JOHT 9: Going Ballistic

[stickmaker]

The Joy of High Tech

by

Rodford Edmiston

Being the occasionally interesting ramblings of a major-league technophile.

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. And if you find a mistake, please let me know about it.

Going Ballistic

Supersonic transports are in the news again, as they seem to be every few years. Many researchers are working on Mach 1+ cruise aircraft, including for the next Air Force One and Air Force Two. However, some aviation prognosticators are stating that in order to be worth the research money required to create them, new airliners must fly faster than Mach 3. The consensus is that this sort of performance is required to make them desirable over improved versions of existing planes. Well, the prognosticators are wrong. Not about the economics of the situation, but about going from current speeds and altitudes for civilian transport aircraft to Mach 3+ at 25,000 meters or more being a significant jump. That is merely an extrapolation of current conditions. Indeed, such developments are actually behind predictions of the sixties, which said we would already be flying Mach 5 airliners by this time. 

The real "quantum jump" (following the popular usage rather than physics terminology) would be a suborbital transport. These could take off at any one place on Earth and land at another in about an hour. To do this the vehicle has to boost out of the atmosphere and take a suborbital ballistic path.

Purely ballistic manned suborbital flight has occurred, but rarely. In fact, the only examples I can think of offhand are the early Mercury flights, which used a smaller booster than the one which carried John Glenn into orbit in the same type of capsule. This sort of flight is not very efficient, at least in terms of energy. Still, it is the fastest way we know to get from one place to another on Earth, barring trains running in evacuated tubes under the Earth's surface at similar velocities. With a rocket launch, a ballistic suborbital flight, atmospheric re-entry and a rocket landing (perhaps aided by parachute) a flight form New York to Tokyo would take a bit over an hour, ground to ground. 

This is not a new concept. During the Second World War, researchers evaluating ways of improving V-2 (model number A-4) rocket altitude and range performance noticed something interesting; put wings on it and the range could be greatly extend. This led to the A-9/A-10 proposal, which would have essentially put a winged V-2 on top of a booster, resulting in a maximum range of 5000 kilometers, in contrast to a bit over 300 km for the basic V-2 with the same payload. This projected range would have allowed targets on the eastern seaboard of the US to be hit from Europe. Some tests were made and some plans drawn, but nothing practical came of the idea. The biggest problem with the concept was that the payload was limited to the same 1000 kilograms as for the V-2. Without nuclear explosives or radiological packages or some devastating biological weapon, what was the point?

Later in the war, Austrian engineer Dr. Eugen Sanger and collaborator Dr. Irene Bredt authored the "Sanger-Bredt Report." This outlined the idea for a craft which could take off from Germany, bomb a site in the US, and land on the other side of the world two and a half hours later. This "antipodal bomber" would have been huge vehicle at launch, carrying a relatively small bomb load. Aiming accuracy would have been a major problem, but it was technically feasible. There were other problems, though; for instance, the antipodal options for Germany were primarily Australia and New Zealand, both Allied territory. 

In spite of these problems the Antipodal Bomber (the term was soon capitalized) made a lot of converts. By taking off and accelerating to 6000 meters per second it would reach an altitude of 162 kilometers, then drop down to 40 km some 3500 km downrange. Whereupon it would bounce off the denser lower atmosphere (well, dense in comparison to the "air" at the peak of the flight) and rebound to an altitude of 125 km. Another 2500 km and it again would hit bottom and bounce back up, again not quite as high as the previous peak. On the third bounce the bomber would have been over New York. After the ninth bounce the craft would go into an extended hypersonic glide for perhaps six thousand kilometers, then descended for a conventional landing. 

Increase the maximum velocity to 7000 mps and the craft would go all the way around, landing back where it started... just 3 hours and 40 minutes later.

Now, this is a simple concept but a bit inelegant. All that bouncing... So, in 1949, Dr. Hsue-shen Tsien of the California Institute of Technology developed an alternative plan, using a flight from Los Angeles to New York as his example. The craft would boost in a steep climb for 150 seconds, coast to a peak of over 450 kilometers, re-enter the atmosphere some 15 minutes later and some 2000 kilometers downrange, level off at 43 kilometers and glide for another 2800 km. Total time, ground to ground, a little over an hour. The trip works just as well the other way. 

The difference here is that gliding without the bounce is less efficient, since more of the flight is spent actually flying; that is, moving at high speed in the upper atmosphere, subject to air drag. Of course, if the craft is optimized for high-speed, high-altitude gliding the difference is reduced. 

