JWST

giovanni

Well-known member
Now that it’s launched, what’s your involvement with the project going to be? Like, is there any remote maintenance or anything like that that could be necessary?
 

Chuck D. Bones

Circuit Wizard
Now that it’s launched, what’s your involvement with the project going to be? Like, is there any remote maintenance or anything like that that could be necessary?
We'll only get a call if something looks "funny." The cooler system gets turned on around day 77, which is mid-March.
 

peccary

Well-known member
We'll only get a call if something looks "funny." The cooler system gets turned on around day 77, which is mid-March.
I was doing a little reading on the telescope yesterday and discovered that the extremely low temp is what actually allows it to be able to detect the light/radiation at such a distance, how rad that you were a part of that.

Are you going to be a part of the team that builds whatever robot that's going to go out and perform maintenance on the JWST as well?
 

Chuck D. Bones

Circuit Wizard
The motors are geared-down and slow. There are several steps and I expect that each step needs to complete and be verified before the next step is initiated. AFAIK there are no on-board cameras monitoring the deployment. There are limit switches that will indicate that a boom is fully extended. The software can count motor rotations so it should know when a cable is fully tensioned. If they wanted to, NASA could point Hubble at JWST and see what's happening.
 

Chuck D. Bones

Circuit Wizard
The electronics development took place over a period of years. Between the initial design cycle, modifications and then rigorous design reviews, the number of simulations had to be in the hundreds. Different parts were simulated separately and then the simulations were integrated. The routed digital board was simulated as a whole to evaluate signal integrity and timing margin. The FPGA internals were simulated and their results fed into the digital board simulations. The power conversion circuits and the precision analog circuits were simulated in Cadence SPICE. I ran time-domain simulations of a Sigma-Delta Modulator using Excel. I had a team working on it.

Then there were the guys designing the mechanical coolers. They had a network of computers dedicated to running transient fluid flow simulations.

On top of that was the usual thermal and mechanical vibration simulations. Designing equipment for space requires a level of rigor that has to be experienced to be believed.
 

giovanni

Well-known member
I believe it. I saw a video about the Apollo mission computers and the crazy things they had to do to ensure not only that the hardware wouldn’t fail, but also the software. If I remember correctly, the software was in fact failing at landing but all the fail safes they built into it made it so that the landing was still successful. Very exciting stuff!
 

Chuck D. Bones

Circuit Wizard
JWST has completed tensioning three of the five sunshield layers. They'll tension the last two tomorrow.
In other news, they have fine-tuned the solar array regulators to optimize the efficiency and array temperature. News outlets try to make this into something dramatic, it isn't. It's SOP.

At this moment, the hot side of the sunshield is at 59°C. It will get hotter.
The spacecraft equipment panel average temp is 19°C. This is where most of the on-board electronics dumps its heat. It will warm up a bit when more of the equipment gets turned on.
The average primary mirror temp is -132°C. It will get colder.
The ISIM (Integrated Science Instrument Module) radiator temperature is -194°C. This is on the back side of the primary mirror and is where all of the low temperature optics and detectors are located. It will get colder.
 

Chuck D. Bones

Circuit Wizard
The sunshield deployment completed successfully yesterday. This morning, the secondary mirror struts were unfolded to position the secondary mirror out in front of the primary mirror. Here's some video:
You can skip thru it to see some detailed animations of the light path, the instruments and some ground test videos. All the more impressive when you see people standing next to the telescope.
 
Top