A Small Story

It was a slow news day, which is kind of good in a way because life was interrupting anyway and decreasing the amount of attention I had to pay, but not good in every other way. I listened to the NASA teleconference about Starliner but it was close to content free, it's just that someone (Steve Stich?) said he wanted a decision by mid-month instead of the end of the month and scheduled this one.

The small story is that NASA has shut down an old satellite that (like so many) far exceeded its expected life and accomplishments. Its last commands were to reduce its altitude, increasing drag to speed its de-orbiting. It's expected to reenter before the end of the year. One of the aspects that makes it hard to predict is that the atmosphere expands and contracts with solar activity and we're clearly at much higher activity than we've been in quite some time. Just today, there was another X1.1 solar flare. The electromagnetic effects get here at the speed of light while it can take days for a Coronal Mass Ejection to get here.

The satellite is called NEOWISE, a 15 year old satellite that was the first one launched to survey the sky for near earth objects. The name appears to be a combination of Near Earth Object and Wide-field Infrared Survey Explorer. NEOWISE was launched in December 2009, on a seven month mission. That's right, we're four months short of 15 years out of a seven month mission. 

In fact, it was launched as WISE, lived out a mission and then was put in hibernation.

After WISE completed checkouts and ended its primary all-sky astronomical survey, NASA put the spacecraft into hibernation in 2011 after its supply of frozen hydrogen coolant ran out, reducing the sensitivity of its infrared detectors. But astronomers saw that the telescope could still detect objects closer to Earth, and NASA reactivated the mission in 2013 for another decade of observations.
...
"We never thought it would last this long," said Amy Mainzer, NEOWISE's principal investigator from the University of Arizona and UCLA.

While a lot of NEOs have been found, most have been found with ground-based telescopes. Where orbiting telescopes stand out is observing in the infrared.  Earth's atmosphere absorbs most of the infrared light coming from faint objects like asteroids. Warm space rocks.  

The common tradeoff with telescopes and camera lenses involves field of view vs. magnification. Larger telescope optics (mirror or lens) tend toward higher magnification and smaller fields of view. NEOWISE's mirror is 16-inches diameter, compared to something like the James Webb Space Telescope, which has a multiple piece mirror that totals 256 inches aperture, 16 times the aperture of NEOWISE. Of course, the side of that trade NEOWISE wins is a wider field of view. 

But its wide field of view allowed NEOWISE to scour the sky for infrared light sources, making it well-suited for studying large populations of objects. One of the mission's most famous discoveries was a comet officially named C/2020 F3, more commonly known as Comet NEOWISE, which became visible to the naked eye in 2020. As the comet moved closer to Earth, large telescopes like Hubble were able to take a closer look.

“The NEOWISE mission has been an extraordinary success story as it helped us better understand our place in the universe by tracking asteroids and comets that could be hazardous for us on Earth,” said Nicola Fox, associate administrator of NASA's science mission directorate.

Artist's concept of the NEOWISE satellite with a comet (upper right) and a sweeping belt of "space rocks".  Image credit: NASA/JPL-CalTech

WISE, and then the extended mission of NEOWISE, helped scientists estimate there are approximately 25,000 near-Earth objects. 

It's impressive results, but it's just the start. A replacement is in the works called NEO Surveyor, which will be placed so it orbits around the L1 Lagrange point nearly 1 million miles from Earth and the same neighborhood as NASA's Solar and Heliospheric Observatory Satellite SOHO. Launch is currently targeted for 2027.