Ep. 604: Balloon Astronomy

When you think about the world’s observatories, I’m sure you’re imagining huge telescopes perched atop mountain peaks, or space telescopes like Hubble. But you might be surprised to learn that some telescopes are carried high into the atmosphere on board balloons. What can they accomplish?

Download MP3 | Show Notes | Transcript

Show Notes

Cassini at Saturn (NASA)

How Weather Balloons Work (How Stuff Works)

BALLOON Observations (NASA)

Cosmic Microwave Background (Planck Satellite)

What is a Sounding Rocket? (NASA)

High-Altitude Balloons Take First Steps toward Space (Office of Naval Research)

BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) (Stratocat)

Wilkinson Microwave Anisotropy Probe (WMAP) (NASA)

The Big Bang (NASA)

Stratospheric Balloon Bases in the World (Stratocat)

SPIDER (Suborbital Polarimeter for Inflation Dust and the Epoch of Reionization) (Stratocat)

SOFIA Stratospheric Observatory for Infrared Astronomy (USRA)

The Jet Stream (NWS)

Kittinger (Air Force Magazine)

DOCUMENTARY: BLAST (Balloon-Borne, Large-Aperture, Submillimeter Telescope)

Starburst Galaxy (Universe Today)

Photometry (astronomy) (Wikipedia)

Compton scattering (Wikipedia)

HERO (High Energy Replicated Optics) (Stratocat)

HEFT (High Energy Focusing Telescope) (Stratocat)


Balloon-borne telescope (Wikipedia)


Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast, Episode 604, Balloon Astronomy. Welcome to Astronomy Cast, our weekly facts based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey Pamela, how’re you doing?

Dr. Gay:                      I’m doing well. We have hit full on spring. Sleeves. Sleeves can go away now. It’s kind-of awesome.

Fraser:                         Yup. I’m now in shorts for the next six months. No matter what the weather does. It’s a hard switch over. I’ll put a coat on, but shorts from here on out.

Dr. Gay:                      I feel this way about real shoes. I shall be living in sandals and Tevas from now on.

Fraser:                         Yeah, perfect. The weather’s great. Except, of course, that means the garden is freaking out, and all of the dandelions and all the weeding that needs to be done, I’m spending so much time in the garden. It’s just crazy to catch up.

Dr. Gay:                      Our back lawn is a mixture of clover, violets, wild strawberries, and onion and basil that went to seed and joined the lawn. So, when the lawn gets mowed, it smells very confusing. Very confusing.

Fraser:                         That’s great. All right. So, when you think about the world’s observatories, I’m sure you’re imagining huge telescopes perched atop mountain peaks, or space telescopes like Hubble. But you might be surprised to learn that some telescopes are carried high into the atmosphere on board balloons. What can they accomplish? And we will learn that in a second, but first let’s have a break. And we’re back. All right Pamela, balloon astronomy, what?

Dr. Gay:                      This is one of my favorite things, because it allows you to start to do the science that is most effectively done from outer space, without the cost or, I guess danger’s too strong a word, but the same risks that are required to going to space. So, if you’re a graduate student and you wanna develop and ultraviolet experiment, you can’t do it from sea level. You probably can’t do it from the top of a mountain peak. And launching things into space is getting cheaper and cheaper and cheaper, but it is still beyond the reach of your normal graduate student research fund. But a balloon. You can start to get above the parts of our atmosphere that block millimeter wavelengths, that block ultraviolet, and by getting out of the way of the atmosphere, new kinds of science can be done.

Fraser:                         Aren’t telescopes heavy?

Dr. Gay:                      Well, big telescopes are heavy. Not all science requires big telescopes, though. If your choice is no science or build things as lightweight as possible, you just build as lightweight as possible. And you have to remember that there are satellites out there that are doing amazing science and they’re the size of a car. And some of them are called things like Cassini. And so, balloons can actually carry human sized cargos, car sized cargos, which means small telescopes with lots of awesome instrumentation, totally possible to fly.

