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SLS Design ‘Looks Strong’ After Review

August 13th, 2014

NASA’s long-cherished goal of -returning to space with a human-rated vehicle capable of supporting a new era of deep-space exploration is closing in on a crucial phase as the agency’s space launch system (SLS) moves from development toward -testing.

Work underway ranges from assembly of the SLS launch vehicle and pathfinder Orion crew capsule to preparations for test-firing first-stage engines and development of the supporting ground infrastructure for the creation of a 21st-century launch complex at Kennedy Space Center in Florida.SLS design

“We are on track to deliver our hardware to meet the December 2017 launch date today,” says SLS program manager Todd May. “We are preparing to get to critical design review (CDR) late next spring and we have four major components of the rocket that have to go through CDRs over the next eight months or so.” Speaking at the American Institute of Aeronautics and Astronautics Space 2014 conference August 4-7, May noted that the bulk of activity remains focused on test and development of the vehicle’s massive core stage.

“That’s where most of the activity is. We completed the CDR for the core stage last month, five months ahead of schedule, and there are no showstoppers. The design is looking pretty strong,” he said. Avionics are being put through their paces in a systems-integration facility at NASA’s Marshall Space Flight Center in Huntsville, Alabama, and the ninth version of the flight software was “just released a few weeks ago,” May adds. In 2015, the avionics will be shipped to NASA’s Michoud Assembly Facility in New Orleans, where the core stage is being manufactured, and integrated onto the rocket.

“The build-up of structural test hardware and flight hardware at Michoud is going really well. We have got the major machines making the core structure and, as of next week, the fifth and final machine will be up and running,” May says. Developed by SLS core-stage prime contractor Boeing, the tools include the circumferential dome weld tool which performs circumferential friction stir welds to make dome assemblies for the cryogenic tanks and a “Gore” welding tool to undertake vertical friction stir welds. The last tool is the 170-ft.-tall vertical weld center, which has been developed to join barrel panels together. This forms whole barrels for the two pressurized tanks, the intertank, forward skirt and aft engine section. Another machine is the segmented ring tool, which has already made support rings for the first SLS core stage. The rings provide stiffness between domes and barrels.

Three of the five structural test articles needed for the assembly of the hydrogen qualification tank have also been built, and “we have one of the qualification domes ready to go,” May says. “The next thing will be getting into the VAC [Vertical Assembly Center] and rolling these together.” The VAC, also measuring 170 ft. tall, will join domes, rings and barrels together to complete the tanks, or dry structure assemblies. The tool, which is 78 ft. wide, also will perform nondestructive evaluation on the completed welds. “Next, we will do the pathfinder liquid oxygen tank,” May says.

A critical design review of the rocket’s Aerojet Rocketdyne RS-25 engines is also planned for later this fall. “The CDR is actually a misnomer. The engines are already built, so they are considered a constraint to the systems-engineering process for designing the vehicle, but we will validate the interfaces with the vehicle and there are a few other things about them that are different from the versions that flew on the space shuttle. They have a lower limit on inlet temperature and a higher inlet pressure, for example,” May says.

A new controller, derived from the J-2X upper-stage engine, is being developed for the RS-25, along with new software. “We have put the first RS-25 into the test stand at NASA Stennis, and we are waiting for the first controller and its software before starting that this fall,” he adds.

The CDR for the boosters, a modified five-segment space shuttle solid booster, is “in process right now,” May says, while NASA is in the midst of defining the contract for the interim cryogenic propulsion system (ICPS) that will power the Orion multipurpose crew vehicle out of Earth orbit. The ICPS sits atop the main-core stage and forms part of the overall stack that comprises the crew vehicle, a stage adapter, separation system and launch vehicle stage adapter. The propulsion unit, which sits between the two adapters, will be based on a modified 2016 production version of the Delta IV cryogenic second stage with an Aerojet Rocketdyne RL -10B-2 engine. “We have defined our other three major contracts, which represent 97% of the cost of the first flight,” May says.

NASA is also making headway toward the first flight of the Orion on a Delta IV heavy, now scheduled for launch on Dec. 4. The exploration flight test (EFT-1) will evaluate the vehicle and the performance of its heat shield during reentry from a 3,600-mi.-high orbit. “We are finishing the pyrotechnic systems installation and putting the back shelf on the crew module,” says NASA Orion program manager Mark Geyer.

Next steps include loading the ammonia and propylene (for thermal control system), and preparations for stacking the Orion and service module on top of the vehicle. The capsule and service module were united inside the operations and checkout building at Kennedy Space Center in early June and are undergoing electrical, avionics and other tests.

“EFT-1 is much more than just flight test, it is about 40% of the development, demonstration, test and evaluation to get to human flight,” adds Geyer. “About half the software we need to fly people will fly on EFT-1, so all the entry, guidance and navigation software and all the key pyro events will be tested. The avionics are the same, and we will add another string when we get people, as well as a few boxes you only need when we have people.”

Beyond December’s mission, Exploration Mission 1 (EM-1) “is the next big flight on SLS,” May notes. “We are now going through the process of machining the barrel of our welding pathfinder—that’s the last thing we do before beginning the flight vehicle structure.” NASA and Lockheed Martin, prime developer of the Orion, also completed the preliminary design review with the European Space Agency (ESA) on the service module in mid-May. The review, which was delayed last year when it emerged that the preliminary design was too heavy, will be followed by a critical design review at the end of 2015, clearing the way for Orion’s uncrewed first flight in 2017.

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Image Credit: NASA.

Original Author: Guy Norris at Aviation Week
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