The a16z Show - a16z Podcast: From Hidden Figure to Sonic BOOM

Episode Date: March 22, 2017

An aerospace engineer who worked for NASA for over 40 years, Dr. Christine Darden is one of the mathematicians that the book and movie Hidden Figures was based on. Darden eventually would lead the sonic boom team, going on to become the first African-American woman in senior management at NASA. In this intimate conversation with a16z’s general partner Jeff Jordan, held at the SF Jazz Center, Darden shares with Jordan how she first fell in love with geometry and math; the effect that Sputnik had on our culture (and her); and what it was like to work at NASA in the 1960s. And finally, Darden shares with us all the secrets of the sonic boom. Stay Updated:Find a16z on YouTube: YouTubeFind a16z on XFind a16z on LinkedInListen to the a16z Show on SpotifyListen to the a16z Show on Apple PodcastsFollow our host: https://twitter.com/eriktorenberg Please note that the content here is for informational purposes only; should NOT be taken as legal, business, tax, or investment advice or be used to evaluate any investment or security; and is not directed at any investors or potential investors in any a16z fund. a16z and its affiliates may maintain investments in the companies discussed. For more details please see a16z.com/disclosures. Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

Hi, and welcome to the A16Z podcast. Today's episode is based on an event with Dr. Christine Darden, one of the mathematician's hidden figures was based on, in conversation with general partner Jeff Jordan, about her career and experience at NASA and all the secrets of the sonic boom. You were galvanized by Sputnik. I think it was at 1957? Yes, I was a senior in high school when Sputnik went up.

And my job at high school was to collect the morning newspaper and put it on the spindle in the library. And I remember the day I went out and saw the headline of Sputnik. And so I can just remember what happened to the whole country after that. All of us had gone through drills of hiding under our chairs at school because we were afraid of the Russians dropping a bomb. The guy says they're up there and they'll be flying a bomb over us. We were all worried about that.

And so the schools were galvanized. The students were encouraged to go into STEM. horses and take them. Our yearbook had a solar system theme, and we did all of that because of Sputnik going up, and so it was very much so. And did that influence what you studied in college? Well, not necessarily the Sputnik. I happen to have a geometry teacher that just made me fall in love with geometry and math. And so that sort of sealed the deal that I wanted to go toward the math than physical sciences rather than biological sciences. And that affected my decision to go into math and physics.

And then with that, you were kind of sound like you were on a path to become a teacher, and then you got diverted by a... Well, I was on the path to become a teacher. I wanted to do what we said, get a general studies job in math, but my father said, I want you to be able to get a job when you finish school. And so you get a teacher certificate. So I did do that. And actually, as electives, I took the math courses. I wouldn't have had to take as a teacher. So I took all the rest of them as electives. And then NASA's precursor was NACA?

NASA's precursor was NACA, which started in 1917, yes. 1917. And how did you find out about the opportunities? I guess I really didn't. I actually went back to school. I taught for three years. and I had gotten married and everything. And my husband got a fellowship to go to school to get a master's. And I said, well, I need to get a job up there around the school. I applied at several counties around the school in Virginia. I got a letter from one asking for a letter of recommendation.

And my principal said, I'll give you a letter of recommendation, but I want your contract back. I don't want to be looking for a good math teacher in August. So I gave it back and I said, I'll get this job. And I never heard from them again, but I had begun to take in-service classes at the same school where he was going. And my teacher was the head of the math department there. And so when I went up the next weekend, I told him I was looking for a job and I needed a job. And he says, well, let me take you across the hall to the head of the physics department. He's looking for a research assistant in aerosol physics.

When I went home that night, I had a research assistantship in aerosol physics. Okay. And that, I mean, it was just wonderful. And so that allowed me to get a master's degree in applied mathematics. I did my research in the physics. And when I graduated, I went to the placement office just before I graduated. And she said, you should have come early. NASA was here recruiting yesterday.

And I said, I didn't even know about it. She says, well, I tell you what, you fill out the application and bring it back to me and I'll send it in. And she did. and I heard from NASA in three or four weeks offering me a job. What was the state of NASA when you got there, both from the perspective of an African-American as well as a woman? What was the environment? Actually, it's amazing that the book portrays NASA as one of the most enlightened employers in the area at the time. So can you describe what you found?

