Thursday, January 24, 2013

Where Is The Spaceplane?

I started this blog with writing in mind, but I have so much more to say than that, especially on technology and modern space travel. So, today begins the series with my favorite subject, the spaceplane.

The Space Shuttle was great, but it wasn't a spaceplane. The X-37 is neat, but again, more rocket than plane. Ah, but what about Spaceship One and Spaceship Two. They are a nice hybrid, but they can't make it to orbit. What I'm talking about is a real, surface to orbit, spaceplane. Where is it? Why don't we have one and is it even possible to build one? I've spend a lot of time looking into this and doing the research and here is what I have come up with.

There are a lot of proposals out there, but they all are flawed in some way. Plus a lot of people say it can't be done. One of the things I learned a long time ago about aircraft design is that you can't just make it bigger and expect it to fly. So size of the airframe is as of as much concern as weight. One of the fatal flaws so many design have is the reliance on both rocket to orbit and using hydrogen as the primary fuel. Rockets are inefficient and take more fuel and hydrogen, even in liquid form, takes several times the volume as liquid oxygen. Both of these are found in most spaceplane concepts and both increase the needed size of the airframe. For a design to work, these two ideas need to come off the table. Hydrogen may be light and the most powerful fuel, but for a spaceplane the sheer volume it takes becomes an issue. Not to mention the increased strength and engineering the fuel tank requires.

But if it isn't hydrogen, what do you use? Quite simple, if you are ditching the idea of rocket to orbit, and replacing it with a staged vehicle, the first stage is a specially designed jet engine. You use a petroleum based fuel that will work for the jet and the later rocket stage. Same fuel, one main fuel tank, plus the liquid oxygen tank for the rocket stage. We have used it before. The Saturn V first stage used petroleum based rocket fuel with liquid oxygen to get off the ground. So the most powerful rocket ever used did not use hydrogen. Using hydrogen for a spaceplane is a mistake and it's all in the volume.

I have toyed with several configurations that would work for a jet/rocket staged ascent. Unlike the previously mentioned Saturn V or the Space Shuttle, my concept does not involve dropping away any piece of the vehicle. One intact vehicle, surface to orbit and back. The specifics of how the engines would be placed and designed I leave to the engineers, but I've taken my concepts from proven technology. To start with, I based my concept on the SR-71. It is the fastest and highest flying jet aircraft ever built and it is likely that its true operational parameters are still classified and exceed the officially released data. Still, I'm just going off of the official data. It has two very powerful jet engines in a unique and duplicateable configuration. Add to the a well placed rocket or two and you have sufficient thrust from surface to orbit.

To make a workable payload, I have expanded the design by 1 meter in width, which should have negligible impact on the aerodynamics while still giving a passenger cabin approximately the size of a large SUV. It also enlarges the fuel tanks to hold the volume of fuel needed. The additional weight should be offset by improvements in materials, aerodynamics, and engine performance to yield a vehicle with much the same operating parameters, at least as a jet. From the fuel consumption rates of the SR-71, and from the known formulas for rocket launches, using jet power up to a minimum of 80,000 feet at mach 3.5 leaves more than sufficient fuel to reach most any normal orbit, such as the International Space Station.

What is also important to any efficient spaceplane design is to make sure it a hardy vehicle with a very short (as in minutes or hours) turn around after each mission before it flies again. It needs to be built on commercial and military aviation principles and efficiency. Only a vehicle like this is going to make space tourism practical and affordable.

So, back to the answer I originally posed, where is the spaceplane? It is lost in misguided efforts that have not made substantial progress because the engineering needed to achieve them is too great. We need to be looking at what works. Fuel efficiency does not mean you are using the right fuel. There are other considerations. Size is also an issue. The reason I'm proposing this idea to start with is because the size is manageable and it can be used to perfect the technology and gradually scale up the concept into something that can hold as much cargo as the Space Shuttle. But you have to start somewhere. We could have had this design flying more than a decade ago. Instead we have design after design using hydrogen, often concepts for larger vehicles, that run into the issue with fuel volume.

I see this time and again in all manner of engineering projects, though sometimes they eventually hit on what works. But all too often the concept starts with a flaw and never goes anywhere because of the flaw in the concept, not because of any later problem during development. An ideal case was the Venture Star and its X-33 scaled test bed. The program was scrapped because of a failure to meet the design requirements for its hydrogen tank. The design was sound but when the strict goals were not met, it was cancelled. Even that design could benefit from replacing hydrogen with a petroleum based rocket fuel. It would either allow a sleeker design or more cargo/passenger volume.

Engineers need to keep their minds open to all possibilities. Sometimes taking a look at alternate avenues can provide a solution. Sometimes an abandoned technology may be the solution to a modern problem. In this case, I have highlighted a couple of areas where a 21st century spaceplane can be built using virtually abandoned mid 20th century technology.

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