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James Webb telescope reaches its final destination in space, million miles away

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Re: James Webb telescope reaches its final destination in space, million miles away

#341

Post by enave3 »

kzrdude wrote: post #219
enave3 wrote: post #116

Earlier quoted context omitted.

> What was the intended mission? There were several. A couple of examples: the shuttle could delay release of a payload, maneuver while in orbit, release the payload, then maneuver again. So conceptually, you just put a satellite into an orbit and your enemy doesn't know exactly what orbit its in. I'm sure eventually they would find it, but the military still wants stuff like that. Another example is the ability to g…

Isn't the shuttle so big that it would be easy to track and see it?

yes, but no country can track a given object in LEO for its entire orbit (unless it's transmitting its position to another satellite).

So the idea is that the shuttle launches with a secret payload, and every 90 minutes you see it pass overhead. This goes on for days or weeks. Eventually it lands.

What happened? Well what you don't know is that on day 2, while it was over the Pacific and you weren't tracking it, it fired the OMS, deployed a payload, then fired the OMS again to return to it's previous orbit.

There's a whole other satellite out there and you don't know about it until you find it by some other means. And eventually you will find it. But the military is happy to pay for that short window of subterfuge.

Re: James Webb telescope reaches its final destination in space, million miles away

#342

Post by sumedh »

jvanderbot wrote: post #231
arcticfox wrote: post #33

Earlier quoted context omitted.

If it was a SpaceX rocket, it would be getting ready to fly again. Expendable rockets have been putting up payloads for 60 years at this point, SpaceX has been flying reusable rockets for less than a decade.

This is absolutely true but entirely uninformative in this context. It's also a bit hilarious as it reinforces GP's suggestion that you can't involve or invoke SpaceX without a breathless-sounding shower of accolades stealing the show from the main payload / mission.

Because SpaceX made rocket launch interesting by having cameras on the rocket, did Ariane have cameras on their rockets?

Re: James Webb telescope reaches its final destination in space, million miles away

#343

Post by pfdietz »

NikolaeVarius wrote: post #108
pfdietz wrote: post #50

Earlier quoted context omitted.

That's not what I was implying. I'm implying the mass (and volume, and especially servicability) constraints required expensive engineering. Those constraints are relaxed with much cheaper launch, especially if in-space assembly and maintenance (by astronauts!) becomes affordable.

Its nice to be able to design things around Sci-Fi. However, still in 2022, there is no spacecraft that allows EVAs anywhere.

Exactly the same kind of snark could have been uttered about lower cost launch before SpaceX upset the apple cart. It would not require enormous changes for something like Hubble servicing to be done with a Crew Dragon.

Re: James Webb telescope reaches its final destination in space, million miles away

#344

Post by wolverine876 »

pfdietz wrote: post #332
wolverine876 wrote: post #313

Earlier quoted context omitted.

The Nixon bit isn't well known, but thanks for the reference. I've never heard the rest. Is there a source? It's easy to attribute political reasons to whatever Congress does, because Congress is filled with politicians. But members have other motives too, and private businesses, despite the hype, have plenty of corrupt and political motives - throwing contracts to allies and friends, undermining enemies, etc. - thou…

https://arstechnica.com/science/2019/08/rocket-scientist-say... which references https://twitter.com/SciGuySpace/status/1156294287245660160 Quote: > Digging through some old notes. Found this quote from a few years ago from a senior academic engineering source at the time. > "Senator Shelby called NASA and said if he hears one more word about propellant depots he’s going to cancel the space technology program."

The evidence is someone (person A) on Twitter's old notes about a story someone else (person B) told them, about an event involving persons C and D (and potentially others), with no indication of person B actually witnessing it.

Aren't we supposed to start by considering the accuracy of the information?

Re: James Webb telescope reaches its final destination in space, million miles away

#345

Post by pfdietz »

wolverine876 wrote: post #344
pfdietz wrote: post #332

Earlier quoted context omitted.

https://arstechnica.com/science/2019/08/rocket-scientist-say... which references https://twitter.com/SciGuySpace/status/1156294287245660160 Quote: > Digging through some old notes. Found this quote from a few years ago from a senior academic engineering source at the time. > "Senator Shelby called NASA and said if he hears one more word about propellant depots he’s going to cancel the space technology program."

The evidence is someone (person A) on Twitter's old notes about a story someone else (person B) told them, about an event involving persons C and D (and potentially others), with no indication of person B actually witnessing it. Aren't we supposed to start by considering the accuracy of the information?

That person is a very respected space journalist. If you are still dubious, that's a "you" problem, not a "me" problem, and I encourage you to expend your own effort to deal with it.

