First 12 mirrors installed in James Webb telescope

[Borgholio]

http://www.nasa.gov/feature/goddard/201 ... pe-mirrors

One dozen flight mirrors are now installed on NASA's James Webb Space Telescope, out of the eighteen mirror segments that make up the primary mirror. The assembly of the primary mirror is an important milestone for the Webb telescope, but is just one component of this huge and complex observatory.

Since December 2015, the team of scientists and engineers have been working tirelessly to install all the primary mirror segments onto the telescope structure in the large clean room at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The twelfth mirror was installed on January 2, 2016.

"This milestone signifies that all of the hexagonal shaped mirrors on the fixed central section of the telescope structure are installed and only the 3 mirrors on each wing are left for installation," said Lee Feinberg, NASA's Optical Telescope Element Manager at NASA Goddard. "The incredibly skilled and dedicated team assembling the telescope continues to find ways to do things faster and more efficiently."

Each hexagonal-shaped segment measures just over 4.2 feet (1.3 meters) across and weighs approximately 88 pounds (40 kilograms). After being pieced together, the 18 primary mirror segments will work together as one large 21.3-foot (6.5-meter) mirror. The primary mirror will unfold and adjust to shape after launch. The mirrors are made of ultra-lightweight beryllium. The mirrors are placed on the telescope's backplane using a robotic arm, guided by engineers. The full installation is expected to be completed in a few months.

The mirrors were built by Ball Aerospace & Technologies Corp., Boulder, Colorado. Ball is the principal subcontractor to Northrop Grumman for the optical technology and lightweight mirror system. The installation of the mirrors onto the telescope structure is performed by Harris Corporation of Rochester, New York. Harris Corporation leads integration and testing for the telescope.

While the mirror assembly is a very significant milestone, there are many more steps involved in assembling the Webb telescope. The primary mirror and the tennis-court-sized sunshield are the largest and most visible components of the Webb telescope. However, there are four smaller components that are less visible, yet critical. The instruments that will fly aboard Webb - cameras and spectrographs with detectors able to record extremely faint signals — are part of the Integrated Science Instrument Module (ISIM), which is currently undergoing its final cryogenic vacuum test and will be integrated with the mirror later this year.

The Near InfraRed Spectrograph (NIRSpec) has programmable microshutters which enable observation up to 100 objects simultaneously. The Near Infrared Camera (NIRCam) is equipped with coronagraphs, instruments that allow astronomers to take pictures of very faint objects around a central bright object, like stellar systems.

The Webb telescope also has a cryocooler for cooling the Mid-Infrared Instrument (MIRI) to a very cold 7 Kelvin so they can work. MIRI has both a camera and a spectrograph that sees light in the mid-infrared region of the electromagnetic spectrum, with wavelengths that are longer than our eyes see. There's also the Fine Guidance Sensor (FGS) allows Webb to point precisely, so that it can obtain high-quality images.

Over the next two years in preparation for launch, various components of the Webb telescope will endure rigorous environmental and optical testing. The sunshield will be joined with the spacecraft bus (main structure) followed by more testing. The Webb telescope is planned for launch in 2018.

The James Webb Space Telescope is the scientific successor to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb is an international project led by NASA with its partners, the European Space Agency and the Canadian Space Agency.

For more information about NASA's Webb telescope and all of its components, visit: www.nasa.gov/webb or jwst.nasa.gov

For more information about the mirror installation, visit: http://www.nasa.gov/press-release/nasa- ... stallation

Jesus, this thing is going to be huge.

[Zeropoint]

I'm really looking forward to seeing what this telescope can show us. The data coming back from Hubble has been awesome in both the new AND old senses of the word, and its mirror is so much smaller than Webb's.

Hmm, Wikipedia says that the Webb telescope is mainly infrared, only seeing up to orange. That could reduce the emotional impact of the pictures on the average layperson a bit, maybe.

[Napoleon the Clown]

I'm really looking forward to seeing what this telescope can show us. The data coming back from Hubble has been awesome in both the new AND old senses of the word, and its mirror is so much smaller than Webb's.

Hmm, Wikipedia says that the Webb telescope is mainly infrared, only seeing up to orange. That could reduce the emotional impact of the pictures on the average layperson a bit, maybe.

Most astronomy pictures are false color, anyway. And we can see more things in infrared than in visible spectrum, anyway. James Webb will send back some pretty damned impressive images.