Well, there were no women supervisors to say, maybe in human resources in some of those offices, but in the engineering sections, the women were typically the secretaries or the computers that were supporting some of the groups. I went into a computer section which supported the reentry physics branch, which was the branch that had done the calculations of getting the satellites back into the atmosphere. But they had done all of that before I got there. They had done all those calculations. So there typically were not any females in the technical side in, in, uh, in, uh, advances in everything. And this was black and white. Females, yes. And so it was a, it was a predominantly male atmosphere and predominantly males who hadn't worked with women. Right. Okay. Yeah.

And I said it like that because as I was there longer and you began to see the young engineers come in who had been in school with women in engineering, their attitude was entirely different. over working with women. Yeah, I think I read that a little before you joined in the early 60s, there was low single-digit number of women of any race in engineering. That's true. Yeah, only a few. So what were your first impressions?

Well, of course, I was excited at first. I mean, I'm working at NASA. Yeah, I got a job. I'm working at NASA. I didn't really know what I had been hired to do. And then I realized, you know, that I was in a support role that the engineers would bring in equations. We were to solve the equations and give them the answers. And very often, we didn't know what the equations were for in the first place nor what the answers meant.

And I began to find that unsatisfactory, but that's the way it was. A few of them would explain what an equation was for, but not all of them. And so I think if I get the sequence of events right, you find yourself a couple years in, there's some changes at NASA, and you overhear that you might be subject to a riff, a downsizing? That is correct. And that riffless was rescinded. And so I, but I did say, well, I'm going to go and I had already asked some of my immediate supervisors about moving into engineering. But I decided to go to a higher level supervisor. And so I went to the director and asked. I mean, you went. Yeah, it was several levels up. He was a director. I asked, I said, well, why is it that the men coming here with the same background?

I had, degrees in mathematics or applied mathematics were put in engineering sections and able to work on their own projects and write their own papers, and the females are put into computer sections which are support, and you don't get promoted very well. His response was that nobody had ever asked that question before. And he also commented on the fact that so many of the women coming there to work actually found husbands there and then got married and went home. and that that was, you know, they don't want to waste money on women doing things like that. But I told him that that probably was not true of the African-American women. They would probably continue to work.

And I got transferred to an engineering section. I got a promotion because I hadn't had a promotion in five years. And in that riff list, I was actually being bumped by somebody hired at the same time, who had gotten promoted twice. Yeah. So I got a satisfactory. result out of that. You did. Yes. That would be a satisfactory result. I agree with you. One of your first assignments was to write a computer program for Sonic Boom. You're in the Sonic

Boom area. First, explain to what a Sonic Boom is. Literal arts majors what a Sonic Boom is. Okay. Well, I told your young assistant that when I talk to students, I explain it with a balloon. and I say, you've got a certain air pressure on your ear in this room. But if I sat here and blew up the balloon, the balloon is going up because the pressure in the air in the balloon is getting higher. So if I pop the balloon, there's a shockwave set up at this balloon going out in all directions at the speed of sound, and it's got a higher pressure. So when that shock wave gets to your ear, it immediately jumps from a low pressure to a high pressure. And that change in pressure, that instantaneous change in pressure is what you hear. That's the pop of a balloon.

And when an airplane is traveling supersonically, the same thing happens. All of the disturbances caused by that airplane going faster than the speed of sound are contained within a cone that's attached to the front of that airplane. And this is like an ice cream cone in all directions. And it is not only when the airplane goes through Mach 1, which means through the speed of sound, it goes with that airplane the whole time it is flying faster than the speed of sound. So if an airplane flew from California to Virginia, that cone would go all the way from California to Virginia, and that cone would intersect the ground all the way from California to Virginia. So before the cone intersects the ground, you are on the ground. you are in that normal air pressure on the ground,

but exactly where it intersects the ground, you suddenly get into that cone with the higher pressure. And so that, again, is this instantaneous change in pressure, and that's when you hear the sonic boom. And the sonic boom, it can be pretty bad. It can be okay. We're hoping that we can design it to be okay. But it could break glass.

It could damage the damage. sheetrock in a house. And when they did a lot of flight test in the 60s, around Chicago and around Oklahoma City, people were calling saying, you know, you broke my glass, you cracked my sheetrock so they could get paid for the damage to their houses and things. And it was that during that time that this country actually passed a law that there could be no commercial supersonic flight overland. And so that is that, that, I'm not sure. exactly when that was passed. But that was

a reason, in the early 70s, the United States, Russia, and the English and French were planning to build a supersonic passenger plane. The United States canceled their program, and Boeing had to lay off a lot of engineers because they had hired up engineers

to build this supersonic transport. The English and French built theirs, and it was called the Concord. The Russians built theirs. It was the T-U-1-4. And it had an accident at an air show in France, I believe, and caught a fire. And so the Russians never flew there as a passenger jet.

