From Hubble to Webb

NASA has announced some more details on the James Webb telescope, slated to replace Hubble as the most important such instrument in orbit. Hubble is located in an elliptical low Earth orbit, with an orbital height of 589km and an orbital velocity of 7,500 m/s. The Webb will be located at Lagrange Point 2. This is an area where gravity will keep the telescope in a sun-earth line. As a result, the telescope will always be in the shadow of the Earth. NASA has a report on the transition.

Hubble has been one of NASAs great successes over the last 17 years, both in terms of the quality scientific information generated and in terms of the way the project reflects upon the organization. By finally offering an astronomical vantage point not affected by the Earth’s atmosphere, Hubble has been able to make unprecedented observations and discoveries. For example, consider the various exoplanets discovered in recent years, either because of how they obscure stars by passing in front of them or cause stars to wobble with their gravitational pull. Hubble was also ideally placed to observe the impact of Comet Shoemaker-Levy 9 into Jupiter. I remember watching the video feed from that at the Vancouver Planetarium, back in 1994. Some pretty stunning images of the universe have also been generated.

Just yesterday, Hubble may have observed a ring of dark matter. Given the disjoint between how galaxies behave gravitationally and the number and mass of stars we can observe, scientists have speculated that most of the material composition of the universe consists of dark matter and dark energy. The former has gravitational effects but does not interact with electromagnetic radiation. The latter is hypothetically involved in universal expansion: serving as one possible explanation for why the universe is expanding at an expanding rate, as observed through the Doppler shift. Data from the remainder of Hubble’s operational life and the full span of the Webb telescope’s operation may help with the refinement or rejection of both of these ideas, with coincidental improvement in our understanding about the contents and evolution of the universe.

Hubble has been discussed here before. A song about the Doppler shift has also been linked.

Author: Milan


24 thoughts on “From Hubble to Webb”

  1. Also, why does it have a sunshield if it “will always be in the shadow of the Earth?”

  2. It is unconventional looking for a good reason. Although JWST has a planned mass half that of the Hubble, its primary mirror (a 6.5 meter diameter beryllium reflector) has a collecting area which is almost 6 times larger.

  3. “The Webb Telescope will be situated at the second Lagrange point (L2) of the Sun-Earth system, about one million miles from the Earth. The combined gravitational forces of the Sun and the Earth can almost hold a spacecraft at this point, and it takes relatively little rocket thrust to keep the spacecraft near L2. The cold and stable temperature of the L2 point will allow it to make the very sensitive infrared observations needed.”

  4. Lagrangian or Lagrange Point: Lagrange Points mark positions where the gravitational pull of the two large masses precisely equals the centripetal force required to rotate with them. Used for positioning satellites in space, where minimum fuel will be required to maintain a stable orbit.

  5. Best answer:

    “After a transfer trajectory, the spacecraft will operate approximately 1.5 million kilometres from the Earth, in an orbit around the second Lagrange point of the Sun-Earth system, L2.

    With the aid of a tennis-court sized deployable sun shield, the 6.5 m JWST telescope will be kept in perpetual shadow. This allows the payload to cool to the extremely low temperatures required to keep the instrument’s own infrared emission from overwhelming the signals from the astronomical targets.”

  6. Gaia mapping the stars of the Milky Way

    L2 is a great place from which to observe the larger Universe. A spacecraft would not have to make constant orbits of Earth, which result in it passing in and out of Earth’s shadow and causing it to heat up and cool down, distorting its view. Free from this restriction and far away from the heat radiated by Earth, L2 provides a much more stable viewpoint.

    ESA has a number of missions that will make use of this spot in the coming years. L2 will become home to ESA missions such as Herschel, Planck, Gaia and the James Webb Space Telescope.

  7. Why does JWST need to be at L2?

    JWST requires a distant orbit for several reasons. JWST will observe primarily the infrared light from faint and very distant objects. But all objects, including telescopes, also emit infrared light. To avoid swamping the very faint astronomical signals with radiation from the telescope, the telescope and its instruments must be very cold (Operating Temperature: under 50 K (-370 deg F)). Therefore, JWST has a large shield that blocks the light from the Sun, Earth, and Moon, which otherwise would heat up the telescope, and interfere with the observations.

    To have this work, JWST must be in an orbit where all three of these objects are in about the same direction. The most convenient point is the second Lagrange point (L2) of the Sun-Earth system, a semi-stable point in the gravitational potential around the Sun and Earth. The L2 point lies outside Earth’s orbit while it is going around the Sun, keeping all three in a line at all times. The combined gravitational forces of the Sun and the Earth can almost hold a spacecraft at this point, and it takes relatively little rocket thrust to keep the spacecraft near L2. The cold and stable temperature environment of the L2 point will allow JWST to make the very sensitive infrared observations needed.

