Webb’s Journey to L2 Is Nearly Complete | Hacker News Reader

Webb’s Journey to L2 Is Nearly Complete

blogs.nasa.gov

135 pointsjordanpg33 comments

About three more hours to go and then the injection burn will commence. That is the most critical step still remaining of the deployment steps, everything has worked perfectly so far.

What an amazing accomplishment.

If you are wondering why the satellite is still moving with 200 m/s that is because there is a component that is already out of the plane of the ecliptic which will be conserved to help reduce the amount of fuel required for the orbit insertion, so it won't go to 'zero'. This is a bit confusing, especially because of the language on some of NASA's websites where they suggest that the satellite will come to a stop, this is true but only in one axis, the one relative to Earth.

In the same vein: Webb hasn't really arrived at L2, but at a point almost 800,000 km away from it, perpendicular to the line Earth-L2 (which of course is a moving system itself!). So Webb will be orbiting in a plane perpendicular to Earth-L2 at a very large distance from L2, which guarantees that it will have power (because the solar panels will be continuously in sunlight).

Edit: two more hours to go. JWST is still moving at roughly the speed of a commercial airliner (730 km/h).

Edit: one more hour to go, and NASA just posted this image to show the orbit in an easy to digest format:

https://jwst.nasa.gov/content/webbLaunch/assets/images/orbit...

> Utilizing thrust every three weeks or so from small rocket engines aboard Webb will keep it orbiting L2[...]

Yes, because L2 is not a point of stable equilibrium. This means an object left there will have a local tendency of leaving its position the more it gets way from it, like the top of a round hill. OTOH, Lagrange points L4 and L5 are points of stable equilibrium. This means an object left there will have a local tendency of returning to its position the more it gets way from it, like the bottom of a round pit.

Considering the age of the Earth, it is very likely that the Sun-Earth L4 and L5 Lagrange points store an accumulated material that was captured by the local "gravity well". I wonder what kind of stones and dust may lie there.

Why has it never been explored?

In October, NASA launched the mission Lucy which will study the Trojan asteroids which have sat in the L4 and L5 points between Jupiter and the Sun since the beginning of the solar system.

https://www.nasa.gov/mission_pages/lucy/main/index https://www.youtube.com/watch?v=zbwSSdtWUNE

https://svs.gsfc.nasa.gov/3591

There are two "Trojan" astroids oscillating around L4:

https://en.wikipedia.org/wiki/2010_TK7

https://en.wikipedia.org/wiki/2020_XL5

This is a good list of objects at Lagrange points, bit of a Wikipedia hole:

https://en.wikipedia.org/wiki/List_of_objects_at_Lagrange_po...

L4 and 5 are perturbed by the rest of the Solar system, mainly Jupiter, so not much long-term accumulation should be expected.

It's not the only reason to orbit L2 instead of staying at L2. Webb needs enough light from the sun on its solar panels to power its instruments, so it needs to stay out of the Earth's shadow.

Related very good news: thanks to the very precise orbital injection, Webb has excess propelllant that will be used for station-keeping, significatively prolonging the mission: https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-exces...

With the innovation of satellite life extenders like MEV-2, fuel is less of an issue. Webb has reaction wheels and cryocoolers which may have their own lifetimes and become the limiter.

https://www.seradata.com/mev-2-satellite-life-extender-space...

Yes, a surprising amount of stuff on the satellite is mechanical. After reading up on Webb's construction and the way the incredible thermal separation of the hot side and the cold side is achieved, as well as the sensors and the cryocoolers my respect for the designers and builders has gone up a couple of notches.

For US$10 billion, it had damned better work first time. Stoked that it's all gone beautifully well so far.

The cryocooler is needed only for one instrument. Hopefully it lasts a long time but after that they can still continue use other instruments.

Also see the Where is Webb? dashboard-

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

It's almost there, but there will still be about six months of cooling down and calibration before we see anything from it.

We are very likely to see first images much sooner than that. Although first science needs to wait for full cooling and alignment, they will be producing images during that process. The expectation is that some of these images will be published, mostly for PR.

