You may see one more star up in the night sky soon, only this one will be man-made

George Mason University will be the site of the recently approved Landolt NASA Space Mission. The mission will kick off in 2029 by launching a light into the sky that will help scientists determine the brightness of stars so they can more accurately study how fast the universe is growing. Leading the mission is GMU associate professor Peter Plavchan, who joined me earlier to discuss.

Interview Transcript: 

Eric White  So why don’t we just start with an overview of how this all came together? And what exactly you all are trying to accomplish with this mission?  

Peter Plavchan  Well,if you want to go way back, you could call it a lightbulb moment. Right? So we had, I was thinking about the challenges we have in astrophysics, and how with certain missions, like the NASA Kepler mission and the NASA test mission, I can point at any star in the sky and measure if it changes in brightness by as little as 0.001%, right? 10 parts per million. But if I point to that same star in the sky, and ask how many actual photons per second are coming from that star, I have to do a little bit of … I might get that number accurate to a few percent. And that’s a big gap of our knowledge. And so I started thinking I had a light bulb moment, what can we do to bridge that gap?  

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Eric White  So the gist of it is to send something up into the sky that you know the exact photons that it is letting off so that that way you can then compare and contrast to the stars that you’re seeing. I know I’m oversimplifying it, but is that the basic idea?   

Peter Plavchan  Yeah, absolutely. So I had this idea back in 2017. And there’s plenty of history we can get into. But I was looking at how we measure the brightness of things in the sky. And it dawned on me unintended, that we haven’t changed how we do this. For half a century, we have been using the same four stars in the sky as our anchors, and how we map what our sensors see or digital cameras or going back even further in time, our photomultiplier tubes are equivalent to film these photographic plates, we look at these four stars, and we say okay, here’s a model of how we think the stars work. So that makes a prediction of how bright it should be. And that’s how we map from what we measure on our sensors, to what the actual physical brightnesses are being emitted by the stars in the sky. So those four stars are Vega, which everyone hopefully knows about. You can see it in northern sky most of the year. And three white dwarf stars, which came in vogue a little bit later, that had been anchoring the calibration for the Hubble Space Telescope. What has changed in the last half century, of course, is our sensors or digital cameras, the technology behind those, as well as the models that we have for the atmospheres and radiation coming from those stars. They’ve gotten more sophisticated over the decades, but the way we approach it hasn’t changed. So like, do we believe these models? Do we trust these models? Are they are they doing what we think they do. And in fact, just a couple of years ago. Right when we were getting ready to propose this mission, a new model came out for these three white dwarf stars and the old model and new model disagreed by more than a percent in their predictions of how bright that white dwarf star should be. So if the models are disagreeing with each other, the natural question is, how close are they to the ground truth? So how could we measure the ground truth and that’s when we decided to launch something by working in partnership with NIST, which is like ground zero for how we measure the brightness of things, they set the standard for the country, and then put that in space and look at it with our telescopes. So we know without a doubt, how much light is putting out?  

Eric White  And what do folks like yourself and other NASA astrophysicist use the brightness of stars to determine obviously, there’s an interest in knowing what the universe is doing? Because you know, that’s kind of the bread and butter of space. But do they use that for mapping other routes for other missions? What sorts of tools are at their disposal? If they know that information is super accurate?   

