2014.B.3.2 An External-Occulter Formation Flying Solar Coronagraph Instrument on CubeSats


Neerav Shah (1)
Joseph Davila (1)





coronagraph, solar, heliophysics, formation flying


Current operational spacecraft with a solar coronagraph include: SOlar and Heliospheric Observatory’s Large Angle Spectrometric Coronagraph (SOHO LASCO), and Solar TErrestrial RElations Observatory’s white-light coronagraphs (STEREO Cor1 and Cor2). Both missions have limited operations remaining as are beyond their designed life of 3 years (17 years for SOHO and 8 years for STEREO). Therefore there is a need to replace the on-orbit images taken by these instruments. Numerous instrument and mission concepts are being conceived to replace these in-space coronagraphs. A set of these concepts is the formation flying distributed external occulter where one spacecraft caries an occulter disk and the other spacecraft caries a coronagraph camera. Orders of magnitude improvement in image quality is attainable with this distributed instrument concept.

A dual-spacecraft formation flying solar coronagraph mission aboard two three-unit (3U) CubeSats will be presented. One spacecraft is used to block the Sun while the other spacecraft images the Sun’s corona from within the shadow of the first spacecraft. The shadow casting spacecraft is called the Occulter Spacecraft (OSC) while the imaging spacecraft is called the Coronagraph Spacecraft (CSC).

This talk will discuss the science goals along with a guidance, navigation, and control (GN&C) technique to attain and maintain the distributed instrument system. Science goals drive the formation geometry. The geometry translates to requirements on the formation, and ultimately requirements on the individual spacecraft. In order to have continuous observations of the Sun the mission will operate at the first Sun-Earth Lagrangian point, L1. At L1 the differential gravitational forces between the two spacecraft are minimized allowing the spacecraft to achieve the precise alignment required to make a science measurement. Once in orbit at L1 a series of complex rendezvous and proximity operations must be conducted to bring the spacecraft into coarse alignment. Then it is the job of the fine alignment system to achieve the required alignment for science operations to be conducted. We discuss a technique that relies on a single instrument combined with navigation algorithms to independently measure the relative and absolute alignment of the formation, the Solar Formation Alignment Camera (S-FAC).


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