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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

#181

Post by CamperBob2 »

lamontcg wrote: post #175
CamperBob2 wrote: post #165

Earlier quoted context omitted.

Spamming a bunch of hubble-sized instruments up into orbit won't accomplish the same thing. It will, and then some, once we get optical interferometry nailed down. JWST is great, and needed to be done, and I'm glad it's finally getting deployed. But if I had an argument to make against it, it would be, "Let's wait until we know how to do this properly. We're not there yet." That's a weak argument and should almost ne…

> That's a weak argument and should almost never be heeded Well that's an incredibly strong opinion with almost nothing to back it up. Maybe it all goes boom tomorrow on launch or the deployment is ultimately completely FUBAR'd and you can feel satisfied with yourself, but I don't buy that your principle is what we should always follow. Hopefully we start getting data from JWST in a few months and then I invite the s…

True, I don't disagree with any of that, but:

Maybe it all goes boom tomorrow on launch or the deployment is ultimately completely FUBAR'd and you can feel satisfied with yourself

A more charitable interpretation of my post would read something like this: "If it does go boom, we can either start building a new one now and try again in 20 years, or we can wait 15 years and build multiple better, cheaper ones in 5 more. Meanwhile, maybe a few hundred other researchers can get funded with the same money."

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

#182

Post by CamperBob2 »

aargh_aargh wrote: post #170
CamperBob2 wrote: post #165

Earlier quoted context omitted.

Spamming a bunch of hubble-sized instruments up into orbit won't accomplish the same thing. It will, and then some, once we get optical interferometry nailed down. JWST is great, and needed to be done, and I'm glad it's finally getting deployed. But if I had an argument to make against it, it would be, "Let's wait until we know how to do this properly. We're not there yet." That's a weak argument and should almost ne…

The reason we can't achieve the same resolution as JWST with interferometry has been mentioned in a recent startalk podcast. The distance between the telescopes would have to be coordinated to a precision somewhere on the order of nanometers.

The distance between the telescopes would have to be coordinated to a precision somewhere on the order of nanometers.

That'll happen. It's fundamentally a timing problem, and we can already build clocks that will tell you what floor of the building they're on.

Less hand-wavingly, it's fundamentally a data-acquisition and correlation problem of the sort that was solved long ago for microwave VLBI. Back in the day, the individual stations had their own maser clocks, but now I imagine they're all GNSS-based. It is by no means trivial to go from RF interferometry to optical, or to move the antenna elements from earth to space, but that's the basic approach that will ultimately be used.

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

#183

Post by captn3m0 »

azalemeth wrote: post #155
onphonenow wrote: post #151

Earlier quoted context omitted.

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

I'd bet that the vast majority of that cost isn't going to be materials -- it'll be staff time to design and optimise the telescope and make something that can work, including where necessary how to make new materials or processes to make that telescope. I'm not saying the actual hardware is cheap by any stretch of the imagination, but making three different telescopes isn't a linear function of that budget. They're…

The seemingly costly part of JWST - The Gold Mirrors are cheaper than one might guess, for eg. it’s a 0.1 micron coating that only used 45g of gold.

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

#185

Post by picture »

captn3m0 wrote: post #183
azalemeth wrote: post #155

Earlier quoted context omitted.

I'd bet that the vast majority of that cost isn't going to be materials -- it'll be staff time to design and optimise the telescope and make something that can work, including where necessary how to make new materials or processes to make that telescope. I'm not saying the actual hardware is cheap by any stretch of the imagination, but making three different telescopes isn't a linear function of that budget. They're…

The seemingly costly part of JWST - The Gold Mirrors are cheaper than one might guess, for eg. it’s a 0.1 micron coating that only used 45g of gold.

The material cost for a lot of "high technology" things can be very small, but the process is expensive. For example fancy chips are only some x grams of silicon, and expensive inverted mesa quartz crystals might cost a good bit while only being x microns thick piece of quartz..

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

#186

Post by pkaye »

onphonenow wrote: post #151
wslack wrote: post #82

Earlier quoted context omitted.

I suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

To make an infrared telescope significantly better they need it in an orbit not facing the sun always. But other types of lower cost projects might be feasible.

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

#188

Post by petschge »

lamontcg wrote: post #174
petschge wrote: post #171

Earlier quoted context omitted.

The reason why we are barely getting started into VLBI in the IR on the ground (and nothing that I have heard of yet in space) is that the different apertures need to be stable relative to each other with a precision better than a small fraction of a wavelength. (One tenth, one twelves and one twenties are often used, depending basically on which performance drop relative to the theoretical optimum you are willing to…

That's kinda what I guessed. So on the ground you can measure the distance between two observatories that are a few hundred meters apart with incredibly high precision and track that over time as the ground under them slowly deforms and moves.

Geodesy is indeed one of the side products of VLBI observations on Earth.
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