Amy Shira Teitel is a freelance space writer whose work appears regularly on Discovery News Space and Motherboard among many others. She blogs, mainly about the history of spaceflight, at Vintage Space, and tweets at @astVintageSpace.

Last week, NASA announced its next planetary mission. In 2016 the agency is going back to the surface of Mars with a spacecraft called InSight. The missions selection irked some who were hoping to see approval for one of the other, more ambitious missions up for funding:either a hopping probe sent to a comet or a sailing probe sent to the methane seas of Saturns moon Titan. Others were irked by NASAs ambiguity over the missions cost during the press announcement.

An artists rendition of InSight deploying its seismometer and heat-flow experiments on Mars.

InSight is part of NASAs Discovery program, a series of low-cost missions each designed to answer one specific question. For InSight, that question is why Mars evolved into such a different terrestrial planet than the Earth, a mystery it will investigate by probing a few meters into the Martian surface. The agency says InSights selection was based on its low costcurrently capped at $425 million excluding launch costsand relatively low risk. It has, in short, fewer known unknowns than the other proposals.

But while InSight costs less than half a billion itself, the total value of the mission by the time it launches will be closer to $2 billion. How can NASA get that much zoom for so few bucks? By harnessing technologies developed for and proven on previous missions. The research, development, and testing that has gone into every previous lander take a lot of guesswork out of this mission, helping it fly for (relatively) cheap.

Aside from the Moon, Mars is the only body in the solar system that NASA has landed on more than once. With every mission, the agency learns a little more, and by recycling the technology and methods that work, its able to limit expensive test programs. This has played no small part in NASAs success on the Red Planet thus far. When it comes to the vital task of getting landers safely to the surface, NASA has been reusing the same method for decades. It has its roots way back in the Apollo days.

Amosaic of Mars Chryse Planitia created from images taken by Viking 1.

NASA first demonstrated how to make effective Mars landings with the Viking missions, a pair of twin landers that reached the surface in 1976. Each was sent to Mars with an elaborate, three-stage system for slowing the craft down for a gentle landing. The first stage was an aeroshell, a case designed to create enough drag to slow the landers descent without building up too much heat from atmospheric friction that it melted the instruments inside. For the second braking mechanism, NASA took advantage of the fact that Mars, unlike the Moon, has an atmospherethey used a parachute. And the final descent was made with the help of retrorockets, which fire opposite a landers direction of travel. They slowed the landers to a gentle touchdown, at which point a sensor in the leg shut the rockets down.

This approach seemed sound, but it required a lot of real-world testing to make sure it would work. One particular challenge was that Mars thin atmosphere meant that the lander would still be falling faster than the speed of sound when the chute needs to deploy. To test parachutes in a hypersonic, low-atmosphere environment, engineers put plentiful Apollo-era funding to good use. They ran a series of tests that sent a payload into Earths thin upper atmosphere with a balloon, accelerated it past the speed of sound, then deployed the parachute. It was an expensive test NASA hasnt repeated since 1968, but it worked and did offer a good stand in for the Martian environment.

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NASA’s Key to Efficient Mars Landings: Reduce, Reuse, Recycle | The Crux