Sending a balloon to space
We're putting some screams into space, to test the old claim that "in space, no one can hear you scream. To find out how, Chris Smith spoke to Dave Ansell and Omar Gad...
Omar - I actually am very passionate about electronics and how they've advanced over the years. And the thing that made me want to do this the first time was exposing, you know, these types of electronics that you can actually buy anywhere, to harsh environments, such as space, and see how they fare. I think that that is a very good indicator of how well we've progressed in the side of electrical engineering and electronics in general.
Chris - So you thought you'd get in touch to see if we wanted to come on your balloon with you. So let's let everyone in on the secret, what we decided to do. I suggested to Omar, you know you've heard this claim: “no one can hear you scream in space” but actually we could test the physics of this, of how sound is transmitted through a gas and actually work out whether or not as the gas gets thinner with altitude the sound does disappear. Then we thought, how do we actually test this? Which is where Dave got involved. So what did you think when you heard us saying we're going to try and do this? What was it that first went through your mind? Oh my goodness is that Chris Smith again?
Dave: That was part of it! But I mean, so basically we need a way of producing sound and a way of recording that sound. I did have a long diversion into trying to produce horns of various different types to take up into space, but we’re going to - let's go for the simple thing. We've got a loud speaker and a microphone. You play something. It could be your scream. So if you want to send us in a scream, you can get it played in space.
Chris - Well actually Dave, Mark Litton sent me one yesterday. Would you like to hear Mark's scream? This is what he would like us to send into near space for him. I'll see if I get this to play.
Mark - *scream*
Chris - Well that's Mark's contribution to our effort. And actually Sue Marchant then heard that we were doing this Sue Marchant from the BBC eastern region. And she said “well I want to be part of this” and so she's done us a scream. You better hold onto your hats for Sue’s scream! Here it is.
Sue - Oh! Did you hear that? Ow! Did you hear that? Ooow! I bet you heard that!
Chris - So there you go. So we've got a range of screams we could put on there and you've done some as well.
Dave - Yeah. Sue's is particularly nice, it’s got a range of volumes, so if we get the volume wrong...
Chris - But tell us about the apparatus, first of all, that you've designed, because the key thing here is if we just put a speaker in a box then the vibrations could come out of the speaker transmit through the box to the microphone, which is also stuck on the box and then it would just cheat and that wouldn't test sound transmission through air. So what have you done to get round that?
Dave - So basically we've tried to isolate both the microphone and the loudspeaker from the box. - *background scream* - There you can hear Omar’s scream, in fact, that we’ve been testing it with!
Chris - He's just plugged it in. So basically we've isolated the microphone and the speaker so we know the sound can only go through the gas.
Dave - So they're both hanging on springs to damp out any resonances you might get on those springs.
Chris - Dave’s got a picture of this on the internet and there’s also a video of this. So Omar you've written the software. Because we're sending a computer to do this, because we're actually going to do it properly and every increment of altitude we're going to make a recording right?
Omar - Yes. Yes. This was just part of the test script and making it run every five seconds, but in the real scenario we'll probably gonna make it run every five minutes. So on here as well we have a G.P.S. tracker, as well as a pressure sensor and that will be able to also calculate the altitude. And then we'll be able to feed that information into the main micro-controller that will then couple this sound that we recorded with how high it was when the sound was played.
Chris - So we're going to basically be able to plot a graph of how loud it is with increasing altitude and we will see, therefore, we can relay that the pressure, and we can see how the sound is going to change, if it does. You're using a Raspberry Pi computer to do all this. How do you know it'll survive at 3000th of the pressure you get at the surface? Dave, how can we mitigate against that?
Dave - So I got a vacuum pump in my shed. It's not a perfect vacuum pump, it won't get quite that low but I've pumped it down to maybe 70/80 millibars and everything seems to work fine.
Chris - So you've got the rig there with a mechanically decoupled microphone and speaker and the Raspberry Pi stuck on the outside. You put that in a vacuum chamber and you had Omar screams running through it. So is that what you sent me? Because you sent me that audio this afternoon, is that what you sent?
Dave - That's what I sent, yes.
Chris - Because I've got your two test runs here, so I can play this one and you can talk us through what we're hearing. Here's the first one that you sent me.
Dave - So that is probably at full atmosphere.
Chris - That's that's a ground level.
Dave - Yeah.
Chris - And then this was the second one you sent me.
*White noise sound with quieter scream*
Dave - You can hear the air being pumped out, that it's at a much lower pressure and you should be able to hear that it’s much quieter as well.
Chris - Yeah it was a much more threadbare scream and that's not because your apparatus is falling to pieces?
Dave - Hopefully not. It should be that there’s just basically less air their, so as the loudspeaker moves, it moves less air, so there’s less air moving inside the box, so you get less forces on the microphone.
Chris - And of course, we're recording all of this on the way up and then the balloon gets to 120,000 feet. How do we get the balloon back?
Omar - Because there is less air pressure there the helium in the balloon will force the balloon to actually expand and expand and expand until it pops and falls back down to Earth.
Chris - How do we know where it's going to come down?
Omar - So we have a receiver on the ground and a transmitter up in the box on the balloon.
Chris - Because I want my computer back!
Omar - Obviously we'd be able to use that information to actually literally chase it using a car.
Chris - Super! When's the balloon going up?
Omar - Twenty ninth of June.
Chris - It's definitely gonna be then is it? We're gonna do it then?
Omar - Well yes. Most likely then. I keep checking the weather every day to make sure that the weather is as good as possible for the launch. And it does seem that it will be that day.
Dave - The worry is that if the wind direction’s in the wrong direction it ends up in the middle of the sea and then we don't get any data back at all!