September 30, 2014

Space Telescopes, Part I: Optical.

 
(Credit: NASA/ESA/S. Gallagher/J. English).
(Credit: NASA/ESA/S. Gallagher/J. English).
 

 Hickson Group 31 of galaxies as imaged by Hubble.

   This weeks’ expose will kick off our four part series on orbiting space telescopes. For starters, we’ll begin with the most familiar; the optical wavelength. True, we as humans are biased towards this narrow band of the spectrum; we love to see pretty pictures that we can relate to.  But beyond this, telescopes that operate in the visual wavelengths have no less than revolutionized astronomy, as well as laid promise for perhaps giving us images of exo-Earths in our lifetimes. What follows is a rapid fire list of what was, is, and what to look for up and coming in the realm of optical astronomy in space:

Past:

Hipparcos- Launched in August 1989 by the European Space Agency on a highly elliptical Earth orbit, The High Precision Parallax Collecting Satellite was the first telescope to operate in the visual spectrum placed in space. Hipparcos operated for almost four years, refining the stellar parallax of over 100,000 stars down to the +11th magnitude. Hipparcos utilized a 29 cm Schmidt telescope, and refined not only stellar parallax and distance but also the radial velocity of stars, the kinematics of our local Milky Way, and refined the distance measurements to such standard candles as the famous Cepheid variable stars.

Present:

Hubble- What hasn’t been written about the Hubble Space Telescope, that most famous of all space telescopes? Since its launch in the 1990’s, Hubble on its own has single-handedly revolutionized the field of astronomy. Off to a rocky start due to its defective mirror identified after deployment on STS-31, Hubble has transcended to become a pop icon of our age, with images appearing everywhere from screensavers to Star Trek episodes to badly written new age tomes. (You gotta love the power of NASA.gov and the public domain!) Hubble has revolutionized the field of astronomy, and an entire generation of astronomers owe their PhDs to this single telescope. Not to mention astro-bloggers, who can always count on mentioning Hubble at least once a week! Hubble has gone from NASA’s boondoggle to one of its greatest successes, and will most likely be remembered as one of the greatest achievements of the U.S. Space Shuttle Program. The STS-61 repair mission in 1993 fixed the ailing optics by the addition of COSTAR, and last year’s STS-125 repair mission saw a servicing call to Hubble one last time… Just how much longer will Hubble last? This week, we celebrate the 20th anniversary of Hubble in orbit; she’ll be sorely missed on that hopefully far off date that she gets de-orbited!  

 COROT- Launched in December 2006, the Convection, Rotation & planetary Transit satellite is a joint mission between the French Space Agency (CNES) and the ESA. Placed in a polar Earth orbit, it is designed to look for transiting super-Earths as well as study stellar seismology. To date, COROT has discovered 9 exoplanets, including COROT-7b, just 1.7 Earths in diameter. COROT utilizes a 27 cm, off-axis primary mirror.

(Credit: Canadian Space Agency).

  MOST payload in the laboratory.

MOST- Never heard of the Micro-variability and Oscillations of Stars Telescope? Launched in 2003 on a polar orbit, MOST is Canada’s first and only space telescope. MOST is tiny and would easily fit in the trunk of your car. MOST is entirely dedicated to astro-seismology, and uses a 15cm (the Astroguyz’ Celestron SCT is 20cm!) Maksutov reflecting telescope. MOST could, in theory, detect exoplanet transits, although this capability has yet to be demonstrated. The tiny size has earned the optical munchkin the name the “Humble Space Telescope!”

Kepler- Hunting exoplanets is the name of the space telescope game, and NASA’s newly launched Kepler Space telescope has already raised the bar since its launch early last year. Placed in an Earth-trailing heliocentric orbit, Kepler’s 3+ year mission will involve it staring at a star rich area of the Milky Way along the Cygnus/Lyra/Draco border. Its quarry is transiting exoplanets, given away by their minute fluctuation in the stars’ brightness as they cross the tiny disk of the star as seen from Kepler’s vantage point. To date, Kepler has confirmed 6 exoplanets and 177 candidate objects for further scrutiny. Will Kepler single-handedly vault the number of known exo-world into the thousands?

