Joint Dark Energy Mission

The Joint Dark Energy Mission (JDEM) was an Einstein probe that planned to focus on investigating dark energy. JDEM was a partnership between NASA and the U.S. Department of Energy.

In August 2010, the Board on Physics and Astronomy of the National Science Foundation recommended the Wide Field Infrared Survey Telescope (WFIRST) mission, a renamed JDEM-Omega proposal which has superseded SNAP, Destiny, and ADEPT, as the highest priority for development in the decade around 2020.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 L2 Lagrange point. The expected cost is around $1.6 billion.

JDEM proposal
JDEM design proposal

Earlier proposals

Dark Energy Space Telescope (Destiny)

The Dark Energy Space Telescope (Destiny), was a planned project by NASA and DOE, designed to perform precision measurements of the universe to provide an understanding of dark energy. The space observatory 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 the universe by measuring millions of galaxies in a weak gravitational lensing survey. The Destiny spacecraft features an optical telescope with a 1.65m primary mirror. The telescope images infrared light onto an array of solid-state detectors. The mission is designed to be deployed in a halo orbit about the sun-earth L2 Lagrangian point.[1]

The Destiny proposal has been superseded by the Wide Field Infrared Survey Telescope.

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 detect these supernovas when they are at their brightest moment.[2] The mission is proposed as an experiment for Joint Dark Energy Mission (JDEM). JDEM is a partnership between NASA and the U.S. Department of Energy. The projected cost ranges from $500 million to $1 billion. The cost will be split between NASA and Department of Energy.[3] 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.[4] 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 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.[5]

The SNAP will use 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 and the other 36 detect infrared light. 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.[6]

JDEM has recognized several potential problems of the SNAP project:

  1. 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.
  2. Hypothetical gray dust could contaminate results. Gray dust absorbs wavelengths of all light, making supernovas dimmer than they actually are.
  3. The behavior of supernovas could potentially be altered by its binary-star system.
  4. Any objects between the viewed supernova and the SNAP could gravitationally produce inaccurate results.[7]

See also


  1. ^ Destiny project website
  2. ^ An Integral Field Spectrograph for SNAP Supernova Identification,
  3. ^ SNAP-Kent, "Archived copy" (PDF). Archived from the original (PDF) on 2013-05-10. Retrieved 2013-09-28.CS1 maint: Archived copy as title (link)
  4. ^ SNAP homepage,
  5. ^ How Is SNAP Going to Learn About Dark Energy?,
  6. ^ Spacecraft and orbit,
  7. ^ Supernova/Acceleration Probe (SNAP): An Experiment to Measure the Properties of the Accelerating Universe,

External links

Beyond Einstein program

The Beyond Einstein program is a NASA project designed to explore the limits of Einstein's theory of General Relativity. The project includes two space observatories, and several observational cosmology probes. The program culminates with the Einstein Vision probes, after completion of the Great Observatories program.

Constellation-X and the Laser Interferometer Space Antenna (LISA) have been promoted by NASA as the Einstein Great Observatories, to differentiate them from the current generation. However, they are not a part of the Great Observatories program.

Charles V. Shank

Charles Vernon (Chuck) Shank (born July 12, 1943) is an American physicist, best known as the director of the Lawrence Berkeley National Laboratory from 1989 to 2004.

Dark energy

In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.Assuming that the standard model of cosmology is correct, the best current measurements indicate that dark energy contributes 68% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contribute 27% and 5%, respectively, and other components such as neutrinos and photons contribute a very small amount. The density of dark energy is very low (~ 7 × 10−30 g/cm3) much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the mass–energy of the universe because it is uniform across space.Two proposed forms for dark energy are the cosmological constant, representing a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to the zero-point radiation of space i.e. the vacuum energy. Scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow.

Lambda-CDM model

The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) and associated with dark energy; second, the postulated cold dark matter (abbreviated CDM); and third, ordinary matter. It is frequently referred to as the standard model of Big Bang cosmology because it is the simplest model that provides a reasonably good account of the following properties of the cosmos:

the existence and structure of the cosmic microwave background

the large-scale structure in the distribution of galaxies

the abundances of hydrogen (including deuterium), helium, and lithium

the accelerating expansion of the universe observed in the light from distant galaxies and supernovaeThe model assumes that general relativity is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a concordance cosmology, after a period of time when disparate observed properties of the universe appeared mutually inconsistent, and there was no consensus on the makeup of the energy density of the universe.

