Is liquid hydrogen rocket propeller pollution free? If one searches for the different fuel types used in rockets, one can find that over the years, NASA and other space agencies have used both solid fuels and liquid fuels. I can see that more and more rockets are propelled by using a combination of Liquid Hydrogen (LH) - Liquid Oxygen (LOX). Then, I assumed that the reaction would be:
$$\ce{2H2(l) + O2(l) -&gt;[heat] 2H_2O(v)}\tag{1}$$

By looking at this reaction, one can see that the product of this reaction is water (which most probably will be in a vapor state). Now, I have three questions:


Is this reaction correct?
If the product is water, does that mean that such a combustion reaction is pollution free? 
I assume that I am wrong thinking that is pollution free. What would be the polluting agent in this situation and how bad is it, compared to let's say the burning of the same amount of Kerosene?


Thank you!
I'll address you questions in order:  

1) Yes, that is basically the correct reaction, although not quite balanced;  here is how I would write it:  

$$\ce{2H2(l) + O2(l) -&gt; 2H_2O(g)}$$  

2) Ideally, if there were no side reactions, then yes, this particular reaction is "polution free", and the only product is water.  

3) You are correct in your thinking that in the end this does not represent a net pollution-free energy source.  

The reason for this doesn't lie in the reaction taking place at the rocket, but in how they produced the hydrogen in the first place. Unfortunately, there are no significant deposits of $\ce{H2}$ on our planet waiting to be pumped out and used as fuel. So we  have to make it, which requires engergy.  

This means that the $\ce{H2}$ is not a net energy source, rather it is essentially acting as a battery, storing the energy from some other source. So, you can think of the actual pollutants of the $\ce{H2}$ rocket fuel as being the products from whatever process went into generating it in the first place.  This largely depends on what part of the world the hydrogen generation took place. They could have burned coal or other fossil fuel to produce the energy, or they could have built a dam to generate hydroelectric power, etc.  Any of the negative aspects of producing a particular type of energy would be considered a negative product of the $\ce{H2}$ production.