valenumr
- 469
- 193
Merry Christmas!
Is it significant that the first mcc burn was substantially later than planned? Also any info on the planned delta V expectations vs reality?mfb said: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.mfb said: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.
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.sophiecentaur said: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).
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.sophiecentaur said: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 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.mfb said: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.
Just like chucking a ball into the air!Borg said: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.![]()
A Google search on JWST mcc-1a duration gives this text:hutchphd said: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?
Reference: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.
Wow that is a very complete treatment. Thanks much.Jonathan Scott said:A Google search on JWST mcc-1a duration gives this text:
Reference:
https://ntrs.nasa.gov/api/citations/20140008868/downloads/20140008868.pdf
I'd like to know as well!hutchphd said: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?
Oops..valenumr said:I'd like to know as well!
1 last night and 0.83 this morning GMT.Borg said: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 the management, it's keeping its backside covered.Jonathan Scott said:it can't turn round without exposing sensitive components to the sun.
Different from the "Where is..." link above your post?anorlunda said:Does anyone have a link to get access to the real time data?
Yes, they would be seeing an earlier form of the Milky Way.finney said:Webb telescope will be looking deep into the universe (back into earlier universe) so if someone is looking at the milky way from the farthest known galaxy would they think they were seeing an earlier universe?
Very cool (pun intended.) Where did you find that data?mfb said:4 days 8 hours after launch:
View attachment 294873
We already have a large difference between hot and cold side.
Next step is the deployable tower, increasing the separation between spacecraft and sunshield before the latter is expanded.
The telescope part rotates/tilts, the sunshield part stays where it is because it needs to keep shielding the Sun. Reaction wheels take care of that.KurtLudwig said:1. How is JWST pointed?
If the telescope rotates with respect to the sun-shield, then the secondary mirror will be in sunlight. Please explain in detail.mfb said:Momentum flap deployed, sunshield cover removed. We are passing many of the single points of failure now.
The cold side has warmed up a bit since my last post, it's now -45 degrees at the mirror and -145 degrees at the instruments. I expect it to cool down again once the sunshield deployment starts.The telescope part rotates/tilts, the sunshield part stays where it is because it needs to keep shielding the Sun. Reaction wheels take care of that.
An L2 halo orbit has to be perpendicular to the L2/Sun direction because only these two dimensions are an attractive potential. You can't orbit L2 along the L2/Sun direction. About 800,000 km, as you can find on the Wikipedia page.
all 107 membrane release devices associated with the sunshield deployment — every single one of which had to work in order for the sunshield to deploy — have now successfully released.
We are getting through all the scary parts, and it's going great!mfb said:The requirement to stay in the shadow limits the observable range in the sky. Here is a discussion and here are more technical details (PDF download). Within +-5 degrees of roll the sunshade can keep its 3D orientation, for more it has to rotate around the JWST/Sun axis. It keeps its orientation relative to the Sun independent of the pitch angle.
New blog updates:
Webb Ready for Sunshield Deployment and Cooldown
First of Two Sunshield Mid-Booms Deploys
With Webb’s Mid-Booms Extended, Sunshield Takes Shape
The sunshield is now fully extended. It's not under tension yet, but it's enough to cool down the telescope side significantly. Tensioning the five layers will take at least two days.
That's a massive chunk of single points of failures:
If I am picturing correctly, the flap corrects for pitch. But I don't really know. It is a very interesting concept if one thinks about it.KurtLudwig said:If the telescope rotates with respect to the sun-shield, then the secondary mirror will be in sunlight. Please explain in detail.
If the telescope tilts, it and the secondary mirror will still be shielded.
I think it's all scary. Until data arrives at Earth with the expected quality, it ain't over.valenumr said:We are getting through all the scary parts, and it's going great!
Can you hold your breath for 5 months until the temperature stabilizes?JLowe said:Until data arrives at Earth with the expected quality, it ain't over.