In the late 1960s, NASA was considering future applications for its Apollo hardware under the aptly named Apollo Applications program. One popular target for an AAP mission was Venus, our cosmic neighbour that was a scientific enigma at the time; admittedly our knowledge of Venus still isn’t complete. The space agency briefly looked at a plan that would see a crew of astronauts sent into orbit around Venus.
In 1962, NASA’s Mariner 2 probe began unraveling the mysteries of Venus. During its flyby missions, the probe returned enough data to tell scientists that Venus lacks a strong magnetic field, has extremely high surface temperatures, and that the radiation levels in interplanetary space are no more dangerous than the radiation anywhere else outside Earth’s protective magnetic field. Mariner 2 also told NASA scientists that there were more secrets locked under Venus’ cloud cover. It was a planet worth further investigation.
To look at possible future Venusian missions, NASA turned to Bellcomm Inc., a division of AT&T established in 1963 to assist the space agency with research, development, and overall documentation of systems integration. Bellcomm prepared a detailed proposal for a manned flyby of Venus using Apollo hardware and propulsion to guide and control the spacecraft. The Lunar Module was replaced with an Environmental Service Unit, and the Saturn V’s upper SIV-B stage was repurposed during the interplanetary transit by the crew of three astronauts into an additional living and recreational quarters. This mission, of course, never flew.
But even as a study, there’s one big problem with flybys: they give the crew one relatively short chance to observe and study their target planet up close. Mariner 2 surveyed Venus during its interplanetary transit, but it only had 45 minutes of really close observations. The manned flyby offered the crew a similarly fleeting opportunity, hardly enough to make the 400 day mission worth it.
An orbital mission could change that. In 1967, NASA’s Lewis Research Center in Cleveland, Ohio prepared a study for a manned orbital mission of Venus, again using existing Apollo hardware and propulsion systems.
The study looked at launch dates between 1975 and 1986 and took 1980 as the sample. It was geometrically a horrible year to fly to Venus; the alignments of the planets made it a very fuel intensive transit. But if the worst case scenario was plausible, a best case scenario was more likely to gain traction.
The crew would launch, park briefly in Earth orbit, then fire their main engine to begin their transit to Venus. One mid-course correction was built into the mission in this earliest planning stage. Once at Venus, the crew would enter a highly elliptical orbit with an eccentricity of 0.9. (By comparison, a 0.0 eccentricity is a perfect circle and the Earth’s orbit around the sun has an eccentricity of only about 0.02.) This orbit was ideal; it was easy to achieve without burning through a substantial amount of fuel making for a lighter payload at launch and took the spacecraft close to the planet at its perigee. At its closest point the spacecraft would come within 3 Venus radii from the planet, giving the crew a great chance to take measurements and make observations. Proximity to the surface would be incredibly important since most of the instruments on board, like radio mapping equipment that gather data by sending signals and receiving the reflection, would only work if they could pierce through Venus’ thick cloud cover.
While the highly elliptical orbit took the spacecraft up close to Venus, it was only marginally better than a flyby. The best case scenario would give the crew just over two days worth of time under the magic 3 Venus radii mark during their time in orbit.
The 1980-launch mission the plan focused on only had the crew parked at Venus for 40 days; the full mission would last 565 days. After burning its main engine in Earth orbit, the 197,000 pound spacecraft would take 320 days to get to Venus then another 205 to return to Earth. The crew would reenter the atmosphere traveling 48,000 feet per second, rely on aerodynamic breaking and parachutes before splashing down at the end of the mission.
The limiting factor of the proposed mission to Venus was the launch weight. If the rocket couldn’t lift the necessary propellant for a fast transit and low orbit, there was no way to shorten the mission. Nuclear propellants under development in the mid-1960s had the best potential to lower the launch weight by as much as 50 percent. A cheaper, faster mission would follow.
Spending 320 days getting to Venus for a little over two days worth of up close study might seem insane, but it was better than the same mission to Mars, even using a best-case launch window. Using the same hardware and mission profile, getting to Mars was significantly more fuel intensive making it a more expensive mission to launch.
An orbital mission around Mars would take a total of 451 days. The much heavier spacecraft weighing 394,000 pounds when it launched from Earth orbit would take 252 days to get to Mars. Once it arrived at the red planet, the crew would spend just 20 days in orbit before beginning the 178 day journey back to Earth. The spacecraft returning from Mars would be traveling 52,000 feet per second as it reentered before splashdown.
The best case scenario for a Mars orbital mission was worse than the best case scenario for a Venus orbital mission, but neither was good enough to save the Apollo Applications Program. At least robots have managed much simpler and cheaper missions to return a wealth of information about both our cosmic neighbours.
Edward A. Willis, Jr. “Manned Venus Orbiting Mission.” Lewis Research Center Cleveland, Ohio. NASA. 1967.