It's very lightweight and has a high surface area. The 15mph figure might be slightly low, I'd have to check the simulation results for the exact weight and dimensions but I think our criterion was 20mph with no chute so it should be less than that.
Interestingly another British student balloon project, MiHAB, launched the day after ours and had a successful flight although it did suffer the worst possible type of parachute failure - the chute detached completely. After free-falling from 24km it ended up with a slightly dented corner in its polystyrene foam and no damage to anything inside. I think the measured terminal velocity of that payload was about 30mph, so it must have had a higher ballistic coefficient than ours.
wunderground.com
I agree the Met Office website isn't all it could be but they're very helpful in selling people weather balloons at quite reasonable prices.
Yes, it can.
The sky starts to go black at about 50-60k ft (15-18km). Our balloon was nearly twice as high. At 32km the air density is very low, about 1% of what it is at sea level, and the balloon expands to a diameter of about 7m from its initial 1.5m. When it can't expand any more, it bursts.
We deliberately waited for a day when the jetstream was relatively calm, it was around 40 knots that day which isn't much at all. Also it helped that the low altitude winds were close to opposite the jetstream winds so it went west and then east. And we put quite a bit of excess helium in to get a rapid ascent rate, around 1000 ft/min. So it was up through the relatively shallow band of jetstream (20000~40000 ft) quite quickly. The winds above that are slow indeed.
We started following it after it had reached about 28km on the ascent (we predicted that it should burst around 28-29km, the balloon ended up being a bit stronger than spec and it burst at 32km) and found it about 30 minutes after landing. The GPS is nice to have, it would have taken much longer to do it by radio direction finding. Anyway these things usually land in fields because there are lots of fields around, and despite the purple parachute they aren't blindingly obvious unless you're looking for them. So I don't think it's too likely that someone else would find it first. If they did, hopefully they'd be nice and call the phone number printed on it.
If the parachute fails (unlikely but not impossible) it will "plummet" at a stately 15 mph. We decided to have a launch criterion that it must not visibly damage a melon when dropped on it at a velocity matching the terminal velocity for a no-parachute descent. The testing for that was a lot of fun and we did get through a couple of melons before reaching the right combination of foam material, thickness and shape but now we are confident that it wouldn't hurt someone if it hit them even with a parachute failure. The chances of hitting anyone are very slim anyway, these things always land in fields. Plus we have software running on the balloon that predicts the landing location based on recorded and predicted wind speeds, and aerodynamic characteristics, and will operate the cutdown to release the payload early if it threatens to land in the sea or a heavily built-up area.
Re:Since when does insurance bring people to life
on
Space On a Shoestring
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· Score: 1
Carl already gets woken up around 6:30am most days by pilots calling the number they've seen on the NOTAM.
"Are you launching in the next half hour?"
"No I'm in bed, leave me alone"
Re: GSM text messaging while flying
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Space On a Shoestring
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· Score: 2, Interesting
Yes we will be trying a directional GSM antenna on a later flight, just out of interest more than anything else. The results from the radio were so good that we are planning to spend the next couple of flights proving that a GSM phone is not required, that would save considerable mass and money.
Camera it is! Plus potentially scientific or student experiments that would like 3 minutes of freefall for considerably less than the price of most sounding rockets.
The next step after the 100km rocket is a bit tentative but we would like to add control systems sufficient to put it through a fairly small window in space and time, as a concept demonstrator for something that would latch onto a rotating space tether.
At the moment we have no plans to launch anything into orbit. Without MAJOR sponsorship and a LOT of skill and time, orbit is out of the reach of amateur and student projects IMO. See the development cost of Pegasus, or look at SpaceX and how many $M they have spent so far despite being very lean and efficient.
In experiments with light aircraft and with the balloon we found that ordinary GSM mobile phones / cellphones stop working at about 2km, 6000ft altitude. There are a few ideas as to why but my best bet is that it's caused by the phone being able to see several towers operating on the same frequency, which you can rarely/never do from the ground.
We had telemetry from the two 434MHz radios during the flight and the GSM phone was a backup to send the landing site location if it landed in an area of poor radio reception (which was not unlikely - when the balloon is in the air it should be possible to receive transmissions from the 10mW transmitter at a distance of at least 400km but when it's on the ground, especially with the antenna facing down, you're lucky to hear it within 1km)
Exactly. Apparently if the Bomb Squad etc find a mysterious object with a phone number on it they will always call the phone number before blowing it up.
