Some background on the Nancy Grace Roman Space Telescope

I've mentioned a couple of times that NASA's next big telescope, the Nancy Grace Roman Space Telescope is launching Sunday morning on a Falcon Heavy at 7:26AM EDT, but I suppose I was quietly assuming that everyone has an idea about what that telescope is. 

I've been covering the NGRST since I first heard of it in February of 2022, and I thought maybe the good thing to do would be repost important parts of what I've covered. Rather than just post links to older posts, I'll "cut and paste" the important stuff.  

From NASA's Next Big Space Telescope 

I stumbled across a story today of an instrument that I should have known about but that had undergone a name change.  It was first referred to as the WFIRST, Wide Field Infra Red Space Telescope, a long but descriptive name for its mission.  It was recently renamed the Nancy Grace Roman Space Telescope by NASA; the name pays tribute to the late NASA executive and first Chief Astronomer who was one of the driving forces in getting the Hubble Space Telescope program through its hurdles.  

The telescope was named in a poll of astronomers as the next most important space telescope behind the James Webb Space Telescope.  Why?  The old name said wide field and that's the telescope's feature. 

That graphic gives the impression that the NGRST can capture 2,000 square degrees of sky in one shot, compared to 1.6 square degrees from the Hubble Space Telescope.  That's not quite right.  The NGRST's field of 2,000 degrees divided by the 1.6 of the HST says NGRST is 1,250 times bigger.  The NGRST website's FAQ says it's field of view is 100 times larger:

It has a primary mirror that is 2.4 meters in diameter (7.9 feet), and is the same size as the Hubble Space Telescope's primary mirror. The mirror has the same sensitivity as Hubble’s primary mirror but will only be one fifth the weight, showcasing an advancement in telescope technology. It will have the sensitivity and resolution comparable to Hubble, but with a field of view 100 times larger, combining excellent image quality with survey power.

Like the JWST, the NGRST will be sent to orbit around the L2 Lagrange point, about 930,000 miles away from earth in the direction radially away from Earth.  The mission is focused on the search for dark matter, dark energy and exoplanets, and will only carry two instruments:

The Roman Space Telescope will have two instruments, the Wide Field Instrument (WFI) and the Coronagraph Instrument (CGI) technology demonstration. The WFI provides wide field imaging and spectroscopy, with performance characteristics optimized for cosmology and exoplanet surveys. The CGI provides high contrast imaging and spectroscopy for observations of exoplanets and debris disks. The WFI is a 288-megapixel multi-band near-infrared camera, providing a sharpness of images comparable to that achieved by the Hubble Space Telescope over a 0.28 square degree field of view, 100 times larger than that of Hubble. The Coronagraphic Instrument is a high-contrast, small field of view camera and spectrometer covering visible and near-infrared wavelengths using novel starlight-suppression technology.

Rendering of NGRST, from NASA

Let me bounce back to the present to throw in that the one thing that stood out to me in that first article was that it said, "target date for launch is currently set for May of '27 and they claim to be on schedule" and, of course, August of '26 is pretty far ahead of "on schedule" when they said it would be ready to fly by May of '27. Fortuitously, they had to schedule the launch on the Falcon Heavy because when they were getting bids, nothing else was available. I've always thought that if you called Gwynne Shotwell, SpaceX CEO, to arrange a launch like this, you'd give her all the details and she'd come back with something like "gee, it's too big for a Falcon 9... how about next month?" or something that knocked your socks off like that. 

Moving up to a recent post from this April, The Nancy Grace Roman Space Telescope is complete

Here's where it gets wild. The September launch for the NGRST is eight months ahead of schedule, and under budget. When's the last time you heard something like that? I'm not sure I ever have.

According to NASA, Roman's primary mirror measures about 7.9 feet (2.4 meters) wide, which is similar to Hubble's. However, Roman has the ability to take images that capture a patch of the sky at least 100 times larger than Hubble can.

"Its surveying capabilities are over 1,000 times faster than Hubble, and can chart 200 times more sky in a single image," NASA administrator Jared Isaacman said during the conference. "What would take Hubble 2,000 years to process, Roman can do in a year — the images it captures will be so large there is not a screen in existence large enough to show them."

To put that into context, over its approximately 35 years of service so far, Hubble has gathered about 400 terabytes of data; once fully operational at its workstation in space, Roman should be able to create 500 terabytes of data per year.

The collection of different space telescopes; the Hubble, James Webb, and more, allow ground based astronomers to choose the right instrument for the objects they want to study in the sky.

Compared to the JWST, Roman's images — taken with its aptly named Wide Field Instrument (WFI) — will be 50 times wider but more shallow, because Roman doesn't need to access the deep universe the way the JWST does. As we discussed, it can't see infrared like the JWST can and therefore would be wasted in looking too far back.

More specifically, WFI is composed of a 300-megapixel visible-to-near-infrared imaging camera and slitless spectrometer (a special tool that allows scientists to capture light dispersion of objects in a field of view). But there is something uniquely special about that shallow, panoramic view.

The wide and shallow field will be well suited to surveying space, not getting too much information from things that it can't look closer at. 

They can just survey and hope to find a cool lead to zoom in on. This offers Roman the ability to catch events that transpire very quickly, such as fast radio bursts, and increases the chances that scientists can witness remarkable supernovas, colliding neutron stars and other easy-to-miss phenomena right as they happen.

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Well, as the kids used to say, whoomp there it is. I think that's more science on the NGRST than you're going to get anywhere else.