[Borgholio]

IIRC going infrared is the only way to peer into the core of the galaxy, due to the sheer amount of dust and gas in that region.

[Sea Skimmer]

The images from Webb should be staggering. We should be able to see through the Milky Way for the first time ever, and while using a lens with something like eight times the effective aperture of Hubble.

Coverage is .6 to 28 micron wavelengths using four different imagers. Hubble covered .1 to 2.5 microns, but its main imager was visual and UV in the .1 to .8 micron range. Many of its 'visual' images released to the public make heavy use of the UV portion of its coverage and sometimes the near IR capability which was fairly weak. Near IR wavelengths behaves a lot differently then higher bands of IR, its not nearly as penetrating and generally a product of reflected energy rather then heat emissions. So its value for seeing through dust and gas in space is very low.

Human vision covers about .38 to .78 microns, but not with equal sensitivity, person to person sensitivity at the ends can vary radically from 'not seen' to those women whom functionally see an extra color compared to normal RGB vision. Most of the energy sensed is .4 to .7 range.

Hubble was great for being a modified spy satellite but its NRO origins meant it was never the ideal system for deep space coverage, nor was its orbit ideal. But it was something NASA could afford, and put on the shuttle. Webb shows what an ideal clean sheet design on a better booster (out to the L2 point) costs, near nine billion dollars and so in the process much money its endangered every other NASA research mission, but its utterly worth that and even a much higher price. Because its impossible to do this mission from the ground. We can now more or less match visual and UV Hubble from the ground already, some telescopes under construction should be much better on very clear nights, and at far less cost then any useful orbital telescope. That's also meant people with much lower resource scales then the US government can and have been building such devices, which is good since it makes it all the more reasonable for NASA to just drain the bank into one satellite. Now we just have to hope it doesn't fail on launch.

Crappy thing is the satellite has to be helium cooled to make this all worthwhile, and once the onboard helium supply runs out it simply won't work. It won't be able to linger on and on like hubble has. And we can't put it in a low orbit where it could be serviced in a reasonable fashion because the heat load from the earth would be too high, defeating the point of the cryocooling.

[Guardsman Bass]

Now we just have to hope it doesn't fail on launch.

That's what I'm worried about, although I'm sure they'll take a ton of precautions with this. I've always thought they should build two or three of these things at a time, in case one of them is lost when the rocket blows up on the launch pad.

Speaking of the cryo-cooling, if between now and 2028 they decide to change the focus of NASA's crewed space program back to the Moon (presumably as part of some international moon base effort), could they put an infrared telescope on the far side of the Moon and cool it by dumping heat into the lunar regolith/bedrock?

[Borgholio]

Speaking of the cryo-cooling, if between now and 2028 they decide to change the focus of NASA's crewed space program back to the Moon (presumably as part of some international moon base effort), could they put an infrared telescope on the far side of the Moon and cool it by dumping heat into the lunar regolith/bedrock?

While it's not as cold as cryo-cooling, the dark side of the moon can reach as low as 240 below zero. That ought to be enough itself to keep the telescope cool without having to create a heat exchanger with the lunar bedrock.

[Sea Skimmer]

Two or three of them would cost rather very unrealistically more money, and while they'd safeguard against launch failure they'd do nothing for the risks of an undetected flaw in the spacecraft itself if they were built together. So that's just not an effective use of resources. If it blows up, we'll just have to build another one and wait another decade for results. Even if the money existed to build several it'd be better to spend that on other forms of orbital sensor, mainly bigger space based radio telescopes. That way we gamble on all of them working and getting maximum diversity of data. Probability strongly favors all work, so that's the approach to take.

An IR telescope on the dark side of the moon would certainly work well, but the rock itself wouldn't be a useful heat sink. While the moon is very cold the surface temperature even on the dark side is still far higher then deep space. Google suggest about -243F while deep space is more like -450F. Webb intends to operate at -370F. Big difference in these terms. Though it will do so while exposed to direct sunlight, using a shroud and some very fancy insulation.

The moon conducts some solar heat, and it has earthquakes which generate some internal heat, that's why even the dark side is warmer then deep space. The earthquakes also mean wobble, and with telescopes like this designed for absurdly long range viewing that's undesirable. The L2 point is a nice stable place for the spacecraft to park.

