Chronology: Piloted Flybys 1.0

The crew of a piloted flyby spacecraft prepares to retrieve the upper stage of a Mars Surface Sample Returner probe. Image credit: NASA.

In the 1960s NASA expended at least as much study effort on piloted missions that would fly past Mars and Venus without stopping as it did on missions to land crews on Mars. Piloted flybys were seen as a low-cost stepping stone linking Apollo lunar landings and staffed space stations in Earth orbit with piloted planetary landing missions. It is in that context that we must judge and try to understand them today.

Chronology is a vital component of history. In this blog, however, my posts do not always appear in chronological order. Hence the need for "Chronology" posts like this one that enable the reader to access posts on a particular topic in the proper chronological order. Other posts of this type are listed under "More Information" below. 

EMPIRE Building: Ford Aeronutronic's 1962 Plan for Piloted Mars/Venus Flybys

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

Apollo to Mars & Venus: North American Aviation's 1965 Plan for Piloted Planetary Flybys in the 1970s

A New Step in Spaceflight Evolution: To Mars by Flyby-Landing Excursion Mode (1966)

To Mars by Way of Eros (1966)

Relighting the FIRE: A 1966 Proposal for Piloted Interplanetary Mission Reentry Tests

NASA's Planetary Joint Action Group Piloted Mars Flyby Study (1966)

The First Voyager (1967)

Apollo Ends at Venus: a 1967 Proposal for Single-Launch Piloted Venus Flybys in 1972, 1973, and 1975

Venus as Proving Ground: A 1967 Proposal for a Piloted Venus Orbiter

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

Floaters, Armored Landers, Radar Orbiters, and Drop Sondes: Automated Probes for Piloted Venus Flybys (1967-1968)

MSSR as MEM (1967-1968)

Things to Do During a Venus-Mars-Venus Piloted Flyby Mission (1968)

Flyby's Last Gasp: North American Rockwell's S-IIB Interplanetary Booster (1968)

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

Two for the Price of One: 1980s Piloted Missions with Stopovers at Mars and Venus (1969)

Revival: A Piloted Mars Flyby in the 1990s (1985)

Footsteps to Mars (1993)

More Information

Chronology: Apollo X, Apollo Extension System, and Apollo Applications Program (AAP) 1.0

Chronology: Asteroids, Comets, and Other Small Bodies of the Solar System 1.0

Chronology: Venus 1.0

Chronology: Apollo-to-Shuttle Transition 2.0

Chronology: Failure Was an Option 1.0

Chronology: Space Station 1.0

Chronology: Apollo X, Apollo Extension System, and Apollo Applications Program (AAP) 1.0

Repurposing Apollo: a modified Apollo Command and Service Module (CSM) (upper right) spacecraft moves through space docked with an Apollo Telescope Mount (ATM) derived from the Lunar Module (LM) lander. NASA's Apollo Applications Program (AAP) would have seen ATMs operating alone, with docked CSMs, and docked with AAP Orbital Workshops. Image credit: uncertain, but probably Grumman, makers of the LM.

This is the latest in a series of chronology posts in this blog. I usually write posts separately, with little regard for how they fit with others; these posts enable me to preserve that approach, which I find productive, while also linking separate posts to tell a larger story. This chronology post focuses on the Apollo Applications Program (AAP).

Begun formally in 1965, AAP grew from the Apollo Extension System, Apollo X, Manned Orbital Research Laboratory, and related proposals of the first half of the 1960s. Though backed by President Lyndon Baines Johnson, who saw it as a logical Apollo successor program, AAP suffered from repeated funding shortfalls and internal NASA squabbling.

The Apollo 1 fire (27 January 1967) took place within the main Apollo Program, but it was the final straw for AAP. The program was not formally ended, however, until the Skylab Program took over some of its Earth-orbital objectives in 1970.

AAP evolved into the three J-class Apollo missions (1971-1972) and four Skylab missions (1973-1974). Some have sought to portray the 1975 Apollo-Soyuz Test Project (ASTP) flight as an AAP successor; it is, however, better seen as a spinoff of Integrated Program Plan (IPP) space rescue planning. Nixon-era politics obscured ASTP's link with the IPP.

