Uuum: wrong, again. The hypergolic propellants used mean that ignition in space is 100% reliable. This is vital. Hypergolic propellants have been used in all space-based chemical engines. The ones designed by Isaev's design bureau were the only ones to be 100% reliable. (The current hypergolic engines in the Soyuz, Progress and Russian-segment of the ISS are all direct descendants of that superb engine design.) The fact that they are corrosive is an issue. But one has to live with that with chemical engines in space. Space probes use hypergolic propellants. The Shuttle did. It is NOT a "nasty Russian rubbish design" thing.