Cosmic Origins Spectrograph

Cosmic Origins Spectrograph
Name	Cosmic Origins Spectrograph
Operator	National Aeronautics and Space Administration
Launch	2009
Mission	Hubble Space Telescope
Type	Ultraviolet spectrograph

Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph is an ultraviolet spectrograph installed on Hubble Space Telescope during STS-125 servicing, designed to probe the composition, kinematics, and ionization of diffuse astrophysical plasmas. Developed by a collaboration led by the Goddard Space Flight Center with contributions from institutions including University of Colorado, the instrument expanded Hubble’s sensitivity in the far-ultraviolet and near-ultraviolet bands to enable studies spanning intergalactic medium, galactic halo, stellar winds, and exoplanet upper atmospheres. Its deployment represents a milestone in the legacy of space ultraviolet astronomy alongside instruments such as the Far Ultraviolet Spectroscopic Explorer and the International Ultraviolet Explorer.

Overview

The instrument was conceived in response to recommendations from the Astrophysics Strategic Plan and the Decadal Survey that prioritized ultraviolet spectroscopy for studying baryon cycles and chemical enrichment. Funded and managed by NASA with hardware and science teams from the Space Telescope Science Institute and university partners, the spectrograph operates on the principle of dispersing incoming ultraviolet photons across microchannel plate detectors to record high-sensitivity spectra. The project draws on heritage from laboratory programs at Goddard Space Flight Center and flight experience from missions like Copernicus and Orbiting Astronomical Observatory.

Design and Instrumentation

The optical train incorporates diffraction gratings optimized for the far-ultraviolet (FUV) and near-ultraviolet (NUV), feeding two separate detector systems. The FUV channel uses photon-counting, cross-delay line microchannel plate detectors developed with expertise from University of California, Berkeley and tested in facilities associated with Jet Propulsion Laboratory, while the NUV channel employs advanced multi-anode detectors influenced by technologies from Space Telescope European Coordinating Facility. Grating mounts and mechanisms were engineered at the Ball Aerospace facilities; electronics and thermal control reflect standards used by Lockheed Martin for space instruments. The entrance aperture and internal baffles echo designs seen on predecessors such as International Ultraviolet Explorer. Detailed instrument calibration strategies were developed in collaboration with calibration teams at National Institute of Standards and Technology and heritage spectrometers from Godard laboratory programs.

Scientific Objectives and Capabilities

COS was optimized to achieve extremely high sensitivity for faint targets, targeting spectral resolution and throughput sufficient for observations of the diffuse intergalactic medium and weak absorption lines from highly ionized species. Primary science goals included mapping the baryon content of the low-redshift universe related to studies by Sloan Digital Sky Survey, investigating chemical enrichment processes informed by results from Chandra X-ray Observatory and Spitzer Space Telescope, and characterizing ultraviolet signatures of star formation traced in observations by Galaxy Evolution Explorer. The instrument enables measurements of key resonance lines such as Lyman-alpha, and metal lines like O VI and C IV, connecting to theoretical frameworks advanced at institutions like Princeton University and Harvard-Smithsonian Center for Astrophysics. The high throughput allowed time-resolved spectroscopy for transient investigations coordinated with facilities such as Keck Observatory and Very Large Telescope.

Flight History and Deployment

Installed during STS-125 by astronauts on a servicing mission to Hubble Space Telescope, the spectrograph replaced an earlier instrument to restore and enhance ultraviolet capabilities. The servicing involved coordination between Johnson Space Center, Kennedy Space Center, and the European Space Agency for integration and checkout. After on-orbit activation, commissioning sequences were executed by teams at the Space Telescope Science Institute and Goddard Space Flight Center to verify performance against prelaunch models. Routine operations have been managed through observing proposals reviewed by the Time Allocation Committee administered by the Space Telescope Science Institute, with data distributed to investigators at universities and observatories worldwide, including California Institute of Technology and University of Cambridge researchers.

Key Discoveries and Scientific Impact

COS enabled breakthroughs in mapping the cosmic web by detecting low-density absorbers that account for a substantial fraction of baryons predicted by cosmological models from Planck (spacecraft) and Wilkinson Microwave Anisotropy Probe. Observations of the circumgalactic medium around galaxies provided empirical constraints complementing simulations from groups at Max Planck Institute for Astrophysics and University of California, Santa Cruz. Studies using COS informed our understanding of galactic feedback processes linked to work on starburst galaxies observed with Hubble Space Telescope instruments and ground-based facilities like Subaru Telescope. COS spectra of transiting exoplanets revealed atmospheric escape signatures consistent with models developed at University of Arizona and reported in collaborations including European Southern Observatory partners. The instrument’s legacy continues to influence mission planning for future ultraviolet missions advocated in the Decadal Survey.

Calibration, Data Products, and Operations

Calibration pipelines were developed by the Space Telescope Science Institute software teams using reference standards tied to measurements from the National Institute of Standards and Technology and empirical stellar calibrators from archives maintained by European Space Agency partners. The COS Calibration Pipeline produces extracted, wavelength-calibrated spectra and flux products that feed into archives such as the Mikulski Archive for Space Telescopes and analysis tools used at institutions like Johns Hopkins University and University of Colorado Boulder. Observing modes include multiple grating settings and aperture choices to balance spectral resolution and sensitivity, enabling coordinated programs with facilities like Green Bank Observatory and Arecibo Observatory prior to its decommissioning. Ongoing instrument monitoring and periodic recalibration have been coordinated by teams at Goddard Space Flight Center and the Space Telescope Science Institute to maintain COS performance for the astronomical community.

Category:Ultraviolet spectrographs Category:Hubble Space Telescope instruments