Background information:

1. Space shuttle's main engines (not the boosters) are hydrogen-powered.

2. There are (experimental) hydrogen-powered cars which actually burn hydrogen instead of gasoline (I'm not talking fuel cells, but hydrogen-based combustion engines!).

Considering that, would it be possible to have jet planes using hydrogen instead of kerosene? Would the re-design costs for the engines be prohibitively high? Would keeping the hydrogen liquid be too expensive at the airports and maybe impossible in the plane tanks? Would it be too dangerous, because of hydrogen's high inflammability?

If not, why is no-one working on that? Why is there development on cleaner cars, but not airplanes?