astronomy

Submillimeter Wave Astronomy Satellite

Submillimeter Wave Astronomy Satellite is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Submillimeter Wave Astronomy Satellite rather than just read about it. In short: Submillimeter Wave Astronomy Satellite (SWAS, also Explorer 74 and SMEX-3) is a NASA submillimetre astronomy satellite, and is the fourth spacecraft in the Small Explorer program (SMEX). It was launched on 6 December 1998, at 00:57:54 UTC, from Vandenberg Air Force Base aboard a Pegasus XL launch vehicle.

Key takeaways

Submillimeter Wave Astronomy Satellite belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Submillimeter Wave Astronomy Satellite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Submillimeter Wave Astronomy Satellite from memory before moving on to harder problems.

Reference excerpt

Submillimeter Wave Astronomy Satellite (SWAS, also Explorer 74 and SMEX-3) is a NASA submillimetre astronomy satellite, and is the fourth spacecraft in the Small Explorer program (SMEX). It was launched on 6 December 1998, at 00:57:54 UTC, from Vandenberg Air Force Base aboard a Pegasus XL launch vehicle. The telescope was designed by the Smithsonian Astrophysical Observatory (SAO) and integrated by Ball Aerospace, while the spacecraft was built by NASA's Goddard Space Flight Center (GSFC). The mission's principal investigator is Gary J. Melnick.

History The Submillimeter Wave Astronomy Satellite mission was approved on 1 April 1989. The project began with the Mission Definition Phase, officially starting on 29 September 1989, and running through 31 January 1992. During this time, the mission underwent a conceptual design review on 8 June 1990, and a demonstration of the Schottky receivers and acousto-optical spectrometer concept was performed on 8 November 1991.

Development The mission's Development Phase ran from February 1992, through May 1996. The Submillimeter Wave Telescope underwent a preliminary design review on 13 May 1992, and a critical design review (CDR) on 23 February 1993. Ball Aerospace was responsible for the construction of and integration of components into the telescope. The University of Cologne delivered the acousto-optical spectrometer to Ball for integration into the telescope on 2 December 1993, while Millitech Corporation delivered the Schottky receivers to Ball on 20 June 1994. Ball delivered the finished telescope to Goddard Space Flight Center on 20 December 1994. GSFC, which was responsible for construction of the spacecraft bus, conducted integration of spacecraft and instruments from January through March 1995. Spacecraft qualification and testing took place between 1 April 1995, and 15 December 1995. After this, SWAS was placed into storage until 1 September 1998, when launch preparation was begun.

Mission SWAS was designed to study the chemical composition, energy balance and structure of interstellar clouds, both galactic and extragalactic, and investigate the processes of stellar and planetary formation. Its sole instrument is a telescope operating in the submillimeter wavelengths of far infrared and microwave radiation. The telescope is composed of three main components: a 55 × 71 cm (22 × 28 in) elliptical off-axis Cassegrain reflector with a beam width of 4 arcminutes at operating frequencies, two Schottky diode receivers, and an acousto-optical spectrometer. The system is sensitive to frequencies between 487–557 GHz (538–616 μm), which allows it to focus on the spectral lines of molecular oxygen (O2) at 487.249 GHz; neutral carbon (C i) at 492.161 GHz; isotopic water (H218O) at 548.676 GHz; isotopic carbon monoxide (13CO) at 550.927 GHz; and water (H2O) at 556.936 GHz. Detailed 1° x 1° maps of giant molecular and dark cloud cores are generated from a grid of measurements taken at 3.7 arcminutes spacings. SWAS's submillimeter radiometers are a pair of passively cooled subharmonic Schottky diode receivers, with receiver noise figures of 2500-3000 K. An acousto-optical spectrometer (AOS) was provided by the University of Cologne, in Germany. Outputs of the two SWAS receivers are combined to form a final intermediate frequency, which extends from 1.4 to 2.8 GHz and is dispersed into 1400 1-MHz channels by the AOS. SWAS is designed to make pointed observations stabilized on three axes, with a position accuracy of about 38 arcseconds, and jitter of about 24 arcseconds. Attitude information is obtained from gyroscopes whose drift is corrected via a star tracker. Momentum wheels are used to maneuver the spacecraft.

Experiment

Submillimeter Wave Telescope

The SWAS instrument is a submillimeter-wave telescope that incorporates dual heterodyne radiometers and an acousto-optical spectrometer. SWAS will measure water, molecular oxygen, atomic carbon, and isotopic carbon monoxide spectral line emissions from galactic interstellar clouds in the wavelength range 540-616 micrometres. Such submillimetre wave radiation cannot be detected from the ground because of atmospheric attenuation. The SWAS measurements will provide new information about the physical conditions (density and temperature) and chemistry in star-forming molecular clouds.

Launch The spacecraft was delivered to Orbital Sciences Corporation at Vandenberg Air Force Base on 2 November 1998, for integration onto their Pegasus XL launch vehicle. Launch occurred on 6 December 1998, at 00:57:54 UTC, from Orbital Sciences' Stargazer L-1011 TriStar mothership. Its initial orbit was a near-circular 638 × 651 km (396 × 405 mi) with an inclination of 69.90°. SWAS was originally scheduled to launch in June 1995 but was delayed due to back-to-back launch failures of the Pegasus XL launch vehicle in June 1994 and June 1995. A launch opportunity in January 1997 was again canceled due to a Pegasus XL launch failure in November 1996. The commissioning phase of the mission lasted until 19 December 1998, when the telescope began producing useful science data. The SWAS mission had a planned duration of two years and a cost estimate of US$60 million, but mission extensions allowed for five and a half years of continuous science operations. During this time, data was taken on more than 200 astronomical objects. The decision was made to end science and spacecraft operations on 21 July 2004, at which time the spacecraft was placed into hibernation.

Deep Impact mission To support the Deep Impact mission at comet 9P/Tempel, SWAS was brought out of hibernation on 1 June 2005. Vehicle check-out was completed on 5 June 2005 with no discernible degradation of equipment found. SWAS observations of the comet focused on isotopic water output both before and after the Deep Impact impactor struck the comet's nucleus on 4 July 2005. While water output was found to naturally vary by more than a factor of three during the observation campaign, SWAS data showed that there was no excessive release of water due to the impact event. After three months of observation, SWAS was once again placed into hibernation on 1 September 2005. As of 2023, SWAS remains in Earth orbit on stand-by.

Illustrations

Worked examples

Example 1 — a first encounter with Submillimeter Wave Astronomy Satellite

Start with the simplest possible case. Write down what Submillimeter Wave Astronomy Satellite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Submillimeter Wave Astronomy Satellite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Submillimeter Wave Astronomy Satellite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Submillimeter Wave Astronomy Satellite

In research: Submillimeter Wave Astronomy Satellite appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Submillimeter Wave Astronomy Satellite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Submillimeter Wave Astronomy Satellite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Explorers Program, Satellites orbiting Earth, Space telescopes, so understanding it makes those chapters shorter.
In everyday life: Look for Submillimeter Wave Astronomy Satellite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Submillimeter Wave Astronomy Satellite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Submillimeter Wave Astronomy Satellite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Submillimeter Wave Astronomy Satellite in simple terms?

Why does Submillimeter Wave Astronomy Satellite matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Submillimeter Wave Astronomy Satellite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Submillimeter Wave Astronomy Satellite.