Mechanical engineer Maurizio Porfiri, of the Polytechnic Institute of New York University, designs robot fish. A few years ago, he found that real fish would mill about his aquatic robot, and now he's trying to understand why. His research suggests that it has less to do with how the robot looks, than how it makes fish feel.

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IRA FLATOW, HOST:

A private company has unveiled plans to mine precious metals and water from nearby asteroids. Planetary Resources co-founder Eric Anderson discusses the various stages of the mining process and how the excavated minerals could impact future space exploration and innovation on Earth.

A blind Chinese activist, one of the country's most prominent, has made an audacious escape from house arrest and is safe from Chinese authorities, according to his supporters.

Yet days after Chen Guangchen fled his home, it's not clear exactly where he is. A diplomatic source indicates that he is inside the U.S. embassy, but this has not been confirmed officially.

Chen has attracted international attention with his efforts to prevent forced illegal abortions in China. Secretary of State Hillary Clinton has spoken out in support of him.

Can the repeated brain injuries suffered by some athletes cause problems with brain function later in life? A new play, Headstrong, opening next week in New York, looks at athletes and head trauma, and the high price some athletes end up paying for playing the game.

In The Idea Factory: Bell Labs and the Great Age of American Innovation, Jon Gertner writes of the legendary innovations developed at AT&T's Bell Labs, from lasers and transistors to solar cells and cell phones, and discusses how the lab became a hotbed for new ideas.

He's flown the space shuttle five times, and performed eight spacewalks to service the Hubble telescope. Now astronaut and astrophysicist John Grunsfeld heads up NASA's Science Mission Directorate, where he manages scientific investigations on the home planet--and beyond.

After tough criticism from Republicans, the Obama administration withdrew its proposal for new rules to limit child labor on farms.

The AP reports that yesterday, the Labor Department withdrew the proposed rules "that would ban children younger than 16 from using most power-driven farm equipment, including tractors. The rules also would prevent those younger than 18 from working in feed lots, grain bins and stockyards."

"Major college football is on the verge of implementing a playoff, its own version of the final four — two semifinals and a title game," The Associated Press writes.

Or, as The Wall Street Journal reports:

Mitt Romney sweeps five primaries and all but locks up the GOP nomination. Even Newt Gingrich agrees Romney is the presumptive nominee. More veepstakes speculation on Sen. Marco Rubio of Florida and Sen. Rob Portman of Ohio. Two centrist House Democrats bite the dust in Pennsylvnaia, while Utah GOP Sen. Orrin Hatch lives to fight another day.

NPR's Ken Rudin and guest host Mara Liasson have the latest political news in this week's roundup.