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June 27, 2000
QuestChat with George Raiche

Research Scientist
NASA Ames Research Center, Moffett Field, CA


Tue Jun 27 11:42:11 2000

[ Oran/NASAChatHost - 7 - 10:00:51 ]
Hello and welcome to today's Aerospace/Space Team Online chat with George Raiche from NASA Ames Research Center. Atmospheric entry is an extremely stressful time for a spacecraft, and it must be designed carefully to withstand entry conditions. George Raiche studies how spacecraft perform as they enter a planet's atmosphere, in order to improve their designs.

[ Oran/NASAChatHost - 8 - 10:01:13 ]
And now, here is George Raiche to answer your questions.

[ GeorgeRaiche/ARC - 10 - 10:01:44 ]
RE: [Oran/NASAChatHost] And now, here is George Raiche to answer your questions.
Hi everyone. Fire away!

[ Oran/NASAChatHost - 12 - 10:04:19 ]
RE: [Elena] Hi! My name's Elena and I'm Italian.Here it's 7 p.m.!! What time will the chat start?
Elena, George is now online and ready to answer your questions. So please send them in!

[ GeorgeRaiche/ARC - 13 - 10:05:47 ]
RE: [JimL/SebringFL] First time entry. Would like to present two questons and remain an observer unless questioned. JimL/SebringFL would like to know more about the shielding of the shuttle from re-entry heating. I understand besides ablution (shield melts away) and our current ceramic tiles, there is another method that is possible but not available now due to lack of available power. It involves charging the shuttle body positively thus pushing the heated positive air particles away from the hull. This produces a heat shield away from the shuttle body. Is this theoretical only or possible awaiting the necessary power generators able to be fitted into the shuttle space and weight requirements?
Hi JimL; Not all of the heated air is made of ions. If it were possible to move the ions back from the surface, the neutral species (like N and O atoms) would be unaffected. Radiation--the emission of photons from the air species--is also a significant heating source that is not ionic. So removing the (positive) ions from the vicinity of the heat shield would have a limited cooling effect, at best.

[ GeorgeRaiche/ARC - 16 - 10:10:53 ]
RE: [JimL/SebringFL] JimL/SebringFL would like to know if aerodynamic lift truly exists or is it like centrifugal versus centripetal force? Lifting bodies have no wings, and weight measurements under a hovering helicopter show only the weight of thrust with no reduction due to the classic term "lift" if it existed! Is Michaelangelio'9s air screw More accurate than Bernoulli'9s Lift as you design lifting bodies?
Hi JimL; A "lifting body" is just that--a vehicle body that is shaped to give it enough useful lift. For a hypersonic vehicle, it turns out that wings (and other things that stick out) are a real problem because during atmospheric entry, their relatively sharp leading edges get extremely hot. So a perfect reentry shape would not have wings. But you need to be able to control the vehicle (and steer it at subsonic speeds), so the design of winglets and control surfaces is a major research area. And sorry--I can't intervene in a debate between Michaelangelo and Bernoulli!

[ GeorgeRaiche/ARC - 17 - 10:14:12 ]
RE: [Elena] Hi!My name's Elena.George,when a space shuttle goes up into space,just overstepped the atmosphere,the booster gets removed from the spacecraft:what happens to it? Maybe,it'll be recovered? How?
Buona sera, Elena! (I hope I spelled that correctly!) The boosters--the solid rocket motors--are ejected from the shuttle just a few minutes before orbit. NASA tries to recover them--they have parachutes and flotation gear to land in the water. If we recover them we disassemble them to study how they reacted to launch, and then we rebuild them for another launch.

[ GeorgeRaiche/ARC - 20 - 10:23:07 ]
RE: [JimL] JimL/SebringFL would like to know if the angle of attack on re-entry is controlled more By the amount of heating or just to srave off reflection back into space?
That's an interesting, and complex, question. There are a couple of concepts here. By "angle of attack" I assume you mean the angle between an axis of the spacecraft and its direction of motion (the velocity vector). The other important angle is that of the spacecraft velocity vector relative to a point on the Earth. When the shuttle enters, it is oriented so that the base points along its direction of motion. This is so that the blunt, well-shielded surface sees the most heating. You want a blunt surface forward, because the shock wave over a blunt surface stands off more than a shock wave over a sharp surface.

