Coronagraphy and exoplanet imaging · 1998

Codex

A coronagraph with a deformable mirror for Hubble, designed to image Jupiter-like planets.

Proposal

P97-751, dated April 1997

Role

Deputy Principal Investigator and lead conceptual designer; PI Robert A. Brown

Target

Planet detection at 10⁻¹⁰ contrast; λ/2500 rms wavefront stability

Hardware

140-actuator deformable mirror, Gaussian occulting mask, selectable Lyot stops, ACS flight-spare CCD

Codex was proposed as a new axial instrument for Hubble that combined three functions: a coronagraph to suppress diffracted light, a deformable mirror to cancel the scatter from the telescope's own mirror ripple, and deliberate interferometric cancellation of what remained. Simulations in the proposal reached the 10⁻¹⁰ level needed to see a Jupiter-like planet around a nearby star, a thousandfold better than the ACS coronagraph then being built.

Its central idea was a new on-board algorithm for setting the deformable mirror directly from science images. Each residual speckle is cancelled by a mirror ripple of matching spatial frequency, with the phase found by stepping the ripple through four positions. This dark-hole speckle nulling became the basis of the high-contrast testbed work that followed for TPF and Eclipse.

The team brought together the PIs of WFPC2 and ACS, the inventors of COSTAR, and JPL's deformable-mirror group. The proposal derived its wavefront requirement from Brown and Burrows (1990).

From the archive

• HST Coronagraph (design note, c. 1995–96) →

Papers

• 1990
  On the feasibility of detecting extrasolar planets by reflected starlight using the Hubble Space Telescope

  Brown, R. A.; Burrows, C. J.

  Icarus 87, 484

  DOI