Apollo Extension System Flight Mission Assignment Plan (1965)

Relighting the FIRE: A 1966 Proposal for Piloted Interplanetary Mission Reentry Tests

Saturn-Apollo Applications: Combining Missions to Save Rockets, Spacecraft, and Money (1966)

"Without Hiatus": The Apollo Applications Program In June 1966

Apollo Applications Program: Lunar Module Relay Experiment Laboratory (1966)

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

Apollo Ends at Venus: A 1967 Proposal for Single-Launch Piloted Venus Flybys in 1972, 1973, and 1975

To "G" Or Not To "G" (1968)

A Forgotten Rocket: The Saturn IB

Rocket Belts and Rocket Chairs: Lunar Flying Units

As originally conceived, AAP would have included many lunar-orbital and lunar-surface missions. Pictured here is an LM-derived, automatically landed LM Shelter designed to support two astronauts during a surface stay lasting 14 days (one lunar daylight period). The astronauts would have arrived separately in an LM-derived "Taxi" spacecraft. Image credit: Grumman.

Chronology: Asteroids, Comets, and Other Small Bodies of the Solar System 1.0

1 Ceres is complex and shows signs of ongoing surface activity. Image credit: NASA.

Chronology is essential to understanding history, yet in this blog I write posts about planned space missions more or less at random, with little regard for the order in which they occurred. Because of this, I occasionally feel moved to publish omnibus chronological posts like this one. So far, I've applied the chronological treatment to groups of posts on Space Stations, catastrophic failure during space missions, missions to Venus, and the Apollo-to-Shuttle Transition. 

This post's topic is tied to Asteroid Day 2020. It establishes chronology for posts related to some of the Sun-orbiting small bodies of the Solar System: specifically, asteroids, comets, dwarf planets, and Kuiper Belt Objects (KBOs). In this introductory essay, I'll start with the largest members of these four broad classes. 

1 Ceres is an asteroid and a dwarf planet, much as 134340 Pluto is a KBO and a dwarf planet. Ceres, discovered on the first day of the 19th century, is the queen of the Main Belt between Mars and Jupiter, much as Pluto is the king of the Kuiper Belt, which begins just inside the orbit of Neptune. Clyde Tombaugh discovered Pluto on 18 February 1930, at Lowell Observatory.

Ceres is the largest and most massive asteroid. Pluto remains the largest known KBO, though new discoveries could nudge it from the top spot. Pluto is not the most massive Solar System body known beyond Neptune; that honor presently belongs to 136199 Eris, another KBO and dwarf planet, which for a time was thought to be larger than Pluto.

Ceres was not immediately classified as an asteroid when it was discovered. It was widely considered to be a planet until the 1850s, by which time new data — the discovery of more than a dozen other bodies orbiting with it between Mars and Jupiter — had made clear to everyone that it should be classified as the first known example of a new class of small Solar System body. Ceres pro forma became the first asteroid.

In similar fashion, Pluto was widely considered to be a planet until the early 2000s. Beginning in 1992, space scientists discovered that Pluto has siblings. This confirmed the existence of the long-hypothesized Kuiper Belt. The parallel with Ceres was not lost on scientists. Pluto became pro forma the first KBO.

In science, classification is fundamentally about clear communication, which is essential for collaborative research. Classification is not treated as a frivolous matter by most scientists. Only after sufficient data has been obtained, exchanged, and debated is an initial classification changed. 

Since the 1990s, scientific debate has taken place among space scientists via digital communication, enabling far more participation than in the past. The formal in-person poll that reclassified Pluto as a dwarf planet on 24 August 2006 included only a small percentage of the tens of thousands of space scientists scattered around the world; the matter of Pluto's classification had, however, already been widely debated. 

In fact, the vote marked the end of a 76-year-long scientific process. When first discovered, Pluto was assumed to have a mass about six times that of Earth. It had to be that massive to have enough gravitational pull to account for observed deviations in the orbit of Neptune, which is another story (you can read about it among the posts linked below). Pluto did not, however, show a disk, which implied that it was very dark, very dense, or both. 

Pluto's orbit also crossed that of Neptune, which made it unique among the planets. Planet-crossing is common among small bodies such as asteroids, but who ever heard of an asteroid with six times the mass of Earth?

Discovery in 1978 of Charon, Pluto's largest moon, enabled scientists to calculate Pluto's mass accurately for the first time. It has just one-fifth of 1% of Earth's mass, or less than 20% of the mass of Earth's Moon. They then determined Pluto's diameter; it measures less than three times the diameter of Ceres, or about two-thirds the diameter of Earth's Moon. It is astonishing that Tombaugh was able to spot Pluto using the crude astronomical tools available in 1930.

This is as good a place as any to express my view that the term "dwarf planet" should be retired. It is not especially useful to scientists, does not enhance public understanding so is worse than useless for science education, and appears to be moribund. Though perhaps a dozen KBOs discovered since 2006 appear to qualify for the label, none have been added to the initial list of five (in addition to the three I have already mentioned, they include Haumea and Makemake).

