Space Planes - The Future of Flying

Space planes are a completely different way of getting to space. However obvious, it is necessary to explain what space planes are; planes capable of escaping the Earth's gravitational pull and flying into space.

1.1 Problems with current methods

In a world that is always changing, always advancing and always moving forward, NASA's current space shuttle is not going to be sufficient. Before space tourism is even considered, there must be a way to get there. The shuttle has been in use for over 30 years. It is expensive, and inefficient. In any three year span it would be surprising to see the shuttle leave the Earth more than once, and unheard of to see it go up three times.

1.2 Space Planes may be a solution

Many companies are actively doing research and testing on how to fix this problem. They are working on designs that will limit costs, and increase the ability to make frequent trips to space. One popular idea up to this point has been space planes. Space planes are a combination of an ordinary aviation plane, and a rocket. These space planes are being designed and configured by many different companies in many different fashions.

1.3 Significance of Problems

There are currently people talking about inhabiting the moon. NASA is planning on building a base on the moon. Many scientists believe that as fast as resources are being consumed, in a short period of time humans may need to inhabit the moon just to survive. Others just want to use the moon for tourism. One Japanese company is designing a hotel to build on the moon. While many of these projects have already begun, it is foolish to believe that anything like this will be completed if engineers do not find a better way to travel in and out of the Earth's atmosphere.

2. Space Planes in Detail

It is hard to specifically describe "space planes" because of the fact that they can vary so much from one concept to another.

2.1 Multiple Types of Propulsion

There is no uniform design that must be followed when building a space plane. Every company does it their own way, but the basic idea of a space plane is to be able to climb to the edge of the Earth's atmosphere with regular jet engine and then accelerate vertically with a rocket engine to put it out of the Earth's gravitational pull. There are two ways of doing this. Many space planes like SpaceShipOne and SpaceShipTwo are part of a two vehicle system-the first part being a carrier jet plane that hauls the "shuttle" vehicle up to an altitude appropriate for take-off and the second being a "shuttle" equipped with a rocket engine that is not fired up until maximum altitude is reached (Jackson 2006). The shuttle part of the system is usually very small while the carrier is one of the largest jet planes ever built.

The second way of creating a space plane is a single vehicle that can fly through the atmosphere and then out of the atmosphere into space. These space planes which include the British Ascender are equipped with jet engines to fly through the atmosphere and small rocket engines to give them the push they need once they reach an altitude where burning oxygen in a jet engine is no longer an option.

When it comes down to it space planes are just a way of limiting the amount of rocket fuel that must be carried and burned in each trip to space. If the distance a vehicle must travel is lowered, the energy it needs to make the trip is also lowered.

2.2 Advantages of Space Planes

Cost, efficiency and safety are all believed to be huge advantages of taking space planes into outer space. The current shuttle is a disaster from a financial stand point. According to NASA's own website, the shuttle cost $1.7 billion to build, and another $450 million every time it leaves the Earth (NASA 2005.). With expenses like that is it a bit ridiculous to think space tourism will ever become reality. Likewise, to operate a base on the moon, NASA would need to be capable of making multiple trips back and forth in short periods of time. At a cost of half a billion dollars each, that will not happen.

Companies that have space planes in the works believe the finished products may be able to go into and out of the Earth's atmosphere more than once a week. Many people question how much energy is really saved by launching from the upper atmosphere, but the real question is how much fuel is saved. So little rocket fuel is used because a smaller distance is being traveled and the shuttle is so much smaller and lighter. This makes each launch cheaper and much easier to reproduce. Half of the launch is a regular plane flight that pilots make every day.

Efficiency plays into cost. It is extremely inefficient to launch the shuttle repeatedly in short periods of time because of the enormous cost. With that said, it is not currently possible to launch the shuttle more than once in a year anyways. Too much planning, calculating and figuring must be considered before every launch. It is not reliable enough to send back and forth. Space planes such as the British Ascender will be capable of launching and returning to Earth in the same day (Jackson 2006). Because of the regular plane take off and landing these launches and landings are also much easier to reproduce. Less calculating, planning and preparing has to go into each trip. Think about how many planes leave airports every day. The goal is to recreate that ability with an airplane that will fly into space.

