Stratospheric Observatory for Infrared Astronomy

Infobox Observatory
name = SOFIA


caption = The 747SP, which now serves as NASA's SOFIA, on a test flight in 1997. Still mostly in United Airlines livery, a black square was painted on the aft fuselage to indicate the area that would house the telescope.
organization = Universities Space Research Association
location = Edwards Air Force Base, California
coords = coord|34|54|20|N|117|53|01|W|region:US_type:airport
altitude = ground: 702 m (2,302 ft); airborne: 12.5 km (41,000 ft)
weather =
established =
closed =
website= [http://www.sofia.usra.edu/ SOFIA Science Center]
telescope1_name = SOFIA
telescope1_type = 2.5 meter (98.4 inch) reflector

The Stratospheric Observatory for Infrared Astronomy (SOFIA), is a joint project of NASA and the German Aerospace Center (DLR). Universities Space Research Association (USRA) was awarded the prime contract by NASA in 1996 for development, operation of the observatory and management of the American part while the DSI (Deutsches SOFIA Institut) manage the German part (mainly science and telescope related).

Facility

SOFIA is a Boeing 747SP airliner, formerly flown commercially by United Airlines and Pan Am, modified to carry a 2.5 meter diameter reflecting telescope for infrared astronomy observations at altitudes of about 41,000 feet (~12 km) in the stratosphere. The water vapor in the Earth's atmosphere blocks some infrared wavelengths from reaching the ground, but SOFIA's flight capability allows it to rise above almost all of the water vapor in the Earth's atmosphere. At the aircraft's cruising altitude, 85% of the full infrared range will be available. The aircraft can also travel to almost any point on the Earth's surface, allowing observation from the northern and southern hemispheres.

Once ready for use, it is hoped that observing flights will be flown 3 or 4 nights a week for the next 20 years. SOFIA will be based at NASA's Dryden Flight Research Center at Edwards AFB, California (near Lancaster, CA).

The telescope

SOFIA uses a 2.5-meter reflector telescope, which has an oversized primary mirror (2.7 meters in diameter) in common with most large infra-red telescopes. The telescope looks out of a large door in the side of the fuselage near the airplane's tail, and will initially carry nine instruments for infrared astronomy at wavelengths from 1–655 micrometres and high-speed optical astronomy at wavelengths from 0.3–1.1 micrometres. Although SOFIA’s telescope is by far the largest ever to be placed in an aircraft, compared to normal ground-based research observatories it is only medium-sized.

The project also has its own mirror coating facility in Moffett Field allowing a fast recoating of the primary mirror.

DLR is responsible for the entire telescope assembly (whereas NASA is responsible for the plane). The manufacturing of the telescope was subcontracted to European industry (The telescope is German, the mirror is French-made and the secondary mirror mechanism is Swiss-made).

For each mission one interchangeable science instrument will be attached to the telescope. Two groups of general purpose instruments are available. In addition an investigator can also design and build a special purpose instrument.

The open cavity housing the telescope will be exposed to high-speed turbulent winds. In addition, the vibrations and motions of the aircraft introduce observing difficulties. The telescope was designed to be very light-weight, and the mount includes a system to isolate the instrument from vibration. The telescope cabin must be pre-cooled prior to aircraft takeoff so that the telescope matches the external temperature (thus avoiding thermally-induced shape changes). Prior to landing the cabin is flooded with nitrogen gas in order to avoid condensation of moisture on the chilled instrument.cite conference
first=Alfred | last=Krabbe | title=SOFIA telescope
booktitle=Proceedings of SPIE: Astronomical Telescopes and Instrumentation
publisher=SPIE — The International Society for Optical Engineering
pages=276–281 | date=March, 2007 | location=Munich, Germany
url=http://arxiv.org/abs/astro-ph/0004253
accessdate = 2007-06-07 ]

The aircraft

The SOFIA aircraft is a Boeing 747SP with a distinguished history. It was originally acquired by Pan American World Airways and was delivered in May 1977. The "SP" designates that this is a special short-body version of the 747, designed for longer flights than the basic model. [cite web | url=http://www.sofia.usra.edu/Sofia/aircraft/sofia_ac.htm | title=The SOFIA Boeing 747SP] United Airlines purchased the plane in February 1986, and removed it from active service in December 1995. Two years later, NASA purchased it from United for use by the SOFIA project. A series of "baseline" flight tests were conducted in 1997 prior to heavy modification of the aircraft by L-3 Communications Integrated Systems of Waco, Texas for its new role as a flying astronomical observatory. A dismantled section from another 747SP was used as a full-size mock-up to ensure proper modification.

