Once we get to this level of complexity on string concatenation, we should switch to string.format

    return string.Format("Executing maneuver: {0}m/s{3}Remaining duration: {1}{3}{2}", 
        RemainingDelta.ToString("F2"), 
        EngineActivated ? RTUtil.FormatDuration(RemainingTime) : "-:-",
        base.Description,
        Environment.NewLine);