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Sara: Hi, this is Sara Mitchell coming to you from NASA's Goddard Space Flight 

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Center, and I have a very special Skype call today with some

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of the members of the SuperTIGER team who are calling me from

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Antarctica. Hi guys, welcome! [Jason] Hello

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[Sara] Tell me a bit about yourselves. [Jason] So, my name is Jason Link,

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I am a scientist working at NASA Goddard,

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I am down here for the SuperTIGER flight, this is my third

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trip down. All of them have in fact been for the TIGER instrument.

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Starting in 2001....

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and, ah, Nathan? [Nathan] Hi my name is

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Nathan Walsh, I am a graduate student at Washington University

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and this is my first trip down to Antarctica.

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to work on SuperTIGER, which I will be doing my thesis work

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using the data that we get from it.

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[Brian] Hello, I am Brian Rauch, I'm a research assistant professor at Washington University.

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I have worked on TIGER since I was an

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undergrad, I worked on it as a graduate student and I'm still on it, and this is my

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second time to Antarctica. [Sarah] So where are you guys right now?

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[Jason] So we right now are in Crary Lab which is the main

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scientific laboratory at McMurdo Base in Antarctica.

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We are in fact in the staging area for

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where they take equipment out into the field. 

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[Sara] Terrific. So, what is SuperTIGER? [Brian] SuperTIGER is

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a large-area ultra-heavy cosmic ray detector.

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It's a balloon-born instrument meant to fly at stratospheric altitudes.

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[Sara] Ok, why is it called SuperTIGER?

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[Brian] Well, SuperTIGER is a 

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follow-on to the original TIGER experiment, which is a contrived acronym.

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TIGER stands for Trans-Iron Galactic Element Recorder, so

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what makes SuperTIGER super is that it is much larger than the

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original TIGER, approximately four times the active area, and so

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essentially it's a super-sized TIGER, so it's a SuperTIGER.

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[Sara] Well, so what does your SuperTIGER observe?

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[Jason] So as Brian mentioned, our SuperTIGER measures 

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galactic cosmic rays, specifically ultra-heavy, galactic

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cosmic rays. [Sarah] What are cosmic rays and why are they interesting?

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[Jason] So, cosmic rays are high-energy particles that originate

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outside the solar system, propagate through the 

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galaxy and some of them come here to Earth where we detect them.

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They're particularly interesting for a lot of reasons. One is

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they are one of two kinds of matter from outside the solar system that we can

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directly sample. The other being

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stellar dust. Another reason they're interesting is that these particles

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can be at incredibly high energies, much higher

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than any accelerators here on Earth can produce, so

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it's a way to study not only material from

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outside the solar system, but to look at very high-energy particles

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and understand the building blocks of nature.

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[Sara] Wow. Well, so, in particular you're studying

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ultra-heavy cosmic rays, what can they tell us about

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cosmic rays in general and the universe?

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[Nathan] So, ultra-heavy cosmic rays are

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cosmic rays that are made up of elements with about 30 protons or more,

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and these elements are ones that are

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synthesized in extreme conditions like supernova, or

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binary neutron star mergers, so if we

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can measure the ultra-heavy cosmic rays, it can tell us

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more about how cosmic rays are formed in these types of events,

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and also how they're accelerated. [Sara] So you mentioned

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binary neutron star mergers, and just this past month

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there was a huge announcement of a neutron star merger that was observed

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both in light and gravitational waves, and this was a big deal

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because it was the first time that that was seen in both of those messengers.

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How does this relate to the research you're doing with SuperTIGER?

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[Nathan] So, well, as you said, LIGO measured the gravitational wave

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signal from that event and that was first time that's happened.

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And Fermi measured 

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the same, or they were able to look at it afterwards and see the gamma-ray

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signal coming from that same event and so basically

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we're in an age where multi-messenger astronomy

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is possible and cosmic rays that could come from that event

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offer a third, in addition to other

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messengers, that we can use to look at these events.

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[Brian] Well, cosmic rays wouldn't come directly to us

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from that event because cosmic rays, being charged,

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are deflected by magnetic fields and they take a lot longer to get here and don't travel

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a direct path. But, cosmic rays from similar events

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would be, would give a signature that would be indicative of this kind of

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binary neutron star merger event. [Jason] And one of these

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interesting things that we are able to do, is to

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look at what elements we detect here at Earth,

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and propagate it back to the source, which is believed

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for many of the ultra-heavies, to be binary neutron star mergers.