Pan Am had named this aircraft "Clipper Lindbergh" in honor of the famous aviator Charles Lindbergh. The aircraft was personally christened by Lindbergh's widow, Anne Morrow Lindbergh, on the occasion of the 50th anniversary of her husband's historic flight from New York to Paris in 1927, although the aircraft had been officially placed into service on May 6, 1977. Similarly, Lindbergh's grandson, Erik Lindbergh, re-christened the aircraft "Clipper Lindbergh" on May 21, 2007 at L-3's Waco facilities. [cite news
last=Hautaluoma | first=Grey | coauthors=Hagenauer, Beth
date=2007-05-11 | publisher=NASA
title=NASA's SOFIA to be Rededicated on Historic Lindbergh Anniversary
url=http://www.nasa.gov/home/hqnews/2007/may/HQ_M07052_SOFIA_event.html
accessdate=2008-07-23 ]

The telescope is mounted in the aft part of the aircraft behind a pressurized bulkhead. The telecope's focal point is located at a science instruments suite in the pressurized section. In the center of the aircraft is the mission control and science operations section, while the forward section hosts the education and public outreach area.

Project development

The first use of an aircraft for performing infrared observations occurred in 1965 when Gerard P. Kuiper used the NASA Convair 900 to study Venus. Three years later, Frank Low used the Ames Learjet to perform observations of Jupiter and nebulae. [cite conference
first=E. F. | last=Erickson | coauthors=Davidson, J. A.
title=SOFIA: The future of airborne astronomy
booktitle=Proceedings of the Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust
pages=707-773
publisher=Astronomical Society of the Pacific
date=July, 1994 | location=Mountain View, CA
url=http://adsabs.harvard.edu/abs/1976IAUS...73...75P
accessdate = 2008-07-04 ] In 1969, planning beganfor mounting a convert|36|in|mm|sing=on telescope on an airborne platform. The goal of this instrument was to perform astronomy from the stratosphere, where there was a much lower optical depth from water vapor absorbing infrared radiation. This project was named the Kuiper Airborne Observatory, and it was dedicated on May 21, 1975. The telescope became instrumental in numerous scientific studies, including the discovery of the ring system around the planet Uranus. [cite web
last=Mewhinney | first=Mike | date=2005-05-24
url=http://www.nasa.gov/vision/universe/watchtheskies/kuiper.html
title=Kuiper Airborne Observatory Marks 30th Anniversary of its Dedication
publisher=NASA | accessdate=2008-07-04 ]

The proposal for a larger aircraft-mounted telescope was officially presented in 1984, which called for a Boeing 747 to carry a three meter telescope. The preliminary system concept was published in 1987 in the "Red Book". It was agreed that Germany would contribute 20% of the total cost, and they would provide the telescope. However, the reunification of Germany and budget cuts at NASA led to a five year slide in the project. NASA then contracted the work out to the Universities Space Research Association (USRA), and in 1996, NASA and DARA signed a memorandum of understanding for the building and operation of SOFIA. [cite book
last=Titz | first=Ruth
coauthors=Roeser, Hans-Peter | year=1998
title=SOFIA : astronomy and technology in the 21st century
publisher=Berlin: Wissenschaft und Technik
isbn=3896855581
url=http://arxiv.org/abs/astro-ph/9908345
accessdate=2008-07-04 ]

The SOFIA telescope's primary mirror was manufactured out of Zerodur, a glass-ceramic composite produced by Schott AG that has almost zero thermal expansion. REOSC, the optical department of the SAGEM Group in France, performed weight reduction by milling honeycomb-shaped pockets out of the back. They finished polishing the mirror on December 14, 1999, achieving an accuracy of 8.5 nm over the optical surface. [cite news
author=Staff | date=1999-12-14
title=REOSC Delivers the Best Astronomical Mirror in the World to ESO
publisher=European Southern Observatory
url=http://www.eso.org/public/outreach/press-rel/pr-1999/pr-19-99.html
accessdate=2008-07-23 ] The hyperbolic-shaped secondary mirror was made out of silicon carbide,with polishing completed by May 2000. [cite conference
first=Alfred | last=Krabbe | title=The SOFIA Telescope
booktitle=Proceedings of SPIE: Airborne Telescope Systems
date=March 2000 | location=Munich, Germany
url=http://arxiv.org/abs/astro-ph/0004253
accessdate=2007-01-08 ]

