AutoDock 1.0 : Docking Procedures

SpacePort 9000 is a docking station in Low Earth orbit. It handles traffic between Earth, Moon and Mars. The SpacePort is designed to efficiently work with Earth Shuttles that carry around 500 people to Cargo ships that can carry 500 tons of cargo. We will be developing the software responsible for managing the docking port and orbit allocation on the SpacePort. Docking software will be responsible for allocating one of the 32 docking ports on the SpacePort. Orbit allocation software will assign an orbit to every ship that wishes to dock with the SpacePort.

Even though SpacePort 9000 will initially be deployed around Earth, it is designed to work with any planet designated as the parent planet. Planet related parameters need to be specified while configuring the SpacePort.

AutoDock 1.0: Docking Procedures

SpacePort uses the AutoDock 1.0 that has been ratified by the 25 nations involved in space exploration. The standard specifies in detail all the messages that will be exchanged between a docking station and a spacecraft requesting docking. The docking procedure is completely automatic with manual override possible at any stage.

A brief summary of the message exchange between docking stations is presented below:

Docking Station Detection and Contact

• A space docking station, supporting AutoDock will use an assigned broadcast channel giving detailed information about the capabilities of the docking station. The broadcast should also include the frequency band on which the initial docking request will be accepted.

• All AutoDock compliant space ships will continuously scan all the AutoDock broadcast channels, checking for valid broadcasts.

• All the valid docking stations sensed by the Spaceship will be listed on the dashboard monitor.

• The crew of the space ship will select the docking station for docking.

• Once the docking station has been selected, the space ship will send out a "Docking Request" to the docking station.

• The docking station will then check if the system has enough resources to permit docking.

• If the docking station has sufficient resources, it replies with "Docking Permitted". The exact orbit location, planet information (i.e. Earth, Moon or Mars) is provided in the response.

Orbit Assignment 

• The space ship then requests an orbit assignment from the docking station by using the "Orbit Request" message. (An orbit needs to be assigned because AutoDock 1.0 does not support direct docking. Moreover, Space Regulation 1.66.33 clause 2 restricts docking stations to allow only one docking or undocking procedure to be active at any given time. Due to these requirements, spacecrafts are typically assigned a temporary orbit before docking.)

• The docking station assigns the orbit based on the following rules

  • Spacecrafts approaching from other planets that use gravity-assists to slow down should be assigned the outer most orbits.

  • Spacecrafts approaching from the parent planet should be assigned the inner most orbits.

• The docking station responds with "Orbit Assign" message, giving details about the actual orbit assigned to the spacecraft.

• The spacecraft then calculates the thruster firing sequence for reaching the assigned orbit. If the spacecraft is approaching from other planets it decides on the optimum combination of thruster firing and gravity to slow down the craft to attain the orbit. Spacecrafts approaching from the parent planet have to accelerate to attain the assigned orbit.

Ready For Docking

• Once the spacecraft has attained the assigned orbit, it sends "Ready For Docking" message to the docking station.

• The docking station then responds with "Standby For Docking" message, specifying the expected time in which the docking will be permitted.

• The docking station will wait at the point if a docking or undocking is in progress for some other craft.

• The docking station sends "Proceed For Docking" message to the spacecraft. The docking port number is specified in this message.

• Again, the spacecraft fires its thrusters to reach the assigned port.

• The spacecraft attains the same orbit and velocity as the docking station.

Docking!

•  When the spacecraft is 2000 meters from the docking station, it sends "Docking Alignment Request".

• "Docking Alignment Request" signifies that the spacecraft is now in the same orbit as the docking station. This means that the orbit that was assigned earlier can now be freed up.

• The docking station responds with series of "Docking Adjustment" messages, at each stage asking the craft to adjust its position and velocity with respect to the docking port.

• The spaceship acknowledges each of these adjustments by "Docking Adjustment Ack" messages.

• Finally the docking station sends "Dock Now" message to the spacecraft.

• The space craft finishes the actual docking and responds with "Docking Completed"

• The docking station then sends "Air Quality Command" specifying the air pressure and composition on the station.

• The docking station adjusts its air quality to match that of the docking station and responds with "Air Quality Achieved"

• At this point the docking station opens the airlock and sends "End of Docking Procedure"

• The spacecraft acknowledges with "End of Docking Response". This signifies that docking has been completed!