Since the retirement¹ of its shuttle fleet in 2011, the U.S. space agency NASA has had to rely on Russian space vehicles to carry astronauts to the International Space Station. In the meantime, NASA’s engineers are developing components² of a new system for launching manned capsules way beyond the low earth orbit - to an asteroid³ and even to Mars.

At NASA’s George C. Marshall Space Flight Center in Huntsville, Alabama, engineers are preparing for a crucial test of a booster engine that will help the main rocket escape the earth’s gravity. The agency says it's the largest booster ever developed for a manned spacecraft.

The Space Launch System, or SLS, consists of a main rocket and two solid-fuel boosters. It will propel the new manned capsule Orion into deep space.

During liftoff the engines create so much noise that the sound waves can actually damage the payload.

That is why other NASA engineers are testing a water-based sound suppression system on a scaled-down model of the launch vehicle.

“Past experience has shown that without this scale model testing, there could be not only problems with the design loads, with the environment, components could fail," said Space Launch System engineer, Douglas Counter. "So this is very critical.”

At one of the indoor laboratories, engineers are assembling components of the system that will integrate and control all parts of the rocket.

“This is essentially⁴ the brain and nervous system of your rocket. The flight computers are your brain," said Space Launch System engineer Curt⁵ Jackson. "The various data systems, the various sensors⁶, data from the different boxes -- kind of like your nervous system -- flow to the brain.”

Congress has not yet approved next year’s budget for NASA so the agency is trying to save money by relying on unused components, like the RS-25 rocket engines, built for the retired⁷ shuttles.

“We've got 16 RS-25 engines left over from the shuttle program," said engine test project manager Gary Benton. "And, since the engine was highly reliable and reusable, we're able to take these engines and use them for the first four flights of SLS.”

The rocket test stand in Mississippi, was built in the Apollo era, but project manager Richard Rauch says it was designed to be flexible for testing various engines.

“What we're doing is re-purposing some of that old hardware -- some of that structural⁸ hardware -- a lot of the propellant and cryopiping, to make it adaptable⁹ to what's required for the SLS core stage,” he said.

At another site in Louisiana, workers have already started welding sections of almost a 100 meter long main rocket. Engineers from NASA and the main contractor¹⁰ Boeing had to design huge welding tools.

NASA says the new Space Launch System is being designed to be flexible for both crewed and cargo¹¹ missions. Testing of the core stage will begin in 2016 and the first launch is planned for 2017, though no astronauts will be on board.