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September 19, 2000
QuestChat with George Raiche

Research Scientist in the Reacting Flow Environments Branch
NASA Ames Research Center,

Mountain View, California

[ Terri/NASAChatHost - 1 - 08:17:13 ]
If you attempt to post messages in the chat room at this time, they will not appear on your screen. However, they will remain in our chat queue and may be posted during the chat. We invite you to return to the chat room on Tuesday, September 19, 2000 at 10:0 a.m. for our chat with George Raiche. We look forward to hearing from you then!

[ Terri/NASAChatHost - 12 - 10:00:01 ]
Good morning all! Today's chat will feature, George Raiche, a Research Scientist in the Reacting Flow Environments Branch at NASA Ames Research Center. Thank you for joining us George. In a second I will post a few questions from our that are awaiting your answers. Please be patient, chatters, I will post your questions as George answers the preceding ones.

[ GeorgeRaiche/ARC - 17 - 10:03:52 ]
RE: [MrThomasStudents] What kind of grades did you receive in math and science?
Hi; I HATED math at first, and got some really bad grades! But I loved science, and as I took more science, I began to see how the math could be useful. I still don't really like math by itself, but it allows me to think about scientific questions in ways that would be impossible otherwise. That's the kind of math I like. (I hope Mr. Thomas is not your math teacher!)

[ GeorgeRaiche/ARC - 18 - 10:06:19 ]
RE: [MrThomasStudents] What kind of things did you take apart as a child?
I took apart a camera that I found in the house once. I also disassemble my dad's electric razor one morning. He wasn't too happy about that! Once, my dad bought me an old mechanical camera at a yard sale. It didn't work, but I was able to fix it. That was the first thing I was able to fix. Then I got some old engines and fixed them, including on the old motorcycle I rode.

[ GeorgeRaiche/ARC - 22 - 10:12:27 ]
RE: [MrThomasStudents] What is the most interesting project you are involved in presently?
Right now I'm trying to concentrate on one project, which is to understand the arcjet test environment. We use the arcjets to test thermal protection materials. But because the conditions in the arcjet airflow are so extreme, it's hard to measure the conditions accurately. That means there's uncertainty about the test conditions. This translates into uncertainties about how thick a heatshield needs to be to survive entry. To be safe, we make the heatshield extra thick. But that extra thickness means extra mass, which we don't want. So by reducing uncertainties in test conditions, we can reduce the thickness of the heatshield. That's a pretty interesting project!

[ GeorgeRaiche/ARC - 24 - 10:14:22 ]
RE: [MrThomasStudents] Are you interested in any other parts of NASA other than what you work in?
I'm interested in a lot of what NASA does! That was one of the reasons I joined--there are many different things going on. Getting into space is so complex that it takes many different disciplines to be successful. That means that people with many different backgrounds work together here.

[ GeorgeRaiche/ARC - 29 - 10:21:29 ]
RE: [pedro] How heavy is the shuttle prior to takeoff?
Hi Pedro; This is a little embarrasing--I don't know the total weight! I do know that the external tank carries half a million tons of fuel and oxygen at launch. The solid rocket motors weigh over a million pounds each!

[ GeorgeRaiche/ARC - 30 - 10:23:55 ]
RE: [Brett] Is there a certain window of time for reentry and if so what happens if you miss it?
Hi Brett; The reentry window is designed to bring the shuttle down onto a specific point on Earth. Since the landing is done without engines, the shuttle can't choose a different landing site at the last moment. If one window is missed for, say, a F lorida landing, they just hold it in orbit and try again later.

[ Terri/NASAChatHost - 31 - 10:27:07 ]
Please don't forget to fill out our survey. Thank you.

[ GeorgeRaiche/ARC - 34 - 10:30:22 ]
RE: [Andy] When the shuttle re enters the atmosphere why doesn't it come in as a streamlined shape like a high diver ??
Hi Jim; T hat's an excellent question, and the answer isn't at all obvious. Solving that problem was a major breakthrough. You would think that the easiest way to get a vehicle through the atmosphere is to make it very pointed. That's true from an aerodynamic st andpoint--it reduces resistance against the air. That's why fighter jets tend to be pointed. But while a fighter jet takes 3 or 4 seconds to fly one mile, the shuttle entry speed is about 10 miles per second! At those speeds, atmospheric heating is the hardest engineering problem. A very pointy surface generates a shock layer close to it, which heats up. But the pointed surface can't conduct heat away from the point rapidly, so it gets extremely hot. A blunt surface sets up the shock wave further aw ay, and also is better at conducting heat away from the surface. So for thermal reasons, a blunt surface is easier to manage than a sharp or pointed surface.

