SOLRAD 7A

Key takeaways

SOLRAD 7A belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SOLRAD 7A to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SOLRAD 7A from memory before moving on to harder problems.

Reference excerpt

SOLRAD 7A was the seventh solar X-ray monitoring satellite in the SOLRAD series, and the fourth to successfully orbit the Earth. It was boosted into orbit along with four other military satellites atop a Thor Augmented Delta-Agena D rocket on January 11, 1964. Data returned by SOLRAD 7A dramatically revised scientific models of the solar corona.

History The SOLRAD science satellite program was conceived in 1958 to observe the Sun in the X-ray spectrum. It was quickly combined, to provide civilian cover (launches being unclassified at that time), with the concurrently conceived United States Naval Research Laboratory's GRAB satellite project, which would collect information on foreign radars and communications installations. There were five SOLRAD/GRAB missions between 1960 and 1962, with the scientific SOLRAD experiments sharing satellite space with GRAB's intelligence payload. Two of the missions were successful. In 1962, all U.S. overhead reconnaissance projects were consolidated under the National Reconnaissance Office (NRO), which elected to continue and expand the GRAB mission starting July 1962 with a next-generation set of satellites, code-named POPPY. With the initiation of POPPY, SOLRAD experiments would no longer be carried on electronic spy satellites; rather, they would now get their own satellites, launched alongside POPPY missions to provide some measure of mission cover. The first POPPY mission was launched on December 13, 1962, along with several other satellites on a mission similar to that of SOLRAD 3, complete with an Injun (satellite) ionospheric research satellite. The mission was successful, despite POPPY 1's elliptical (rather than the planned circular) orbit, and data was returned for 28 months. No SOLRAD was launched concurrent with this first POPPY mission. SOLRAD 6, the first of the second-generation SOLRADs, was launched alongside POPPY 2 on June 15, 1963, but decayed into the atmosphere on August 1, 1963, returning little data.

Spacecraft SOLRAD 7A was equipped with ionization chambers to monitor solar X-Rays in the wavelength ranges of 1–8 Å, 8–12 Å, and 44–60 Å. This satellite contained five X-ray photometers, four UV photometers, and two systems to accurately determine the solar aspect angle. Its purposes were to monitor the soft component of solar X-rays (2 to 60 Å) and the low-frequency portion of the solar hydrogen Lyman-alpha emission spectrum (1225 to 1350 Å), and to transmit measurements back to Earth.

Mission and results Launched on January 11, 1964, along with four other spacecraft aboard a Thor Augmented Delta-Agena D, (including POPPY 3, an electronic signals intelligence (ELINT) surveillance package) its orbit was nearly circular at 900 kilometers (560 mi). SOLRAD 7A's spin axis was roughly perpendicular to the Sun-satellite direction with an initial spin rate of about two revolutions per second; however, the magnetic brooms produced varying torques by interacting with the Earth's magnetic field resulting in a slow precession of the spin axis. SOLRAD 7A transmitted data in real time on 136 MHz, providing 10 to 20 minutes of data at a pass to ground stations. The satellite's 44- to 55-Å and 8- to 16-Å detectors both failed soon after launch, but data was continuously returned from its other instruments until September 1964. Sporadic data were received until February 1965. In addition to the intended recipients, several European observatories successfully recorded the telemetry. Dubbed "SOLRAD 6" by several sources, the satellite reported comparatively low solar X-ray emission levels during its time in orbit. After February 5, 1965, no usable data were obtained from the satellite, although it continued operating until July 1966. From SOLRAD 7A data, it was concluded that the X-ray region of the solar corona was a series of small cells that flared and decayed rapidly, emitting hard X-rays in the process. This dramatically change previous models: Earthbound telescopes had only been able to detect the very hot, flashing gas those cells created, the net result making the corona seem a homogeneous region extending 1,000,000 miles (1,609,344 km) from the Sun. The operational period of the satellite allowed it to contribute to the International Quiet Solar Year, an international scientific program mounted to gather information about the Sun during the nadir of its 11-year luminosity cycle (Jan. 1, 1964, through Dec. 31, 1965). SOLRAD 7A data indicated that the Sun's X-ray output was at a minimum during May, June and July 1964.

Legacy and status The satellite is still in orbit and its position can be tracked online. COSPAR satellite ID: 1964-001D

Worked examples

Example 1 — a first encounter with SOLRAD 7A

Start with the simplest possible case. Write down what SOLRAD 7A claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 SOLRAD 7A 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 SOLRAD 7A 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 SOLRAD 7A

In research: SOLRAD 7A appears in science 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 SOLRAD 7A 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: SOLRAD 7A is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1964 in spaceflight, SOLRAD, Satellites of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for SOLRAD 7A 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.

How to study SOLRAD 7A in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SOLRAD 7A 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 SOLRAD 7A out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SOLRAD 7A in simple terms?

SOLRAD 7A was the seventh solar X-ray monitoring satellite in the SOLRAD series, and the fourth to successfully orbit the Earth. It was boosted into orbit along with four other military satellites atop a Thor Augmented Delta-Agena D rocket on January 11, 1964.

Why does SOLRAD 7A matter?

Because it connects several science 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 SOLRAD 7A?

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 SOLRAD 7A.