Balloon into orbit ?

[Gib Bogle]

To be in orbit you need to have a sufficiently high tangential speed. I don't know what that is, but when you watch a satellite moving across the night sky you get some idea.

[Gib Bogle]

Great story!

[dennis]

Are you sure H2 is smaller than He? Hydrogen is a molecule with 2 atoms, helium is just one helium atom.

[Steve Firth]

Ian Jackson wrote: [snip]

on for ever?

All of the techniques discussed here are used in high altitude survey balloons. stratospheric balloons are launched looking like spring onions with a small "bulb" and a long "stalk". As the ascend pleats and pockets in the balloon expand and the envelope becomes spherical.

Balloons are fitted with over-pressure valves to vent gas, but this doesn't help them to go higher, it stops them from exploding and falling to earth at an impressive speed.

Some excellent DIY design skills on display in the thread.

[Ian Jackson]

But, at these altitudes, what is the speed of sound?

[The Natural Philosopher]

Complex, since its temperature dependent as well.

[RobertL]

Getting into space and getting into orbit are two different things. You might get into space by using a balloon to get near the top of the atmospehre and then a small rocket to do the final climb above it. To get into orbit you need a very high horizontal velocity (about 5000 m/s) and I don't think a ballon would help.

Robert

[Brian Gaff]

Its not the hieght its the speed. Lower orbits are faster orbits. Of course if you just wanted to hover above most of the atmosphere then a balloon might be OK. It could not go above the atmosphere no matter how you did it, as the weight has to be buoyant in something and nothingness is nothingness, so to speak. What has been proposed before and is under active development is taking a rocket in a balloon to a high altitude as then there would be much less friction and hence it would be easier to go faster since the drag is less. You only have to look at what fell off the shuttle as it passed the denser atmosphere to see the problems of ground launches, there are also issues with rocket efficiency at sea level as well.

I believe a feasible lateral speed for low earth orbit is around 17000 mph. The idea as I'm sure you are aware is to achieve a situation where free fall is fast enough to never come close enough to the planet to get friction from the atmosphere. With nothing to slow it down, it will carry on but of course even at the height of the space station, there are factors like pressure from the suns emissions, and some molecules of gas from our atmosphere such as free radicals and other ionised gasses to slow it down so it has to be reboosted periodically.

Brian

[Halmyre]

A Hydrogen molecule (H2) has two protons and a Helium atom has two protons and two neutrons, so a He atom is twice (approximately) the size of a Hydrogen molecule.

-- Halmyre

[Bernard Peek]

Gas diffusion isn't dependent on the size of the molecule, it's dependent on its mass. Specifically it's inversely proportional to the square root of the molecular mass. As you say, hydrogen has half the molecular mass of helium so hydrogen will diffuse faster.

See Graham's law.

's_law

[funkyoldcortina]

The Register launched a paper plane into space...

[Davey]

For fun, I tried the sentence beginning 'Some farmers..' and switched the words 'fields' and 'wives' around.

--=20 Davey.

[Alan Braggins]

You can never escape gravity _totally_. But if there's enough air for a balloon to have lift, there's enough gravity to keep that air there. But that doesn't stop you being in orbit, gravity is what keeps things in orbit instead of heading off in a straight line forever. The more gravity there is, the faster you have to move to stay in orbit.

However at any height where there is enough air for a balloon to have lift, there will be enough air to cause enough drag that an orbit passing through that point won't be stable.

On the other hand, balloons have reached some pretty astonishing altitudes, sometimes considered "the edge of space" or "near space":

there have been serious proposals for using balloons or airships as part of a system which would end up launching a payload into orbit:

[Tim Streater]

You can't escape from gravity *at all*, never mind partially or totally. The earth's gravitational influence extends to the edge of the universe, as does that of all masses.

[The Other Mike]

Usually, but not for this launch, they are hacked Canon Ixus models.

The fact that they were showing the video during the ascent was a

They commonly, and near universally use one of these

is maybe 1km range on the ground, but a few 100km in the air - one flight was tracked over 500km across Europe recently using a chain of receivers.

Also GSM trackers are used on the ground that phone home the coordinates by SMS to locate the landed package.

Tracking can be done real time, using a network of recievers - pity they didn't show this on the programme. The laptop on the dash was only showing the raw telemetry data, with a suitable internet connection you can see the altitude and position overlaid on Google Maps.

You can also predict landing spots using an online facility that lets you input the aunch site and predicted ballon burst altitude (again this was not shown but I can understand the reasons for that - the site would be very quickly overloaded if every tom dick or harry started plugging imaginary balloon launches in)

[The Other Mike]

you avoid being near controlled airspace at launch then you can launch pretty much a anywhere in the UK.

The use of prediction software usually avoids launches that will end up either in cities or the sea. The payloads are deliberately light and you'd be really unlucky to have one enter an engine in flight. There are substantially more meteorological balloons launched to similar altitudes across the UK and long experience has shown they present near zero hazard to aviation.

It's a big sky and there are very few helium / hydrogen balloon launches across the UK.

[Huge]

Presumably at some point the influence approaches the Planck limits (not sure how they apply to gravity) at which point it is no longer possible to measure it.

[Davey]

Yes, I remember about NOTAMS from when I was learning to fly, in the US.

It's good to know that there is little danger from these balloons.

Where was this particular event held, did anybody hear?

[Jethro]

The map screen showed Saffron Waldon, and I believe the Man Lab is somewhere in Cambridgeshire ....

[Martin Bonner]

The helium atom may be twice the mass, but the hydrogen molecule is bigger. Wikipedia says the hydrogen molecule bond length in 74pm, whereas the helium atom is only 33pm across.