Most media sources stated that the fallen pieces were from a Russian SL-4 rocket. The SL-4 designation was accepted by the United States and other countries for the Soyuz family of launch rockets when the USSR (Union of Soviet Socialist Republics) kept its naming system a secret from the Western world—before the Cold War ended. However, today, a more accurate description for the object that streaked across the sky above Wyoming is: pieces of a spent upper stage of a Russian Soyuz-2.1b rocket.
As first written on December 28, 2006, in the ITwire article “Exoplanet search begins with French launch of Corot telescope satellite”, the spacecraft Corot, on December 27th, was lifted into space by Russian launcher Soyuz-2.1b from the Baikonur Cosmodrome in Kazakhstan. Eight days later it was reported by the world news media that pieces of a spent Russian rocket, which launched the Corot telescope satellite mission, streaked across the sky and impacted in Wyoming.
In summary about the Corot mission, the French Corot spacecraft, which was launched into space by the Soyuz-2.1b rocket, is the first-ever spacecraft to be dedicated to the study of planets outside of the Earth’s solar system, what are called exoplanets. After a successful launch, the Corot telescope satellite is now in its polar orbit with an average altitude of 896 kilometer (887-kilometer by 915.8-kilometer orbit with an inclination of 90.03 degrees toward the equator). Additional information about the Corot satellite and its mission can be acquired at: http://www.esa.int/SPECIALS/COROT/SEMMY0D4VUE_0.html.
The Russian vehicle Soyuz-2.1b had its initial flight with the December 27, 2006 launch of the French Corot satellite. It is an expendable three-stage launch system. The first stage of the Soyuz-2.1b consists of four identical conical liquid booster rockets, and the second stage has one cylindrical rocket. However, what is unique about the Soyuz-2.1b is its new third-stage.
The Soyuz-2.1b contains a new RD-0124 engine for its third stage, what is called an Improved Block I, based on the Block I engine (RD-0110). The RD-0124 engine possesses a height of 2.327 meters (7.635 feet), diameter of 1.470 meters (4.823 feet), thrust of 294 kilonewtons (66 kilopounds-force), estimated specific impulse (by weight) of 359 seconds at liftoff, and a chamber pressure of 16.2 megapascals (2,350 pounds per square inch). The third stage, itself, possesses a length of 6.7 meters (22 feet), diameter of 2.66 meters (8.73 feet), gross mass of 25.2 tons (55,600 pounds-mass), propellant mass of 21.4 to 22.9 tons (47,200 to 50,500 pounds-mass), and dry mass of 2,355 kg (5,190 pounds-mass).
The RD-0124 engine possesses a new closed-cycle system, which redirects oxidizer gas back into the combustion chamber after driving the engine pumps, rather than being wasted when dumped overboard. Such an improvement in performance adds over 900 kilograms to the payload capacity. It also contains a new all-digital flight control system with terminal guidance system.
So far, NORAD and the U.S. Northern Command have not discovered any extensive damage from the pieces of the spent upper stage of a Soyuz-2.1b rocket that hit the ground near Riverton, Wyoming. NORAD does not believe that any hazardous materials were contained in the rocket debris, although caution should always be maintained if coming upon unknown debris in the Wyoming area.
Note: Statistics come from Wikipedia.com and the International Reference Guide to Space Launch Systems, Third Edition, Iaskowitz, Hopkins, and Hopkins.
