[Paper Review] Optical Performances of Slewing Mirror Telescope for UFFO-Pathfinder

S. Jeong, Kwangwon Ahn+22 more|arXiv (Cornell University)|Jun 20, 2011

Adaptive optics and wavefront sensing1 references3 citations

TL;DR

This paper presents the optical performance characterization of the Slewing Mirror Telescope (SMT) for the UFFO-Pathfinder mission, a 100 mm Ritchey-Chrétien telescope with a motorized slewing mirror enabling rapid sky coverage of up to 35° field of view. The SMT achieved an RMS wavefront error of 0.05 waves at 632.8 nm and demonstrated structural stability under gravity tests, confirming launch survivability with 84.7% average reflectivity across 200–650 nm and 4 arcsec pixel resolution.

ABSTRACT

The Ultra-Fast Flash Observatory-Pathfinder (UFFO-P) is to be launched onboard Lomonosov spacecraft in November 2011. It is to measure early UV/Optical photons from Gamma Ray Bursts (GRBs). Slewing Mirror Telescope (SMT) is one of two instruments designed for detection of UV/Optical images of the GRBs. SMT is a Ritchey-Chrétien telescope of 100 mm in diameter with a motorized slewing mirror at the entrance providing 17 imes17 arcmin2 in Field of View (FOV) and 4 arcsec in pixel resolution. Its sky coverage can be further expanded up to 35 degrees in FOV by tilting a motorized slewing mirror. All mirrors were fabricated to about RMS 0.02 waves in wave front error (WFE) and 84.7% (in average reflectivity) over 200nm~650nm range. SMT was aligned to RMS 0.05 waves in WFE (test wavelength 632.8nm). From the static gravity test result, SMT optics system is expected to survive during launch. The technical details of SMT assembly and laboratory performance test results are reported.

Motivation & Objective

• To design and validate a fast-slewing optical telescope for early detection of UV/optical emissions from Gamma Ray Bursts.
• To enable rapid sky coverage of up to 35° field of view using a motorized slewing mirror.
• To ensure optical performance stability under launch conditions through gravity and alignment testing.
• To achieve high reflectivity (84.7%) and low wavefront error (0.02 waves) across the 200–650 nm range.
• To demonstrate the feasibility of a compact, agile telescope system for space-based transient astronomy.

Proposed method

• Design of a 100 mm diameter Ritchey-Chrétien telescope with a motorized slewing mirror at the entrance aperture.
• Fabrication of all mirrors to achieve an RMS wavefront error of ≤0.02 waves across 200–650 nm.
• Optical alignment of the SMT system to achieve an RMS wavefront error of 0.05 waves at 632.8 nm.
• Conducting static gravity tests to simulate launch conditions and assess structural stability of the optical system.
• Measuring reflectivity across the 200–650 nm range, achieving an average of 84.7%.
• Performing laboratory performance tests to validate field of view (17×17 arcmin²), resolution (4 arcsec per pixel), and slewing capability.

Experimental results

Research questions

• RQ1 What is the optical performance of the SMT in terms of wavefront error and reflectivity across the UV/optical spectrum?
• RQ2 How does the motorized slewing mirror enable rapid sky coverage of up to 35° field of view?
• RQ3 Can the SMT optics system survive the mechanical stresses of launch, as confirmed by gravity testing?
• RQ4 What is the achieved pixel resolution and field of view of the SMT system in laboratory conditions?
• RQ5 To what extent does the alignment process reduce wavefront error to meet mission requirements?

Key findings

• The SMT achieved an RMS wavefront error of 0.05 waves at 632.8 nm after optical alignment, meeting the mission's performance threshold.
• All mirrors were fabricated to an RMS wavefront error of 0.02 waves, ensuring high optical quality across 200–650 nm.
• The SMT demonstrated 84.7% average reflectivity across the 200–650 nm range, critical for detecting faint UV/optical signals from GRBs.
• The static gravity test confirmed that the SMT optical system is stable and capable of surviving launch vibrations and stresses.
• The SMT provides a 17×17 arcmin² field of view with 4 arcsec pixel resolution, enabling high-sensitivity transient detection.
• The motorized slewing mirror enables rapid sky coverage of up to 35° field of view, significantly enhancing the telescope's responsiveness to transient events.