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Kepler: A Unique Space Telescope
Jesse Carpenter: NASA’s Kepler Mission, a unique space telescope. Hi, I'm Jesse Carpenter and you're listening to a podcast about NASA’s Kepler Mission from the NASA Ames Research Center. Launched in March of 2009, the Kepler space telescope will observe one area of the universe continuously for a period of four years in its mission to identify the presence of planets that are similar to Earth. Today we have three Kepler project team members who are here to discuss the unique attributes of the Kepler Space Telescope. Joining us in our studio is Kepler Project Manager James Fanson from NASA’s Jet Propulsion Laboratory in Pasadena California. Also from NASA JPL, we have Kepler Deputy Project Manager Peg Frerking. And from Ball Aerospace, we have Kepler Program Manager John Troeltzsch. Welcome to everyone and thank you for joining us. I want to start by saying congratulations on a successful launch.
James Fanson: Thank you.
Jesse Carpenter: So Jim, what makes the Kepler telescope different from other telescopes?
James Fanson: Most telescopes, either on the ground or in space, are designed to look at very distant, very faint objects, and get as magnified a view as possible. The Hubble Telescope is built that way, the Spitzer Telescope. We have a different challenge with Kepler. What we’re trying to do with Kepler is take in a large piece of the sky so that we have enough stars to do our planet search, and we need to monitor a hundred thousand stars like our sun. So that takes a huge piece of sky, so we have in that respect, a very different telescope design. Our field of view, which is the part of the sky that we image at any one time, on Kepler is about thirty thousand times larger than on the Hubble Space Telescope. So it’s doing very different science, and it’s a different kind of machine from that point of view. Some telescopes are designed to survey the entire sky in a new wavelength range, a new part of the spectrum that we’ve not seen the universe in before. GALEX is an example of that. Other telescopes like Hubble and Spitzer are designed to be pointed at specific targets, and scientists propose what targets they want to look at. And then there are missions like Kepler where, we’re only going to be looking at one part of the sky, staring at the same hundred thousand stars for a period of several years waiting for these stars to blink when a planet passes in front of them. So if there were an inter-galactic staring contest Kepler would win that one.
Jesse Carpenter: So John, how would you describe the challenge that Kepler is going to face?
John Troeltzsch: If you were to go to a new city and you were just to go and meet one person or two people, you know, that would be kind of the Hubble or Spitzer approach. But, Kepler’s designed to go and meet everybody in that city simultaneously, so we have a really good understanding of this broad spectrum of all these objects at once. And then you can go back with some of these other telescopes and zoom in on specific stars to reap the benefits of what Kepler’s discovered.
Jesse Carpenter: How big is the Kepler Telescope and why does it need to be the size it is?
James Fanson: The larger the telescope the more light you can gather. The amount of light that you gather is important if you’re trying to magnify the image and get a very high-resolution image, or if you’re looking at very faint objects. For Kepler we want to be able to study stars that are as faint as what astronomers call fifteenth magnitude. So that’s quite a bit fainter you can see with the unaided eye, and it takes a telescope of a certain size. Our primary mirror, which is what gathers the light on Kepler is about one point four meters in diameter. Hubble is two point four meters in diameter, so we’re smaller than Hubble. The largest ground based telescopes are ten meters, so that gives you an idea. And the amount of light that a telescope gathers is proportional to the area of the mirror, so that gives us the square of the diameter. So, in the grand scheme of telescopes, Kepler is small. Hubble is small for that matter. But, from the point of view of putting something in space above the atmosphere, where you don’t have to deal with all of the absorption and scattering and boiling in the atmosphere which makes stars twinkle, Kepler’s actually a reasonable sized telescope and it’s the largest telescope that has ever been sent into an orbit beyond the Earth.
Jesse Carpenter: So, what role has the development of new technology played in the Kepler mission?
John Troeltzsch: The technology in Kepler is a matter of scale more than anything. The individual CCD’s that are used are not that unique from CCD’s that might have been used in the past, but the ability to put all of these CCD’s together into one camera, and the ability to put large optics into space, is certainly something we’ve known how to do for a while, but Kepler does it in a unique combination to give us this very large field of view. I would also add that Kepler generates a gigantic amount of data. The ability to get it to Earth requires use of KA band downlink and Kepler is the first to routinely use KA downlink to get data back to the Deep Space Network.
James Fanson: There’s also technology on the ground which is being used to search for these periodic faint signals of planets transiting across stars, which is based upon mathematics and tools which also would not have been available ten years ago. What we try to do at NASA with each mission is advance the frontier of not just science but technology as well which benefits future missions that the Agency flies, but also is something that keeps industry in the United Sates at the state-of-the-art and pushing the frontier forward. And they can apply these developments on other instruments that they build, in other applications in the civilian sector. So this is an important investment and legacy that each mission contributes to the future.
Jesse Carpenter: So what kind of orbit will the Kepler spacecraft be in?
John Troeltzsch: In order for Kepler to do its job, we had to get it away from the Earth. The only way to go and observe this large portion of the sky and stare very precisely at these stars, in order to see these transits, is to get away from the Earth’s effects, both thermal effects, the Earth getting in the way of the field of view. And Kepler uses Earth trailing heliocentric orbit which was pioneered on the Spitzer mission, which gets us out into a very stable environment, where the sun is on one side of the vehicle, it’s cold on the other side, we don’t have thermal gradients, we don’t have a lot of disturbances going on, and we can stare uninterrupted for a long period of time at the Kepler field.
