With NASA’s brand new space observatory on schedule in its commissioning phase, the science team outlined their plan to make the most of this $10 billion opportunity.
The James Webb Space Telescope arrived a few days ago at its destination at Earth-Sun Lagrange Point 2 (L2), which is about 930,000 miles (1.5 million kilometers) from our planet.
Lead researchers from Webb’s science team presented their plan at a town hall Friday, Jan. 28, hosted online by the Space Telescope Science Institute (STScI) in Baltimore.
The town hall took place as engineers continued to work on commissioning the observatory. A key step, the commissioning of its scientific instruments, occurred this week. Technicians also continue to align the mirrors and prepare the observatory for another five months of commissioning.
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Jonathan Gardner, deputy principal scientist for Project Webb at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, covered the final months of preparation before giving a brief update on how things are going in orbit. In a nutshell, everything is going according to plan, he noted.
“There have been 50 major deployments; they were all successful,” he said of the telescope mirror deployment, as an example of Webb’s major milestones.
Meanwhile, amateurs and professionals are already returning data from backyard observatories and professional locations. For example, he said, people have also taken “light curves” at places such as the National Science Foundation’s Green Bank Telescope.
Webb’s brightness changes in a repeatable six-hour cycle as the observatory’s solar array reflects a reflection of sunlight back to Earth, during its steady rotation, Gardner said. “The sunshade reflects sunlight directly onto the Earth, and [sometimes] has a glow and at other times it’s a more diffuse light,” Gardner said.
Commissioning will take several more months, said Mike McElwain, Webb Observatory project scientist at Goddard.
“We’re going to align the telescope; it’s a roughly three-month process that we plan to start early next week,” he said, noting that the telescope’s optical performance will be evaluated for (among other ) determine the amount of stray light produced by the optics.
Optical commissioning will include several complex steps – sometimes sequential and sometimes iterative – such as identifying images, aligning different mirror segments and possibly phasing the segments to a fraction of a wavelength, a noted McElwain.
To guide the alignment of the mirrors, the Webb team will focus each of the 18 primary mirror segments on a bright, distant star called HD 84406, which is part of the constellation Ursa Major (“the Big Dipper”).
An “additional layer of complexity” during commissioning, McElwain noted, is that the telescope’s performance will change as it continues to cool. Eventually, Webb’s operating temperature will be around 45 Kelvin or degrees above absolute zero, which equates to minus 379 degrees Fahrenheit (minus 228 degrees Celsius), but commissioning continues as the telescope changes in temperature.
Webb will still have a slight “jitter”, however, due to the expected vibrations of the reaction wheel and cryocooler. The telescope will also drift very slightly over time, due to solar heating over the observatory. While these disruptions to the telescope should be very minimal, engineers will periodically make necessary adjustments, McElwain said.
The team is now preparing to move into science operations by commissioning the instruments, an activity that was due to begin last week when the instruments turn on, said Jane Rigby, Webb operations project scientist at Goddard.
The instruments coming to life will kick off, Rigby said, “an intense two-month period as we check out the science instruments and get them ready for science operations.”
Commissioning shows that instruments can be calibrated, she noted, but calibration will not be completed during the commissioning period. “Each observing mode has specific quantitative criteria for science readiness that say, ‘Okay, this looks ready to go,'” Rigby said. “That doesn’t mean it’s perfect, [but] that means it looks like it’s ready to start science operations.”
Full calibration will await Cycle 1, the first round of early science, which is expected to take place after the mission’s six months, around June 25. That means the instruments will be fully ready for operations amid this data collection, she said. (A sampling of Cycle 1 observations includes coronagraphic observations of debris desks around brighter stars and a star that has a transiting super-Earth planet.)
Around the same time will come an early release of sightings, including the first images. There will be a set of showcase images “designed to be on the front pages of media around the world,” Rigby said. But all commissioning data will be made public at that time, including “the good, the bad and the ugly”. The Webb team has been silent on the exact images that will be released at this time.
Rigby repeated past estimates suggesting Webb will have about 20 years of fuel on board, but said that estimate will need to be refined as the telescope periodically fires the thruster to “drain the momentum” of induced torque on the observatory. by the solar wind.
“That angular momentum is absorbed by the reaction wheels, but then we have to spin those reaction wheels by firing the thrusters,” Rigby said, estimating that this activity will take place every three weeks. But the issue limiting Webb’s lifespan, she added, will likely be instrument health rather than fuel.
Normal science operations for Webb are already underway, said Klaus Pontoppidan, Webb project scientist at STScI.
“Cycle 1” proposals for early science, available on the STScI website, are already approved and scheduled, he said. It’s all in a long-term schedule, and then every 10 days or so the team draws up a shorter-term schedule that tries to be flexible for unforeseen events such as “targets of opportunity”, i.e. ie short-term phenomena in the sky like comets or supernovae.
“Round 2” proposals for operational science will likely be due in January 2023, assuming the schedule continues to run as planned. An exact date for submitting the proposal will be determined as it goes live, he said.
Webb will likely be in high demand for telescope time given his ambitious science agenda, which ranges from learning about the early universe to studying celestial objects.
The Q&A session included questions about Webb’s observing budget increase, any efforts to increase fairness, diversity and inclusion in science submissions, and a previous proposal to rename the telescope.
Officials, including Webb Program Scientist Eric Smith (at NASA Headquarters), encouraged community participants to continue asking the team these questions in order to adjust future science cycle proposals.
In the case of Webb’s name change, however, that decision was made by NASA’s senior team and the telescope team is focused on getting the telescope operational, he said.