During 2002, the main components of the telescope were assembledin Augsburg, Germany. These consisted of the primary mirrorassembly, the main optical support and the suspension assembly.After successful integration tests were made to check thesystem, the components were shipped to Waco, Texas on boardan Airbus Beluga aircraft. They arrived on September 4, 2002. [cite journal
last=Casey | first=Sean C.
title=The SOFIA program: astronomers return to the stratosphere
journal=Advances in Space Research
year=2004 | volume=34 | issue=3 | pages=77–115
doi=10.1016/j.asr.2003.05.026 ] SOFIA completed its first ground-based "on-sky" test on August 18-19, 2004 by taking an image of the star Polaris. [cite news
last=Mewhinney | first=Michael | date=2004-09-09
title=NASA Airborne Observatory Sees Stars For First Time
publisher=SOFIA Science Center
url=http://www.sofia.usra.edu/News/news_2004/09-09-04_Observatory_Sees_Stars.html | accessdate=2008-07-23 ]

In February 2006, following delays, and costs which increased from US$185 million to $330 million, [cite web
url=http://space.newscientist.com/article/dn8712-nasa-leaves-jumbojet-telescope-on-the-runway.html
work=NewScientist.com news service
title=NASA leaves jumbo-jet telescope on the runway
date=2006-02-13 | first=Maggie | last=McKee] ,NASA placed the project "under review" and suspended funding. On the 15 June 2006, SOFIA passed the review when NASA concluded that there were no insurmountable technical or programmatic challenges to the continued development of SOFIA. [cite web
url=http://www.nasa.gov/home/hqnews/2006/jun/HQ_06240_SOFIA_update.html
title=NASA Astronomical Observatory Passes Hurdle
date=2006-06-15 NASA Headquarters press release 06-240] [cite web
url=http://www.space.com/spacenews/archive06/Sofia_052906.html
work=Space News Business Report
title=NASA Expected To Save SOFIA
first=Brian | last=Berger | date=2006-05-30 ]

The first school children to see it were students from Waco Montessori School.Fact|date=July 2008

The maiden flight of SOFIA took place on 26 April 2007 at the L-3 Integrated Systems' (L-3 IS) Waco, Texas facility. [cite news
last=Martin | first=Lance
coauthors=Backman, Dana | date=2007-04-26
title=SOFIA Airborne Observatory Completes First Test Flight
publisher=SOFIA Science Center
url=http://www.sofia.usra.edu/News/news_2007/04_26_07/
accessdate=2008-07-23] After a brief test program was conducted in Waco to partially expand the flight envelope and perform post-maintenance checks, the aircraft was moved to Edwards Air Force Base on May 31, 2007. The first phase of loads and flight testing was used to check the aircraft characteristics with the external telescope cavity door closed. This phase was successfully completed by January,2008 at NASA-Dryden F.R.C.cite news
last=Hautaluoma | first=Grey | coauthors=Hagenauer, Beth
title=SOFIA Completes Closed-Door Test Flights
date=2008-01-16 | publisher=NASA
url=http://www.nasa.gov/home/hqnews/2008/jan/HQ_08010_SOFIA_Flight_Series_End.html
accessdate=2008-07-23 ]

In late 2008, the aircraft will undergo flight tests at high altitude cruising speed with the telescope door open. This test phase is scheduled to run through the middle of 2009, after which SOFIA will begin limited science observation flights. Normal science observation flights should begin in 2011 and the observatory is slated for full capability by 2014.

Scientific research

The primary science objectives of SOFIA are to study the composition of planetary atmospheres and surfaces; to investigate the structure, evolution and composition of
comets; to determine the physics and chemistry of the interstellar medium; and to explore the formation of stars and other stellar objects.

References

External links

* [http://www.sofia.usra.edu/ USRA SOFIA website]
* [http://solarsystem.nasa.gov/missions/profile.cfm?MCode=SOFIA SOFIA Mission Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://solarsystem.dlr.de/Missions/SOFIA/ SOFIA Website des DLR] (de)
* [http://antwrp.gsfc.nasa.gov/apod/ap060225.html SOFIA on Astronomy Picture of the Day]
* [http://www.l-3com.com/ L-3 Communications Integrated Systems]
* [http://www.evergreenairlines.com/EIA/index.html Evergreen International Airlines]

See also

* Kuiper Airborne Observatory
* Infrared astronomy
* Far infrared astronomy