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.
The concept of a pulse-detonation engine isn't new. The concept reportedly originated in Russia in the mid-20th century, and the US Air Force even tested one aboard an aircraft in 2008. However, it has largely been the stuff of sci-fi in rockets, in no small part due to the added risk of stress. You are producing continuous explosions, after all. Russia's test shows that the technology could finally be practical for spaceflight. If scientists can translate their experiments to practical rockets, you could see more frequent (not to mention more ambitious) space missions going forward.