.

The lower painting above shows Glaser’s invention at work. The intense sunlight of space strikes solar cells, which are hidden from view (the image does, however, provide a good look at the backside of a completed SPS). Millions of silicon or gallium arsenide cells efficiently convert the sunlight into electricity.

The kilometer-wide steerable microwave transmission antenna at the lower end of the SPS converts the electricity into microwaves and focuses a microwave beam on a rectenna on Earth, nearly 36,000 kilometers away. The beam appears in the illustration as a ghostly cone; in reality, the microwaves would be invisible.

DOE and NASA envisioned building the 60 rectennas required for the SPS system from coast to coast along the 35° latitude line. Cities on or near that line include Bakersfield, California; Flagstaff, Arizona; Albuquerque, New Mexico; Amarillo, Texas; Oklahoma City, Oklahoma; Little Rock, Arkansas; Memphis and Chattanooga, Tennessee; and Charlotte, North Carolina. If one flew between these cities, one would overfly rectennas on the ground in different settings – forest, farm fields, mountains, swamp, desert – every 50 kilometers or so.

The 1970s saw growing awareness of environmental problems and the dangers of terrorism. DOE and NASA took pains to seek public input so that they could attempt to calm public fears. Most people polled worried about the microwave beams linking the SPSs with their rectennas on Earth. Some expressed concern about the environmental impact of the beams, while others feared that terrorists might seize control of an SPS and turn its beam on a city.

NASA pointed out that the beam would be de-focused to reduce risk to the Earth’s upper atmosphere, aircraft, and people working at the rectennas. As depicted in the painting, limited agriculture could take place under the rectennas, directly in the path of the microwave beams.

In addition, the microwave transmitter on the SPS could be designed to shut off if its beam drifted. DOE and NASA expected that each rectenna would have around it a “buffer” zone of uninhabited land; if the beam drifted a small distance before it turned off automatically, only the ring-shaped buffer would be affected.

In this final image of this post, we see the SPS fleet near the end of 2015; that is, halfway through the 30-year construction program, when 30 satellites would form a bright line across the southern night sky as viewed from the contiguous United States. A DOE document explained that each satellite would shine a little brighter than Venus. The satellites would appear about as far apart as the stars making up Orion’s belt. Widely available 7-x-50 binoculars would reveal each satellite’s rectangular shape.

The string of satellites would remain still against the background of moving stars and planets. In reality, of course, the stars and planets would remain still relative to the rotating Earth and the SPSs would keep up with Earth’s rotation.

Every six months, in spring and autumn, each SPS would pass through Earth’s shadow near midnight for several days in succession. During its brief shadow passage, a satellite would not produce electricity. One by one, starting with the eastern satellites, the SPSs would redden and grow dark. After about 10 minutes in eclipse, each would return to its full brightness.

The DOE/NASA SPS study generated thousands of pages of planning documents. Future Beyond Apollo posts will describe some of the SPS-related plans in detail.

References:

“Power from the Sun: Its Future,” Peter Glaser, Science, Vol. 162, 22 November 1968.

The Solar Power Satellite Concept: The Past Decade and the Next Decade, JSC-14898, July 1979.

Some Questions and Answers About the Satellite Power System (SPS), DOE/ER-0049/1, U.S. Department of Energy, Office of Energy Research, Satellite Power System Project Office, January 1980.

Satellite Power System Concept Development and Evaluation Program, Volume I: Technical Assessment Summary Report, NASA Technical Memorandum 58232, NASA Lyndon B. Johnson Space Center, November 1980.

Related Beyond Apollo Posts:

NASA Tries to PEP Up Shuttle/Spacelab (1981)

Evolution vs. Revolution: The 1970s Battle For NASA’s Future

As some of you might be aware, the WIRED website underwent some cleanup and upgrades a couple of weeks ago. Those fixes started to take effect and all us bloggers began to feel our way around a new blogging interface; then, out of nowhere, we got slammed with a malware attack. I’m a simple historian, so I don’t begin to understand all the technical jiggery-pokery. Suffice it to say, it was not a happy time.

Now, however, we’re back, thanks to the unyielding resolve and tireless efforts of the WIRED tech crew. Huzzah, huzzah, brave tech-minded gentlemen and ladies!

I didn’t spend the downtime napping. Assuming that this brief note successfully posts to Beyond Apollo – that is, that I’ve used the new security and blogger interfaces correctly – I plan to complete a really nifty visual essay in the next few days. The image at the top of this post – painted by a Boeing artist for NASA – will be part of it.

And, before I forget, Happy Yuri’s Night to one and all. Get out under the stars tonight, have a look at the gibbous moon and brilliant glowing Mars, and spare a thought for Vostok 1 and its brave occupant Yuri Gagarin, who became the first human in orbit 53 years ago today.

