Liquid oxygen is one of the cheapest manufactured substances on Earth. In large quantities, it costs pennies per kilogram - cheaper than milk or beer.

Trying to build a spaceship by making an aeroplane fly faster and higher is like trying to build an aeroplane by making locomotives faster and lighter - with a lot of effort, perhaps you could get something that more or less works, but it really isn't the right way to proceed.

Rocket engines generally are simpler than jet engines, not more complicated.

Henry Spencer Quotes