What might have been: Visiting Mars and Venus with Apollo

[rhoenix]

Imagine three astronauts, 125 million miles from the Earth, talking to Mission Control with a four-minute time lag. They have seen nothing out their windows but stars in the blackness of space for the last 150 days. With a carefully timed burn, they slow into orbit around Venus, and as they loop around the planet, they get their first look at its thick cloud layer just 7,000 miles below.

It might sound like the plot of a science fiction movie, but in the late 1960s, NASA investigated missions that would send humans to Venus and Mars using Apollo-era technology. These missions would fly in the 1970s and 1980s to capitalize on what many expected would be a surge of interest in manned spaceflight after the Apollo lunar landings. They would be daring missions, but they would also be feasible with what was on hand.

The Apollo applications program

NASA’s Apollo program hit a turning point in 1965. Roughly halfway between its inception and the end-of-decade lunar landing deadline, the program was both making headway and losing popular support. Money was desperately needed elsewhere, namely at home to deal with social issues and in Southeast Asia where the Vietnam War raged.

Worries over Apollo’s post-lunar-landing future led to the creation of the Apollo Applications Program. It was the agency’s attempt to preserve the team that brought Apollo to life and use their experience to develop new missions that would extend humanity's reach into space. At the core of these missions would be scientific gain, not political need. These weren't full mission proposals; instead, they were meant to show what NASA could do with the existing Apollo technology if it decided to.

The first vague goals of the program were to establish a manned orbiting laboratory and to send missions to the nearest planets using Apollo hardware—two goals that would give NASA reason to continue production of its Apollo-Saturn configurations. But these goals weren’t firm enough. NASA couldn’t continue building single-use Apollo spacecraft and Saturn V rockets without a concrete mission in the pipeline.

To find one, the agency turned to Bellcomm Inc., a division of AT&T established in March of 1962 to support the space agency by evaluating theoretical missions and performing independent analysis. It was Bellcomm that presented NASA with possible manned missions to Venus and Mars.

Visit scenic Venus!

On August 27, 1962, NASA launched history’s first probe to Venus. Mariner 2 passed within 21,000 miles of the planet’s surface on December 14 before settling into a heliocentric orbit. It was a flyby mission rather than a thorough exploration of our neighbor, but it did find that Venus lacks a strong magnetic field and has an extremely high surface temperature. Mariner 2 also found that the radiation environment approaching Venus is no more damaging than anywhere else outside the Earth’s magnetic field. This fact, combined with the certainty that there were more secrets locked beneath Venus’ clouds, made it a worthy target for a manned mission.

Adding to the appeal was the belief (still tenable in the mid-1960s) that Venus’ clouds might hide a surface that astronauts could land on and explore. Venus was, in short, a compelling target that could give the Apollo Applications Program some much-needed direction.

In Bellcomm’s view, getting there wouldn’t require much new. One of the keys behind Apollo’s success, evident even before any missions flew to the Moon, was the spacecraft’s modular design. Having a tripartite spacecraft—a lunar module to land on the Moon, a service module as the main propulsion unit, and the Earth-return command module—meant the crew could discard sections once they were no longer needed. This kept the whole stack within the launch capacity of a single Saturn V rocket.

Bellcomm’s proposed Venus mission took the same modular approach, building a tripartite spacecraft that could launch on a single Saturn V. The Venusian mission would reuse the Apollo Command and Service Modules (the CSM) as the main spacecraft. The gumdrop shaped Command Module would reprise its role as the core vehicle, the one in which the crew would launch and splash down. It would be virtually unchanged from the lunar module save for the addition of 430 pounds of ablative material that would keep the crew safe during atmospheric reentry—a crew coming home from Venus would be traveling a lot faster than a crew returning from the Moon.

Otherwise, the spacecraft would be largely the same. The CSM’s computer would be the primary supplier of guidance information and navigation control throughout the mission, as was the case on Apollo missions to the Moon. It would be a simple matter of changing its program to keep the spacecraft on a Venus flyby trajectory. The CSM would also remain the primary communications center for the mission, managing the connections between modules and serving as the main link to flight directors in mission control. For its part, NASA would track the CSM from Earth with the same ground-based radio signal tracking system it had used since the Mercury Program.

