Goddard Space Flight Center
1 Solar Coronagraphs Goddard Space Flight Center
• Observe off-disk coronal emissions from Sun. • Dominant noise source: – Diffraction of on-disk light around the occulter – Vignetting on externally occulted coronagraphs • Noise inversely proportional to the occulter/detector distance – Better signal to noise – Closer to the corona 2 Near-future state of Coronagraphs Goddard Space Flight Center • External Occulter on extended boom – Deployable boom extends occulter out to a several meters – Mechanical and thermal issues in alignment
• Formation Flying: – One spacecraft serves as occulter – Other spacecraft serves as detector – E.g., ESA Proba-3 – Top Challenges: ESA Proba-3 • Alignment of two spacecraft with target (i.e, formation flying Technical technology) • Perceived risk (mass, volume, cost) associated with flying two spacecraft in formation Programmatic 3 Demonstration on CubeSats Goddard Space Flight Center • Purpose: • Development Path – Low-cost, low-risk – Tech Demo (VTDM, CANYVAL-X) – Demonstrate novel GN&C techniques – Science Demo (TBD) – Science on CubeSats – Full Scale Mission (TBD)
Virtual Telescope Demonstration CubeSat Astronomy by NASA and Yonsei using Virtual Telescope Alignment Mission (VTDM) – Experiment (CANYVAL-X) 4 Mission Operations Considerations Goddard Space Flight Center
• Relative disturbances high in Low Earth Orbit – Drag, Gravity gradient dominate – Complex proximity operations and station-keeping maneuvers – High fuel consumption – Minimal science gathering
• Lagrange or Drift-away orbit – Eliminates issues with LEO – Relative dynamics become nearly linear – Power an issue: one spacecraft in shadow – Deep space communications – CubSats in deep space? The Virtual Telescope Demonstration Mission (VTDM) redezvous and proximity operations phase in LEO Ideal for Science Mission (Shah, N., et.al.)
5 Science Demo Mission Goals (1)
Goddard Space Flight Center Nominal FOV Image with occulter blocking Sun
Image shifted in FOV (Coronagraph orientation change)
Occulter shape change (Occulter SC orientation change)
Reduced image capture / Increased occulter size Occulter shifted off of Sun (decreased relative (relative transverse position range) change) (converse is increased image capture due to increased range)
6 Science Demo Mission Goals (2) Goddard Space Flight Center • Observe dynamics of solar phenomena extending away from the sun. • Reduce background image noise distortions • Collect enough photons from 5 to 20 solar radii • Keep Coronagraph camera within shadow of occulter
• Roughly Translates to: – Image corona in visible light from 5 to 20 Solar Radii – 1 arcminute pointing towards the Sun center – 5 second exposure time
7 Formation Alignment Requirements Goddard Space Flight Center
Coronagrpah Occulter Spacecraft Spacecraft (CSC) (OSC) Absolute Attitude 0.5 degrees 1 arcminute Knowledge Absolute Attitude ~degree ~arcminute Control Transverse +- 1.6 arcmin @15 m = +- 0.6 Relative Position cm Knowledge (1/10 of solar radii) Transverse uN control available Relative Position Control
Occulter Spacecraft (OSC)
Coronagraph Spacecraft (CSC) 8 How Do We Measure the Formation Axis?
Goddard Space Flight Center
Solar Formation Alignment Camera (S-FAC) Single instrument to measure relative position wrt formation axis (i.e., inertial line of sight)
Attitude Coronagraph Spacecraft
Formation Axis Relative Transverse Position
S-FAC Algorithm objective: - Move dot (CSC) towards x (target) - Move x to center of focal plane - Difference in dot and x represent transverse position errors off formation axis S-FAC Focal Plane 9 Conclusions Goddard Space Flight Center • Dominant noise source in traditional coronagraphs inversely proportional to distance between occulter and detector • Formation flying of two spacecraft offers greatest opportunity to reduce these errors • Formation flying complications in LEO: disturbances result in minimized science observation • Lagrange or Drift away orbit ideal • Various demo on CubeSats to increase TRL – S-FAC – Distributed Coronagraph • Reduce risk for full scale mission
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