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)