Re: James Webb telescope reaches its final destination in space, million miles away

#346

Post by Laremere »

snakeboy wrote: post #85
Laremere wrote: post #74

Earlier quoted context omitted.

Destin has also peaked (or very close to it) in importance of person interviewed, as he interviewed Obama during their presidency. Though, sadly not an hour long. https://youtu.be/GpWQHFzrEqc

Just out of curiosity, is it considered best practice these days to use the gender-neutral "their" even with a specific subject (Obama) who is known to use masculine pronouns for himself?

Just noticed this. I'm puzzled why my comment attracted downvotes.

I typically lean towards gender neutral terms in my speech, but this actually wasn't one of those cases. I had originally used "his", but noticed it resulted in he/him/his referring to two different people. "Destin has also peaked [...], as he interviewed Obama during their presidency." vs "Destin has also peaked [...], as he interviewed Obama during his presidency."

Obviously, Obama was president and Destin wasn't, but the sentence still reads more weirdly with the grammatical implication that Destin was president.

Re: James Webb telescope reaches its final destination in space, million miles away

#347

Post by beerandt »

whatshisface wrote: post #325
beerandt wrote: post #311

Earlier quoted context omitted.

That's what army mapping service essentially did with early radar distance measuring projects. Huge expensive fleet of 18-wheeler trucks failure. And classical surveying methods beat it in every way at the time. But it was the direct predecessor to microwave communications. It was just portable military distance measuring equipment (like the model-99 dme w/ ~1cm @50km) that used a signal they found easy to piggyback…

It's difficult to say without access to the counterfactual world where GPS was invented based on civilian microwave communication which itself would have evolved from civilian radio communication. We live in a world where the DoD redistributes money away from private industry and towards another sector of private industry, and it is hard to say what would happen if R&D tax laws were changed to move that money back fr…

Maybe microwave transmission, but the economics of GPS or GNSS in general would preclude civilian investment in such an expensive constellation without obvious revenue channels.

And it's moot for both these cases because the technology was needed for direct military applications anyway.

What's the practical or ideological benefit of industry-industry R&D when the military is going to be the only customer, or at least the only paying customer for the first years/decades of use?

I agree with you in general, with it being better for governments not picking the winners of markets or deciding who gets research money.

But military is such a unique (yet universally needed) type of market, that practicality here means treating them as a large customer with unique product needs ( products unlikely to be revenue generating on the public market), even if you don't treat it as direct government allocation or a fixed/manipulated market.

The only way I can think of to avoid that entirely would be some libertarian version of an all private, defense-by-contract type military.

And then you'd have concerns about whether that could hold up to peer adversaries, and dozens of other wildcard concerns.

Re: James Webb telescope reaches its final destination in space, million miles away

#348

Post by ridgeguy »

jacquesm wrote: post #330
ridgeguy wrote: post #283

Earlier quoted context omitted.

Here's a good paper on the mirror actuators [1]. Skimming, they look like hexapod rotary stepper architecture that would not need power to hold a position, only to change position. [1] https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden....

Steppers make good sense for that application, what a beautiful design. 7 nm step size with a repeat accuracy of 1 nm is insane precision.

It is a beautiful design, isn't it?

I'll speculate that the engineers who designed this and other ground-breaking aspects of JWST feel the same euphoria that Beethoven might have felt on completing his 9th symphony.

I think beauty wears many masks, but she's in every human effort to bring something new into the world.

Re: James Webb telescope reaches its final destination in space, million miles away

#349

Post by _ph_ »

spookthesunset wrote: post #189
_ph_ wrote: post #82

I am quite relieved that all the deployment worked out and so looking forward to the first images. I hope, planning for a true Hubble successor (a telescope in the visual range) starts soon. Maybe a one-off Starship could be the telescope housing, it would enable an 8m mirror without any folding, just the tip of the Starship would open up once in orbit.

Why not go for a much larger folding mirror?

Price, simplicity. 8m mirror size would equal some of the largest telescopes currently on the ground. A lost of cost could be saved, if the whole teslescope could be completely assembled on ground. Later iterations could have larger mirrors, but just having a Hubble replacement with modern cameras would be a huge step, having a 4x larger mirror will be magnificient enough.

Re: James Webb telescope reaches its final destination in space, million miles away

#350

Post by readthenotes1 »

anon_123g987 wrote: post #46
readthenotes1 wrote: post #23

Earlier quoted context omitted.

The human is not to scale if that's the Webb telescope.

A human standing next to a full-size replica: https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F... It looks the same to me.

6.5 m across 5 hexes. The human is maybe 1.25 hexes tall.

About 1.6m or 5'3". That's a dry short adult human.

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