Warp Drive in a De Sitter Universe

Generalizing the result of H. Ellis who embedded a warp bubble in the background of a black hole, we introduce a warp bubble in a de Sitter universe. We show that under certain conditions (namely, that the bubble is moving in the radial direction at a velocity equal to the speed of the expansion of the universe), it is possible for the bubble to have strictly non--negative energy density, with the weak and null energy satisfied up to a total divergence term that averages to zero. We discuss the implications of this result and its possible applications to models of dark energy like "dark fluid" and quintessence, as well as to physical systems like Casimir cavities and analogue gravity setups.