NASA's Viking 1 lander took this photo on July 23, 1976, just three days after touching down on the Red Planet.

NASA's life-hunting Viking mission to Mars was the most complex robotic exploration effort of its day, but the space agency initially wanted it to be even more ambitious.

Viking consisted of two spacecraft, each one an orbiter-lander duo. Viking 1 and Viking 2 launched a few weeks apart in 1975; the Viking 1 lander touched down on Mars 40 years ago today (July 20), while its Viking 2 counterpart followed suit on Sept. 3, 1976.

Viking was one of NASA's most successful missions. The orbiters and landers returned a tremendous amount of data, allowing scientists to flesh out a basic understanding of Mars for the first time. The two landers also famously found ambiguous signs of microbial activity on the Red Planet, inspiring a debate about Mars life that continues to this day. [Viking 1: The Historic First Mars Landing in Pictures]

Things could have worked out differently, however, because Viking wasn't always Viking. The project was originally called Voyager, and it was born big.

Voyager took shape in the early 1960s, and was viewed as a step toward eventually sending astronauts to the Red Planet. Voyager would have used the gigantic Saturn V rocket, which NASA was developing primarily for the Apollo moon missions.

The Saturn V — the most powerful rocket ever built — could have blasted 39,700 lbs. (18,000 kilograms) toward Mars in one go, according to the NASA History Series book "On Mars: Exploration of the Red Planet," by Edward Ezell and Linda Ezell.

That's a lot of payload. For perspective, each Viking orbiter-and-lander spacecraft ended up weighing a total of 6,395 lbs. (2,900 kg) fully fueled, and each one launched separately, on a different Titan-IIIE rocket. But both Vikings could have launched atop the same Saturn V, with a lot of margin left over for more science instruments, more technology demonstrations or anything else mission team members wanted to add.

Engineers and planners at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, which managed Voyager, were leery about it, viewing the program as impractical given the funding, facilities and knowledge available at the time, JPL historian Erik Conway said Tuesday (July 19) during a NASA-hosted discussion of Viking's legacy. But the decision-makers at the space agency's headquarters in Washington, D.C. were gung-ho, he added.

So what happened? Voyager died because of some bad timing on the part of NASA's Manned Spacecraft Center (MSC) in Houston (which is now called Johnson Space Center), Conway said.

In August 1967, the MSC put out a request for proposals about ways to return samples from Mars or Venus using astronauts in the 1975-1982 time frame. According to "On Mars," this request infuriated Rep. Joseph Karth (D-Minn.), who was acting chairman of the House Subcommittee on NASA Oversight at the time.

Karth had been a fan of Voyager. But, as related in "On Mars," Karth told Aviation Week & Space Technology that he was "absolutely astounded" by the request, especially because Congress had repeatedly warned NASA against "new starts" in the already-expensive Apollo era.

"Very bluntly, a manned mission to Mars or Venus by 1975 or 1977 is now and always has been out of the question — and anyone who persists in this kind of misallocation of resources at this time is going to be stopped," Karth said.

That indeed came to pass, in short order. And, "in the process of stopping it, Voyager went away, too," Conway said.

NASA selected the basic Viking mission plan, and its name, before the end of 1968, he added.

But Voyager came back to life, albeit in name only. The moniker was recycled for a pair of NASA missions that explored Jupiter, Saturn, Uranus and Neptune, and then famously kept on flying through the solar system's far outer reaches.

In August 2012, Voyager 1 became the first human-made object ever to reach interstellar space, and Voyager 2 should achieve that milestone soon as well. Both spacecraft remain operational today.

You can read much more about how Voyager morphed into Viking in "On Mars," which is available online: http://history.nasa.gov/SP-4212/ch4.html

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