The Joint Dark Energy Mission (JDEM) was an Einstein probe that planned to focus on investigating

dark energy In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...

. JDEM was a partnership between

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

and the

U.S. Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear we ...

(DOE). In August 2010, the Board on Physics and Astronomy of the

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

(NSF) recommended the Wide Field Infrared Survey Telescope (WFIRST) mission, a renamed JDEM-Omega proposal which has superseded SNAP, Destiny, and Advanced Dark Energy Physics Telescope (ADEPT), as the highest priority for development in the decade around 2020.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 Hg1−''x''Cd''x''Te or mercury cadmium telluride (also cadmium mercury telluride, MCT, MerCad Telluride, MerCadTel, MerCaT or CMT) is a chemical compound of cadmium telluride (CdTe) and mercury telluride (HgTe) with a tunable bandgap spanning th ...

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 gravitational influence of two massive orbiting bodies. Mathematically, this involves 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. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

to provide an understanding of

. The

space telescope A space telescope (also known as 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 ...

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

supernovae A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...

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 pa ...

in the universe by measuring millions of

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and 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 Sys ...

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 ...

survey. The Destiny

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

features an optical

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

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 that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

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, non-planar orbit associated with 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 th ...

about the Sun-Earth

. The Destiny proposal has been superseded by the Wide Field Infrared Survey Telescope (WFIRST).

SuperNova Acceleration Probe (SNAP)

The SuperNova Acceleration Probe (SNAP) mission was proposed 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 needed to be able to detect these supernova when they are at their brightest moment. The mission was 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 was also planned to observe the small distortions of light from distant galaxies to reveal more about the expansion history of the universe. SNAP was initially planned to launch in 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 increase in frequency and e ...

from supernovas than what is seen from Earth. The SNAP would detect redshifts of 1.7 from distant supernovas up to 10 billion light years away. At this distance, the acceleration of the universe is easily seen. To measure the presence of dark energy, a process called weak lensing can be used. The SNAP would have used an optical setup called the three-mirror anastigmat. 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, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...

and the other 36 detect

infrared light Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those o ...

. 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 would 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 recognized several potential problems of the SNAP project: * The supernovas that SNAP would 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 Wide Field Infrared Survey Telescope (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