On December 18, 2015, President Obama signed an omnibus spending bill that funded the federal government through the rest of fiscal year 2016, which ends on September 30. The bill, which passed the House and Senate with comfortable margins, included $19.3 billion dollars for NASA—an increase of $1.3 billion from last year. Many NASA programs got the funding they requested or received even more. Back in October, when Casey Dreier first mentioned this possible outcome, he called it the "everybody wins" scenario.

For some programs, the bill included specific provisions on how funds must be spent. That's the case for NASA's human exploration program, a $4 billion budgetary line item that includes Orion, the Space Launch System, ground systems, and research and development. SLS received $2 billion—$640 million more than requested—with $85 million earmarked specifically for development on the rocket's new upper stage.

The first SLS flight will send Orion on an uncrewed trip to lunar orbit in 2018. For that mission, the rocket will fly with an off-the-shelf upper stage called the Interim Cryogenic Propulsion Stage, or ICPS. The ICPS is a modified United Launch Alliance Delta IV upper stage. It's not rated to carry humans.

The second flight, Exploration Mission 2, is also headed to lunar orbit—but with humans. That means NASA needs to either human-rate the ICPS at an additional cost, or have a new upper stage ready to fly by EM-2 (currently scheduled sometime between 2021 and 2023). The latter is the preferred choice, since long-term SLS plans call for a more powerful upper stage anyway. The new stage will be called the Exploration Upper Stage, or EUS.