Attachment Settings

The Attachment Settings enable the specification of configurations of satellites where one or more child satellites are initially attached to a parent satellite. You can specify the attached locations of the children in the selected coordinate frame along with deployment times and an impulsive change in the relative velocity between the parent and child during deployment.

This topic covers the following material:

• Settings associated with configuring deployments; see the table below
• Details on the simulation and estimation of deployments

Attachment Settings
Setting	Description
Role	Select one of the following options: None – This means the satellite is not involved in a deployment operation as either a parent or child. This is the default setting. Parent – This means the satellite can serve as a platform for deploying child satellites. Use EventList to configure child satellite attachments and deployments. Child – This satellite can deploy from a parent satellite. You cannot set this option directly. Role becomes set to Child for a satellite when you associate a child satellite with a deployment event using the parent satellite EventList.
Parent	Displays the name of the parent of a child satellite after you associate the child with the parent in the EventList of the parent. It is only visible when Role is set to Child.
EventList	This is a list of child satellite deployment events. It is only visible when Role is set to Parent. Use the following settings to specify a deployment event: Enabled – Setting this to true means a deployment event will occur during a run of the Simulator or Filter. Satellite – Enter the name of the child satellite to be deployed. Epoch – Enter the time at which the child satellite will be deployed. Type – Choose the type of event; Deployment is the only option. Frame - Specify the coordinate frame for ODTK to use to compute the child satellite's initial position and deployment maneuver velocity. The options are: Gaussian (RIC), ICRF, Inertial, and Parent Body. At deployment, the child satellite velocity will differ from the parent satellite velocity by the specified DeltaV. When you choose the Parent Body frame, the child velocity will additionally include the effect of the rotational rate of the parent body frame relative to the central body inertial frame on the the velocity of the AttachPoint. If the AttachPoint coordinates are all zero, the rotational effect on the velocity will also be zero. When you select a frame other than Parent Body, there is no rotational effect on the child satellite velocity. AttachPoint – Specify the location of the child satellite center of mass in the selected coordinate frame of the satellite during the time when the child is attached to the parent. Use this to set the initial position of the child satellite during deployment. DeltaV – Specify the initial separation velocity between the child and parent satellites at the moment of deployment, in the selected coordinate frame. ODTK uses the relative mass ratios to determine how much adjustment of inertial velocity to apply to the parent and child satellites. DeltaVUncertainty – This is the sigma uncertainty in the initial separation velocity between the child and parent satellites at the moment of deployment, specified in the selected coordinate frame. ODTK uses it during the generation of random perturbations by the simulator and to inflate the velocity covariance in the filter. MeasurementExclusionSpan – Specify the duration of time between the moment of deployment and when ODTK should start simulating or processing measurements on the deployed child satellite. ODTK will not simulate measurements to the child satellite during the exclusion span. ODTK ignores existing measurements in the exclusion span during filtering.

Simulation and estimation across a deployment event

Neither the ODTK Simulator nor the Filter will execute across a deployment event in a single run, and least squares estimation for deployment events is not available at all. Instead, the simulator or filter process runs up to the time of deployment and then restarts at the deployment time. It is, therefore, important to have the writing of restart records enabled when modeling a deployment event. If an enabled deployment event is within the span of a Simulator or Filter run, the run automatically stops at the deployment time. When executing prior to the time of a child satellite deployment, the child satellite is not in state space, even if it appears explicitly in the SatelliteList or the SatelliteList is empty, indicating the use of all available satellites.

ODTK computes the initial position for the child satellite at the deployment time from the parent position, the offset of the child center of mass in the selected coordinate frame, and the parent attitude at the time of deployment. ODTK computes the initial velocity of the child satellite from the parent position, the angular velocity in the selected coordinate frame, the separation Delta-V, and the parent attitude at the time of deployment. During simulation, ODTK applies a random perturbation for the initial separation velocity, with a portion of the perturbation going to both the parent and child velocities based on the post-deployment mass ratios.

Use of instant maneuvers

The deployment modeling capability inserts instant maneuvers into the simulation and estimation processes for the child and parent satellites to model the effect of the deployment on the trajectories of both objects. Modeling the deployment in this way enables the use of existing ODTK maneuver summary reports to evaluate the effect of the deployment. ODTK does not insert these instant maneuvers into the actual satellite objects, so they are not visible in the InstantManeuverList in the satellite settings.

Mass considerations

The parent satellite will assume the additional mass of attached child satellites during orbit propagation prior to the deployment of the children. During the deployment process, the instant maneuver used to model the impulse on the child satellite will indicate zero mass loss, allowing the child satellite to begin its free-flying phase with its original mass. The instant maneuver used to model the impulse on the parent satellite will indicate a mass loss equal to the mass of the child satellite. ODTK does not model the change in the parent satellite center-of-mass location during deployment.

Post-deployment processing

After a child satellite has deployed, you should remove it from the parent satellite EventList or the entry for that child should be disabled in the list. Either action will result in ODTK setting the Role of the child satellite back to None and recognizing the parent and child satellites as independent satellites. You should make this change after the runs containing the deployment event have completed.

Recommended workflow

A typical situation will involve child satellites being attached to the parent at launch and remaining in that configuration until deployed. In this case, follow these steps:

1. Create an initial configuration with all children attached to the parent.
2. Configure the parent and all child satellites individually.
3. Attach the children to the parent by creating entries in the EventList of the parent.
4. Simulate measurements from launch until the first deployment.
5. Simulate over the deployment event, starting in AutoRestart mode.
6. Disable the deployed satellite entry from parent EventList.
7. Simulate measurements over the remaining interval of interest, starting in AutoRestart mode.
8. Perform an estimation using measurements from launch until first deployment.
9. Estimate over the deployment event, starting in AutoRestart mode.
10. Remove the deployed satellite entry from parent EventList.
11. Perform an estimation using measurements over the remaining interval of interest, starting in AutoRestart mode.
12. Repeat these steps for subsequent deployments, if needed.

ODTK limitations for deployments

Deployments are specialized activities and have a number of restrictions within ODTK.

• LeastSquares processing is not available while the satellite has a Role of Child.
• LeastSquares processing is not available for a Parent Role satellite when there is a deployment event within the fit span.
• Ephemeris predictions from the Simulator or Filter will not model deployment events that fall within the prediction span.
• Ephemeris prediction from a Parent Role satellite will not model deployment events that fall within the prediction span.