Chandra X-ray Observatory
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NASA's Chandra X-ray Observatory was launched in 1999. In a hair-raising
event-filled launch on Space Shuttle Columbia flight STS-93, Eileen
Collins and her crew risked their lives to deploy this ground-breaking
scientific instrument. Since then Chandra has provided a series of
scientific discoveries, notably (in combo with optical weak lensing
measurements) the best evidence for the reality of dark matter. Demand
for the observatory remains high and the rate of scientific publications
from it continues steady. Engineers expect Chandra is capable of
continuing to operate effectively for up to another decade, although
thermal insulation issues have complicated mission planning (requiring a
1% increase in the operating budget to keep everything healthy, rather
than a small budget decrease that might otherwise have been possible).
Chandra is considered by the astronomy community as one of the most
scientifically effective missions per dollar.

Nevertheless, NASA has decided that Chandra should be shut down to
address the overall budget cuts faced by the agency. Although the
official FY2025 President's Budget Request language says the proposed
reductions are for a 'minimum mission', the reality is that reducing the
annual budget of $60M in FY2023 to $41M in FY2025 and $27M in FY2026
means shutting down the mission and firing most of the staff. (Conflict
of interest disclaimer: I am one of those staff.) The remaining money
would be used for wrapping up the archive and so forth - the public data
archive is used repeatedly for lots of additional science papers.

This decision is not yet final, since the president's budget is followed
by revisions made by Congress before it is enacted. Nevertheless at the moment
that is the plan, and it means that scientists using Hubble and JWST
will no longer be able to complement those observations with similarly sharp
images in the X-ray. (For example, you see a glowing gas cloud in JWST,
but without the Chandra data you can't see the compact binary star that is
responsible for pumping energy into that cloud).

No replacement for Chandra is in the works anywhere in the world.
China's Einstein Probe (just launched), the Japan-US XRISM mission
(recently operational), Europe's XMM-Newton and its proposed (but also
budgetarily threatened) replacement Athena are fantastic X-ray
observatories but none of them can take the sharp images that can be
used for comparisons with HST and JWST. The plan implies a gap in
astronomy's capability for a generation or more, and the end of a US
dominance in X-ray astronomy that has for the most part lasted since the
discovery of Sco X-1 in 1962.