Almost sounds like a too good to be true excuse for strolling off chasing pretty views with the new toy ;).

The scope can’t image anything at all right now, and it will be quite a while before it can.

Each mirror segment was firmly supported to withstand the violent forces at launch. In the past few days, the two 3-segment wings swung into position and every mirror segment moved slightly so that now they can be aimed by their actuators. Each segment has actuators on the perimeter that will fine tune the pointing and one in the center that can deform it slightly to change focus. Each one will now need to be fine tuned. There are also many adjustments to be done in the secondary optics.

Inevitably, surprises will crop up as well and have to be dealt with. They do this quietly now for PR reasons. While the Hubble was being commissioned, some engineers talked freely about the things they were dealing with. At first it was very interesting to follow along. But once it was determined that the primary trouble was misconfiguration of the objective, all the chatter stopped. Since then all space missions tightly control their press. This is understandable but makes it a little less fun to follow along.

The good news is that most of the single use motors and actuators have done their thing and and are now retired. The ones that remain (like the mirror pointers) are based on designs that have worked many years on many spacecrafts. It is great to see the project get to this stage. I can’t wait to read about what we find out there.

Thanks, now I'm looking forward to the inevitable (even more) pop-sci explanation: "imagine waking up double-vision drunk, but instead of two eyes going astray it's eighteen eyes. And it all happens while you know for a fact that you won't be able to tell up from down anytime soon"

IIRC the plan is to wait until everything is calibrated and tested before releasing any images, to allow the first public images to "wow" everyone.

From a PR perspective that would not be very smart. Everbody wants to know that it works in principle and if the images that it can make today are not quite as good as the ones that it will make six months from now that gives more points in time to make the public aware of what the telescope can do and what an amazing achievement it is.

I fully expect NASA to release a 'first light' image in the near future and if they do not I'll be sorely disappointed.

Measured in a choice of 'English <or> Metric'.

It's always a bit jarring to see scientific data presented in non-metric units, even in the US. But as an American, I only understand density in terms of Libraries of Congress per Olympic Sized Swimming Pools

What is the base unit of "Libraries of Congress per Olympic Sized Swimming Pools"? Does the expansion rate of the LoC match the expansion rate of the universe?

It's interesting that the Metric temperature measurements aren't in Kelvin.

It is even more interesting that it is in coulomb and not degree Celsius or Kelvin.

It's clearly in Celsius, which is the metric system's temperature unit and it is clearly stated on the website's about page:

By default the page loads and displays distances in miles, temperatures in Fahrenheit, ie English units (also known as Imperial or USCS system units). If you wish to have the page load and display in kilometers and temperatures in Celsius, ie metric system units use the urls below to select your preferred units.

GP means they should have used a Capital 'C'.

It is a [small] capital C but a capital C is the symbol for coulomb, the correct symbol for degree Celsius °C.

The Liberia, Myanmar, and USA still use the imperial system of measure.[1]

It is fascinating to see a generation of people insist on the wrong thing simply because they don't understand the right/better thing.

Or because it is of foreign origin.[2] There have been dangerous incidents because of conversion failure.[3]

[1] https://www.statista.com/chart/18300/countries-using-the-met...

[2] https://en.wikipedia.org/wiki/Metrication_opposition#Metrica...

[3] https://en.wikipedia.org/wiki/Metrication#Accidents_and_inci...

The real question is, what happens to this page when distance hits 0.

Reminds me of this old, favorite LOL: https://www.youtube.com/watch?v=QOtuX0jL85Y

30 minutes to go :-). It's 319KM to L2 orbit as I type this.

In all the animations I’ve seen of the orbit around L2, it appears to be elliptical rather than circular. Is that an optical illusion, or is there a benefit to such a path?

See: https://youtu.be/524fcGyki5c

AFAIK the elliptical orbit shown is not (easily) possible (source: Kerbal Space Center) I think they want to show a "vertical" orbit around L2 (where "horizontal" would be earth's orbit around the sun). It's slightly better visible in the youtube movie.

It has since been completed it seems: https://blogs.nasa.gov/webb/2022/01/24/orbital-insertion-bur...

Reply on news.ycombinator.com