Maintain NMC RPO Sequence

The Maintain Natural Motion Circumnavigation (NMC) RPO sequence maintains an NMC when the target and chase satellites experience differential forces. Generally, this force differential is due to drag and solar radiation pressure (SRP). These are the dominant differential forces when operating in proximity, as the differences in gravity and relative third body perturbations are very small when the relative positions are within 100 km.

Drag and SRP differences between the target and chase satellites are largely due to different size, area, mass, and shape. To effectively use this sequence, you must pay special attention to those parameters by using the Update_Spacecraft_Parameters sequence in the right places.

The Maintain NMC sequence utilizes a reference satellite that creates an NMC with matched force models to the target. The chase satellite has different spacecraft parameters (area, mass, size, and shape) that cause the NMC to deviate from the reference NMC. This requires station-keeping maneuvers to stay on the desired NMC.

With this sequence, you can specify the duration to maintain the NMC and the maximum error from the desired NMC. From those inputs, this sequence computes all required Delta-Vs to stay within that maximum error from the ideal NMC.

The first two pictures below show the maintaining of an NMC with a maximum error of 5 meters for one revolution. In this GEO example, the Delta-V required for a 100% Cr difference was approximately 1 cm/sec for one revolution. The last picture shows what would have happened to the NMC if there were no station-keeping maneuvers, with the relative orbit shown in red.

Watch the following video to learn more about the RPO sequence on this page.

Sequence parameters

Option	Description
Maintain_Duration	Enter the duration to maintain the NMC.
Maintain_MaxError	Enter, in distance units, the maximum error from the reference NMC.
Maintain_Reference	Enter, as a string, the name of the reference satellite that has the ephemeris for the reference NMC.
Engine_Name	Enter, as a string, the name of the finite maneuver engine model.
Maneuver_Type	Select the type of maneuver, "Impulsive" or "Finite," from the drop-down list.
WhoAmI	Enter, as a string, the name of the current satellite.
Sequence_Name	Enter, as a string, the name of this sequence. This is nominally Maintain_NMC, but if you insert the sequence multiple times in the MCS, Astrogator adds a monotonically increasing number to the end of the name ( Maintain_NMC1, Maintain_NMC2, etc).