This Week in Rocket History: STS-93 and the Chandra X-ray Observatory

by | Jul 29, 2021 | Daily Space, Space History, Spacecraft | 0 comments

IMAGE: This image of NASA’s Chandra X-ray Observatory following deployment from the Space Shuttle Columbia was taken from High Definition Television (HDTV) shot by Columbia Astronaut Mission Specialist Cady Coleman, during the STS-93 mission. Chandra, the world’s most powerful x-ray telescope, was developed by NASA’s Marshall Space Flight Center in Huntsville, Ala. CREDIT: Cady Coleman/NASA

This week in rocket history, we have a groundbreaking mission in x-ray astronomy involving the Space Shuttle Columbia.

STS-93 launched from Kennedy Space Center pad 39B on July 23, 1999, at 16:31 UTC, with shuttle Columbia carrying the Chandra X-ray Observatory.  It was the third Great Observatory to launch, after the Hubble Space Telescope and Compton Gamma Ray Observatory. Originally called the Advanced X-ray Astrophysics Facility, it was renamed after Indian-American physicist Subrahmanyan Chandrasekhar who contributed to the knowledge of white dwarfs and other aspects of stellar evolution. Chandra, which also means “moon” in Sanskrit, was chosen by a student essay contest in April 1998 which received 6,000 entries.

Counting the spacecraft, its Inertial Upper Stage (IUS), and support equipment, the payload weighed 22.75 metric tons, the heaviest ever payload launched on the shuttle.

Columbia landed back at KSC on July 28, 1999, at 02:20 UTC after traveling 1.8 million miles in space across a mission duration of 4 days, 22 hours, 49 minutes, and 37 seconds.

Putting this massive telescope in space was necessary because the Earth’s atmosphere blocks the transmission of x-rays. This is, on the whole, good because it means people aren’t constantly barraged by high-energy photons unless you’re an x-ray astronomer. That same protective atmosphere is blocking your perfectly good science. So, in order to study the earliest parts of the universe, scientists need to send equipment to space and hope nothing malfunctions because there’s no practical way it can be repaired. Chandra is also in a very high orbit — 6,731 kilometers by 14,285 kilometers in perigee and apogee, respectively. This orbit was necessary to get the spacecraft above the radiation belts for most of its orbit. It was achieved both with the IUS and the spacecraft’s onboard engine after deployment from the shuttle.

400IMAGE: Illustration of grazing incidence. The scale in this image is exaggerated – the angle of incidence (the angle between the mirror surface and the X-ray) is actually shallower. CREDIT: NASA’s Imagine the Universe

X-ray telescopes are kind of neat because they function differently from optical telescopes. An x-ray photon would go right through a conventional mirror, so to create a focused image, the mirror in an x-ray telescope is almost parallel to the incoming light, creating what is called grazing incidence.

Chandra’s telescope is composed of two sets of four curved mirrors, one behind the other, that each ever so gradually bends the path of those high-energy photons. The combination of this careful and creative engineering and Chandra’s sensitive detectors has made this mission a workhorse many scientists can’t imagine working without. It was only designed to last five years but has kept on producing science for 22 years and counting.

You can expect to keep hearing more about Chandra’s results right here on the Daily Space, hopefully for many more years to come.

More Information


Tyrel Johnson & Jatila van der Veen – Winners of the Chandra-Naming Contest – Where Are They Now? (Chandra Chronicles)

Chandra X-ray Observatory Quick Facts (NASA)

Chandra X-Ray Observatory – Orbit (Heavens Above)


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