Wide Field Infrared Survey Telescope or ‘WFIRST’ is an infrared space observatory based on a design proposal for ‘Joint Dark Energy Mission’ between ‘Department of Energy’ and NASA. It formally became a NASA mission on Feb 17, 2016. Primary mission time is 6 years during which the mission will collect data for examining expansion history of Universe and growth of large scale structures to assess the effect of Dark Energy. It will also find exoplanets in Milky Way, in order to take forth the survey started by ‘Kepler Mission’. Exoplanets are planets orbiting stars other than our Sun. Exoplanet data will be analyzed for signs of other habitable worlds in Milky Way. Mission is set to be launched in mid 20’s making it NASA’s first space mission dedicated to understanding Dark Energy. It will be second such mission after ESA’s Euclid spacecraft.
‘WFIRST’ will have a 288 Megapixel wide field camera with HgCdTe focal plane array having 110 milliarcsecond pixels, operating in near infrared band (0.7-2.0 micron). Its field of view will be 100 times wider than that of Hubble Infrared Instrument. A grism will be integrated for wide field slitless spectroscopy and for small field spectroscopy it will be using an integral field spectrograph. Grism is a combination of Prism and Grating which allows a central wavelength to pass undeviated. With this wide field instrument, WFIRST will observe distant Supernovae, Weak Gravitational Lensing and Baryon Acoustic Oscillation to obtain data for understanding ‘nature of Dark Energy’.
Mission will also include a custom built, high contrast, advanced stellar Coronagraph for imaging exoplanets directly. It will work in the wavelengths of (0.4-1.0) micrometer and will also provide spectra of planets. Coronagraph, invented by French Astronomer Bernard Lyot in 1939, suppresses starlight using masks, mirror and lenses. It blocks the light from Star while allowing light from surrounding sources to pass, which enables it to see planets which are otherwise not visible due to overwhelming brightness of their host Star. Mission will observe Gravitational Micro Lensing signature of planets which is brief brightening of Stars due to a passing by planet, to detect exoplanets.
WFIRST will be able to look as far as HST with the help of its 2.4m primary mirror Anastigmat Telescope and with its integrated Wide Field Instrument, will have a field of view 100 times wider than HST. Mission will launch on an Evolved Expendable Launch Vehicle or ‘EELV’ from Cape Canaveral to Sun-Earth L2 Halo Orbit with a launch mass of 4166 Kg. Spacecraft will operate in near infrared and visible bands. Data will be transmitted to Earth station in Ka band. Project is managed from Goddard Space Flight Center ‘GSFC’. GSFC also supervises work on system integration, spacecraft bus and wide field instrument. Stellar Coronagraph and Telescope is managed by Jet Propulsion Laboratory ‘JPL’. Space Telescope Science Institute, as a partner, will be concerned with data processing, data analysis and data archiving. Neil Gehrels chairs the Formulation Science Working Group with deputy chairs David Spergel and Jeremy Kasdin. Gehrels is also the Project Scientist and Kasdin the lead scientist for Coronagraph. David Spergel and Jeremy Kasdin are Princeton University professors.
Coronagraph’s ability to provide high contrast images of exoplanets in habitable zone of Planetary Systems is in doubt which has led to discussions on including a Starshade in the mission. Starshade is a giant screen about the size of a baseball field and of the shape of a Sunflower with paper thin petals. This foldable screen can be loaded on a rocket and transported about 50000 km directly ahead of the Telescope, where it can be unfurled and deployed. It works by blocking Starlight and supposed to help in obtaining much higher contrast images of exoplanets than a Coronagraph. Because it can help provide desirable quality images of exoplanets in habitable zone of Planetary Systems, a Starshade is highly desirable by Scientists but the technology is not fully tested and NASA budget cannot support a speedy development right now. In a better scenario, both Coronagraph and Starshade should be in the mission as their function is complementary.
References:
1) https://wfirst.gsfc.nasa.gov/
2) https://exoplanets.nasa.gov/resources/1015/
3) https://arxiv.org/ftp/arxiv/papers/1411/1411.0313.pdf
Image credits goes to respective sources.
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