[ GeorgeRaiche/ARC - 35 - 10:32:08 ]
RE: [Jim] Terri, I'm loosing connection so I would like to send a question ahead of time and monitor the chat as I can get through. I am a si ngle user and have talked with George before. My question to George: JimL/SebringFL would like to know more about your most interesting work with plasma. How is it generated? What controls do you have over the plasma flow? Is it like a cyclotron (i.e. contained) or more like the gun of a television tube where only deflection by charged plates is possible?
Hi; We control the plasma by controlling the current and the rate of air flow. We also contain the plasma by isolating it electric ally, and using magnetic fields to swirl it along the heater tube. It's not a cyclotron, though.

[ GeorgeRaiche/ARC - 37 - 10:35:00 ]
RE: [MrThomasStudents] What is your everyday schedule at NASA?
Hi; My typical schedule is to get up in the morning, check my e-mail, and then take the commuter train to NASA--we're near San Jose, California, and the traffic is horrible. Some days I do office work, like analyzing data or planning new experiments. Other days I work in the lab. If the arcjets are scheduled to run on any day, chances are I'll be in the lab with an experiment.

[ GeorgeRaiche/ARC - 38 - 10:37:10 ]
RE: [MrThomasStudents] Besides birdwatching and being a scientist, what else do you enjoy doing?
I like to go to movies and to go hiking or walking around in San Francisco. I also have been spending time trying to photograph some of the birds I see. That takes a lot of time!

[ GeorgeRaiche/ARC - 39 - 10:38:52 ]
RE: [Terri/NASAChatHost] Meaghan7th/StCathRiv Is it a fun and exciting job or is it stressful and hard?
Yes! It is usually very interesting work. Some of the office work is not fun, but it's necessary for doing the exciting stuff. And sometimes we have deadlines for making a measurement, or writing a paper, and that can be very stressful. Sort of like school.

[ GeorgeRaiche/ARC - 44 - 10:44:51 ]
RE: [Jadon] What speed does the shuttle reach leaving the earths atmosphere?
Hi Jadon; The typical orbital velocity--what the sh uttle needs to make to hold it's orbit-is about 17000 miles/hour. That varies, depending on the average altitude. As the shuttle (or any orbiting body) goes higher, the speed goes down.

[ GeorgeRaiche/ARC - 47 - 10:46:43 ]
RE: [Nathan] What temp. must the shuttle withstand?
Hi Nathan; The shuttle surface temperature on its bottom--near the nose, wher e it's hottest--is about 5000 degrees F. That's about as hot as the surface of the sun!

[ GeorgeRaiche/ARC - 48 - 10:49:25 ]
RE: [Brett] How long does it take to make a single shuttle?
Hi Brett; That's a hard question to answer, because so few shuttles g et built and because a single shuttle is never really "finished"--they're constantly being overhauled and upgraded. A full overhaul can take over a year--even just the routine turnaround after a flight can be several months. If you ordered one tomorrow, though, I would expect it to take a couple of years.

[ GeorgeRaiche/ARC - 50 - 10:51:06 ]
RE: [TODD/SCOTT] Being in the NASA atmosphere day in and day out have you ever developed the desire to be one of the astronauts aboard the shut tle ready to launch?
Hi; I think every NASA employee thinks about being an astronaut! It takes years of specialized training, but I think a trip into space might be worth it!

[ GeorgeRaiche/ARC - 51 - 10:55:53 ]
RE: [Andy] If there is no advantage to the shuttle being a pointy shape (see the answer on re entry)... why is it shaped this way at all ?? Su rely it would be better to have all blunt surfaces for ease of reentry or is this just aesthetics ??
Hi Andy; That's a good point. When I responded before, I was talking about the heating problem. Once the shuttle comes through its hypersonic flight regime--that is, once the maximum heating period is over, and its speed falls under Mach 3 or so, the heating is less important than the aerodynamics. At transonic and subsonic speeds the shuttle needs to fly like an aircraft, with a high lift to drag ratio. So at low speeds, aerodynamics do become important, which is why the shuttle has an aircraft shape. During hypersonic heating, the shuttle is oriented so that its bottom points along the line of flight--that presents a blunt surface to the airflow. But once the heat pulse is over, the shuttle rotates so that its nose points forward. This reduces the aerodynamic stresses.

[ MrThomasstudents - 56 - 10:57:48 ]
Thanks for your efforts and time to talk to us. We have alot of information to share with other students. Thanks again.

[ MrThomasStudents - 57 - 10:57:48 ]
Do you still see your mother?

[ Terri/NASAChatHost - 58 - 10:59:12 ]
Hello All! George has offered to remain a while longer in order to attempt to answer your most of your questions.

