Science in the news Voyager s 11 billion mile journey

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1 Name:... Date:... Read the article from The Week magazine Voyager s 11 billion mile journey. The Voyager 1 spacecraft was launched on the 5 th September Together with Voyager 2, which was launched on the 20 th August 1977, they were designed to conduct close-up studies of Jupiter and Saturn and were built to last 5 years. When the article was published on the 30 th March 2013 they were still going and about to leave the solar system. Answer the following questions: 1. a. How far had Voyager 1 travelled since it was launched? 1. b. Calculate the average speed of the spacecraft in km/s. (1 mile = 1.6 km) The Voyager mission took advantage of the geometric arrangement of the planets in the late 1970 s and the 1980 s. This arrangement of Jupiter, Saturn, Uranus and Neptune shown below only occurs every 175 years and it allowed the spacecraft to accomplish the four planet tour in the minimum amount of time. Image adapted from image courtesy NASA/JPL-Caltech Page 1 of 6

2 2. a. Which planets did Voyager 1 visit? b. Voyager 2 visited all four planets; draw its path on the diagram. c. What do you notice about the Voyager launch dates and their journeys? Why are their flight paths so different? 3. Using data from the table below explain why this arrangement of Jupiter, Saturn, Uranus and Neptune rarely occurs. Jupiter Saturn Uranus Neptune Orbital period (Earth years) What was the advantage of launching Voyager when the planets were in this arrangement? The voyager spacecraft are equipped to carry out 10 different experiments. The results of the experiments are sent back to Earth using a spacecraft radio. Radio waves travel at the speed of light (approx m/sec). In 2013 Voyager 1 is approximately km from Earth and getting further away all of the time. 5. How long does it take a radio transmission of data from Voyager 1 to reach the Earth? Page 2 of 6

3 Voyager spacecraft cannot use solar panels for producing electricity for the on-board systems in the same way as satellites orbiting the Earth. 6. Explain why Solar panels cannot be used on the voyager missions Instead, each of the spacecraft is powered by a radioisotope thermoelectric generator (RTG) that converts heat produced by the natural radioactive decay of plutonium to electricity. 7. How do you think the electricity is used aboard the spacecraft? Page 3 of 6

4 Much of what we know about the outer planets and their moons is as a result of the Voyager missions since the data would have been impossible to collect from Earth. Now Voyager is beginning to leave our solar system and it is sending back data from interstellar space. Some of the instruments have had to be turned off to save power. However, there are some instruments that will continue to send back data for perhaps another 30 years. 8. Why do you think it has been necessary to save power? The Voyager spacecraft are carrying a number of objects that were thought to be representative of humanity in Looking at the article, which items would you include from the original inventory if a similar mission were launched today? What other items might you include to make them more relevant today? (Source: Page 4 of 6

5 Teaching notes and answers The resource is based around the article Voyager s 11 billion mile journey from p.19 of The Week magazine (issue 913, 30 March 2013). The magazine page can be downloaded from For further background information go to voyager.jpl.nasa.gov (weblink available at time of publication). Answers 1 a) 11 billion miles b) 11 billion miles x 1.6 = 17.6 billion km = km 36 years = 36 x x 24 x 60 x60 s = s speed = distance time = km s = 15.5 km/s 2 a) Jupiter and Saturn b) Image courtesy NASA/JPL-Caltech c) Voyager 2 was launched 2 weeks before Voyager 1. Voyager 1 reached Jupiter and Saturn before Voyager 2. Voyager 2 took full advantage of the unusual alignment of the planets and had a trajectory that enabled it to reach all 4 planets even though it was slower Page 5 of 6

6 Cont. 3. Each planet has a different length of orbit. Taking Jupiter and Saturn as examples, Jupiter completes roughly 2.5 orbits for each orbit of Saturn. If Jupiter and Saturn start at a position in line and on the same side from the Sun, by the time Saturn has completed one orbit, Jupiter will be on the opposite side of the Sun. 4. This arrangement allows Voyager to swing from one planet to the next without the need of large on-board propulsion systems. The flyby of each planet increases its velocity enough to deliver it to its next destination and also decreases journey times. 5. Time = distance speed Ensure that all data is in the same units. Time = m m/sec = seconds (just over 17 hours) 6. Voyager travels too far away from the Sun and there will be insufficient light energy for the solar panels to produce enough electricity. 7. The electricity powers the spacecraft instruments, computers, radio and other systems. 8. The instruments rely on a generator using plutonium as its fuel source. Plutonium decays and releases heat energy and has a half-life of 87.7 years ( 238 Pu). In other words after 87.7 years half of the Plutonium will have decayed and the efficiency of the battery will be at half of its original value. This is not enough to power all of the instruments. 9. Pupils own answers. This provides a good opportunity to discuss the immense technological advances since Page 6 of 6