With the first launch of the heavy-lift Space Launch System drawing nigh for no later than November 2018, NASA is already trying to plan the first crewed space mission beyond low Earth orbit for the early 2020s. However, budget uncertainties plus a couple of congressional mandates are causing uncertainty for the launch manifest for the SLS.

The problem is that Congress has mandated that the exploration upper stage (EUS) be used for the second launch of the SLS. The 2018 launch will use a less powerful interim cryogenic propulsion stage to loft the Orion spacecraft beyond the moon and back. However, the EUS will be used on all subsequent missions involving the SLS.

NASA does not want the first use of the EUS to include a crew, the theory being that it should be tested with an uncrewed mission to “human rate” the hardware. That mandate means that another uncrewed launch of the SLS has to occur before people are allowed to ride on top of it into deep space.

Congress has also mandated that the Europa mission include a lander, meaning that the SLS is the only launch vehicle powerful enough to send the probe to the moon of Jupiter. The Europa mission could launch in 2022, providing the uncrewed test of the EUS, but causing the first crewed mission to slip from 2021, NASA’s preferred date, to 2023.

NASA is also wrestling over what the first crewed mission should look like. The preferred mission would be a lunar orbital mission, similar to Apollo 8. The space agency is also looking at some other missions, one involving a distant retrograde orbit around the moon, another requiring a visit to the L2 point beyond the moon, and another that includes a two-stage mission involving Earth orbit followed by a loop around the moon.

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The pace of the missions is being determined by lean and uncertain budgets NASA has had to contend with over the past decade and a half. Given funding, the space agency could quicken the pace of its planned deep space missions. But such a development will have to await the perusal of the next president.