Hypersonics, bombers, and space access
by Taylor Dinerman
|Space launch vehicle developers have no reason to get excited about the 2018 bomber. However, the 2035 one is another matter entirely.|
The B-52s now flying came off the assembly line in the early 1960s, so when they are retired in the 2018–2020 timeframe they will be old enough to be drawing Social Security. A replacement will have some very big shoes to fill. Technologically, however, the replacement will not be ambitious: it will have excellent self-protection, both passive and active, and will certainly carry a heavy payload of smart or very smart weapons. It will probably not be supersonic, let alone hypersonic, and thus will not require any exotic materials or propulsion technologies. If the USAF ever wants to use these technologies on a bomber or other combat aircraft it will have to wait until 2035 or thereabouts.
The space launch vehicle developers have no reason to get excited about the 2018 bomber. However, the 2035 one is another matter entirely. By then the Air Force and the rest of the DoD will have carried out more than two decades of work on hypersonic technology and will have flown numerous test items that build, one way or another, on the work of team that designed and built the X-43A. The Air Force says that it plans to spend $275 million on technologies for Advanced Long Range Strike between 2008 and 2011. This investment, if carefully shared by those who are working on new materials and propulsion and on flight demonstrators, will set the stage for some truly spectacular experimental flying machines in the middle of the next decade.
For the time being NASA is working with DARPA and with the Air Force Research Laboratory (AFRL) on a series of hypersonic demonstrations that will push the limits of today’s technology. The X-51A is something of a replacement for the now canceled X-43C. It is currently planned to be a hydrocarbon-fueled scramjet capable of between Mach 4.5 and Mach 6.5. Officials hope that this design, while not as fast as the X-43, will lead to vehicles or missiles that will be of more military relevance.
If the Air Force really does want very rapid global strike capability, though, it could simply arm a few Minuteman ICBMs with conventional warheads. There are plenty of objections to this but if they were launched out of specially-built silos, maybe based at Vandenberg in California, launching them would not instantly set off a nuclear war, or, as other nations got used to the idea, a nuclear alert. After all, no one thinks that an accidental war could be set off when a few B-2s take off from Missouri or when B-52s are launched from Louisiana.
Conventionally-armed ICBMs would be just a stopgap measure. They would be extremely expensive and would be of limited use. Only the President acting on his or her own responsibility would be allowed to fire these weapons. There are only a few targets that would be worthwhile for such systems, such as Osama bin Laden’s cave (if it were ever identified with perfect accuracy) or a similar politically-important object.
|The effort to develop hypersonics for the 2035 bomber and its possible derivatives may be the last time that air and space industry will cross-fertilize themselves in a big way.|
In contrast, a 2035 bomber would be able to hit its targets and return and repeat the process, just like an ordinary bomber. Thus it would have to have many of the characteristics of an RLV. Given the physics of the problem it is doubtful that a robust military craft with an effective weapons payload would be able to reach orbit. It could, however, serve as the basis for a first stage of a two stage to orbit (TSTO) vehicle. Without the military equipment or weapons and with a much lighter structure (since it would not be required to maneuver at hypersonic speeds), such a first stage could be the vehicle the space industry needs to really reduce the cost of access to orbit.
Another use for this technology would be in the Marine Corps’ SUSTAIN concept. This is an assault vehicle that would go into orbit and then land a squad of 13 combat-equipped Marines anywhere on Earth within 90 minutes. While the idea seems somewhat fanciful, it could have real military utility and the US Marine Corps has a history of supporting innovative, high-payoff technology that is not to be underestimated.
When asked about this technology at a Congressional hearing, NASA Administrator Mike Griffin said, “Hypersonics is a part of the fundamental research that NASA wants to do.” The money to fund this work comes out of the agency’s aeronautics budget rather than out of the Exploration Systems budget. For both the Air Force and for NASA this is an interesting case where the needs of the “air” side of the house and those of the “space” side of the house overlap, at least to a limited extent.
Air and space technologies have been growing apart for many years now. The connection is not wholly severed, however, and since the big aerospace firms still dominate the industry, no one should anticipate a full divorce for many years to come. Already a few small and medium-sized pure space companies have emerged, such as Orbital Sciences Corporation in the US and Surrey Satellite Technology Ltd. in the UK. As more firms like these succeed, and as the larger older firms reorganize themselves to fit the changing nature of the technological landscape, the differences will grow much wider.
The effort to develop hypersonics for the 2035 bomber and its possible derivatives may be the last time that air and space industry will cross-fertilize themselves in a big way. There will always be some ideas, systems, and materials that will be shared by aircraft and spacecraft, but that could be said today for cars and airplanes which both use composites, advanced alloys, computers, and other items. Over the next twenty or so years the US government has the chance to invest in some truly groundbreaking science and technology. It should not confine this effort to simply a better bomber, but should look at this effort as a national one intended to enhance and radically improve America’s overall aerospace industry.