This week, astronauts aboard the space shuttle Discovery undertook an unprecedented spacewalk, making repairs to the underbelly of the shuttle in preparation for its expected return to Earth next week. During the spacewalk, Stephen Robinson rode the shuttle's robotic arm down underneath the craft, and removed two tufts of 'gap filler' material that were protruding from between some of the shuttle's heat-protective tiles. NASA engineers were concerned that the fabriclike material sticking out from between the tiles could have made the belly of the shuttle heat unevenly, threatening the landing. We'll get an update on the mission, and talk about what remains for the shuttle team before their descent.

Then, we'll turn our attention to an advance in cloning. This week a group of researchers in South Korea reported in the journal Nature that they have successfully cloned a dog. Although that may not seem like a major achievement, given that Dolly the cloned sheep was born in 1996, the reproductive system of dogs has a reputation for being finicky. The Korean team had to create over 1000 embryos to eventually produce just two cloned dogs, one of which died after only a few weeks. The surviving dog, named Snuppy (''Seoul National University puppy") is an Afghan hound -- though the dog that carried the developing embryo was a yellow Labrador retriever. Scientists cautioned that the technique was not yet available for the easy cloning of your favorite pets -- duplicating the cloning technique used here would probably cost over a million dollars. We'll talk about the cloning advance and what it could mean for research.

Finally, we'll take a historical look at one of the giants of modern chemistry. Fritz Haber won the Nobel Prize in 1918 for his development of a process "for the synthesis of ammonia from its elements" -- a way of taking nitrogen from the air and combining it with hydrogen to make ammonia. The advance helped satisfy a worldwide demand for nitrogen-based fertilizers. However, Haber was also a key figure in the development of poison gas as a weapon of war. We'll talk about him, with the author of a new book on the life and work of Fritz Haber. Call in with your questions and comments at 1-800-989-8255 (2-3 Eastern). Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests:
Bill Harwood
CBS News Space Consultant
Johnson Space Center Bureau
Houston, Texas

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Duane C. Kraemer, D.V.M., Ph.D.
Professor, Department of Veterinary Physiology & Pharmacology
Texas A&M University
College Station, Texas

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Daniel Charles
Author, "Master Mind: The Rise and Fall of Fritz Haber, the Nobel Laureate who Launched the Age of Chemical Warfare"
Contributing Correspondent, Science Desk, NPR
Washington, DC

Books/Articles Discussed:

"Master Mind: The Rise and Fall of Fritz Haber, the Nobel Laureate who Launched the Age of Chemical Warfare," by Dan Charles. Ecco, 2005.

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This segment produced by Corey Binns