Docking Adapter

SWITCH TO API

Description

The Docking Adapter is a component that can be attached to a Spacecraft and enable docking between two spacecraft, as part of Rendezvous, Close-Proximity Operations, and Docking (RCPOD) activities. The docking adapter can connect the root spacecraft it is attached to to another docking adapter and will handle the automatic connection between the two spacecraft when they are within a suitable angle and target from each other.

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Example Use Cases

• Docking with a Target Spacecraft: Facilitates automatic docking between two complying spacecraft when the distance and angle between the adapters is within the minimum range.

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Module Implementation

The docking adapter must have a target that can be attached to. Setting a target docking adapter, on another spacecraft, can be set using Set Docking Adapter. This sets up the Capture Distance, $r_c$, which is the maximum distance between the two docking adapters before the attachment is made in meters, and the Capture Angle, ${\theta }_c$, which is the maximum angle the two adapters can be misaligned in degrees before the attachment is made.

The docking adapter calculates whether the target docking adapter is within range by using a standard distance check, where it will dock if $r\le r_c$, with $r$ being calculated by the difference between the two objects in inertial world space. It will also only dock if $\Delta \theta \le {\theta }_c$, where the angle difference $\Delta \theta$ is calculated based on the up axis vector of the two objects:

$$\Delta \theta ={\cos }^{-1}({\uparrow }_A\cdot {\uparrow }_B)\times \frac{180}{\pi }$$

where ${\uparrow }_A$ defines the up axis of the first and second docking adapters in the inertial world frame.

When one spacecraft is docked to the other spacecraft, the ‘child’ spacecraft’s dynamics are tracked by the ‘hub’ spacecraft. The contributions of the effectors, such as mass components and reaction wheels, are contributed to the hub instead of the child while the docking occurs. When the spacecraft is docked, the spacecraft with the bigger mass is chosen to be the hub. If the two spacecraft have equal mass, then the first adapter spacecraft added will be the hub spacecraft.

When the two spacecraft are docked, linear momentum is conserved. This is calculated by the different in the relative inertial velocities, $\Delta v$, where $\Delta v=v_c-v_h$, for $v_c$ and $v_h$ being the velocity of the child and the hub respectively in the inertial world frame. Then, the velocity of the hub is updated directly to ensure momentum of the two-part system is conserved:

$$v_h=v_h+\frac{m_c}{m_h}\Delta v$$

where $m_c$ is the total mass of the child and $m_h$ is the total mass of the hub before the docking procedure is completed.

Calling Undock on the docking adapter will release the dock from the two spacecraft, if they are connected. This will maintain both angular and linear momentum of the objects, but will not apply any kick-off forces between the two spacecraft. Once undocked, the target of the root adapter will be set to none again, ensuring the process does not immediately reset.

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Assumptions/Limitations

• If no other docking adapter is connected, the docking adapter will not attach to any other spacecraft.
• When the other docking adapter, specified as the Target, is within the suitable bounds of the current adapter, the spacecraft will be docked. By default, the lighter spacecraft will be docked with the larger spacecraft.
• The docking adapter cannot dock with a non-docking adapter spacecraft. The spacecraft has functionality for docking with debris, but cannot be automatically triggered by this component.
• Each docking adapter can only have one docking target at a time, but it can be changed during the simulation.