Airship to Orbit

The interesting thing about John Powell's ideas is that it requires a lot less mass.  How?  It uses the atmosphere instead of fighting it.

His airship to orbit proposition depends upon the following assumptions:

• That from 140,000 feet to 200,000 feet, his craft will operate as an airship
• From 200,000 feet to 260,000 feet, his craft will transition from airship to airplane
• From 260,000 feet to orbit, his craft will be like an airplane

260,000 feet is but 65,000 feet from the Karman Line that separates space from the atmosphere.  That means he only has to climb that far from the point that it stops being an airship and becomes an airplane.  At 325,000 feet, he needs to reach orbital velocity.

This implies that he gets a lot of the lift needed from the velocity.  That also implies not much velocity is needed to stay at 200,000 feet and below.  Presumably, he needs velocity to transition from 200,000 feet to 260,000 feet.  Even more velocity between 260,000 feet and orbit.

The energy requirements are spread out over time.  A conventional orbiter requires so much mass because it requires so much fuel.  The fuel has to be expended quickly, which intensifies the expenditure of energy over a short time period.  It's a race against time, as the fuel is expended at a rate that won't allow it to burn for long.  The Shuttle got to orbit in 8 minutes.  His airship may take days to get to orbit.  The reduction in mass makes it much more efficient in using its mass.  Consequently, it will use less energy and much less fuel.

Useful mass fraction is crazy high with his airship proposition.  (Provided that it works, of course.)  A conventional rocket may be well south of 5% of a rocket being useful mass.  This thing may be 50% or higher.

Skeptics will say that he won't have enough energy and the drag will be too much to overcome.  I don't know who is right on this one.

Perhaps it won't be as difficult to reach orbit when you're on Mars with one of these things.  The velocity required is less than 1/2 of what is required to reach orbit on Earth.  The significance of that should not be underestimated, but will be just the same.