The Nancy Grace Roman Space Telescope

Podcast Transcript

Assuming everything goes well, sometime in late 2026, NASA’s next major space observatory will launch: The Nancy Grace Roman Space Telescope.

Assuming the launch and deployment go well, it will map large areas of the universe to understand why cosmic expansion is accelerating and how galaxies and dark matter evolved.

It will also survey stars to discover thousands of planets, including cold and free-floating worlds, while testing technology for the direct imaging of planets around other stars.

Learn more about the Nancy Grace Roman Space Telescope and how it could revolutionize astronomy on this episode of Everything Everywhere Daily.

To understand the development of the Nancy Grace Roman Space Telescope, we have to go back over 25 years.

In the late 1990s and early 2000s, cosmology entered a transformative period with the discovery that the expansion of the universe is accelerating. This finding, based on observations of distant supernovae, raised fundamental questions about the nature of dark energy and whether Einstein’s theory of gravity works on cosmic scales.

At the same time, astronomers increasingly recognized that answering these questions would require very large datasets rather than small numbers of exquisitely detailed observations of single objects.

Ground-based surveys were growing rapidly, but atmospheric limitations made it challenging to achieve the precision and stability needed for weak gravitational lensing and infrared measurements at cosmological distances.

At the same time, exoplanet discovery was exploding. Early discoveries showed that planetary systems were far more diverse than expected, but most known planets were close to their stars due to observational limitations.

Astronomers realized that understanding how planetary systems form and evolve would require a census of cold, distant planets, including those beyond the point in a solar system where water froze and even planets not bound to any star.

Gravitational microlensing offered a way to do this, but only with a wide-field, space-based telescope capable of monitoring tens of millions of stars simultaneously.

Gravitational microlensing occurs when a foreground star’s gravity briefly magnifies the light of a more distant background star. It is using gravity at a cosmic level in the same way that a glass lens would.

These needs came together in the 2010 U.S. National Academies decadal survey, which sets priorities for astronomy and astrophysics. The survey identified a wide-field infrared space telescope as its top large mission recommendation for the decade.

The concept emphasized three pillars: dark energy studies, exoplanet microlensing, and general-purpose infrared surveys. At this stage, the mission was known as WFIRST, the Wide Field Infrared Survey Telescope. It was envisioned as a modestly sized observatory designed to deliver survey-scale science at a fraction of the cost of earlier flagship space telescopes.

A turning point came in 2012, when the U.S. National Reconnaissance Office, the agency that manages spy satellites, transferred two unused 2.4-meter space telescope optical assemblies to NASA. These telescopes were comparable in size to Hubble’s mirror but had been built for entirely different purposes. Their availability dramatically changed the mission’s potential.

NASA revised WFIRST to use one of these larger mirrors, enabling much higher resolution and sensitivity while preserving the wide field survey concept. This single event elevated the mission from a medium-scale survey telescope into something much closer to a flagship observatory in scientific capability, without requiring the cost of building a large mirror from scratch.

As the mission matured through the 2010s, it absorbed additional ambitions while navigating budget pressures and technical challenges. The addition of a high-contrast coronagraph, an optical instrument that blocks or suppresses a star’s light so that much fainter objects nearby could be seen, was intended primarily as a technology demonstration.

It reflected NASA’s longer-term goal of eventually imaging Earth-like exoplanets.

At the same time, the mission had to be carefully managed to avoid the cost overruns that had plagued earlier large space telescopes. This led to repeated design reviews, descoping discussions, and a strong emphasis on keeping Roman focused on survey science rather than trying to be all things at once.

In 2020, NASA renamed the mission in honor of Nancy Grace Roman, often called the mother of Hubble. The renaming was more than symbolic. Roman had been instrumental in establishing space telescopes as a core part of NASA’s scientific identity and had championed the idea that space observatories should serve broad scientific communities rather than narrow interests.

The assembly of the telescope has been led by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with contributions from numerous industry partners.

The telescope passed its Critical Design Review in September 2021, with flight hardware fabrication completed by 2024, followed by mission integration.

The project faced significant challenges from the COVID-19 pandemic, resulting in an estimated $400 million impact and schedule delays.

On November 25, 2025, technicians joined the inner and outer segments of the telescope in the large clean room at Goddard Space Flight Center, marking completion of the observatory’s assembly. The spacecraft now enters its final testing phase before moving to Kennedy Space Center in summer 2026 for launch preparations.

So, how exactly will the Roman telescope work and achieve its goals, and what makes this different from other space telescopes?

For starters, the Roman Space Telescope was deliberately designed with a very wide field of view because many of the questions it is meant to answer are statistical in nature and cannot be tackled by narrow-field observatories, no matter how sharp they are.

The Wide Field Instrument it carries will have a 300-megapixel multi-band near-infrared camera with a field of view at least 100 times larger than Hubble’s, covering 0.28 square degrees.

The Wide Field Instrument operates across wavelengths from 0.48 to 2.3 micrometers, spanning visible to near-infrared light. It includes eight imaging filters, a grism for spectroscopy, and a low-resolution prism.

Roman’s wide field allows it to observe enormous areas of the sky quickly and repeatedly, combining the space-based image quality of a telescope with the survey-scale coverage of a sky survey, in a way no previous telescope has achieved.

Most flagship space telescopes, especially Hubble and James Webb, are optimized for depth rather than breadth. They excel at studying individual objects or small regions of sky in extraordinary detail, but they are slow at building large, uniform surveys.

