IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, we’re going to dive into the hidden and underappreciated world of seaweed. Plus, what a new study says about the cost of cancer treatments. And as a belated Valentine’s Day treat, we’ll learn about the physics of how chocolate feels in your mouth. So go ahead and grab that box of leftover chocolate.

But first, the news has been dominated by updates about suspicious objects being detected in the stratosphere. This bonanza started with a balloon from China, then escalated into other objects, and now even Russian spy balloons shot down over Kyiv, the capital of Ukraine, this week. And although this might sound like a new problem, there are probably thousands of balloons floating above us– a few for spying, others for studying things like near-space or the weather.

So today we’re going to look into the technology behind balloons and focus a bit on what kinds of electrical spying balloons are capable of. Here to tell us more is Dr. David Stupples, professor of electronic and radio engineering and director of electronic warfare research at City University of London. Welcome to Science Friday.

DAVID STUPPLES: I’m very pleased to be here. And hello to all your guests.

IRA FLATOW: Dr. Stupples, I feel like I’ve heard the word “spy balloons” more in the last two weeks than I have in my entire life. What’s your take on all of this news? Is it surprising?

DAVID STUPPLES: No, not really. As you mentioned in your introduction the balloons are used for a variety of things, including looking at the weather and also looking at the winds in the stratosphere, the jet stream. So they’ve been around for a long time. They’ve also been around, of course, for people who want to spy on other people because it’s a way that you can sneak up onto them because they’re very quiet. And you can spy on them from above. So they’ve been around for hundreds of years. But today, they’re much more sophisticated.

IRA FLATOW: Is there any way to tell whether a balloon is a spying balloon or a corporate or research balloon?

DAVID STUPPLES: Not really because they normally have the fabric, which is inflated and lifting the payload. The payload will have solar panels on to provide them power. And they will also be carrying electronics and antennas. So that’s a weather balloon and a spy balloon. So you probably can’t tell the difference. I suppose the spy balloon or reconnaissance balloon might be larger.

IRA FLATOW: Could you tell, of course, after you’ve taken it down what the payload is, whether it was spying or just doing some sort of other surveillance?

DAVID STUPPLES: Certainly. As soon as they get the electronics back to the laboratories, they will know exactly what that balloon has been doing.

IRA FLATOW: Is this stratosphere the altitude where the balloons are flying? Is this the new spy versus spy battleground?

DAVID STUPPLES: Well, I think it is, in some way, because the balloon, when it was first entered the states from Canada– I’m talking about the first one now– was probably between 20 and 30 kilometers. So up to 100,000 feet. So it was certainly in the stratosphere. And it was certainly being driven by the jet streams up there, the high speed winds. So it could be seen by the ground, but only if you’re looking for it.

IRA FLATOW: Only if you’re looking for it. And it seems to me that from the reports we’ve been hearing over this time period that they haven’t always been looking for them, or would you say they always have been?

DAVID STUPPLES: No. Well, I don’t think so, just take the United States for the moment. If you took the air defense radars, the ones that protect the country from attack, these would be looking for moving objects. And I’m talking about fast moving objects, so like aircraft.

So they would have a device called Doppler shift facility on board, which will actually look for a moving object. What it does then is to take away or static objects, which would appear as clutter on the screen. So if the radar is set up to look for aircraft, it probably wouldn’t see balloons. And I know for a fact, it wouldn’t.

IRA FLATOW: Hm. Can you recalibrate the radar so it can find balloons?

DAVID STUPPLES: Yes, they can. And of course, NORAD announced this recently, saying that they were going to calibrate the Doppler so that it would look for very slow flying objects. And yeah, it can do that. But of course, then you’re left with the fact that the balloon is not a very good radar reflective material. So it would probably only work on the metal parts of that or the parts which would actually reflect the radar. And they are quite small. So first of all, the Doppler will shift is a problem. But then you’ve got the problem of having to wait until it gets close enough to see it.

IRA FLATOW: So this is not as easy as it sounds, is what you’re saying.

DAVID STUPPLES: No, it’s not, and I sympathize totally with the US Air Force on this. I mean, they didn’t expect this type of spying on this scale. And that’s, of course, if it is spying. And so therefore, the systems wouldn’t be set up to see them or find them in the first place.

IRA FLATOW: Hm. What’s the difference between the data we get from balloons versus satellites out in space?

DAVID STUPPLES: No, the problem there is that the– first of all, let’s just take two types of satellite, the ones that rotate around the Earth at the same rate as the Earth– and those are called geostationary satellites. Those are at 36,000 kilometers above the Earth’s surface. So what would happen then is any signal, any radio signal, whatever it is, on the ground, if it’s very weak, might not be heard by that satellite. So that’s the first thing.

So then you say, well, OK, then, let’s have a much lower satellite. So we have one in what they call low Earth orbit. But the problem then is, is that the satellite will then orbit the Earth. And it would take about 70 to 80 minutes to orbit the Earth. But as it’s orbiting, the Earth is turning. So it would see it once, and then not again probably for 14 hours. And then it would fly over the same point again. And in the technical terms, we call that dwell time. So the satellite is dwelling on the target for, let’s say, 20 minutes in every 14 hours. So one satellite would miss an awful lot on the ground.

