Take a look at some of the tallest rockets in history, and NASA's latest entry: the Space Launch System to fly in 2017.
Like the Ares I-X and NASA shuttles, the towering Saturn V launched from the Kennedy Space Center in Florida. It stood 363 feet (110 meters) high and remains the most powerful rocket ever built, even though the last one flew in 1973.
The rocket could launch payloads of up to 45 tons to the moon, or 120 tons into Earth orbit. It weighed 6.5 million pounds (3 million kg) fully fueled at liftoff. The Ares I-X weighs 1.8 million pounds (816,466 kg), slightly less than the full Ares I rocket.
That last Saturn V was a modified version that launched NASA's Skylab space station. Smaller versions of the Saturn rocket were used to launch astronauts to Skylab, with the last one — a 224-foot (68-meter) Saturn 1B — launching in 1975 to fly Apollo astronauts to meet a Soviet Soyuz spacecraft during the Apollo-Soyuz joint mission.
The giant rocket stood nearly 345 feet (104 meters) tall, had five distinct stages and resembled a huge, tapering cone that was about 55 feet (17 meters) wide at the base. During launch, it weighed 6.1 million pounds (2.7 million kg) and was envisioned to launch payloads of up to 95 tons to space to send cosmonauts to the moon, according to the Russian space history website Russianspaceweb.com. [Infographic: Moscow's Secret Moon Plan - The N-1 Rocket]
But the N-1 rocket never successfully reached space, despite four attempted launches. It exploded during all four attempts between 1969 and 1972.
The former Soviet Union did have other hefty rockets in its space launch inventory: the enormous D-1E and D-1 variants of the Proton used for the 1968 lunar probe missions and 1971 Salyut 1 space station launch. Neither came close to the N-1's towering stature.
Today, Russia still uses Proton rockets and smaller Soyuz boosters to launch satellites into orbit, though cosmonauts continue to ride only Soyuz rockets into orbit. The country is also developing a new family of Angara rockets.
Standing 235 feet (72 meters) tall, the Delta 4 Heavy made its launch debut in 2004, but suffered a sensor glitch that prevented it from reaching its intended orbit. The problem was promptly fixed. The rocket most recently launched a classified satellite for the National Reconnaissance Office in January.
The Delta 4 Heavy is actually a group of three boosters, each called a Common Booster Core, arranged in a line to give it a three-column look. At least two more Delta 4 Heavy missions are expected on the books for future classified satellite launches, according to Spaceflight Now.
The rocket is capable of launching payloads of up to 24 tons to low-Earth orbit and 11 tons toward the geosynchronous orbits used by communications satellites, according to Spaceflight Now. The Delta 4 Heavy is also touted to be able to launch 11-ton payloads on trans-lunar injection orbit routes toward the moon and 8.8-ton payloads on Mars-bound trajectories, Spaceflight Now has reported.
The first stage of the Ares 1 rocket was built by shuttle solid rocket booster builder ATK, which has since repurposed the design for its new commercial rocket: the Liberty booster.
NASA officials say the SLS is a Saturn 5-class rocket that can also be used to launch cargo, equipment and science experiments to Earth's orbit and destinations beyond. It could also serve as a backup booster for trips to low-Earth orbit, the agency says.
According to NASA, the SLS will have an initial lift capacity of 70 metric tons and will be expandable to 130 metric tons. The first developmental flight, or mission, is targeted for the end of 2017.
On the ground, each NASA space shuttle — there are three today: Discovery, Atlantis and Endeavour — is about 122 feet (37 meters) long from nose to stern and stands 56 feet (17 meters) tall. They have a wingspan of about 78 feet (23 meters).
But in launch position, the orbiter is perched on the side of its 15-story external fuel tank and flanked by two solid rocket boosters. A shuttle on the launch pad measures 184 feet (56 meters) tall from the tip of the external tank down to the aft skirts of its twin solid rocket boosters.
The space shuttle has a 60-foot (18 meter) long payload bay that is 15 feet (4.5 meters) wide. Orbiters can haul large payloads into orbit, making the shuttle the only spacecraft capable of launching massive segments of the International Space Station, which occupied the bulk of the shuttle fleet's flight manifest for more than a decade.
NASA launched 135 shuttle missions since the fleet's debut flight made by Columbia in April 1981. There have been two failures: The shuttle Challenger and seven astronauts were lost just after launch in January 1986 due to an O-ring seal leak in a solid rocket booster that led to an explosion. The shuttle Columbia broke apart during re-entry in February 2003 due wing heat shield damage. Seven astronauts were killed.
After each accident, NASA stood down from shuttle flights to make safety improvements.