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Gravity Assist: Explorer 1 & Jim Green’s ‘Gravity Assist’ (1)
March 1, 2018
Gravity Assist producer Laurie Cantillo and NASA Planetary Science Director Jim Green at the NASA TV studios in Washington, D.C. Credits: NASA The year was 1958; the space race was on. NASA’s first space satellite, Explorer 1, launched a Geiger counter and miniature tape recorder into space that registered astonishingly high radiation levels above Earth. This discovery gave humanity its first glimpse of the Van Allen radiation belts, named for James Van Allen. What you may not know about this famous scientist is that he mentored an aspiring student named Jim Green, now NASA’s Planetary Science Director. Jim discusses his Van Allen ‘gravity assist,’ Explorer 1, and what we’ve learned about these strange belts of energetic particles that surround Earth, other planets, and even a moon!
Jim Green: Our solar system is a wondrous place with a single star, our Sun, and everything that orbits around it: planets, moons, asteroids and comets. What do we know about this beautiful solar system we call home? It’s part of an even larger cosmos with billions of other solar systems. Hi, I’m Jim Green, Director of Planetary Science at NASA and this is Gravity Assist.
Laurie Cantillo: I’m Laurie Cantillo with the science division here at NASA headquarters and we’re going to do something a little different today to launch season two of Gravity Assist. We’re talking about mind-blowing science discoveries and one of them happened 60 years ago with our Explorer 1 mission, which revealed these intense radiation belts that we have around Earth; they’re called Van Allen belts.
It’s a cool story so to tell it we’re going to turn the tables on our host, Jim Green, and find out about his gravity assist. That’s the term we use to describe an event or a person in your life who helped you figure out what you really love to do and forever changed your path in life. So, Jim Green, what was your gravity assist?James Van Allen of the University of Iowa poses with a rocket model. Van Allen designed one of three science instruments on Explorer 1. The cosmic ray experiment was essentially a Geiger counter that clicked as it detected cosmic rays. This experiment and a future one led Van Allen to conclude that a doughnut-shaped radiation belt wrapped around Earth. This became known as the Van Allen radiation belt. Credits: Frederick W. Kent Collection, University of Iowa ArchivesJim Green: Well, thanks, Laurie. You’ve done a fabulous job helping me with our Gravity Assist interviews over this first season, and I’m delighted to be able to kick off the second season and talk about some of my experiences. My gravity assists really started in high school.
I had a high school chemistry teacher who ended up with the keys of an observatory, a donated telescope. It turned out it was a 12-inch Alvan Clark refractor and for you amateur astronomers out there I’m sure your jaws have dropped.
Laurie Cantillo: They still make those? (laughs)
Jim Green: Alvan has gone out of business but I think this was made in probably in the ‘30s.
Laurie Cantillo: Okay.
Jim Green: Yeah, in the ‘30s, 1936 or so I think is when it was made. But this particular telescope, a fabulous telescope. I had it at my beck and call for a couple of years in high school and I made instruments for it.
I studied stars, I studied the planets, I took pictured that ended up in Sky & Telescope and I took images of the Sun every day for three months during one summer and three months during another summer. So, at the end of my high school I knew exactly what I wanted to do and that was get into college and get a degree in astronomy but that didn’t end there.
Many of our scientists, as you’ve heard in many of our other podcasts, they’ve had multiple gravity assists along the way and mine really started my first year at the University of Iowa. I was born and raised in Burlington, Iowa. It’s just a small town on the Mississippi and University of Iowa was one of the big universities in Iowa and I took astronomy 101 with about 400 other students.
Laurie Cantillo: I know what that’s like.
Jim Green: The place was packed. I walked in the first day and the only places available were up front.
Laurie Cantillo: That’s what you get.
Jim Green: Well, I always enjoyed sitting up front. I wear glasses and so my eyes aren’t really that good, so I would indeed sit up front. But I was taught by James Van Allen and --.
Laurie Cantillo: Whoa, THE --?
Jim Green: Yeah, the James Van Allen and we’ll learn more about him because, indeed, he was the first investigator of our first experiment ever in space on the spacecraft Explorer 1.Credits: NASASo, at the end of first semester of astronomy 101 I got an A, thank goodness.
Laurie Cantillo: You’d better have. The Planetary Science Director getting less than an A; I don’t think so.
Jim Green: Well, I wasn’t always great in school. The ups and downs happened, and we always have to remember you’ve got to stay the course. But second semester I had an opportunity to take a small two-credit hour course and so I took readings in astronomy and it was taught by his “staff.” You know, that’s what it says in the course catalog.
