Webb Telescope Took a Snapshot of Jupiter, NASA Report Shows

[Buster's Uncle]

Webb Telescope Took a Snapshot of Jupiter, NASA Report Shows
Ed Browne - 2h ago
Newsweek


Scientists working with the James Webb Space Telescope have quietly released an image of the planet Jupiter as part of an earlier test of the telescope's abilities.

Webb has captured the world's attention this week after NASA released a suite of images on Monday and Tuesday, representing the first publicly-available proper images the telescope has taken since it was launched in December.

The images included far-away galaxies and nebulae, and Webb also captured data on the atmosphere of a distant planet.

As part of the wider data release, NASA, along with the European Space Agency (ESA) and the Canadian Space Agency (CSA), released a commissioning report Tuesday outlining Webb's science performance capabilities over a six-month testing period following its launch.

As part of the testing period, scientists put Webb through its paces regarding its ability to track objects around the solar system at speeds of up to 67 milliarcseconds per second—a measure of how fast it can watch something move in front of it. Suffice it to say, 67 milliarcseconds per second is twice as fast as Webb was designed for.

One of these tracking tests saw Webb being tasked with tracking Jupiter as it moved at an apparent speed of around 3.3 milliarcseconds per second, which was achieved. Below is the photo that Webb managed to capture, which also shows that a number of Jupiter's moons were observed.

The test, according to the report, "demonstrated that JWST can track moving targets even when there is scattered light from a bright Jovian planet."

A caption read: "The exposure time was 75 s. The Jovian moons Europa, Thebe, and Metis are labeled. The shadow of Europa is also visible, just to the left of the Great Red Spot. The stretch is fairly harsh to bring out the faint moons as well as Jupiter's ring."

This was only one of Webb's tracking tests, however. Scientists stepped up speeds all the way to 67 milliarcseconds per second, at which point it was tracking the asteroid 2004 JX20.

Webb was able to track all of the objects successfully, opening up the exciting possibility that the telescope could be used for observing near-Earth asteroids and comets.

In general, the report contained a glowing assessment of Webb's abilities, with its authors noting that the telescope's performance was better than expected "almost across the board"—and that various characteristics such as the cleanliness of its mirrors and the alignment of its optical equipment exceed requirements.

"In most cases, JWST will go deeper faster than expected," the report read. "In addition, JWST has enough propellant onboard to last at least 20 years.

"The authors acknowledge the tremendous amount of work by the entire international mission team to bring JWST through commissioning into science operations."



© NASA/ESA/CSA/STScl
A closer screenshot of the James Webb Space Telescope's image of Jupiter taken from its July 12 commissioning report. The Jupiter image was part of a test of Webb's ability to track objects. NASA/ESA/CSA/STScl


https://www.msn.com/en-us/news/technology/webb-telescope-took-a-snapshot-of-jupiter-nasa-report-shows/ar-AAZzCk1?rc=1&ocid=winp1taskbar&cvid=7d01985c3cd144b59abc6b2d2f09c047

[Geo]

If only we could see such snapshots from exoplanet. 

[Unorthodox]

Only 20 years worth of propellant? 

Yikes. 

Wonder how much of that is for tracking vs how much is for maintaining orbit. 

[Buster's Uncle]

Wouldn't they use gyros for tracking?

[Unorthodox]

It's complicated on the Webb. 

The reaction wheels are rocket assisted to a degree that's not been specified.  So, I'm curious if it's the stabilization that's going to burn out in 20 years, you have a completely dead stick as you can't point it reliably, where the maintaining orbit motors, you likely have a grace period of usefulness past that provided contact can be maintained.  But it sounds like 20 years is double the initial estimate of 10. 

JWST Propulsion
JWST's propulsion system provides maneuvering capability for orbital insertion, station keeping, and spacecraft momentum management.

The JWST propulsion subsystem is the part of the spacecraft bus that provides the means to correct JWST's orbit at the second Lagrange point (L2), to control attitude in certain ACS modes, and to unload stored momentum from the reaction wheels (when necessary). JWST nominally carries enough propellant for a 10.5-year mission, pending actual on-orbit performance.

Orbit correction maneuvers, also referred to as Delta-V maneuvers, are used to augment the launch vehicle injection velocity and to maintain a transfer trajectory into orbit about L2, and then to maintain the JWST orbit around L2 (station-keeping maneuvers) for the life of the mission. There are two types of thrusters for these functions. They are mounted on the spacecraft bus to avoid introducing contamination or heat sources near the OTE/ISIM side of the observatory. The Secondary Combustion Augmented Thrusters (SCAT) are used for orbit correction (Delta-V and station-keeping), and mono-propellant rocket engines (MRE-1) are used for attitude control and momentum unloading of the reaction wheels.

The SCATs are bi-propellant thrusters, using hydrazine (N2H4) and dinitrogen tetroxide (N2O4) as fuel and oxidizer, respectively. They operate in "blowdown mode" with one tank for each type of propellant and using gaseous helium as a pressurizing agent. There are 2 pairs of SCAT thrusters (paired for redundancy). One pair is located near the center of the bottom of the spacecraft bus where JWST attaches to the launch vehicle. These are used for the first Delta-V maneuvers to reach L2 with the correct velocity for the operational orbit. These maneuvers are executed before the sun shield is deployed.

The other pair of SCAT thrusters is mounted on a boom on the side of the spacecraft opposite the solar array, oriented such that their thrust direction passes through the deployed observatory's center of mass. These are used for the orbit insertion Delta-V maneuver and station-keeping maneuvers. This pair of SCAT thrusters are used after the observatory is fully is deployed.

The MRE-1 thrusters use hydrazine as a propellant. There are 8 MRE-1s located on the spacecraft and are oriented so that torque can be applied in roll, pitch, or yaw control axes. For momentum unloads, these thrusters are fired so that the applied torque provides the desired change in the angular momentum of the reaction wheels.

[Geo]

I was under the impression that the cryo-cooling 'fuel' was the main bottleneck for endurance. But that's perhaps only for a part of the instruments?

[Unorthodox]

I was under the impression that the cryo-cooling 'fuel' was the main bottleneck for endurance. But that's perhaps only for a part of the instruments?

AFAIK that's a closed system, similar to a refridgerator, you don't lose fuel, but the recirculating pump will eventually wear out.