Hubble's Future in the Webb Era

Perhaps you’ve heard: The James Webb Space Telescope (JWST) is the latest and greatest observatory in space, wowing the astronomical community with amazing images released last week.

But amid all the excitement, the Hubble Space Telescope — NASA’s orbital transformational observatory now for more than 32 years — continues its exploration and discovery.

"We believe that we can keep Hubble doing the ground-breaking science it is known for through the latter part of this decade and possibly into the next," says public affairs officer Claire Andreoli (NASA Goddard).

Hubble: From Trouble to Triumph

Deployed on April 25, 1990, from the cargo bay of the U.S. space shuttle Discovery, Hubble got off to a rocky start: A defective mirror wasn’t discovered until after deployment and calibration. Three years later, astronauts repaired the defect with "corrective lenses," named the Corrective Optics Space Telescope Axial Replacement (COSTAR) package, which they placed in the telescope during the STS-61/Servicing Mission One.

Four servicing missions followed, each one deploying upgrades and new instruments, but the Atlantis STS-125 mission in 2009 would be the last: Hubble is now on its own. Despite some scares, including a brief computer glitch last year, Hubble’s doing just fine.

“Hubble is still going strong and continues to have an important and unique role to play in cutting edge astronomy research,” says Misty Bentz (Georgia State University) “It also remains popular with astronomy researchers, as the latest call for proposals in March 2022 received five times the number of proposal requests that could be accommodated!”

Hubble's 2022 Highlights

Hubble's observations over the years have helped scientists determine the rate of the universe's expansion, identify moons of Pluto, and shed light on exotic worlds. (See "Celebrating 30 Years" for some of Hubble's most mesmerizing images.)

Even in this year alone, Hubble has broken records while capturing stunning imagery:

• Hubble recently discovered the most distant star known, dubbed Earendel. The images show Earendel as it was 12.9 billion years ago, only 900 million years after the Big Bang.

• The telescope continues to capture stunning views, such as this deep stare at the globular cluster Terzan 2 in Scorpius:

• Hubble is contributing to a currently underway project called the Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES). This program is using 1,000 orbits of Hubble time, in particular its unique capabilities in the ultraviolet part of the spectrum, to study star formation.

• The mission also recently imaged Comet Bernardinelli-Bernstein (C/2014 UN271), confirming that it's the most massive Oort Cloud comet known. The new observations show that its nucleus is an estimated 137 kilometers (85 miles) across. Comet Bernardinelli-Bernstein will reach perihelion outside the orbit of Saturn in 2031.

Webb's Complement

Hubble has an important role play in the new JWST era, because even though Webb was often billed as Hubble's successor, the two telescopes are actually quite different.

“Hubble provides high-resolution ultraviolet and visible imaging and spectroscopy, whereas JWST is optimized for the infrared,” Bentz says. “Hubble continues to dominate in studies of nearby stars and galaxies, as well as accreting supermassive black holes.”

In fact, Bentz is leading a new program that uses Hubble to detect Cepheid variables in three galaxies, in order to determine their distances. “Cepheids are most variable at blue wavelengths, where JWST cannot observe,” Bentz explains. “Furthermore, JWST is very slow to move from one target to another, so it is not optimized for returning to the same target again and again, as is needed in study of variable objects like Cepheids.”

There are also plans afoot to utilize Hubble for complementary, simultaneous observations with other observatories, including JWST. Such multiwavelength observations can help gain an understanding that studies in ultraviolet, visible, or infrared alone cannot.

As an example, Bentz points to the neutron star merger that the LIGO and Virgo Collaborations detected in 2017. “Astronomers around the world collected observations at every wavelength possible to learn as much as we could about the physical processes happening during the collision and its messy aftermath,” Bentz says.

Hubble's Fate

In its most recent review of Hubble operations, NASA announced that it would support the observatory through June 2026. In fact, current estimates suggest the observatory can stay in a high-enough orbit for operations to continue until the mid-2030s and beyond; its solar arrays and batteries are also in great shape.

The limiting factor comes down to the gyros that the space telescope uses to turn and lock onto targets. While almost all the observatory's systems are redundant, meaning there's still a back-up available if one piece fails, the gyros are one of the few exceptions. Hubble launched with six, but three have failed.

"The telescope is currently operating with three gyros and no spares," Andreoli says. However, while it takes three gyros to enable efficient operations, observations are still possible, albeit less efficient, with only one gyro.

Engineers have found clever ways to keep missions going well past their warranty: Witness the "warm" mission on Spitzer when its coolant ran out, or Kepler’s extended K2 mission after the second of its four reaction wheels failed. Likewise, after the payload computer gave Hubble problems last summer, team engineers got things back up and running, and they're still working to improve operational processes.

Once the Hubble mission ends, hopefully a long time from now, NASA plans to bring it down in a controlled manner. On the last servicing mission, astronauts installed a Soft Capture Mechanism on the base of Hubble. It could be used by a robotic mission to boost the telescope's orbit, but more likely it will prepare it for a controlled reentry when the time comes.

While it's still up there, you might be able to see Hubble in orbit: The telescope is in a 28.5°-inclination orbit, meaning it’s a frequent naked-eye sight for observers at latitudes between 35 °S and 35°N, which includes the southern part of the United States.

An entire generation of astronomers have come of age with Hubble in space, and it remains a vital component in the toolbox of modern astronomers. Expect more great science to come from this venerable space telescope.

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