And so, when the course started at a designated time in Van Allen Hall room 701 I went to that room, opened the door and it looked like a warehouse. It was this huge room. Printouts all over tables, magnetic tapes and bookcases and a cluttered room from that perspective. These rooms were storerooms, and I’m standing in the doorway going through this course catalog figuring out I must have messed up.
Laurie Cantillo: Wrong place. Wrong time.
Jim Green: And so, from behind the bookcase Dr. Van Allen said “Jim, this is the place and you’re my only student.” So instead of being taught by a grad student, I had a full semester with James Van Allen! And when he found out that I had taken pictures within Alvan Clark refractor and in particular the solar set, it was during solar maximum in the late ‘60s, early ‘70s and he said “Well, let’s do some things. Let’s do some research with this data,” and I go, “Research? What’s research?” So, we talked about it. I showed him the data, he loved it. And the big suggestion that came from him is, “Why don’t you look at how fast the Sun spins? Let’s do that by looking at the sunspots and how long it takes for them to go around.” Indeed, I had plenty of data to make measurements of a solar rotation. I did the same research that had been done about 70 years earlier and wrote a science paper, just an introduction and discussions and abstracts and all of the stuff, components of a paper and he was the referee. And so, at the end of that semester I knew what research was all about and that gravity assist was absolutely unbelievable.
Laurie Cantillo: It’s cool how many people will cite teachers as being that gravity assist—and good for you! I’m certainly glad you took that class.
Jim Green: Yeah, me, too. But that connects really well with what this year is all about. This is the 60th anniversary of NASA. And it kicked off with our first successful spacecraft called Explorer 1.
Now you can get online and probably go to some of the images that the National Air and Space Museum post and you can see what the Explorer 1 rocket looks like. It’s about 2.5 stories tall and it’s a huge beautiful rocket that had on top of it an experiment, a Geiger-Mueller tube that looked at cosmic rays. That was Van Allen’s experiment and on the side of it are two letters, two huge letters painted on the side “U and E” and so everyone knows about it. You can see it’s very distinctive and that’s the way that goes but I finally found out the story behind UE.
Laurie Cantillo: Yeah, why not U and S?
Jim Green: Could have been. So, here’s how it goes. After I graduated from the University of Iowa I ended up at Marshall Space Flight Center at NASA, it’s one of the 10 NASA centers and it’s a fabulous place. They do all kinds of things.
This is where (Wernher) Von Braun was then they were building a series of rockets. So, Van Allen came down, I invited him to give a talk and then I had a big reception over at my house. And so, I had scientists and engineers from the center and I was walking around with a tray of hors d’oeuvres. So, I walk out up Van and many of us students called Dr. Van Allen Van, it was a very endearing term and he loved it and never batted an eye over that.
And so, I walked up and there Van was talking to one of our engineers, actually it was my next-door neighbor, Jack Waite, who worked with Von Braun and I’m standing there -- would you like an hors d’oeuvre? -- and Jack says, “Dr. Van Allen, do you know what U E means?” So, wow, I had to hear this, man.
Laurie Cantillo: Yeah, no kidding. Great time to be there.
Jim Green: I’d seen U E I don’t know how many times, I didn’t know what it meant and Dr. Van Allen said, ”No, I don’t think I ever knew what that meant.” And so, Jack says, “Well, here we are in Huntsville, Alabama.” This is where the Redstone Arsenal is -- and currently the Marshall Space Flight Center sits on that -- but Marshall hadn’t been put in place at that time. So Jack said, “There are nine unique letters in (the word) Huntsville: U is two and E is nine and so U E is a code for a number, 29.
And Van Allen said, “Why didn’t you just put 29 on the rocket? Just paint 29?” And Jack said, “Well, we didn’t want to do that, because if we put 29 on the rocket the press would ask us what happened to the other 28?”
Laurie Cantillo: 28, yeah, that’s a good point.
Jim Green: And the problem with that is they all blew up and so Van looks at me and I look at him, and I’m thinking, “Thank God U E didn’t blow up,” but that’s the way it was early on.
We were struggling in this nation to be able to build rockets that work and get things into space. Sputnik had been orbiting the earth for months earlier. USSR was celebrating their launch of Sputnik, which occurred on October 4, and that was last year’s celebration, they had their 60th. So, in 1957 Sputnik went up and here we are in 1958 January 31, Explorer 1 takes off and gets into orbit.
What a fantastic time that was. I mean the press conference was something like 2:30 in the morning at the National Academy and that’s the very famous picture you see Dr. Van Allen, Pickering from Jet Propulsion Laboratory which helped build the experiment and integrate it into the rocket, and then of course Von Braun which got the rocket into space.
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