  8. It’s curiously appropriate that an unmanned telescope should emerge as a symbol of science, since it was instruments generallyâ€”and telescopes in particularâ€”that jump-started the scientific revolution. We tend to think of science in terms of great minds conjuring big ideas (an image that Edwin Hubble himself encouraged, at least when it came to his own research), but that paradigm is largely a holdover from prescientific days, when knowledge was sought principally in philosophers’ books. In science, instruments can trump arguments. The disinterested verdict of Galileo’s telescope did more than Galileo’s arguments to lay bare the shortcomings of the regnant Earth-centered model of the cosmos, and Newton’s mechanics endured less for their indubitable elegance than for their being able to predict what astronomers would see through their telescopes. Galileo’s contemporary Johannes Kepler, whom Immanuel Kant called “the most acute thinker ever born,” was quick to grasp that straightforward observations using scientific instruments could sweep away centuries of intelligent but ignorant discourse. Although he was a mathematical theorist who never owned a telescope, Kepler celebrated Galileo’s innovation in an ode, addressing the telescope as, “You much knowing tube, more precious than any scepter.”

    Hubble is Galileo’s telescope flung into a Keplerian orbit, and if these two early scientists came back to life today, I expect they would be impressed less by its technological sophistication than by its potential to bring things to light that challenge old ideasâ€”and to publish them on the Internet, science having always been about making knowledge available.


  9. Funding edict for mission has NASA over a barrel

    Planet-hunting telescope cost could hold back other space projects.

    “With the agency forced to beef up its financial commitment to the Space Interferometry Mission (SIM), there may be a two-year delay to Hubble’s successor, the James Webb Space Telescope (JWST). And other future flagship missions to study dark energy, gravity waves and X-ray astronomy might be cancelled altogether, warns Jon Morse, director of the agency’s astrophysics division.”

  10. John Mather On the Building of the James Webb Space Telescope
    on Saturday March 21, @10:15AM

    “Why is the James Webb Space Telescope (scheduled to launch in 2013) taking so long to build? Hasn’t it had a huge cost over-run and several delays? Nobel Prize winner John Mather is the Project Scientist for JWST, and he addresses these questions and more in an in-depth interview, one of the few he’s given about this next-generation telescope and successor to the Hubble Space Telescope. Quoting: ‘The hardest thing to build was the mirror, because we needed something that is way bigger than Hubble. But you can’t possibly lift something that big or fit it into a rocket, so you need something that is lighter weight but nonetheless larger, so it has to have the ability to fold up. The mirror is made of light-weight beryllium, and has 18 hexagonal segments. The telescope folds up like a butterfly in its chrysalis and will have to completely undo itself. It’s a rather elaborate process that will take many hours. The telescope is huge, at 6.5 meters (21 feet), so it’s pretty impressive.'”

  11. How Do Space Pictures Get So Pretty?
    Photoshop, of course.
    By Daniel Engber
    Posted Wednesday, Sept. 9, 2009, at 4:56 PM ET

    To create an image suitable for public viewing, the scientists send the FITS files over to a public outreach team. Specialists on the teamâ€”who tend to be astronomers with graduate degrees and a passion for graphics and photographyâ€”begin the process of converting the information into the images sent out in press releases.

    First, they put the image into a file format appropriate for media. That means that the data from the FITS files, which show a range of about 65,000 shades of grey, must be squeezed into a standard JPEG or TIFF file, with only 256 shades. This process is counterintuitively called “stretching” the data and must be done carefully to preserve important features and enhance details in the finished product.

    Then each grey-scale image is assigned a color. In reality, each shot already represents a colorâ€”the wavelength of light captured by the filter when that picture was taken. But in some cases the images represent colors that we wouldn’t be able to see. (The Spitzer, for example, registers the infrared spectrum.) To create a composite image that has the full range of colors seen by the human eye, an astronomer picks one image and makes it red, picks another and makes it blue, and completes the set by coloring a third image green. When he overlays the three images, one on top of the other, they produce a full-color picture. (Televisions and computer monitors create color in the same way.)

    Sometimes the team assigns new colors even when the original pictures were taken in the visible spectrum. An object that would in real life comprise several indistinguishable shades of red might be represented to the public as the composite of three pictures in red, green, and blue. As a general rule, professional “visualizers” try to assign red to the image showing the longest wavelengths of light and blue to the one showing the shortest. (This parallels the relationship among the colors in the visible spectrum.)

    Finally, the colorized images are cropped, rotated to the most dramatic orientation, and cleaned of instrument errors and other unsightly blemishes. Most of this work is done in Photoshop, using a freely downloaded plug-in that allows users to convert from the FITS format. (The original telescope images are also available, so you can create your own color gas cloud picture at home.)

