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Core stage for NASA’s Space Launch System mega rocket stacked

The first core stage fore NASA's Space Launch System is lowered between the two five-segment solid rocket boosters that have already been assembled on the mobile launcher in the Vehicle Assembly Building's High Bay 3. Credit: NASA

The first core stage fore NASA’s Space Launch System is lowered between the two five-segment solid rocket boosters that have already been assembled on the mobile launcher in the Vehicle Assembly Building’s High Bay 3. Credit: NASA

The core stage for NASA’s Space Launch System rocket has been placed between twin solid rocket boosters on the mobile launcher in preparation for the Artemis 1 mission later this year.

After years of development and delays, including several months because of an anomaly during the final Green Run test earlier this year, the first SLS rocket is finally taking shape inside the Vehicle Assembly Building at NASA’s Kennedy Space Center in Florida.

The first SLS core stage is lifted in the Vehicle Assembly Building's transfer aisle. Credit: NASA

The first SLS core stage is lifted in the Vehicle Assembly Building’s transfer aisle. Credit: NASA

Over the weekend of June 10, 2021, the SLS core was raised from horizontal to vertical in the VAB’s transfer aisle and moved over and into High Bay 3 to be placed between the two already-assembled five-segment solid rocket boosters on the mobile launcher.

“After the core stage arrived on April 27, engineers with Exploration Ground Systems and contractor Jacobs brought the core stage into the VAB for processing work and then lifted it into place with one of the five overhead cranes in the facility,” NASA said in a news release on June 14.

Once Green Run testing at NASA’s Stennis Space Center in Mississippi wrapped up in March, the core was sent by barge to KSC, arriving in late April. Since then, engineers had been preparing the stage for this historic moment.

The core stage, which is in many ways based on the space shuttle’s external tank, is 27 feet (8.4 meters) wide and 212 feet (65 meters) tall. It was assembled at NASA’s Michoud Assembly Facility in New Orleans, which is also where the space shuttle’s external tank and the Saturn 5’s first stage, the S-1C, were built.

An infographic on the Space Launch System and how it compares to the space shuttle external tank. Credit: Derek Richardson / Spaceflight Insider / Orbital Velocity

An infographic on the Space Launch System and how it compares to the space shuttle external tank. Credit: Derek Richardson / Spaceflight Insider / Orbital Velocity

It has five main parts: the forward skirt, the liquid oxygen tank, the Intertank, the liquid hydrogen tank and the engine section.

When fueled, the liquid oxygen tank holds 196,000 gallons (742,000 liters) of liquid oxygen at minus 297 degrees Fahrenheit (minus 183 degrees Celsius) and the liquid hydrogen tank holds 537,000 gallons (2.03 million liters) of liquid hydrogen at minus 423 degrees Fahrenheit (minus 253 degrees Celsius).

The SLS core is lowered between the two five-segment solid rocket boosters in High Bay 3. Credit: NASA

The SLS core is lowered between the two five-segment solid rocket boosters in High Bay 3. Credit: NASA

The engine section has four upgraded space shuttle era RS-25 engines which produce a combined thrust of nearly 1.7 million pounds (7,500 kilonewtons) at liftoff.

When fully stacked with an Interim Cryogenic Propulsion Stage and the Orion spacecraft stack, the Block 1 variant of the SLS is expected to stand 322 feet (98 meters) from the base of the mobile launcher to the top of the launch abort system.

Combined with the two five-segment solid rocket boosters, the liftoff thrust of the rocket is expected to be nearly 8.8 million pounds (40,000 kilonewtons).

Just like the four-segment shuttle-era solid rocket boosters, the five segment motors are designed to burn for the first two minutes of flight. The core stage with its four RS-25 engines will continue burning nearly all the way to orbit — about eight minutes after launch.

The ICPS with its RL10 engine will finish the job of placing itself and the Orion spacecraft (minus the Launch Abort System, which is jettisoned shortly after the boosters fall away) into orbit.

The uncrewed Orion spacecraft will then be sent on a multi-week mission around the Moon to certify it and the SLS for human flight on the next mission, Artemis 2.

Assembling this first SLS rocket atop a mobile launcher inside the VAB started in November 2020 when the first pieces of the five-segment solid rocket boosters were stacked. This culminated in the nose cones of each booster in March 2021.

Now that the core is between the boosters, the next step will be for the Launch Vehicle Stage Adapter, which is basically an interstage, to be added to the top of the core.

From there, the ICPS and then the Orion stage adapter will be installed.

The SLS core is lowered between the two five-segment solid rocket boosters in High Bay 3. Credit: NASA

Credit: NASA

Once the ICPS and Orion Stage Adapter are stacked, likely later this month or early July, a mass simulator for the Orion stack will be added first in order to perform a Modal test — essentially ensuring the stack can actually withstand the various vibrations expected to be imposed on it during ascent.

Once those tests are completed, the pre-assembled Orion stack — which includes the spacecraft adapter, the European Service Module and its encapsulation panels, the Orion crew module and the Launch Abort System — will then be added to the top, capping off the assembly of the first human-rated Moon-bound rocket since 1972.

However, it’ll still likely require several more months of tests and evaluations before the full SLS atop the mobile launcher is rolled to nearby Launch Complex 39B for a wet dress rehearsal and then a launch.

As of right now, NASA is still targeting late November for Artemis 1. However, it is still possible further delays could push this maiden flight into the first part of 2022.

Video courtesy of NASA

Video courtesy of Orbital Velocity

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Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a blog about the International Space Station, called Orbital Velocity.

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