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1. Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 14:32:00 UTC Santa Claes 🇸🇪🇭🇰🎅
   Someone posted a question if you can see the JWST with a telescope on Earth and I thought pffft of course not, could you see a bus parked on the moon? And now move that bus four times as far away as the moon.
   
   And then people posted pictures of the JWST taken in the backyards of amateurs with tracking equipment.
   
   It is just a dot, yes, but it is actually a dot slightly bigger and brighter than the stars around it.
   
   That said, you can't see it with binoculars as you can with e.g. the ISS.
   
   #JWST #JamesWebb #JamesWebbSpaceTelescope
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 14:59:22 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Some people, journalists and JWST fans alike, are claiming that it's in the Earth's shadow.
     
     No. The JWST has solar panels. It's on a very wide orbit around L2 so that the moon will never come between it and the astronomers who want to communicate with it, and so that Earth will never come between the sun and the solar panels.
     
     The heat shield needs to shield against the full power of the sun all on its own.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:06:36 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Many of the infographics out there are very symbolic, like a subway map; They're not to scale and everything is circles. Webb's orbit around L2 is often shown as similar or smaller than the moon's orbit around Earth. Here is an accurate illustration.
     
     
     
     Image: NASA/STScl
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:22:14 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Animation of Webb's complex orbit around the sun while orbiting L2
     
     farside.link/invidious/watch?l…
     
     www.youtube.com/watch?list=TLG…
     
     /via jwst.nasa.gov/content/about/or…
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:36:22 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • Daniel Appelquist
     @torgo I haven't seen a real explanation, but here's how I imagine it works out.
     
     What keeps us in orbit around L2 is the composant of Earth's gravity in the plane of our L2 orbit and what allows us to go with the same orbital period around the sun as Earth, even though we're farther away and should have a longer period, is the composant perpendicular to our L2 orbit, pointing toward the Sun.
   • Daniel Appelquist (torgo@mastodon.social)'s status on Wednesday, 26-Jan-2022 15:36:23 UTC Daniel Appelquist

     in reply to

     @clacke I still don’t understand how an object can orbit “around” L2 (which is a point in space, right?). Do you happen to have a link to a good explainer because I haven’t been able to find one.

   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:37:30 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • Daniel Appelquist
     If you look at just Earth and a satellite, and you have the satellite go a million miles toward you and then half a million miles up and you kick it hard to the right, it would spiral down to Earth, right? It would be on a kind of orbit around a line going down to earth, and that orbit would move toward Earth, probably pass it and oscillate like a pendulum.
     
     But now we add the sun. So Earth orbits the sun and our orbit also orbits the sun and the way it plays out at L2 is that actually we're heading in the tangent just fast enough that our orbit never falls toward Earth.
     
     @torgo
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:46:13 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • Daniel Appelquist
     It's screwy for sure. I only figured this out just now (if I did indeed figure it out, don't take my word for it, there is no math here, only geometrical intuition).
     
     And the orbital shape is really weird. As the L2 orbit also needs to go around the sun it will be a bit bent around the sun, so it looks a bit saddle-shaped. It's not a stable orbit, it's merely a "helpful" orbit. They will do corrective burns once every 21 days for ten years until the fuel runs out.
     
     They actually put a refueling hatch on there, with handles for a craft to hold onto, but currently no such mission is in the pipeline.
     
     @torgo
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 15:53:10 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     If the scientific return from the telescope is great, in a few years they will have to figure out what is cheaper, sending a complicated refueling mission out there or sending a complicated Webb 2 out there.
     
     From what I understand a lot of the cost for Webb is R&D, so probably sending a clone will be far cheaper than 1 GUSD? What's the material and fuel cost?
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:07:17 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     > Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion.
     
     > Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021
     
     So I guess material and 5 years ops is about 2 GUSD for NASA.
     
     > The European Space Agency provided the Ariane 5 launch vehicle and two of the four science instruments for an estimated cost of €700 million.
     
     That's a bit less than 0.8 GUSD.
     
     > The Canadian Space Agency contributed sensors and scientific instrumentation, which cost approximately CA$200 million.
     
     That's a bit less than 0.2 GUSD.
     
     So about 3 GUSD for launching a clone on a 5-year mission?
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:21:23 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     So what would a robotic refuel mission cost? No scientific equipment, but they baked that into the ESA launch cost there. Let's pretend all instruments are equal, then the launch cost is around 0.5 GUSD. No ops cost for the refueler, but either you pay ops for Webb 2 or you pay ops for Webb 1 round 2, so I guess it needs to be included for a fair comparison, as I included ops in Webb 2. The null cost here is "stop looking at prehistoric space".
     
     > $861 million is planned to support five years of operations
     
     Ok, 0.9 GUSD.
     
     Material cost: Tank, pump, navigation, robot arm or something. Probably much cheaper than scientific instruments? 0.1 GUSD as opposed to 0.4 GUSD for the instruments?
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:21:55 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     So that's 1.5 GUSD for the refuel mission, but they've never done a refuel mission before. How much R&D is that? Webb would be 2 GUSD R&D originally but ballooned to 7 GUSD extra and 8 years extra.
     