Fraser:                         So, let’s talk about the physics and the atmospherics of launching a balloon with some kind of telescope payload. What kind of altitude are they typically deployed to?

Dr. Gay:                      What is amazing is, some of them are actually getting high enough up that they are above the blue sky. There are balloons that go so many miles up that you aren’t starting to cross that 60 miles you’re in space, but you’re close enough to that boundary that you look below you to see the blue sky. And even on the daylight side of  the planet, you can see the darkness of space. As long as you don’t look directly at the sun, it’s still gonna block the darkness of space.

Fraser:                         And probably even start to see the curvature of the Earth.

Dr. Gay:                      Easily. Not all go this high. Many are just trying to get up 60,000 feet, twice the height of commercial airliner. But they do go significantly higher for some experiments.

Fraser:                         And so, when you imagine you’ve got these balloons up at this kind of altitude – we’ve seen lots of people launch weather balloons. They’ll go and they’ll put some payload, some stuffed animal, or camera, or whatever and they’ll put it on a weather balloon, and off it goes, higher and higher and higher, and it always ends when the weather balloon pops because it’s expanding to the point that it breaks. That’s the inevitable end of every weather balloon that gets sent up.

Dr. Gay:                      Yes.

Fraser:                         So, why don’t these pop?

Dr. Gay:                      Well, in some cases they do and we just have the instrumentation is on parachutes. During the 2017 eclipse there was actually, all across the United States, a variety of different research teams that set up weather balloons, launched them precisely timed prior to the eclipse crossing their place on the planet, and from their perch high above the stadiums and schools and all the other places they launched from, they observed the passage of the Earth’s shadow across our planet while also taking observations of the sun itself. And so, in these cases yeah, in many cases did just pop, and parachutes are an answer. Also some stuff just gets lost in the oceans. It’s okay now.

Fraser:                         But there are some that are designed to last a lot longer and not pop, and they actually regulate their altitude.

Dr. Gay:                      Yes. And so these more complex systems are what often get used for longer term experiments, where folks are, for instance, working to measure the cosmic microwave background in high resolution from balloons that are able to carry instrumentation that until recently, we weren’t able to build and trust on orbit. Sometimes you wanna launch things on balloons a few times before you build that billion dollar space telescope.

Fraser:                         I’m imagining – I guess with the ones that are popping, people launch telescopes on sounding rockets. And they have this parabolic flight, they go up, they come back down. And so, you think a balloon that’s gonna take its time to get up is just as good as a – and probably a little more cargo than a sounding rocket. Maybe not, I don’t know.

Dr. Gay:                      They’ve launched 36” telescopes.

Fraser:                         On balloons?

Dr. Gay:                      Yeah.

Fraser:                         So then, once you’ve reached those kinds of altitudes, I’m assuming, then certain kinds of astronomy become possible once you’re up above the bulk of the Earth’s atmosphere. So, what regimes can you access at that point?

Dr. Gay:                      This is where you start seeing ultraviolet, x-ray, gamma ray on the blue-ward side of what we see with our eyeballs. On the red-ward side, you start seeing the gaps that the atmosphere blocks that prevents us from readily seeing microwave wavelengths. And some of the other molecular lines in our atmosphere basically says hey, you can’t see this part of the radio spectrum. So, it allows us to see things our atmosphere blocks. And the most exciting stuff, in some cases, is what we’re starting to see in those blue-ward side of  things. Some of the coolest, earliest experiments just looked at our own sun back in the late 1950s when we really didn’t have a space program yet, we were using balloons to, for the first time, see granulation features on the surface of the sun.

The first flights were taking photos and then rescuing the cargo, and it was only in 1959 that television transmitters allowed us to do real time science from high atmosphere.

