While a large number of issues could be explored in the now more than fifty years of space access, here are five central legacies, number three will blow your mind. (Sorry, I couldn’t resist).
- The limitations of chemical rocket technology
Space access has rested firmly on the shoulders of chemical rockets for boosting payloads into Earth-orbit and beyond. From the first experiments by Robert H. Goddard in the 1920s through the pathbreaking V-2 missile of World War II and the mighty Saturn V Moon rocket, to the most sophisticated spacecraft ever built, the Space Shuttle, the basic principles have not changed. However, chemical rockets are notoriously inefficient and costly to operate. In future generations, spaceflight must move beyond this technology to embrace another approach to reaching space.
A key issue to be wrestled with in the 21st century is how to move beyond these chemical fuels to develop new types of propulsion systems that may be far more cost effective, reliable, and expeditious in operation. A useful analogy is the transition from propeller-driven aircraft to jets. American aeronautical engineers essentially ignored jet propulsion and focused R&D efforts on incrementally improving propeller-driven aircraft. They failed to grasp its inherent superiority. While a relatively simple propulsion system in its principals, the jet required a unique combination of metallurgical capability, cooling and velocity control, and an unconventional understanding of Newton’s third law of motion for its effectiveness to be realized. The modern air system is based on this propulsion system.
It may well be that there is a revolutionary propulsion system around the corner for space access that will move us beyond chemical rocket technology in the 21st century. For instance, instead of the initial chemical launch, spaceflight might begin with horizontal acceleration along a track. Using magnetic levitation to eliminate friction, linear electric motors will accelerate the vehicle to more than 1,000 mph before it leaves the track and fires its main engines. This MagLifter launch facility might enable space vehicles to be launched toward orbit in a more airplane-like manner. Because of the inherent limitations of chemical rocket technology, it appears that some new propulsion capability is essential to future space access.
2. The ICBM legacy of space access
A second major legacy concerning space access is that it relies on launchers—especially Atlas and Delta—that began development as intercontinental ballistic missiles (ICBM) in the 1950s. At present the United States still relies on the descendants of these ballistic missiles for most of its space access requirements. Even though they have enjoyed incremental improvement since first flight, there seems no way to escape their beginnings in technology (dating back to the 1950s) and their primary task of launching nuclear warheads.
Movement beyond these launchers has remained a dream in the opening of space access to wider operations. Like the earlier experience with propeller-driven aircraft, we have incrementally improved launchers for the last 40 years without making a major breakthrough in technology. Accordingly, America today has a very efficient and mature ELV launch capability that is still unable to overcome the limitations of the first generation. After many decades of effort, access to space remains a difficult challenge.
3. The Value of RLVs versus ELVs
Many aerospace engineers believe that the long-term solutions to the world’s launch needs are a series of completely reusable launch vehicles (RLV). A debate has raged between those who believe RLVs are the only—or at least the best—answer and those who emphasize the continuing place of expendable launch vehicles (ELV) in future space access operations. RLV advocates have been convincing in their argument that the only course leading to “efficient transportation to and from the earth” would RLVs and have made the case repeatedly since the late 1960s. Their model for a prosperous future in space is the airline industry, with its thousands of flights per year and its exceptionally safe and reliable operations. Several models exist for future RLVs, however, and all compete for the attention—and the development dollars—of the Federal government.
But is that true. The reality, ELV advocates warn, is that the probability of all RLV components operating without catastrophic failure throughout the lifetime of the vehicle cannot be assumed to be 100 percent. Indeed, the launch reliability rate of even relatively “simple” ELVs—those without upper stages or spacecraft propulsion modules and with significant operational experience—peaks at 98 percent with the Delta II and that took thirty years of operations to achieve. To be sure, most ELVs achieve a reliability rate of 90-92 percent, again only after a maturing of the system has taken place. The Space Shuttle, a partially reusable system, has attained a reliability rate of 98 percent, but only through extensive and costly redundant systems and safety checks.
In the case of a new RLV, or a new ELV for that matter, a higher failure rate has to be assumed because of a lack of experience with the system. Moreover, RLV use doubles the time of exposure of the vehicle to failure because it must also be recovered and be reusable after refurbishment. To counter this challenge, more reliability has to be built into the system and this exponentially increases both R&D and operational costs.
4. The costly nature of space access
Lowering the cost of space access has long been the major goal of rocketeers. Thus far they have largely been unsuccessful in doing so. Space travel started out and remains an exceptionally costly enterprise. The best expendable launch vehicles (ELV) still cost about $10,000 per pound from Earth to orbit. The result is that spaceflight remains an enormously costly business. No wonder that it has been the province of governments, a few high-end communications satellite companies, and other unique users.
Even the most modest space launchers, placing relatively small satellites of less than 4,000 pounds into orbit, still average some $25-$50 million per flight, or about $10,000-$40,000 per pound depending on the launch system. The mighty Saturn V Moon rocket, the most powerful launch system ever developed, had a thrust at launch of 7.5 million pounds of thrust. It could place into orbit a massive payload of 262,000 pounds, but to do so cost an enormous $113.1 million per launch ($460 million in 2016 dollars). And those are just basic launch costs to orbit; they do not include the cost of satellite development, indemnification, boost to optimum orbit, ground support and transportation, operations, and the like.
If getting in low-Earth orbit is the critical element in space exploration, and I believe it is since if you can’t get there you can’t do anything else, then why are there not aggressive efforts to build that new launcher that will be cost-effective, reliable, and flexible?
5. Launch vehicle reliability
Launcher reliability has been a problem from the beginning. For total missions conducted between 1957 and 1980, there was a 15 percent failure rate. In missions conducted between 1980 and 2016, less than 5 percent failed. As a result the American aerospace industry has learned from early failures and made corrections necessary to mature the systems in operation. But there are still notable failures to the present.
This reliability rate is the envy of the world, as all other nations have a reliability rate of only about 80 percent for all launches undertaken since the beginning of the space age. But there are still notable failures to the present. In U.S. launcher failure histories fully two-thirds of the catastrophes in liquid propulsion launchers resulted from subsystem failures other than engines. It is important to focus sustained attention on these subsystems in design, testing, and operations to enhance reliability.
Perhaps the entry of new launchers such as the Falcon 9 and Antares, as well as others, may change this dynamic in the future. Collectively, however, I believe these represent the core legacies from the past and the challenges for the future of space access.