As I stated in the answer to another question, LH2 suffers some serious drawbacks compared to other fuels.
Off the top of my head, they are
Extremely low density, resulting in:
- Lower mass-fraction because of high tank mass
- High aerodynamic drag due to tank volume
- Larger and heavier vehicle structure due to tank volume
Boiloff and tank seepage, resulting in:
- Even higher tank mass because of the need for insulation
- More complicated tank arrangements because of the inability to butt LH2 tanks against relatively warm cryopropellants like LOX.
- Long-term storage issues from propellant boiloff
The only possible advantages I can think of are
- Marginally higher specific impulse
- Producing only water as a byproduct, keeping environmentalists happy.
In light of all this, what rationale is there for a LH2/LOX Rocket?