The right space and time

World-renowned NASA physicist Edward C. Stone speaks during his 2017 Winter Enrichment Program keynote address. Photo by Lilit Hovhannisyan

Renowned California Institute of Technology (Caltech) physicist Edward C. Stone gave a keynote address on January 9 at KAUST as part of the eighth annual Winter Enrichment Program (WEP). As the project scientist for NASA’s unmanned Voyager Mission since 1972 at the Jet Propulsion Laboratory (JPL), Stone shared insights into his career and the evolution of space exploration.

As a graduate student at the University of Chicago during the 1950s, Stone was originally focused on becoming a nuclear physicist, but as the Space Age dawned with the launch of Sputnik in 1957, he found a new calling.

“Fortunately I was there at the beginning, and I was able to build an instrument to launch into space in 1961, and then from that I moved to Caltech, where I’ve been now for over 50 years,” Stone said.

He originally joined Caltech as a researcher and became a full faculty member in 1967. In 1972, Stone became the project scientist for JPL’s Voyager Mission, which is run by Caltech. Stone was also the director of JPL from 1991 to 2001.

An engineering challenge for the ages

This crescent view of Jupiter was taken by NASA Voyager 1 on March 24, 1979. Courtesy of NASA/JPL.​

The Voyager missions (1 and 2) were the first fully automated and totally computer-controlled spacecrafts. Astonishingly, their computers have around 4,000 words of memory—minuscule by today's standards.

“Your smartphone has 240,000 times more memory than all the computers that the Voyager crafts have,” he told the WEP audience.

With the technology of the time, Ed Stone’s Voyager team aimed to coordinate a scientific study of Jupiter, Saturn, Uranus and Neptune. A clever solution to achieve this engineering feat came from an unlikely source. In 1965, a Caltech graduate student who was working at JPL for the summer was given the task of looking for opportunities for a craft to fly by a planet.

“It turned out that what the research intern had discovered was that in 1977, a spacecraft could fly by Jupiter, on to Saturn, on to Uranus and then finally on to Neptune all in that order. Once in every 176 years, they are all together on the same side of the sun, so that became the urgency in creating a new kind of spacecraft that could actually go this far and deep into space,” Stone explained.

1977 was also the year when Voyager 1 and Voyager 2 were launched on September 5 and August 20, respectively. The Voyager missions went to Jupiter, Saturn, Uranus and Neptune from 1977 to 1989.

“After that, we continued on what’s called the Voyager Interstellar mission hoping to get outside the bubble the sun created around itself. That happened in 2012. Voyager 1 is now in interstellar space, the space between the stars,” Stone added.

Former Director of the Jet Propulsion Laboratories at Caltech, Edward C. Stone, talks about the exploration of Neptune's moon Triton, made possible by a flyby conducted as part of the Voyager 2 mission.​ Photo by Lilit Hovhannisyan​​​

Dimming messages

Another consideration when planning the deployment of the Voyager crafts was how to power them. Solar energy wasn’t an option because the sun's rays become much too dim once the Voyagers get very far away from the sun. Instead, the natural radioactive decay of plutonium-238, which creates heat used as a source of energy, was used. Because of its radioactive decay, it means that there is less and less energy to power the craft with each passing year.

The JPL team turns off 4 watts at a time every year. Based on this accumulated loss of 4 watts per year, it’s estimated they’ll have enough electrical power to run for another 10 years with the instruments JPL has. After that, it will become necessary to turn off the instruments one-by-one. According to estimates the will no longer hear transmissions from the Voyager crafts around 2030.

Current learning and future hopes

During the course of their exploratory journey, the Voyager crafts have revealed many exciting new findings.

“Time after time, our view of the solar system has expanded since Voyager,” Stone said. “The first big surprise was that the moon of Jupiter, called Io, has 10 times the volcanic activity of Earth. Before that, the only known active volcanoes were on Earth, and here was a small moon with 10 times as much. That was a big surprise."

Although the Voyagers will no longer be transmitting within the next 15 years, they will continue in their journey. The JPL team has inserted phonograph records known as the Voyager Golden Records aboard both Voyager spacecrafts containing selected sounds and images from Earth’s diverse cultures and civilizations. Those records are intended for any intelligent extraterrestrial life form that may one day find them.

“The big question is: Is there life out there? The impact of finding microbial life elsewhere in the universe would be enormous,” said Stone.

- By Meres J. Weche, KAUST News