Most importantly on a deep space mission, the CSM would be the crew’s lifeboat. The only module capable of flying on battery power—a necessity during the Earth re-entry phase—the CSM was the module in which the crew could take refuge in the event of an abort after launch. With its batteries fully charged, the Venus-bound CSM would have enough power and emergency rations to keep a crew alive for 60 days. There was an additional three weeks' supply of rations for the crew to use in case they landed in a remote desert at the end of a mission. It was the same provision Apollo crews had on board.

But the Command Module was far too cramped for a mission of this duration. Conveniently, a mission to Venus had no use for a Lunar Module, so this vehicle was scrapped and replaced with the larger Environmental Support Module (ESM). This would provide life support and environmental control for the duration of the mission and serve as the main experimental bay where the crew would work. But the ESM didn’t launch docked with the CSM; the astronauts would have to join the two modules in flight. Doing so mimicked the way Apollo astronauts captured the LM on their way to the Moon. Once on their way to Venus, the crew would turn the CSM around and pull the ESM out of its launch casing.

The final module of the Apollo-Venus stack was the SIV-B (pronounced “S-4-B”). This was the upper stage of the Saturn V, and its main function was to propel the spacecraft out of Earth orbit and off toward Venus. While Apollo crews jettisoned this spent rocket stage once they were on their way to the Moon, a crew going to Venus would keep this stage attached, refurbishing it en route into a habitat module, their primary living and recreational space. Everything they would need for this extensive refitting would be stored in the ESM. The refurbished SIV-B would also be the main source of power for the mission. Being the largest module, solar panels arranged on the outside would gather enough sunlight to power all three modules throughout the mission, all while keeping the CSM’s batteries charged in case of an emergency abort.

All three modules would be reinforced to protect the crew from micrometeoroids or larger meteoroids, though neither was expected to be a significant hazard. Instead, solar flares were the main danger facing a crew flying toward the Sun. Flying by Venus, the crew would be about 0.7 AU from our star (about 65.1 million miles). As a precautionary measure, the ESM would be reinforced with a special radiation shield. It would be a safe haven for astronauts during a solar storm.

The mission profile

A 1967 Bellcomm report outlined a potential Venus mission that would launch during a month-long window opening on October 31, 1973. It was an ideal time to launch. Not only would the planets be aligned for a fast transit to Venus, it was predicted to be a year of low solar activity.

The crew would stop briefly in Earth orbit after launching from Cape Canaveral, taking a moment to check that all their systems were up and running. Then they would fire their SVI-B’s engine, gaining the speed needed for a transit to Venus. This burn would mark the beginning of a 123-day outbound leg during which the crew would observe deep space and various bodies in our solar system using a UV, X-ray, and infrared capable telescope mounted in the ESM.

Following a launch during the November 1973 window, the crew would reach Venus sometime around March 3, 1974, and the planet would become their primary science target. Using the telescope’s broad spectrum to look beyond Venus’ thick clouds, the crew would gather data on Venus’ surface, the chemical composition of the lower atmospheric levels, its gravitational field, and the properties of its various cloud layers. They might even release robotic probes, small vehicles that would send data back to the spacecraft in real time about the atmosphere as they completed their one-way missions to the surface.

Swinging around Venus would give the crew enough momentum to return to Earth. Planetary geometry following that November 1973 launch window meant the return trip would take a full 273 days.

Throughout the mission—during the outbound leg, Venus encounter, and inbound leg—the crew would constantly transfer science data back to mission control. This was a way to limit the crew’s landing payload to film and cameras—the Command Module could only hold so much. It was also a way to keep the Earth-bound mission scientists firmly in the loop. With continual data, they could direct the crew to change experiments or repeat observations.

The crew would return to Earth, splashing down like Apollo missions from the Moon, sometime around December 1, 1974. Taking into account the month-long launch window, this proposed mission would last up to 400 days.

Living in space for 400 days

The 400-day mission would tax both the crew and the spacecraft, but it wasn’t impossible. The key was sophisticated onboard recycling and storage systems.

The crew would launch with 500 pounds of water: 100 pounds stored in the ESM would be recycled throughout the mission to provide the crew with fresh drinking water, while the other 400 pounds stored in the CSM would be reserved for emergencies. The cabin environment would be similarly recycled. Instead of the lithium hydroxide canisters that Apollo missions took to the Moon (which use carbon filters to remove carbon dioxide from air but the canisters can’t be reused), the Apollo-Venus mission would rely on a molecular sieve. This would absorb atmospheric water from the astronauts’ perspiration and exhalation in a silica gel bed. Rather than vacuum-vent this water with the carbon dioxide, it would be condensed in a heat exchanger, releasing breathable oxygen and usable hydrogen. There would be lithium hydroxide canisters on board, but like the excess water in the CSM, they would be reserved for emergencies.