So, now it’s time to push the button and see what happens. In three, two, one. . .

Hello, Beyond Apollo fans! WIRED has been doing some updates & maintenance all over its site over the past couple of weeks, so I’ve been staying out of the way until the dust clears. I’ve been at work on several posts; and, as often happens when I work on posts with no immediate likelihood of posting, I’ve wandered all over the wonderful world of space history.

Which is fun for me, but which isn’t all that productive.

I plan to post in the next day or so a photo-essay on Solar Power Satellites as conceived in the 1970s. That will provide context for another post on a 1980 study of how to salvage Solar Power Satellites at the end of their service life, which should appear by this weekend.

Beyond Apollo is a space history blog with a difference. Rather than focus on missions that flew, nostalgia, or personalities, I explore space history in a much more original way: that is, through missions and programs that did not happen.

Some call these “might-have-beens.” Some Beyond Apollo posts describe “might-have-beens,” but I think that others describe “probably-could-never-have-beens” and “I-wonder-what-they-were-smokings.”

What’s the point of focusing on what wasn’t? First of all, many of the missions and programs that didn’t happen are fascinating. Also, the vast majority of proposed space missions and programs never leave the drawing board or conference publication, so unflown missions are actually more representative than flown ones.

There’s also the “perspective” factor. Unflown missions provide a different way of looking at space history. For example, historians of the Space Shuttle really miss the point if they do not study late 1960s/early 1970s plans for big space stations, for the Shuttle was originally proposed as a crew rotation/resupply vehicle for a Saturn V-launched core station. As the Saturn V rocket went away, the Shuttle’s role had to change dramatically.

Thank you for reading Beyond Apollo.

This is the last of seven consecutive Best of Beyond Apollo posts celebrating the second anniversary of Beyond Apollo’s move to WIRED Science Blogs. Each installment includes links to and images from five of my favorite Beyond Apollo posts – except for this final one, which includes three extra posts as a bonus.

EMPIRE Building: Ford Aeronutronic’s Mars-Venus Pilot Flyby Study (1962). Image: Ford Aeronutronic/NASA.

Linking Space Station and Mars: The IMUSE Strategy (1985). Image: NASA.

A Forgotten Pioneer of Mars Resource Utilization (1962-1963). Image: U.S. Army.

Mars Sample Return Site Selection & Sample Acquisition Study (1980). Image: NASA.

Modular Space Station Evolving from Gemini (1962). Image: NASA.

The Last Days of the Nuclear Shuttle (1971). Image: NASA/David S. F. Portree.

NASA Tries to PEP Up Shuttle-Spacelab (1981). Image: NASA.

Mercury Space Observatory (1964). Image: NASA.

Last Wednesday marked the beginning of Beyond Apollo’s third year as a WIRED Science Blog. To observe this auspicious occasion (and create a useful sampler to which I can refer prospective readers), I had planned to post five of my favorite Beyond Apollo posts each day through this past Saturday. An attempted upgrade of the entire WIRED site intervened, however, pushing my Friday post to today (and my Saturday post to tomorrow).

The best-laid plans of mice and men often go awry. Which is, if you think about it, what Beyond Apollo is all about. Except, I guess, it would be space mice and space men (and women) in this instance.

Skylab-Salyut Space Laboratory (1972). Image: Junior Miranda.

Ernst’s Ions Week Concludes: NERVA-Ion Mars Mission (1966). Image: NASA.

Mars in 1995! (1980-1981) Image: © David A. Hardy/http://www.astroart.org. Used by permission.

Piloted Split/Sprint Mission to Mars (1987). Image: Science Applications International Corporation/NASA.

Naming the Space Station (1988). Image: NASA.

Yesterday Beyond Apollo marked the beginning of its third year as a WIRED Science Blog. To celebrate and to create an easy-to-access wide-ranging Beyond Apollo sampler, on Sunday I began posting five of my personal favorite Beyond Apollo posts each day.

The original plan was to wind it up this Saturday, but I’ve just learned that WIRED Science Blogs will be undergoing maintenance starting Friday evening and lasting through the weekend. So, my planned Friday and Saturday posts will appear on Monday and Tuesday. Another side-effect of the forthcoming maintenance: all past Beyond Apollo reader comments will be absent for some indeterminate (but likely short) period of time.

Today’s Best of Beyond Apollo installment looks at four studies of potential space disasters that fortunately never happened and one that unfortunately did. The four that didn’t happen were technical in nature; the one that did was political and managerial.

The Eagle Has Crashed (1966). Image: NASA.

Lunar Accident Site Investigation (1967). Image: NASA/Arizona State University.

Marooned in Lunar Orbit (1968). Image: NASA.

If Galileo Had Fallen to Earth (1988). Image: NASA.

Canceled: Apollo 15 and Apollo 19 (1970). Image: NASA.