Letter: Propellants Aren’t the Problem; Cut Costs with Reusable Rockets
The commentary by Jonathan Coopersmith in the Feb. 6 issue [“Reaching for the Stars — Affordably,” page 19] was quite correct in identifying the enormous cost of putting payloads into orbit as “the major challenge facing spaceflight today,” and in calling for a drastic reduction in that cost. But the author aims at the wrong target in identifying the reasons for the enormous cost.
It is simply not true that “rockets … cannot … radically reduce the cost of reaching orbit.” The fact that all existing launchers use chemical rockets and are enormously expensive does not mean that existing launchers are enormously expensive because they use chemical rockets. Correlation does not imply causation: Two different things can happen at the same time without one thing causing the other.
It is perfectly true that rocket-powered launch vehicles are almost all (about 90 percent) propellants at liftoff, but that does not mean that propellants are the reason for the enormous cost. That assumption is one of the oldest and most durable myths of the Space Age, but it is no truer today than it was 50 years ago. In fact, propellants are cheap. The cost of the propellants for a liquid-fuel expendable launch vehicle (ELV) is a negligible portion of the total cost of a launch. The real reason for the enormous cost is the “E” in “ELV”: 50 years after Sputnik we are still throwing our launch vehicles away after using them once, and a pound of expended hardware costs orders of magnitude more than a pound of propellants. The specific propulsion technologies employed are almost irrelevant — with expendable launchers, we couldn’t reduce costs even with anti-gravity.
It is also true that NASA has expended considerable effort since the 1980s on launch vehicle programs. The problem is that those efforts were spent on the wrong things. Since the Challenger disaster, NASA has tried twice to develop a shuttle replacement, with the National Aero-Space Plane (NASP) and X-33, two single-stage, horizontal landing designs. Those designs were chosen for no other reason than they were the most difficult ways to develop a launch vehicle that NASA could imagine, and they therefore promised to “push the technology” and justify massive amounts of technology development work for their research centers. That is the exact opposite of the proper way to do engineering.
We have had the technology to develop reliable, fully-reusable, two-stage launch vehicles for over 40 years. NASP and X-33 failed largely because they were single-stage designs, but single-stage is not a requirement for low cost. Indeed, low cost requires generous safety factors to ensure high reliability, and that requires two stages at this point. Low cost demands the use of proven technologies exclusively.
The bottom line is that if we want low launch costs any time in the foreseeable future, we would be ill advised to discard the only technology that is known to work, and the only one that has ever put a pound of payload into orbit. What we need to do is use it properly by developing, as soon as possible, a fully-reusable, two-stage design (with a relatively simple vertical take-off and landing operating mode to reduce development and maintenance costs) and optimize it for high reliability and maintainability (rather than absolute maximum performance with absolute minimum mass, like the shuttle). We could have developed such a vehicle for less than what we spent on the shuttle. Had NASA done so, we would have had low-cost space transportation decades ago.