Planetary Radio • Sep 06, 2017

Sailing on the Light of the Sun With Lou Friedman

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On This Episode

Jason headshot sept 2020

Jason Davis

Senior Editor for The Planetary Society

Friedman louis print

Louis D. Friedman

Co-Founder and Executive Director Emeritus for The Planetary Society

The co-founder and Executive Director Emeritus of the Planetary Society returns for a conversation about the allure of sailing through space. Digital editor Jason Davis reviews three exciting space sail projects, and LightSail Program Manager Bruce Betts provides a LightSail 2 update before giving us his regular What’s Up report. There are two space trivia contests to close out before we offer a new opportunity to win the weekly prize package.

LightSail 1 with solar sails deployed
LightSail 1 with solar sails deployed LightSail 1 captured this image of its deployed solar sails in Earth orbit on June 8, 2015.Image: The Planetary Society
Heliogyro solar sail concept
Heliogyro solar sail concept The heliogyro solar sail had 12 spinning blades that were each four miles long. Here, the spacecraft approaches Halley’s Comet.Image: NASA / JPL
NEA Scout artist's concept
NEA Scout artist's concept Image: NASA

This week's question:

How long is the longest dimension of the Cassini spacecraft, not counting the booms—the main spacecraft’s structure before deployment?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, September 13th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

To within a minute, what is the longest possible time of totality for a solar eclipse seen from Earth?


The longest possible time of totality (in the current era) for a solar eclipse seen from Earth is about 7.5 minutes.

Question from the week before:

What is the funny word used when three celestial bodies are lined up, as in an eclipse? It’s not “stooges.”


Syzygy is the funny word that describes the alignment of three or more celestial bodies.