APOD: JWST: Mirrors and Masked Men (2010 Mar 12)

[APOD Robot]

JWST: Mirrors and Masked Men

Explanation: Who are these masked men? Technicians from Ball Aerospace and NASA at Marshall Space Flight Center's X-ray and Cryogenic Facility, of course, testing primary mirror segments of the James Webb Space Telescope (JWST). Scheduled for launch in 2014, JWST will be optimized for the infrared exploration of the early Universe, utilizing a primary mirror 21.3 feet across, composed of 18 hexagonal segments. Here, a group of JWST mirror segments are being prepared for tests to assure they meet the exacting mission requirements. The technicians' suits and masks help prevent contamination of the mirror surfaces. At the Marshall X-ray and Cryogenic Facility, the mirrors are tested in the large circular chamber after evacuating the air and cooling the chamber to -400 degrees Fahrenheit (only 60 degrees above absolute zero). The extremely low pressure and temperature simulate the JWST mirror operating environment in space. JWST mirror segment testing will continue for the next 18 months.

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[orin stepanek]

The one mirror looks curled on top. I take it that that is what it is reflecting! It makes a good optical illusion though.

[RJN]

Caption contest: "After disposing of Willy Wonka, the Oompa-Loompas began to take on more ambitious projects."

[DaveBone]

Caption Contest - Today NASA announced progress on the Death Ray. Skywalker and Company claim announcement is fraudulent.

[Redbone]

It appears that we are actually learning from experience? I hope so. It is awfully embarassing to spend so much money on sending a big telescope into space and then finding out that the mirror cannot focus correctly, requiring more expensive missions to jury rig it enought to work.

Seeing that we are taking the time to extensively test this one is encouraging. It doesn't completely eliminate the possibility of making a mistake, but it does reduce the risk. Of course there is always a certain amount of risk on such a complex project, but I do hope that it succeeds as planned. If we average 20 years between telescopes, none of us are going to live long enough to appreciate more than a couple of them.

So, who wants to bet that if the Webb is successful that it will see farther than the Hubble by several billion years?

[Chris Peterson]

It appears that we are actually learning from experience? I hope so. It is awfully embarassing to spend so much money on sending a big telescope into space and then finding out that the mirror cannot focus correctly, requiring more expensive missions to jury rig it enought to work.

Curiously, the original figuring error with the HST turned out to be serendipitous. The value of the optical and image processing technology developed as a response is far greater than the cost of actually correcting the flaw. Funny how these things happen sometimes.

[Clinker]

Does the mirror on the bottom left have a bad coating job or is that an artifact of the photo?

Clinker

[Chris Peterson]

Does the mirror on the bottom left have a bad coating job or is that an artifact of the photo?

Probably neither. The surface of the mirror seems to be scattering a light source that is off-axis (maybe the photographer's flash). Even the smoothest mirrors with the best coatings look awful when you directly illuminate them. The visual impression is of a bad coating, but these mirrors work with near perfection, despite appearances.

[Amir]

So, who wants to bet that if the Webb is successful that it will see farther than the Hubble by several billion years?

i'll bet, but you may wanna reconsider!
Hubble has already made it to almost boundaries of the universe & JWST is believed to be able to observe objects from just 100 million years after the Big Bang.
so it could be several million years but at several billion years further, there is nothing to see!

[bystander]

Caption Contest - Today NASA announced progress on the Death Ray. Skywalker and Company claim announcement is fraudulent.

I had posted an article yesterday that was along those lines:

http://asterisk.apod.com/vie ... 74#p117374

[Redbone]

So, who wants to bet that if the Webb is successful that it will see farther than the Hubble by several billion years?

i'll bet, but you may wanna reconsider!
Hubble has already made it to almost boundaries of the universe & JWST is believed to be able to observe objects from just 100 million years after the Big Bang.
so it could be several million years but at several billion years further, there is nothing to see!

It's a bet, several billion. That's locking down the current estimate at ~14 billion, the Webb will push it closer to 20.

[biddie67]

Is it just an effect of the mirrows that the technicians' suits are so loose and bulky? If not, are they a one-size-fits-all? Are they recycled and cleaned up for reuse or are they disposed after one use?

[neufer]

Caption contest: Honey, I shrunk the kids.

[bystander]

So, who wants to bet that if the Webb is successful that it will see farther than the Hubble by several billion years?

i'll bet, but you may wanna reconsider!
Hubble has already made it to almost boundaries of the universe & JWST is believed to be able to observe objects from just 100 million years after the Big Bang.
so it could be several million years but at several billion years further, there is nothing to see!