Overall issue is not really dissipating large amounts of heat such that a large heat sink is required, the issue is one of absolute temperature reduction. Helium radiating (or better yet evaporating) to deep space is nearly the best possible way to get low temperatures, going any lower tends to turn into lab experimental stuff like laser cooling. The problem is since helium is the smallest atom, which is also why its the best coolant, it will leak out of tanks and pipework made out of any material, which means a finite lifespan before too much leaks out to continue to function. Webb is being designed on the basis of a five year mission, but its possible it will leak less then expected and last longer, as long as 10 years. It is however also possible that other systems will fail before the helium supply is depleted.

It'd probably be much easier to design a way to resupply Webb at the L2 point then land the parts for Webb on the Moon and make it work on that surface. But given how bleeding edge is technology is, its probably not worth trying to engineer the spacecraft to have an exceptionally long life. It already cost billions more to design then intended! Keep in mind this sucker has a bunch of moving parts on it. So did Hubble, but not as much so, and even with the servicing missions Hubble just had some luck involved. IIRC it was intended for a four year mission.

Some, even many spacecraft are actually very likely to exceed the 'design' mission lifespan, as this is in part simply a budget planning issue for NASA, you do have to pay money to operate these spacecraft and the required ground stations, but like most things some spacecraft are also simply much more complex and demanding then others. Webb is just far up the scale. On the other hand some communications satellites have lasted decades and only failed from falling out of orbit.

[Sea Skimmer]

So apparently the brains of the world have in fact reached the point of a proposal being formulated for a true Hubble visual-near IR replacement as of mid 2015, and somehow I am not surprised that it has to be stupid huge to be useful. 12 meter lens! And a starting cost estimate of 10 billion dollars. Webb is only 500% over its original budget estimate....

High Definition Space Telescope. Its pretty silly but apparently if we build this big we'd be able to get decent resolution of exoplanets at 100 light years. Desired parking location is also at the L2 point.



Not holding my breath for this happening. Not because I think such a thing never will but because one of the several reasons why there was no quick interest in a Hubble replacement was that the relevant tech world was and is kind of waiting for some other technology concepts, such as folding mirrior, to be proven or disproven in other roles (spy satellites). If that tech works out it could be a path to building completely massive telescopes at far lower costs. For an idea of the size this might allow, think that image above x4, rounded off.

The below image is far too large to inline, but it shows a lot of the new and upcoming ground based optical telescopes in comparison and gives a good idea just why they can think about matching Hubble from the ground.
https://upload.wikimedia.org/wikipedia/ ... rs.svg.png

[Borgholio]

Not holding my breath for this happening.

Nor I but it would be stupidly exciting to get an image of an extra-solar planet...and see the glint of their orbital mirror looking back at us.

[Sea Skimmer]

Well if anyone is that advanced 100 light years away we should probably get some radio traffic from them shortly! My understanding is radio/radar signals at levels we now can generate should propagate at least 200ly before they would be drown out by the background noise.

Though that limitation has some still debated assumptions in it IIRC, if not ones likely to radically change the value, and also might be usefully extended by vastly more powerful transmitters then anything now imagined, such building a phased array of phased arrays of gigawatt class transmitters across the entire solar system and aiming them (with lead computation) at specific planets of other solar systems. Put that in the 5 trillion dollar idea bank. Blowing up the sun also might get us noticed.

[Borgholio]

Well if anyone is that advanced 100 light years away we should probably get some radio traffic from them shortly! My understanding is radio/radar signals at levels we now can generate should propagate at least 200ly before they would be drown out by the background noise.

I think it was Seth Shostak who said our odds of finding life go up a few percent every year and have been doing so since the 50's as our instruments become more sensitive. Given how things are going, I wonder if our first glimpse of alien life will be through an optical telescope or a probe to the outer planets instead of radio?

[Jub]

I wonder if the James Webb could be refueled by unmanned probes. I mean, I doubt that capability was designed into it, but NASA has pulled crazy life extension missions from their brilliant minds before.

[Sea Skimmer]

The total radiated energy of all the lights we have glowing on the earth is a lot higher then the energy of our radio broadcasts, so that idea might have some merit, but we have no ability to focus that kind of energy either so I am doubtful that it would provide more effective range. Indeed long term the effective brightness of the earth may actually be reduced as we improve the quality of our street lighting designs and energy use in general.

