A pair of Canadian teens, Mathew Ho and Asad Muhammad, recently sent another weather balloon up into “space” — the stratosphere actually — and received a lot of press coverage, because they sent their camera up with a little Lego minifig holding a Canadian flag in the foreground:
The engineering behind Lego Man’s balloon voyage is interesting:
It soared 24 kilometres into the stratosphere via balloon then landed 97 minutes later in dense bush near Rice Lake, south of Peterborough — a remarkably close return considering January’s winter winds were howling.
“We actually had a lot of control on that factor,” says Ho of Lego Man’s capsule touching down 122 kilometres away from the soccer pitch.
“The thing is, the more you fill your balloon, the faster it will go and the sooner it will pop.”
A helium-filled balloon pops at what’s called the burst altitude, says Barth Netterfield, a professor in the departments of physics and astronomy at the University of Toronto. The higher the altitude, the lower the air pressure and the greater the gassy force within the balloon pushing out on the latex.
“You’ve got a balloon and you’ve got a fixed amount of helium in it. So as the balloon goes up, the pressure outside is going down so the balloon is going to stretch,” explains Netterfield.
“The higher you go, the more the balloon expands until, eventually, the rubber isn’t strong enough and it bursts.”
Lego Man’s cream-coloured latex balloon was 2.6 metres in diameter at launch. Netterfield estimates it could have expanded about 10 times that size just prior to bursting.
The students didn’t want their tiny, stiff-limbed captain to be blown too far away — or into water — because they wanted to retrieve him. So Ho and Muhammad planned for Lego Man to hit burst altitude quickly.
The boys emptied a 931-cubic-foot tank of helium into the professional quality weather balloon they bought online, filling it to capacity.
“If you fill your balloon, say, halfway, it will reach a higher max altitude but then obviously it’s got a lot more time in the air so it has a lot more time that it could be affected by wind,” explains Ho.
“A perfect flight plan would be just up and down, on the same spot. The less we had to drive (to retrieve Lego Man) that was our goal, especially since we’re surrounded by so many lakes. There were so many problems that could go wrong.
They found a second method to estimate their project’s likely landing by typing “weather balloon trajectory forecast” into Google.
“It’s almost a bare page, it’s extremely cool,” Ho says of the University of Wyoming’s weather balloon website. It calculates trajectory based on conditions like prevailing winds, launch coordinates and balloon engineering.
“You can enter the coordinates of your launch site, your predicted altitude and it will actually map it on Google Earth.”
Is there some reason why everyone uses expensive helium, rather than hydrogen, for disposable balloons headed for the stratosphere?
Anyway, these weather balloon projects remind me of the silly-sounding rockoon concept. Gas-filled balloons can provide tremendous lift, and rockets face tremendous drag in dense air, so why not use a balloon to lift a rocket into the upper atmosphere before igniting it?
The original concept was developed by Cmdr. Lee Lewis, Cmdr. G. Halvorson, S. F. Singer, and James A. Van Allen during the Aerobee rocket firing cruise of the U.S.S. Norton Sound on March 1, 1949.
A serious disadvantage is that balloons cannot be steered and consequently neither the direction the launched rocket moves in nor the region where it will fall is easily adjustable. Therefore, a large area for the fall of the rocket is required for safety reasons.
That seems easy enough to overcome — you just need to send up a dirigible balloon, or airship.
It looks like some modern teams are taking another look at the idea:
More recently, the JP Aerospace company has developed and used rockoons as part of its space access plans. Additionally, Iowa State University has started a program to develop rockoons. And significant work has been recently done by the Romanian space company ARCASPACE.
JP Aerospace’s Airship To Orbit has more “moving parts” than I would have imagined:
A conventional airship (“Ascender”) lifts payloads up to 30 to 43 kilometers above the ground — roughly the maximum altitude a conventional airship can achieve. At this altitude the second component, a docking station (“Dark Sky Station”), acts as a resupply station for the third stage. The third stage is an orbital airship (“Orbital Ascender”), which takes payloads to low earth orbit (i.e., it accelerates itself horizontally to orbital velocity and gains an altitude in excess of 100 km) over several days.
With a hat tip to Ilkka, transporting hydrogen is an ultrahazardous activity, involving strict liability.
Buying helium is fast and easy. This may solve the puzzle.