Swift- A wonderful mission that gets way too little press is NASA’s Swift Gamma-Ray Burst Mission. This platform actually carries a battery of three telescopes operating in four different wavelengths, only one of which, the Ultraviolet/Optical Telescope, (UVOT) is a 30cm visual instrument. Swift is dedicated to catching Gamma Ray Bursts in the act. Its sky-spanning Burst Alert Telescope (BAT) can pinpoint the source in gamma rays to within 4 arc minutes in 15 minutes time, and then swivel the UVOT into action to attempt and catch a matching optical or ultraviolet transient.    

TPF_I

TPF-1: An artists’ conception. (Credit: NASA).  

The Future:

Astrosat- Ah… the future of optical astronomy in space is where the cool stuff is at. Next year, watch for the Indian Space Agencies’ entry into the optical space telescope game, in a little cube known as Astrosat. Astrosat is like a miniaturized Swiss Army knife of a telescope, housing five different instruments covering an array of wavelengths, including optical. This will enable Astrosat to carry out analysis of objects over the continuous spectrum, as well as back up ground-based observations.

The Dark Energy Space Telescope-  This one sounds like something a super-villian would use to conquer the Earth… Also known as DESTiny, this proposed space telescope would monitor 3,000 extra-galactic Type Ia supernovae for three years in an effort to pin down the elusive quantity of dark energy that is speeding up the expansion of our universe. DESTiny would house a 1.65 meter primary mirror, and be parked in a halo orbit around the Sun-Earth L2 Lagrangian point. If funded, expect launch of DESTiny to be deployed no earlier than 2013.   

Gaia- A successor to Hipparcos, the Gaia space telescope is scheduled for launch in the summer of 2012 to further refine astrometric measurements. The goal is to measure the positions of one billion stars down to magnitude +20. Much like ESA’s SOHO satellite, Gaia will be stationed at the L2 point in a Lissajous (look it up, we had to!) orbit.

The SIM Lite Astrometric Observatory- NASAs currently shelved Space Interferometry Mission, also the space telescope formerly known as PlanetQuest, SIM Lite would open a powerful new window as it uses Interferometry via its twin 0.5 meter telescopes to search for terrestrial planets around nearby sun-like stars. Originally scheduled for launch in 2005, all technology milestones were met before Congress pulled the plug! As of this writing, it looks like SIM Lite won’t get into its Earth-trailing heliocentric orbit to begin work no earlier than 2015.

599px-The_Earth_seen_from_Apollo_17

A future view of an exo-Earth? (Picture simulated by author using Photoshop and a Apollo 17 image).

The Terrestrial Planet Finder Series- More ambitious than SIM, two design projects are currently under consideration by NASA; an Infrared Interferometer, known as TPF-I, and a Visible Light Coronagraph named TPF-C. Both would look exclusively for Earth-like worlds around nearby stars, and could be perhaps the first telescopes to obtain a spectrum of these worlds, looking for key chemical markers such as free O2, O3, and CH4, all signs that something biologically interesting is afoot. TPF-I would utilize four optical assemblies on a fixed structure to create a large nulling interferometer, while TPF-C would use one large telescope complete with specialty masking optics. ESA has a similar proposal on the drawing board, currently known as Darwin.  

 Life Finder- …And then there are those telescopes further down the road that just make you go hmmmm…. Beyond the realm of the post-TPF instruments lay scopes variously named Life Finder, Exo-Earth Detector, and most interestingly, the Exo-Earth Imager. EEI could consist of a constellation of 100 free flying 3 meter telescopes which would combine to produce actual images of earthlike worlds around other stars… just think, in our lifetimes we could conceivably have a screensaver of an exo-earth! Farther afield, how about a telescope that takes advantage of the unique gravitational lensing properties of our Sun at around 600 A.U.? Or a large, reflective crystalline cloud acting as one enormous space-based mirror? Or a vast, liquid mercury rotating mirror on the lunar far side? Perhaps some future space telescope engineer in kindergarten is reading this blog, and thinking cool

So there you have it, humanities arsenal of optical space telescopes, real and proposed. Stay tuned in two weeks’ time as we delve into part II, the ultraviolet spectrum of instruments!

planetquest_gasses-browse

Key spectral signatures of Earth-like life.

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