The advantage of radio is we can focus it for transmitting with advanced antenna design, if we feel like it, and this would also by nature be in a manner which can be rapidly steered (so you can ping many planets over and over again, one at a time), and building giant receivers for it spread over large distances are much cheaper and more reasonable to build, operate and signal process then truly colossal optical anything. By example we already have a integrated radio telescope arrays spanning most of the US, Canada and part of South America. The USAF also has a radar that spans the entire US with seven different stations. They only work for certain things, but they exist, and many forms of radio emission are not functionally affected by the atmosphere so they have no advantage of being in space except lower noise pollution from earth based transmitters. That's the main reason to want to put them into solar orbit, which IIRC one already is. Though it depends on the exact type. Such wide area coordination with optical detection is way harder.

Optical detection would probably work best if we constantly set off clusters of nuclear bombs in deep space. We might even be able to devise a way to make a nuclear shaped charge with an enhanced flash effect directed at other solar systems. But I'm not too sure this would actually be useful compared to other uses of such a level of resources. One thing about radio is alien transmitters, and receivers are largely omnidirectional (unless built otherwise on purpose) which simply makes it more likely for a signal-receiver combination to actually occur. Brute force of more equipment can overcome this on both ends, but that's a question of resources, economics ect... with finite funding radio is more likely then optical. Doesn't mean it will be first.

A probe is unlikely to result in detection of alien life, unless it actually reaches another solar system, for a basic reason of signal processing. Space is huge, and a probe is only going to have so much processing power and memory to work with, and its antenna or lens or what have you, isn't going to be that big either. So merely going to the outer solar system is unlikely to be much advantage at all compared to better equipped facilities closer to earth, with a down link to huge earth based computers. The smaller your sensor the less data you'll collect, and the more processing you'll need to extract useful information from said data. Very simple, very annoying. But that's why we are going huge for telescopes now that its technologically possible to build them at all.

We'd certainly gain some real advantage from placing large telescopes in the outer solar system, though perhaps not a vast one. It would depend on for example how much closer to -450F this could let Webb get. Honestly I think that kind of mission will happen long before we have say, a manned Mars base. Unmanned Mars base is a different story.

[Borgholio]

Optical detection would probably work best if we constantly set off clusters of nuclear bombs in deep space.

That would use lots of nukes...a high power laser might indeed be more efficient in the long run.

A probe is unlikely to result in detection of alien life, unless it actually reaches another solar system,

Actually I was referring to the detection of life on one of the moons in the outer solar system, such as Europa. Won't be a technological civilization but it would still technically be alien life.

[Sea Skimmer]

I wonder if the James Webb could be refueled by unmanned probes. I mean, I doubt that capability was designed into it, but NASA has pulled crazy life extension missions from their brilliant minds before.

I've tried to find out if they left provisions for that or not in the past, and again for twenty minutes now, with no clear answer, which almost certainly means no, and it was definitely not intended to be astronaut serviceable.

Right now we could probably think about doing an unmanned mission, but when Webb started being designed in the 1990s an unmanned service mission wasn't too plausible, and no manned means existed or was projected that would be able to reach it. A pity since all you'd need is a fill port once docked, but in the absence of a realistic planned and funded service mission it'd be dumb to leave an accessible fill port on it, because a valve would lead to increase the leakage rate over a more robust form of sealing it up.

Also since they originally didn't think the damn thing would be so expensive, less incentive out of hand to allow the life to be extended. Ironic problem, but of course once costs inflated the last thing anyone would want to do is add new features like a docking capability that would yet further increase costs.

[Sea Skimmer]

Actually I was referring to the detection of life on one of the moons in the outer solar system, such as Europa. Won't be a technological civilization but it would still technically be alien life.

Ah, well with us talking about radios and what not I made false assumptions. Though then another fun question comes up, if we find life in the outer system, and it turns out it's bacteria blasted into space from the earth by a comet impact a half billion years ago, does it still count as alien?

As far as lasers go they could be very useful but I'm not sure what our dispersion is going to end up being at that kind of distance. And it would be a very narrow band signal, which has its pluses, but I kinda like the nukes because it's not just bright but broadband at the same time. Some of that will really depend on how laser technology actually pans out. Obviously we can always build large arrays of multiple lasers, but we may never be able to build any one laser of all that high a power without using chemical fuels. And if we use chemical fuel this sort of application is going to guzzle it down. Its really unclear how far electrically powered lasers can go.