It's a bet, several billion. That's locking down the current estimate at ~14 billion, the Webb will push it closer to 20.

You both may want to reconsider: years, millions of years, or even billions of years are not measures of distance, but measures of time. Now, if you wanted to talk light years, you might have something to talk about, but you would have to settle on a distance scale first. While the age of the universe is estimated at 13.7 billion years, the radius of the observable universe (the furthest we can possibly see) is estimated at 46.5 billion light years.

The deepest images taken by Hubble are estimated to be at a time when the universe was just 600 million years old. How far away is that? I don't know, but it is doubtful that the JWST can see much more than 300 million years further back into time than the HST.

[Amir]

yes, you are right.
the radius of the observable universe didn't came to my mind!! i'm still right though, nothing more then several million (light!) years. but we can wait until 2014 to see what happens!!

how the universe became so big in just 13.7 Billion years?
& what's the reason they can't observe the whole observable universe? our telescopes are not big enough?

[bystander]

I'm sure somebody will correct me if I'm wrong.

The CMBR is a relic of first light, that point in time (recombination) when photons became free to travel unimpeded, about 380,000 yrs after the BB. Certainly we can not see any further back in time than that. The size of the observable universe is based on the assumption that photons have had enough time to reach us (13.7 billion years, the age of the universe). However, before reionization, the universe was considered to be opaque. It is doubtful that any telescope dependent upon light (emr) can see back before this time.

[bystander]

6 Fun Facts about the James Webb Space Telescope
Scientific American - 2010 March 12
Slide Show: 6 Fun Facts about the JWST

[neufer]

Hubble has already made it to almost boundaries of the universe & JWST is believed to be able to observe objects from just 100 million years after the Big Bang.

The deepest images taken by Hubble are estimated to be at a time when the universe was just 600 million years old. How far away is that? I don't know, but it is doubtful that the JWST can see much more than 300 million years further back into time than the HST.

# LOS comoving distance: The distance between two points measured along a path defined at the present cosmological time.

# Lookback time: This is how long ago light left an object of given redshift.

• 600 million years old = z ~ 7 [HST]
  300 million years old = z ~ 12 [JWST]
  100 million years old = z ~ 25 [JWST?]

<<Currently, the objects with the highest known redshifts are galaxies and the objects producing gamma ray bursts. The most reliable redshifts are from spectroscopic data, and the highest confirmed spectroscopic redshift of a galaxy is that of IOK-1, at a redshift z = 6.96. Slightly less reliable are Lyman-break redshifts, the highest of which is the lensed galaxy A1689-zD1 at a redshift z = 7.6 and the next highest being z = 7.0 while as-yet unconfirmed reports by Ellis R. et al. from a gravitational lens observed in a distant galaxy cluster may indicate a galaxy with a redshift of z = 10.1 [corresponding to just 370 million years after the Big Bang].

The most distant observed gamma ray burst was GRB 090423, which had a redshift of 8.2.

The most distant known quasar, CFHQS J2329-0301, is at z = 6.43. The highest known redshift radio galaxy (TN J0924-2201) is at a redshift z = 5.2 and the highest known redshift molecular material is the detection of emission from the CO molecule from the quasar SDSS J1148+5251 at z = 6.42.

Extremely red objects (EROs) are astronomical sources of radiation that radiate energy in the red and near infrared part of the electromagnetic spectrum. These may be starburst galaxies that have a high redshift accompanied by reddening from intervening dust, or they could be highly redshifted elliptical galaxies with an older (and therefore redder) stellar population. Objects that are even redder than EROs are termed hyper extremely red objects (HEROs).

The Cosmic Microwave Background has a redshift of more than 1,000, corresponding to an age of approximately 379,000 years after the Big Bang.>>

<<In astronomy, Himiko is a large [Lyman-alpha blob] found at red-shift z=6.6 that predates similar Lyman-alpha blobs.
Researchers say it "may represent the most massive object ever discovered in the early universe.">>

• z ~ 7 Lyman-alpha UV => 1.0 µm (infrared)
  z ~ 12 Lyman-alpha UV => 1.6 µm (infrared)
  z ~ 25 Lyman-alpha UV => 3.2 µm (infrared)
  ..........................................................
  Hubble NICMOS: 0.8 to 2.4 µm (infrared)
  Webb Telescope: 0.6 to 28 µm (infrared)