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So we can actually quantify

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the amount of heavy material that might be produced, which is something that

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they can't quite yet do with the photon measurements.

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that they're making. [Sara] Well, that's terrific, and it's wonderful

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to see all the messengers coming together in astronomy.

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So you mentioned that there have been other TIGER and SuperTIGER flights

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How many flights have occurred before this one this year?

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[Brian] Well, there've been essentially three

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TIGER-like instruments. The first TIGER was more of a proof-of-concept,

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It flew once after three campaigns, and it demonstrated

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that the instrument configuration, the instrument design, was good to measure

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cosmic rays past iron into the UH range. And then there was TIGER 

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LDB, that Jason worked on as a graduate student, and I did

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analysis for and supported the flight, second flight, for as a graduate student.

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And, you know, given the results, the preliminary results,

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in the UH range. And then that flew twice, in 2001-2003.

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And now SuperTIGER has flown once and we're going for its second flight.

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[Sara] So, what results do you hope to get from this flight, and what do you hope to learn

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that adds to what you got from the earlier TIGER flights?

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[Jason] The ultra-heavy elements that we're measuring, have not been measured, or measured

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well, by any other instrument. So we are truly making some of the 

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first measurements of the individual element abundances, and

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these are very, very rare elements, so we need a large instrument with a

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very long exposure time in order to get 10

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15, 20 events, which is about the minimum we need to

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be, to have good statistics to be able to do science.

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[Brian] What distinguishes TIGER and SuperTIGER from previous

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measurements is the ability to resolve individual elements, without 

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the confusion. [Sara] The elements you're measuring are the elements that we

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have here on Earth, so you're making direct connections between the things that we're

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made of, and that our world around us is made of, and these cosmic rays that

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you're catching. [Jason] Yes. In fact,

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people might be interested, but if you look at many of the

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materials we use day-to-day: gold, platinum,

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lead, that all came from these 

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high-energy astrophysical events, in the heart of stars, and

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that is what we're in fact studying. [Sara] Awesome.

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So, changing gears a little bit, how does the SuperTIGER instrument

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work? In layman's terms.

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[Nathan] So, the instrument is made

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up of layers of detectors, and there's three different

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types, and when a cosmic ray passes through the

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detector it deposits energy in each layer and that energy

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is in the form light, and that's how we collect it, using 

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photomultiplier tubes, which essentially give us a signal

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telling us how bright the light was when it 

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passed through the detector.

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[Sara] So, when people talk about measuring cosmic rays, you're really not "catching" them,

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you're detecting them as they pass through your instrument.

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[Nathan] Yes. Yes. [Brian] In fact, if we see

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a sign that a cosmic ray has done more than just lose energy

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passing through--if it were to collide with a nucleus within the detector--

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and interact--that's an even we really can't analyze. We require the event to

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pass through all the active parts of the detector without interacting for us to be able

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analyze it. [Sara] So who built SuperTIGER? Where

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was it built? [Brian] Well, SuperTIGER is a collaboration of four

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institutions: Washington University in St. Louis, NASA Goddard

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Space Flight Center, CalTech, with Jet Propulsion

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Lab, so I guess that really makes us five institutions

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and also the University of Minnesota.

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Wash. U. and Goddard

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do most of the construction. [Sarah] So it really takes a village. [Jason] Yes.

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And it should also be mentioned that TIGER is an evolution from the very

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first flight to where we are today and after each flight we

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have improved on the instrument, and made

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everything better. So when you say "who built it?", this starts

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back with the folks who, in the 90's, built the first

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TIGER instrument and it went through various iterations to where we are today.

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[Sara] So, I think the big question would be

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why does this have to go to Antarctica? Why can't you just fly this anywhere?

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[Nathan] Well, there's

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a few reasons I guess, but the main one

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is that this is the place we can fly the longest.

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safely. Above Antarctica,

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during the summer here, a circumpolar vortex sets up,

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so the wind basically circulates around the pole

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and our balloon typically follows that path and

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stays above Antarctica. So we can keep it up for as long

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as possible. [Brian] Another particularly important reason

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for flying in Antarctica, especially if you consider that we want to fly for a long time,

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like 55 days, is that we need power. And back in the old

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days when we started, we would fly with just batteries, but that works for maybe a day.

