Robotic Exploration: Voyager, Mars Rovers & the Outer Solar System

History of Space Exploration

Chapter 9 · Robotic Exploration: Voyager, Mars Rovers & the Outer Solar System

The earlier chapters mostly followed people. This one follows machines: the two Voyager probes launched in 1977 and the rovers that have driven on Mars. The sources are three reference articles, on the Voyager programme, the Mars rovers and the Opportunity rover. Two of them give different numbers for how long Opportunity ran, and the Voyager figures are dated to 2024, so the chapter marks what is fixed and what is not.

Voyager

Both probes launched in 1977 to exploit a rare planetary alignment occurring "once every 175 years," which enabled gravity-assist trajectories through the outer planets.

	Voyager 2	Voyager 1
Launch order	Launched first	Launched second
Planets flown by	Jupiter, Saturn, Uranus, Neptune	Jupiter and Saturn, on a trajectory optimised for Saturn's moon Titan
Heliopause crossing	5 November 2018	25 August 2012
Distance (2024)	20.4 billion km, 55,000 km/hour	24.5 billion km, 61,000 km/hour

Dates and Distances the Source Does Not Give The article does not give the encounter date for any planet, and it gives the distances "as of 2024," so they are already out of date. I did not find the launch dates or the names of the instruments, so the chapter does not state them. I also did not find how "interstellar space" is defined for the crossings. The source uses the heliopause, and I do not define it.

The Golden Record

Each probe carries a 12-inch golden phonograph record with "pictures and sounds of Earth" selected by a committee chaired by Carl Sagan.

Pale Blue Dot

Voyager 1 photographed Earth on 14 February 1990 from 6 billion kilometres away, an image later popularised by Sagan.

Power

Power has declined from about 470 W at launch to about 268 W by 2011. Communications are expected through 2036, though "additional science instruments may need to be turned off." Both have adequate power and propellant through at least 2026.

Machines Outlasting Their Plan Voyager 1 crossed the heliopause 35 years after launch. The source does not say what the original mission length was, so I cannot state how far the probes exceeded it. The Opportunity rover, below, has a stated plan to compare.

Mars Rovers

Rover	Dates	What the source says
Sojourner	4 July to 27 September 1997	Communications lost 27 September. Just over 100 metres driven.
Spirit	4 January 2004 to 22 March 2010	Exceeded the original mission by nearly six years and drove 7.73 km. "Its wheels became trapped in sand." NASA ceased reactivation attempts on 25 May 2011.
Opportunity	25 January 2004 to 10 June 2018	45.16 km driven. Last status came when a global dust storm blocked sunlight. The mission was declared complete on 13 February 2019.
Curiosity	6 August 2012, operational as of September 2026	"Still operational."
Perseverance	18 February 2021, operational as of September 2026	Carried the helicopter Ingenuity, whose mission ended.
Zhurong	22 May 2021 to 20 May 2022	1,921 metres driven. Deactivated because of approaching sandstorms and the Martian winter, and dust buildup prevented reactivation.

Perseverance carries samples cached for future Mars sample-return missions, advancing NASA's objectives for evidence of habitability and organic carbon. The source does not say whether any sample-return mission has been funded, and I did not find out.

Opportunity in Detail

Opportunity landed on 25 January 2004 in Eagle crater, Meridiani Planum. It was planned for 90 sols (about 92.5 Earth days). Its rover article calls its longevity record 5,352 sols (15 Earth years), and its own article says it operated 5,111 sols (14 years, 138 Earth days), roughly 57 times its design specification.

Two Durations The two articles disagree: 5,352 sols against 5,111. The difference is 241 sols, or roughly eight Earth months, and neither article explains it. One possibility is that they count different end dates, but the sources do not say, and I have not checked. The 57-times figure matches 5,111 divided by 90, which is 56.8, so I treat 5,111 as the consistent one, though that is my arithmetic, not a source's choice. Of the two Earth-time figures, 14 years 138 days from January 2004 does reach June 2018, which fits the last-contact date. So the "15 years" is a rounding or a different end point.

Water, and the End

The rover found "hematite and past presence of water on the surface of Mars" through regolith and rock sampling, and discovered meteorites and investigated mineral compositions suggesting ancient water-related geologic processes. A massive dust storm struck Mars in early June 2018, reducing solar power. Last contact was on 10 June 2018, and NASA declared the mission complete on 13 February 2019 after over 1,000 unsuccessful recovery signals.

"My Battery Is Low" A popular line says Opportunity's last message was "My battery is low and it's getting dark." The source says the journalist Jacob Margolis tweeted an interpretive translation of the final telemetry, and that this was not a message Opportunity sent. Margolis later clarified that he had "poetically" rephrased NASA officials' interpretations of the rover's low power and atmospheric opacity, "never to imply the rover had sent the specific words." The line is an interpretation of data, and the machine did not write it.

What I Did Not Verify I did not find the science of Voyager's planetary encounters, the design of the Golden Record's contents, how Curiosity and Perseverance work, Ingenuity's flights, the reasons for Sojourner's loss, or any robotic missions beyond these (Cassini, New Horizons, the Moon, Venus, asteroids). The chapter also does not verify the "as of September 2026" status of two rovers against a live source. It reports two probes and six rovers.

Hands-On Exercises

Exercise 1

Make a table of the six rovers with landing year, end or status, and one fact, using only the chapter, and mark which entries are only "as of" a date.

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Exercise 2

A student writes "Opportunity's last message was 'My battery is low and it's getting dark.'" Correct it using the chapter.

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Exercise 3

Explain how you would handle the two figures for Opportunity's operating time in a piece of writing.

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Quick Reference

Voyager: both launched 1977; Voyager 2 flew by four planets, Voyager 1 two; heliopause crossings 25 August 2012 and 5 November 2018; Golden Record; Pale Blue Dot 14 February 1990
Rovers: Sojourner 1997; Spirit and Opportunity 2004; Curiosity 2012; Perseverance and Zhurong 2021
Opportunity: planned 90 sols; ran 5,111 sols by one article and 5,352 by another; 45.16 km; last contact 10 June 2018
Myth: "My battery is low" was a journalist's paraphrase
Not covered: Cassini, New Horizons, the science