Broadcast 3218 Dr. Marc Rayman

02 Nov 2018 Dr. Marc Rayman
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Guest:  Dr. Marc Rayman; Topics:  The conclusion of the Dawn Mission to Vesta and Ceres with updates for both celestial bodies.

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We welcomed back to the show Dr. Marc Rayman from JPL to share with us the conclusion of the fabulous Dawn Mission which visited two targets, Vesta and Ceres.  Dawn ran out of fuel (hydrazine) for pointing and orientation and is now in its permanent lasting elliptical orbit (at least for multiple decades) ranging from 22 miles above the surface of Ceres to about 2500 miles from the surface.  Marc explained this orbit and why it was chosen, plus why it was a stable orbit.  In the process of explaining why and how the mission ended, we talked about failing reaction wheels needed for pointing and orientation and how the Dawn team learned to fly Dawn using hydrazine fuel and thrusters not meant for that purpose.  Learning to do this extended the life of Dawn by many valuable years so don't miss what Mark has to say on this subject. 

Other topics discussed in the first segment Ceres and Vesta findings, especially surprise discoveries.  For Ceres, Mark talked about crater walls, bright spots, crater walls showing sharp light and dark boundaries with some sort of flow having existed at one time.  He also talked about the salt as part of the bright spots, sodium carbonate and how it got there via a one time in the early history of Ceres where there was a global water ocean. 

Listeners sent in several email questions about both Vesta and Ceres but the focus seemed to be more on Ceres.  Marc talked about the two target mission which he said was only possible due to ion propulsion.  Our guest had much to say about ion propulsion as compared to chemical propulsion and why it opened the door for missions such as Dawn which he said could not have been done using chemical propulsion. 

Before the first segment ended, Cheryl sent in a note asking about lessons learned from Dawn that would prove useful for future planetary missions.  Besides the ion propulsion, Marc pointed out several additional important lessons learned.

We started the second segment talking about the size of both Vesta and Ceres with our guest pointing out that Ceres was a dwarf planet like Pluto but discovered much much earlier than Pluto. Also, both Ceres (the bigger of the two) and Vesta comprise 45%  of the total asteroid belt mass.  Marc compared Ceres to other asteroids and comets that we hear about through other missions.  This discussion should help put the size and importance of Ceres and Vesta into sharp context and focus. 

Marc was asked about soft landing on Ceres as ESA did with Comet 67 P and Rosetta.  He said the propulsion on Ceres was not strong enough to allow for a soft landing due to Ceres gravity.  He then brought up the subject of Earth contamination on Ceres as a reason not to land on it.  We had an interesting planetary protection and contamination discussion so don't miss it. 

As we were nearing the end of our program,  Larry as about the a top ten list of discoveries for Vesta and Ceres.  Randy sent in a note asking about the differences with the Applied Physics Lab and JPL.   Harry from Portland asked about a public popularity rating of the NASA planetary missions.  You certainly want to hear how Marc responded to Harry's questions.  As we were about to end, I asked Marc about the possibility of student experiments someday flying on these planetary missions.  Marc said it was now possible to do that and it might happen.  Again, listen to all of what he said about possible student payloads on a planetary mission. 

Marc offered us Dawn Mission closing comments regarding the 11 year mission.  Don't miss them.  Please post your questions/comments on TSS blog for this show.  You can reach Dr. Rayman through me or his JPL website page.

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