||It has been suggested that this article be merged into Joint Dark Energy Mission. (Discuss) Proposed since September 2010.|
||This article's factual accuracy may be compromised due to out-of-date information. (February 2013)|
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. 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. 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 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. 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.
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 wavelengths of all 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.
See also 
- Supernova/Acceleration Probe (SNAP) project website at the Lawrence Berkeley National Laboratory
- Sonoma State University SNAP project website
- An Integral Field Spectrograph for SNAP Supernova Identification, http://arxiv.org/ftp/astro-ph/papers/0210/0210087.pdf
- SNAP-Kent, http://www.fnal.gov/directorate/New_Initiatives/SNAP-Kent.pdf
- SNAP homepage, http://snap.lbl.gov/science/index.php
- How Is SNAP Going to Learn About Dark Energy?, http://snap.lbl.gov/science/how.php
- Spacecraft and orbit, http://snap.lbl.gov/mission/spacecraft.php
- Supernova/Acceleration Probe (SNAP): An Experiment to Measure the Properties of the Accelerating Universe, http://supernova.lbl.gov/~evlinder/snap_sum.pdf