Opportunity and endurance this week on planetary radio.

Hi everyone and welcome back. I'm Matt Kaplan.

The big news came from the Red Planet last week. The Mars Exploration Rover team announced that opportunity had reached

Endurance Crater.

You'll hear part at the Jet Propulsion Lab press conference followed by exclusive comments from planetary

scientist Bill Christensen.

He's responsible for the vital mini test instruments on both rovers.

Bruce Betts is watching comets and giving away another t-shirt on

what's up and we'll get underway right now as Emily answers another of your

great questions. I'll be right back. Hi, I'm Emily Loch Duwala with questions and answers.

A listener asked, a story about Voyager 1 made me wonder, how is the exact position of a spacecraft in space calculated?

The positions of functioning spacecraft can be calculated by spacecraft navigators using information from the deep space network of radio antennas.

To find the voyagers, the tracking antennas have to be precisely pointed toward a signal broadcast by the spacecraft.

The tracking antennas, measuring 30 to 70 meters across,

are moved back and forth across the expected direction to Voyager

until the strength of the radio signal from the spacecraft is at a maximum.

This process defines the direction in the sky where the spacecraft is,

or at least where it was when the signal left the spacecraft.

The direction is half the problem.

The other half is distance.

Figuring out the distance to the spacecraft

involves something called ranging.

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