Right, but at 91 million miles, it’s not really all that significant anymore. That is, quite literally, halfway across the solar system. It’ll be around the distance that Venus is from us when it is at its brightest.
Right, and even if it still presents any sort of significant source of IR at that distance, it will be 30 degrees below the solar shade with the shade pointed at the Sun.
Like I said, it being 90 times farther, meaning a much more robust mission profile being required, as well as needing more capability in radio transmission hardware, for the small gain of not needing as much station keeping is probably the biggest trade-off. Just getting it there would probably require about the same delta-v as years of station keeping at L2.
Also, I think that something in orbit around L4 or L5 would tend to pick up a rotation, canceling of which could eat significantly into any savings from not having to stay at the more unstable L2.
It’s not like they first decided that they wanted a Lagrange point, and then decided which one. If they hadn’t gone with L2, then they probably would have gone with some completely different orbit that wasn’t a Lagrange point at all, such as a high Earth orbit.
Here is a 17 minute YouTube by Scott Manley where he covers a good bit of the info in this thread. He posted it the evening of the 24th so it was a day before the launch, Starting about 6:20 he talks about the limits of the directions the telescope can be aimed at with diagrams that makes it a lot clearer for me.
An interesting test of whether planners are serious about service missions (unmanned or manned) would be whether the telescope has some kind of service port on the exterior. If there’s a docking plate someplace to allow fluid transfer, that suggests missions are planned or at least contemplated. Likewise a simple external interface for an instrument bay, or power or communications systems.
In DesertDog’s link, Scott Manley says there were talks of including such a thing in 2007, but he hasn’t seen any likely looking ports in any pictures he’s seen.
It’s not just docking. If the Webb wasn’t designed for in-soace repair, it might not be possible to get at critical components like cameras or sunshield motors or whatever without dismantling the thing. It’s a marvel of packaging, and if they knew they didn’t have to worry about repairability it could be just about impossible to get at critical components in space. Hubble had swappable modules designed to be pulled out and replaced in space, and even those gave astronauts fits.
Does the JWST have the ability to see itself? Are there observation cameras mounted on it that would allow the scope to be inspected from Earth? I would think a troubleshooting process would be greatly aided by actually seeing what went wrong during deployment, for example. Cameras are tiny and cheap, but not when Webb was designed.
From what I recall of a Q&A with one of the project scientists (paraphrasing from memory):
Q: Can the JWST be serviced?
A: No. It wasn’t designed to be serviced, and is also very delicate.
Q: Could it be refueled to extend its operational life?
A: It’s possible, but it wouldn’t be easy. It would require robots.
On a different update, the JWST has now reached the orbit of the moon. Its speed is way down to about 0.7 miles/sec, down from an original 1.7+ miles/sec.
My neighbor, who is very interested in this project (but, IMHO, not necessarily a reliable reporter) tells me he hears that JWST includes a refueling port – just in case they ever have the ability to refuel it.
ETA: Here is a stackexchange discussion of the possibility. This all appears to be old, and appears to be largely speculation and “rumors”, not clear announcements by NASA or anybody. One idea mentioned is that the docking mechanism, by which the telescope was mounted to the original booster rocket, could be re-used as a docking port in the future.
This does not give me a warm fuzzy feeling about the possibility of success. Instead, it reminds me of what happened with Galileo’s high gain antenna, and that’s not a good thing.
For those who don’t remember, Galileo’s high gain antenna failed to deploy correctly and they ended up having to use the low gain antenna for all the data. The antenna deployment mechanism was essentially the same as what umbrellas have and three of the struts got stuck. IIRC, they concluded that the failure was caused by vibration during transport causing the graphite lubricant to fall out of the deployment mechanism. (Unfortunately, they couldn’t do what you do with a stuck umbrella and work the slide back and forth, since they’d repurposed the circuit that would retract the slide for something else.)
Having 300+ actions to occur to deploy it is certainly a cliff hanging scenario. Consider all the years prior to this that they’ve had to perfect deployment in space. Imagine the early Astronauts on the moon having to pound a fuel cell into place because they hadn’t properly taken into consideration the conditions on the surface.
For those who may not know, Dr. Becky is an astrophysicist and research fellow at the University of Oxford. She runs a YouTube channel on astronomy and is known for (in her own words) “an unnatural level of enthusiasm”. She won the 2020 Caroline Herschel Prize Lectureship from the Royal Astronomical Society and notably the 2020 Mary Somerville Medal and Prize, given “for exceptional early career contributions to public engagement in physics”. I hope she gets the chance to personally work with the JWST. She certainly has a prestigious university behind her.
Part of the sun shield has now deployed, the first of a series of major deployments.
One strange thing – I read that we would be getting hot side and cold side temperature readings within one to two days after launch. It’s been three and a half days and still no temperature telemetry, at least not on the real time reporting site. No indication that anything is wrong, just curious. Perhaps after the sun shield is fully deployed.
Is there, or will there be a camera, focused on the telescope itself, allowing us to view it? Probably wouldn’t be very exciting once it’s fully operational, but still.
She won the 2020 Caroline Herschel Prize Lectureship from the Royal Astronomical Society and notably the 2020 Mary Somerville Medal and Prize, given “for exceptional early career contributions to public engagement in physics”. I hope she gets the chance to personally work with the JWST. She certainly has a prestigious university behind her.