The Myth of Air-Launching Space Shuttles: Why Rockets Reign Supreme
When people think about launching a space shuttle, the image that typically comes to mind is a massive rocket blasting off from a launch pad, accompanied by a deafening roar and plumes of smoke. However, there are instances where space shuttles, like the Space Shuttle Enterprise, were transported from one place to another using a modified 747. This question inevitably leads to a series of misconceptions about the capabilities and limitations of these spacecraft. This article aims to clarify the reasons why not all space shuttles were air-launched and explain why rockets are more suitable for the task.
Why the Space Shuttle Enterprise and the Russian Shuttles Were Not Air-Launched
One possible misconception is why some space shuttles, such as the Space Shuttle Enterprise, and their Russian counterparts, which also adopted a similar design, were never air-launched. The truth is much simpler and more rooted in physics.
Let's delve into the reasons why air-launching space shuttles was not a viable option for most of 's Space Shuttle Enterprise, for instance, was primarily an atmospheric test vehicle and was not designed to achieve orbit. It was always intended to be transported using a 747 for ground-based tests and the final approach to landing at Kennedy Space Center in Florida. This was because, under the current design, the Enterprise could never reach the necessary altitude and velocity to achieve orbit on its own.
The Real Challenge of Spaceflight: Velocity
The primary challenge in spaceflight is not about reaching high altitudes, but about achieving the necessary velocity to orbit. In fact, the altitude at which the International Space Station (ISS) orbits is relatively simple for the space shuttle to reach; it's only around 400 kilometers (about 250 miles) above the Earth's surface. What's truly difficult is getting the spacecraft to move at the requisite speed.
To achieve orbit, the space shuttle or any other spacecraft must reach an escape velocity of approximately 17,500 miles per hour (mph) or more. This is a daunting requirement, and it involves not just speeding up, but also climbing out of the Earth's gravitational well. A 747, as impressive as it is, can provide a speed boost of about 500 mph, which is not nearly enough to achieve the necessary velocity for orbital insertion.
Why Rockets Are Unmatched for Orbital Speed and Altitude
The solution to reaching the desired speed is simple: utilize a rocket. Rockets are specifically designed to produce the immense amounts of thrust needed to accelerate a spacecraft from zero to orbital velocity. Unlike a 747, which is primarily a long-range passenger airliner, a rocket is built with one purpose in mind: to carry a payload into space. NASA, as well as its counterparts, turned to rockets for this exact reason.
The space shuttle's main engines rely on an External Tank (ET) for fuel, and the Orbital Maneuvering System (OMS) engines are not powerful enough for reusable missions. In a typical launch, the space shuttle, after leaving the 747, uses its own main engines and OMS to achieve the necessary speed and altitude to enter orbit. The ET cannot be used up and must be discarded, but it significantly aids in reaching the high speeds required for orbit.
Why the 747 Was Never Used for Main Launches
Many might wonder why the 747 wasn't used as the main launch vehicle for the space shuttle. The answer lies in the sheer amount of fuel required for orbital insertion. A 747 cannot lift the massive amounts of fuel needed to provide the necessary thrust for orbital velocity. The combined weight of the fuel, the rocket engines, and the spacecraft itself is simply too much for a 747 to handle. Additionally, the 747 only provides a speed boost that the shuttle's main engines must compensate for to reach the required velocity.
Conclusion: The Irreplaceable Role of Rockets in Spaceflight
In conclusion, the design and operational limitations of space shuttles, as well as the inherent physics of space travel, mean that rockets are an indispensable part of the process. While air-launching might seem like a clever and efficient solution, the reality is that it fails to address the critical need for tremendous speed and altitude. Rockets, with their specialized engines and payload capabilities, are the only viable means of achieving the high velocities required for orbital insertion.
The takeaway from this article is that understanding the physics of space travel and the limitations of different vehicles is crucial in appreciating why rockets reign supreme in orbital launches. While the idea of air-launching seems intriguing, the reality is that it is more complex and less practical compared to the reliable and efficient use of rockets.