The James Webb Space Telescope

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The James Webb Space Telescope
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Introduction

• The James Webb Space Telescope
• The James Webb Space Telescope, also called Webb
  or JWST, is a large, space-based observatory,
  optimized for infrared wavelengths, which will
  complement and extend the discoveries of the
  Hubble Space Telescope. It will have longer
  wavelength coverage and greatly improved
  sensitivity. The longer wavelengths enable Webb
  to look further back in time to find the first
  galaxies that formed in the early Universe, and
  to peer inside dust clouds where stars and
  planetary systems are forming today. It is
  scheduled for launch in 2013.

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James E .Webb

• This space-based observatory is named after James
  E. Webb (1906- 1992), NASA's second
  administrator. Webb is best known for leading
  Apollo, a series of lunar exploration programs
  that landed the first humans on the Moon.
  However, he also initiated a vigorous space
  science program that was responsible for more
  than 75 launches during his tenure, including
  America's first interplanetary explorers.

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How will Webb be better?

• Webb is designed to look deeper into space to see
  the earliest stars and galaxies that formed in
  the Universe and to look deep into nearby dust
  clouds to study the formation of stars and
  planets. In order to do this, Webb will have a
  much larger primary mirror than Hubble (2.5 times
  larger in diameter, or about 6 times larger in
  area), giving it more light-gathering power. It
  also will have infrared instruments with longer
  wavelength coverage and greatly improved
  sensitivity than Hubble. Finally, Webb will
  operate much farther from Earth, maintaining its
  extremely cold operating temperature, stable
  pointing and higher observing efficiency than
  with the Earth-orbiting Hubble.

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How long will the mission last?

• Webb will have a mission lifetime of not less
  than 5-1/2 years after launch, with the goal of
  having a lifetime greater than 10 years. The
  lifetime is limited by the amount of fuel used
  for maintaining the orbit, and by the testing and
  redundancy that ensures that everything on the
  spacecraft will work. Webb will carry fuel for a
  10-year lifetime the project will do mission
  assurance testing to guarantee 5 years of
  scientific operations starting at the end of the
  commissioning period 6 months after launch.

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Servicing Webb

• Hubble is in low-Earth orbit, located
  approximately 600 kilometers away from the Earth,
  and is therefore readily accessible for servicing
  using the Space Shuttle. Webb will be operated at
  the second Sun-Earth Lagrange point, located
  approximately 1.5 million kilometers away from
  the Earth, and will therefore be beyond the reach
  of any manned vehicle currently being planned for
  the next decade. In the early days of the Webb
  project, studies were conducted to evaluate the
  benefits, practicality and cost of servicing Webb
  either by human space flight, by robotic
  missions, or by some combination such as
  retrieval to low-Earth orbit. Those studies
  concluded that the potential benefits of
  servicing do not offset the increases in mission
  complexity, mass and cost that would be required
  to make Webb serviceable, or to conduct the
  servicing mission itself.

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Size of the Webb

• The diameter of the primary mirror, will be about
  6.5 meters (21 feet) for Webb. This is about 2.7
  times larger than the diameter of Hubble, or
  about 6 times larger in area. The Webb will have
  a mass of approximately 6,500 kg, with a weight
  of 14,300 lbs on Earth (in orbit, everything is
  weightless), a little more than half the mass of
  Hubble. The largest structure of Webb will be its
  sunshade, which must be able to shield the
  deployed primary mirror and the tower that holds
  the secondary mirror. The sunshade is
  approximately the size of a tennis court.

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Communication

• The Webb will send science and engineering data
  to Earth using a high frequency radio
  transmitter. Large radio antennas that are part
  of the NASA Deep Space Network will receive the
  signals and forward them to the Webb Science and
  Operation Center at the Space Telescope Science
  Institute in Baltimore, Maryland, USA.

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Orbit

• Webb is going to the second Lagrange (L2) point,
  which is 1 million miles (1.5 million km) away
  from Earth, and it just takes a while to travel
  such a distance. During the trip to L2, Webb will
  be fully deployed, will cool down to its
  operating temperature, and its systems will begin
  to be checked out and adjusted. These
  commissioning procedures will continue until 6
  months after launch, at which point routine
  scientific operations will begin.
• Webb will observe primarily the infrared light
  from faint and very distant objects. To avoid
  swamping the very faint astronomical signals with
  radiation from the telescope, the telescope and
  its instruments must be very cold.
• Webb's operating temperature is less than 50
  degrees above absolute zero 50 Kelvin, (-225
  Celcius, or -370 deg F). Therefore, Webb 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, Webb will be in
  an orbit where all three of these objects are in
  about the same direction the second Lagrange
  point (L2) of the Sun-Earth system has this
  property.

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How far will Webb look?

• One of the main goals of Webb is to detect some
  of the very first star formation in the Universe.
  This is thought to happen somewhere between
  redshift 15 and 30. At those redshifts, the
  Universe was only one or two percent of its
  current age. The Universe is now 13.7 billion
  years old, and these redshifts correspond to 100
  to 250 million years after the Big Bang. The
  light from the first galaxies has traveled for
  about 13.5 billion years, over a distance of 13.5
  billion light-years.

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Resources

• http//www.jwst.nasa.gov/