SDSS-V Algorithms: Fast, Collision-Free Trajectory Planning for Heavily Overlapping Robotic Fiber Positioners

Robotic fiber positioner (RFP) arrays are becoming heavily adopted in wide field massively multiplexed spectroscopic survey instruments. RFP arrays decrease nightly operational overheads through rapid reconfiguration between fields and exposures. In comparison to similar instruments, SDSS-V has selected a very dense RFP packing scheme where any point in a field is typically accessible to three or more robots. This design provides flexibility in target assignment. However, the task of collision-less trajectory planning is especially challenging. We present two multi-agent distributed control strategies that are highly efficient and computationally inexpensive for determining collision-free paths for RFPs in heavily overlapping workspaces. We demonstrate that a reconfiguration path between two arbitrary robot configurations can be efficiently found if "folded" state, in which all robot arms are retracted and aligned in a lattice-like orientation, is inserted between the initial and final states. Although developed for SDSS-V, the approach we describe is generic and so applicable to a wide range of RFP designs and layouts. Robotic fiber positioner technology continues to advance rapidly, and in the near future ultra-densely packed RFP designs may be feasible. Our algorithms are especially capable in routing paths in very crowded environments, where we see efficient results even in regimes significantly more crowded than the SDSS-V RFP design.Comment: To be published in the Astronomical Journa

Uncooperative Rendezvous and Docking for MicroSats

This paper proposes a solution to perform active debris removal with a cost effective microsatellite. A complex aspect of debris removal in space is the detection and positive identification of the debris, medium to close approach as well as the orbital rendezvous and following on-site operations. These aspects will require a mix of several technologies, some of which already exist, and some of which will need to be miniaturized and adapted for programs such as CleanSpace One. The rendezvous phases in particular will require a good knowledge of the position of the chaser as well as that of the target. In the CleanSpace One concept, the approach and in-orbit maneuvering will be performed by a micropropulsion system based on miniature thrusters. This concept also proposes that grabbing will be done by means of a robotic claw, which will adapt itself to the form of a non-cooperating object. These are key technologies that currently being developed in EPFL laboratories. The overall microsatellite uses CubeSat and COTS technologies

Astro2020 APC White Paper: The MegaMapper: a z > 2 spectroscopic instrument for the study of Inflation and Dark Energy

MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at

Precision Positioning of Microrobots for Multi-Object Spectrographs

How does one study the evolution of the Milky Way, or the expansion of the Universe, or explore the mysteries of Dark energy? To investigate these complex topics, astronomers require data, and a great deal of it, in the form of the spectra of stars, galaxies, and quasars. In recent years remarkable efforts have been made to develop telescopes and instruments that can measure more light spectra in parallel than ever before. One solution for building these instruments, called Multi-Object Spectrographs, requires the use of several hundreds of small precise automated robots in the telescope's focal plane. Each robot can position an optical fiber with micrometer precision along the focal surface in order to capture and transmit the light of a celestial object to a spectrograph, which then measures the spectrum with great precision. In the future, new instruments will be able to measure over 10000 celestial objects simultaneously, which would consequently require the implementation of as many optical fiber positioners. To assure the development and successful operation of the instrument, every single fiber positioner requires design and validation testing. Tools for such quality assurance have yet to be developed. This thesis proposes solutions to verify, calibrate, control, and operate optical fiber positioners with two actuated rotation axes, serially linked. A metrology system is presented which is capable of accurately measuring position and alignment of the optical fiber, and a detailed model describing the correct behavior of the positioner is introduced. Based on the model, an automated measurement procedure enables calibration and validation of the positioners. The introduced measurement procedure identifies not only flaws in performance, but also various error sources, which help to detect possible design and manufacturing problems. Finally, a method is proposed on how to operate these positioners in the focal plane. Taken together, the results of this thesis can inform the present and future manufacturer of Multi-Object Spectrographs

Design and performances of an optical metrology system to test position and tilt accuracy of fiber positioners

This paper describes the design of an optical metrology system for fiber positioners. The system can be used for accurate calibration and verification of fiber positioners with SCARA-like RR planar kinematics. It is capable of measuring accurately the absolute position and tilt of the fiber tip over the whole workspace of the positioner. The metrology system works by back illuminating the optical fiber of the positioner with a laser. The position and tilt of the exiting cone at the tip of the fiber is measured with two optical cameras

