Hephaestus, our reusable Aerospike engine, will enable single-stage-to-orbit for the launch vehicle it is propelling. This changes the playing field when considering the logistics of a launch:

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A single stage eliminates the risk of stage seperation failure as well as second stage engine ignition failure.

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For re-usable launch vehicles, it is much cheaper and faster to refurbish a single stage for launch as opposed to multiple stages. Effectively decreasing the turnaround times and costs between launches.