Pegasus Rockets
Published on Apr 12, 2007 at 12:57 pm.
1 Comment.
Filed under rockets.
In a couple of weeks, NASA plans to launch a satellite to study the highest altitude clouds of Earth. This launch will be on a Pegasus rocket. The Pegasus, produced by Orbital Sciences Corporation, was the first privately produced commercial launch vehicle for putting payloads into low Earth orbit. With the first launch being April 5, 1990, Pegasus has had a wonderful track record, having made 37 launches, 34 of which were successful.
The Pegasus rocket is an interesting launch platform.  Pegasus is 17.6 meters long and 1.27 meters diameter. The rocket is fitted with wings having a span of 6.7 meters. It can carry a payload of 443 kilograms. The normal way to launch a rocket is to launch it from the surface of the Earth. Pegasus, though, is actually carried about 12 kilometers high by a converted L-1011 aircraft. The parent aircraft then drops the Pegasus. A few seconds later, the rocket’s first stage engine, a solid fueled rocket, ignites. For the first part of the flight, the engine propels the rocket forward and upward. Some lift is provided by the small wings on the Pegasus (which looks at first glance very similar to a cruise missile, only slightly larger than most). About the time time that the first stage is exhausted, the rocket is high enough for the wings and fins to provide little lift and control. By the time that the second stage is exhausted, the rocket is at such a high altitude that it is basically in a vacuum. The third stage puts the payload into orbit. A fourth stage can be added, if needed, to achieve a higher orbit.
An advantage that Pegasus has over traditional ground launched rockets is that there is no need for a permanent launch facility. The carrier aircraft is easier to maintain than a launch pad. Furthermore, a Pegasus can be launched from pretty much anywhere the paying client wants (though it is preferable to launch over open ocean for safety purposes). A fixed launch pad, of course, is limited to one launch location. Furthermore, the aircraft does the work of lifting the rocket the first 12 kilometers, meaning that the rocket itself needs less propellant and mass to go the rest of the way. This also saves money.
Overall, it is quite a good idea, and it has proved itself valuable for both commercial satellites and for government science missions. This is currently the best launch vehicle for lightweight low Earth orbit satellites, so NASA is contracting to use it to launch the AIM mission (Aeronomy of Ice in the Mesosphere) in a couple of weeks. However, there are a number of other companies working to produce their own lightweight launch vehicles, so soon Pegasus is going to have some competition.
-Astroprof
Images courtesy of Orbital and NASA
Astroprof’s Page » AIMing at Earth on April 26, 2007 at 1:10 pm: 1
[…] Well, that is an ominous sounding title. No, I don’t mean that alien space battlecruisers are aiming destructor beams at Earth. Rather, I am refering to yesterday’s launch of the Aeronomy of Ice in the Mesosphere (AIM) spacecraft aboard a Pegasus XL rocket. […]