Press release with more details: https://www.nasa.gov/press-release/nasa-s-webb-telescope-rea...
James Webb is fully deployed
71–80 of 522 posts
Re: James Webb is fully deployed
#72What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope.
But aren't there other ways to orient in space?
1. use pressure from the solar wind
2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.
Re: James Webb is fully deployed
#73One of the big numbers that been thrown around is that JWST has 344 single points of failure in its mission. Now that deployment has been completed, is there somewhere that lists how many of those points we have passed?
>344 single points of failure How can a system have more that one single point of failure?
Single point of failure is a term for non-redundant, critical parts of a system:
Re: James Webb is fully deployed
#74Earlier quoted context omitted.
If you're in a car being held above the ground by a chain, every single link is a potential single-point of failure.
In a real chain, only one link is actually the weakest, and it is at that link where the chain will break, in the hypothetical you offer.
Which is true, but also not what's being discussed, which is "single point of failures", not "weakest link".
Re: James Webb is fully deployed
#75Since 90% of the cost is probably in R+D of the telescope, one could build and deploy another for another 10%. Why isn't this done? Why is every space telescope completely unique?
Re: James Webb is fully deployed
#76What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.
IIRC the thrusters are also used for station-keeping since practical Lagrange orbits are unstable.
Re: James Webb is fully deployed
#77What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.
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Re: James Webb is fully deployed
#78What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.
Reaction wheels let you orient but they don’t allow you to maintain an orbit.
Re: James Webb is fully deployed
#79Earlier quoted context omitted.
It'll take a few weeks after L2 insertion to cool the components and another 5 months to calibrate the instruments.
I'm hoping that the 5 months of calibration time is one of those where the engineers were asked "how long", so they thought about it and then padded the shit out of it, then the PMs took that number and padded it yet again. After all that, it only takes a few weeks. It'll be the first milestone JWST would meet early, so not too likely. We've only waited decades, so a few more months isn't that bad. At least it is off…
Similar question was just asked during press conference and the answer was "telescope is cooling a bit faster than we simulated but it is not a significant difference, it might be ready one or two days ahead of current estimation".
Current timeline is for getting all 4 cameras to work, but I think only one needs cryogenic cooling, other 3 could work with just sunshield. In another answer one of the engineers said that first images will be released once telescope is fully operational (aka all 4 instruments cooled down).
Re: James Webb is fully deployed
#80What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.
not sure about 1, but it already orients itself using reaction wheels, which are basically what you are describing with 2.
The issue is that its position at the lagrange point L2 is an unstable equilibrium, which requires occasional adjustment using thrusters. In terms of gravitational potential energy, its position in space is a saddle point, not a local minimum.