  12. Planck Telescope Is Coolest Spacecraft Ever

    By timothy on that’s-certainly-what-the-moon-rabbits-think

    Hugh Pickens writes “Launched in May, BBC reports that Europe’s Planck observatory has reached its operating temperature, a staggering minus 273.05C â€” just a tenth of a degree above what scientists term “absolute zero.” and although laboratory set-ups have got closer to absolute zero than Planck, researchers say it is unlikely there is anywhere in space currently that is colder than their astronomical satellite. This frigidity should ensure the bolometers will be at their most sensitive as they look for variations in the temperature of the Cosmic Microwave Background (CMB) that are about a million times smaller than one degree â€” comparable to measuring from Earth the heat produced by a rabbit sitting on the Moon. Planck has been sent to an observation position around the second Lagrange point of the Sun-Earth system, L2, some 1.5 million km from Earth and Planck will help provide answers to one of the most important sets of questions asked in modern science â€” how did the Universe begin, how did it evolve to the state we observe today, and how will it continue to evolve in the future. Planck’s objectives include mapping of Cosmic Microwave Background anisotropies with improved sensitivity and angular resolution, determination of the Hubble constant, testing inflationary models of the early Universe, and measuring amplitude of structures in Cosmic Microwave Background. ‘We will be probing regimes that have never been studied before where the physics is very, very uncertain,’ says Planck investigator Professor George Efstathiou from Cambridge University. ‘It’s possible we could find a signature from before the Big Bang; or it’s possible we could find the signature of another Universe and then we’d have experimental evidence that we are part of a multi-verse.'”

  13. Hubble Accuracy Surpassed By Earthbound Telescope

    “A high-speed adaptive optics system helped the Large Binocular Telescope (on Earth) to beat the accuracy of the Hubble Space Telescope’s observations. ‘A special sensor detects atmospheric distortions in real time and controls the mirror to adjust its position to compensate, effectively canceling out the blurring. The mirror can make adjustments every one-thousandth of a second, with accuracy to better than ten nanometers.’ Now, that’s what I call real-time. This nifty trick multiplied the Strehl ratio (optical quality) of the LBT by about 80 times. The new system was tested in May and June, so hopefully we’ll soon see more space around us in higher resolution on Google Sky.”

  14. Costs of Nasa JWST to replace Hubble telescope balloon
    By Jonathan Amos
    Science correspondent, BBC News

    The scale of the delay and cost overrun blighting Nasa’s James Webb Space Telescope has been laid bare by a panel called in to review the project.

    The group believes the final budget for Hubble’s successor is likely to climb to at least $6.5bn, for a launch that is possible in September 2015.

    But even this assessment is optimistic, say the panel members.

    The head of the US space agency has accepted that “cost performance and coordination have been lacking”.

    Charles Bolden has ordered a reorganisation of the project and has changed the management at its top.

    Estimates for JWST’s total cost to build, launch and operate have steadily increased over the years from $3.5bn to $5bn.

    Along with the cost growth, the schedule has also eroded.

  15. James Webb: Swallowing the biggest space telescope

    The door has closed on the James Webb Space Telescope (JWST).

    The successor to Hubble has been locked tight inside a giant chamber where it will undergo a series of tests to simulate conditions off Earth.

    Engineers must first pump out all the air, and then chill down the telescope to fantastically low temperatures.

    In about 30 days’ time, they should be ready to start the checks that ensure JWST’s spectacular mirrors can focus light properly.

    “The operational temperature on orbit is about 30 kelvins – 30 degrees above absolute zero; but we’re going to test JWST to slightly lower,” explains Juli Lander, a US space agency (Nasa) engineer on the project.

    “We’re going to see if we can push on the hardware and the instruments a bit to give us a little margin on orbit,” she told BBC News.

    JWST is on track to be launched on a European Ariane rocket in just over a year from now. It will carry technologies capable of peering even deeper into space than Hubble – to detect the light coming from the very first stars to shine in the Universe.

  16. Conceived in the late 1980s as a way to peer back over 13.5 billion years of cosmic history to see the faint infrared light from the universeâ€™s very first stars and galaxies, JWST today is being tasked with an ever-growing menu of other scientific duties. Scientists now see its stargazing power, which by some metrics is 100 times greater than that of the famed Hubble Space Telescope, as a promissory note: The future of practically every branch of astronomy will be unquestionably brightened by JWSTâ€™s successful launch and operation. But due to its steadily escalating cost and continually delayed send-off (which recently slipped from 2018 to 2019), this telescopic time machine is now under increasingly intense congressional scrutiny.

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