[GLIMPSE logo]


Galactic Legacy Infrared Mid- Plane Survey Extraordinaire

A Spitzer Legacy Science Program

[Spitzer logo]
      to Spitzer home page

About GLIMPSE and Spitzer

GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) is one of the experiments that will use the Spitzer (formerly called SIRTF, for Space Infrared Telescope Facility) satellite and telescope. GLIMPSE will conduct a survey of the inner part of our galaxy, the Milky Way.


 survey area ]

The boxes indicate approximate coverage of the inner Milky Way Galaxy by the GLIMPSE survey

Spitzer is the final element in NASA's Great Observatories Program, and part of the Astronomical Search for Origins program. GLIMPSE is part of the Spitzer Legacy Science Program, which was designed to maximize the scientific utility of Spitzer by yielding an early and long-lasting scientific heritage. The Great Observatories program consists of four space borne observatories, the Hubble Space Telescope (HST), the Compton Gamma Ray Observatory (CGRO), the Chandra X-Ray Observatory (CXO), and Spitzer.

[IMAGE - Spitzer in 


[JPL/NASA] Artist's conception of Spitzer in orbit

Radiation covers a wide spectrum of wavelengths, including visible light, as well as much our eyes can't see, such as infrared and x-rays. Each of the Great Observatories collect data from different wavelengths. The Hubble Space Telescope observes mostly visible light, and takes pictures of stars and galaxies and gas clouds, the Compton Gamma Ray Observatory, gamma rays (extremely high energy radiation), Chandra, x-rays and black holes, quasars, high temperature gases, and Spitzer, infrared (3-180 microns).


 wavelength chart from gamma to radio waves]

Gamma rays and X-rays are at the short end of the radiation wavelengths, while Infrared rays are much longer. Visible light comprises only a very small amount of the spectrum.

NASA's Origins Program seeks to answer two questions: Where do we come from? and Are we alone? by searching for life sustaining planets, and learning more about how stars and galaxies are formed, and about the Universe in general.

Spitzer's launch date was August 25, 2003, from Kennedy Space Center. It will go into an orbit trailing Earth's orbit, around the sun. It will drift away from earth about 0.1 AU per year (1 Astronomical Unit, AU, is the distance between the sun and the earth, about 93 million miles.) The orbit gives a good view of about 1/3 of the sky at a time Spitzer will send data for 2-1/2 to 5 years.

A. solar panel

B. solar panel shield

C. spacecraft shield

D. spacecraft bus

E. low gain antennae


 Spitzer outline with labels]

F. telescope barrel baffle

G. outer shell

H. low thrust helium vent

I. star tracker aperture shield

J. helium servicing lines

K. star trackers and IRUs (gyros)

L. cold gas nozzles

M. high gain antenna

Spitzer satellite diagram adapted from http://sirtf.caltech.edu/technology/overview.shtml


  • Launch Date: August 25, 2003
  • Delta 7920H ELV / Cape Canaveral, Florida
  • Estimated Lifetime: 2.5 years (minimum); 5+ years (goal)
  • Orbit: Earth-trailing, Heliocentric
  • Wavelength Coverage: 3 - 180 microns
  • Telescope: 85 cm diameter (33.5 Inches), f/12 lightweight Beryllium, cooled to less 5.5 K
  • Diffraction Limit: 6.5 microns
  • Science Capabilities:
    • Imaging / Photometry, 3-180 microns
    • Spectroscopy, 5-40 microns
    • Spectrophotometry, 50-100 microns
  • Planetary Tracking: 1 arcsec / sec
  • Cryogen / Volume: Liquid Helium / 360 liters (95 Gallons)
  • Launch Mass: 950 kg (2094 lb) [Observatory: 851.5 kg, Cover: 6.0 kg, Helium: 50.4 kg, Nitrogen Propellant: 15.6 kg]

The spacecraft has a warm part, which includes the solar panels, supports, power and telecommunications, and a cold section in which the instruments are cooled to less than 5.5K, almost as cold as space. Spitzer has three instruments to collect data, an infrared camera (IRAC), a spectrograph and a photometer. The instruments are very sensitive, and the sun, moon and earth are too bright for them. The instruments will survey the rest of the sky. The instruments need to be cold, otherwise they would "see" their own heat. Because the instruments must be very cold to work, the Spitzer satellite will be shaded from the sun by the earth, and has a sunshade that is also a solar array for a power supply. This helps save on liquid helium, which used to keep the instruments cold. The spacecraft will bring 95 gallons of liquid helium to help cool the instruments.

University groups worked on re-designing Spitzer to be smaller and less expensive than the original design, changing from a massive (about 6 meters high and 5700 kg) observatory with development costs in excess of 2.2 billion dollars to a modest-sized (about 3 meters high and 750 kg; but still powerful) observatory with costs of less than 0.5 billion dollars. The design is simple and uses engineering innovations. All the instruments are made of lightweight beryllium. Since they are all the same material, they are more dimensionally stable, and thermal expansion problems are minimized.

Conducting the survey in infrared light will show us things we can't see with our eyes, and things that are blocked from our view by Earth's atmosphere. The Spitzer instruments can detect infrared light and some visible light. Away from Earth's atmosphere there is a clearer view, without dust and water vapor.

The Spitzer/GLIMPSE survey can show us planets, star formation regions, comets, brown dwarfs, other galaxies, and more. We can learn about our own and other galactic development and structure, and about the "missing mass" of the Universe.


Some introductory and general links of interest:

to GLIMPSE home page

to UW-Madison Astronomy Department home page

to [UW-Madison 

 logo]University of Wisconsin-Madison home page

this page is: http://www.astro.wisc.edu/glimpse/glimpse-about.html

January 18, 2004

webmaster: meade (at) astro.wisc.edu