Comment Re:Airship one headed in the right direction (Score 1) 43
Cheaper way would be a large high altitude jet to carry the rocket to the edge of space.
The problem is - it's not really cheaper. Fuel is cheap, large high altitude jets aren't
More to the point, the high altitude jet doesn't help much.
Let's suppose we need to send something to the ISS. The ISS averages around 260 miles above sea level and orbits at about 17,000 mph.
So, our plane takes off at the equator and flies at 700 mph up to 11 miles (60,000 feet) above the ground. We launch rockets near the equator and to the East if possible to take advantage of the 1000 mph rotational velocity and our plane should do so as well -- so that means we need 16,000 mph more speed.
So, our high altitude high speed jet has provided 1/23rd of the speed and 1/23rd of the altitude needed to reach the ISS, and our rocket needs to provide the rest. (The fact that both worked out to 1/23 is just a coincidence.)
However, kinetic energy is porportional to speed *squared*, so really, the plane has only provided 1/500th of the kinetic energy needed to reach the ISS and 1/23rd of the potential energy. At the ISS. a kilogram of matter has about 30 MJ/kg worth of kinetic energy and about 3.4 MJ/kg of energy from the increased altitude (vs. sea level.) Note that the energy from the 17,000 mph is almost 10x as high as the energy from being 260 miles higher than sea level.
I haven't worked all of this out exactly, but it looks like putting your rocket on a plane and taking it up to 60,000 feet at 700 mph before launching saves less than 1% of the total energy needed to get to the ISS -- so it sounds good, but in practice it makes a lot more sense to just make your rocket a little bigger and launch from the ground.