A once-canceled space telescope is set to launch into Earth orbit, where it will search for undiscovered black holes in the Milky Way and at the hearts of other galaxies.

The Nuclear Spectroscopic Telescope Array will hunt for black holes that have been obscured by the dust and gas floating through space and measure how fast some of them are spinning. NuSTAR will also examine with fresh eyes the remnants of exploded stars known as supernovae.

“It’s a very exciting mission,” said Roger Blandford, director of the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University and a member of the NuSTAR science team. “It opens up a new window on the universe.”

Black holes, supernovae and other cosmic sources can give off light across the whole electromagnetic spectrum, from low-energy infrared waves to high-energy gamma radiation. But much of that light is invisible even to the Hubble Space Telescope and the ChandraX-rayObservatory, which are focused on the infrared, visible, ultraviolet and low-energyX-rayportions of the spectrum.

In addition, much of the lower-energy light gets absorbed by gas and dust floating through space, essentially blocking these objects from view.

NuSTAR will capture high-energy X-rays emanating from these cosmic bodies. But it’s hard for instruments to detect the rays directly — they tend to go straight through. These are, after all, the same kind of X-rays dentists use to penetrate your skin and take images of your teeth, explained Caltech astrophysicist Fiona Harrison, the mission’s principal investigator.

To catch these X-rays, NuSTAR will position its highly reflective mirrors at an angle that’s almost parallel to incoming light. That way, when an X-ray hits the mirrors at such a glancing angle, it can then be bounced right into the detector, about 30 feet away at the end of a mast.

The steep angle reduces the amount of light that can be captured, so to compensate, NuSTAR’s mirrors are arranged in 133 conical nested shells, like so many Russian dolls.

Older focusing X-ray telescopes could capture light at energies as high as about 15 kiloelectron volts; NuSTAR will go even higher, up to 79 KeV.

By examining how black holes grow, NuSTAR will help astrophysicists understand the growth of galaxies, said Martin Elvis, a scientist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, who was not involved in planning the mission.

With its special ability to focus high-energy X-rays, the telescope will be able to explore a variety of other X-ray sources, including neutron stars and the processes that superheat the halo of particles around the sun, known as the corona.

Wednesday’s scheduled NuSTAR launch comes just days short of the 50th anniversary of X-ray astronomy, Elvis said. It’s also a time when tight budgets have kept NASA from embarking on major long-term projects for X-ray astronomy.

NuSTAR, which is managed by the Jet Propulsion Laboratory in La Canada Flintridge, is part of NASA’s Small Explorer program, missions designed to do more with less. With a price tag of $165 million, the two-year mission costs about one-tenth as much as building Chandra did.

The telescope will be launched from a plane in midair, rather than straight from the ground, to limit fuel costs. The plane is scheduled to take off from Kwajalein Atoll in the Marshall Islands at 8:30 a.m.

But even these modest missions are not safe from budget cuts. Last week, NASA announced that it had cut the Gravity and Extreme Magnetism Small Explorer for cost reasons.

NuSTAR was canceled in 2006 because of funding pressures within NASA. It was reinstated in 2007.

amina.khan@latimes.com