Peter Plavchan  Yeah, you had me worried for a second because we got way into the technical details right away, which is okay, I’m glad we had an audience that’s interested in that. But there’s some amazing science that we’re going to do with this mission, and it’s potentially transformative. And when we thought this mission, I’m an exoplanet astronomer, so I study fancy terms. I’m a discoverer of worlds, the fate of entire planets hangs in the balance of the statistical analysis that I do, right. So kind of imagine a planet vanishing if the statistics show is not real. So we’ve found over 5000 planets around other stars, and it’s been an incredible time over the past quarter century kind of a Golden Age of Discovery of these worlds. So when I was thinking about this problem, I was interested in addressing, how big are these planets? How big are their host stars? How hot are the planets? Like, are they actually in the habitable zone? Are they too hot, too cold. And for the past 25 years, we’ve mostly just kind of wave our hands a little bit and said, it’s roughly the right temperature, give or take. But we wanted to get those numbers more accurately known. And it turns out that until about 2016, about eight years ago, we only knew very precise measurements of the distances to stars from the prior to the Gaia mission, we only knew about 250,000 stellar distances. The Gaia mission when it launched in 26, to 2015 or so gave us the distances to over a billion stars to suddenly, we knew very accurate distances to a lot of these stars that hosts the exoplanet systems we are discovering, and that was no longer question. There’s been this long standing question is the star this size, is it this size, we don’t really know. But we could make some good educated guesses. Well, now we know the distance to the stars really well. And it turns out what limits our understanding now of the habitability conditions, the sizes of these other worlds, is that calibration, how we map what we see with our telescopes, to the physical amount of radiation coming from those stars, hitting those planets and reaching our telescopes here on the ground. So that was what drove me to kind of think about this problem in particular, but then I met some other people, other scientists in my community, and it turns out, they have the same problem. So in cosmology, right, we’re looking at an expanding universe. We’ve known that for almost 100 years now. 1929, Edwin Hubble discovered that the further away a galaxy was, the faster it was moving away from us. And Nobel Prize was awarded a decade ago, when we not only do we discover that the universe is expanding, but how fast that expansion is happening is accelerating. And the way in which we measure that is by comparing the explosions of certain types of nearby supernovas, to very distant supernovas. And it turns out their ability to calibrate the brightnesses of those distant supernova explosions that happened billions of years ago, billions of light years away to these nearby supernovas also depends on our ability to map how bright something is in the sky that we see with our sensor to real physical amounts of radiation. So two different fields in astrophysics very far separated, right, nearby exoplanets and distant supernova explosions, same problem. That’s how this mission got born, is going to answer some great questions. And to add one more bit to that NASA right now is investing in building the Roman Space Telescope and the James Webb Space Telescope. And the National Science Foundation is investing in the Vera C. Rubin observatory down in high Atacama Desert of Chile. All three of these, the case of Rubin a $400 million ish telescope, the Roman observatory, a $3 billion plus mission, the web observatory performing beautifully over $10 billion of US taxpayer money invested, all of them are doing amazing science. But it turns out, we can make that science so much better if we could improve that mapping of brightness to physical units and what we measure with our telescopes. So all three of these facilities, which are coming online, are already online, in the case of the Webb telescope, are going to benefit from this mission when it launches in a few years. We’re speaking with Professor Peter Plavchan, he is with George Mason University. So I’ll get into the actual device itself in a second. But I’m just kind of surprised. And I want to know if that was your reaction that this wasn’t thought of before. I mean, it’s kind of a basic tenet of science that you need a control right to measure something. Why wasn’t this already an idea that NASA was working on?  So that’s a great question. And we have to get a little bit into the history of this. And, you know, there’s an old saying, like, every idea out there has already been thought of there’s nothing under the sun that someone hasn’t already come up with or under the night sky in this case. And when I came up with the idea in 2017, I was like, Oh, look how creative I am. But no, no, I wasn’t the first one to think of this. And people have been thinking about this and working on it for decades. So you go back to the 1970s they would launch sounding rockets into the upper atmosphere to look at Vega and these white dwarf stars. Some early infrared observatories would actually like spit out these little spheres that would radiate heat, and since they knew how big those spheres were, and temperatures of the spheres, they can kind of calibrate their telescopes that way, but it was a much cruder level. And so I wasn’t the only one that started thinking about this recently. And I ended up meeting as we started getting further and developing this concept. About five years ago, we started bringing together a team of people that were interested in doing this. And since the news about our selection came out, other people been coming out of the woodwork, I’d say, Yeah, you know, we’ve been wanting to do this for years. So right time, right idea, and right science.  

Eric White  So let’s talk about the actual device that’s going to be up there. What is it? Is it going to be just a rocket with a flashlight on it? What? What’s it going to be?  

