The James Webb Space Telescope

[Borg]

Livestream says 90 minutes.

20 minutes according to this livestream from NASA.
https://www.nasa.gov/content/live-coverage-of-nasa-spacexs-24th-cargo-launch-to-the-space-station

 

[mfb]

Then refresh it. 20 minutes now.

185,000 viewers here:


10 minutes until the final weather briefing, 13 minutes until the rocket takes control of itself.

 

[DennisN]

Then refresh it. 20 minutes now.

You beat me to it.

 

[Borg]

20 minutes according to this livestream from NASA.
https://www.nasa.gov/content/live-coverage-of-nasa-spacexs-24th-cargo-launch-to-the-space-station

FYI, the other streams are 10+ seconds behind my link.

 

[mfb]

Final 7 minutes. Weather is good, the synchronized countdown sequence has begun where the rocket takes care of most of its operations. Fuel loading is almost complete, a little bit of venting can be seen.

 

[DennisN]

Ok, time to wish the James Webb Space Telescope a safe flight and all the best!

 

[Borg]

2 minutes to go.

 

[mfb]

450,000 watching the NASA stream as the launch is less than a minute away.

 

[mfb]

And it's flying...

 

[Borg]

Not updating yet but here's a page for the post-launch sequences.
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

 

[mfb]

Changing too rapidly during launch I guess.

Approaching first stage separation.

 

[Borg]

Just needed to read further.

NOTE: speed and distance data becomes available on the Where Is Webb? page after upper stage separation. Temperature data becomes available 1-2 days after launch.

 

[Borg]

Now 10 times higher than Captain Kirk has gone.

 

[mfb]

Second engine cutoff. Separation in about 2 minutes. Trajectory is still nominal: It will go to L2.

Edit: Separation. Ariane 5 did its job, JWST is on its own.

 

[Borg]

Separated and leaving earth!

BEST CHRISTMAS PRESENT EVER!

 

[valenumr]

Merry Christmas!

 

[mfb]

First solar panel deployed, it produces its own power now.
"Where is Webb" has data.

 

[DennisN]

What an amazing view from the onboard camera when the JWST separated!
I just sat and watched in awe.

 

[Borg]

Indeed!

 

[mfb]

The next major event will be the first mid-course correction burn in about 12 hours. In one day it will deploy its high gain antenna.
Major unfolding will only start in three days.

The teams will run tons of tests now to verify everything is healthy.

 

[Borg]

Where is Webb page shows JWST beyond geosynchronous orbit and 2.5% of its journey to L2 complete! It's going to be a long 29 days but I have lots of hope for a successful mission!

 

[mfb]

155,000 km, 10.7% - but that's 10% of the distance not the time. The telescope is fast early on and slows down as its distance to Earth increases.
The first mid-course correction should happen within the next hour. Doing it early in the flight improves the efficiency - both from a smaller accumulated position error and from the Oberth effect.

 

[valenumr]

155,000 km, 10.7% - but that's 10% of the distance not the time. The telescope is fast early on and slows down as its distance to Earth increases.
The first mid-course correction should happen within the next hour. Doing it early in the flight improves the efficiency - both from a smaller accumulated position error and from the Oberth effect.

Is it significant that the first mcc burn was substantially later than planned? Also any info on the planned delta V expectations vs reality?

 

[collinsmark]

155,000 km, 10.7% - but that's 10% of the distance not the time. The telescope is fast early on and slows down as its distance to Earth increases.
The first mid-course correction should happen within the next hour. Doing it early in the flight improves the efficiency - both from a smaller accumulated position error and from the Oberth effect.

Correct.

One quick note though, performing maneuvers early on are only more efficient via the Oberth effect if they are prograde (in the direction of motion) or retrograde (in the opposite direction of motion). More-so, JWST has severe limitations concerning retrograde maneuvers at this point in its trajectory. If it accidentally overshoots its prograde maneuvers, it could potentially doom itself to zipping past L2 with little or no way to recover.*

For directions orthogonal to the direction of motion (e.g., "normal," "anti-normal," "radial-in," "radial-out"), the Oberth effect actually hurts the efficiency, rather than helps. For maneuvers in these directions, it may be best to wait until the Earth's and Sun's gravitational tug slows it down a little. This competes with the idea that since a small change to an orbit now will have a large change to the orbital position later, that generally speaking, orbital adjustments should be done sooner rather than later. My point here is that the Oberth effect itself only helps the efficiency of prograde/retrograde maneuvers, and decreases the efficiencies of orthogonal maneuvers, in and of itself.

