Another feature available in navigation in OPS 2 is the landing site update function, which allows the crew to select different runways to be used in the entry guidance computations. The crew interfaces with this capability through the universal pointing display only in major mode 201. One of on-orbit software's several features, universal pointing is used to compute attitude changes required to point a specified orbiter body axis at a specified target, to maneuver to a predetermined attitude, to rotate the orbiter about a specified body axis or to maintain attitude hold. Another guidance feature is PEG 7, or external delta-velocity, targeting for OMS or RCS burns. In this mode, guidance sends the commands to flight control to execute a burn specified by an ignition time and delta velocities in the local vertical coordinate system at ignition.
Commands continue to be generated until the original delta-velocity requirement is met.
This option is available in major mode 202 via the orbit maneuver execute display. The third guidance capability is an on-orbit targeting scheme that is used to compute the parameters required to move the orbiter to a specified target offset position in a given amount of time. This feature, which is used to do onboard targeting of rendezvous maneuvers, is enabled via the orbit targeting CRT display. The actual thrusting period is still accomplished via the orbit maneuver execute display. The orbit flight control software includes an RCS DAP, an OMS thrust vector control DAP, a module called an attitude processor to calculate vehicle attitude and logic to govern which DAP is selected.