Chandra X-ray Observatory Tracker
NASA's flagship X-ray telescope, launched 23 July 1999 aboard Space Shuttle Columbia on mission STS-93. Twenty-seven years on, still the sharpest X-ray telescope ever built and still returning science from a 63.5-hour highly elliptical orbit that reaches a third of the way to the Moon.
Cassiopeia A: A Quarter-Century of the Shattered Star
A new composite of Cassiopeia A, one of Chandra's first-light targets in 1999, marks 25 years of X-ray imaging of the young supernova remnant. Motion of individual knots is now measurable, revealing how the shock wave is heating the surrounding interstellar medium.
A Great Observatory Still Great at 27
Chandra was the third of NASA's four Great Observatories, sitting alongside Hubble (optical / UV), the Compton Gamma-Ray Observatory (retired 2000), and Spitzer (infrared, retired 2020). It is named after Nobel laureate Subrahmanyan Chandrasekhar, whose 1930s work on stellar death predicted much of what Chandra now images.
Four Instruments Behind the Mirrors
Chandra's optics focus X-rays onto one of two focal-plane detectors. Two grating spectrometers can swing in front of the detectors to spread the X-ray light into its component wavelengths for spectroscopy.
27 Years, Six Highlights
What Chandra Has Actually Seen
Twenty-seven years of X-ray astronomy has reshaped our picture of the most extreme places in the universe.
Chandra vs Hubble, JWST and Roman
Each of the modern NASA space telescopes sees a different slice of the electromagnetic spectrum. Chandra is the only one that sees X-rays.
Why Chandra Sees What Nothing Else Can
X-rays are the highest-energy light in the electromagnetic spectrum that ordinary telescopes can even attempt. Earth's atmosphere blocks them completely, so any X-ray telescope has to be in space. And X-rays do not reflect off ordinary mirrors: they punch straight through. Chandra's solution is a set of four nested pairs of grazing-incidence mirrors, so smoothly polished that photons skip off them like stones across a pond and are focused half a metre away onto a detector.
Why the strange orbit
Chandra's roughly 12,300 by 136,500 km highly elliptical orbit is not a mistake. The Van Allen radiation belts saturate any X-ray detector that dwells inside them, so Chandra was placed on an orbit that spends about 75 percent of every 63.5-hour circuit safely above the belts. The trade-off is that Chandra cannot be reached by a servicing mission, unlike Hubble which sits in easy Shuttle-era reach at 480 km.
The 2024 budget saga
In early 2024 NASA's proposed FY25 budget cut Chandra operations by roughly 40 percent, effectively wind-down funding. A community-led #SaveChandra campaign, joined by editorial boards and thousands of professional astronomers, prompted congressional appropriators to restore a significant portion of the funding. Chandra remains operational and continues to produce peer-reviewed science, though the mission's out-year funding is not settled.
What comes next
No US-led mission of comparable X-ray angular resolution is expected before the 2030s. ESA's Athena and NASA's proposed AXIS and Lynx concepts sit at that timeline. Every year Chandra operates is a year of X-ray astronomy that could not otherwise happen.
Chandra X-ray Observatory, Frequently Asked
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