James Webb Space Telescope

[Nibb31]

If this equipment needs service Nasa better have a manned space program capable of reaching L2. We will see just how effective the unmanned space program will be, I give Webb 5 years befor some major crppling error occurs.

It can't be serviced in space because there are no parts that are accessible to astronauts in EVA suits. There are no hand rails and there are fragile and delicate parts that would either interfere with any EVA activity or might be damaged if they are approached by another spacecraft. When you have something as delicate as JWST, you don't want an Orion thrusting fuel particles all around it.

To be serviceable in space, a satellite needs to be especially designed for it, including lots of extra hardware, extra complexity, and extra safety features that cost money and add mass. Most space probes and observation satellites are not designed for servicing and they work fine. They didn't design Gaia, or DISCOVR, or Curiosity, or New Horizons te be serviceable. There is no reason to believe that JWST is more prone to failure than others.

[r4pt0r]

Question: I was trying to find out how the JWST would compare to hubble.

One source told me the JWST could "see at a resolution of 0.1 arc-seconds, which means that it could resolve a penny 24 miles (40 kilometres) away or a football 340 miles (550 kilometres) away"

another source told me about the hubble "Hubble's so-called angular resolution — or sharpness — is measured as the smallest angle on the sky that it can resolve (i.e. see sharply). This is 1/10 of an arcsecond (one degree is 3600 arcseconds). If Hubble looked at the Earth — from its orbit of approximately 600 km above the earth’s surface — this would in theory correspond to 0.3 metres or 30 cm




So I really dont get what the improvement will be, other than the Webb specializing in infrared(not to belittle that feat).

[Shpaget]

JWST is not intended to be Hubble 2.0. Hubble is primarily UV and visible light telescope, while JW is infrared, with only marginal visible capability (not full visible spectrum). They are different machines, for different purposes.

Also JW has a much larger (around 7 times) primary mirror, providing the ability to collect more light from very faint distant objects.

[UmbralRaptor]

I'd describe JWST as a Spitzer replacement (due to wavelength range) that has Hubble-level costs. This also does amusing things to the difference in mirror sizes.

[kiwi1960]

I'd possibly call it a waste of time... mainly because without the Shuttle, its not going to be easy to service or repair...

 

remember the fiasco with the bad lens in Hubble?

 

[Shpaget]

1 hour ago, kiwi1960 said:

I'd possibly call it a waste of time... mainly because without the Shuttle, its not going to be easy to service or repair.

 

Even if Shuttle was operational, it would not be capable of reaching JWST.

Shuttle was barely able to reach ISS which is 400 km up. JWST will be orbiting the Sun-Earth L2 point, which is about a million and a half km higher.

Yes, servicability of Hubble was a nice feature, but certanly not a requirement for a space mission. After all, how many other space missions you know of that were servicable?

[r4pt0r]

On 8/6/2016 at 11:23 PM, kiwi1960 said:

I'd possibly call it a waste of time... mainly because without the Shuttle, its not going to be easy to service or repair...

 

remember the fiasco with the bad lens in Hubble?

 

concerning yes, but they didnt even include an anchor point to secure it from so it can be worked on in space. They know once it launches, thats it. done. there is no getting to it.

a flaw in my opinion as well, but i suppose real life isnt ksp and a  repaircraft or mission cant be whipped up in a few short minutes on 30k funds.

Edited August 8, 2016 by r4pt0r

[Streetwind]

You make it sound like the JWST team had a choice...

The practical reality is, when the mission plans were drafted in 1996, we (as in the whole of humankind) did not have a spacecraft capable of safely taking humans out into solar orbit and back, nor did we have any sort of precedent or mission architecture for such a mission.

When the mission was approved and construction started, we did not have a suitable spacecraft or mission architecture.

Now that the construction is drawing to a close, we do not have a suitable spacecraft or mission architecture.

When JWST launches in 2018, we will not have a suitable spacecraft or mission architecture.

When JWST's primary mission ends in 2023-2024, then we might have a suitable spacecraft. Maybe. Possibly. If the massive cost overruns or the two US presidency changes before then don't kill the Orion program, and if it avoids being delayed even more than it already is. And if somebody coughs up the > 1 billion dollar cost for an SLS-Orion launch. And then we still wouldn't have a precedent, and the mission would be complete pioneer work. Among the difficulties facing such a mission is the fact that Orion does not have an airlock - its EVA strategy is "evacuate the entire vessel and then refill it from gas flasks once everyone is back inside". They can do this exactly once. So if they need to go back out to do something, it won't work. Unless you send an airlock-equipped habitat along. Do I have to mention that there won't be an airlock-equipped habitat for Orion in existance in 2023...?