Another problem with the shuttle is its unmatched power. Referring back to NASA's website again, the space shuttle's 3 main engines can produce 37 million horsepower. In comparison, the shuttle uses 37 times the energy that the Hoover Dam produces (NASA 2005). This makes the shuttle very dangerous. Any small failure can be very costly, in dollars and lives. The fact that space planes will be much more similar to the design of a jet airplane increases the safety. The launch and landings are obviously many times safer because of the ability to use a runway. Wings on the space planes will also prevent danger if an engine is to fail. The plane will be able to glide back down to the Earth safely or even return with its jet engines if the rocket engine was to fail.

2.3 Disadvantages of Space Planes

The main disadvantage of space planes is the limits that surround them. Jet engines carry the payload for the beginning of the trip, instantly limiting the size of the payload. While the smaller amount of rocket fuel is an advantage, the inability to carry more useful materials and supplies could be a huge disadvantage. Another limit is the amount of people that one space plane would be capable of carrying. Up to this point, the largest number of occupants that can fit in a single space plane is four in the British Ascender. If space planes are going to be used to go back and forth from Earth to a moon base, their main purpose would probably be to deliver supplies and or people to the moon base. If they are incapable of delivering these supplies, the whole idea goes to waste.

3. The Maks (Russian Space Plane)

The Maks (Multipurpose Aerospace System) is a Russian space plane currently being developed by NPO Molniya. The preliminary design arrived in the 1980s but was cancelled. Recent changes in markets and technology have led to NPO Molniya reopening the project.

3.1 Maks Design and Propulsion

The Maks is a two stage space plane as described earlier. The first stage is an Antonov AN-225 carrier plane. The Antonov is the world's largest airplane ever built (has the highest payload capability) and for that reason has been chosen to carry the Space Stage of the Maks (Bratukhin 1997). The space stage of the Maks is not as set in stone. There are three proposed ideas, which may end up all being built and used. The Maks-OS would be a reusable space stage that could carry a crew of 2-6 members. The Maks-T will be an unmanned version of the space stage capable of launching payloads of 5000kg into geostationary orbit. The final version, the Maks-M would be a fully reusable space plane

capable of landing and launching a second time without maintenance. The Maks will take off from an airport runway and ascend up to 9km above the Earth's surface (Bratukhin 1997). At this point the Antonov will dip slightly down before pulling up hard. As the plane pulls up the rocket engines will be ignited and the space stage will be launched. The first flight of the Maks is expected to happen in 2008.

3.2 Advantages of the Maks

The target of the Maks was to be cheap. NPO Molniya came up with the designs and the prototype to be cheap. That was the one and only goal for this system. The Maks is supposed to be capable of making trips into space at a very low cost. A few things make this very easy for the Maks. Intelligent design of the product allows for it to use an aircraft that has already been created, tested and in production. This means half of the job is done before they ever start. Another cost dropping attribute of the Maks is its ability to refuel from the Antonov AN-225. Once perfected, NPO says that the Maks will be able to refuel in the air from the AN-225 much like many military aircraft are capable of doing. This will mean the Maks-M can go on a mission, refuel and go on a second mission without ever touching back down on Earth (Bratukhin 1997). If this became reality the efficiency of the system would be unbelievable and unmatched.

