NASA has completed an important three day Technical Interchange Meeting regarding the agency’s upcoming flagship Europa Clipper mission. The probe, set to launch on the first science mission of the SLS rocket, currently holds a No Earlier Than launch date of 4 June 2022 – a date that is highly dependent on the SLS Mobile Launcher’s readiness and a desire/need to build a completely new Mobile Launcher for crewed SLS missions beyond EM-1.
The Mobile Launcher issue:
The significant shift in upper stages from the Block 1 to Block 1B SLS variants immediately following the EM-1 mission has, for several years, made the Mobile Launcher (ML) one of the greatest long pole items for all post-EM-1 flights of the SLS.
At the core of the issue is the Exploration Upper Stage (EUS) – SLS’s permanent upper stage that will not be ready for the EM-1 mission and will thus make its debut sometime later.
To account for this and to get the EM-1 mission off the ground as soon as possible, NASA made the decision years ago to create what is known as the Block 1 version of the SLS – a variant that uses an Interim Cryogenic Propulsion Stage (ICPS) instead of the EUS.
The ICPS is in fact a slightly modified Delta Cryogenic Second Stage used on United Launch Alliance’s Delta IV rocket family, and it is significantly shorter than the planned EUS.
When NASA decided to convert the Ares I ML for use by the SLS, the ML already had certain elements installed – like electrical rooms – that were optimally placed for Ares I, not SLS.
Thus, a great deal of workarounds were needed to route pipes and electrical lines around the ML for SLS based on the existing layout and placement of assets, with all of this work done to fit the height and servicing requirements of the SLS Block 1 vehicle and its ICPS upper stage.
Since the ICPS will only be used on the inaugural flight of SLS, with the EUS then debuting on the second SLS mission, significant modifications are required to the ML in order to allow it to properly service the SLS Block 1B.
Officially, NASA cites 33 months of work for ML conversion from Block 1 to Block 1B once the EM-1 mission has launched.
According to L2 processing information, EM-1’s launch date is now a “best case” No Earlier Than (NET) December 2019 with a more likely and “risk informed” date of Quarter 2 2020 – with May 2020 cited as the most likely timeframe for EM-1.
Moreover, safety concerns with the ML conversion plan are now central to NASA’s post-EM-1 plans, with NASA’s Aerospace Safety Advisory Panel (ASAP) noting their concern that such conversion and down time will lead to increased safety risks for SLS given the amount of time that will lapse between the rocket’s first and second flights.
However, NASASpaceflight.com has learned that the “safety issue” surrounding ML conversion referred to by the ASAP largely centers not on the gap between launches (as even a new ML will not reduce the gap between the first and second flights of SLS) but instead the total weight of the existing ML.
At present, the SLS Block 1 ML will end up being roughly 200,000 lbs overweight.
The recently upgraded Super Crawler, CT-2, was built to carry 18.5 million lbs, but the combined weight of the SLS Block 1 and ML at rollout will now be at least 18.7 million lbs.
That in itself is not an issue, as all NASA products have a safety factor of four. Thus, CT-2 is more than capable of carrying an 18.7 million pound ML/SLS Block 1 to Pad-B.
The bigger safety issue is post-EM-1 and all of the modifications needed to the ML for the SLS Block 1B – modifications that will bring the ML to 1-1.2 million lbs overweight – with a total SLS Block 1B/ML combined rollout weight of 19.5 to 19.7 million lbs.
That creates a lower than desired safety factor of 3.78 to 3.74.
The ML’s weight problem traces directly back to the decision to modify the existing Ares I ML following the cancellation of the Constellation Project instead of building a new ML specifically for SLS.
Designers had to work with what was already built for Ares I, and all of the workarounds for already-installed and unmoveable equipment and rooms added a great deal of complexity and a significant amount of weight to the ML design.
With the now-understood safety factors for SLS Block 1B ML’s weight, from NASA’s standpoint, a completely new ML for EM-2 and beyond is desired… with a caveat.
The caveat is that NASA wants a new ML (ML-2) for SLS Block 1B crew launches only, with the existing ML (called ML-1) modified after EM-1 to serve as the SLS uncrewed cargo mission launch platform.
Thus, the current desired plan is to complete ML-1 for the EM-1 mission of SLS/Orion in 2019 or 2020.
Once EM-1 has launched, ML-1 would be taken to the park site north of the VAB (Vehicle Assembly Building) where it will be modified for SLS Block 1B cargo flights only.