The ΛCDM model can be extended by adding cosmological inflation, quintessence and other elements that are current areas of speculation and research in cosmology.

Some alternative models challenge the assumptions of the ΛCDM model. Examples of these are modified Newtonian dynamics, entropic gravity, modified gravity, theories of large-scale variations in the matter density of the universe, bimetric gravity, and scale invariance of empty space.

Michael Lampton

Michael Logan Lampton (born March 1, 1941) is an American astronaut, founder of the optical ray tracing company Stellar Software, and known for his paper on electroacoustics with Susan M Lea, The theory of maximally flat loudspeaker systems.

Neil Gehrels

Cornelis A. "Neil" Gehrels (October 3, 1952 – February 6, 2017) was an American astrophysicist specializing in the field of gamma-ray astronomy. He was Chief of the Astroparticle Physics Laboratory at NASA's Goddard Space Flight Center from 1995 until his death, and was best known for his work developing the field from early balloon instruments to today's space observatories such as the NASA Swift mission, for which he was the Principal Investigator. He was leading the WFIRST wide-field infrared telescope forward toward a launch in the mid-2020s. He was a member of the National Academy of Sciences and the American Academy of Arts and Sciences.

Gehrels died on February 6, 2017, at the age of 64. On January 10th, 2018, NASA announced that Swift had been renamed the Neil Gehrels Swift Observatory, in his honor..

Tod R. Lauer

Tod R. Lauer (born 1957) is an American astronomer on the research staff of the National Optical Astronomy Observatory. He was a member of the Hubble Space Telescope Wide Field and Planetary Camera team, and is a founding member of the Nuker Team. His research interests includes observational searches for massive black holes in the centers of galaxies, the structure of elliptical galaxies, stellar populations, large-scale structure of the universe, and astronomical image processing. He was the Principal Investigator of the Destiny JDEM concept study, one of the precursors to the Wide Field Infrared Survey Telescope mission. Asteroid 3135 Lauer is named for him. He appears in an episode of the documentary series Naked Science. He joined the New Horizons Pluto team in order to apply his extensive experience with deep space imaging to the New Horizons data, yielding significantly clearer and mathematically accurate images of Pluto and Charon.

Wide Field Infrared Survey Telescope

The Wide Field Infrared Survey Telescope (WFIRST) is a NASA infrared space observatory currently under development. WFIRST was recommended in 2010 by United States National Research Council Decadal Survey committee as the top priority for the next decade of astronomy. On February 17, 2016, WFIRST was approved for development and launch.WFIRST is based on an existing 2.4 m wide field-of-view telescope and will carry two scientific instruments. The Wide-Field Instrument is a 288-megapixel multi-band near-infrared camera, providing a sharpness of images comparable to that achieved by the Hubble Space Telescope (HST) over a 0.28 square degree field of view, 100 times larger than that of the HST. The Coronagraphic Instrument is a high-contrast, small field-of-view camera and spectrometer covering visible and near-infrared wavelengths using novel starlight-suppression technology.

The design of WFIRST is based on one of the proposed designs for the Joint Dark Energy Mission between NASA and DOE. WFIRST adds some extra capabilities to the original JDEM proposal, including a search for extra-solar planets using gravitational microlensing. In its present incarnation (2015), a large fraction of its primary mission will be focused on probing the expansion history of the Universe and the growth of cosmic structure with multiple methods in overlapping redshift ranges, with the goal of precisely measuring the effects of dark energy, the consistency of general relativity, and the curvature of spacetime.

On February 12, 2018, development on the WFIRST mission was proposed to be terminated in the President's FY19 budget request, due to a reduction in the overall NASA astrophysics budget and higher priorities elsewhere in the agency. In March 2018 Congress approved funding to continue making progress on WFIRST until at least September 30, 2018, in a bill stating that Congress "rejects the cancellation of scientific priorities recommended by the National Academy of Sciences decadal survey process". In testimony before Congress in July 2018, NASA administrator Jim Bridenstine proposed slowing down the development of WFIRST in order to accommodate a cost increase in the James Webb Space Telescope (JWST), which would result in decreased funding for WFIRST in 2020/2021. In the President's FY20 budget request, termination of WFIRST was proposed again, due to cost overruns and higher priority for JWST.

Yun Wang

Yun Wang (born 1964) is a poet and cosmologist. She is originally from Gaoping, a small town near Zunyi, in Guizhou Province, China.

(Mission completed)
See also

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