[ Terri/NASAChatHost - 59 - 10:59:41 ]
Please don't forget to fill out the chat survey. Thank you!

[ GeorgeRaiche/ARC - 60 - 11:01:30 ]
RE: [Terri/NASAChatHost] Lauren7th/StCathRiv In your biography you said that the best part of your job is working with very smart people. When you work with the smart people does it ever make you feel not as smart? Have you ever been mistreated at NASA because of your >race or religion?
Hi Lauren; I think you will find that when you work with smart people, they see what you have to offer and you will feel as smart as they seem. What you find out pretty fast is that nobody knows all the answers. Anyone who thinks they do gets proved wrong in a hurry! And you learn much more when you work with smart people. Pretty soon you'll know as much as they do, and you'll all know more because of what you bring to the group. NASA works very hard to evaluate its workers based on what they do, not who they are. We struggle with everything else that our society involves, but we have a real commitment to fairness.

[ GeorgeRaiche/ARC - 61 - 11:03:03 ]
RE: [pedro] How many G's are felt upon reentry?
Hi Pedro; Once again, I don't know the exact answer! But humans can't function under much more than about 5 Gs, so I would guess that's the limit.

[ Jadon - 62 - 11:04:08 ]
When did you first begin getting interested in NASA and space travel? and how did you get involved in it?

[ Brett - 63 - 11:04:08 ]
Is it true that Chrysler has more computer power than NASA?

[ GeorgeRaiche/ARC - 64 - 11:07:00 ]
RE: [MrThomasStudents] Is your wife involved with what you do at Ames?
Hi; Physical chemistry is a branch of chemistry where we' re not interested so much in making things. What we're interested in is trying to understand why certain chemical reactions occur, and why others don't. For example, why does a piece of paper burn, but a rock doesn't? We tend to study very simple chemi cal reactions in great detail, with lots of computer simulation, to try to find theories about why molecules react the way they do. My wife has nothing to do with NASA--she teaches Spanish at a local university. And I do see my mom and dad--they live in Boston, so I try to visit about once a month.

[ TODD/SCOTT - 65 - 11:08:41 ]
How recent was the latest major breakthrough of technology in your area of design?

[ TODD/SCOTT - 66 - 11:08:41 ]
Hey there, do you by chance know my teachers cousin, Gerald Fuller (from Stanford)???

[ GeorgeRaiche/ARC - 67 - 11:08:50 ]
RE: [TODD/SCOTT] What type of textile would be needed to withstand the temperature of the sun???
Hi; We use cloth based on silico n dioxide fibers, carbon fibers, zirconia fibers, and other ceramics. Generally, these all have very high melting points and are resistant to oxidation.

[ Jim - 68 - 11:10:57 ]
JimL/SebringFL would like to know more about your most interesting work with plasma. How is it generated? What controls do you have over the plasma flow? Is it like a cyclotron or more like the gun of a televis ion tube where only deflection is possible

[ Terri/NASAChatHost - 69 - 11:10:57 ]
Tony7th/StCathRiv How long will it take to process all the SRJM data? Do you think you will ever go into space?

[ GeorgeRaiche/ARC - 70 - 11:12:25 ]
RE: [Brett] Is it true that Chrysler has more computer power than NASA?
Hi Brett; I think we could give Chrysler a run for it! O ne true fact is that the computer you're using has far more computing capacity than the Shuttle's main computer. But there are two things to keep in mind. First, anything that goes into space needs to be hardened against radiation (which on Earth is blo cked by the atmosphere and Earth's magnetic field). Second, the shuttle's computers must not crash during critical times (which would be most of the time). So a space computer has very different requirements from a desktop computer.

[ GeorgeRaiche/ARC - 71 - 11:14:34 ]
RE: [Jadon] When did you first begin getting interested in NASA and space travel? and how did you get involved in it?
Hi Jadon; W hen I was in second and third grade, the moon landings were just starting. The Viking mission to Mars came a few years later. That's what got me excited about space. Also, I was a big Star Trek fan.

[ Terri/NASAChatHost - 72 - 11:15:40 ]
Thank you, George for your participation in our NASAQuest chat. We found your answers to our chatter's interesting questions to be very intriguing.

[ Terri/NASAChatHost - 73 - 11:16:32 ]
We look forward to your participation in our chats and webcasts in the near future.

[ GeorgeRaiche/ARC - 74 - 11:16:43 ]
RE: [Terri/NASAChatHost] Thank you, George for your participation in our NASAQuest chat. We found your answers to our chatt er's interesting questions to be very intriguing.
I appreciate everyone's interest, and the great questions! I'll look forward to the next chat!

[ Terri/NASAChatHost - 75 - 11:18:15 ]
This chat has ended. Thank you for participating!


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