3.3 Disadvantages of the Maks

As referenced earlier, the biggest disadvantage of all space planes are their limits. The final version of the Maks might only have room for as few as two crew members. The limited size of the payload may be another problem. The Maks is intended to be useful on frequent trips to space for a low cost. The point being that there is no advantage of going back and forth without purpose. The Maks was designed to transport crew and supplies to the ISS (International Space Station). If the Maks system is incapable of carrying a large enough payload it may be a failure. If multiple trips are needed to carry out tasks that formerly only took one trip, the money saved per trip may be exhausted by the extra trips. Another disadvantage of any two stage space plane is the fact that there must be two vehicles operating successfully. While one of them is a plane that is already in production and has proven its ability, it will have to be altered and used for different things that it has in the past. The opportunity for failure is definitely increased.

4. Scramjets

Scramjets (Supersonic Combustion Ramjet) are a whole different concept of space planes. The only thing even comparable between scramjets and the two vehicle space planes is their goal: to reach space frequently at a low cost.

4.1 Design/Propulsion of Scramjets

Scramjets are a very new technology. In fact, a true passenger scramjet has never been built or tested, but many models and prototypes are being designed and tested. According to NASA, a scramjet is an engine that burns oxygen as it passes through the engine in flight (Hughes 2007). This eliminates the need to carry an oxidizer. Similar to a jet engine, which burns oxygen in the atmosphere, much less fuel must be carried by the vehicle.

4.2 Advantages of Scramjets

First and foremost, the advantage of a scramjet is the fact that it does not need to carry an oxidizer, in comparison to a normal rocket which must increase in size as the distance and velocity that it must travel are increased. This allows the scamjet to be much smaller, lighter and/or carry a much heavier payload. Another huge advantage to scramjets is the ability to travel and incredible speeds. Not just orbital speeds when in space, but scramjets may be used for travel on Earth through the atmosphere as well. Currently, the world's fastest plane is the Air Force's SR-71, which is capable of speeds up to Mach 3.4 (2700 mph), these scramjets are believed to be able to reach speeds of Mach 12 (9,000 mph) to Mach 24 (18,000 mph) (Jones 2004). At 18,000 mph the scramjets would be traveling faster than the space shuttle is upon re-entry. This would make them very advantageous for military purposes. Military interest is a huge advantage when it comes to funding and support. Originally it was believed that scramjets would be problematic for the military because the extreme heat that they give off would make them easy to detect. Upon further review, the scramjets have no need to be stealth because at the speed they would be traveling they would be untouchable by anything else on Earth. If need be, any place on Earth could be reached in just over 90 minutes (Jones 2004).

4.3 Disadvantages of Scramjets

Mostly due to the fact that scramjets are such a new idea, the current disadvantages and problems are numerous. One major disadvantage becomes obvious when the propulsion system of the scramjet is more specifically explained. Until supersonic speeds are reached, it is not possible for scramjets to use oxygen flowing through the engine as a fuel. This means that the jet must be carried to supersonic speeds by another vehicle, or have an alternative jet engine to take it to that speed before transferring to the scramjet. Another problem arises before a scramjet can make it into orbit, it will need another (possibly third) engine to exit the pull of the Earth's gravity. Many "disadvantages" of scramjets are theories because a lot of it has not been tested, other disadvantages (or advantages) could come up as research continues.

5. The Future of Flying

The future of flying whether it be within the Earth's atmosphere or space travel may very well revolve around space planes.

5.1 Reasons to Change

The reasons to find a solution to these problems are obvious, people want to make advancements in space, and some day the human civilization may rely on possibilities of life on a different planet or the moon. If civilization is ever to come to that, I would hate to see us fail because of a lack of research and development in an area where there were multiple solutions available.

5.2 Best Choice

There may not be a better solution in this case. The different vehicles are built to solve the problems in different ways. It is too early to know for sure which will be the most effective and efficient. Research needs to be continued on both until a clear cut winner is produced.

5.3 Importance of Solution

As of right now, this problem may not seem that important. The shuttle has been used for over 35 years and it is still capable of doing almost everything it is asked to do. This is a problem of the future that will only grow in importance as time goes on.

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Jackson, Thomas A. (2006) Power for a Space Plane. Scientific American.

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Professional Engineering. June 13^th 2007.

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