It wasn’t just the environmental control system that differed from Apollo lunar missions: the whole environment would be different on a mission heading to Venus. While Mercury, Gemini, and Apollo missions all used a pure oxygen environment, the Apollo-Venus mission would be the first to fly with a dual gas system: 70 percent oxygen and 30 percent nitrogen at five pounds per square inch. This decision wasn’t rooted in a fear of an onboard fire. Rather, no one was sure how a crew would react physiologically to 400 days in a pure oxygen environment. This heavier and more complicated system was outweighed by the potential benefits to the crew’s safety.

Like the environmental system, the crew was to be self-contained on this mission. Thirty pounds of medical supplies meant astronauts would have to treat one another, fixing anything from minor cuts and bruises to wounds and minor surgery. They also wouldn’t be dumping any trash overboard on this mission. With over 300 pounds of fecal containment bags and germicides stored in the ESM, the astronauts would neutralize and store all their waste and excess food.

From a human factors standpoint, the astronauts’ daily lives would strike a balance between work and play. Ten hours out of every day would be dedicated to mission goals—experiments, observations, and general maintenance of the spacecraft. Their remaining time was scheduled as leisure. There would be dedicated sleep periods and meal times. Each astronaut would have two hours of relaxation time each day where they could read, watch movies, or play games (all items that were included in the mission’s launch weight). Each astronaut would also have a mandatory two-hour-long exercise period on a stationary bike, a measure NASA hoped would limit muscular atrophy. Any remaining time would be dedicated to personal hygiene.

Sending humans into Venus orbit: NASA Lewis’ proposal

Bellcomm’s 1967 proposal for a manned Venus flyby was certainly a viable mission, but it had one major drawback. The 400-day flight offered the crew just a fleeting close look at the planet. An orbital mission would give the crew more time to study Venus up close, offering a stronger justification for such a lengthy mission. It was NASA’s Lewis Research Center in Cleveland, Ohio that found a way to get humans into orbit around Venus.

A Venus orbital mission would follow the same path as the flyby, but the necessary planetary alignment for the crew to go into orbit increased the total length of the journey. An unfavorable launch window could make the outbound leg of this mission last up to 320 days. When they did finally reach their target, a short burn would put the spacecraft into a highly elliptical orbit. After just 40 days—planetary geometry didn’t allow for a longer stay—the crew would fire their main engine to begin the 205-day journey back to Earth for a splashdown.

During their time at Venus, the crew would pass within three Venus radii of the surface once every orbit, close enough that radio mapping equipment could see the surface through the clouds. But this highly elliptical orbit was only marginally better than a flyby. A crew at Venus for 40 days would have accumulated just over two days worth of up-close observations; the fleeting passes didn’t amount to much.

While a 565-day mission for two days worth of up-close observations wasn’t ideal, it was better than taking the same mission profile to Mars. Even if it launched during an ideal launch window, this mission to Mars would require more fuel and resources, making it a more expensive mission to fly. Following an equivalent profile, it would take a crew 252 days to reach the red planet, where they would stay for just 20 days before having to leave and begin the 178-day journey back home.

But there was another way to send people to our planetary neighbors that promised a better return on investment: visit both planets on the same mission.

Bellcomm’s planetary billiards

It wasn’t just Venus that Bellcomm identified as a possible target planet for post-Apollo missions. Mars was another attractive target. The research agency identified a number of Mars flyby opportunities between 1978 and 1986, still in the time frame when people anticipated an increased interest in manned spaceflight thanks to the Apollo lunar landings. Like the Venus flyby, this flight would use a free return trajectory; the crew would slingshot around the planet and return straight home. Throughout the flight, astronauts would make observations and run experiments, deploying probes at Mars that would return more detailed information in real time. There was even a chance one probe could land on Mars and return a soil sample to the crew before they left the planet’s vicinity.

But while the free return trajectory flight to Mars conserved fuel, going to Mars demanded a lot of fuel at the outset. Even the favorable launch windows were more fuel intensive than Venus flyby profiles. So Bellcomm offered an interesting solution. NASA could have a crew visit Venus first and use the momentum gained from that flyby to propel themselves to Mars. It was the same basic approach to navigation that the Voyager spacecraft followed in the 1970s.