[neufer]

<<The JWST's primary scientific mission has four main components: to search for light from the first stars and galaxies which formed in the Universe after the Big Bang, to study the formation and evolution of galaxies, to understand the formation of stars and planetary systems, and to study planetary systems and the origins of life. All of these jobs are more effectively done in the near-infrared than the visible. Due to a combination of redshift, dust obscuration, and the intrinsically low temperatures of many of the sources to be studied, the JWST must operate at infrared wavelengths, spanning the wavelength range from 0.6 to 28 micrometres. In order to ensure that the observations are not hampered by infrared emission from the telescope and instruments themselves, the entire observatory must be cold. It must be well-shielded from the Sun so that it can radiatively cool to roughly 40 K (−230 °C, −390 °F). To this end, JWST will incorporate a large metalized fan-fold sunshield, which will unfurl to block infrared radiation from the Sun, Earth and Moon. The telescope's location at the Sun-Earth L2 Lagrange point ensures that the Earth and Sun occupy roughly the same relative position in the telescope's view, and thus make the operation of this shield possible.>>

<<On the side of the Earth away from the Sun, the orbital period of an object would normally be greater than that of the Earth. The extra pull of the Earth's gravity decreases the orbital period of the object, and at the L2 point that orbital period becomes equal to the Earth's.

The Sun–Earth L2 is a good spot for space-based observatories. Because an object around L2 will maintain the same orientation with respect to the Sun and Earth, shielding and calibration are much simpler. It is, however, slightly beyond the reach of Earth's umbra, so solar radiation is not completely blocked. The Wilkinson Microwave Anisotropy Probe, Herschel Space Observatory and Planck space observatory are already in orbit around the Sun–Earth L2. The Gaia probe and James Webb Space Telescope will be placed at the Sun–Earth L2.

Although the L2 is nominally unstable along the radial line of the bodies, it turns out that it is possible to find stable periodic orbits around these points, at least in the restricted three-body problem. Quasi-periodic (i.e. bounded but not precisely repeating) orbits following Lissajous curve trajectories do exist. These quasi-periodic Lissajous orbits are what most of Lagrangian point missions to date have used. Although they are not perfectly stable, a relatively modest effort at station keeping can allow a spacecraft to stay in a desired Lissajous orbit for an extended period of time.>>

[hstarbuck]

It is so amazing that this telescope will be in (around) a Lagrangian point much further out than the moon.

Repairs will almost certainly be out of the question. Also cool that as the light from some objects 13 GLY away reaches us 13 GY later these objects and the rest of the Universe is expanding so that the current distance is really much more. Information travel has its limits (c; we don't know what these stars/galaxies are doing today) and benefits (we see the past). Question: In the Hubble Deep Field we see galaxies containing (I assume) billions of stars. If we looked further back in time before the first galaxies were formed(through distance) can we expect to see individual stars ? It seems that these stars might be too small to image.

[neufer]

Question: In the Hubble Deep Field we see galaxies containing (I assume) billions of stars. If we looked further back in time before the first galaxies were formed(through distance) can we expect to see individual stars ? It seems that these stars might be too small to image.

There may be all sorts of strange beasts lurking out there for JWST to observe:

<<In astronomy, Himiko is a large [Lyman-alpha blob] found at red-shift z=6.6 that predates similar Lyman-alpha blobs.
Researchers say it "may represent the most massive object ever discovered in the early universe.">>

http://www.universetoday.com/2010/03/09 ... -universe/

[BMAONE23]

It might not be too far away to work on if the VASIMR engine works as proposed Travel to the JWST could be a matter of hours to a couple of days

[neufer]

It might not be too far away to work on if the VASIMR engine works as proposed Travel to the JWST could be a matter of hours to a couple of days

It makes so much more sense to send up multiple JWSTs.

[Chris Peterson]

It might not be too far away to work on if the VASIMR engine works as proposed Travel to the JWST could be a matter of hours to a couple of days

The JWST isn't designed to be serviced. It was a mistake to make the HST serviceable, and I don't think that mistake is going to be repeated. It's almost always cheaper to replace a failed piece of space hardware than it is to service it in space. New engine technology isn't going to change that.

[rstevenson]

... It was a mistake to make the HST serviceable, and I don't think that mistake is going to be repeated. ...

But aren't we all glad they made that particular mistake, so they could fix the other mistake they made?

Rob