It flew only in Russia as a cargo airplane. I got one chance to fly in Concord. And if I remember right, it would go subsonic over the land, get over the ocean, go supersonic. And then I remember them landing in Washington, Dallas Airport and Washington, D.C. They were back to Sub-Sahic. Yeah. So that, yeah, because of the laws, they could not fly. And in fact, it at one time flew from Washington to Houston,

and that would be an entire leg of the journey subsonically. Very expensive, though, because very high drag, and the airplane was burning up lots of gas and doing that trip. So that is true. United States was not the only one that had the laws against supersonic flight. It was many countries around the world. In fact, most countries around the world prohibited that. And so the only legs that they could fly supersonically were over water.

And because they didn't have people buying very many concords, they only built 13 of them. And so it did not make money. It was very expensive to fly. I think I called once and asked what was the price of a ticket back in the 70s. And it was like $1,000 even back then and pretty expensive. And so the United States, so the lesson actually became, if you're really going to have a profitable supersonic airplane, it really needs to have some overland routes. And so this is why working on the sonic boom became so very important in the early 70s. And can we reduce this to a level where people in this room would say, oh, no, I could live with that noise.

And it's not bothering me at all. And that's what we were working on when I got put on Sonic Boom work. And so one of your first assignments was to take a well-known equation and put it in the program. We had a system of equations. This paper gave several governing equations that would give us minimum area that we would need for this airplane or minimizing area, an area that would minimize the Sonic Boom. And so I was able to complete that program. It was a system of partial differential equations.

And that gave us the equivalent area that we wanted to design an airplane to fit. That was about 1972. Okay. Once the computer code was running, then we would put in the mock number, the length of the airplane, the weight of the airplane. And I left that one. There were four variables for the airplane. And so if we wanted to design a minimum sonic boom plane, it would give us the area. So I and one of the guys who was working with me now sat down and started to design airplanes.

We started out with just a wing and a fuselage. And we would calculate the volume of that airplane and get that area. Then we would calculate the lift of that airplane. And the lift, of course, is generated mostly by the wings. We would add those two together and compare it with the ideal. And then we would, of course, be off. And we would have to go back and change the design. and recalculated and do it again until we got them very close together.

We said this is about as close as we can get it kind of hand drawing that. And then we took the design to the model makers and they built us five-inch steel models that cost $6,000 or $7,000 because they had to be very exact in thickness and everything. And then we went to the wind tunnel and tested the airplanes at the design mock number, whatever that was. And we would measure the pressure inside that cone because that cone would hit the wall in the tunnel. So we would put one of the pressure probes inside the cone, the other pressure probe outside the cone and get the difference of that pressure jump when people would hear that sonic bone. And we saw that the theory looked like it was working. I mean, this is what we were

trying to, this is our experiment that said these equations were right. We look like we're headed in the right direction. And we started making our designs more realistic. We put engines on the plane. We've used twisting camber in the wings and things like that. And then finally, when we thought we had a good design, we actually came out to California. And actually, by this time, I think another company was helping with us. We got two F5s from the military. And we took just volume and changed the volume of the area distribution of the airplane, just using volume of the F5 of one F5 and then we flew a second F5 with no changes. We flew them out at Dryden Research Center down near L.A. And we measured that the signatures coming off of those two airplanes all the way

to the ground, first using F-15s and then slower airplanes and maybe some balloons and then finally measuring on the ground. And we were able to show that, yes, this theory is working. We were getting a big N-wave with the unmodified F-5, but we could see. the changes but where we had modified the F-5. And folks were shouting, shouting then, like you saw them, shouting in the control room when the shuttle came home. Yeah, which is great. Yeah.

And so this became your life's work. Well, it did. I spent about 20 years working on that. 20 years work on that. And you progressed throughout the, in the group, you progressed to your organization. Well, we did. We actually had a funding cut out during one. period of this, during one of these periods. And when we funding came back, it was for the

environmental portion of a high-speed civil transport. Well, Sonic Bone was one of the environmental portions. So they asked me to come back and get the program back together for the Sonic Boom. And so I actually went all over the country looking for people who had worked in Sonic Boom at all the NASA centers at universities, at Boeing, at McDonald's. Douglas and everything. And they came back to NASA for like a three-day meeting for us to decide how should we approach, you know, this program now. And we decided the design, which we had been doing before, was one way. The second, we needed to know what people would accept. And so we started putting computers in people's houses and randomly playing sonic bones.