Fraser:                         Yeah. So, it’s like this – we think that we have to have space telescopes but in fact, there are ways to get at those parts of the electromagnetic spectrum that you wouldn’t necessarily absolutely need to do. So we’re gonna talk about some specific missions in a second but first, let’s have another break. And we’re back. So now we’ve talked about what it’s good for. Let’s talk about some specific missions that have actually been balloon based observatories.

Dr. Gay:                      The one that really, for me, brought it home how powerful this is, is BOOMERANG. This was a mission that took off in the late 1990s, and taking off, in this case, meant filling a balloon in Antarctica, and circling the bottom of the world, is that what we call Antarctica? And this was a cosmic microwave background experiment that predated WMAP and it’s amazing detail. And it was in BOOMERANG that we first started to see some of the hints of what would be possible.

And we started to understand that we have the ability to use the cosmic microwave background to measure the expansion of the universe and get details out of what happened between the big bang and the, well, universe becoming what we see today about 400,000 years in.

Fraser:                         Right. So, with previous surveys they were able to detect the existence of the cosmic microwave background, that it’s there at the temperature that would be predicted. But the question was, would you see variations in the background? And with an instrument like BOOMERANG, they were able to start seeing temperature variations that could then give them hints of larger structures, and that would help connect the dots between the geometry of the universe and the structure of what we see today, as a precursor. It’s really a clever idea, that you build these precursor instruments, launch them, and then use that to then build a proper space telescope.

Dr. Gay:                      It’s beautiful and exciting and harrowing science. Because first of all, you have to construct something that is going to safely fly to over 100,000 feet, 42 kilometers up. You have to deliver it to Antarctica in this case. You have to stand out in the cold when the weather is just right, fill the balloon, hope nothing tears, hope everything goes smoothly, launch it up, hope that you can safely retrieve everything. BOOMERANG flew multiple times. And if it works, it’s significantly cheaper than a spacecraft, you get to tinker with your electronics between each flight. This is real, iterative, experimental science that you get to play while freezing and possible contemplating penguins.

Fraser:                         There’s some pictures that I’ve seen, much more recent one, I think it was a BLAST, or there’s an even more recent one just a couple of years ago. And you look at the photograph and there’s this crane truck in Antarctica where they’re hanging the balloon and the instruments, they’re preparing to launch it. You’re like, yeah, I’ve seen a crane truck. Then you think, wait a minute. They got a crane truck to Antarctica, to the south pole. That must have been difficult. So let’s talk about some other missions that have done balloon astronomy.

Dr. Gay:                      One of the more recent missions that falls into the category of science, I didn’t even imagine we’d be trying to do, is an instrument called SPIDER. This is a polarimeter, which means that the instrument looks to see how the light is, essentially, rotating or oriented. Light is a wave that travels through space. The length of that wave determines the color of the light. But that wave, with its amplitude, has an orientation as it comes towards us, and it can even be rotating as it comes towards us. And so, with polarimetry, you measure the orientation of that wave front as it travels towards you.

This can tell us things about how light is scattered, what dust is out there, what magnetic fields are out there, what physics is causing light from different objects to either be randomly aligned or coordinated in its motion across the universe. Now, SPIDER – it’s another one of these where we’re going to do really cool science we can’t do from the ground. It’s looking in the submillimeter. And it’s looking for primordial gravitational waves.  

Fraser:                         That’s crazy. So, you’ve got a balloon based submillimeter telescope that’s being launched, that is searching for gravitational waves from the beginning of the universe.

Dr. Gay:                      Yes. You have to understand calculus just to read their science goals. It’s that kind of research. But they’re essentially looking for the kinds of things that might be seen in the cosmic microwave background that will explain to us what kind of inflationary universe was there that might help us understand how our own Milky Way galaxy is interfering with our ability to see things beyond our galaxy. It’s a super complicated mission with flight duration times on the order of 17 days and so far, it’s mapped about 10% of the sky.

I remember we were at an AAS meeting once when Sean Carroll was talking about someday being able to observe things that happened prior to the formation of the cosmic microwave background. And me and my little observational brain were like, no. I was wrong. I was so wrong.

