Orbital Operations – 2 Rendezvous & Proximity Operations

Rendezvous & Proximity Operations A rotating frame is used for planning and executing a rendezvous operation because of the fixed relative position of the target with respect to the chase spacecraft For the following charts will use the International Space Station as the fixed target, and the Space Shuttle will be used as the chase craft Reference frame is rotating at the ISS orbital period of 91.3 min, 345 km circular orbital altitude

Rendezvous & Proximity Operations Rotating reference frame with target centered showing relative motion of chase vehicle for higher and lower circular orbits Eccentric orbits for chase spacecraft shown in next slide

Orbital Ops

Rendezvous & Proximity Operations A rendezvous sequence begins with the chase craft in a lower catch-up orbit to close the phase angle with the target Repositioning burns bring the spacecraft to a one-orbit closure maneuver carefully planned with an apogee at the target orbit semimajor axis A Terminal Initiation (Ti) burn is made at this point for a final rendezvous exactly one orbit later Final approach brings the chase craft to the target craft just as it reaches the target’s position

Rendezvous & Proximity Operations Small midcourse corrections are made to bring the chase craft to the exact point of rendezvous Two types of rendezvous maneuvers are available V-bar (along velocity vector, the line of flight) R-bar (along the vertical axis pointing to Earth’s center R-bar and V-bar approaches follow relative motion sequences shown in earlier slide

Orbital Ops

Orbital Ops

Orbital Ops

Orbital Ops

Rendezvous Operations Rendezvous and Proximity Operations Program (RPOP) is a recent guidance and navigational piloting-aid software addition RPOP runs on a laptop computer onboard the Space Shuttle Orbiter Provides information to make flying an efficient trajectory easier for the Orbiter crew Provides the crew with situational awareness during the rendezvous and proximity operations phases of flight A 360-degree Orbiter pitch maneuver has been developed to allow ISS-based photography of the Orbiter’s underside and wing leading edge during its approach to the International Space Station This maneuver is called the R-Bar pitch maneuver (RPM) RPM requires the pilot to meet strict relative position and velocity requirements prior to initiation of the pitch maneuver to avoid potential collision with ISS and overabundance of propellant usage

Rendezvous Operations Rendezvous and Proximity Operations Program Several new guidance and navigation capabilities were developed and implemented in RPOP to support the RPM The new guidance capabilities include algorithms to provide the pilot with translational hand controller (THC) recommendations to efficiently acquire the R-Bar, set-up and initiate the RPM, and recover from the RPM and initiate the twice orbital rate R-Bar to V-Bar approach (TORVA) maneuver The Trajectory Control Sensor (TCS) Kalman filter was enhanced to provide better navigation performance during the RPM when the sensor is no longer tracking ISS These new capabilities in RPOP increase the piloting efficiency by reducing trajectory dispersions and propellant usage leading up to and recovering from the RPM

STS-117 RPM

Deorbit and Landing

Hydraulic and flight systems are tested under OPS Mode 3 software Deorbit Deorbit procedures for the Orbiter begin with systems checkout before deorbit burn Hydraulic and flight systems are tested under OPS Mode 3 software Orbiter is commanded to rotate 180o from the direction of flight by the RCS Digital Auto Pilot (DAP) controls

Orbiter's reentry characteristics are based on Deorbit Deorbit Δ V burn is approximately 2.5 min duration and 220 fps in velocity Orbiter is again rotated around the yaw axis 180o along with a 40o pitch up attitude in preparation for atmospheric reentry Orbiter's reentry characteristics are based on Maximum load Temperature limits Dynamical (flight) stability factors

Deorbit Historical reentry parameters

Deorbit Reentry limit boundaries

Deorbit Entry Phase Description Reentry Attitude hold prior to entry.  Phi (roll angle) = 00, alpha (pitch) = 400. Temperature control Drag level commanded to meet thermal constraints.  Phi varies, alpha = 400. Equilibrium glide Transition between temperature control and constant drag phase. Also optimum for high/low energy case.  Phi varies, alpha = 400. Constant drag Drag constant.  Phi varies, alpha = 400 to 370. Transition Transition to TAEM interface.  Phi varies, alpha = 370 to 130.

Deorbit Reentry limit boundaries

Deorbit Reentry limit boundaries