From the October 2026 issue

How do professional astronomers book time on JWST or Hubble?

Proposals are submitted annually by scientists who wish to use these facilities, and are reviewed by the Telescope Allocation Committee.
By | Published: October 5, 2026

Photograph from a NASA Live broadcast showing a spacecraft against the blackness of space, its reflective solar panels and faceted gold and silver surfaces catching sunlight at left, with the curved blue limb of Earth and white clouds filling the upper right corner. The NASA logo and LIVE label appear at upper right, with a small mission logo at lower left.
When the James Webb Space Telescope — seen here as it separated from its rocket — launched in December 2021, it joined the Hubble Space Telescope as a space-based resource for scientists all over the world. A Telescope Allocation Committee reviews proposals for the two telescopes’ use each year, choosing programs based on impact and feasibility. Credit: Arianespace, ESA, NASA, CSA, CNES

How do professional astronomers book time on JWST or Hubble?

Frank Coulter
Tauranga, New Zealand

The opportunity to use either the Hubble Space Telescope (HST) or James Webb Space Telescope (JWST) as what NASA calls a general observer is available to scientists all over the world each year. The science program for both telescopes is led by the Space Telescope Science Institute (STScI) in Baltimore, and proposals are submitted annually by scientists anxiously awaiting new discoveries with these facilities across all areas of astrophysics and planetary science. Every proposal specifies how much observing time it requires, measured in hours for JWST and orbits for HST. (HST orbits Earth roughly every 95 minutes.) The proposals are then reviewed by an international team of scientists, known as a Telescope Allocation Committee (TAC). This group evaluates and ranks the possibilities using a well-defined set of criteria that includes in-field impact, out-of-field impact, suitability, and feasibility. This is done in a dual-anonymous manner in which proposers and TAC members are not revealed to each other. The ranked programs are then provided to the STScI director, who makes the final decision on the programs selected for a given observing cycle. 

The call for proposals is made annually to ensure the science conducted with these telescopes remains state of the art and provides the opportunity for new discoveries to be followed up as well as new users to advance the field. But, on occasion, there is an urgent need to use one of these observatories for observations that could not have been requested in the annual proposal cycle and cannot wait for the next. An example of this would be to observe an unexpected phenomenon, such as a supernova, in a timely manner. These types of programs are proposed at any time under the STScI Director’s Discretionary Time, and include small programs proposed by community members and larger initiatives deemed essential by the director.

Finally, anyone in the world can access HST or JWST data that has been archived, which typically happens one year from the date of the observation. This public archive is known as the Barbara A. Mikulski Archive for Space Telescopes (MAST), and includes all HST and JWST data. 

Stefanie Milam
JWST Project Scientist for Policy and Science Community, NASA Goddard Space Flight Center, Greenbelt, Maryland

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