There's another mid-course correction scheduled in a couple of days (MCC1b).

*[Edit: And it is for this reason that Ariane-5's second stage intentionally cut short of placing the JWST directly on a path to L2. Overshooting L2 could doom the mission. So JWST will make up the difference during its mid-course correction burns (in addition to its final insertion burn), where the JWST thrusters have more fine control.]

 

[sophiecentaur]

We (i.e. I) find to easy to forget the relevance of some aspects of big projects. The L2 position is not stable so the situation is very different from setting a course for orbiting round a massive object. The inverse law for GPE of a target planet provides a certain amount of help for getting into orbit, once you are near. There is no such central force around L2 so I imagine everything needs much more precision and you have to make your own quasi orbit around L2 (to avoid being eclipsed by Earth). L4 and L5 would probably be less problematical in that respect. L4 and L5 probably have their own disadvantages. Those points are a long way away (many minutes of signal path delay) and a much longer journey time.

 

[Jonathan Scott]

We (i.e. I) fond to easy to forget the relevance of some aspects of big projects. The L2 position is not stable so the situation is very different from setting a course for orbiting round a massive object. The inverse law for GPE of a target planet provides a certain amount of help for getting into orbit, once you are near. There is no such central force around L2 so I imagine everything needs much more precision and you have to make your own quasi orbit around L2 (to avoid being eclipsed by Earth).

There are at least quasi-stable "Halo orbits" around L2 as described in the Wikipedia article Lagrange Point. These can be quite extended to avoid eclipsing.

L4 and L5 would probably be less problematical in that respect. L4 and L5 probably have their own disadvantages. Those points are a long way away (many minutes of signal path delay) and a much longer journey time.

The L2 point is relatively close but enables the sun shade to hide all of the sun, the Earth and the moon at the same time.

 

[Borg]

155,000 km, 10.7% - but that's 10% of the distance not the time. The telescope is fast early on and slows down as its distance to Earth increases.

The cruising speed yesterday was in excess of 2.5 miles/second. Today, it's down to less than 1.1. It's going to take a month to get to L2 at this rate.

 

[sophiecentaur]

The cruising speed yesterday was in excess of 2.5 miles/second. Today, it's down to less than 1.1. It's going to take a month to get to L2 at this rate.

Just like chucking a ball into the air!

 

[pinball1970]

Six and a half hours, Tracking Webb!



The shorter version.

 

[hutchphd]

QUERY:
Does anyone know whether the length of the first correction burn (65 minutes) was of an "expected" duration? How much of the total onboard fuel inventory does that represent?

 

[Jonathan Scott]

QUERY:
Does anyone know whether the length of the first correction burn (65 minutes) was of an "expected" duration? How much of the total onboard fuel inventory does that represent?

A Google search on JWST mcc-1a duration gives this text:

The first, MCC-1a, is expected to be a long, continuous burn (potentially up to 3 hours) performed approximately twelve hours after launch. The concept for this maneuver is to execute 95% of the nominal maneuver that would take the observatory directly into the LPO.

Reference:
https://ntrs.nasa.gov/api/citations/20140008868/downloads/20140008868.pdf

 

[Jonathan Scott]

JWST has an unusual constraint that it can't slow down, only speed up, because the delta-V thrusters in the current configuration are only at the back end, and it can't turn round without exposing sensitive components to the sun. So it has to be very careful not to speed up too much.

 

[hutchphd]

A Google search on JWST mcc-1a duration gives this text:
Reference:
https://ntrs.nasa.gov/api/citations/20140008868/downloads/20140008868.pdf

Wow that is a very complete treatment. Thanks much.

 

[valenumr]

QUERY:
Does anyone know whether the length of the first correction burn (65 minutes) was of an "expected" duration? How much of the total onboard fuel inventory does that represent?

I'd like to know as well!

 

[valenumr]

I'd like to know as well!

Oops..
Didn t get to the reference before I posted. Seems like 65 minute burn is really good.