While the Senate version of the NASA authorization bill, S. 3729, made it clear that the heavy-lift launch vehicle it calls for, the Space Launch System, should be developed by “extend[ing] or modify[ing] existing vehicle development and associated contracts”, it wasn’t specific beyond that in terms of vehicle design. However, as Space News reported Friday, the report accompanying the bill goes into additional detail about their desired vehicle design. From section 302 of the report:
The Committee anticipates that in order to meet the specified vehicle capabilities and requirements, the most cost-effective and `evolvable’ design concept is likely to follow what is known as an `in-line’ vehicle design, with a large center tank structure with attached multiple liquid propulsion engines and, at a minimum, two solid rocket motors composed of at least four segments being attached to the tank structure to form the core, initial stage of the propulsion vehicle. The Committee will closely monitor NASA’s early planning and design efforts to ensure compliance with the intent of this section.
While Space News concludes that this means the new heavy-lifter would look a lot like Ares 5, it’s possible that variants of the Jupiter vehicle proposed by the DIRECT team may also qualify. The use of “in-line” in the report language would seem to indicate they are not interested in any sidemount vehicle concepts under study recently, however.
There’s a bigger question, though, addressed in the article: should Congress be in the business of mandating a specific vehicle design? Doug Cooke, NASA associate administrator for exploration systems, told Space News that he would like to “broaden the trade space” for any HLV mandated by Congress “to make sure we don’t preclude possible answers that might be the optimum overall”. Even beyond the vehicle design question, though, are other issues, such as whether the vehicle can be developed by the end of 2016 (as mandated in the legislation) with the authorized funding, and also what exactly the vehicle would be launching in 2017 and following years, given the lack of existing or planned payloads that require a vehicle capable of placing at least 70 tons in LEO. It could be used to launch Orion, of course, but it would be overkill (and potentially costly), and the 70-100 tons could be too small for some proposed exploration architectures, as former NASA administrator Mike Griffin noted earlier this month.