Marco Concha Charles Petruzzo June 28, 2001 SuperNova/ Acceleration Probe (SNAP) Flight Dynamics

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 2 Flight Dynamics Topics  Driving Requirements and Assumptions  Orbit Comparison Table  Prometheus  Prometheus Circular  Deployment Scenarios  Tracking Visibility Scenarios  Trades to Consider  Issues and Concerns

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 3 Driving Requirements and Assumptions  View North and South Ecliptic Poles  Maximize Downlink capability (coverage and rate)  Prometheus Orbit Scenario  19 x 57 Re mission orbit  lunar swingby deployment  source: High Earth Orbit Design for Lunar-Assisted Medium Class Explorer Missions, McGiffen, D. A. and Matthews, M., 2001 Flight Mechanics Symposium, NASA Goddard Space Flight Center.

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 4 Options Considered Orbit Comparison Table

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 5 Prometheus Orbit  “Prometheus Long”  source:  1.High Earth Orbit Design for Lunar-Assisted Medium Class Explorer Missions, McGiffen, D. A. and Matthews, M., 2001 Flight Mechanics Symposium, NASA Goddard Space Flight Center.  2. Mission Feasibility Study for the KRONOS High Earth Orbit, McGiffen, D. A. and Matthews, M., CSC , NASA Task Order S G,  Pros  Above Van Allen Belts  No orbit corrections required during mission orbit  No Earth occultation  Eclipse seasons: typically one event per year  Cons  Can’t use torque rods for momentum management; Propulsion?  Tracking gaps (0-35 hours dependant on inclination, station configuration)  Difficult to analyze and design but lunar flyby not a new technique  Lifetime Goal TBD refer to KRONOS paper  Disposal TBD refer to NSS

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 6 Fly-by Scenarios  Non Encounter  Leading Edge: Lower perigee  Trailing Edge: Raise perigee  Very Near Encounter !

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 7 Tracking Visibility Scenarios  0, 20, 40, 65 degrees inclination  3 stations: Tokyo, Berkeley, Lyon  5 stations: Tokyo, Berkeley, Lyon, Hawaii, Santiago

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 8 Coverage Example: 3 Stations

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 9 Prometheus Circular Orbit  V to lower apogee  Initial State: 40 Re x 63 Re  Assuming a fly-by can raise perigee to 40 Re (instead of baseline 19 Re)  Model Hohman Transfer  V to lower apogee  Impulsive thrust modeled; in reality may require multiple burns  To achieve a 40 Re circular orbit would require a 136 m/s burn.  Propellant Required  V = 136 m/s  I sp = 220 sec  M initial = 1600 kg  M prop = 96 kg

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 10 Trades to Consider  Tracking Coverage  Number of stations versus Coverage Gaps  Prometheus Orbit Apogee  V to Lower Apogee (Propellant mass) versus Mass to Orbit

SNAP, June 25-28, 2001 Goddard Space Flight Center Flight Dynamics Page 11 Issues and Concerns  Refer to TBD’s in Orbit Comparison Table  Lunar swingby  Transfer to mission orbit via swingby - How high can perigee be raised? What is the maneuver precision and risk mitigation required for this limit?  Analytically intensive, will require high degree of skill. Iterative design process is slow, will limit solution space. Optimal solution may be elusive.