     My uneducated guess is that they will ask for 2.5 GUSD for the refuel mission and they will get that because it's less than 3 GUSD. Then it will have cost overruns and end up at 5.5 GUSD but hey, now we'll know how to fly robotic refueling missions!
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:22:34 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Ooos, the source I was quoting is www.planetary.org/articles/cos…
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:30:11 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     But here's another question: When Webb runs out of fuel, why would that be the end of the mission?
     
     The L2 orbit is neat, but when the platform starts drifting into a solar orbit and lag behind Earth it will still have radio, it will still have gyroscopes and it will still have sensors, it will still have cooling. That's all running on solar power, isn't it? I'm sure they'll be able to pull many years of science off that craft, refueling or not.
     
     And before even leaving Earth's grip it would still be on an L2-ish orbit-ish I assume. No idea for how long.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 16:39:02 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Correction: That's supposed to say "far cheaper than 10 GUSD".
     
     But as we see later in the thread the total was closer to 12 GUSD even.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 19:07:05 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • Isaac Ji Kuo
     @isaackuo Oh yeah good point, if it drifts far away enough from L2 that Earth's radiation sneaks around the shield, then it wouldn't be very useful anymore.
     
     So I wonder how soon that happens after station-keeping shuts down.
   • Isaac Ji Kuo (isaackuo@mastodon.social)'s status on Wednesday, 26-Jan-2022 19:07:06 UTC Isaac Ji Kuo

     in reply to

     @clacke There are much closer sun-sync orbits which can keep a satellite lit by the Sun all the time.

     What JWST's L2 position provides is a nice wide field of view where both the Sun AND the Earth is blocked by the sun shield. The thermal glow of the Earth isn't a problem for Hubble, but it would be for the far more temperature sensitive JWST.

   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Wednesday, 26-Jan-2022 19:39:02 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to
     Or, instead of either refueling or sending up an identical mission, they'll splurge on sending up Webb's 50% bigger brother with instruments to replace both Webb and Hubble. Woah.
     
     farside.link/invidious/watch?v…
     
     youtube.com/watch?v=YH_w5StGoE…
     
     #Luvoir #LuvoirTelescope
   • LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864} (lnxw48a1@nu.federati.net)'s status on Wednesday, 26-Jan-2022 21:17:45 UTC LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864}

     in reply to
     @clacke I assumed that the directional antennas have a relatively narrow range of motion. So even if i#JWST could still function, it might not be able to talk to earth.
     
     But another thought came to mind: without fuel in the thrusters, would solar wind's pressure against the sunshield eventually twist the direction (despite gyroscopes) and destroy the instruments?
   • LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864} (lnxw48a1@nu.federati.net)'s status on Wednesday, 26-Jan-2022 22:06:59 UTC LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864}

     in reply to
     https://wwwcache.wral.com/asset/weather/2022/01/22/20093640/jwst_orbit-DMID1-5tnbcstb1-640x480.jpg is the image itself without all the clutter around it.
   • LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864} (lnxw48a1@nu.federati.net)'s status on Wednesday, 26-Jan-2022 22:23:54 UTC LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864}

     in reply to

     • LinuxWalt (@lnxw48a1) {3EB165E0-5BB1-45D2-9E7D-93B31821F864}
     https://blogs.nasa.gov/webb/2022/01/24/orbital-insertion-burn-a-success-webb-arrives-at-l2/
     
     "Momentum unloading" seems to be what I was thinking about.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Saturday, 29-Jan-2022 02:31:25 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • Daniel Appelquist
     @torgo Found an excellent L2 orbit explainer. Luckily the explanation agrees with my intuition in this thread. =)
     
     Launch Pad Astronomy: "How James Webb Orbits 'Nothing' "
     
     farside.link/invidious/watch?v…
     
     www.youtube.com/watch?v=ybn8-_…
   • Daniel Appelquist (torgo@mastodon.social)'s status on Sunday, 30-Jan-2022 14:09:11 UTC Daniel Appelquist

     in reply to

     @clacke wow! This is exactly what I was looking for. Thanks! Also, orbital mechanics is really complicated! :)

     Santa Claes 🇸🇪🇭🇰🎅 likes this.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Monday, 04-Apr-2022 00:30:22 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • 🌸🌹2ck 🌱🐇
     @2ck Just normal ISO prefix. People use all kinds of home-grown abbreviations for millions and billions of money unit. Why, when we have standard prefixes?
   • 🌸🌹2ck 🌱🐇 (2ck@qoto.org)'s status on Monday, 04-Apr-2022 00:30:23 UTC 🌸🌹2ck 🌱🐇

     in reply to

     @clacke I have literally never seen anyone use GUSD to mean a billion US dollars: where did you pick that up?

     Santa Claes 🇸🇪🇭🇰🎅 likes this.
   • Santa Claes 🇸🇪🇭🇰🎅 (clacke@libranet.de)'s status on Monday, 04-Apr-2022 00:31:40 UTC Santa Claes 🇸🇪🇭🇰🎅

     in reply to

     • 🌸🌹2ck 🌱🐇
     @2ck I haven't seen anyone do it either. Someone has to start. =)