The CAA were very good about it actually... didn't give us any trouble at all. I think you have to apply at least a month in advance for permission to launch a balloon that will enter controlled airspace (which covers the entire UK from 24500ft up) and they will give you an "exemption" for a certain launch site for a certain period (couple of months). They issue a NOTAM to warn pilots. Then you have to notify the local air traffic control facility 24 hours and then 5 minutes in advance.
Aww come on guys who put that link up? It was just a little unedited footage for the BBC. Now you've gone and broken one of the servers. Go look at the pictures instead, they're better than the video.
We did extensive drop tests to make sure that the payload wouldn't hurt anybody if it landed on them even if the parachute failed to open properly. The casing is made of a type of foam that is very good at absorbing impacts, and the whole thing doesn't weigh very much. If it landed on you with the parachute open you'd just brush it off. If it landed on you without the parachute you'd get a bruised head but would be okay.
Our launches are insured with £5m public liability cover. Arranging this insurance was quite difficult though.
Good point - though I don't see why caesium should be restricted post 9/11, it's completely impractical as an explosive. Would cost crazy money for enough to do any damage to anything, while you can make things like acetone peroxide from off-the-shelf materials (most of the suicide bombs used by the Palestinian terrorists use acetone peroxide as the explosive).
Actually, yeah - caesium reference frequencies, i.e. "atomic clocks" actually do count the vibrations of caesium atoms. It can even be done by amateurs.
That guy has clocks accurate to better than 1 part in 10^13, which means that the clock will only be wrong in its count of 9,192,631,770 vibrations/second once every thousand seconds.
The gravitational assists carried out by probes in our own solar system work in a similar way but don't usually involve swinging around the sun. Instead the idea is to come up behind another planet, e.g. Venus, as it travels around its orbit. As you approach the planet from behind you experience an attraction causing you to accelerate. You then move out away from the planet, while still remaining behind it (w.r.t. its direction of travel) until you are pretty far away and outside most of its gravitational field. This results in extra momentum for you, and less momentum for the planet - it slows slightly in its orbit.
What I don't understand is a different type of gravitational assist manoever. I have read that it's possible to get a great boost in velocity by approaching close to a large body, e.g. the sun, then burning a rocket engine near the time of closest approach. Somehow the delta-v from the rocket is multiplied several times. Can anyone explain how this one works? Or is it bullshit?
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It's very lightweight and has a high surface area. The 15mph figure might be slightly low, I'd have to check the simulation results for the exact weight and dimensions but I think our criterion was 20mph with no chute so it should be less than that. Interestingly another British student balloon project, MiHAB, launched the day after ours and had a successful flight although it did suffer the worst possible type of parachute failure - the chute detached completely. After free-falling from 24km it ended up with a slightly dented corner in its polystyrene foam and no damage to anything inside. I think the measured terminal velocity of that payload was about 30mph, so it must have had a higher ballistic coefficient than ours.
We have a video and some photos, I'll try to get them online.
wunderground.com I agree the Met Office website isn't all it could be but they're very helpful in selling people weather balloons at quite reasonable prices.
Yes, it can. The sky starts to go black at about 50-60k ft (15-18km). Our balloon was nearly twice as high. At 32km the air density is very low, about 1% of what it is at sea level, and the balloon expands to a diameter of about 7m from its initial 1.5m. When it can't expand any more, it bursts.
Someone did have the hilarious idea of putting a bike helmet on the bottom, open side downwards.
We deliberately waited for a day when the jetstream was relatively calm, it was around 40 knots that day which isn't much at all. Also it helped that the low altitude winds were close to opposite the jetstream winds so it went west and then east. And we put quite a bit of excess helium in to get a rapid ascent rate, around 1000 ft/min. So it was up through the relatively shallow band of jetstream (20000~40000 ft) quite quickly. The winds above that are slow indeed. We started following it after it had reached about 28km on the ascent (we predicted that it should burst around 28-29km, the balloon ended up being a bit stronger than spec and it burst at 32km) and found it about 30 minutes after landing. The GPS is nice to have, it would have taken much longer to do it by radio direction finding. Anyway these things usually land in fields because there are lots of fields around, and despite the purple parachute they aren't blindingly obvious unless you're looking for them. So I don't think it's too likely that someone else would find it first. If they did, hopefully they'd be nice and call the phone number printed on it.
