High-Flying Science: How and Why We Sent a Refrigerator Halfway to Space

There’s a gap within the backside of the ocean. … Not less than, that’s how I keep in mind the youngsters’s tune beginning off. 

Every verse of the tune would pile one other merchandise into the opening on the backside of the ocean, culminating in one thing ridiculous. The tune would lead to one thing like, “There’s a bug on a automobile, on a home, on a log, on a frog in a gap on the backside of the ocean.” 

That tune floated again into my thoughts as I recalled my journey within the New Mexico desert final summer season. 

NIST had beforehand developed instruments referred to as transition edge sensors (TES), which solely work at extraordinarily chilly temperatures. Researchers use these sensors to review something from a remnant of the Huge Bang, generally known as the cosmic microwave background, to X-rays and gamma-rays coming from distant supernovas and black holes. 

I examine physics at Washington College in St. Louis. In collaboration with NIST, we needed to put these sensors — and a scientific fridge wanted to chill them down — onto a balloon that may fly excessive above most of Earth’s ambiance. If I had been to summarize our efforts, I’d modify the tune to go one thing like this: 

There are superconductors in a field underneath a fridge in a cryostat on a gondola underneath a balloon on the prime of the sky.

There are superconductors in a field …

TESs are superconductors (effectively, not only a superconductor, however the superconductor is one in every of its key parts) that enable us to see radiation generally known as gamma rays and measure their vitality with very excessive precision. It’s like a cutting-edge digicam, however we use it to take footage of sunshine that’s tens of 1000’s of instances as energetic as the sunshine our eyes see on daily basis.

We love how the cameras in our cellphones present cleaner and crisper footage every year. Likewise, astrophysicists work exhausting to get higher footage of gamma rays coming from celestial objects resembling black holes and neutron stars, which produce numerous this radiation.

Our gamma-ray digicam consists of many TESs, all held inside our “detector field.”

… underneath a fridge in a cryostat on a gondola underneath a balloon on the prime of the sky.

To maintain the TESs at simply the best temperature for them to work, we have to deliver them to a fraction of a level above absolute zero, which is round minus 273 levels Celsius or minus 459 levels Fahrenheit — colder than outer house!

Happily, we’ve loads of scientific dilution fridges (DRs) that may simply obtain such temperatures within the lab. Much less fortuitously, although, they’re typically fairly giant, spanning the width and peak of a standard lab room. And we will solely acquire the mandatory X-rays or gamma rays at about 40 kilometers (25 miles) into the sky as a result of the nearer we get to Earth’s floor, the extra the photons are blocked out by the ambiance. That’s roughly three to 4 instances the peak at which a industrial airplane flies.

Due to this fact, we needed to see if a miniature DR might be flown on a science balloon at such a peak and if it might efficiently cool the TESs whereas within the sky. That’s fairly the logistical problem!

We located each the TES detector field and the mini-DR inside our hermetic chamber to take care of extraordinarily low temperatures. (We name this hermetic chamber a “cryostat.”) The cryostat first took the tools right down to the “straightforward” temperature of 4 kelvin (roughly, a balmy minus 269 levels Celsius or minus 452 levels Fahrenheit). Then, the mini-DR took it the remainder of the best way to 100 millikelvins (a fraction of 1 diploma Fahrenheit above a temperature of absolute zero). 

Lastly, we loaded the cryostat onto a sturdy, inflexible metallic body we name the “gondola.” We mounted the gondola beneath the science balloon. 

After which we would have liked to truly launch the balloon. 

Stepping again a bit:

As we labored within the desert day in and day trip, our crew would go to a hangar at a former Air Pressure base to attempt to put collectively and check the tools for this science balloon flight.

Admittedly, once I first began my Ph.D. at Washington College in St. Louis, I had not even imagined that I might spend weeks in a tiny city in New Mexico doing this. 

After I was a first-year graduate pupil, I didn’t even know which space of physics I needed to dive into for my diploma. However sooner or later, Henric Krawczynski, one of many professors in our physics division, got here to talk at our weekly seminar class. He talked about his computations in addition to his numerous balloon missions. Earlier than this, I hadn’t thought I needed to do experiments. “In spite of everything,” I assumed, “don’t the driving concepts of physics come from the theories?”

