Time to Revisit the Aerospace Plane Concept in Light of this Disaster

In light of today's Columbia disaster, it is perhaps time to revisit the intentions behind the now-cancelled National Aerospace Plane (the X-30) program. That program, in many ways, addressed what are apparently many of the problems that led to this explosion and loss of life.

In the early 1980s, the Reagan Administration, through DARPA (the Defense Advanced Projects Research Agency) formed a team of services (the Air Force, Navy, Strategic Defense) and NASA to design and build a scramjet-powered spaceplane that had aicraft-like operational characteristics. The goal was to make a space plane that was genuinely reusable, unlike the shuttles, which require tremendous overhead, support, and time to launch. As much as anything, this feature of the Aerospace Plane would have afforded quick response to emergencies in space---something we simply do not have today. More than that, its design, operation, and construction, while not eliminating all of the problems that have plagued the shuttles, offered some solutions to those we have seen.

Briefly, the X-30 was conceived as a 50-000-lb. swept-wing aircraft that "was" a flying engine. The forebody was an intake; the aft, an exhaust. Several giant scramjet engines were conceived to power this vessel on liquid slush hydrogen fuel. But the beauty of the scramjet was that it mixed the hydrogen with the air outside, giving off water vapor as a by-product. The significance of this concept should not be minimized: by using rockets, a shuttle essentially is like Columbus needing to take the water he sails through along with him. But the X-30 proposed to use the medium of air as PART of the fuel mixture.

Ultimately, the scramjet technology halted the whole program. In 1995, it was killed because the scramjets had not come along as fast as hoped. This, it turned out, was a flaw, not in the techology itself, but in the way the program was "sold" to the administration and the congress. I will return to this in a moment. What is important, though, is that the design of the aircraft used radical new materials for a thick "skin" that eliminated the need for the Shuttle-type tiles---which apparently is where some of the problems originated with Columbia. But even if this is not the case, in voyage after voyage, the expensive tiles simply burn up, and must be completely replaced after one flight. That is not a characteristic of "routine" flight!

How could the Aerospace Plane keep cool enough to survive the phenomenal temperatures? Again, the key was in the frozen slush fuel. In another radical design---and one aspect of the program that appeared to work to perfection---the frozen slushy hydrogen was pumped THROUGH the aircraft, to the leading edges of the wings and nose first, then to less hot areas, then finally to the engines, where it was burned. Thus, the fuel's journey heated it for burning, while cooling the aircraft's (already radically improved) metal edges.

In the seven years I served as the NASP program historian, the engineers and scientists made light-year leaps in materials, producing and manufacturing radical new compound materials that jacked up the ability of a leading edge to sustain heat. During that same time, the program effectively made, stored, pumped, and burned hydrogen slush fuel---one of its most visible triumphs.

This comes only a few days after the President announced a new government initiative to research hydrogen power for cars. It is an idea whose time has come, although Ronald Reagan thought of it first when he embraced the X-30 program.

There were several, substantial, technical hurdles in the program, but most were overcome. The greatest obstacle remained getting the scramjet to perform at levels that would allow speeds of Mach 10, Mach 20, and Mach 25 to reach orbit. Needless to say, this was a titanic feat. Still, the potential benefits of aircraft-like performance addressed several issues that have plagued the shuttles.

*Powered landings. If a shuttle had power in descent, rather than free-falling like a rock, and problems developed, having the ability to pull up or even slow the descent might make the difference between life and death. Certainly if the vehicle gets below 20,000 feet, power can make all the difference in the world. NASP would have had it; the shuttles don't.

*Routine aircraft-like operations (i.e., horizontal take-off, for example) eliminate the massive infrastructures of the shuttles, and could allow rescue attempts for astronauts stranded in space, or to ship needed repair items or equipment to them. Such an option does not exist today.

*X-30 design promised to eliminate many of the tile-related/o-ring related problems of the shuttles. There would be certainly very little rocket fuel aboard (only enough for space-maneuvering rockets). There would OBVIOUSLY be new challenges, and new equipment failures, but we could at least escape some of the weaknesses of the shuttle system.

So what happened to the Aerospace Plane? Robert Williams, the genius behind the program, determined that he could only get funding if he "sold" the administration and Congress on an actual aircraft---not scramjet engines or tests. Thus, he put the cart before the horse, but did get his funding. A further hurdle involved the fact that the U.S. HAS NO wind tunnels of testing any speed higher than Mach 8, and then only for fractions of a second. Instead of building massive new tunnels, Williams planned to make the aircraft into an X-15-type flying test bed, but on a much grander scale.

