Magnetospheric Multi-Scale Mission

The Magnetospheric Multi-Scale Mission (MMS) consists of four spinning spacecraft flying in a tetrahedral formation in highly elliptical earth orbits to study the phenomenon of magnetic reconnection on the dayside magnetopause and the nightside neutral sheet. A mission of this type presents many flight dynamics challenges. During FY08, MMS Phase B development and associated analyses proceeded with a System Design Review(SDR)in June. A PDR was held in mid-2009 for this in-house mission.

Navigation work in 2008 focused on supporting the development of the Interspacecraft Ranging and Alarm System (IRAS), a weak signal GPS receiver and a crosslink receiver/transmitter with GEONS embedded software for onboard orbit determination. Efforts included:

• Documenting covariance sampling techniques
  
• Defining statistical analysis techniques
  
• Analysis of solar radiation pressure model accuracy requirements
  
• Analysis of one-way forward Doppler to augment the GPS and crosslink measurements
  
• Analysis of crosslink message size reductions and associated reduction in the GEONS configuration from solving for all four satellites simultaneously to solving for the local satellite only
  
• Documentation of assumptions for intra-formation collision probability analysis
  
• Evaluation of the existing Collision Assessment Tool
  
• Analysis of the consistency of IRAS and GEONS measurement models
  
• Analysis of IRAS TRL6 test data
  
• Baseline testing to validate the crosslink simulator for IRAS
  
• Orbit determination sensitivity analysis of the commissioning phase
  
• Monte Carlo analysis of an MMS Phase 2b, 10 km formation maintenance maneuver which is expected to be the most stringent navigation scenario.

Mission design efforts involved launch window expansion around the days analyzed for the MDR; finite burn analysis of several propulsion thrust options; a comprehensive fuel budget estimate; analysis of eclipse periods relative to launch orbit and mission attitude conditions; contact analysis for antenna design and mission operations planning; launch vehicle-related analysis; development of a method for raising the apogee of all four MMS within the science and engineering constraints and off-nominal case analysis; analysis of the impact of maneuver timing, magnitude, and direction errors on the relative orbits; analytic and Monte Carlo analysis of the interspacecraft range, range-rate, and relative acceleration for IRAS operating limits; simulation of truth data for Constellation HiFi development testing and for IRAS TRL-6 testing; and formation stability analysis.

Several design strategies that seek to improve the long-term stability properties of MMS formations were investigated. These techniques employ nonlinear programming to optimize a formation performance metric, subject to periodicity constraints. Neglecting error sources, these techniques reduce maneuver frequency by a factor of two.