Fraser:                         Well, I mean, this leads back to the BICEP II discovery that was made. And that was a telescope, I think, that was also in Antarctica where they thought they had detected these primordial gravitational waves and it turned out to be dust, which it always is. And so, that team is working on another telescope down in Chile, but now you can see sort-of iterate, iterate, iterate. Just keep going with this idea and take it to the nth degree. That sounds great. So, submillimeter. That’s a tricky wavelength for us to be able to see with the – from the ground?

Dr. Gay:                      The OH molecule and water molecules in our sky are hard on millimeter and infrared.

Fraser:                         Right.

Dr. Gay:                      And so, for some of these redder than your eyeball can see but not quite all the way into the radio wavelengths, you need to go up to where it’s dry. You can do better by going up to the extraordinarily dry, high altitude Atacama desert facilities. But a balloon over the desert of Antarctica? That’s kind-of the best you can do without actually going into orbit.

Fraser:                         That sounds great, I like that. Do you have any other examples of balloon missions?

Dr. Gay:                      Oh, there’s so many. One of the things that really gets me is the earliest ones actually included humans.

Fraser:                         They flew with their telescopes? They observed – I just imagine that would be terrifying.

Dr. Gay:                      So, the one thing that we haven’t really gotten into is the difficulties of dealing with the fact that your instrument is on a balloon. So, if you have a space telescope, you’re gyroscopically stabilized, something spins, you don’t move, you move around the Earth in a predictable way, everything is good. You build a telescope on the surface of the planet, you occasionally deal with earthquakes, you occasionally deal with wind noise, tides cause your telescope to go up and down in ways that only matter with pulsars.

Fraser:                         Clouds.

Dr. Gay:                      Well, yeah, I’m ignoring the weather.

Fraser:                         All right.

Dr. Gay:                      With a space telescope and a ground based telescope, you’re not worried about the vibrations that you get with something like SOFIA or a balloon. And with SOFIA, you’re not worried about getting spun around.

Fraser:                         Right. Right. The jet stream.

Dr. Gay:                      Yeah. Weather balloons are subjected to the jet stream, and all the high altitude winds, not just the jet stream. And so this means they have to figure out how to compensate. So, early on they’re like we’re gonna launch humans, figure this stuff out. Humans are essentially in space suits. This is part of how we tested early space suits. And eventually, we just started launching the balloons by themselves. Although controlling them still continues to be a problem.

Fraser:                         That does sound a bit like a two-for, that you have an astronaut testing out a space suit and at the same time, have them work the telescope. It’s perfect. All right, we will continue this conversation in a second, but it’s time for another break. All right, we’re back. okay. So, when we last saw our heroes, they were talking about balloon based observatories and some of the interesting missions. Now, I mentioned it briefly earlier, there was this telescope mission called BLAST which was another submillimeter telescope. There’s actually a pretty fascinating documentary that you should be able to find on one of the streaming services. I forget what it’s called, but if you do a search for BLAST telescope, or balloon telescope. You know the one I’m talking about?

Dr. Gay:                      It didn’t live as long as it should’ve. It failed to live through its third flight, and had to be rebuilt. They kept the name, but it’s not the same.

Fraser:                         I mean, imagine a telescope that you lose after the third flight. And imagine the trials and tribulations of taking this thing – did they launch this one from Antarctica or the Arctic, I forget?

Dr. Gay:                      This one was the one that dangled from a crane that you mentioned earlier.

Fraser:                         Yeah.

Dr. Gay:                      And this was a 2 meter mirror submillimeter telescope. So, it was another one of these really huge things. And it was used to measure the red shifts of star bursting galaxies to help pin down, using photometry. So, this is where you take filtered images and you measure the black body radiation, how it gets shifted by the red shift of the galaxy. So, it was using photometry with filters to get at the red shifts of galaxies, doing all of this is the far infrared, and it helped us see just where are the star bursting galaxies in our universe.

