Top NASA human exploration administrators briefed the Human Exploration Operations (HEO) committee of the NASA Advisory Council (NAC) on March 26, providing an update on development, testing, and preparations for the first integrated flight of the Orion crew spacecraft and the Space Launch System (SLS) rocket. Exploration Mission-1 (EM-1) is currently expected to launch in 2020.
The pacing items for reaching launch readiness, referred to as “critical paths” in the schedule, continue to be construction of the first SLS Core Stage and the first Orion European Service Module (ESM). The agency is targeting the end of 2019 as a target launch date, but both critical path items are running around three months behind that schedule.
Core Stage and ESM still critical path
The first ESM flight unit, Flight Model-1 (FM-1), is being assembled at an Airbus Defence and Space facility in Bremen, Germany. Airbus DS is the prime contractor for the ESM.
FM-1 was expected to be shipped from Bremen to the Kennedy Space Center (KSC) in Florida in April to begin integration with the other major Orion elements, the Crew Module (CM) and Crew Module Adapter (CMA).
KSC is the final assembly and integration site where Orion prime contractor Lockheed Martin puts the whole spacecraft together for launch.
Most of the EM-1 hardware elements are both concurrently in development and under construction, and issues with first-time manufacturing, production, and assembly have slowed down work to fully assemble and test FM-1 before it can be shipped to the launch site. The module is currently estimated to be “on dock” at KSC in June, which would put it a couple of months behind, but recently work has stayed closer to schedule.
“I will say remarkably that they have held pretty much the same delivery date, plus or minus a couple of days now, for four months”, Exploration Systems Development (ESD) Deputy Associate Administrator Bill Hill said at the top of ESD’s presentation to the NAC HEO committee.
“I attribute that to the attention that the ESA (European Space Agency) leadership has paid to this as well as the fact that we’ve now got pretty much all of our hardware boxes there for integration.”
Although not discussed, a slide on the status of FM-1 in the ESD presentation indicated that installations of the hypergolic propellant tanks and Orbital Maneuvering System Engine (OMS-E) are beginning.
Over the last week Airbus tweeted images of the two pairs of fuel and oxidizer tanks and installation of one of them.
The EM-1 Orion spacecraft brings together working versions of all three major elements for the first time; the assembled spacecraft will be shipped to the Plum Brook Station at NASA’ Glenn Research Center in Cleveland, Ohio, to go through a series of first-time development tests before returning to KSC for final launch preparations.
In order to meet the end of 2019 target date, the Orion hardware elements will be assembled and go through checkout testing at KSC before going to Plum Brook.
The schedule which had ESM FM-1 arriving at KSC in April had the full spacecraft going to Plum Brook at the end of the year and returning to KSC in May, 2019.
All of that work in Florida and Ohio is also first-time work and NASA is estimating there is three to four months “risk” to reaching the “ship to Plum Brook” and “ready for final launch preparations” milestones for their target date. Another presentation slide outlined updated scheduled milestones at KSC after the ESM arrives.
ESM structural mate to the CMA is scheduled for July. Mating of the Crew Module to fully assembled Service Module is scheduled for December. Shipment to Plum Brook is currently scheduled for next February.
Similarly, the first SLS Core Stage, Core Stage-1 (CS-1) is under construction at the Michoud Assembly Facility (MAF) in New Orleans, Louisiana. The end of 2019, beginning of 2020 schedule showed prime contractor Boeing completing assembly of CS-1 at the end of this year, when it would be shipped to the Stennis Space Center in Mississippi for a Stage “Green Run” in the first half of 2019.
The critical path in the Core Stage schedule remains assembly and integration of all the hardware in the engine section. The schedule had completion of the engine section in May, but Hill said work there is behind.
“We are still struggling a bit with the engine section,” he said. “We recently had an issue with contamination in our tubes within there. We believe we’ve turned the corner on that and understand it. We have those tubes cleaned and so we’re looking there to find further mitigation to getting the engine section done.”
Managers are frequently looking for ways to mitigate schedule delays by coming up with ideas for completing the remaining work faster. “On the schedule today it still says ‘May/June’ but we’re projecting it may be August, so that’s a couple of months risk and we’ll see how that works out,” Hill explained.
For the Green Run, the stage will be bolted into the B-2 test stand at Stennis and go through a series of tests culminating in a eight-minute long, flight-duration test firing of the four RS-25 Core Stage engines.
The engines are one of the only flight-proven elements and the test will be focused on validating the performance of the new stage and its elements, such countdown and launch sequencing, propulsion system operations, thrust vector control, and avionics and software.
Hill noted that another watch item for the schedule has to do with the ground side of the Green Run. “We’re also very challenged with what’s called the ‘Stage Controller,'” he said.
