I've been struggling with the following concept for years now - maybe somebody here can help. Imagine two identical rockets facing each other in deep space with their engines turned off with a spring between them. Turn their eingines on and they exert a force such that they compress the spring. Eventually the compressing force of the rockets exactly equals the restoring force of the spring - the compressing stops and the spring is kept in a compressed steady state by the force of the rockets. Now, the act of compressing a spring requires work to be done...and energy consumed. The equation for the work done - FdotD or (1/2)kx(squared) - makes sense for the process of compressing the spring. Got it. But what about the energy required to keep the spring compressed? I can see the fuel guage of the rockets go lower over time while the compression is maintained so I know energy is being consumed. So, very specifically, is there anything in the literature describing the energy consumed in the act of MAINTAINING the steady state compression of the spring similar to the well known (1/2)kx(squared) description of the act of PRODUCING the compression? Please note the request for applicable references in the established literature. Thanks.