Full-scale MAF transportation test in the Spring
Before the checkouts at Stennis, NASA’s Core Stage transportation elements first went through a full dress-rehearsal in late April and early May for the sequence of moves that they’ll be making with Core Stage-1, the first flight article when it leaves MAF to get ready for Artemis 1.
(Photo Caption: Technicians at MAF drive the Pathfinder from the factory out to the dock on April 26. The overland transportation carrier for Core Stages is a bigger, stronger structure than those used for Space Shuttle External Tanks in order to handle their larger size and weight.)
Pathfinder was shipped to MAF on a commercial barge two years ago and sat outside during its time there. Delays in the assembly of the first Core Stage flight article and completion of the STAs meant that some get-ahead fit-checks inside the Michoud facility were not performed.
On April 26, the Pathfinder was driven out to the Pegasus barge for a run-through of the trip to Stennis. Starting outside the west end of Building 103, the MPTS carried the Pathfinder on an approximately mile-long route on the streets inside MAF to the dock where Pegasus was berthed.
The move from the industrial area at MAF out to the Pegasus barge was the first major usage of the simulator to checkout the MPTS elements for the first time using the equipment that will carry Core Stage-1 late this year to Stennis.
Due to their size, most of the flight and structural test articles (STA) are shipped horizontally, with the article bolted into NASA’s Multi Purpose Transportation System (MPTS).
Rocket structures are also generally optimized for the loads they take during launch and ascent, not so much for ground transportation. The MPTS is GSE that allows for careful transport of the large Core Stage hardware. Structural support hardware attaches from the flight/test hardware to the remotely-controlled SPMTs.
(Photo Caption: Pathfinder is lined up by the four SPMTs to roll onto Pegasus at the dock at MAF on April 26. The simulator has the same dimensions, weight, and center of gravity as a flight Core Stage article. On the Pegasus barge, the carriers at the front and back are positioned over eight structural connection points where the SPMTs lower them onto pedestals at each point to secure the carrier and stage to the barge deck. After the SPMTs let go, they are driven to the middle of the barge and chained down to the deck during water transportation.)
The stage STAs were built and tested as individual elements (engine section, intertank, LH2 tank, and LOX tank), with simulators on both ends of the qualification article attached to hardware interface structures (HIS). For handling them, a common HIS is attached on both ends to the simulators and each HIS is attached to a table-shaped multipurpose carrier (MPC).
As commanded by nearby operators, four remotely-controlled SPMTs roll underneath the MPCs (two for each) and pick them up to move the whole assembly.
A different MPTS configuration is used for a full Core Stage. A common HIS connects to one MPC via transportation fixtures on the engine section similar to the STAs, but two forward HIS elements connect the forward end to the other MPC via the SRB forward attach points on opposite sides of the intertank.
Pegasus trip to Stennis in May
Pegasus carried the Pathfinder from MAF to Stennis in early May. “We came out here to Intercoastal Waterway, we took a left, it’s right here, and then we followed that until we got to the Pearl River and then we turned left on the Pearl River and went all the way north to Stennis,” Alan Murphy, NASA Marine Operations Lead, said at MAF in late June. “That’s about a 12-hour trip, if we time the bridges right.”
Originally built in 1999, Pegasus was used to transport Space Shuttle External Tanks from MAF to the Kennedy Space Center (and in a few cases, the reverse). It was two-hundred sixty feet long at the end of the Shuttle era, but SLS Core Stages are almost sixty feet longer than Shuttle tanks and much heavier, so the middle section of the barge was removed and replaced with a reinforced section fifty feet longer designed to handle the higher cargo weight, bringing the overall length to three-hundred ten feet.
(Photo Caption: Two tugboats (lower right) help complete the Pegasus trip at Stennis in early May from MAF. Several of the rocket engine test facilities can be seen in the upper left part of the image. The test stand of the B Test Complex at Stennis is the farthest in the background here. Direct water access to the complex is available for testing large rocket stages in the B-2 position of the stand.)
“That goes back to the weight of this as it loads on versus the External Tank,” Murphy explained. “External Tank was fairly light, especially the mover part of it.”
