If you ask Russia, modern rockets are hindered by not just their engines, but their fuel -- the chemicals just aren't powerful enough to carry increasingly heavier loads and keep costs in check. To that end, the country's Advanced Research Foundation has conducted what it says is the first successful test of a full-size pulse-detonation engine (where rapid-fire detonation waves combust the fuel and oxidizer) running "clean" fuel. The oxygen-kerosene mix isn't so much eco-friendly (although it does burn more cleanly) as very efficient. Its high thermodynamic performance, combined with the extra efficiency of pulse-detonation itself, would let rockets either carry more cargo into space or reduce costs by getting vehicles into orbit faster.