I was reading an article about deep underground life that feeds on hydrogen. The article suggested the hydrogen was produced by irradiation of water by underground uranium.
That made me wonder if it would be possible to generate the hydrogen used for fuel of a rocket rather than carry it along.
The simplest idea would be an underwater launch.
You would use UV rays to separate the hydrogen and oxygen like plants do with photosynthesis or by using radioactive elements.
Key question: how big would a UV source need to be to produce the amount of hydrogen fuel you would need for a suborbital or orbital launch? I think they have large UV lasers for military purposes. Would just using a radiation source like uranium be a simpler method of doing it?
I was also wondering if you could collect sufficient water from the atmosphere for a ground launch. In this case you would *want* to launch during a rainstorm(!) A problem is that most weather and water occurs in the troposphere, the lowest 12 km of the atmosphere. For a orbital launch you would want to get in the 200 km range.
How would you collect the water? A physical collector would be simply a funnel but it would have to be quite large to collect the water. I'm guessing the size of a football field. You would then have the problem of accelerating the funnel against the air and the impinging water. But remember the advantage I'm envisioning here is not having to carry that huge amount of fuel. Remember from your rocket equation a large cost of accelerating a rocket comes from accelerating the fuel itself.
From this web page, the weight of the shuttle external tank with the liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds per second and the amount of hydrogen 465 pounds per second.

Plus, what if you didn't have to use a *physical* collector. Could magnetic fields be used to collect the water? Recent experiments show that water itself can be levitated by magnetic fields. This is because it is diamagnetic:

Diamagnetic Water
http://www.matchrockets.com/water/diamagh2o.html

In this case perhaps you wouldn't have to launch during a rainstorm. If the magnetic field is extensive enough you could collect the amount of water normally in the air.
As the page on diamagnetic levitation shows the magnetic fields have to be quite strong for this to work. Another possibility would be to electrify the air above the rocket by sending a strong electrical charge through it, as with a lightning strike. The air and water withing the range of the electrical charge becomes temporarily ionized. Then a magnetic field of any intensity would be able to attract the water molecules. Unfortunately, this would also attact the ionized air molecules as well.

Bob Clark