Jetpack International's T-73 achieves vertical takeoff with an actual jet engine as opposed to the rocket engines used by the majority of jetpack models. This allows it to have longer flight time (9 minutes as opposed to 30 seconds). Some fighter planes also manage VTOL with a jet engine, the...
When combustion occurs in a rocket engine, most of the high speed fluid passes out the back as exhaust. But surely some of it flows back through the fuel and oxidizer injector tubes? Wouldn't this decrease efficiency (and potentially even lead to safety risks)?
I recently saw an Elon Musk talk on YouTube where he commented on how if Earth's gravity were just a little stronger, then it would have been impossible to generate enough thrust to get into space. He cited that as the reason why only a handful of national governments have successfully reached...