Targeted for an unmanned test flight in 2017 around the moon, the first Space Launch System (SLS) will stand 320 feet (97.5 meters) and weigh in at 5.5 million pounds (2.5 million kilograms). Three space shuttle main engines (SSMEs) and two solid rocket boosters (SRBs), both inherited from the space shuttle program, will provide the 8.4 million pounds (3.8 million kilograms) of liftoff thrust necessary to propel the rocket's lower stage, interstage and six-person Orion Multi-Purpose Crew Vehicle (MPCV) into space. Imagine a tube taller than the Statue of Liberty, weighing as much as 24 fully loaded 747s and kicking out the horsepower equivalent of 13,400 locomotives, and you begin to get the picture.
At build-out, the SLS will tower an additional 80 feet (24 meters) and tip the scales at another 1 million pounds (450,000 kilograms). It will sport two additional RS-25 engines on the lowest stage, and a new upper stage will carry the J-2X, an updated version of the rocket engine that thrust Apollo's Saturn Vs into history. This taller, beefier SLS will boast rocket boosters that might burn solid or liquid fuel. Altogether, these lifters will churn out 1 million extra pounds (450,000 kilograms) of thrust, which will translate into 130 metric tons (286,000 pounds) of cargo lifting capacity -- nearly double that of the first SLS to be built, and 109 percent of the lift capacity of the Saturn V. Hauling all that extra cargo calls for some extra trunk space so, instead of an interstage, the late-model SLS will be spacious enough to carry nine school buses.
By design, the SLS will undergo component and equipment changes throughout its operational life span. In part, this is because it was conceived as a modular, multipurpose craft, reconfigurable according to mission requirements, but it's also because NASA is required by Congress to initially rely on shuttle vendors and incorporate leftover space shuttle components, such as the reusable SSMEs and SRBs. Later, they will be replaced by disposable engines and a five-stage booster rocket originally designed for the Constellation Program.
NASA plans to use the early, smaller version of the SLS to ferry cargo and astronauts to low-Earth orbit, primarily to service the International Space Station. Later configurations might support missions to space beyond Earth orbit, including missions to the asteroid belt or Mars.
Impressive? You bet, but as we'll see in the next section, when it comes to politics and multibillion-dollar spacecraft, the devil is in the details.