physics

Solwind

Solwind is a physics 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 Solwind rather than just read about it. In short: P78-1 or Solwind was a United States satellite launched aboard an Atlas F rocket from Vandenberg Air Force Base in California on February 24, 1979. The satellite's mission was extended by several weeks, so that it operated until it was destroyed in orbit on September 13, 1985, to test the ASM-135 ASAT anti-satellite missile.

Key takeaways

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

Reference excerpt

P78-1 or Solwind was a United States satellite launched aboard an Atlas F rocket from Vandenberg Air Force Base in California on February 24, 1979. The satellite's mission was extended by several weeks, so that it operated until it was destroyed in orbit on September 13, 1985, to test the ASM-135 ASAT anti-satellite missile.

Construction and payload The satellite's Orbiting Solar Observatory (OSO) platform included a solar-oriented sail and a rotating wheel section. Ball Aerospace was the primary contractor for design and construction, and provided the attitude control and determination computer programs. The P78-1 carried a gamma-ray spectrometer, a white-light coronagraph, an extreme-ultraviolet imager, an X-ray spectrometer, a high-latitude particle spectrometer, an aerosol monitor, and an X-ray monitor. The X-ray monitor, designated NRL-608 or XMON, was a collaboration between the Naval Research Laboratory and Los Alamos National Laboratory. The white-light coronagraph and the ultraviolet imager were combined in a single package, designated NRL-401 or SOLWIND, which was built by the Naval Research Laboratory. The coronagraph was the flight spare of the white-light coronagraph on the OSO-7 satellite. The ultraviolet imager used a CCD imager, one of the first uses of a CCD in space.

Discovery of comets

P78-1 was the first satellite in space to discover a comet in general and a sungrazing comet in particular. In total, 9 sungrazing comets, all belonging to the Kreutz group, were discovered on images taken by the Solwind coronagraph:

Apart from these yet another comet C/1984 R1 (Solwind) was found by Rainer Kracht, a German amateur astronomer, on 23 July 2005 in Solwind's images of 17 Sep 1984. Its perihelion distance of 0.1051 AU was at least ten times larger than that of the previously found true sungrazers.

Destruction

By 1985, the satellite's batteries were degrading. This caused more and more frequent "under-voltage cutoffs", a condition where the satellite detected a low main bus voltage and automatically shut down all non-vital systems. In addition, the last of the three tape recorders failed in the spring of 1985, so data collection could only occur while the spacecraft was in contact with a ground station. A normal contact lasted only about 15 minutes, so this was a serious impediment. Special arrangements could be made to string several contacts together. As a result of these failures, ever-increasing amounts of time and network resources were spent reconfiguring the satellite for normal operation. Data collection from the few remaining payloads was severely limited. Because of the additional burden on the Air Force Satellite Control Network (e.g., extra support and antenna time at the tracking stations), discussions were already underway to terminate the mission.

This led to the satellite being chosen as a test target for an ASM-135 ASAT anti-satellite missile. The mission was extended for several weeks solely to support the test. During this final phase, the satellite was often allowed to remain in the under-voltage condition for several days at a time. On September 13, 1985, the satellite was destroyed in orbit at 20:43 UTC at 35°N 126°W with an altitude of 525 kilometres (326 mi) by an ASM-135 ASAT launched from a US Air Force F-15 Eagle fighter aircraft. The test resulted in 285 cataloged pieces of orbital debris. 1 piece of debris remained in orbit to at least May 2004, but had deorbited by 2008. The last piece of debris, COSPAR 1979-017GX, SATCAT 16564, deorbited 9 May 2004 according to SATCAT. The test outraged some scientists because although five of P78-1's instruments had failed at the time of the test, two instruments remained in operation, and the satellite was what one solar physicist called "the backbone of coronal research through the last seven years".

Illustrations

Worked examples

Example 1 — a first encounter with Solwind

Start with the simplest possible case. Write down what Solwind claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Solwind 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 Solwind 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 Solwind

In research: Solwind appears in physics 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 Solwind 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: Solwind is common in secondary-school and first-year university syllabi. It links to neighbouring topics Intentionally destroyed artificial satellites, Satellite collisions, Satellites of the United States Air Force, so understanding it makes those chapters shorter.
In everyday life: Look for Solwind 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 Solwind in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Solwind 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.
Explain Solwind out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Solwind in simple terms?

Why does Solwind matter?

Because it connects several physics 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 Solwind?

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 Solwind.