With just over two years to go until the rocket’s maiden launch, Charlie Blackwell-Thompson, NASA’s launch director for the first Space Launch System (SLS) mission, has provided an extensive overview of the preliminary plans of the rocket’s debut countdown, including its Wet Dress Rehearsal (WDR) milestone on Pad 39B.



SLS Debut:

The SLS will launch NASA’s Orion human exploration spacecraft on a three-week trip to orbit the Moon on the Exploration Mission-1 (EM-1) mission; the current schedule is targeting launch towards the end of 2018.

Ms. Blackwell-Thompson – who will be in charge of launching SLS – provided an overview to NASASpaceflight.com of some of the testing and operations involved in that first launch campaign, which will bring together the new SLS launch vehicle with a new version of the Orion spacecraft, and new and updated launch facilities and support hardware currently under construction at the Kennedy Space Center (KSC) in Florida.

In parallel with the development of the Orion spacecraft and SLS launch vehicle, the Ground Systems Development and Operations (GSDO) Program at KSC is itself busy working on all the services necessary to assemble, checkout, and launch Orion and SLS.

In addition to preparing facilities such as Launch Pad 39B and Vehicle Assembly Building (VAB) High Bay 3 and support hardware such as Crawler Transporter-2 and the Mobile Launcher, GSDO is working on the procedures and automation necessary to prepare and launch SLS with Orion for the first time on EM-1.

Although planning for the first SLS/Orion launch countdown is well underway, Ms. Blackwell-Thompson cautioned that it is still under development.

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“Our launch countdown right now is just under two days long, and of course, that will change — there will be some ebb and flow as the vehicle and the systems mature and we understand the work,” she explained. “Based on the requirements that are on the books today, we sit at just under 46 hours long in launch countdown — it’s actually 45 hours and 40 minutes long.

“We have two holds in the countdown; we have one prior to tanking where we’ll go and we’ll make sure that we’re ready to commit the vehicle to cryo load, and then we have one at T-10 minutes — that hold is 30 minutes long.

“I would liken it to the T-9 minute hold in Shuttle where you do your polls and get your final launch window determination and ensure that you’re ready to pick up with the terminal portion of the count.”

As launch director, Ms. Blackwell-Thompson will oversee countdown activities with the launch team from Firing Room 1 at the Launch Control Center, located adjacent to the Vehicle Assembly Building.

As she noted, on launch day, during the final planned hold in the countdown, she will poll the launch team and mission managers to verify that they are ready to proceed and then give the final direction to pick up the countdown for launch.

Ms. Blackwell-Thompson is a firing room veteran, having served in the NASA Test Director position on the launch team during several Shuttle launch countdowns at the end of the program and as Assistant Launch Director for STS-133.

In the interview, she provided a high-level overview of launch countdown activities for the launch team:

“The layout of the countdown is Day 1 we have call-to-stations, we have our Orion power-up, [we] get the comm system checked out, [and we get the] GNC system — the [spacecraft] navigation system — checked out. In parallel with that, we’re working our preps for cryo load.

“We have some preps in the [propellant] storage area that we go and do, we also do our pneumatics checkout, we have engine preps that we’re working. Somewhere after we get all of that work done, we begin to look at our pad configuration — any hand rail removals, positioning of the flame deflector, moving the Engine Service Platform — getting that down and away to the launch position, [and] getting air to GN2 [purge] changeover so we can get inerted prior to cryo load.”

“One of the differences from Shuttle is that the cryo loading operations are quite a bit longer and we have a way in which we have to stagger the load just based on the configuration of the vehicle,” she continued.

“So we start loading just under eight hours prior to launch, and so we’ll get through cryo load and then once we come out of cryo load we have…a little over two hours worth of work to do.

“Obviously, we don’t have a crew on this mission, so we can have a very streamlined countdown after we get the vehicle tanked. We have some range safety checkouts, those take about 90 minutes, and then once we finish up those checkouts we’ll work our way down to the hold at T-10 [minutes].

“Then we have a 30 minute hold and then we’ll pick up the count at T-10 and we’ll count down to T-0.”

As with Shuttle, there will be a Ground Launch Sequencer (GLS) automatically directing the terminal countdown in concert with the SLS flight computer on the launch vehicle.

“Certainly, we’ll have a GLS that will be sequencing all of the work down to when we hand off the on-board [vehicle] sequencer,” Ms. Blackwell-Thompson said.

Another similarity to the Shuttle launch process is a series of GLS milestones, where the terminal countdown can be held for a short period of time if there’s a problem and then continued if that problem is resolved without the need to recycle back to the start of the automatic sequence.

“We have milestones all along [the terminal count], some of them are similar to what we had with Shuttle, some of them may be a little bit different,” she explained.

“We pick up at T-10, down about T-6 [minutes] the crew access arm comes back, we start [Core Stage] APUs somewhere around five [minutes], we terminate replenish, pressurize the tanks, [and] the ‘Go for ALS’ [the launch vehicle sequencer] is at T-33 seconds.”