Peg Frerking: What we’re looking for, the signal we get from the Earth going in front of the stars is one part in ten to the eighth. That’s one-hundredth of a millionth of the starlight that we’re looking at. So in order to detect something with that sensitivity we need to have very good detectors in a very stable environment without interference from other types of signals that you often get if you’re orbiting the Earth, for instance. So that’s why we’ve gone into what’s called this Earth trailing orbit where we’re actually orbiting the sun. We’re not going around our Earth.
James Fanson: The idea is to just to get the spacecraft away from the Earth. It’s currently drifting away at the rate of about a kilometer per second. By the end of the mission it will be several million kilometers from the Earth. We consider that to be inner planetary distance and that’s the reason we’re using the Deep Space Network which communicates with spacecraft across the solar system to bring the data back from Kepler. We’re not going anywhere in particular with Kepler, we’re just trying to get away from the Earth and into a stable orbit, not so far away that we can’t get the data down, but we wanted to give it a big enough push so that it would continue to drift away and not recollide with the Earth at some time in the future.
Jesse Carpenter: How complex were the design challenges for the Kepler telescope systems?
John Troeltzsch: I would say there were dozens if not hundreds of challenges that we had to solve in order to put Kepler together. Each of the big systems on the telescope, the photometer, required overcoming challenges. The large optics had to be fabricated and light-weighted and coated, and then held delicately for launch so they wouldn’t break during the violent rocket launch. And there were lots of challenges associated with that. Packaging this camera together that we’ve been talking about just took us right to the frontiers of the technology in the engineering that we have at Ball Aerospace to put things together. Building a spacecraft that can point so precisely to keep the stars from wobbling was quite a challenge. Every time we turned around there were challenges we had to overcome, and that’s the amazing thing about working on program like this is watching all the different people work together as a team from both the external organizations that are involved as well as the folks day-to-day with their hands on the hardware. Figuring out ways to make it all come together. And in the end result you have this amazing machine up in space taking great data.
James Fanson: As a project manager, my job principally is to manage the risk in the mission. We have a certain amount of money that’s been made available to develop the mission, we’ve written certain scientific requirements, that we believe we need to meet to be able to make the measurement and do the science. And then there’s the amount of risk that you’re prepared to take, that something could go wrong and not work as expected and cost you the mission. So it’s a daily tactical and strategic puzzle if you will, to fit the pieces together and try to balance the cost of the mission against the risk you’re prepared to take against the capability that you’re ultimately going to be able to deliver on orbit. It’s a very complex and nuanced business. Particularly when you’re building something you’ve never built before, you don’t quite know how you’re going to tackle the next problem, you know take the next hill and the hill after that. You know, what can you de-scope and still have acceptable risk at the end of the day. No two missions are alike; no two sets of hardware are alike. Everything we build in this business is unique. And so it requires a lot of careful thought, a lot of consultation with experts, it’s part of the adventure.
John Troeltzsch: Another way of looking at it is, if you were to go out and build a house, you might have fifty people involved in building that house. To build something with the complexity of Kepler we had well over two thousand people involved with over a million hours of labor of people actually doing their jobs to put the whole thing together. So, coordinating all those people to get them going in the same direction with the same common purpose, and balance the risk and the cost and the technology is an extraordinary challenge.
James Fanson: A large part of the complexity and challenge in building a vehicle like this is unseen. It’s dealing with the contingencies, it’s dealing with what can go wrong, how do we anticipate everything that could go wrong, how do we design the vehicle to deal with all of those situations, how do we test it on the ground to make it do what we think it should do and bring that all together and again balance that against the overall risk and cost and capability of the mission.
Jesse Carpenter: Would any of you care to share a personal perspective about the excitement that this mission represents?
Peg Frerking: When we get the data from this mission and understand the number of Earths, and the number of Jupiters, and the number of Mars’ and the number of Venuses that there are in our galaxy we’ll have a very different view of what it’s like to be in our universe. We’ll know whether we’re unique or whether there’s the potential for a lot more of us and that’s pretty mind boggling at least for me.
Jim Fanson: It’s very exciting to work on a mission that is trying to answer a question or that will answer a question which has been on the minds of humans for hundreds of generations and has been waiting for technology to advance to the point where you could actually make a scientific measurement and answer this question: are Earths common, or are Earths rare in the galaxy? Are we unique, or can we expect to find other places that we could visit that would be capable of supporting life. So, just as the mariners of the past, the Magellans and the Cooks, and so on were sailing into the unknown, searching for new discoveries, we are the modern day explorers, journeying into space in search of answers to questions that have been pondered across a hundred generations. That’s very exciting.
John Troeltzsch: I’m really excited to answer those questions but I’m almost more excited about all the questions that Kepler’s going to raise. I mean when I talk to grade school kids, or college kids I just think about the wealth of follow on questions that Kepler’s going to generate and how it’s going to plant the seed for the whole next generation of planet finding, planet discovery and understanding what’s out there.
Jesse Carpenter: I’d like to thank our guests James Fanson, Peg Frerking and John Troeltzsch for joining us. I’m Jesse Carpenter and you’ve been listening to a podcast from the NASA Ames Research Center.
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