skyandtelescope.com • AUGUST 2019 19
ment, a calorimeter designed to measure X-ray spectra at
extremely high resolution, was moved to another mission.
And the team gave up servicing: Chandra had been intended
for occasional upgrades, as the Hubble Space Telescope was,
but NASA offi cials chose a new, high-Earth orbit, out of range
of astronauts, to ensure that servicing would remain off the
table. That change came with a side benefi t, though: This
orbit, unlike Hubble’s, allowed more time for observing, with
less time spent in our planet’s potentially damaging radiation
belts. The high orbit also avoided the thermal, mechanical,
and power stresses that spacecraft in lower orbits feel when
they shift from daylight to darkness every 90 to 100 minutes.
Meanwhile, another X-ray telescope was in development
on the other side of the ocean. In 1985 the European Space
Agency decided to build the X-ray Multi-Mirror Mission, later
known as XMM-Newton. Designed to cover the same energy
range as Chandra, the two telescopes are complementary:
Chandra’s focus is sharp X-ray vision, while XMM-Newton’s
aim is to gather as many photons as possible.
“To say it bluntly, it’s a huge light bucket,” says Axel
Schwope (Leibniz Institute for Astrophysics Potsdam, Ger-
many). XMM-Newton’s design called for three X-ray tele-
scopes, each with 58 mirror pairs nested like so many Russian
dolls. Although coarser than Chandra’s mirrors, the sheer
number of them invites photons in at an unprecedented rate.
As a result, XMM-Newton’s images aren’t as sharp but con-
tain a wealth of energy information.
Finally, on July 23, 1999, NASA Commander Eileen Col-
lins and her crew deployed the Chandra X-ray Observatory.
Less than half a year later, on December 10, XMM-Newton
climbed into space aboard the Ariane 504 rocket.From First Light to Legacy
The fi rst observation through any new telescope may provoke
anxiety. But Chandra’s fi rst light proved especially nerve-
racking — and then enlightening. One of the fi rst sources
Chandra sighted was PKS 0637-752, a quasar that the astron-
omers expected to appear as a point of light if Chandra’s mir-
rors were bringing the X-rays to a proper focus. “Immediately
we see this big elongation on the side and it’s like, ‘Oh my
god! The mirror’s broken!’” Elvis says. The smeared image was
reminiscent of the initial ones taken by Hubble, which had
launched almost a decade before with fl awed mirrors.
“So we’re looking to see, is there a problem with the
aspect, are we jittering, is there really something wrong that’s
causing this?” Tananbaum says. It was Tom Aldcroft, thenuCHANDRA Chandra has four nested mirror pairs, compared to XMM-
Newton’s 58 mirror pairs, so it collects fewer photons for any given
celestial target. But those mirrors are so incredibly smooth, they provide
unprecedented spatial resolution, providing image detail equivalent to
that of optical telescopes.uuSTARDEATH Chandra’s image of Cassiopeia A, the bloom of gas left
over after a massive star went supernova some 340 years ago, reveals a
star turned inside out. While iron (purple) was fused in the stellar core just
before it collapsed into a neutron star, the shockwave blasted clumps of
the element far from the remnant’s center.pTO ORBIT Eileen Collins, the fi rst female Space Shuttle commander,
led the team that placed Chandra in high-Earth orbit. The astronauts
pose with a model of the spacecraft. From the left: Eileen Collins, Steven
Hawley, Jerry Ashby, Michel Tognini, and Cady Coleman.90 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
GranatROSATAdvanced Satellite for Cosmology and Astronomy (ASCA)AlexisBroad Band X-ray
Telescope (STS 35)Diffuse X-ray
Spectrometer (STS 54)EurecaRossi X-ray Timing Explorer (RXTE)Indian Remote-sensing Satellite (IRS) P3Beppo Satellite for X-ray Astronomy (BeppoSAX)ChandraXMM-Newton
Advanced Research and Global Observation SatelliteCOLL
INSAND^ CREW:
NASA;^ CHANDRAM
IRRORS:^EAST
MAN-
KODAK;^SUPERNOVA^ REMNANT
:^ NASA^ /CXC^ /SAO