Randomly playing sonic bones. How do you randomly play a sonic bone? Well, the computer was doing it. The computer was generating them randomly, and then they were supposed to go back and give their immediate reaction to the sonic bone. And then the third thing, we were concerned about, these airplanes are flying at 40 or 50,000 feet. What happens to that signal coming through the atmosphere of 40 or 50,000 feet? So we actually went down to white sands and did some flight test in the morning when the atmosphere was quiet, and we would see what would happen. And then in the afternoon, when it heated up and there was a lot of turbulence in the atmosphere. So that was the third part. You know, what would the atmosphere do to this signal? And so we launched into that program for the next few

years, actually looking at all three areas of that. What did the atmosphere do to the sonic? Well, the turbulence you could see, you could see that you had more scatter in the signal, but you could still see the effects of the shaping that we had in there. Okay, so it still didn't work. So you did this in a concerted way. Did you have to be? Did you have to? have other areas of specialization while you were at NASA? Actually, I worked on supersonics doing some designing the flaps on supersonic airplanes for a while. But it was mostly the sonic boom that I did. And then at the end of my career, I actually went into management.

When they were getting ready to cut the sonic boom funding again, I applied for and got into a career development program and went into senior management. And became the first African-American woman. and senior management. How do you advise young scientists when striking a balance between specialization and generalizing, a more generalized approach? Well, you know, mine was sort of depending on where I was assigned. And very often that's what happens.

You sort of come out of school with a general education. You've got the math background and the physics background. But if you get assigned to a particular area, you are actually supposed to go to a deeper level in that area. And so that requires you to spend some time working to that deeper level. And so we find that actually most of the people that would come to NASA, once they started working in the engine area or the hypersonic engine area, they spent their careers working in that area. There wasn't a lot of lateral movement.

And so there was not a lot of lateral movement once you got there and became known as an expert in a certain area, yes. So the NASA you left almost 40 years. from when you joined, how was it different? You described the beginning state. Very few women engineers. Okay, well, by the time I left, we had seen far more women coming into the system.

And though we had had, in the intermediate times, we had had some female supervisors that had difficulty managing men who did not particularly like to work for women. By the time I left, we actually had a center director who was female. And so women were pretty much working in many, many areas of the center by that time. It had completely morphed. Yes, yes. Which is fantastic.

You've had a very successful career. You also have children, grandchildren, great-grandchildren. How did you address the balance thing during your career? That was pretty hard. I actually thought of quitting my children. job at NASA when my last child was born. And my mother told me, well, that's a really good job you have. Maybe you should keep it. So, I mean, so I had to deal with the babysitters or the child care centers and things like that. And during the summer, it was very difficult because they would be out of

school and I would be working. And so that was difficult. But I do know that I had opportunities She's to go to NASA headquarters earlier in my career, and I would not do things like that because I didn't want my child. I wouldn't leave her at home. And by that time, I think only the youngest one was there. And so I made sure I stayed at home, and she wouldn't have to change schools or anything until I went to headquarters. So the movie in the book, Hidden Figures, seems to have, it's gotten a lot of praise, but it seems to have struck a court. and galvanized people? Why do you think that is? Well, you know, maybe I'm thinking that folks didn't realize that what black women were working on at the

time. So we were working on some pretty important topics. And I think that's part of what is galvanizing. And as far as our school children and everything, maybe these are role models that they've never seen anywhere. And we always say that people need to see somebody doing a job And I think maybe that's it. I think there are several lessons in that movie and all over the country, people seem to be showing the movie to school students and saying, look how these women work.

Look how they do their jobs. Even though they're running into all of these problems of prejudice and things like that, they're still doing their work and they're doing it well. And so that's a lesson you need to learn. I think the lesson of Dorothy Vaughn saying, look, the job is getting ready to change. change and we're going to lose our jobs if we don't learn to do something new.

Right. I think that's an important lesson for school children. That was when computers were coming. That's right. Computers are coming in. They're going to replace these human computers who are very much slower. So she says, I think you better learn how to do Fortran so that you can actually run the computer and not be out of a job.

And that's something that is happening every day in our lives. And so I think that's a very important. lesson that people need to learn. That's what Silicon Valley is wired about. Absolutely. We call them disruptive technology. So do we. For you personally, was there a moment when you felt like you no longer had to prove yourself?