Asteroid exploration has advanced rapidly since the 1990s, in part because missions bound for other worlds often can find one or more asteroids to visit along their flight path. Galileo, bound for Jupiter orbit, became the first spacecraft to fly past an asteroid, 951 Gaspra, on 29 October 1991. Two years later, it flew past 243 Ida, in the process imaging Dactyl, the first asteroid moon to be found.

Dedicated asteroid missions began in February 1999 with a bit of a flub; the NEAR Shoemaker spacecraft suffered a computer glitch and missed its first opportunity to enter orbit about the near-Earth asteroid 433 Eros. A year later, NEAR Shoemaker fired its engines to slow itself so that Eros could capture it, making it the first asteroid orbiter. On 12 February 2001, it ended its mission with a bonus rough landing on Eros — the first asteroid landing.

The Dawn spacecraft entered orbit around 4 Vesta in July 2011, thus becoming the first spacecraft to orbit a Main Belt asteroid. It moved on to Ceres, achieving orbit around the largest asteroid in March 2015. 

2015 was a hot year for small-body exploration. NASA's New Horizons spacecraft performed a Pluto fast flyby in July of that year, making it the first spacecraft to visit a KBO. New Horizons flew past a second, smaller KBO, 486958 Arrokoth, in January 2019. Arrokoth is the most distant Solar System body yet explored by a spacecraft.

Dedicated comet missions began in 1985-1986, when a four-spacecraft European-Japanese-Soviet "armada" explored 1P/Halley, the most famous comet. The spacecraft did not try to match orbits with Halley, which revolves around the Sun "backwards" relative to the planets; instead, they carried out fast flybys. In March 1986, Europe's Giotto spacecraft raced past Halley's dark nucleus at a relative velocity of 68 kilometers per second.

Europe's Rosetta spacecraft orbited 67P/Churyumov-Gerasimenko from August 2014 to September 2016. It was the first comet orbiter. Rosetta's time-at-target bracketed the comet's closest approach to the Sun, enabling unprecedented close-up observations of activity triggered by solar heating. Rosetta released the Philae lander on 12 November 2015; though it did not land properly, Philae returned images and other data from the surface for about three days.

An exciting new frontier in small body exploration is now opening. In October 2017, the first asteroid known to have originated outside the Solar System, 1I/'Oumuamua, was discovered. We know that it originated elsewhere in the Milky Way because it is moving too quickly for the Sun's gravity to do more than bend its course before it returns to interstellar space. The first interstellar comet, 2I/Borisov, was found in August 2019.

These new discoveries have inspired proposals for intercept missions. None has so far advanced to the point of serious consideration. Both bodies will, however, remain within range of expected human spaceflight technology for a few decades at least, and the list of known interstellar visitors seems likely to grow, providing new candidate star-roving small bodies for exploration.

The links below lead to posts related to small Solar System bodies dated from 1962 through 2005. In addition, three posts not firmly linked to specific years are included at the bottom of the list.

Pluto, Doorway to the Stars (1962)

To Mars by Way of Eros (1966)

Missions to Comet d'Arrest and Asteroid Eros in the 1970s (1966)

MIT Saves the World: Project Icarus (1967)

Things to Do During a Venus-Mars-Venus Piloted Flyby Mission (1967)

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

Multiple Asteroid Flyby Missions (1971)

Cometary Explorer (1973)

A 1974 Plan for the Slow Flyby of Comet Encke

Earth-Approaching Asteroids as Targets for Exploration (1978)

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

Visions of Spaceflight, c. 2001 (1984)

Catching Some Comet Dust: Giotto II (1985)

New Horizons II (2004-2005)

The Challenge of the Planets, Part Two: High Energy

The Challenge of the Planets, Part Three: Gravity

Pluto: An Alternate History

Chronology: Venus 1.0

Digital elevation model of one hemisphere of Venus based on Magellan radar mapper data. Blue and purple signify low elevations, shades of green signify intermediate elevations, and red, pink, and tan signify high elevations. The tallest mountain on Venus, Skadi Mons, is part of Maxwell Montes, the light colored "tadpole" feature near the top of the image. Image credit: NASA.

Chronology is the exoskeleton of history; without its supporting structure, events collapse in an unrecognizable heap. Because this blog presents historical spaceflight plans and their context in random order, without the benefit of an overarching chronology, I periodically write a post which places in chronological order posts in this blog that cover a specific subject area.

