Space On a Shoestring

An anonymous reader writes, "Three engineering students from Cambridge University plan to send an unmanned craft into space for £1,000 ($1,880) and have just sent a test mission up 32 km for a lot less. Their snaps from the upper atmosphere are impressive, and were taken by a balloon equipped with off-the-shelf technology including GSM text messaging, radio communications, and an ordinary 5-megapixel camera. They now plan to use a similar craft as a launching stage to get a cheap rocket into space." There's also a video of the balloon launch.

Comments

Very cool hobby...

[Cherita Chen]

High altitude balooning is a very cool hobby to get involved in... Two very informative links on the subject are included below.

http://www.grc.nasa.gov/WWW/K-12/Numbers/Math/Math ematical_Thinking/designing_a_high_altitude.htm

http://www.amsat.org/amsat/balloons/balloon.htm

Re:Very cool hobby...

[another_henry]

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.

Re: GSM text messaging

[GrahamCox]

I'm sure the phones will work at more or less any height - the higher the better. The problem is that at very high altitudes, the phone "sees" hundreds of cell base stations at once, and the system isn't really designed to deal with this. Even if one cell can decide it will take the initial call, cell switching will be occurring every few seconds as the signal strength fluctuates. The problem multiplies if you are crossing those cells at 500mph. Instead the on board mini-station grabs the call and keeps hold of it, allowing a single dedicated downlink to maintain sanity in the system.

At least this is my only partially-informed assumption (a long time ago I was a radio negineer, but I don't know about the actual implementation details of GSM.) But logically, allowing in-flight GSM phone calls is a bad idea because of the reasoning above. The system is designed on the assumption that calls will be made on the ground, therefore range-limited, and thus can only possibly be routed by one or two base stations, not hundreds.

Re: GSM text messaging while flying

[Technician]

I had signal for a decent phone call up to ~5,000 feet and could send SMS to around ~6,000 feet, soon after this I lost signal.

More likely you had too much signal. From altitude you tie up one RF channel on several dozen towers in range instead of running at reduced power on the closest tower. This blanket coverage of dozens of towers tying up a channel without the ability to hand your signal to a single tower and free up the frequency on other towers for use by others is why they don't permit phone use on aircraft. If the system is smart, it may have shut down your phone to clear the frequency as the towers noticed an even signal strength from one phone over dozens of towers. You simply did not get a tower assignment at altitude.