[Borgholio]

Actually I was referring to the detection of life on one of the moons in the outer solar system, such as Europa. Won't be a technological civilization but it would still technically be alien life.

Ah, well with us talking about radios and what not I made assumptions. Though then another fun question comes up, if we find life in the outer system, and it turns out it's bacteria blasted into space from the earth by a comet impact a half billion years ago, does it still count as alien?

That's an interesting question...I guess it depends on how far back you have to go to consider something alien. If the bacteria blasted off the Earth evolved into something different over the last half billion years, then while the original bacteria are clearly not alien, their descendants are since they technically evolved on another world. But then again, I'm sure some people might want to go one step backwards and say that it's not alien unless the DNA of the creature has no link whatsoever to anything on another world, past or present.

[Jub]

I've tried to find out if they left provisions for that or not in the past, and again for twenty minutes now, with no clear answer, which almost certainly means no, and it was definitely not intended to be astronaut serviceable.

Right now we could probably think about doing an unmanned mission, but when Webb started being designed in the 1990s an unmanned service mission wasn't too plausible, and no manned means existed or was projected that would be able to reach it. A pity since all you'd need is a fill port once docked, but in the absence of a realistic planned and funded service mission it'd be dumb to leave an accessible fill port on it, because a valve would lead to increase the leakage rate over a more robust form of sealing it up.

Also since they originally didn't think the damn thing would be so expensive, less incentive out of hand to allow the life to be extended. Ironic problem, but of course once costs inflated the last thing anyone would want to do is add new features like a docking capability that would yet further increase costs.

I wonder if a probe could be designed to dock with the telescope after the tank has been drained, drill a hole into the side of the tank, run a hose over the hole, and allow continued operations from a new tank brought over by the probe. Once that new tank is done the old probe could undock, and float away leaving a refueling port.

Such an operation would be expensive, but far less so than losing a billion dollar telescope.

[Sea Skimmer]

I'm sure you could in fact design a probe to do that. The only really big sticking point would be avoiding FOD inside the tank, or pipe, and I'm sure that could be dealt with somehow. I am FAR less confident you could do so for less then several billion dollars of R&D and launch costs. Higher if we needed to do in orbit testing of the required precision maneuvering system, though the USAF has funded some of that in the last decade for TOTALLY NOT ASAT purposes. But also using very very small satellites.

The actual cost to build and orbit the final Webb satellite though appears to be in the 2-2.5 billion dollar range, with everything else being to get to that point including full scale prototyping and what not, so such a price might might still be justified, but only if it actually led to getting another 5-10 years out of the satellite. That's a big gamble given all the moving parts and possibility of such a risky service mission failing at its own high cost. Its just not going to happen on our present space technology basis. We have too many new things to do yet.

[Jub]

I'm sure you could in fact design a probe to do that. The only really big sticking point would be avoiding FOD inside the tank, or pipe, and I'm sure that could be dealt with somehow. I am FAR less confident you could do so for less then several billion dollars of R&D and launch costs. Higher if we needed to do in orbit testing of the required precision maneuvering system, though the USAF has funded some of that in the last decade for TOTALLY NOT ASAT purposes. But also using very very small satellites.

The actual cost to build and orbit the final Webb satellite though appears to be in the 2-2.5 billion dollar range, with everything else being to get to that point including full scale prototyping and what not, so such a price might might still be justified, but only if it actually led to getting another 5-10 years out of the satellite. That's a big gamble given all the moving parts and possibility of such a risky service mission failing at its own high cost. Its just not going to happen on our present space technology basis. We have too many new things to do yet.

That's pretty much what I had guessed. Fessible, but unlikely unless NASA suddenly starts getting Apollo level funding again.

[jwl]

Speaking of the cryo-cooling, if between now and 2028 they decide to change the focus of NASA's crewed space program back to the Moon (presumably as part of some international moon base effort), could they put an infrared telescope on the far side of the Moon and cool it by dumping heat into the lunar regolith/bedrock?

While it's not as cold as cryo-cooling, the dark side of the moon can reach as low as 240 below zero. That ought to be enough itself to keep the telescope cool without having to create a heat exchanger with the lunar bedrock.

The dark side of the moon will soon become the light side of the moon during daytime, so that's not going to work if it needs constant cooling. You might be able to keep it constantly cooled by putting it in a crater which never sees sunlight, but in doing so you'll block out most of the stars that the telescope is supposed to be looking at.