Block 1 SLS configuration may fly more than once
During a routine hearing with the House Subcommittee on Space on March 7, 2018, NASA’s then-acting administrator—Robert Lightfoot—said that, should NASA have a second mobile launcher (ML), the agency’s Space Launch System (SLS) may fly several times in the Block 1 form before the infrastructure is ready for the more-powerful Block 1B configuration of the super-heavy lift rocket.
Exploration Mission-1 (EM-1) was to be the only mission to fly on the first-generation version of the rocket, but now may be joined several more missions utilizing the Block 1 design.
This potential manifest shakeup comes from the funding for construction of a second ML, designated as part of the recently-passed Consolidated Appropriations Act. Though the agency had not requested funding for the second platform, it could allow NASA to fly crew significantly more quickly than it would have otherwise been capable of doing.
“What the advantage of a second mobile launch platform gives you is I could fly on the mobile launch platform I’m building today, and I could potentially fly Orion if I bought another Interim Cryogenic Propulsion Stage—an upper stage—so I could fly quicker, fly humans quicker, probably in the 2022 time frame,” Lightfoot told the Subcommittee when asked what would be the advantage of a second ML.
NASA had projected a pause of at least 33 months between the first two SLS flights as the agency worked to modify the sole platform to support the larger Block 1B vehicle. However, with the construction of a new ML now funded with a $350 million appropriation, NASA could—theoretically—cut that gap by a significant margin.
Sooner is better, right?
While the option to fly crew sooner on SLS may appear to be a no-brainer, it doesn’t come without complications.
Block 1 of SLS uses a modified Delta Cryogenic Second Stage from a United Launch Alliance (ULA) Delta IV rocket for its second stage. In its SLS configuration, the propulsion element is known as the Interim Cryogenic Propulsion Stage (ICPS), but NASA has only purchased one flight unit from the company.
With vehicle components, especially those related to propulsion, taking months—or even years—to manufacture, any shortening of launch gap could be erased if NASA doesn’t procure an additional ICPS in a timely manner.
Additionally, and crucially, the ICPS has not been rated to fly a crewed vehicle. In order to certify the Delta IV-derived stage for human spaceflight, the ICPS would likely have to undergo costly and time-consuming tests before the agency could launch astronauts on Exploration Mission-2 (EM-2) using a Block 1 SLS.
Moreover, NASA’s Europa Clipper mission—which is congressionally mandated to launch on SLS—may now fly on a Block 1 vehicle rather than the more powerful Block 1B. The super-heavy-lift-vehicle has the capability to deliver a greater payload to the Jovian system without the need to use a series gravity-assist maneuvers that would be required should the spacecraft fly on a less-expensive, less-capable rocket. However, the spacecraft was planned to fly on the more-powerful Block 1B version, which would include a new Exploration Upper Stage (EUS).
Should the mission fly on a base Block 1 vehicle, it is less clear if the time-saving is still enough to justify flying on SLS. SpaceFlight Insider has reached out to NASA to see what impact, if any, flying Europa Clipper on a Block 1 may have on the mission and will provide an update when that information becomes available.
Should the U.S. space agency decide to wait until Block 1B’s more-capable EUS is ready, flights of that configuration could have to wait until the mid-2020s should development of the new cryogenic stage take longer than expected.
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.