Roman flips that balance. Its field of view is about one hundred times larger than Hubble’s infrared view while maintaining comparable resolution, which means it can map large cosmic volumes efficiently instead of stitching together thousands of tiny pointings over many years.

This wide field is essential for Roman’s dark energy mission. Understanding why the universe’s expansion is accelerating requires measuring subtle patterns across millions or even billions of galaxies.

Weak gravitational lensing, one of Roman’s key techniques, depends on averaging tiny shape distortions across vast galaxy samples to overcome noise and systematic errors.

A narrow-field telescope cannot collect those samples fast enough or uniformly enough to achieve the required precision. Roman’s wide field lets it build consistent maps of cosmic structures over large fractions of the sky, which is critical for testing whether dark energy is a new form of energy or a sign that gravity behaves differently on the largest scales.

The wide field is equally important for Roman’s exoplanet work. Its primary planet survey uses gravitational microlensing, which relies on rare, brief alignments between foreground stars and background stars in the dense star fields of the Milky Way’s bulge.

To catch enough of these events, Roman must monitor tens of millions of stars continuously. A narrow field telescope would miss most events simply because it could not watch enough stars at once.

Roman’s wide field allows it to act like a planet census machine, detecting populations of cold, distant planets and even free-floating planets not orbiting stars, that other methods struggle to find.

To achieve this, it will carry the Coronagraph Instrument. It is a technology demonstration system designed to directly image exoplanets by blocking starlight, achieving part-per-billion suppression.

Operating in the 575-825 nanometer range, it will test technologies for future missions, such as the Habitable Worlds Observatory, which might be launched sometime around 2041.

Roman’s survey power also enables science that is difficult or impractical for other telescopes, even when it is not the primary mission.

It will create deep, wide infrared maps that serve as reference datasets for astronomy, revealing rare objects such as very distant quasars, early massive galaxies, faint dwarf galaxies around the Milky Way, and transient events such as supernovae across large cosmic distances.

These are discoveries that depend on coverage and statistics rather than on zooming in on a single target.

The primary mirror on the Roman is approximately the same size as that on the Hubble Space Telescope; but it is about 25% lighter due to design improvements.

However, the amount of data returned will be staggering, much larger than what the Hubble produces. It is estimated to gather 20,000 terabytes, or 20 petabytes, of data during its primary mission.

The primary mission will be for 5 years, with a potential 5-year extended mission. Unlike some infrared telescopes that rely on coolant, Roman doesn’t require cryogenic cooling for its primary operations, so fuel is the limiting factor.

The observatory has been designed to support robotic refueling in space, enabling operations beyond the planned 10-year total mission duration if NASA chooses to pursue that option.

Unlike the Hubble, the Roman will not be in Earth orbit.

The Roman Space Telescope will operate near the Sun–Earth second Lagrange point, known as L2, because this location provides a uniquely stable and efficient environment for precision space astronomy.

L2 lies about 1.5 million kilometers from Earth, directly opposite the direction of the Sun, where the combined gravity of the Earth and Sun allows a spacecraft to orbit the Sun in step with Earth while maintaining a nearly constant relative position.

What makes L2 special is geometric stability rather than perfect gravitational balance. From Roman’s perspective, the Sun, Earth, and Moon all remain clustered in roughly the same direction in the sky.

This allows the telescope to keep its sunshield oriented consistently, protecting its instruments from heat and stray light while maintaining a very stable thermal environment. This is why it doesn’t need coolant.

Thermal stability is critical for Roman because tiny temperature changes can distort optics and detectors, degrading the precision needed for weak gravitational lensing measurements and infrared surveys.

While we can’t know the future, NASA has a good track record for missions that go well beyond their original planned length. The Hubble mission has been ongoing for 35 years, and it is still in operation.

We obviously don’t know what will be discovered until the mission actually starts.

However, assuming everything goes well, scientists anticipate Roman will:

Measure light from approximately one billion galaxies.
Discover tens of thousands of supernovae.
Find thousands of exoplanets through microlensing.
Map billions of stars and galaxies with unprecedented detail.

I’m sure there will be some spectacular images released from the Roman telescope, but that is not the primary goal of this mission. It is to gather data. Lots of data.

With it, we will be able to develop a better map of our galaxy and develop a better understanding of our universe.

Hopefully, sometime in late 2026, the Nancy Grace Roman telescope will launch and be deployed. Pay attention to the news developments because they should be interesting.

Perhaps someday in 2027, I’ll be able to do another update on what we have learned from the Roman mission and how our knowledge of the universe has changed.

The Executive Producer of Everything Everywhere Daily is Charles Daniel. The Associate Producers are Austin Oetken and Cameron Kieffer.

I have several short reviews today. The first comes from listener avgeek a340 on Spotify. They Write:

Hi, I love the show. When I’m doing stuff for school, I see if you have an episode about it. Thanks for the best show.

The next is from Your neighbor in lowa from Apple Podcasts in the United States. They write:

Completionist club!

Great show! Love the variety! Today I joined the completionist club! Yay!

Finally, Podcast lover1234 on Apple Podcast writes:

Great show

It’s just good. 5 star easily. Mic drop

Thank you all of you. The comments are always appreciated.

Remember, if you leave a review on any major podcast platform, you, too, can have it read on the show.