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Guest: Dr. Marc Rayman. Topics: As the Dawn Mission Director, Dr. Rayman talked about Vesta, Ceres, ion propulsion & much more. Please direct all comments & questions regarding Space Show programs/guest(s) to the Space Show blog, http://thespaceshow.wordpress.com. Comments & questions should be relevant to the specific Space Show program. Written Transcripts of Space Show programs are a violation of our copyright & are not permitted without prior written consent, even if for your own use. We do not permit the commercial use of Space Show programs or any part thereof, nor do we permit editing, YouTube clips, or clips placed on other private channels & websites. Space Show programs can be quoted, but the quote must be cited or referenced using the proper citation format. Contact The Space Show for further information. In addition, please remember that your Amazon purchases can help support The Space Show/OGLF. See www.onegiantleapfoundation.org/amazon.htm. For those listening to archives using live365.com & rating the programs, please email me as to why you assign a specific rating to the show. This will help me bring better programming to the audience. We welcomed Dr. Marc Rayman to the program to discuss the Dawn Mission to both Vesta & Ceres. To find out more about Dawn, visit http://dawn.jpl.nasa.gov. Also check out Dr. Rayman's blog The Dawn Journal @ http://dawn.jpl.nasa.gov/mission/journal.asp. Visit the DS1 site & archives by Dr. Rayman @ http://nmp.jpl.nasa.gov/ds1. During the first segment of our 91 minute program, Dr. Rayman introduced us to the Dawn mission which first went to Vesta & is now closing in on its second destination, Ceres. We talked about the mission being specifically chosen to visit both Vesta & Ceres & that Vesta data is still undergoing analysis. Dr. Rayman described Vesta's Rheasilvia Crater 300 miles in diameter formed by an impact about one billion years ago. We also talked about Vesta meteorites on Earth. Dwayne called regarding competing theories about Ceres, planets having changed positions at one time, & Dawn mission limitations. Perry wanted to know what information the team most wanted to get from Ceres. Dr. Rayman said they wanted to know basics such as what it looks like, what it was made of, ice, etc. Other listeners wanted to know about Ceres compared to Mars access. Here, Dr. Rayman had much to say as the subject came up again in the second segment. Doug wanted to know about the large bright spot on Ceres plus other questions. In the second segment, Dr. Rayman told us about his Dawn Journal (blog) per the above URL. I asked our guest if he thought of Dawn & other science missions as competitive with human spaceflight missions. Don't miss his reply as I believe it was very special. BJohn sent several emails asking for Dr. Rayman's favorite targets, especially for future missions. He also asked about using nuclear power rather than solar. Our guest described the solar arrays & why solar was chosen for Dawn. Ion propulsion came up & was a major discussion topic for the balance of our program. Dr. Rayman described how ion propulsion worked, why it used a slow but steady acceleration, & its advantages over chemical propulsion. Matt asked about RTG development for future missions . Doug sent us another question based on the low Ceres gravity & landing on Ceres to pre-position supplies in advance of a crew. Our guest pointed out it was far more complicated than Doug implied given that the Ceres orbit was tipped more than 10 degrees from the ecliptic. Make sure you hear this explanation. Among the many questions Matt asked, he wanted to know about the German component of the Dawn mission. As we approached the end of our show, Dr. Rayman gave us a preview of what to expect as we get very close to Ceres, gradually getting as low as Earth & ISS. Please post comments/questions on TSS blog above. The guest, callers, & those sending emails can be reached through me.