However one factor caught with me. (He didn’t say it exactly this manner, however that is my takeaway.)

We’ve 4 primary forces in physics, from the robust pressure and the weak pressure to the electromagnetic pressure and gravity, that specify each different bodily legislation. We are able to check the primary three with the particle colliders right here on Earth. However one of the best ways to check essentially the most excessive gravitational results is a laboratory among the many stars — resembling round black holes and neutron stars, a number of the densest objects within the universe.

But when we wish to make any progress with testing the basics of physics round such objects, we have to first perceive them effectively sufficient. We are able to study extra about them by getting a clearer image, for instance, of the stuff falling into the black gap or the supplies that make up the neutron star. And we will get this clearer image by exactly measuring the gamma rays coming from these objects with TESs!

And that’s why we needed to ship a DR up with our TESs nearly midway to house to take footage of gamma rays. We’re making an attempt to see what clues this radiation can present us about a number of the wildest, most mysterious objects in our universe — and, finally, what that teaches us about elementary physics legal guidelines. 

Now stepping again to the current:

After we completed placing collectively our tools in New Mexico, we waited for the possibility to launch our balloon.

Every evening that we had a possible launch alternative, we awoke at round 9 p.m. We ready our experiment and waited to listen to whether or not the 1 a.m. determination from NASA’s Columbia Science Ballooning Facility would clear us for launch. A number of instances, they referred to as us off, as they determined that one other balloon mission would go first. 

Even for the first-in-line balloon mission, so many issues needed to go proper earlier than an precise launch. Listed here are just some of the components: 

• The wind on the bottom and on the peak of the huge balloon needed to be calm sufficient.
• There couldn’t be any rain.
• NASA needed to calculate a lower than 0.01% likelihood of the balloon and tools hitting an individual in the course of the flight. (Worry not, reader, you’re in secure arms.)

Every time when NASA referred to as off our launch try in favor of one other mission, we needed to repeat all of our preparations once more the next evening. 

Our day (or evening) got here finally, with the queue lastly emptied of all different missions. Something might nonetheless have gone improper, canceling our launch. This had occurred 14 instances on one other balloon mission of ours. I feared the worst. 

However as a substitute, when our flip got here, we launched on the primary attempt!

Our findings — and what’s subsequent?

Throughout this flight, we demonstrated that our detector field might certainly measure the specified radiation. We even achieved a temperature of round 90 millikelvins above absolute zero on the detector field throughout flight! 

Nevertheless, we didn’t handle to get the temperature fairly as steady as wanted to get the state-of-the-art vitality decision that we will already get from TESs on the bottom. We might work on this in our lab again in St. Louis and fly once more from New Mexico.

Personally, I’ve discovered fairly a bit, each concerning the science of those detectors and about this complete technique of scientific ballooning. Over the previous few years, I’ve gained a a lot deeper appreciation and understanding of the experimental aspect of astrophysics. We are able to theorize all we wish, however with out taking precise information, we’ll by no means know actuality from mere potentialities. 

I additionally now understand how a lot effort it takes to get a balloon mission to work! However I’ve additionally skilled the rewards of success, particularly whereas working with so many others (together with our pivotal collaborators on the College of New Hampshire and at NIST) to get one thing to work for the very first time.

Ending with a bang!

Folks typically ask me: How does the balloon come down? Are you able to management the place it lands?

Sadly, we will solely take out a balloon of that quantity by sending it up with explosives and blowing it up earlier than permitting the science tools hanging beneath the balloon to fall to Earth beneath a parachute. (That sounds scary, however NASA prioritizes security within the descent calculations, simply because it does previous to launch.)

Bear in mind the tune from the start? At this level, I’d change my tune one final time, to go one thing like this:

There’s a gap within the balloon carrying a gondola carrying a cryostat containing a fridge cooling a field filled with superconductors on the prime of the sky —

— at the very least, proper earlier than it plummets.