Naked Science Forum
General Science => General Science => Topic started by: Paul Anderson on 07/12/2009 09:30:04
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Paul Anderson asked the Naked Scientists:
Hi Chris and Team,
The other day I suggested trying to capture energy from lightning with satellites. As I was catching the bus later that day I was also wondering if lightning goes out into space or just goes downwards towards earth. I thought I have seen it go across the sky. If it just goes downwards because of the size of the earth and thereby some sort of attraction, I wonder if the satellite suggestion holds water (or energy!).
Could the question of how does one capture a large amount of energy in an instant be addressed by looking at how a capacitor works in a radio set? Once in a capacitor the energy could be slowly dissipated through circuitry to charge batteries or whatever.
If one wanted to expand the capture area of a satellite then one might consider dangling wires or nets from a satellite but I wonder if that might not cause some sort of cosmic drag which would encourage the satellite to eventually spiral into the earth prematurely and shorten the life of the satellite.
Another consideration is the height of the satellites. If lightning occurs at the altitude of clouds, for the most efficient capture of lightning, would the satellite also need to be at that altitude, and would that then impinge on the satellite's ability to remain in orbit.
I am waiting for someone to say that if lightning struck a satellite, it would destroy the satellite. Last century I was in a BOAC VC10 flight from Bombay, spiralling over Heathrow with a plane above us and a plane beneath us.. In my opinion, our aircraft was struck by lightning twice, even though the pilot said it had missed us, but the aircraft shuddered and the lights went out, and I am reasonably sure there was some sort of flash and noise, but my mind may be embellishing it now as it happened back in the 1970s. Anyway, we landed safely and then the poor old Indian lady sitting next to me vomited. The point of this is that the aircraft was not destroyed.
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Regards
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Paul
NZ
What do you think?
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Lightning is an atmospheric phenomenon, whereas satellites need to stay out of the atmosphere if they are not to quickly de-orbit and burn up. Lightning sprites reach up to around 90km altitude, but this is still too low for satellites, and the sprites are more like what you get in a florescent light tube or an aurora rather than lighting bolts.
Then there's the issue of lightning being essentially random in location and timing, so how do you ensure that collecting equipment is in the right place at the right time?
Finally, there's the problem of storing such a large amount of energy in such a short period of time. A country sized layden jar might work, but it wouldn't be feasible.
Lightning strikes on aircraft are pretty common, and with metal skinned aircraft, present few problems. The current flows through the metal skin, keeping it away from most of the sensitive electronics, although they may experience a surge and temporarily shutdown, requiring a reset.
I'm not sure how composite construction aircraft deal with lightning strikes though, so I've just e-mailed a gliding friend to ask and I'll get back later on this when I hear from him.
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It turns out that most gliders do not incorporate any special features to counter/cope with the effects of lightning strikes. From my friend...
"The classic strike, on an ASK-21 out of the London GC at Dunstable, had the strike enter at one of the aileron push-rods, travel through the control system to the other wing where it exited through the other aileron push-rod. Ohmic heating blew the skins off both wings and cut the fuselage in half apart as it went through the control linkage and blew both canopies out. The rudder cables remained intact and neither pilot felt any shock. Both parachuted down safely."
Interestingly, the AAIB report found that one of the aluminium control tube linkages, which was 16mm outer diameter, with a 1mm wall thickness, was collapsed into a more or less solid bar due to the magnetic effects of the current flowing through it...
The bellcrank and the outer articulation rod were not recovered but most of the long centre rod, which was made from an aluminium alloy tube of 16 mm outside diameter and 1 mm wall thickness, was recovered in one section. This tube had suffered burning and arc erosion at each end close to its jointed connections, which were missing, and it exhibited an unusual form of damage over its entire length. It had 'collapsed', or had been 'crushed', as a result of the intense magnetic field generated by the conduction of the lightning current, to form an almost solid irregularly shaped 'bar'
It seems likely that the newer largely composite airliners, such as the Airbuses and the upcoming Boeing, probably incorporate some form of conductive mesh set into the outer gel-coat of the composite resin to help disperse the charge over a large area and also act as a Faraday cage to protect the interior controls and electronics.
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It turns out that most gliders do not incorporate any special features to counter/cope with the effects of lightning strikes. From my friend...
"The classic strike, on an ASK-21 out of the London GC at Dunstable, had the strike enter at one of the aileron push-rods, travel through the control system to the other wing where it exited through the other aileron push-rod. Ohmic heating blew the skins off both wings and cut the fuselage in half apart as it went through the control linkage and blew both canopies out. The rudder cables remained intact and neither pilot felt any shock. Both parachuted down safely."
Hi, I see you have been talking about the glider accident, Well I am the passenger that was in the glider that was destroyed by lightning that day. You may be interested to see my "Scrap book" of the days events. Click on this link:- http://sites.google.com/site/thebig40reachfortheskiesagain/ (http://sites.google.com/site/thebig40reachfortheskiesagain/)
The attachment on that page is my Scrapbook with photos of the wreckage etc. there are also radio and tv interviews/reconstructions that you watch / listen to on that page.
I went up again last year with the same pilot, you can read all about it.
Regards
Graeme Cooper