[ GeorgeRaiche/ARC - 22 - 10:30:18 ]
RE: [Elena] I read in your bio that you're a scientist:my biggest dream is working for N.A.S.A.,but not under this position.I'd like to become a flight controller,particularly a CAPCOM: what should I do to get ready for this job?
NASA is a very large organization, and there are many different kinds of jobs available for smart people. (The same is true for our colleagues in the European Space Agency, ESA.) If you look in the NASA web pages they can tell you what qualifications are necessary for different kinds of jobs. Often, flight controllers are people who have engineering or science backgrounds and who have participated in the planning of a mission. NASA also contracts some flight control duties to aerospace companies like Boeing or Lockheed-Martin--those are also large companies and they hire many types of people. However, I believe that only astronauts are used as CAPCOMS! But if you look at the web sites that talk about being an astronaut, they look especially for pilots, scientists, and medical doctors.

[ GeorgeRaiche/ARC - 24 - 10:34:53 ]
RE: [JimL] JimL/SebringFL would like to know if in your plasma research you have Found any way to communicate through that re-entry plasma? If not is There any hope at all i.e., research/theories, to break through that barrier?
The "communications blackout" is caused by ionization of the gases around an entering vehicle--since ions conduct electricity, and radio waves won't penetrate a conducting enclosure (Gauss' Law, I think), it's a hard problem. One approach we're taking is to design vehicles that do not have blunt surfaces. A blunt surface causes the shock wave to stand off, so that reduces heating, but the resulting shock wave is so strong that it produces lots of ions. That cuts communications. A sharp body produces a weak shock wave, with fewer ions, so it's easier to communicate. But the weak shock wave stands close to the vehicle so the heating is intense. We are now testing materials and designs that can take that high heating!

[ GeorgeRaiche/ARC - 26 - 10:36:05 ]
RE: [Bertus] Hi. I just want to know how hot the outside of the shuttle becomes??
Hi Bertus; The outside (bottom) of the shuttle gets up to around 5000 degrees F. That's about as hot as the surface of the sun!

[ GeorgeRaiche/ARC - 28 - 10:38:55 ]
RE: [JimL] JimL/SebringFL would like to say to Dr. Raiche, that his selection of Plasma or As you state it Reacting Flow Environments has got to be the toughest and most Interesting of all the fields. Thankyou for speaking with us. I would like to Know if you have done any work in Plasma drives?
I am glad that there are people who are interested in the work we do for NASA. I don't do any work myself on plasma drives but several of my friends in the group do (there are a couple of different plasma drive designs, by the way!). But many other problems in spaceflight are very challenging and probably won't be solved soon. There is plenty of work to go around!

[ GeorgeRaiche/ARC - 31 - 10:42:06 ]
RE: [Oran/NASAChatHost] Elena, see George's response to your question about CAPCOM in Message #22.
Elena, if you visit the main NASA web page and search around in it, you will find a section on how to become an astronaut. That will give you a good idea on what it takes as far as training. But remember that there are only about a hundred astronauts. Many thousands more of us are needed to keep them flying!

[ GeorgeRaiche/ARC - 32 - 10:43:51 ]
RE: [JimL] JimL/SebringFL as lightning approaches me would like to know if you have discussed the lightning / plasma injections that go into space from The conventional lightning we earth bound critters know? Is anyone doing a study on this phenomena?
That question is pretty well out of my research area! But I know that the chemistry and physics of the upper atmosphere is an important research area, especially as we get more dependent on low-earth-orbit satellite communications.

[ GeorgeRaiche/ARC - 35 - 10:49:32 ]
RE: [Bertus] Wow, Now I have heard that there is a protective layer of silicone underneath the shuttle( Is that correct?)Now when the shuttle reenters and lands safely do they take that old silicone plates (or what) of?? (Excuse the spelling!!)
There's quite a bit of silicon chemistry going on underneath the shuttle! The tiles are mainly silicon dioxide--glass--that's formed into a foam. The major insulating material is just air, held into place by the silicon dioxide foam! Then the tiles are coated with a polymeric coating to make them stronger, and coated with a silicone material to keep them waterproof. The whole coated tile is glued to the shuttle with that rubbery silicone glue. You can buy that in hardware stores. Every tile--and there are thousands--is inspected individually after each flight. If it looks damaged we replace it. One problem with shuttle tile is that it is relatively fragile, and replacing tiles is a lot of work.