This time around, the subject area is Venus. Until the early 1960s, many scientists held out hope that Venus might support life. Even before Mariner II flew past it (14 December 1962), however, scientists had begun to suspect that close examination would undermine their visions of a clement Venus. The cloudy planet soon became an object lesson in the importance of greenhouse gases in planetary atmospheres.

Among the planets, no world has received more visitors than Venus. From the 1960s until the 1980s, Venus was the main planetary exploration target of the Soviet Union; no country placed more spacecraft on the Venusian surface.

Mariner 10 was the first spacecraft to fly by Venus and use it as a gravity-assist way station (5 February 1974); that is, it used the planet's gravity and orbital momentum to change its course and speed, enabling it to conduct three Mercury flybys in 1974-1975. The twin Soviet Vega spacecraft each used a Venus gravity-assist in 1985 to gain enough energy to reach Comet Halley in 1986; during their Venus flybys, they released combination lander/balloon payloads.

Venus helped to rescue the NASA robotic exploration program in the late 1980s. The U.S. space agency had intended to launch the Galileo Jupiter orbiter and probe into low-Earth orbit in May 1986 attached to a powerful Centaur G-prime upper stage in the payload pay of a Space Shuttle Orbiter. Astronauts would have released the stage and spacecraft, then the former would have ignited to boost the latter directly to Jupiter, with arrival in December 1988.

After the Challenger Space Shuttle failure (28 January 1986), however, Centaur G-prime, which burned liquid hydrogen fuel with liquid oxygen oxidizer, was judged to be too volatile to carry on board a piloted spacecraft. In its place, NASA opted for a solid-propellant upper stage and a complex Venus-Earth-Earth Gravity Assist (VEEGA) trajectory. Following launch on board the Shuttle Orbiter Atlantis (18 October 1989), a Venus flyby (10 February 1990) put Galileo on course for Earth gravity-assist flybys in December 1990 and December 1992 with arrival at Jupiter in December 1995.

Galileo had been expected to be the first U.S. planetary spacecraft launched since Pioneer Venus Multiprobe (PVM) left Earth in August 1978; its new reliance on the VEEGA trajectory meant, however, that NASA had to shuffle its planetary mission schedule. Because Galileo needed to use the October 1989 launch window for a direct flight to Venus, the Magellan Venus radar mapper lifted off on board Atlantis (4 May 1989), orbited the Sun one-and-a-half times, and entered Venus polar orbit (10 August 1990). Missions to Venus thus bracketed a nearly 11-year drought in U.S. planetary mission launches.

In recent years, we have seen proposals for piloted Venus orbiter and atmosphere missions. These mark a renewal of interest that began in the 1950s and continued through the 1960s. Had those early plans gone ahead, NASA might have launched astronauts on Venus flyby and orbiter missions in the 1970s and early 1980s. Recent proposals and 1960s proposals have in common reliance on robots to explore the harsh Venusian surface; no humans would land there.

Venus is mentioned with (perhaps surprising) frequency throughout this blog. What follows is a chronological list of links to posts with a significant Venus exploration component.

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

EMPIRE Building: Ford Aeronutronic's 1962 Plan for Piloted Mars/Venus Flybys

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

Venus as Proving Ground: A 1967 Proposal for a Piloted Venus Orbiter

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

Apollo Ends at Venus: A 1967 Proposal for Single-Launch Piloted Venus Flybys in 1972, 1973, and 1975

Floaters, Armored Landers, Radar Orbiters, and Drop Sondes: Automated Probes for Piloted Venus Flybys (1967-1968)

Things to Do During a Venus-Mars-Venus Piloted Flyby Mission (1968)

Two for the Price of One: 1980s Piloted Missions with Stopovers at Mars and Venus (1969)

After Venus: Pioneer Mars Orbiter with Penetrators (1974)

Chronology: Apollo-to-Shuttle Transition 2.0

Three years ago I published on this blog the first of my "Chronology" compilations of links to posts with a common theme. That first chronological compilation brought together links to posts on the transition from Apollo to the Space Shuttle. The aim was to impose chronology on posts that do not occur in chronological order in this blog as an aid to reader understanding.

This, my fourth "Chronology" compilation, updates that first compilation. I've added links to three posts dating from 1968, 1970, and 1972; that is, near the start, at the middle, and near the end of the planning phase of the Apollo-Shuttle transition.

"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost (December 1969)

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

McDonnell Douglas Phase B Space Station (June 1970)

From Monolithic to Modular: NASA Establishes a Baseline Configuration for a Shuttle-Launched Space Station (July 1970)

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

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (August-September 1970)

The Last Days of the Nuclear Shuttle (February 1971)

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

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

"Still Under Active Consideration": Five Proposed Earth-Orbital Apollo Missions for the 1970s (August 1972)

Chronology: Failure Was an Option 1.0

Image credit: NASA.

