NASA’s monster rocket will evolve into an even larger vehicle early in her lifetime, as the Block 1 rocket grows into the workhorse known as the Block 1B. With a large increase in capability – and height – the Block 1B will require a revamp of numerous elements of the KSC ground systems, ranging from major changes to the new Mobile Launcher, through to need for a new LH2 storage sphere at the pad.
SLS Evolution:
The Block 1 SLS is a 70mT capable rocket that will provide up to two test flights with the Orion capsule. Exploration Mission -1 (EM-1) is currently aiming to launch in late 2018, before standing down for several years until the proposed repeat mission, EM-2, this time with a crew.
The plan is still being worked on, not least due to the political uncertainty in NASA’s roadmap during the upcoming change of President.
What is certain in the Block 1 will have a short career, as NASA pushes to bring the more capable Block 1B online – rated as capable of 105mT to LEO. The rocket’s main boost comes from the Exploration Upper Stage (EUS).
The initial plan was to switch to this new upper stage after the crewed EM-2 mission. However, as previously reported by this site, NASA wishes to advance this plan.
The debut of SLS will sport a Delta Cryogenic Second Stage (DCSS), renamed the Interim Cryogenic Propulsion System (ICPS).
As noted in numerous meetings – not least by NASA’s Aerospace Safety Advisory Panel (ASAP) – it would cost around $150m to “human rate” this upper stage ahead of EM-2, a cost that would be associated with just the single use of the stage ahead of moving to the EUS.
The switch to EUS after the first test flight of SLS – and in turn utilizing the gap between the first two SLS missions – would allow for the rocket to enter its workhorse configuration that will be capable of a full mission range envisioned throughout the 2020s.
The official scenario of two Block 1 flights, followed by a change to Block 1B, threatens large gaps between the first three missions. This relates not least to the ground-related changes required between the transition.
Internally, NASA teams are working on the premise that SLS will only launch once in the Block 1 configuration, providing a major test of the rocket and Orion spacecraft during an excursion past the Moon and back.
The most recent documentation also cites the requirements of preparing for Block 1B during the gap after the launch of EM-1. “Modifications are significant and pose a significant challenge to meet EM-2 schedules. between EM-1 (H/W availability) and EM-2 need date,” cited one document relating to major changes to the Mobile Launcher.
The ML – which continues to be revamped following its change of call signs to that of launching the since-cancelled Ares I to SLS – will require major modification ahead of hosting the Block 1B SLS.
Studies show this to be an effort that will require at least 19 months of work to modify the ML to host the taller rocket. Some engineers involved with the KSC ground systems believe it could take three years, costing around $150 million.
Per the requirements, 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 EUS – 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.
However, NASA is already laying the groundwork, sending out solicitations for engineering companies to provide overviews ahead of contract awards.
The latest solicitation was sent out this week, noted “This acquisition is for Architect-Engineer (A-E) Services for the Design and Other Professional Services necessary to Modify and Develop Structural, Mechanical, and Electrical Systems to renovate the Mobile Launcher (ML) at the Kennedy Space Center (KSC), Florida.”
Associated with the request was additional information on the modification requirements, cited as “Significant modifications required to GSE (Ground Support Equipment) systems on the ML to support EM-2/EUS configuration,” again notably showing NASA is working on the premise EM-2 will be launched via the Block 1B SLS.
“All systems above the 220 ft level will require significant installation redesign. Pneumatic system mods and additions. ML has run out of real estate in the base on the tower for new GSE. Moving GSE will drive significant structural changes not accounted for in the study. 100s of long run and short run cables impacted,” added just some of the changes in the overview.
“Major redesign of AC power, lighting, elevator, fire alarm, fire protections, potable/septic water. New electrical room required on the 325 ft level. Significant cable plant demo and rework required.”
The amount of changes did raise the question of why NASA isn’t simply building another ML. However, that would cost even more – several hundred million dollars more – and leave the current ML without a role.
Ironically, having only the one ML is a key reason NASA is unable to increase the launch rate to a level it would prefer of SLS during the Mars missions in the 2030s. SLS will only be able to launch “no more than” three times in any one year.
Additional challenges related to the modification is the mass of the ML, which will be vastly increased not just by the larger rocket, but also via the structural changes to the ML.
“ML reinforcement structurally is feasible, but implementation will be problematic. Adds approx. 530,000 lbs of steel to ML,” added the overview, which continued to list the challenges.
“Tower Impacts. 8 levels will require diagonal modifications. 10 levels will require column modifications. 2 levels will require significant rework to add electrical rooms. Crew level will need to be relocated. Umbilical Arm mounting will require major structural mods. ML Base Impacts. Significant Girder reinforcement required. Truss reinforcement. Significant demo required to complete.”
The pad infrastructure will also require changes, including a new giant sphere to contain additional Liquid Hydrogen to feed the thirsty Block 1B.
The lifeblood of the Space Launch System (SLS) will be Liquid Oxygen (LOX) and Liquid Hydrogen (LH2) – combined at a ratio of about 6:1 to feed the four RS-25 main engines.
For it to remain in a full liquid state, it needs to be cryogenically cooled. The main consideration is the use of the existing storage facility for the LH2 at Pad 39B.
While the pad is undergoing large-scale changes ahead of hosting the Heavy Lift Launch Vehicle (HLV), the current LH2 storage facility is a remnant of the Shuttle era, until it is replaced ahead of the first flight of the Block 1B.
“The Launch Pad Element Integration Team (EIT) held a kick-off meeting this week for the design of the Launch Complex 39-B Liquid Hydrogen (LH2) upgrades,” noted L2 information this week.
“This year-long design effort will lead to the construction of a new 1.4 million gallon liquid hydrogen sphere to support Space Launch System (SLS) Block 1B launches using the Exploration Upper Stage (EUS).”
LH2 storage capacity includes scrub turnaround considerations, which is already going to be a problem for EM-1. Should SLS’ first launch suffer from an abort late in the countdown process – with the on-board LH2 drained back to the LH2 storage tank – the tank will be 330,000 gallons short of being able to support another launch attempt within the required 24 to 48 turnaround window.
To mitigate this issue, the first option involves a convoy of 28 to 30 trailers staged to support the immediate replenishment of the storage tank. During the Shuttle era, these trailers arrived in convoys of road tankers from Louisiana.
The second involves 10 to 12 trailers, offloading their contents at Pad 39B, before being routed approximately five miles to Cape Canaveral Air Force Station Launch Complex 37B to be filled from that pad’s LH2 storage tank, before being routed back to LC-39B for offload.
The new tank will be able to cope with Block 1B’s LH2 storage and scrub turnarounds. However, another new tank will be required for the Block 2 SLS.
Interestingly, as SLS evolves into the Block 2 variant, yet more LH2 storage will be required.
“The largest LH2 demand will be the SLS Block 2 configuration estimated to require up to 3 million gallons of LH2 storage tank capacity,” added additional documentation.
While SLS’ evolution is sensibly aligned to NASA’s proposed roadmap to Mars, it comes with its own set of challenges.
(Images: NASA and L2 which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. ML photo via Marek Cyzio. Europa mission renders by L2 Artist Nathan Koga. The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*))
(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here: http://www.nasaspaceflight.com/l2/)