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Webb flies Ariane 5: watch the launch live on 25 December

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Re: Webb flies Ariane 5: watch the launch live on 25 December

#141

Post by dylan604 »

devoutsalsa wrote: post #107
twistedpair wrote: post #93

Earlier quoted context omitted.

They calculated that. Building a second JWST would have added 10% to the budget, but the budget committee nixed that. YOLO (you only launch once).

The JWST only has a planned mission duration of 10 years. If it’s as epic as everyone claims it could be, there must be a follow up mission planned. So even if it fails, we’ll still see a successor at some point.

>there must be a follow up mission planned

https://www.universetoday.com/139461/what-comes-after-james-...

The write up goes into detail on how missions are planned, and what is in line to follow JWST.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#142

Post by buryat »

twistedpair wrote: post #99
eterm wrote: post #77

Earlier quoted context omitted.

How feasible is a repair mission without the shuttle?

L2 is very far from earth, well beyond the Moon. The Shuttle could never leave Low Earth Orbit, so it's a non-factor in repair missions once JWST is on station.

in Armageddon the Shuttles flew over the moon

Re: Webb flies Ariane 5: watch the launch live on 25 December

#143

Post by jdiez17 »

yk wrote: post #130
dimtion wrote: post #42

I do have a question about JWST that I wasn't able to find a fine answer in other forums. A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so! However, I'm always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if eve…

I hope it's just badly thought through marketing. There is currently a AWS spot during nfl games, that shows a spectacular catch and then proclaims that the catch probability is only 3.6% or something. You are meant to be somehow impressed by the unlikelihood I believe, but that their model thought the catch is unlikely and the guy caught it implies a rejection of their model with p=3.6% The JWST marketing seems to w…

I don't think you are supposed to be impressed by the number of things that could go wrong. At least, that's not how I see it. They talk about the deployment phase with all these complex things that have to go exactly right as "the 30 days of terror." And that's a pretty accurate description of what many people with a stake in the JWST will be feeling. Not awe, but terror. This is a big part of space missions at the bleeding edge of science and technology, and I think it's great that many people are hearing about it!

Re: Webb flies Ariane 5: watch the launch live on 25 December

#144

Post by wmf »

devoutsalsa wrote: post #107
twistedpair wrote: post #93

Earlier quoted context omitted.

They calculated that. Building a second JWST would have added 10% to the budget, but the budget committee nixed that. YOLO (you only launch once).

The JWST only has a planned mission duration of 10 years. If it’s as epic as everyone claims it could be, there must be a follow up mission planned. So even if it fails, we’ll still see a successor at some point.

Since JWST was delayed ten years the successor will probably be delayed 20 years and launch in 2050.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#145

Post by unethical_ban »

InTheArena wrote: post #36
ur-whale wrote: post #18

Earlier quoted context omitted.

> Why isn't SpaceX doing this? Reliability (as in: established track record). Although, if Ariane decides to explode tomorrow, this comment will look ... odd.

This has to be launched by Ariane - it's constraints are tightly bound to what that platform can do, and it's fairing size. Ariane is optimized for GEO insertion, while Falcon is optimized for LEO orbits. You could have used a Falcon, but a payload like this was actually built around the rocket's capability, and this was designed prior to Falcon being a thing. All that said it's worth nothing that SpaceX's flight suc…

Does anyone really think of SpaceX as a scrappy startup? You seem to recognize that this mission was designed and set in stone well before SpaceX was established.

I don't know if JWST needed vertical assembly, but I recall that some spy satellites in the past have had to be launched on Atlas/Delta because they need to be assembled on the rocket vertically (vs. being rolled out to the launchpad horizontally).

Re: Webb flies Ariane 5: watch the launch live on 25 December

#146

Post by dragonwriter »

buryat wrote: post #142
twistedpair wrote: post #99

Earlier quoted context omitted.

L2 is very far from earth, well beyond the Moon. The Shuttle could never leave Low Earth Orbit, so it's a non-factor in repair missions once JWST is on station.

in Armageddon the Shuttles flew over the moon

The shuttle-like craft were explicitly special, more capable craft (visually hinted at by the extra set of boosters and other design differences.)

Not that Armageddon was particularly focussed on reality.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#148

Post by shmageggy »

jacquesm wrote: post #66
WJW wrote: post #64

Earlier quoted context omitted.

Perhaps it's a case of "we're proud that we got it all the way down to only 200 SPOFs in the final design, the earlier designs were way worse".

There is a fair chance of that, actually. If you start enumerating the ones that are obvious even to lay people ( one rocket, one satellite, one set of mirrors and so on) then this is probably an extremely impressive low number.

I've been binging JWST content and definitely recall John Mayer saying in at least one interview that 344 single points of failure was as low as they could get it. And I can believe it. If you watch some of the more detailed interviews, he always stresses how every design choice was heavily labored over and reviewed.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#149

Post by jacquesm »

shmageggy wrote: post #148
jacquesm wrote: post #66

Earlier quoted context omitted.

There is a fair chance of that, actually. If you start enumerating the ones that are obvious even to lay people ( one rocket, one satellite, one set of mirrors and so on) then this is probably an extremely impressive low number.

I've been binging JWST content and definitely recall John Mayer saying in at least one interview that 344 single points of failure was as low as they could get it. And I can believe it. If you watch some of the more detailed interviews, he always stresses how every design choice was heavily labored over and reviewed.

It's an absolutely amazing effort, from the design through all of the problems they had to deal with along the way to seeing it sit there on top of that booster. A few months from now we could be in a completely new era of astronomy.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#150

Post by chriswarbo »

martyvis wrote: post #138
HideousKojima wrote: post #97

Earlier quoted context omitted.

The parts of a ship that thrusters are directly attached to experience acceleration first, the other parts that are further out from the thrusters won't accelerate immediately and if the acceleration is too sudden or extreme could be damaged or break off entirely. And to answer your question in the other response, many thrusters have a minimum thrust, and even that minimum may be too much for the parts when deployed.

By definition, as long as thrusters are firing, you are accelerating.

Acceleration is defined as the change in velocity, and velocity is defined as the change in position (w.r.t. some inertial reference frame). There will always be some bending when thrust is applied at one part of a body; nothing is perfectly rigid.

As an extreme example, imagine a stick one lightyear in length: if we ignite a rocket on one end, firing perpendicular to the stick's length, then the other end cannot start moving for at least a year.

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