Now NASA is planning more SLS Block 1 launches.

With two more launches of the Block 1 version of the Space Launch System now planned, NASA is starting work to procure and human-rate additional upper stages.

NASA originally expected to fly the Block 1 version of the SLS only once before moving to the more powerful Block 1B version of the rocket. The Block 1 uses an upper stage known as the Interim Cryogenic Propulsion Stage (ICPS), based on the Delta 4 upper stage. The Block 1B will replace the ICPS with the Exploration Upper Stage, a larger upper stage under development.

However, with funding from Congress provided in the fiscal year 2018 omnibus appropriations bill to build a second mobile launch platform, NASA now expects to use the Block 1 version more than once. Those additional launches can take place using the existing mobile launch platform while the new one, designed for Block 1B, is built. That move is designed to reduce concerns about a long gap between SLS missions had NASA gone through with original plans to modify the mobile launch platform after the first SLS mission so it could be used for the Block 1B.