MAXIM

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MAXIM

• Flight Dynamics
• Michael Mesarch
• Frank Vaughn
• Marco Concha
• 08/19/99

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Mission Assumptions

• Orbit Assumptions
• Two spacecraft (optics and detector) in
  near-circular Heliocentric orbit at ?1 AU (
  Drift-away orbit)
• Launch in 2007-2010
• Mission Lifetime 3 years required
• Maneuver Requirements
• Desire to point to 150 inertial targets over 3
  year mission lifetime
• Separation along optical axis to be maintained at
  450 km ? 10s of meters
• Misalignment perpendicular to optical axis ? 5 mm

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MAXIM Range from Earth
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MAXIM Trajectory in Solar Rotating Coordinates
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Formation Flying Challenge

• The MAXIM formation flying concept is new -
  combination of previous implementations with a
  wrinkle
• Landsat-7 and EO-1 maintain a constant distance
  between each other in the same orbit while
  imaging the earth - image comparison is achieved
  because of close distance between s/c
• Constellation-X utilizes multiple s/c to observe
  the same target without any restriction on
  relative position
• MAXIM combines both constant separation and
  constant attitude/pointing. The detector s/c must
  fly around the optics s/c continuously during
  an observation - its orbit will continually
  change.

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Stationkeeping and Pointing Control

• Only simple cases have been considered
• Continuous viewing of Ecliptic Pole
• Optics and detector S/C are in circular orbits
  which differ by a small inclination angle to
  achieve initial 450 km separation
• Continuous acceleration of detector S/C away from
  optics S/C at ? 1.7x10-8 (m/s2) will cancel
  relative out-of-plane motion for short periods
• Rotation to view opposite pole requires
  acceleration on the order of 4 degrees of
  magnitude higher
• Long-term effects require additional analysis
• Targets in Ecliptic plane
• Optics and detector S/C are in circular co-planar
  orbits which differ in semi-major axis to achieve
  initial 450 km separation
• Preliminary analysis indicates that maintaining
  450 km separation is feasible in the short-term
  by canceling the initial velocity difference
  between the S/C, but this results in a larger
  separation in the long-term,( i.e, half an orbit
  later).
• How to maintain pointing in this case is not
  clear - requires management of multiple orbital
  variables
• Design of a pointing control strategy will not be
  a trivial undertaking

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Ecliptic Pole Pointing - Uncontrolled
Optics
Detector
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Ecliptic Pole Pointing - Controlled
Detector
Optics
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Further Work

• Perform more detailed analysis on the simple
  cases considered to be certain the dynamics is
  fully understood
• Formulate a pointing control strategy
• Determine control authority (acceleration,thrust)
  required to transition from one target to another
  in a reasonable amount of time (days?)