Well, I always felt like I had to do my job and do it well. So I don't remember thinking of it that way that I didn't have to prove myself, but that I actually thought I was pretty well respected by the people I was working with. And so while I wanted to do my job well, I didn't think of it like I had to prove myself. Okay. What advice would you have for the audience about advocating for your own career? I mean, you more than once had to kind of call attention. Yeah.

Well, that's true. And I actually had decided if I did not get some action, I was going to quit at one point. and go and teach in colleges. Okay. But I think you need to let people know what you want and what you're interested in. And I did that. I did that on several levels. And I wanted to go to school.

I did that and had to kind of get a higher boss to advocate for me to be able to take classes. Oh, that's right. And so I think you need to let people know what it is you're interested in and maybe you would like to do something else. But you also need to make sure you're doing your job very well, you are so that maybe they'll listen to you and maybe be favorable in transferring you to something else you'd like to do. Yep, deliver. You were friends with Catherine Johnson. Actually, you knew were classmates with her daughter, right? Her daughter and our classmates. We were in college together. Catherine was the one who was calculating the orbital reentry codes and competing with the

computers. What lessons did you learn from her? Because, I mean, well, she's a very, gracious person, I think, and she, people like Catherine. She's, she's, she's, she's, she's, she's, she's, she's, she's, she's, um, very gracious. When I, the first day I met her when I went into the church, she, she, uh, when church was over, she walked from the choir all the way to the back to invite me to come join the choir. And I, I think this might have been when I really met her. It was some years after I had started working there, but, but, uh, and she's very good at what she, what she, what she did. And I, what she did. And I think this might have been. And I, did, of course, in her mathematics and everything. And so, you know, Margo kind of counts to me as standing on the shoulders of these three ladies. Because if NASA had hired black females and they had not done the job well, they probably would have stopped hiring them. But the very fact that I got hired and the people with me got hired was because these folks had shown that we, yes, we do do the job and we do it well. Hired and advanced. Yes, yes, yes. Just recognized for the achievement.

There's been a strong movement to focus more on science and math or STEM. Some people say STEAM, if you include the arts. How can all of us advocate towards education? Well, one of the things I tell the young people is, you know, just we were talking about disruptive technologies and there are articles that say most, a high percentage of people have to change jobs at some point in their lives. And if you've got the background of the math and science, you have doubled the number of options in which you possibly could get a job in. If you don't have that background, you have eliminated a lot of jobs. And that's just for the people who don't necessarily want to be engineers or everything.

But the other thing is we need all of the engineers that are in school now who are not taking the, those math and science courses, those who have the capability to be engineers to keep our country ahead, to fill the jobs in this country that all of these companies need, and they're having to go overseas to get people to fill the job. So we need those folks in our country to actually be able to fill those jobs. And so I think in both cases, you've got a case that they need to take, especially in high school if they don't want to go further. But for those who can be engineers, is they need to go all the way so they can take those top jobs. And the importance of education was something that your parents stressed.

My parents stressed that they didn't even have to talk about it. Yes, I had four sisters and brothers who had finished school. What did they greet you at home with? What was the phrase? What did you learn today? Yes, my dad would always ask me that. Which is great. I'm going to ask a few more questions, and then we'll open it up the audience.

So a lightning round with a few closing reflections. You talk a lot about curiosity, and you said that you always encourage your children and grandchildren to maintain curiosity. Why does it matter to you so much? Well, I think that makes us grow. I mean, we want to know why something happens. So we dig deeper to find things out, and I think that's the way we learn. And I also like Dorothy Vaughn's quote in the movie, learn everything you can and be valuable to somebody. I thought that was a very key statement she made.

On inspiration. Who are your role models past and present? Well, I think my family started, my parents and my sisters and brothers. But then my math teachers, and then at some level... You're talking about your geometry teacher. Yes, my geometry teacher. She definitely was one. And then I had supervisors that I thought kind of inspired and helped me. They weren't necessarily official mentors, but they would just say things in conversation that was very good advice that I knew I should listen to. And I try to tell people that you need to listen to those kinds of statements you hear. Did you mentor folks? I certainly did. I actually had a young intern at NASA one summer who had gotten put into a shop area, and she came.

came, she said they showed me all the equipment and then, you know, I've seen it all. And now I'm just kind of standing around. It was in materials and structures. And so she kind of came over complaining. I said, well, I do know a couple of people in that area. Maybe I'll call them. But I said, one of the things I would suggest you do, all of the reports that are written at NASA, they would put them on stands out in the hall.