Permanently removing those items from ML-1 will save significant weight and get ML-1 back into its planned weight range while also saving some time on the reconfiguration schedule post-EM-1.
At the same time, hopefully starting before EM-1 launches, ML-2 would enter construction – being built and designed from the beginning to serve the needs of SLS Block 1B and Block 2 (if Block 2 is in fact ever built).
Newly designed ML-2 would optimally place all of the GSE and support equipment for SLS Block 1B crew to save weight and reduce complexity, and with an SLS Block 1B stacked on it, would have a rollout weight of 18.5 million lbs – meeting NASA’s safety factor of four requirement.
However… this is the desired plan with no money – at present – to execute as Congress must approve the additional funds needed to build a brand new ML, and with such funds becoming available before the start of FY 2019 on 1 October 2018 an extremely unlikely possibility, the ML-2 desire is – at present – just that. A desire.
Mobile Launcher readiness a driving factor for Europa Clipper launch date:
Particularly for SLS, the Congressionally-imposed requirement to launch the agency’s upcoming flagship Europa Clipper mission on the SLS will be directly affected by the ML conversion or new build efforts.
At a major three day Technical Interchange Meeting (TIM) at the Kennedy Space Center recently, NASA noted that the Europa Clipper mission has a formal, target launch date of 4 June 2022, the opening of a 21 day launch window that closes on 25 June.
A backup launch option exists in 2023.
The mission will be the first cargo flight of the SLS and will likely – though not confirmed – be the first SLS Block 1B launch.
The TIM discussed numerous aspects of the mission and its launch readiness – including how the mission fits into the overall opening SLS manifest, the schedule of EM-1, if Europa Clipper will fly before or after EM-2, and how the desired new ML construction for SLS Block 1B crewed flights could affect the mission.
Specifically, the TIM discussed the need to add additional testing to the payload and the SLS Block 1B design if Europa Clipper is indeed the first mission to fly on the SLS Block 1B, along with processing flow items that will involve a huge SLS cargo fairing.
In the larger certification plan for SLS Block 1B, Europa Clipper is highly desired to fly before EM-2 – the first SLS mission to carry crew aboard Orion.
It has been noted by the ASAP, the NASA Advisory Council, and the Astronaut Office that the Astronaut Office is against any plan to fly crew on any SLS – or any rocket, for that matter – that has not flown at least once in its crew launch configuration.
Since EM-1 will use the ICPS Block 1 and EM-2 will use the EUS Block 1B, the Block 1B variant needs to fly at least once before EM-2 for NASA to adhere to its own stated safety guidelines.
The only mission capable of flying before EM-2 on an SLS Block 1B is Europa Clipper, but that launch schedule is highly dependent on Europa Clipper’s readiness to fly, SLS Block 1B’s availability in the desired launch window, and the need for EM-2 to begin construction of the Deep Space Gateway – which is itself a factor in when EM-2 will be ready.
For the Europa Clipper mission, specifically, its readiness is highly dependent on the ML conversion/build situation… which in turn is dependent on when the EM-1 mission actually launches.
If Europa Clipper uses the ML that will be converted after EM-1, Europa Clipper realistically has no chance of making its 2022 launch window.
A 33 month minimum – as stated by NASA – need to convert the ML after the EM-1 mission to service the SLS Block 1B vehicle and a realistic EM-1 launch date of Quarter 2 2020 puts ML readiness for Europa Clipper at Quarter 1 2023.
It is possible that converting the ML for only cargo missions could reduce the time needed for ML conversion to just 24-28 months, which would notionally bring the ML to a “readiness” point for Europa Clipper in the May-October 2022 timeframe – still not in enough time to support the mission in June 2022.
Moreso, even if SLS EM-1 managed its “best case” NET December 2019 launch, the ML still wouldn’t be ready for Europa Clipper under the 33 month conversion plan until September 2022 – three months beyond the close of the 2022 launch window.
If only 24-28 months were needed, the ML could potentially be ready between December 2021 and April/May 2022 – which would just barely make it ready to support all necessary stacking, rollout, and pre-launch activities for a June 2022 launch.
Additionally, a new ML likely wouldn’t solve the time issue for the 2022 launch window.
Given the current U.S. budget appropriations climate and the high unlikelihood of any funds becoming available for a new ML until October 2018, even a new ML would not likely be ready in time to support Europa Clipper in 2022 as a new ML would realistically take at least four years – if not longer – to design and build.
(Images: NASA and L2 artist Nathan Koga – The full hi-res gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)