![JDEM proposal](https://upload.wikimedia.org/wikipedia/commons/b/bd/JDEM_proposal.png)
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 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 agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
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Wide Field Infrared Survey Telescope (WFIRST) mission, a renamed JDEM-Omega proposal which has superseded SNAP, Destiny, and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−xCdxTe 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 the shortwav ...
focal plane array, located at the Sun-Earth L2
Lagrange point. 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
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
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 universe. ...
to provide an understanding of
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 ...
. 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 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 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, p ...
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 observ ...
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 visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
light onto an array of solid-state detectors. The mission is designed to be deployed in a
halo orbit about the Sun-Earth
Lagrange point.
The Destiny proposal has been superseded by the
Wide Field Infrared Survey Telescope (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
supernovae 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 f ...
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 te ...
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
Wide Field Infrared Survey Telescope (WFIRST).
See also
*
Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 201 ...
(2009–2011)
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