“The SPMTs and the MPC and the HIS, which is the hardware interface structure that goes up, all those are really beefy compared to what External Tank used, so with all that extra weight going across the ocean, you have the stress engineers who evaluated it and said we need a thicker deck and we need more supports underneath, so it made more sense to be able to replace that whole section where this is going to be sitting.”
Although the propellant tanks are a prominent feature of the Core Stage, they are only part of its role in the launch vehicle. The stage plays the same combined role as the Orbiters and the External Tank did for the Space Shuttle during its ascent to orbit.
Not only are the propellant tanks themselves are significantly bigger to hold more fuel, but the stage includes a bigger engine compartment resized from the Shuttle Orbiter back end that contains most of the Main Propulsion System and four RS-25 engines in the back. The stage also includes the flight computers upfront and navigation equipment and avionics throughout that serve as the brains of the launch vehicle from liftoff to insertion into Earth orbit.
The Pathfinder was constructed to the estimated 228,000-pound dry weight of a Core Stage, which is about the weight of four last-generation External Tanks or a flight-ready Shuttle Orbiter. The heavier vehicle requires stronger, heavier carrier equipment, which increases the overall load that Pegasus has to carry.
“We have eight pads in there, which was part of the modification we did several years ago in the shipyard,” Murphy noted. The pads have I-beams up underneath, really a lot of support on there to take all the loads we might see on the ocean. That’s part of the reason we went to the shipyard, we had to be able to compensate for the ocean loads, the more weight that we have here versus External Tank, and the extra length.”
For the full stage article or a full-scale simulator like the Pathfinder, when the SPMTs lower the full carrier to release them, the MPCs are set down on eight pedestals, such as when securing the vehicle and MPTS to the deck of the Pegasus. “Those pedestals are kind of interesting because it’s got three-hundred and sixty degrees of adjustment that we can make on them, so when you roll this thing in, if you’re off a little bit we can actually slide those and then we’ve got slots on those you can bolt these pedestals down once you get those on,” Murphy said.
(Photo Caption: The different carrier configurations used for transporting flight and test hardware during the ongoing development phase of the SLS Program. On the left, a pair of SPMTs carries an MPC with a forward HIS connected on both ends to the forward SRB attach fittings of the Core Stage Pathfinder. On the right, the SPMTs carry an MPC with a common HIS supporting one end of the LOX STA. A set of “legs” can be seen in the right image connected to the side of the MPC. The legs were used for securing the lighter STA hardware to Pegasus. For a full Core Stage or Pathfinder, larger pedestals are set up on the Pegasus deck for securing.)
“This was the first time that we tested out the pedestal system, that’s with the Core Stage or the Pathfinder in this instance, which is the same size as the Core Stage, sitting down on the pedestals. Instead of the chaining that you see on the STA where we’re chaining it to the surface, we have to go with a more robust system and that is with the eight pedestals that we have underneath.”
“The Core Stage will roll on and we’ll bolt them down,” he added. “The reason we do that is because we have ocean loads that we have to go through going from here to Kennedy Space Center.”
Murphy noted that with the STAs, a set of “legs” were instead attached to the MPCs that moved with the carrier assembly.
With the shipping and handling practice at MAF and Stennis completed, Pathfinder was loaded back on Pegasus at Stennis for the first ocean trip through the Gulf of Mexico and around the Florida Peninsula to Kennedy Space Center. “You’ve got the Pearl River on this side and when you get over to KSC you’ve got the Banana River, so we’ll go through a lock there,” Murphy said.
“When we get on the ocean we have one big tug. It won’t be a pusher, it will be a puller and it’ll be about a half a mile in front of us, so once we get to the Banana River we can’t use that puller so we have to get two more tugs over there to take us through the Banana River to KSC.”
The barge with Pathfinder has arrived! Next week our @NASAGroundSys team will unload the core stage test article and take it to the Vehicle Assembly Building.
There, our team will practice maneuvering and stacking before the first @NASA_SLS rocket arrives 🚀 pic.twitter.com/xPoM7ONFXm
— NASA's Kennedy Space Center (@NASAKennedy) September 27, 2019
The barge arrived at KSC on Friday, September 27, where the next set of practice sessions for handling a Core Stage will be held.
On September 30 it was removed from the Pegasus Barge in preparation for its testing inside the VAB.
Lead image credit: NASA/Stennis Space Center.