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Deployable Telescope for Compact Spectropolarimeter

Principal Investigator: Kimberly Ennico

Co-Investigators: Abraham Rademacher, Dana Lynch, Amanda Cook

With this Center Innovation Fund we are evaluating the optical and mechanical performance of a collapsible Cassegrain telescope for use as a fore-optic to a compact spectropolarimeter. This effort builds upon previous design work by the NASA Ames Research Center’s Small Spacecraft Division on their mechanical-deployment mechanism for a collapsible 152.4mm diameter f/8 Ritchey-Chretien telescope for a 6U (a “U” is a 10-cm cube) spacecraft with an imager as the payload [1]. The 6U spacecraft measures approximately 30 cm x 20 cm x 10 cm. Deployable larger aperture high-throughput telescopes enable scientific investigations on a small spacecraft platform that would otherwise have required larger packaging environments.

Our spectropolarimeter design requires a high-throughput entrance aperture. Obtaining a smallsat-compatible packaging for a telescope and spectropolarimeter provides a unique instrument for future astrobiology remote sensing applications of Earth, Mars, outer planet icy moons, and biosignature studies of exoplanets. Prior to this effort, our baseline aperture diameter for our instrument compatible with a small-sat architecture was 76.2 mm (3-inch). This new collapsible telescope design potentially increases our collecting area by a factor of four, doubling the aperture diameter.

Our efforts to date have focused on evaluating designs that meet the following requirements for our science instrument application:

  1. The telescope shall have at least a 91.6 cm2 unobscured collecting area.
  2. The telescope's effective f/# shall be faster or equal to f/6.
  3. The distance between the back of primary mirror and system focus shall be at least 6 cm.
  4. At best focus, the telescope system shall deliver spot size and shape repeatability of 10 % at center of the field of view (FOV) and 25 % at the edges of the FOV.
  5. The telescope system shall deliver a bore-sight repeatability of at least 100 microradians.
  6. The telescope system shall deliver a fully-illuminated field over the 50um x 5 mm slit area.

We will select the best design, procure the optics, fabricate the truss and mounting structure, and conduct end-to-end imaging tests with a laboratory test camera and a benchtop version of our spectropolarimeter. We are specifically addressing optical performance, mechanical repeatability, mechanisms and packaging compatibility with small spacecraft payload requirements.

Figure 1: Deployable Telescope Truss Concept

deployable telescope truss

Figure 2: Finalist optical designs for the collapsible telescope under study for cost and performance. Both are compatible with our spectropolarimeter and meet our design requirements.

collapsible telescope