Giving spacecraft a running start on a long rail may significantly reduce launch costs.
Railing toward space. I'm Bob Hirshon and this is Science Update.
The next generation of spacecraft may be much cheaper to launch, thanks to a running start on a horizontal rail up to two miles long. Physicist Stanley Starr of NASA's Kennedy Space Center works on the project. He says that like the third rail of a train track, a rail could provide much of the launch power to an airplane-like craft. That means the craft itself could be much lighter.
If you think about a commercial jet, the jet's engines work the hardest during takeoff. And by assisting that takeoff, we can significantly shrink the mass of those engines.
The craft would take off from the rail like a supersonic jet. Once it reached the upper atmosphere, a more conventional booster would send the payload into space. Starr says the basic technology for the system already exists—it just needs to be taken up a few notches. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Launching a spacecraft or satellite off a rail may sound like a strange step backward in technology. It's certainly more low-key than the rumbling, fiery liftoffs of today's "vertical" launches. And in fact, the rail launch idea doesn't require anything brand-new to work, just significant improvements in existing technologies.
What could be revolutionary, however, are the cost savings. As you heard, the most expensive part of a spacecraft's mission is the launch—the relatively brief journey from the ground to space. To make that trip, the engines have to be powerful enough to get the often-massive craft off the ground, and fight gravity all the way into orbit. With jet engines, powerful means big, and in fact the weight of the engines themselves demands even more fuel and power to lift off. And every extra pound costs a lot of money, mainly in fuel. As a result, launch costs alone for large satellites can run toward $100 million.
The rail launcher concept outsources some of the power, so to speak, to an external device. In one current design, the spacecraft would have two components: a streamlined launcher, which grips the rail around its sides with folded-down wings, and a payload that it carries (the part that's actually going into space). The rail delivers energy (probably electrical) to the craft that helps to get it moving—as fast as Mach 10, or ten times the speed of sound, according to some plans. Then, the spacecraft opens its wings, and uses its momentum and regular combustion engines to shoot up towards the sky. Once it reaches the upper atmosphere, it fires off another engine to put the payload into orbit. Because of the "rail assist," these engines can be considerably smaller than those used in launches today. Meanwhile, the launcher craft returns to land on a conventional runway, so it can be re-used.
There's another advantage to gathering momentum low to the ground: jet engines, like all forms of fire, need oxygen to combust. Conventional airplanes use "air-breathing" engines, meaning they use the oxygen from the air to do so. However, vertical rocket launches can't rely on the air's oxygen, since they quickly shoot up to altitudes with very low oxygen density. So they rely on tanks of compressed oxygen, which are also very heavy. While the new launcher runs on the rail, it remains at sea level, which means it can use oxygen from the air to fire its engines. The craft would still carry oxygen on board for use in the upper atmosphere, but again, it could be much less than what's used now.
Bringing down launch costs would not only reduce expenses for satellites and other technologies we use today; it would also make it possible to perform other space missions that are just too cost-prohibitive right now —including ones nobody has thought of yet.
Now try and answer these questions:
- What is the main concept of the rail-assist launcher?
- Why is it called a rail "assist"?
- What are the advantages of gaining launch speed near ground level, using the rail?
- Why is reducing costs important to space exploration, besides simply saving money?
You may want to check out the October 8, 2010, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: NASA prepares to launch a human-like robot into space, engineers are designing a more efficient system for launching payloads into orbit, why microwaves aren't as dangerous as some people think, and the physics behind the color of clouds.