Unfortunately, the program could not suffer any technical setbacks, because setbacks caused schedule extensions, which cost more money, which caused Congress to stretch out the program yet again. Ever stretch-out ended up taking money from tne X-30 budget, until finally, all the program could do was to fund scramjet tests---exactly what it should have done when the program first started, but which were politically inexpedient.

The U.S. needs to come to grips with the reality that the shuttles are not "routine space access" vehicles, and never will be. Instead, we need to re-focus our space program on a new, hydrogen-fueled vehicle with airplane-like operations, with or without rocket assist.

When our space missions receive no media coverage, or draw no spectators, only then will we have achieved truly "routine" space access. (When was the last time people shook hands and cried when you started your car?)

Shuttles were a good design for the 1970s. It's time for NASA, and America, to come into the 21st century with a new spaceplane that acts like a taxi or a truck, not the Titanic.

I worked on the X-30 project at General Dynamics in Fort Worth. Slush hydrogen was used to get better fuel density. Other things were used for oxidizor (classified then, maybe now) The X-30 was a materials marvel, it could fly through the heat of a volcano. There were rockets at Mach 17+ due to push to space, no air. The problem was the size. Too heavy. Never could get it down. I can't remember the exact fuel eater. We have materials that can take re-entry heat that have structural strength. NASP was made of it.

It's not necessarily true that SSTO won't work "because they quit trying." Many ideas need "vicinities" effects to work. For ex., the internal combustion engine was invented before Henry Ford, and even Ford's cars really didn't transform transportation until several things were in place: good rubber for tires; glass; a critical mass of car owners who demanded better (or any!) roads; Kettering's automatic starter; cheap gas (thank you, Mr. Rockefeller); and a host of other technological innovations that made a car worth OWNING. The same is true with scrams and SSTO: the challenges were so great that NASP had to master all at once. I think the program did a whale of a job getting the materials, the computational fluid dynamics (itself a remarkable breakthrough) and the slush hydrogen. Yes, the engine is key. But few engineers I've talked to think it is impossible---just that they haven't quite hit on the best way of doing it yet.

I think SSTO is the ONLY solution to space travel of any sort. Otherwise, there will never be a true "space station" of the "2001" type built.

I didn't say It's not necessarily true that SSTO won't work "because they quit trying.".

My thinking is they (Gov't programs) are incompetent to make it work. Gov't programs can not change gears fast enough to complete the engineering before funding runs out, and we exchange engineering for funding pursuit. When engineering takes a backseat to marketing, there's plenty of opportunity for Feynman's observation about successful technology to creep in:
For a successful technology, reality must take precedence over public relations, for Nature can not be fooled.

SSTO is very hard. The mass ratio is a killer, because after you add the return systems your payload fraction goes to nil. Given, of course, 1990's engineered materials. NASP is an application of the first obvious, air for oxidizer to improve mass ratio. Scramjet and ramjet engines have an extraordinarily high thrust to weight ratio (I've seen claims of 1000:1 for ramjets). But the physics of flying at high speed in atmosphere conspire to create a huge ding in the mass ratio again. It's not a linear relation.It's not optimal for all missions. It's not a one-size-fits-all.

I don't think FR is an adequate debating forum for this, perusing old USENET archives and AIAA papers I can see ample evidence of brighter lights at work on the physics and engineering. If the FEDGOV is going to spend gigabucks on this process I wish they would do it in a way which leverages the efficiencies of capitalism. I will admit I am a fan of TSTO (two stages to orbit). Considering the cost of materials on orbit, I would rather build a space station from discarded rocket boosters than pay to haul them back and forth from orbit over and over again. Lightweight return modules (namely capsules with heat shields) have a plenty good record.

There needs to be an financial incentive to get this going. If we feel it's proper to do as a nation, for Constitutionally supported purposes, then the appropriate thing is for the FEDGOV to get out there and emit the proper perverse incentive, i.e. pay for pound delivered to orbit, pay for person delivered to orbit, pay for surveys, prizes for research and development, etc. Not do the whole enchilada inhouse.

We fully agree on the difficulty. I think NASP was an exceptional program in TRYING to privatize this as much as possible. It basically set up a cartel of half the airfram manufacturers in the U.S. (and Grumman really had no shot to begin with, and Boeing wasn't that interested); and of 2/3s of the propulsion contractors. So they tried to get a "consortium" or cartel of everyone. Then the government backed off a great deal, allowing the contractors to meet the mission requirements.

One of the problems from the get-go was that this was supposed to be an X program, meaning a test program to measure things. But to get the AF to sign on, they had to demonstrate a payload bay door. That added thousands of pounds of weight. A 50,000 design ballooned to 500,000, and that was too big. Most of the experts---private and government alike---think they can beat the thrust over drag at lower weights.

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