umm, yes, we do.
the Boeing Delta IV Heavy, first launched in 2004, could be used for lunar missions.
Delta IV Heavy, payload to LEO: 25,800 kg
Saturn V, payload to LEO: 119,000 kg
The Aerospace Corporation was asked by NASA three times, in 2005, 2008 and 2009, to assess technical feasibility and cost of human-rating an EELV. Two latter assessments addressed the possibility of replacing the Ares I with Delta IV Heavy. The reports indicate that the Delta IV Heavy meets ISS and lunar target performance requirements.
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The existing Delta IV upper stage can be further upgraded to provide additional potentially important capabilities that enable an affordable and sustainable implementation of the Vision for Space Exploration (Figure 9). Boeing is currently evaluating modifications to the Delta IV upper stage for use as a Trans-Lunar Injection (TLI) or In-Space Transportation (IST) stage, either as an upper stage or as an on-orbit asset, as described in the following section.
The Delta IV upper stage is a stepping stone to a TLI stage, and the TLI stage is a potential stepping stone to an array of other Exploration applications, including cryo depot, lunar landers, and even habitat modules. Further, Delta IV upper stages offer a low-risk, high-fidelity platform for demonstrating the required technology.
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