Pyxis

Pyxis aims to develop a new approach to optical and infrared interferometry for astrophysics—the only way to achieve the highest angular resolution images and measurements. It will serve as a crucial technology demonstration for future formation flying space-interferometry missions and enable for more flexible ground-based stellar interferometry. To that end, Pyxis is a multi-platform, linear-formation, ground-based interferometer in development at the Australian National University's (ANU) Research School of Astronomy & Astrophysics (RSAA) with the following novel key features:

• A frame of reference tied to a precision star tracker on a moveable platform rather than the Earth itself.
• Use of newly affordable precision MEMS accelerometers and laser ring gyroscopes to define the frame of reference.
• Path-differential but not time differential white-light metrology that vastly simplifies system architecture.
• Integrated optical (camera) based coarse metrology.
• Linear array architecture that can be used in low earth orbit rather than just the earth-moon L2 point.

Motivation

Space interferometry is the inevitable endpoint of high angular resolution astrophysics. It has long been recognised as the only way to take mid-infrared spectra of earth like planets (Cockell et al. 2009), and is simulated to have more success than even the largest launchable >$10B coronagraphic telescopes in detecting any habitable planet biosignatures (Kammerer and Quanz, 2018). The reason for this is that the angular resolution of any telescope is directly related to the diameter of its mirror or separation between elements in an interferometer. Once the required diameter becomes too large to construct mechanically or to launch, the only option is to launch parts of the mirror as separate light collector spacecraft with light combined in a beam combiner spacecraft—becoming a space interferometer.

Many previous studies have been made of space interferometer missions, in one of two categories. These were either connected element interferometers (Unwin et al. 2008; Leisawitz et al. 2007), which are much more limited than formation flying, or formation flying interferometers at the Sun-Earth L2 point (Cockell et al. 2009, Le Duigou et al. 2006), which are vastly more expensive than low earth orbit compatible designs, mostly due to launch costs. Two critical technology areas have not been at an adequate level to progress the formation flying optical and infrared interferometry missions: compact, cryogenic compatible nulling beam combiners (the subject of ARC Discovery Project DP19010477), and formation flying itself, including coarse and fine metrology systems—the goal of the Pyxis Project (funded as ARC Discovery Project DP200102383).

System Breakdown

Pyxis is to be based at ANU's Mount Stromlo Observatory, next to the Advanced Instrumentation and Technology Centre (AITC) laboratories. Two science telescope platforms (known as the Deputies) and a single central beam combining platform (known as the Chief) will be located on three separate, wheeled 6-axis platforms able to move to position on a moderately flat surface and then track spatial and angular positions. Starlight is focused and collimated by the telescope primary and secondary mirrors, before reflecting off of 45° flat mirrors to the tip/tilt, fibre injection, and beam combiner systems on the central platform. Spatial locations are measured using accelerometers and a white-light fast metrology system, with the frame of reference of the central beam combiner determined by a combination of a fibre laser gyroscope and star tracker. In addition to the electro-mecanical and control systems, the Pyxis concept can be broadly broken into the following four systems:

Publications

Pyxis: a ground-based demonstrator for formation-flying optical interferometry:
Hansen J.~T. et al., 2023, JATIS, 9, 045001, doi:10.1117/1.JATIS.9.4.045001,

A Linear Formation Flying Astronomical Interferometer in Low Earth Orbit:
Hansen J.~T., Ireland M.~J., 2020, PASA, 37, e019. doi:10.1017/pasa.2020.13,

Linear formation-flying astronomical interferometry in low-Earth orbit: a feasibility study:
Hansen J.~T., Ireland M.~J., Travouillon T., Lagadec T., Mathew J., Herrald N., 2020, SPIE, 11443, 1144366. doi:10.1117/12.2560890,

Compact unambiguous differential path-length metrology with dispersed Fabry-Perot laser diodes for a space interferometer array
Lagadec T., Ireland M., Hansen J., Mathew J., Travouillon T., Madden S., 2020, SPIE, 11446, 114462F. doi:10.1117/12.2561927,