Peter Plavchan  Yeah, so the simplest way to think about it is a light bulb in space. And definitely, this is what NASA considers a very small mission. When you’re operating on that small of a budget for NASA mission, there’s a principle you have to use, called the KISS principle, keep it simple, stupid, right. So we don’t want to have an overly complex payload. And what we’re looking at right now is a series of lasers or light sources that shine light, and that light goes into one of two places. One, it goes points down at the Earth, at a ground based telescope, which we can talk about in a second, or and the other half of the light would go to a sensor on board the spacecraft to monitor how much light the laser is putting out. So we want nice stable lasers that are putting out a steady amount of light. We don’t want a light bulb that’s rapidly changing in temperature and changing its distribution of power at different colors. So we focused in on just a few set of discrete wavelengths with a nice steady power supply to these lasers, so the amount of light coming out is nice and stable. In addition to that we’ve chosen orbits, we’re hoping to put the spacecraft into an orbit was called a geosynchronous orbit or close to geosynchronous orbit, where it orbits the Earth once every time the Earth turns. So from our perspective here on Earth, it’s always in the same part of the sky. And it doesn’t appear to move. It’s the same kind of technology we used to use and still use for satellite communications and our GPS satellites, so that that satellite is going to stay at nice fixed distance between the telescopes on the ground and it place in orbit. So that will also help with things because light spreads out, depending on how far away you are from the light source, we also have to put it far enough away from the telescopes that looks like a star. So we couldn’t say fly a drone above the telescope, that would be too close for these telescopes to get a proper amount of photometric calibration or even a high altitude balloon would be too close. So we had to put it out in space. So the simple part that goes into orbit, it’s actually quite simple. It’s just settled lasers that point to the ground and shine on them. One of the key technological advances we’re taking advantage of here are what are called radiation hearted, single mode fibers. So getting further into that helps stabilize the how much of the light is coming out of lasers. And a lot of the complexity actually happens at the telescopes on the ground, they’re doing this stuff is a lot cheaper than doing it in space. So we can have well characterized filters for the telescopes, and well characterized detectors, what we call flat Fielding. And so a lot of secret sauce is going to happen with those telescopes. When we do the data analysis.   

Eric White  You had slightly mentioned that some other folks have come out of the woodwork to ask you about this project. I’m curious, is this something that not just NASA can use but it’s going to be I imagine utilized by other space agencies in their work as well? Is that what you had in mind when thinking of this project?   

Peter Plavchan  Oh, absolutely. So our mission when it launches roughly targeting 2029 date to be determined. We have right now a one year primary mission scheduled, it’s a very quick development timescale, a very relatively short mission as far as NASA goes. And we’re planning to reserve a fraction of that time for what we call a guest observer program. And a citizen science program. It turns out that when these lasers shine down at these telescopes, it’s not like a little pencil beam, it spreads out. And it’ll spread out about 1000 kilometers or 600 miles or so. So anyone within range, this telescope could look at this artificial star in the sky. Now, unfortunately, or maybe fortunately, depending on who you ask, it’s not going to be bright enough for you to see with your eyes. So, it’s pretty faint, you will need a telescope to see it. But there’s gonna be plenty observatories that are gonna want to point their telescopes at this calibration star and calibrate their facilities. So, we have four ground stations as we’re calling them built into the mission, but we’re going to be looking to open up to other professional and citizen science telescopes, operations for them to look at this star in the sky as well.   

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Eric White  Alright, so finishing up here, you got the approval, the champagne has been poured. What is the first step that you all are going to take to nail that 2029 timeline that you have set for yourself.  

Peter Plavchan  Yeah, so I’ll tell you actually, the first step was not popping champagne. The first step was actually two weeks of panic. Writing the proposal is one thing, winning it and now we have to execute is another. So, we’re past the panic phase. So, we did pop some champagne after that. We are now in what’s called phase A. So, this is the planning phase of the mission. It lasts a little bit under a year. And at the end of that we have to go to NASA and participate in what’s called a mission design review. And the system requirements review and once we get past that milestone where NASA takes a close look at our mission, they’ll make sure that everything looks like we were ready, we can prove to NASA that we’re ready to build this and fly this operate it. That’s when we so quote, unquote start cutting metal and that’s when we start buying the parts and buying products and putting spacecraft together.  Professor Peter Plavchan is with George Mason University. You can find this interview along with a link to more information at Federal News network.com Search the Space Hour. 

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