 

So yeah. This isn't a case of "The JWST team made a poor decision not to set it up to be servicable". There was never a decision in the first place. It is a case of "JWST is not built to be servicable because it cannot be reached by service missions", as far as the planning teams were concerned. Perhaps things will be different for NASA's next telescope after JWST, since NASA is aiming to have an interplanetary capable spacecraft in service at all times by the time that new telescope is ready for launch. No matter where they put it, it should be reachable.

[kiwi1960]

My point was... and still is, even if you missed it.... that nothing is perfect, NASA launched a flawed telescope named Hubble... had they checked the work, they might have found the flaw... but they didn't... if not for the Shuttle... it would still be imperfect today... and it would be an embarrassment to NASA even now, after all these years...

But the Shuttle saved them... the flaw was forgiven when it was fixed, first via a software upgrade and then a replacement lens (or sub lens I think)...

But now.... we have no Shuttle....

IF the rocket carrying the telescope makes it to orbit....

IF the equipment is perfect...

IF it achieves orbit...

IF it doesn't get damaged by all the junk on its way out....

Then I suppose its worth it.... but if not... there is no Shuttle to save them if the find the faulty in Earth Orbit before it leave Earth... I mean, common sense... once its in orbit they test it... like with all long distance and long term missions... and once it leave... there is no way to get it back or easily fix it (unless its software based... you can just upload)...

So.... given NASA's history of embarrassing boo boos... especially with Hubble.... then this COULD be a gigantic waste of money... 

BUT.... I'm a fan of space... of NASA.... of KSP even.... I hope they make it... but NASA isn't perfect, sadly, unlike the Apollo years, they don't have the money to make it 100% perfect or idiot proof... worse when you consider that they still contract to the cheapest tender... and over the years, that tender process has been streamlined for cost efficiency to such an extent, that nothing is ever 100% idiot proof at NASA.... I draw you attention to one Mars pole lander that had one part made in the USA working out its landing out in feet.... and another, made in Europe, working it out in meters... there is a new crater at the North Pole of Mars now... its all that remains of this probe...

But of course... they do have their successes... those photos of Pluto were stunning....

 

[kurja]

And that's different from every other robotic spacecraft except for hst..? These things generally don't have a regular service program once they're out there you know.

[Wjolcz]

1 hour ago, kiwi1960 said:

Then I suppose its worth it.... but if not... there is no Shuttle to save them if the find the faulty in Earth Orbit before it leave Earth... I mean, common sense... once its in orbit they test it... like with all long distance and long term missions... and once it leave... there is no way to get it back or easily fix it (unless its software based... you can just upload)...

You say this as if the shuttle was the only thing ever launched into space and capable of saving things. It's 21st century. We have robots and AFAIK JWST will be serviceable. It will have a docking port for robotic missions, such as the ones that are developed right now (I think I saw an article about how NASA, or some other agency will be sending a probe to refuel and repair some other satellite, but not sure where).

So yeah, maybe it won't be as quick to get to as something that's in LEO, but it seems they already have a plan B in case something goes wrong.

And on topic: I'm ready to see some sweet pictures of exoplanets in 2018!

[cryogen]

On 4/7/2015 at 1:42 PM, Streetwind said:

JWST is a near infrared telescope. Means it loses the extreme versatility of Hubble (which can image pretty much any wavelength you ask it to... or could, before its instruments started breaking).

That's not really fair; JWST has an enormous wavelength range, even more logarithmic range than Hubble. JWST spans 600 nm - 28.5 μm between two cameras (NIRCam and MIRI), while Hubble's cameras span from 115 nm to 1.7 μm, up to 2.4 μm when NICMOS was still operating. 

https://directory.eoportal.org/web/eoportal/satellite-missions/j/jwst

Edited August 9, 2016 by cryogen

[kiwi1960]

1 hour ago, Veeltch said:

You say this as if the shuttle was the only thing ever launched into space and capable of saving things. It's 21st century. We have robots and AFAIK JWST will be serviceable. It will have a docking port for robotic missions, such as the ones that are developed right now (I think I saw an article about how NASA, or some other agency will be sending a probe to refuel and repair some other satellite, but not sure where).

