National Aeronautics and Space Administration

Glenn Research Center

Dr. Thomas Benson

Hypersonic Propulsion

June 27, 2007

Dr. Benson delivered a dynamic presentation on the topic of propulsion systems and vehicles that reach hypersonic speeds. He highlighted some of the main issues in technology and engineering that are centered on weight, aerodynamics, and air-breathing propulsion systems (RAM and SCRAM jets).
According to Dr. Benson, the idea of the current shuttle and rocket system is very inefficient. The current system is comprised of 90% fuel, 10% structure and about 1% payload. In essence it cost 10K to transport 1lb of payload to lower earth orbit, LEO.

To put this into perspective, a gallon of water is 80K. The existing trajectory of the space shuttle is to launch from a vertical position and maintain this path until it exits the atmosphere. This current trajectory is the reason for the large amount of fuel. However, when considering air-breathing vehicles, the path of the vehicle plays a major factor in the heat, aerodynamics, and fuel of the vehicle. As a result engineers and scientist are considering a horizontal and gradual trajectory for the vehicle. This design reduces the amount of fuel that is needed for the flight and Dr. Benson suggested this reduces the size of the vehicle dramatically. However, this idea harbors engineering problems of its own, specifically topics of heat transfer and expansion. Choosing certain materials are very important for this kind of flight because of the substantial heat stress and expansion.

After Dr. Benson presented the main fuel and cost issues that surround the current space shuttle, he explained the strong need for a air-breathing vehicle. The main issues of heat transfer and expansion separate engineers from their goal of a efficient 1 stage space vehicle. The idea of an air breathing propulsion systems is not new to NASA. They were heavily investigated during the mid 60’s and 70’s, when the idea of traveling above Mach 3 were on the forefront of NASA’s vision and goals.

Today, NASA along with aerospace companies is making great strides in engine development that is essential to the development of such vehicles. Among the air breathing engines that are being developed is a SCRAM jet, which is a spin off of the existing RAM jet. The concept behind both vehicles is to compress air entering an inlet nozzle and exploding it out of the exiting diffuser. Even though RAM jets are already in existence, there are a lot of developments and improvements that needed in order to apply the concept to the topic of space travel.

—Larry Bernard Murphy