ALS stands for the “Autonomous Launch Sequencer” in the onboard SLS flight software. After the “handoff” from the GLS to the ALS; the GLS will continue verifying some critical events and issuing some commands, including the familiar ‘Go for Main Engine Start,’ which is planned at the same T-10 second point in the count.

Start commands for the Core Stage RS-25 engines will be staggered by the same 120-millisecond interval used in Shuttle, with the first start command coming at T-6.36 seconds and the engines started in a 1-3-4-2 sequence. After the engines are started, assuming the whole vehicle and spacecraft are ready, the SRBs are ignited at T-0 to commit the vehicle to flight.

As currently envisioned, the launch team working in the firing rooms will be smaller.

“We underwent a pretty significant study as part of our launch team determination. We looked at what the work was in launch countdown, what the requirements were, how many LCCs (Launch Commit Criteria) that you might have, and took a pretty complete look at what the workload of say a team or an individual would be,” she explained.

“The folks that actually will sit in the room are very much a part of determining that, because they’re the smartest folks on [determining] what it takes to get the work done, and they’re the systems engineers.

“Right now, the team in Firing Room 1 sits at about ninety-one people — that number I think will change, it may get bigger, it may get smaller, but right now it’s ninety-one.

“If you compare that to Shuttle, in the prime firing room we had about two-hundred folks and over in Firing Room 2, which was our management firing room, we had about two-hundred fifty folks for Shuttle, so you had a team of about four-hundred, four-fifty.

“We have a team of about ninety-one right now in the prime room [for SLS] and then over in the support room. We’ve done some analysis from a technical support [standpoint] but there will certainly be other support as well. So between the two rooms maybe a hundred and fifty, a hundred and sixty folks – a significantly different sized team than we had for Shuttle.”

Ms. Blackwell-Thomspon noted there are currently sixty console positions in the firing room.

Before reaching the final countdown to launch, the launch team will work through a modified launch countdown, called a Wet Dress Rehearsal (WDR), that will exercise the hardware and the sequence of procedures necessary to reach the point of committing the vehicle to its first flight.

The fully-stacked EM-1 flight vehicle will make its first trip from VAB High Bay 3 to Launch Pad 39B so that the launch team can conduct the WDR, which will see most of the launch countdown exercised down to just before the Core Stage engines are started.

“We’ll do a Wet Dress Rehearsal (where) we’ll rollout, we’ll go through our countdown — essentially it will be a wet-dress for the countdown. We’ll count down to (T-minus) 9.34 seconds, prior to engine start,” Ms. Blackwell-Thompson said.

“We haven’t put together all of the details of the timeline, but we’re highly leveraging what we’re doing in launch [countdown].

“We have a couple of other things that we’ll do as part of wet-dress that we may or may not do in launch because we want to make sure that [the procedures are] verified and validated and I’ll give you an example.

“One of the things that we’ll check out is our ability to go through and do what we call a recycle — if we get down late in launch countdown and we’re going to recycle back to T-10 minutes.

“That’s something that during launch we would only do in a contingency situation — where we had an issue — but you don’t want to do that for the very first time on launch when you have an issue. So that’s something that we would go through and verify during wet-dress.”

The WDR also gives the launch team the opportunity to walk through contingency procedures necessary when problems occur during the countdown and the final automatic sequence.

“We have hold constraints once we get into the terminal count, so once we get inside of T-6 minutes — between T-6 and [T-] one minute, 30 seconds we have about three minutes of hold time there, what we would call a limiting constraint,” Ms. Blackwell-Thompson explained.

“During launch, we would not normally hold during that time unless we had an issue; [but] during wet-dress we will actually hold during that time just to verify our hold constraints and then pick up the clock and count down to [T-] 9.34 [seconds].”

Ms. Blackwell-Thompson noted that prior to the integrated vehicle rolling out to the launch pad for the first time, the launch team will be busy running training simulations for those first countdowns.

“We intend to start our simulations earlier in 2018, so we’ll be doing that as well. We’ll flex [the plan] depending on where we get to, but right now we have somewhere in the neighborhood of sixteen to twenty sims planned.

“Some of them are very much dedicated to looking at cryo loading only — making sure that we have the sequencer running and that we’re ready for any kind of problem that the hardware or the ground systems might throw at us — and then we have a similar number of launch sims as well,” she said.

There’s still a lot of work to go before the team is ready to begin running simulations, and Ms. Blackwell-Thompson talked about what she’ll be doing between now and then.

“Primarily my focus is on launch, but there are lots of tests and lots of activities that we do that are risk mitigations for launch and tests that I will be interested in and participating in,” she said. “In our preparations for launch, [I will be] ensuring that our Launch Commit Criteria is maturing [and] our software and our GLS are getting that incorporated.

“There’re procedures that we’ll be working on, and while we’ll have the procedure proper on the shelf ahead of time, there’s always changes that come up, and things that you have to go look at and incorporate, so certainly there will be plenty to do throughout the flow.

“I’ll definitely be engaged during the test activities, because just like [the rest of] the team, that’s where we’ll learn a lot how about the hardware and the ground systems and the flight systems work together.

“It’s a great opportunity for learning and a great opportunity for working with the team.”

*Click here to read the ascent profile work for SLS’ opening mission*

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