Bellcomm researchers found that Venus and Mars align often, presenting ample opportunities for a dual planet flyby mission. Between 1978 and 1986, there were five favorable launch windows for a Venus-Mars mission. Some dates even offered the potential for the crew to swing by Venus a second time on their way back to Earth, turning the dual planet flyby mission into a triple planet flyby.

One window Bellcomm identified was in 1981. The best-case scenario would see the mission launch on May 26 on a 790-day mission. With a spacecraft similar to the Apollo-based Venus flyby stack, the crew would swing by Venus on December 28, reach Mars on October 5, 1982, and pass Venus again on March 1, 1983 before splashing down on July 25. The least favorable launch date in that 1981 window only added 60 days to the mission, so it was still a viable option. And there were other launch opportunities. One in November of 1978 could have launched either a dual planet flyby mission (Earth-Venus-Mars-Earth) or a triple planet flyby (Earth-Venus-Mars-Venus-Earth).

These multi planet flyby missions, being nearly twice as long as a Venus flyby mission, would push the astronauts and the spacecraft systems to the limit of their endurance. But there was a significant science payoff. Because the planets were always orbiting the Sun and rotating on their own axes, each mission, and even each leg of the same mission, would take astronauts over a different part of the planet. Some trajectories would take the crew to a planet’s day side or near the equator, while others would take them around the dark side or near a pole. In every case, infrared sensors and mapping radar would make the observations astronauts couldn’t do visually. There were no bad paths to take on these missions.

Skylab

From the start, the Apollo Applications Program skirted the real issue: NASA didn’t have enough money to continue building Apollo hardware or launch Apollo-style grand missions, a cash crunch that got worse as the Moon program wound to a close.

But it wasn’t only a lack of funding that doomed the Venus and Mars flyby missions. Bellcomm’s proposals were never intended as a recommendation. Rather, they were a proof-of-concept study, a report designed just to show NASA the types of missions it could launch with Apollo technology and how it could modify that technology as part of the Apollo Applications Program. The ideas were meant to serve as a guide for the agency in developing future missions. But for the most part, they never got beyond the initial Bellcomm studies.

With one exception. NASA’s far-off goals of interplanetary manned missions were reined back in favor of an orbital space station, which finally flew under the familiar moniker Skylab. Rather than refurbish the unit in orbit, a SIV-B Saturn V stage was turned into a laboratory on the ground and launched into Earth orbit on May 14, 1973. Three crews followed, occupying the station for a total of 171 days over the following year.

Skylab’s nine-year operational lifetime seemed ample when it was launched, but by the end of the decade NASA couldn’t maintain it. The station’s orbit decayed and it fell to Earth. Skylab, the last operational hardware of the Apollo Applications Program, burned up in the atmosphere on July 11, 1979, scattering pieces over Australia. The last most Americans saw of it was a piece that ended up on stage at the Miss Universe competition, held that year in Perth.

There are videos and other media links at the article itself, but this makes for fascinating reading, if only for a historical "might have been."

[General Havoc]

Blame game commences in 5... 4... 3...

[rhoenix]

Perhaps, but I'm more fascinated by reading about the plans that were in the works at the time, and the plans to accomplish them.

I don't know what NASA has planned for the future, nor am I very concerned about their calendar any longer - however, seeing the hints of the thought process behind how their missions were planned would help me greatly for my own projects. Seeing the plans for this more audacious set of missions is helpful to me in that regard.

[Josh]

Blame game commences in 5... 4... 3...

Not so much. I mean, I'm a space patriot to the point of boring the shit out of people on the topic, but I also don't believe we would've made the Apollo missions succeed in the first place if they hadn't been treated as Kennedy's legacy. If Kennedy had lived and especially if he'd gone on to lose the '64 election... well, it's all counterfactual so it doesn't really matter. We got to the moon, which was a hell of an accomplishment for the timeframe and technology. That we didn't follow it up is sad and we basically wasted the next couple-three decades dicking around in LEO (I know you hate it when I say that, but compared to what we could've done it was a massive loss.)

But now we're moving forward again and there's no point in lamenting the past. The stars will be ours, no matter what the wussbags and cockbiters with their limited vision and ambition whine about at this point. SpaceX is (overly optimistically probably) talking about dropping the boost costs to orbit to ten bucks a pound. Even if they're wrong by a factor of a hundred, that'll be half of what we're paying now and the real key is that we start actually getting infrastructure in space. 3D printing allows for that, and captured asteroids will provide the raw material.

We are on the path.