These flight plans work for two reasons. You see, there is very little drag at 43 kilometers. Also, when calculating the glide range for supersonic vehicles, you multiply the conventional lift-to-drag (L/D) ratio by the Mach number to estimate the range. Since suborbital bodies re-enter at about Mach 12...

There have been many proposals for suborbital shuttles, ranging from military sortie vehicles to passenger craft. These concepts also range from purely ballistic, all-rocket vehicles to hypersonic aircraft with rocket boosters. 

A few years ago I designed (strictly on paper, so take my numbers with a very large grain of salt) a series of supersonic and hypersonic aircraft, two of which were intended as homebuilts. That is, they could be built in a home workshop by unusually talented builders. One of those, the Forerunner III, had a top speed of over Mach 6. Given a design cruise of thirty minutes, it was subject to considerable aerodynamic heating. I therefore included an active cooling system, using water transpiration through porous ceramic. I got the idea for this from an old report on tests of this idea for use in intercontinental ballistic missile warhead protection. Which meant that I now had an aircraft which - with some modifications - could survive re-entry. 

The Forerunner III used liquid methane (or liquefied natural gas, aka LNG) for fuel, and included liquid oxygen for low-speed operation of the airturboramjet (ATR) engine. LOX/liquid methane (or LOX/LNG, pronounced "lox-ling") has an efficiency only slightly worse than that of LOX/LH2 as a rocket propellant combination. Among other changes, I replaced the existing single-engine underbody nacelle with a larger one containing two ATR engines, extra fuel and oxidizer... and a small LOX/methane rocket engine. 

The basic aircraft could reach Mach 7 at 30,000 meters. That gives about 2000 meters per second initial velocity. Adding another 3000 meters from the rocket gives a suborbital hop of 3100 kilometers. The plane can then level off at 43 kilometers and glide for another 7000 kilometers. Then it descends, the ATR are restarted, and the plane flies to a standard airport. The craft would be about the size of a small business jet and carry two people (pilot and passenger). Anywhere in the world. In a couple of hours. Not counting time spent waiting in the pattern at your destination airport. 

Aside from the joyride aspects, is there sufficient financial justification for building a ballistic transport? Oh, yes... Enough that several groups have developed serious business proposals around such vehicles. 

There are many instances of companies keeping multi-million dollar helicopters on hand to ferry an important person or part to a construction project if something breaks. An all-rocket suborbital craft has similar vertical takeoff and landing characteristics, but with many times the range. Yes, it also costs many times as much as a helicopter. However, what if a broken part has to be shipped from Los Angeles to Sidney (over 12,400 kilometers)? Shipping that part by standard air express services would take two days, and for each hour of that time your machines aren't earning the $7000 they are supposed to, while expenses mount and contracts fall further behind. What sort of premium would you pay a shipper who can get what you need where you need it in one hour instead of 48?* 

I'm not saying that we shouldn't develop supersonic - or even hypersonic - transports. For distances under 5000 kilometers the time difference between traveling at Mach 5 and going suborbital isn't all that great. For longer distances, though, there's a great deal of money out there to be made in fast transport of people and packages. Also, how many folks rode the Concord just to say they had? All we need to do is find someone willing to pay the development costs.

*This is taken from an example given in Halfway to Anywhere by G. Harry Stine, a book on the technology and economics of spaceflight, a work which I recommend. 

Comments

[kengr]

You remind me of the Space Cub proposal. A single stage VTOL rocket that could carry a pilot and few (2-3?) passengers to orbital *altitude* (not orbital velocity)

Cross range capability was around a thousand miles (or it may have been km). Flight time would be under an hour (more like 45 min as I recall)

And landing takeoff was supposed to be doable from a simple pad. Asphalt woudn't be a good idea, but concrete would be ok (again from memory). So an "altered" parking lot would do.

Anyway, someone pointed out that outfits like FedEx would be all over them. Delivery that package up to a 1000 miles in an hour? Oh yeah.

Heck de-rate the Delta-X and you could probably do the same.

Trivia: The Spindrift in "Land of the Giants" was a suborbital shuttle.

They bounce method would work fine for cargo (and some passengers). For regular passenger service, you'd need the ballistic version or the hybrid jet/rocket model.

Maybe we can get the military interested in a "anywhere in an hour" version of the C-131 or the C5A?

As I recall, the work on hypersonic air-breathing engines isn't quite up to what would be needed for a civilian passenger liner.