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So we rely on solar power and fortunately in the summer here the Sun's up all the

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time. It might move and down in the sky some, but it's up and so we have power

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continuously. [Jason] The other important thing about

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flying when it is always daylight, is when you have day/night

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cycling of the balloon you'll lose altitude in the balloon,

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and so here without that day/night cycling, the gas

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is always at roughly the same temperature, so it makes it possible

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to be flying at the high altitudes for a long period of time.

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[Nathan] And the reason why we don't want to change altitude is because 

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if you sink lower in the atmosphere, you have more atmosphere above you,

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and when a cosmic ray is going through the atmosphere it has a higher

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chance of interacting with a particle in the atmosphere

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because it'll be passing through more of it. So the

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higher-up we are, the less atmosphere we have to interfere with

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the cosmic rays that we're measuring. [Brian] And we're above all but a half, 

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about a half a percent of the atmosphere, and even with just that little tiny fraction of

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atmosphere, we lose a very significant fraction, around 50 percent or more,

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of the particles will interact just passing through the atmosphere. [Sara] So

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how high is that in the atmosphere? With just that tiny

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bit above you? [Jason] About 130,000

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feet is the goal that we try to reach, and it's

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usually, and it will all depend on the balloon and the atmospheric

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conditions, but usually it's between about 127 and 130,000

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that we'll start off at. [Brian] SuperTIGER had a wonderful

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balloon, that endured very well, Jason's TIGER flight

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in 2001 had a leaky balloon [Jason] Yes! [Brian] That spanned

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quite a greater, much greater range, but these are

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things you have no control over. [Sara] So, you're

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talking balloons; why a balloon? Why not, just send this up into space? 

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[Jason] So, a balloon has a lot of advantages,

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the first is it's a lot less expensive

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to build and fly on a balloon than to build

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and fly on a rocket experiment. And so

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that allows us to design and build our instrument

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quicker, because we don't have the same expense

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in design and we don't have to go through

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all of the tests that you do for a space mission. For instance, a space mission

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has issues of vibration, which we don't have on a balloon instrument.

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It's also something

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where you can have students

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be far more involved in the building of the instrument. 

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A spacecraft is very technical and very complicated and very often you will need

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a lot of specialized engineers and technicians and it is much harder for

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students to be involved, as you know, Nathan, today, was

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tightening cables and checking things out, and he

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wouldn't have that opportunity on a spacecraft, so there's a lot of

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good things about balloons that let us test

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and move quickly. The other big advantage on SuperTIGER

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is we have very large instrument, which would be very difficult

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to launch into space given its mass and size.

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And we need the instrument size in order to

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measure the cosmic rays.

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[Brian] One advantage to flying on a balloon is that

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you can recover the instrument, right? So you get to fly it again,

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and make improvements and work your way towards

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a space instrument, for instance. I mean, we started...

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TIGER wasn't the very first idea

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along these lines. The group actually worked on previous experiments,

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balloon-born experiments of different types, so one

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can spend a lot of time on development for an experiment that you might hope to one day

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put in space. You can do it iteratively with the balloon and try different things. See 

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what works, see what doesn't, and you can do that very cost effectively.

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[Sara] So, what's your launch window, when does that open?

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[Jason] So, the launch window depends on a couple of things

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coming together. The first being that we have checked out our instrument 

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and it is ready to go, and our goal is to do that by the 

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first week of December. We also need to have the polar vortex

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that Nathan mentioned set-up. That is in the process of doing so

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and the weatherman down here thinks that

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will hopefully have set up the first week of December

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as well. The other thing that we need to have happen

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is we need have a day where we have calm winds

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and clear skies to have a good launch. When that happens

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is anyone's guess with the weather down here in McMurdo, so 

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the first week of December we hope, but

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a lot depends on the weather. [Sara] How big is the SuperTIGER team that's down in

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Antarctica with you right now? [Brian] There will be nine people total deployed. Five from

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Washington University and four from Goddard. [Sara] Well, so thank you for joining me,

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Brian and Nathan and Jason, and best of luck getting ready for launch

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and we'll keep following. Keep up updating us!

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[Jason] We will! [Nathan] All right. [Brian] Thank you. [Jason] Thank you. [Nathan] Thank you.

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[Beeping]

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[Beeping]

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[Beeping]