NASA/JPL This artist's rendition illustrates the formation of rocky bodies in the solar system - how they form and differentiate and evolve into terrestrial planets

NASA is not without its cynics. The agency that was founded on the dreamy, even childlike, premise that America could and should explore the cosmos — because, well, why not? — is a department of government all the same. And that means it’s spent more than half a century fighting the annual budget battles in Washington, trying to wring terrestrial dollars out of hometown lawmakers for missions that will take place everywhere but Earth.

That hasn’t always been easy, and in 1992, then-Administrator Daniel Goldin decided to use the agency’s straitened financial condition as a way to inspire his troops. “Better, Faster, Cheaper,” would be NASA’s new marching orders, he announced — posing his engineers a challenge to do ever more with ever less. The grumbling from within the ranks suggested that not everybody was buying it. “Better, faster, cheaper — pick two,” was the subversive response.

But the agency persisted, most prominently with its now 20-year-old Discovery program — a series of unmanned missions to points throughout the solar system that would be built from off-the-shelf parts, cost-capped in the vicinity of $500 million, and go from blueprint to space with just a year or two between missions. And like it or not naysayers, a generation later, the program has worked spectacularly.

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Since the 1996 launch of the NEAR spacecraft — the Near Earth Asteroid Flyby — nine missions have been dispatched to asteroids, comets, the moon, Mars and Mercury. In 2009, the program’s biggest hit — the Kepler Space Telescope — was launched, and in the three years since, has discovered more than 2,300 candidate exoplanets orbiting distant stars, with years of work still ahead of it. Only one spacecraft in the Discovery fleet, the Comet Nucleus Tour, failed, vanishing from radio contact shortly after it reached space in 2002.

This week, NASA announced its next planned Discovery mission, dubbed InSight, which will take off in 2016 heading for a destination that has been much in the news of late: Mars. Unlike the just arrived Curiosity rover, which landed on the Red Planet on August 6 to study the atmosphere, soil and possible biology of Mars, InSight will peer where no probe has looked before: deep within the planet. In doing so, it could teach us a lot about the early formation of Mars itself, but also about the moon and the three other rocky planets: Mercury, Venus and Earth.

Astronomers have always known that Mars was a good place to go if you wanted to study the entire rocky brood, simply because of is size. It’s bigger than Mercury, but smaller than Earth and Venus, giving it just enough bulk to have gone through the heating and cooling phase that rocky planets experience — differentiating into core, mantle and crust — but too little to have developed plate tectonics. That’s important because the heat and churn of tectonics continuously reshapes the interior of a world, erasing its geological history over and over again. Mars, by contrast, has a fixed anatomy, unchanged inside since shortly after its birth.

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Studying Mars’s interior, says InSight mission director Bruce Banerdt, of NASA’s Jet Propulsion Laboratory (JPL) in an explanatory video, “will allow us to address planetary formation that we’ve only been able to guess at before.”Adds deputy principal investigator Suzanne Smerkan: “We are missing cold, hard data, and this in what this mission will provide.”

InSight will do that in a few, remarkably simple ways. Unlike the SUV-sized, $2.5 billion Curiosity, with its suite of 10 on-board instruments, InSight will cost just $425 million and will carry only three different experimental tools. Two of those will be provided — and paid for — partly by the French Space Agency, Germany’s Max Planck Institute and other European research groups.

The NASA contribution will be a geodetic instrument coupled with a pair of skyward-looking cameras. Together they will measure the planet’s wobble as it is tugged by the sun and its pair of vastly smaller — but vastly closer — moons. This will provide clues to its density, layering and other internal characteristics. The European instruments will be a seismic detector that will listen for Marsquakes and other subsurface activity — much like a planetary stethoscope — and a thermal probe will penetrate up to five meters (16.4 ft.) underground to take the planet’s changing temperature. “We’ll be measuring thermal flux over a full Martian year,” says Banerdt.

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Part of the reason InSight can do so much on the cheap is because it relies on legacy hardware — components that have been tested and proven on earlier missions. Much of the new ship’s design is modeled after the Mars Phoenix probe that touched down on the Red Planet in 2008. “With one spacecraft on a Discovery budget,” Banerdt says, “we’re really going to be able to do the science that for 20 years we thought would cost $1 billion to $1.5 billion and take three or four spacecraft.”

The money that would have been spent on those other ships can instead be rolled into other missions to different destinations, and already Discovery officials have approved the next two spacecraft the program will launch: one to a comet and another to the Saturnian moon Titan. So far at least, better and faster can indeed be cheaper, making it possible for even a hard-pressed NASA to travel on a budget.

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