And it also, because you have to figure out where our own galaxy is when you’re trying to figure out what’s beyond it, it did high resolution maps of the infrared, far infrared, a mission of our own galaxy so that we now understand just what our own galaxy is changing the brightness of out in the distance.

Fraser:                         Yeah. Anyway, if you can, do a search on your Netflexes and your Prime videos and you should be able to find this telescope. I think we’ve got time for maybe one more quick telescope. Do you have another one that you like?

Dr. Gay:                      Oh, man.

Fraser:                         There’s x-ray telescopes, as you say submillimeter –

Dr. Gay:                      I can’t say that I have a favorite of any of these, but x-rays are super hard to observe, people. Super hard. In order to understand where on the sky x-ray photons come from, they use a scattering approach to scatter the photons onto a detector. Then they have a grid of opaque squares that casts a shadow so they can figure out where the photons came from based on the shadow pattern of the x-ray blocking thing above it. And figuring out how to make that technology work, figuring that technology out was something that got to be tested by balloons before we launched things into outer space.

So, there was HERO in the early 2000s, there was HEFT, there is – and this one’s name just brings me joy. There is PoGOLite. PoGOLite. And so, these different telescopes allow us to test and do science, and explore, and innovate flight after flight the technologies that either we just don’t need to orbit or that we need to perfect before we orbit.

Fraser:                         And I wonder then, will we see many more of these kinds of observatories into the future? I mean, the list that I’m looking at has about, at least 12 plus balloon observatories.

Dr. Gay:                      And it’s an incomplete list.

Fraser:                         Yeah, there’s many more smaller ones as well.

Dr. Gay:                      Every university at some point or another has launched a weather balloon with science instruments at least to look at solar granulation for undergrads. This science isn’t well tracked, it’s just published and done quietly off to the side without a lot of the excitement of a space craft.

Fraser:                         Yeah. It’s a nice middle ground. It sets off the same delight as SOFIA, when you think about them installing a 4 meter telescope on the side of an airplane and flying it as high up as you possible can to get above that atmosphere and turn it into a space telescope. It’s another way. You really admire the ingenuity of the astronomers and the engineers who come up with these clever ideas to push the boundaries of what’s possible.

Dr. Gay:                      And it’s just beautiful. I really adore the images that come from these, where you do see that curvature of the Earth, that dangling instrument, hanging from what looks like a jelly fish. These are beautiful, elegant pieces of science hardware. And it’s something that reminds you that there’s a certain romance to science, even today as we move into this high tech future.

Fraser:                         Very cool. Thanks, Pamela.

Dr. Gay:                      My pleasure.

Fraser:                         All right. Did you have some names for us this week?

Dr. Gay:                      I do. So, as always, we are brought to you by you. This show is made possible because we have a crew of humans behind the scenes that herd our catlike habits into being well-behaved content hosts. Nancy, Beth, Rich, Ally, all of them are out there and your contributions through Patreon.com/AstronomyCast make this possible.

We would like to say this week, thank you to Paul L Hayden, Mark Steven Rasnake, Ronald McCoy, Brian Kilby, Marco Iarossi, Jordan Turner, Rayvening, Allen M Price, Mark Van Kooy, Saebre Lark, VocalWarrior24, I can say that one and it’s cool, Leigh Harborne, Mark Phillips, Matthias Heyden, Ruben McCarthy, Geoff MacDonald, Wayne Johnson, Iggy Hammick, Catherine McCabe, Jordan Young, Burry Gowen, Birko Roland, Kevin Lyle, Jeanette Wink, Aurora Lipper, Joe Hook, David, Gerhard Schwarzer, Andrew Poelstra, Brian Cagle, David Truog, Robert Wegner, Venkatesh Chary, and TheGiantNothing. I love your user name. Thank you all, you make this possible.

Fraser:                         Thanks everyone. We’ll see you next week.

Dr. Gay:                      Bye, bye.

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