[ Oran/NASAChatHost - 36 - 10:51:37 ]
EVERYONE, at the conclusion of today's chat, please visit our NASA QuestChat Information Center to send us your thoughts. Use our online surveys at http://quest.nasa.gov/qchats.

[ GeorgeRaiche/ARC - 37 - 10:53:12 ]
RE: [Elena] How much does a CAPCOM approximately earn a year?
NASA (and all US Government agency) pay scales are set by Congress, and you can find that information on the NASA web pages--usually under the Human Resources links. Whenever NASA advertises a job, we tell you what the pay grade would be. Unfortunately, I don't know that information for CAPCOMS. But NASA realizes that most of its employees are highly skilled, and pays them accordingly.

[ GeorgeRaiche/ARC - 39 - 10:55:19 ]
RE: [JimL] JimL/SebringFL would like to know if your research into plasmas and plasma environments has given you some idea of what electricity really is?
What I've learned is that electricity is just the natural response of atoms and molecules to externally-applied forces. I think it's amazing that we've learned to control electricity to the extent that we have, since we can't see its components directly.

[ GeorgeRaiche/ARC - 41 - 10:59:17 ]
RE: [Bertus] Mr.Raiche do the people that service the shuttles take the old protective sillicon plates off the bottom of the shuttle after it has re ertered the earth-and landed savely?
Yes. Each shuttle tile has an individual number and is tracked independently. When the shuttle lands, a team inspects every tile to look for any damage--burn marks, chips, cracks, or melting. If a tile is damaged, the team pulls the tile off--it's glued on--and a new tile goes in. Otherwise, the tile stays in place for the next flight. There are thousands of tiles on the shuttle, and inspecting them is a very slow process.

[ Oran/NASAChatHost - 43 - 11:02:13 ]
EVERYONE, George will remain online with us for a few more minutes. Please continue sending your questions in to us!

[ Bertus - 44 - 11:02:42 ]
Mr.Raiche thanks a lot for your time I must be going now...Bye from South-Africa...

[ GeorgeRaiche/ARC - 45 - 11:02:59 ]
RE: [Bertus] Sorry I send the same question twice...How much does one of this plates cost about in dollars??
To tell you the truth, I don't know how much one tile costs. The material costs are very small--the real expense was in the research costs to invent the tiles. Also, the labor costs to inspect and replace the tiles are far greater than the material cost. It's like repairing a car--the labor charge is usually much more than the parts.

[ GeorgeRaiche/ARC - 47 - 11:05:49 ]
RE: [JimL] JimL/SebringFL would like to know if it is possible to capture and retain some Of the plasma environment within which you work?
These plasmas don't exist unless you apply external energy to them. That's what our plasma and arcjet facilities do. But a plasma is not thermodynamically stable under "normal" conditions, so they decompose very rapidly once the external power source is turned off.

[ GeorgeRaiche/ARC - 48 - 11:08:14 ]
RE: [JimL] JimL/SebringFL back to electricity, George is it positive holes moving like the Civilians say or electrons moving like the military says?
I'm a civilian, and I think of it as moving electrons. It really doesn't make much difference from an analysis point of view. And an electron doesn't know that we call it a negatively charged species.

[ Oran/NASAChatHost - 49 - 11:09:55 ]
This concludes our Aerospace/Space Team Online chat with George Raiche from NASA Ames Research Center. Thank you to everyone for joining us today!!

[ Oran/NASAChatHost - 50 - 11:10:31 ]
Our special thanks to George Raiche for answering our questions and sharing his career experience and expertise with us today!!

[ GeorgeRaiche/ARC - 51 - 11:11:37 ]
RE: [Oran/NASAChatHost] Our special thanks to George Raiche for answering our questions and sharing his career experience and expertise with us today!!
Thanks to everyone for asking questions!

[ Oran/NASAChatHost - 52 - 11:11:55 ]
We invite you, once again to share your thoughts with us on our NASA QuestChat Information Center at http://quest.nasa.gov/qchats.

[ Oran/NASAChatHost - 53 - 11:12:29 ]
An archive of today's chat will be available soon. Thank you again for joining us, and have a great day!!

 
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