So yeah, maybe it won't be as quick to get to as something that's in LEO, but it seems they already have a plan B in case something goes wrong.

And on topic: I'm ready to see some sweet pictures of exoplanets in 2018!

No, its not the only thing... but tell me... does NASA have ANYTHING in service now that can reach it? They rely on the Russians to supply and re-crew the I.S.S. ... and a few private resupply ventures...

Truth is.... NASA has nothing anymore for a manned "service" mission... not for the next few years at any rate.

[cubinator]

On 4/8/2015 at 1:52 AM, Streetwind said:

looking a wee bit like an imperial star destroyer

I can see it now...

*unfolding mirror* [Lead engineer] "Commence primary ignition!"

[Shpaget]

8 hours ago, Veeltch said:

You say this as if the shuttle was the only thing ever launched into space and capable of saving things. It's 21st century. We have robots and AFAIK JWST will be serviceable. It will have a docking port for robotic missions, such as the ones that are developed right now (I think I saw an article about how NASA, or some other agency will be sending a probe to refuel and repair some other satellite, but not sure where).

So yeah, maybe it won't be as quick to get to as something that's in LEO, but it seems they already have a plan B in case something goes wrong.

And on topic: I'm ready to see some sweet pictures of exoplanets in 2018!

JWST is not servicable.
http://jwst.nasa.gov/faq_scientists.html#astronauts

http://jwst.nasa.gov/faq.html#serviceable

It could, hypothetically, be serviced by a robotic mission, since the same launch vehicle that will launch the scope (Ariane 5) can launch the service mission too, but there are other problems as well. Controlling the robot would be tricky due to the 10 second delay for signal round trip. Certainly not impossible, and but they are not counting on being able to repair it.

[HebaruSan]

On 4/7/2015 at 1:42 PM, Streetwind said:

JWST, which will go to a lagrange point

Cool! Which one?

[Streetwind]

6 minutes ago, HebaruSan said:

Cool! Which one?

Earth-Sun L2.

 

Edited August 9, 2016 by Streetwind

[Lollipop]

Hey, Why not put programcan do multitask to scan the sky that can directly measure the habitable zone on every cm in the universe? Or they already did ?

 

[Green Baron]

On 6.8.2016 at 2:11 PM, r4pt0r said:

Question: I was trying to find out how the JWST would compare to hubble.

One source told me the JWST could "see at a resolution of 0.1 arc-seconds, which means that it could resolve a penny 24 miles (40 kilometres) away or a football 340 miles (550 kilometres) away"

another source told me about the hubble "Hubble's so-called angular resolution — or sharpness — is measured as the smallest angle on the sky that it can resolve (i.e. see sharply). This is 1/10 of an arcsecond (one degree is 3600 arcseconds). If Hubble looked at the Earth — from its orbit of approximately 600 km above the earth’s surface — this would in theory correspond to 0.3 metres or 30 cm




So I really dont get what the improvement will be, other than the Webb specializing in infrared(not to belittle that feat).

I can't give you all the backgrounds but here a few rules of thumb i met:

The angular resolution is first and foremost simply a function of main mirror/lens diameter. Rule of thumb after Rayleigh for the minimum distance to resolve two different diffraction discs of stars is a["] = 13,8 / Diameter[cm]. A 115mm telescope has ~1.2", JWST's main mirror has a theoretical 0.02" if my calculator is right, so other elements in the JWST construction must limit the resolution.

For photography the pixel size of the camera must correspond with the optics and here comes the focal length into play. a["] = (Pixel Size/Focal Length) * 206.265. An amateur must buy what is offered, so this is the second limiting factor. They should be just small enough to meet the optics resolution but as big as possible to collect as much light as possible.

 

Atmospheric disturbances limit the resolution even more because they cause the diffraction discs to literally jump around. 3rd rule of thumb is that the atmosphere limits seeing conditions to 1" to 3". That's why 120mm is just the perfect amateur telescope diameter if the equipment is adjusted correctly

 

Edited January 11, 2017 by Green Baron

[Streetwind]

8 hours ago, Lollipop said:

Hey, Why not put programcan do multitask to scan the sky that can directly measure the habitable zone on every cm in the universe? Or they already did ?