A 24 mm diameter fibre positioner for spectroscopic surveys

One of the big research topics in modern cosmology is the mystery of dark Energy. To unveil the secret, cosmologists want to measure precisely the evolution of large scale structures in the universe. One way of doing so is to measure the 3D location of a high number of galaxies. By measuring the redshift of a galaxy, it is possible to find its distance. In order to measure a high number of galaxies in a practical amount of time, we need to observe multiple objects in parallel. Instead of a spectrograph, thousands of optical fibres are placed in the focal plane of a telescope. They will transmit the light of many objects to a spectrograph. Each fibre has to be positioned to several mu m precision in the focal plane of a telescope for each exposure. Each fibre is positioned by a 2-axis fibre positioner. In this paper such a fibre positioner with 24-mm diameter is presented. It is driven by two brushless DC motors in combination with a backlash free gearbox. The positioner has an optimal central fibre path and improved angular alignment. The fibre runs through the centre of the positioner and is only bent at the top to reach its target position. In this way, the flexion and torsion of the fibre are minimal. In addition to the high positioning accuracy, the design is optimized to allow a minimal tilt error of the fibre. This is demonstrated using a novel optical tilt measurement system

Satellite constellation design algorithm for remote sensing of diurnal cycles phenomena

This paper proposes an algorithm to find the smallest satellite constellation satisfying a given set of Earth observation requirements. This methodology is exemplified with the Satellites Observing Lakes and Vegetation Environments (SOLVE) study, which aims at deploying a fleet of small satellites carrying miniaturized hyperspectral spectrometers. A key requirement of this mission is a high temporal resolution through which the ground target can be observed several times a day. Hourly observations are required in this mission in order to capture diurnal changes in water quality and vegetation environments. Given sensor specifications and observation requirements, the proposed algorithm determines orbital parameters of an optimal constellation design via a semi-analytical approach. This approach reveals trade-offs amongst performance metrics and deployment cost, providing better physical intuition for decision making compared to stochastic optimization. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved

SATELLITE CONSTELLATION DESIGN FOR THE SOLVE MISSION INVESTIGATING DIURNAL CYCLES OF VEGETATION PHENOMENA

This paper discusses the problem of finding an optimal satellite constellation for the SOLVE (Satellites Observing Lakes and Vegetation Environments) Mission. A key requirement of this mission is a temporal resolution of several observations per day. A semi-analytical approach is proposed. After some analytical design steps which reduces the problem space to circular sun synchronous orbits, a genetic algorithm is used for finding all remaining orbital parameters. The result is an easy to use tool which allows to study cost impact from given science requirements enabling a good understanding of the relation between temporal, spatial resolution and cost

High density fiber postitioner system for massive spectroscopic surveys

International audienceWe describe here a novel design of a fast high-density robotized fiber positioner system for massive spectroscopic surveys. The fiber positioners are compact, robust, and they can be coordinated, allowing for a high spatial density. Furthermore, the high absolute accuracy removes the need for a metrology system and reduces the reconfiguration time. First, we present the requirements for such a high-density fiber positioner system and put them in relation with the science goals. Then, we discuss the positioner design that accomplishes these requirements (including mechanical design, local control electronics board, overall communication solution, and observation sequencing). Finally, the performance of the proposed design is measured using 25 mm pitch prototypes of the positioners, through a dedicated novel designed test-bench. The related results show that our prototypes fulfil the requirements particularly in terms of positioning precision (<20 µm rms for one single open loop move) and partially in tilt (<0.15 deg)

Precision control of miniature SCARA robots for multi-object spectrographs

Advances in astronomy led to the demand for measuring the spectra of multiple night sky objects simultaneously. Some of these Multi-Object Spectrographs use robotic systems that position optical fibers in the focal plane of the observing telescope. These systems rely on precise fiber placement in order to collect the light spectra of faint stars and galaxies. Here, we present how to design, control, and operate micro SCARA-like robots to position optical fibers to micrometer precision. As an illustrative example, we show the design and performance results of the SDSS-V fiber positioner, which has been build for the Apache Point Observatory and the Las Campanas Observatory with 500 units for each telescope