NASA's James Webb Space Telescope

Exposure Time Calculator (ETC)

The new JWST Exposure Time Calculator (ETC) calculates the detailed performance of the observatory by modeling astronomical scenes consisting of single or multiple point and extended sources in three dimensions (two spatial and one wavelength). It offers full support for all of the JWST observing modes, including the NIRSpec and MIRI integral field units, slitless grism spectroscopy with NIRISS and NIRCam and the MIRI and NIRCam coronagraphs. The ETC has a modern web application graphical user interface, which offers advanced functionality for parameter space studies and comparative calculations.

ETC image

Web Application

The ETC web application represents the official, most up-to-date, version of the JWST ETC. 

Python Engine

We also offer the Python engine used by the web ETC. Users who are interested in scripting ETC calculations on their local machine may use this, along with the associated data package. The version numbers of the engine are aligned with those of the web application. 

  • JWST Python engine quickstart documentation
  • ETC 1.2 was a major release on 12/18/17 and featured:
    • Normalization in surface brightness units for extended sources
    • Wide Aperture Target Acquisition (WATA) mode for NIRSpec
    • Improved PSF handling for coronagraphy
  • ETC 1.1.1 was a patch release on 7/6/17.
  • ETC 1.1 was a major release on 6/1/17 and featured:
    •  Faster performance for all calculation types
    •  New target acquisition modes for all instruments
    •  Improved timing model for both MIR and NIR detectors
    •  Newly reported "Total Integrations" and "Total Exposure Time" to facilitate comparison with APT 25.
  • ETC  1.0 was the first production release  on 1/5/17.