So all of the reports that the people were working with were out there. I said, why don't you walk down that hall? and just kind of look at the reports and see if you see one that interest you and read it. And then go to the author and say, I just read your report and I'm really interested in this work. And I'd like to know so and so and so. And I said, and, you know, maybe you can find yourself working with him, but let him know or ask him some questions about his work. And don't just sit back and wait for something to happen.

And by the end of that summer, she and her mother came back and said, they thought that was some of the best advice she had ever gotten. That's great. Good. And then the future, you've had a front row seat to some just amazing technology change and change. What's the most wildest, most interesting thing that you think will come next or hope will come next? Well, I want to see us get back into space and to actually learn how to maneuver in space. I think that's very important for all of us, for our planet. think we need to be able to do that. And just like getting to the moon kind of got this country focused on one thing years ago, I think getting to either Mars or the asteroids or whatever it

be, I think we need something like that to garner us again, to make us really go after one thing and get it done. We have been getting inundated with space companies looking to do different, you know, doing a different execution. With that, I would love to open it up for questions. We have mics at both ends. If people, please, go ahead. I just want to first thank you for the work that you've done and the role model that you are and helping tell this story that meant a lot to me and to my mom and to my parents. So thank you for that. My question for you is about a twofold. One, as a woman, as a woman of color, who was the first woman of color to be a manager,

you know, what were your strategies in terms of managing people with different backgrounds than you and managing men? Like, how did you navigate what I'm sure was a lot of resistance and what strategies would you have for that? And then my second part of the question would just be any reflections you have on how far have we come and how far we have yet to go when it comes to women and people of color and tech. Okay. One of the things, I guess my whole ethic of working with people is to treat them fairly. to do that. I do know that sometimes some of my coworkers would get upset about things, but as long as I hadn't done anything wrong, I didn't let that bother me.

And so I basically pretty much got along with the people that I worked with. Let's see, the second question was, how far have we come? Well, of course, as you get women, women, white or black, in higher positions, of course, just the proximity of having them there and people getting used to working with you and knowing your abilities and everything. So certainly we have come, you know, further in that arena.

We've had more black females move into management positions, I think, at Langley. And so that has been progress, but we still, don't have very many there. So there's plenty of room for us to come further. I just wanted to ask, do you have a favorite physics equation or math theorem, maybe an algorithm? The favorite physics equation. Well, the thing that governed almost everything we did in aeronautics was in Navi of Stokes equations, which were very, very complicated. But, and they were Your favorite or your least favorite?

Well, they were the ultimate. They were the ultimate equations, yeah. So they were sort of the basis and they were simplified before we got the huge computers that we could solve them with numerically. Hi. Thanks for sharing with everybody. You're a very inspiring person. I have a few questions about your research. What happened to your program were people bothered by the sound on the ground? Okay.

Once, okay, I never got to that. Once we, once we prove the concept, the next step was a Boeing or Gulfstream wanted, the plane that we flew was just kind of a hacked up military airplane. So it was not designed to be a supersonic airplane. And so what they wanted to see was a design for an airplane, a supersonic. aeroplane and a low boom airplane in one plane that was fly at the design altitude everything and show that this generates an acceptable sonic bone. So NASA this year is supposed to be building two X planes. It's taking that long? We're just getting the money, yeah, because to build a full-scale airplane is pretty expensive. But that was 1975, you said.

Okay, well, no, it wasn't 75 when we, the year we did, the flight that was the culminating activity was like 2002. Okay. But it is very expensive to develop a full-scale airplane. And so, yes, we're waiting on the funding. And so I actually saw one of my past coworkers the other day, and he says, yeah, we're in design review, but the federal government is still on a continuing resolution. so they don't even have 2017's budget yet. And they don't know if they're going to get what they'll get in 2018. So they're still waiting for this budget to build this airplane and fly it over all of you in this room to see if you would say, yes, I could live with that.

And so we could build that airplane and have it fly over land. How loud was the sound on the ground? How loud? I don't know. We have always debated whether one-half PSF would be an acceptable level on the ground. We were trying to get it to one level and it would not get any higher. And so somewhere in that range, it would have been our gold. And I'm not quite sure what this design they have now. Did you try mitigating the effects of the supersonic boom from, not from, you know, changing the design of the plane, but from, you know, sending out a different frequency that would destructively interfere it? There were several options of how to do this over the years. Different inventors would come up with different ways of doing it.

And I believe that the consensus was most of them actually took more energy and more effort to try to do what was being doing to disrupt it than just the design itself. Got it. And that turned out to be the chosen approach. Okay. Thank you.