Missions that extend the reach of U-Class/Small spacecraft to cislunar and interplanetary ranges will need higher Delta-V systems.
In order to achieve reliable cislunar access, U-Class spacecraft will need sufficient Delta-V to reach cislunar orbits with their own propulsion capabilities. Additionally, higher delta-V propulsion systems on small spacecraft is required to increase their capability to conduct exploration missions outside of the Earth-Moon system. Current small propulsion systems have insufficient Delta-V and longevity for U-Class spacecraft to extend beyond current mission profiles. Higher thrust is not necessarily the most important performance parameter if a system has a very long lifetime.
Current small spacecraft propulsion systems provide up a few hundred meters/second of on-board propulsion. Future missions may require several hundred or few thousand meters/second.
Chris Baker, Small Spacecraft Technology Program Executive