“The Stage Controller is a hardware/software package that will run the B-2 test stand at Stennis and conduct the Green Run from the facility side. They have been challenged now for the better part of a year and half and we’ve been working with [the SLS Stages Office] to mitigate that [schedule risk] as well.”
After a period of post-test refurbishment in the test stand, CS-1 will be put back on the Pegasus barge for the trip to KSC, where it was expected to arrive in June, 2019, to begin launch preparations. NASA is estimating there is also three to four months risk for the Core Stage to reach its “ready to ship to Stennis” and “on dock at KSC” milestones.
The agency is maintaining the end of 2019, beginning of 2020 EM-1 target date for now, along with its caveats. “EM-1 launch date is no earlier than (NET) December 2019 and represents a time frame that anticipates a majority of the hardware will be ready for final launch integration and flight,” one of the presentation slides to the NAC HEO committee says, adding that “schedule risk of 3-6 months exists and could result in June 2020 launch.”
SRB Throat Plug debris concern
The majority of last week’s briefing was an overview of EM-1 preparations from an integration perspective. NASA’s ESD organization is based at NASA Headquarters in Washington, D.C., and provides overall integration between the three major programs.
In contrast to the more centralized organization structure for the cancelled Constellation program, the three major programs are managed independently: Exploration Ground Systems (EGS) based at KSC, Orion based at the Johnson Space Center (JSC) in Houston, Texas, and SLS based at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama.
Each of the programs has resources to integrate with its other two partners, but ESD provides the overall coordination between all three. During Constellation, the equivalent organizations were projects directly managed by that now-cancelled program.
The focus of the presentation last week was on loads testing and analysis, but Marshall Smith, ESD Cross-Program Systems Integration Director, also provided another periodic update of the top systems engineering and integration (SE&I) issues being tracked by ESD. An overview of fourteen critical integrated issues were presented, ranging from assembly and testing issues to pad stay time to software development.
The top issue currently concerns an impact risk to the RS-25 engine nozzles during liftoff from pieces of the Solid Rocket Booster (SRB) throat plug that break up and exit the nozzle at booster ignition. The RS-25 engines and SRB nozzles are much closer together on SLS than in Shuttle, where the engines were also canted away from the boosters.
Also known as nozzle plugs, they now have to protect the inside of the boosters from the more severe pressure transients of the four nearby RS-25s beginning when they start about six seconds before SRB ignition.
“If you’ll remember, the boosters actually have a throat plug and that’s to keep the environments, the thermal and acoustic environments from causing any issues with the boosters themselves,” Smith explained. “Because of the proximity of the four RS-25s that are right next to the [boosters] now, you’ve got this kind of pocket where all the heat and acoustics comes from.”
“We actually and went through and improved our design, if you will, for the booster throat plug and in the process when we were doing our QM-2 [full-scale booster] test we had some video and we could see that the booster throat plug — we were actually watching that to see how that broke up — broke up into some pieces that were a little larger than we would like,” he continued.
“And so what happens is, as these throat plug pieces come out…they hit the Ignition Over-Pressure / [Sound] Suppression system, the IOP/SS,” Smith said, referring to the deluge of water sprayed under the RS-25 engines and SRBs while they are firing on the launch pad. “Tons of water…comes out [and] it’s like hitting a concrete wall,” he explained.
“When it hits that, it bounces back and it can hit [a RS-25] nozzle,” he continued. “If it hits a nozzle, that’s going to be a bad day for us. So we are actually looking at two things.”
“We are looking at how we can angle the [sound suppression water] nozzles better so that we get this impact and maybe they bounce away from the vehicle. And the other part is we’re looking at redesigning the throat plug itself. So between those two, we think we can solve the problem. We’re on a good trajectory for that, but it’s definitely something we’ve been working recently.”
In response to a request in the last committee meeting in late November, Mr. Smith spent much of the time providing an overview of modeling, testing, and analysis of loads for Orion and SLS. In addition to the first flight hardware built for the spacecraft and launch vehicle elements, an additional structural test article (STA) twin was constructed for testing prior to the first launch.
The Orion STAs continue their test campaign at a Lockheed Martin facility in Colorado; the “combined stack” of Crew Module, ESM, CMA, Launch Abort System (LAS), Service Module spacecraft adapter cone, and Orion Stage Adapter (OSA) elements are currently undergoing tests together that will cover aspects of both the EM-1 and EM-2 missions, the latter of which will be the first crewed Orion flight. The elements are being tested in different flight configurations to verify and validate analytical loads models.
Likewise, the SLS Core Stage STAs are being tested at MSFC. Testing of the engine section STA was completed earlier this year and the intertank STA is being loaded into its test stand for tests that will start at the end of the summer.
The two remaining STAs for the liquid hydrogen and liquid oxygen propellant tanks are scheduled to be delivered to MSFC in September and October for testing that will begin in early 2019.