SLS ML revamp after EM-1 included Europa mission considerations
With work continuing on a lengthy project to convert the Mobile Launcher (ML) for use with the Space Launch System (SLS), a NASA manager has spoken about the challenges of preparing the huge structure for the rocket’s undefined manifest. The hope of SLS involvement with a mission to Europa included considerations for a second ML. However, the confirmed path for ML is for it to undergo another major modification period after just EM-1.
The ML – designed by RS&H (base and structure), along with ASRC Aerospace Corporation (prop systems etc.) – consists of the main support structure that comprises the base, tower and facility ground support systems.
This includes power, communications, conditioned air, water for cooling, wash-down, with the system designed with ignition over-pressure protection in mind.
It was initially built for the Constellation Program (CxP) to host Ares I launches, with a launch specific to the “stick” design of the rocket.
However, the cancellation of the Constellation Program (CxP) resulted in the ML receiving its pink slip.
Parked up near the VAB, rumors of what would happen to the ML ranged from pulling the structure apart for scrap, through to a joke that was circulated throughout the KSC workforce claiming there was interest from Disney for turning it into a fun ride.
Ironically, Disney engineers had already worked with the KSC team on the roller coaster Emergency Egress System (EES) – a giant structure that has since been ruled out as the EES for the SLS.
Although the ML is highly suited to the SLS vehicle, modifications – mainly to the Ares-specific elements of the structure, such as the launch mount – were required, ahead of the Heavy Lift Launch Vehicle’s debut in 2018.
The launch mount was the first major element of the ML to be redesigned.
Over three years later, modification work is continuing, mainly related to the vast number of umbilicals that will be mated with SLS and Orion ahead of launches.
Testing of the arms and umbilicals is taking place at the Launch Equipment Test Facility (LETF) inside the Kennedy Space Center grounds.
However, the modified ML is likely to be just for one SLS launch – Exploration Mission -1 (EM-1) – given the following SLS mission will involve an evolution from the SLS Block 1 to the taller Block 1B.
Exploration Systems Development (ESD) Deputy Associate Administrator Bill Hill explained that the program is still continuing to refine plans for work after EM-1.
At the outset, the development goal of the three ESD programs was Exploration Mission-2 (EM-2); current plans are for EM-2 to introduce both a fully human-rated Orion spacecraft and the higher performance Exploration Upper Stage (EUS).
As with the ramp up to EM-1, all three programs will have their development challenges getting ready for EM-2, which is currently forecast to launch no-later-than April 2023, though ESD maintains schedules pointing to an internal target of August 2021.
Another mission with the possibility of using SLS is Europa Clipper, with a technical launch date in the same time-frame as EM-2.
Mr. Hill said that while in theory both the SLS Block 1 (with ICPS) and Block 1B (with EUS) configurations might be able to support launching a spacecraft to Europa, ESD can realistically only support one launcher configuration within its budget.
“There are some other missions that we’re looking at as an agency, like Europa, that we could probably ‘get away with’ using the ICPS, but to maintain the dual infrastructure (would be expensive),” he explained.
“I had our Ground Systems (program) take a look at what would it cost me to build another Mobile Launcher before EM-2, so I could have one for ICPS and one for (EUS).
“The low end was about 350 million dollars, the high end was about 500 million dollars – and the low end really didn’t do anything for me, because we (would have) to strip the (existing) Mobile Launcher of all its guts, put it on the other one, and if we wanted to go back to the other one we were going to have to replicate all that.
“That coupled with the fact that most of the costs showed up in 2018 and 2018 is going to be a challenging year no matter what we look at.”
With EM-2 now baselined using EUS, GSDO will be making major modifications to the Mobile Launcher after the EM-1 launch, removing the ICPS swing arm, relocating Orion infrastructure, and integrating a new swing arm and infrastructure for EUS.
Those modifications are wide-ranging, with an estimated cost of upwards of 150 million dollars and involving three years of work.
Everything above the Core Stage Forward Skirt Umbilical (CSFSU) – such as the Crew Access Arm – will be changed to cater for the EUS, which is about 35 feet taller than the ICPS.
While the ICPS umbilical arm will become obsolete, it will be replaced by a hydrogen vent arm, a LOX umbilical arm and a LH2 umbilical arm for the EUS.
All the cryo skids will have to be redesigned, while the cryo lines on the ML Tower will also change in both length and diameter, to support the higher propellant flow rates required for filling the RUS – over five times that compared to the ICPS.
Two new hydraulic control systems will have to be built to support the two additional umbilical arms, which is a concern, due to the amount of remaining space to host them on the Tower.
When asked about the possibility of flying a SLS launch in between EM-1 and EM-2, Mr. Hill understandably thought that was unlikely.
“Right now we’re committed to flying EM-1 and EM-2. Some of the modifications that we’re making to the Mobile Launcher are going to be challenging to get in before August of ’21 – or before ’21 when we’re targeting EM-2.
“Frankly I don’t think Europa is going to be ready by then, but we’ll see.”
That was always likely to be the case, with the Europa mission very much in a preliminary stage of evaluation. Also, EM-2 is highly likely to be baselined at the latter program date of 2023.
From an SLS-usage option, the only payloads that have political interest at the moment are the Europa and Mars Sample Return missions. The later has undergone a conceptual design within the SLS Program, involving a Mars lander carrying an ascent vehicle for a Mars sample return mission.
For Europa, two missions would be involved, launching in either 2023 or 2025 from a planning process standpoint within the SLS Program.
Europa is classed internally as the first cargo-only launch of SLS, along SLS’ role with cargo has expanded via the cargo capacity inside the Universal Stage Adapter (USA) under Orion on the Block 1B rocket.
“With Europa, we now realize we’ll probably do two missions – we’ll do one orbiter and orbit for a couple of years, collect surface data and then do a lander later once we select a surface location,” confirmed Mr. Hill from the ESD standpoint – which confirming the very early stage of evaluations.
“So we may be launching two Europa (spacecraft), but that’s downstream, we’re not really looking at that yet.”
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