The Joint Dark Energy Mission (JDEM) was an

Einstein probe The Einstein Probe (EP) is an X-ray space telescope mission by Chinese Academy of Sciences (CAS) in partnership with ESA and the Max Planck Institute for Extraterrestrial Physics (MPE) dedicated to time-domain high-energy astrophysics. The primar ...

that planned to focus on investigating

dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...

. JDEM was a partnership between

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

and the U.S. Department of Energy (DOE). In August 2010, the Board on Physics and Astronomy of the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...

(NSF) recommended the

Wide Field Infrared Survey Telescope The Nancy Grace Roman Space Telescope (shortened as Roman or the Roman Space Telescope, and formerly the Wide-Field Infrared Survey Telescope or WFIRST) is a NASA infrared space telescope currently in development and scheduled to launch by Ma ...

(WFIRST) mission, a renamed JDEM-Omega proposal which has superseded SNAP, Destiny, and Advanced Dark Energy Physics Telescope (ADEPT), as the highest priority for development in the decade around 2020. This would be a 1.5-meter telescope with a 144-megapixel HgCdTe focal plane array, located at the Sun-Earth L2

Lagrange point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of t ...

. The expected cost is around US$1.6 billion.

Earlier proposals

Dark Energy Space Telescope (Destiny)

The Dark Energy Space Telescope (Destiny), was a planned project by

and DOE, designed to perform precision measurements of the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...

to provide an understanding of

. The

space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launch ...

will derive the expansion of the universe by measuring up to 3,000 distant

supernovae A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

each year of its three-year mission lifetime, and will additionally study the structure of

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic part ...

in the universe by measuring millions of

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

in a

weak gravitational lensing While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak le ...

survey. The Destiny

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...

features an optical

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

with a 1.8 metre primary mirror. The telescope images

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

light onto an array of solid-state detectors. The mission is designed to be deployed in a

halo orbit A halo orbit is a periodic, three-dimensional orbit near one of the L1, L2 or L3 Lagrange points in the three-body problem of orbital mechanics. Although a Lagrange point is just a point in empty space, its peculiar characteristic is that it ...

about the Sun-Earth

. The Destiny proposal has been superseded by the

(WFIRST).

SuperNova Acceleration Probe (SNAP)

The SuperNova Acceleration Probe (SNAP) mission is expected to provide an understanding of the mechanism driving the acceleration of the universe and determine the nature of dark energy. To achieve these goals, the spacecraft needs to be able to detect these supernova when they are at their brightest moment. The mission is proposed as an experiment for the JDEM. The satellite observatory would be capable of measuring up to 2,000 distant

each year of its three-year mission lifetime. SNAP will also observe the small distortions of light from distant galaxies to reveal more about the expansion history of the universe. The SNAP is still in the proposal stages, and has yet to receive final approval. Should it be approved, the hoped launch date is 2013. To understand what is driving the acceleration of the universe, scientists need to see greater

redshifts In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...

from supernovas than what is seen from Earth. The SNAP can detect redshifts of 1.7 from distant supernovas up to 10 billion light years away. At this distance, the acceleration of the universe will be easily seen. To measure the presence of dark energy, a process called weak lensing will be used. The SNAP will use an optical setup called the

three-mirror anastigmat A three-mirror anastigmat is an anastigmat telescope built with three curved mirrors, enabling it to minimize all three main optical aberrations – spherical aberration, coma, and astigmatism. This is primarily used to enable wide fields of view, ...

. This consists of a main mirror with a diameter of 2 meters to take in light. It reflects this light to a second mirror. Then this light is transferred to two additional smaller mirrors which direct the light to the spacecraft's instruments. It will also contain 72 different cameras. 36 of them are able to detect

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...

and the other 36 detect

infrared light Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

. Its cameras combined produces the equivalence of a 600 megapixel camera. The resolution of the camera is about 0.2 arcseconds in the visible spectrum and 0.3 arcseconds in the infrared spectrum. The SNAP will also have a spectrograph attached to it. The purpose of it is to detect what type of supernova SNAP is observing, determine the redshift, detect changes between different supernovas, and store supernova spectra for future reference. JDEM has recognized several potential problems of the SNAP project: * The supernovas that SNAP will detect may not all be SN 1a type. Some other 1b and 1c type supernovas have similar spectra which could potentially confuse SNAP. * Hypothetical gray dust could contaminate results. Gray dust absorbs all wavelengths of light, making supernovas dimmer than they actually are. * The behavior of supernovas could potentially be altered by its binary-star system. * Any objects between the viewed supernova and the SNAP could gravitationally produce inaccurate results. The SNAP proposal has been superseded by the

(WFIRST).

References

External links

JDEM at Berkley Lab
{{Space observatories Space telescopes Cancelled spacecraft Spacecraft using halo orbits Dark energy Artificial satellites at Earth-Sun Lagrange points

Earlier proposals

Dark Energy Space Telescope (Destiny)

SuperNova Acceleration Probe (SNAP)

See also

References

External links