Low-cost propellant launch to earth orbit from a tethered balloon

Propellant will be more than 85% of the mass that needs to be lofted into Low Earth Orbit (LEO) in the planned program of Exploration of the Moon, Mars, and beyond. This paper 1,2 describes a possible means for launching thousands of tons of propellant per year into LEO at a cost 15 to 30 times less than the current launch cost per kilogram. The basic idea is to mass-produce very simple, small and relatively low-performance rockets at a cost per kilogram comparable to automobiles, instead of the similar to > 25X greater cost that is customary for current launch vehicles that are produced in small quantities and which are manufactured with performance near the limits of what is possible. These small, simple rockets can reach orbit because they are launched above > 95% of the atmosphere, where the drag losses even on a small rocket are acceptable, and because they can be launched nearly horizontally with very simple guidance based largely on spin-stabilization. Launching above most of the atmosphere is accomplished by winching the rocket up a tether to a balloon. A fuel depot in equatorial orbit passes over the launch site on every orbit (approximately every 90 minutes). One or more rockets can be launched each time the fuel depot passes overhead, so the launch rate can be any multiple of similar to 6000 small rockets per year, a number that is sufficient to reap the benefits of mass production. This approach might allow NASA to have a "propellant rich" exploration architecture that makes it possible to reduce the performance requirements on all space hardware launched into LEO, since there will be abundant propellant to move that hardware out to the moon, to Mars, or beyond. This heavier, lower-performance hardware can be much less expensive and much more reusable than would be possible if so much propellant were not available. As a result, this approach might reduce the overall cost of exploration by an order of magnitude. Think of the tethered balloon as a "flagpole" (Figure 1). The balloon supports a pulley that has the tether looped over it, and winches on the ground can lift the rocket launcher up to the stationary balloon, much as a flag is hoisted up a flagpole. A reloaded launcher goes up to the balloon from one winch as an empty launcher is lowered from the balloon to the other winch. By physically separating the two winches on the ground, the tether lines will not get tangled and the rocket can be dropped freely between the two tether lines for a few seconds before firing so that neither the balloon nor the tether are put at risk of being incinerated by the rocket.