Periodically, I write a post in which I list in chronological order links to posts in this blog which I originally presented in no particular order. History is, after all, in large measure about chronology, so these omnibus posts are meant to aid understanding. This post brings together posts with the label "failure was an option" and is offered as a memorial to the 17 persons who have died on board NASA spacecraft.

The end of January and beginning of February is a time of remembrance for NASA piloted spaceflight. On 27 January 1967, astronauts Gus Grissom, Edward White, and Roger Chaffee lost their lives in the Apollo 1 fire. On 28 January 1986, the crew of Space Shuttle mission STS-51L (Dick Scobee, Michael Smith, Ellison Onizuka, Judith Resnik, Ron McNair, Gregory Jarvis, and Christa McAuliffe) perished after the Orbiter Challenger disintegrated 73 seconds after launch. On 1 February 2003, the STS-107 crew (Rick Husband, William McCool, Michael Anderson, Kalpana Chawla, David Brown, Laurel Clark, and Ilan Ramon) died when the Orbiter Columbia broke up during reentry after a nearly 16-day mission in Earth orbit.

Piloted spaceflight has never been routine, though sometimes, for reasons that have little to do with best practices in space engineering, it has been unwisely treated as such. Throughout the history of U.S. piloted spaceflight, however, NASA and its contractors typically have tried to anticipate possible malfunctions and, where possible, develop procedures for dealing with them.

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

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

North American Aviation's 1965 Plan to Rescue Apollo Astronauts Stranded in Lunar Orbit

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

If an Apollo Lunar Module Crashed on the Moon, Could NASA Investigate the Cause? (1967)

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

A CSM-Only Back-Up Plan for the Apollo 13 Mission to the Moon (1970)

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

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

George Landwehr von Pragenau's Quest for a Stronger, Safer Space Shuttle (1984)

What If a Shuttle Orbiter Struck a Bird? (1988)

NASA's 1992 Plan to Land Soyuz Space Station Lifeboats in Australia

Chronology: Space Station 1.0

Japanese astronaut Aki Hoshide, a member the International Space Station (ISS) Expedition 32 crew, captures a self-portrait during a 5 September 2012 spacewalk. Reflected in his faceplate are U.S., Japanese, and European components of the ISS silhouetted against the Earth and, above his reflected right hand, NASA astronaut Sunita Williams. The brilliant Sun glaring past Hoshide's shoulder and the camera artifacts it creates make an already fascinating image particularly striking. Image credit: NASA.

My blog is only accidentally chronological in arrangement; because of this, occasionally I feel the need to compile a chronological listing of posts on a given topic as an aid to reader understanding. This is one of those times, and the topic this time around is space stations. Enjoy!

One-Man Space Station (August 1960)

Space Station Gemini (December 1962)

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

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (January 1967)

"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation

McDonnell Douglas Phase B Space Station (June 1970)

From Monolithic to Modular: NASA Establishes a Baseline Configuration for a Shuttle-Launched Space Station (July 1970)

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

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

Skylab-Salyut Space Laboratory (June 1972)

What If a Crew Became Stranded On Board the Skylab Space Station? (October 1972)

Reviving and Reusing Skylab in the Space Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters

Evolution vs. Revolution: The 1970s Struggle for NASA's Future (1978)

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

Naming the Space Station (1988)

The 1991 Plan to Turn Space Shuttle Columbia Into a Low-Cost Space Station (July-September 1991)

NASA's 1992 Plan to Land Soyuz Lifeboats in Australia (November 1992)

Chronology: Apollo-Shuttle Transition 1.0

Image credit: NASA.

Blogging history can be awkward — at least the way I do it. I tend to blog about whatever catches my interest as I sift through my files or locate new documents. The result is nothing like chronological, and chronology — the order in which things happened — is obviously essential for understanding history.

Because of this, I've decided to occasionally compile posts on a theme — posts that tell parts of one story — as a "chronological presentation." The posts listed below all can stand alone, but when placed together in chronological order they tell a more comprehensive story. As future posts fill in more gaps, the story will become more complete. Eventually, I'll post a 2.0 version of the link list below (and perhaps a 3.0 version after that).

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost (December 1969)

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

McDonnell Douglas Phase B Space Station (June 1970)

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

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (August-September 1970)

The Last Days of the Nuclear Shuttle (February 1971)

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

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