 

You don't really need to measure the habitable zone - you can calculate it mathematically, just from knowing the basic properties of the star. These properties have already been measured for a huge number of stars, and can easily be re-measured with smaller equipment for individual stars if it becomes necessary. Using JWST for this would be overkill... a bit like using an electron beam microscope to look at microorganisms, where a simple over-the-counter amateur microscope would suffice.

The main thing that makes JWST special is its incredible range, enabled by its huge mirror. It can resolve objects that are so faint and far away that only a handful of photons make it all the way here to us. It likely will be used to look at some known exoplanets, though, just to see if it can resolve their atmospheres.

[Wjolcz]

Direct exoplanet imaging would be amazing. Correct me if I'm wrong, but JWST could be the first ever thing able to determine if there's life on a planet or not.

[Streetwind]

@Veeltch I think I'll have to correct you, then We can already get a good idea of the composition of exoplanet atmospheres from existing instruments. And just because certain elements are present doesn't mean that life is present - it merely makes it more or less likely. Considering that our whole definition of "planet with life on it" is based on a sample size of one makes predictions like this unreliable.

JWST is also not built with instruments designed to hunt for life. It may be able to confirm previously taken spectrums with higher precision, or measure those of an object too far away for other instruments, but there's nothing on it that's specifically able to search for life itself. It's a dedicated astronomy platform, and not of much use for planet hunting, astrography, astrobiology or the like. To quote the official website's statement on one of its four main areas of science: "JWST will tell us more about the atmospheres of extrasolar planets, and perhaps even find the building blocks of life elsewhere in the universe." In other words, it can see and track the materials commonly termend "building blocks of life", and it will most certainly do so, but there's a long way from the presence of water to confirming extraterrestrial life

As far as direct exoplanet imaging goes... I wish! But I'm not sure if it's viable. Keep in mind the quality of images that Hubble managed to take of Pluto. Admittedly, using a lot of work and many different sets of observation data, they were eventually able to refine it into these computer generated images, and JWST is quite a bit more powerful... But then again, Pluto is just some four and a half light-hours away. The closest exoplanet candidate is 4.5 light-years away, nearly 8,800 times the distance. The closest confirmed one is much further still. It's doubtful that any direct imaging would turn up more than a few blurry pixels, if anything at all. Still would be an international sensation, but it wouldn't actually be fun to look at for enthusiasts, and would yield little scientific insight beyond "yep, it's there".

Honestly, a better observation target than an exoplanet would be the purported Planet Nine in our own solar system. If it actually exists and they manage to find it. That would be close enough to get some good pictures, especially with advanced computer aided image processing.

[Green Baron]

Aehm .... no technology we can imagine could make an image of an exoplanet. Even an interferometer the size of earths orbit would not be large enough for an earth size planet at the next star system, not speaking of farther planets. Prove me wrong 'cause i daresay by several magnitudes :-). Also the contrast between a rocky planet and its sun at let's say 10 parsec is far beyond what imaging can do (edit: these days). What probably can be "seen" at that distance is a solar system, infrared from gas giants, we could determine more details about what is known as the "habitable zone"(tm). Which is in the range of a few (like 1-3) AE at 10 pc. That sort of things.

JWST is part of a number of new generation telescopes. I am looking forward to what these instruments can deliver as well, though exoplanets are just a small part in the story.

Yeah, @Streetwind, planet 9 ! I almost forgot about it ...

 

Edited January 11, 2017 by Green Baron

[CSE]

34 minutes ago, Green Baron said:

Even an interferometer the size of earths orbit would not be large enough for an earth size planet at the next star system, not speaking of farther planets. Prove me wrong 'cause i daresay by several magnitudes :-).

I think so; angular resolution should be about 1.22 x 450nm / 2au = 10^-18 radians. With a diffraction-limited instrument, you'd see an Earth-sized target (10⁷m) out to about 10²⁴m or a little under a billion light years. Roughly. You'd get significant details on anything in the Milky way. Basically, you can fit a lot of visible light waves in Earth's orbit's diameter.

As you say, the instrument would probably be held back other limits such as contrast, blurring by intervening dust, infeasibly long exposure times to gather enough light, and so on.

[CSE]

1 hour ago, Streetwind said:

Honestly, a better observation target than an exoplanet would be the purported Planet Nine in our own solar system.

I wonder what it could show of Sedna.