At the close of the year 2015, in close succession, two rockets left the ground, crossed the Karman line (at 100 km altitude) into space, and return intact under their own power to a soft landing on the surface of the earth. In the space business, new rockets are launched at regular intervals, but the now-imminent launch of a used rocket is important news.
In December of 1966, Theodore B. Taylor complained that the high cost of sending anything into even low Earth orbit was “roughly equivalent to using jet transport planes to carry freight from, let us say, Madrid to Moscow, making one flight every few weeks, throwing away each aircraft after each flight, and including the entire construction and operation costs of several major airports in the cost of the flights!”
The now-abandoned Space Shuttle was a reusable spacecraft but failed to reduce launch costs and violated one of the cardinal rules of transport: separate the passengers from the freight. Some day, we will look back and recognize one of the other roadblocks to an efficient launch system: separating the propellant from the fuel.
There is no reason the source of reaction mass (propellant) has to be the same as the source of energy (fuel). Burning a near-explosive mix of chemicals makes the process inherently dangerous and places a hard limit on specific impulse (ISP), a measure of how much acceleration can be derived from a given amount of propellant/fuel. It is also the reason that the original objective of military rocketry—“to make the target more dangerous than the launch site”—took so long to achieve.
The launch business has been crippled, so far, by a vicious circle that has limited the market to expensive payloads—astronauts, military satellites, communication satellites, and deep space probes—consigned by customers who can afford to throw the launch vehicle away after a single use. Reusable rockets are the best hope of breaking this cycle and moving forward on a path leading to low-cost, high-duty-cycle launch systems where the vehicle carries inert propellant, and the energy source remains on the ground.
All the advances in autonomous control, combustion engineering, and computational fluid dynamics that allowed these two rockets to make a controlled descent, after only a handful of attempts, are exactly what will be needed to develop a new generation of launch vehicles that leave chemical combustion behind to ascend on a pulsed energy beam.
We took an important first step in this direction in 2015.