State vector maintenance

What is a state vector?

Put simply, it’s where an orbiting vehicle is and where it is going at a given instant in time.

Shuttle state vector formats

Primarily, we use the Cartesian (X, Y, Z, Xdot, Ydot, Zdot) format in the Aries Mean-of-1950 (M50) coordinate system utilizing feet and feet per second units.

We can support almost any other format for customers and other external commitments

Different units

Different coordinate reference frames (J2000, TDR, etc.)

Different coordinate elements (Two-line Elements, Spherical)

Ground-based Navigation Monitoring

The FDO is responsible for maintaining the best knowledge of the Orbiter’s state vector in a ground-based ephemeris

Raw state vector tracking data provided by TDRS S-band beacon tracking and ground station C-band “skin tracking”

"Least Squares" fit of tracking data provides final state vector

Ephemerides, based on best state vectors, are used for future planning purposes

Upcoming maneuvers, deorbit targeting, deploy opportunities

Acquisition events (TDRS, ground sites, sun/moon lighting, etc.)

The FDO will maintain an ephemeris for each vehicle of interest

On-board Navigation Monitoring

The FDO is responsible for maintaining the quality of the on-board navigation state vector during non-day-of-rendezvous activities.

The FDO will update the on-board state vector as required for targeted maneuvers and to ensure that adequate deorbit/entry capability is maintained.

The predicted on-board state vector downtrack error must be less than 20 NM at next deorbit TIG (FR A4.1.3-1).

The "rule-of-thumb" will have the FDO consider an update if the semi-major axis error is greater than 1000 feet or if a two-orbit prediction of downtrack error is greater than 20,000 feet.

The FDO will provide a GO/NO-GO assessment of the current state vector for crew sleep periods.

When possible, the FDO will uplink a new vector prior to crew sleep.

If mission events do not allow pre-sleep vector uplink, and the current state vector is predicted to violate the criteria in FR A4.1.3-1, the FDO will make every effort to uplink the state vector as soon as possible after crew sleep begins.

The FDO will uplink and maintain a target state vector for Rendezvous NAV target track activities.

The FDO is also responsible for uplinking TDRS vector information to the SM machine.

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