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NASA developed a huge rocket called the Space Launch System (SLS) to launch astronauts to the Moon – and ultimately to Mars. Set to debut in November 2021, the SLS is the most powerful launcher built since the 1960s.
NASA plans to send a man and a woman to the lunar surface by 2024, during the first landing with humans since Apollo 17 in 1972.
Over the past 20 years, astronauts have made routine trips to and from the International Space Station (ISS).
But the Moon is almost 1,000 times farther than the ISS; bringing astronauts there requires a monster rocket.
The SLS is the modern equivalent of the Saturn V, the massive launcher built during the Apollo era. Like Saturn, it is divided into segments, or stages, stacked on top of each other. But the rocket also incorporates space shuttle technology.
The first version of the SLS will be called Block 1. It will undergo a series of upgrades in the coming years in order to be able to launch heavier payloads to destinations beyond low earth orbit.
Block 1 SLS will rise 23 floors above the launch pad, making it taller than the Statue of Liberty.
“It’s really a huge rocket. It’s just breathtaking, ”said John Shannon, vice president and program manager for SLS at rocket prime contractor Boeing. He told BBC News in 2019: “When you see the SLS assembled, you just haven’t seen anything like it since the Saturn V.”
The rocket will launch astronauts into NASA’s next-generation crew vehicle – Orion, propelling it at the speed needed to exit low earth orbit and travel towards the Moon.
How the rocket works
The SLS consists of a giant center stage flanked by two solid rocket boosters (SRBs). The heart houses two large storage tanks: one for liquid hydrogen, the fuel, and another for liquid oxygen, an “oxidizer”, which burns the fuel.
Together they are known as thrusters.
At the base of the center stage are four RS-25 engines, the same that powered the spaceplane-type shuttle orbiter, retired in 2011.
When liquid hydrogen and oxygen are introduced into the engine chambers and ignited by a spark, the chemical reaction produces large amounts of energy and vapor.
Steam exits the engine nozzles at a speed of 16,000 km / h (10,000 mph) to generate thrust – the force that propels a rocket through the air.
SRBs give the rocket extra power to escape the clutches of gravity. These two boosters are over 17 stages long and burn six tons of solid rocket fuel per second. They provide 75% of the total thrust during the first two minutes of flight.
The most powerful rocket of all time?
If we use thrust as a measure, the SLS will be the most powerful rocket ever when flying into space in 2021. Block 1 SLS will generate a thrust of 8.8 million pounds (39.1 Meganewtons ) at launch, 15% more than the Saturn V.
In the 1960s, the Soviet Union built a rocket called the N1, with the aim of reaching the moon. Its first stage could produce 10.2 million pounds (45.4 meganewtons) of thrust. But all four test flights ended in failure.
A future version of the SLS – called Block 2 cargo – is expected to come close to the thrust levels of the N1. But a vehicle called the Starship, developed by Elon Musk’s SpaceX company, is expected to exceed both – producing up to 15 million pounds (66.7 Meganewtons) of thrust. Starship is currently in development, although there is no firm date for its first flight.
SLS in figures
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The rocket will stand 98m (322 feet) large in its initial configuration, or block 1,
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SLS block 1 can send more than 27 tons (59,500 pounds) to lunar orbits – the equivalent of 11 large sport utility vehicles (SUVs)
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A future version of the SLS, called Block 2 Cargo, will be launched 46 tons (101,400 pounds) towards the Moon. That’s 18 big SUVs.
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The SLS will produce 8.8 million pounds (39.1 Meganewtons) of thrust in its Block 1 configuration
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Four The RS-25 engines are located at the base of the center stage; these are the same as those used in the space shuttle
How shuttle technology has been reused
The SLS main stage is based on the outer foam-covered space shuttle tank. This tank supplied three RS-25 engines with propellant at the rear of the shuttle orbiter. Solid rocket boosters play roughly the same role in both vehicles.
But the SLS is a very different beast. A number of components and structures derived from the shuttle have undergone significant design changes due to the different levels of stress that SLS places on them.
As an example of these different constraints, in the space shuttle, the RS-25 engines were tilted up and out of the way of solid rocket thrusters. Moving them next to the SRBs exposes them to more shaking. As a result, every system in the complex section of the SLS engine had to be rigorously tested to ensure that it could withstand vibration.
Why the SLS was built
In February 2010, the Obama administration canceled Constellation – George W Bush’s plan to return to the Moon by 2020. The news came as a devastating blow to workers in five southern states – Alabama, Florida, Louisiana, Mississippi and Texas – where the Nasa human space flight program has funded tens of thousands of jobs.
Some Capitol Hill lawmakers were furious. Richard Shelby, a Republican senator from Alabama, said Congress would “not sit back and watch the reckless abandonment of sound principles, proven track record, a consistent path to success and destruction of our manned flight program “.
As a compromise, lawmakers in affected states insisted on a single super-heavy rocket to replace Constellation launchers canceled by President Obama.
The design of the SLS, which was based on technical studies by NASA, was unveiled in 2011. After work began, delays and cost overruns gave ammunition to critics, who believed NASA should be running. relying on rockets operated by commercial suppliers.
But without significant modifications, no existing thruster has enough power to send Orion, astronauts, and large cargoes to the Moon in one flight. Only the SLS currently has this capability.
A recent surveillance report indicates that NASA will have spent more than $ 17 billion on SLS by the end of fiscal 2020.
But with the rocket’s development phase now complete, the success of a series of eight “Green Run” tests underway on the main stage should pave the way for launch in 2021.
John Shannon, who has been in charge of SLS at Boeing since 2015, explained: “I suspect that once the SLS is in national capacity, it will not be necessary to have another heavy transport vehicle like this during many years. is truly a once in a generation opportunity. “
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