If the parachute fails (unlikely but not impossible) it will "plummet" at a stately 15 mph. We decided to have a launch criterion that it must not visibly damage a melon when dropped on it at a velocity matching the terminal velocity for a no-parachute descent. The testing for that was a lot of fun and we did get through a couple of melons before reaching the right combination of foam material, thickness and shape but now we are confident that it wouldn't hurt someone if it hit them even with a parachute failure. The chances of hitting anyone are very slim anyway, these things always land in fields. Plus we have software running on the balloon that predicts the landing location based on recorded and predicted wind speeds, and aerodynamic characteristics, and will operate the cutdown to release the payload early if it threatens to land in the sea or a heavily built-up area.
uh what
That would (pretty much) be a perpetual motion machine. The energy generated by a conductive tether comes (mostly) from your orbital kinetic energy.
Carl already gets woken up around 6:30am most days by pilots calling the number they've seen on the NOTAM. "Are you launching in the next half hour?" "No I'm in bed, leave me alone"
Yes we will be trying a directional GSM antenna on a later flight, just out of interest more than anything else. The results from the radio were so good that we are planning to spend the next couple of flights proving that a GSM phone is not required, that would save considerable mass and money.
:) Tiger^ is a cool dude.
Camera it is! Plus potentially scientific or student experiments that would like 3 minutes of freefall for considerably less than the price of most sounding rockets. The next step after the 100km rocket is a bit tentative but we would like to add control systems sufficient to put it through a fairly small window in space and time, as a concept demonstrator for something that would latch onto a rotating space tether. At the moment we have no plans to launch anything into orbit. Without MAJOR sponsorship and a LOT of skill and time, orbit is out of the reach of amateur and student projects IMO. See the development cost of Pegasus, or look at SpaceX and how many $M they have spent so far despite being very lean and efficient.
In experiments with light aircraft and with the balloon we found that ordinary GSM mobile phones / cellphones stop working at about 2km, 6000ft altitude. There are a few ideas as to why but my best bet is that it's caused by the phone being able to see several towers operating on the same frequency, which you can rarely/never do from the ground. We had telemetry from the two 434MHz radios during the flight and the GSM phone was a backup to send the landing site location if it landed in an area of poor radio reception (which was not unlikely - when the balloon is in the air it should be possible to receive transmissions from the 10mW transmitter at a distance of at least 400km but when it's on the ground, especially with the antenna facing down, you're lucky to hear it within 1km)
Exactly. Apparently if the Bomb Squad etc find a mysterious object with a phone number on it they will always call the phone number before blowing it up.
The CAA were very good about it actually... didn't give us any trouble at all. I think you have to apply at least a month in advance for permission to launch a balloon that will enter controlled airspace (which covers the entire UK from 24500ft up) and they will give you an "exemption" for a certain launch site for a certain period (couple of months). They issue a NOTAM to warn pilots. Then you have to notify the local air traffic control facility 24 hours and then 5 minutes in advance.
Aww come on guys who put that link up? It was just a little unedited footage for the BBC. Now you've gone and broken one of the servers. Go look at the pictures instead, they're better than the video.
We did extensive drop tests to make sure that the payload wouldn't hurt anybody if it landed on them even if the parachute failed to open properly.
The casing is made of a type of foam that is very good at absorbing impacts, and the whole thing doesn't weigh very much.
If it landed on you with the parachute open you'd just brush it off. If it landed on you without the parachute you'd get a bruised head but would be okay.
Our launches are insured with £5m public liability cover. Arranging this insurance was quite difficult though.
It won't be a supernova like the OP said, though.
Good point - though I don't see why caesium should be restricted post 9/11, it's completely impractical as an explosive. Would cost crazy money for enough to do any damage to anything, while you can make things like acetone peroxide from off-the-shelf materials (most of the suicide bombs used by the Palestinian terrorists use acetone peroxide as the explosive).
That guy has clocks accurate to better than 1 part in 10^13, which means that the clock will only be wrong in its count of 9,192,631,770 vibrations/second once every thousand seconds.
Pathetic, really.
Especially not ever!
Thanks for the info. Looking forward to learning a bit more calculus so I can handle some orbital mechanics :)
The gravitational assists carried out by probes in our own solar system work in a similar way but don't usually involve swinging around the sun. Instead the idea is to come up behind another planet, e.g. Venus, as it travels around its orbit. As you approach the planet from behind you experience an attraction causing you to accelerate. You then move out away from the planet, while still remaining behind it (w.r.t. its direction of travel) until you are pretty far away and outside most of its gravitational field. This results in extra momentum for you, and less momentum for the planet - it slows slightly in its orbit.
What I don't understand is a different type of gravitational assist manoever. I have read that it's possible to get a great boost in velocity by approaching close to a large body, e.g. the sun, then burning a rocket engine near the time of closest approach. Somehow the delta-v from the rocket is multiplied several times. Can anyone explain how this one works? Or is it bullshit?