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NPSAT1

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Description of Directed Study or Thesis 

NPSAT1 will be launched as a secondary payload on the Evolved Expendable Launch Vehicle (EELV) Atlas V.  The Atlas V will provide a medium lift capability in the EELV class of launch vehicles. NPSAT1 will be mated to the Atlas V using the EELV Secondary Payload Adapter (ESPA) and a Lightband separation system.  After separation from the launch carrier, NPSAT1 will startup and begin autonomous operations including battery charging, initial attitude acquisition, and listening for the NPS ground station.

The scope of the study is to develop algorithms to take the initial GPS receiver state vector and perform onboard orbit propagation. The result of the orbit propagator is a time-stamped location report that the spacecraft can use for scheduling of operations and experiments, such as the CERTO radio beacon or listening for the NPS ground station. The GPS receiver provides a time-stamped state vector of the spacecraft (time, lat., lon., alt., and rates). The output should be in the same format.

In addition to the GPS receiver, an onboard SGP4 propagator will be implemented in the event of a hardware failure of the GPS receiver. In this case, a two-line element set will be uploaded to NPSAT1 from the ground and the onboard SGP4 propagator will be used to provide the same report. The SGP4 propagator provides output in XYZ (ECI) coordinates.  This data needs to be converted to the report format.

A 3rd part of the problem is to use the spacecraft navigation report from either of the above propagators to determine when a spacecraft operation or an experiment should be activated / scheduled. This would be done by using the navigation information, i.e., the sub-satellite point, and arriving at a radius on the globe within which the spacecraft can perform the necessary operations such as communicating with the NPS ground station, activating the CERTO beacon, or performing VISIM operations. Part of this solution can be used on a ground station computer as part of the user interface for the experimenter for potential experiment activation or target areas. The report format should provide not only the immediate threshold time of when a target is in view, but also a calculation of duration of opportunity.

Proposed Outline

• NPSAT1 Introduction

• NPSAT1 Spacecraft Startup Operations

• NPSAT1 Normal Operations ("A Day in the Life")

• NPS Ground Segment Description

• Analysis Assumptions and Method

• Correlation and Verification

• Conclusions & Recommendations

Suggested References

• NPSAT1 CDR and Delta-CDR Slides

• "Overview of the Naval Postgraduate School Small Satellite, NPSAT1," by G. Prater, et al.
  22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004, Monterey, California

• "Overview of the NPSAT1 Spacecraft Architecture and Technology Demonstration Satellite," D. Sakoda and J. Horning, Paper SSC02-I-4, 16th Annual AIAA/USU Conference on Small Satellites, Logan, UT 2002.