IRA FLATOW: How common do you suspect that if this is a cheaper way and you don’t need to use satellites for this observation, how common is it for surveillance balloons to be around?

DAVID STUPPLES: Well, it is. I mean, certainly, countries that can’t afford the defense expenditure of the United States, they would have cheaper solutions. One of them would, of course, be very cheap satellites, and the other one would be using air balloons. So this is not new. And of course, what it can do is that it can dwell a long time over a target, perhaps three or four hours before it drifts away again. So it actually, then, is picking up a lot of signals from the ground.

IRA FLATOW: But how do you steer it, then, to get to that target that you’d like it to dwell over? Is it subject to the whims of the jet stream, so to speak?

DAVID STUPPLES: You raise an interesting point there. It’s a lovely point. China and, what, the United States, Russia, UK, whatnot, would study very carefully all of the winds in the upper atmosphere. And these jet streams can be, in fact, monitored and then predicted. So over a period of time, a few days, for instance, you could then predict exactly where or closely where the balloon can fly, even to points where the balloon would be stationary for a period of time, and then move into another jet stream and move away. So because of the sophisticated weather computers, we can do that.

IRA FLATOW: Some of the objects that have been shot down were for national security reasons, but others seem pretty benign. And one big reason for shooting them down is because of air safety for airplanes and such. How big a deal is that?

DAVID STUPPLES: Well, it’s a big deal because these balloons, or certainly the one that flew over the States, was massive. We’re talking– I think the press called it several Greyhound buses in size in probably height and in width. So if this came down into a commercial airway, and it got close to an airline, it would certainly bring the aircraft down. So it’s a big hazard.

The other thing is, of course, is, if you bring it down by shooting it down, then you have really no idea where it will end up because as it drifts down through the various layers of the atmosphere, it will be moved away in different directions by the wind currents.

So where you think it might come down in the Mojave Desert, it will end up really on top of someone’s town or roadway, railway, or even an airport. So it’s quite dangerous. So the US made the right decision there in shooting it down when it was over the water.

IRA FLATOW: And of course, since the payload could be, what, a few hundred pounds, you don’t want that to start falling at terminal velocity, do you?

DAVID STUPPLES: That would give you a nasty headache.

IRA FLATOW: [LAUGHS] Let’s talk about how you shoot them down. The US used missiles, but you really– do you need missiles, or do you need guns? From what I understand, the fully inflated balloon is not like a toy balloon where if you puncture it, it pops. The gas inside is that equal pressure to the gas and the atmosphere. So hitting it with gunfire might put holes in it, but might not take it down.

DAVID STUPPLES: That’s true. I mean, it would eventually come down because the helium would leak out, but if you just put a few holes in it, it would certainly would leak and then descend over time. Hitting it with a missile is really very difficult as well because if it’s a heat seeking missile, the balloon is not putting out any heat. So it’s got very little to home in on. And then the radar controlled missiles work on Doppler again, a moving target. So it’s difficult for them to shoot it down.

And also, if the balloon is, say, 90,000 feet to 100,000 feet, the aircraft– in this case, it was an F-22 Raptor– it can probably get to about 70,000 feet. So it couldn’t put its guns onto the balloon. It’s too far away. So it would have to fire a missile. And that’s a little bit hit and miss as well. So bringing them down is not such a simple task.

IRA FLATOW: And finally, how many balloons do you think there are up there right now and undetected?

DAVID STUPPLES: I don’t think very many because I think that after the NORAD adjusted the radars, they would certainly be looking for this now and they would have other means of locating them. So they’re probably not very many there undetected, but there may be one or two because there are a lot of weather balloons in the US will, in fact, launch weather balloons from different parts of the country once or twice a day.

IRA FLATOW: Hm. So is this normal, or are we in a new normal? Or I mean, if these spy balloons have been around for so long, how normal is it that we’re now only detecting these balloons?

DAVID STUPPLES: Well, that’s a good question. And I’ve often wondered why we haven’t been looking for them. But then I thought to myself, well, I haven’t been looking for them either because I would have expected it to be done from satellite and then from spy aircraft, but of course, the aircraft, such as the rivet joint, can’t fly over China or Russia.

And likewise, the Russian aircraft in China wouldn’t fly above the US because they would be shot down. So the only way of doing it is by satellite. But I’ve said the weaknesses of the satellite system. It was probably just filling a gap that the Chinese, in fact, intended to do under these circumstances. I haven’t heard of any Russian balloons going over the US or the UK, but that’s not to say they haven’t.

IRA FLATOW: David, thank you for joining us.

DAVID STUPPLES: It’s a pleasure, Ira, a pleasure.

IRA FLATOW: Dr. David Stupples is a professor of electronic and radio engineering and director of electronic warfare research at City University of London.

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