Voyager artist concept. (Credit: NASA/JPL)
In 1981, Voyager 2 embarked on an unparalleled journey across the solar system, aiming to deliver unprecedented images of our outer planet. However, while sailing past Saturn, a potential disaster emerged: Voyager 2’s camera platform began to jam. This damage threatens the mission’s primary goal, because without a functioning camera platform, taking pictures of distant planets is nearly impossible.
The challenges are confusing. Initial suspicions were debris interference, but this seems unlikely given the spacecraft’s meticulous assembly. The focus then shifts to potential lubricant distribution problems. But the main question remains. How do you repair damage to a spaceship more than a billion miles away?
The solution is very simple but not certain. The team chose to “train” the camera platform, slowly shaking the gear train to overcome the problem. But there’s a catch: they won’t know whether their long-range solution works until Voyager 2 approaches Uranus, an encounter five years away.
Apparently, it worked and the spacecraft was able to continue its mission.
Now, decades later, the two Voyager interstellar explorers are again showing signs of old age. Keeping them, and spacecraft like them, operational poses a variety of challenges.
Fixing Problems Billions of Miles Away
Voyager’s recent dilemma sheds light on a classic problem also seen on other spacecraft: the buildup of propellant residue in the propellant inlet tubes of its boosters. Over time, residual amounts accumulate, threatening to clog these tubes.
For communications purposes, thrusters are mostly used to keep the antenna pointed toward Earth. A spaceship can rotate in three directions: up and down, left and right, and around its central axis. The thrusters release and reorient the spacecraft automatically to maintain the antenna’s orientation toward Earth.
NASA’s solution to this latest problem is twofold. First, they increased the spacecraft’s rotation range, reducing the firing frequency of the thrusters. Second, they opted for fewer but longer firings, thereby minimizing propellant flow through the tube.
In 2022, the on-board computer responsible for maintaining the orientation of the Voyager 1 spacecraft with Earth began sending mixed status reports. Months passed before mission engineers could identify the problem. The articulation and attitude control system (AACS) misdirects commands, thereby storing them in computer memory rather than executing them. One of these ignored commands caused the AACS standing report to become jumbled before it was sent to the technician in the field.
The team determined that AACS had entered the wrong mode; however, they cannot determine the underlying cause and therefore cannot confirm whether the problem will recur. To overcome this, engineers must design and upload a patch. But it’s still not a perfect solution. Due to the spacecraft’s age and communications time lag (Voyager 1 and Voyager 2 have traveled more than 15 billion and 12 billion miles from Earth, respectively), there is a risk that the patch could overwrite critical code or have other undesirable effects on spaceship.
“This patch is like an insurance policy that will protect us in the future and help us sustain this investigation as long as possible,” said Suzanne Dodd, JPL’s Voyager project manager. “These are the only spacecraft ever to operate in interstellar space, so the data they send back is invaluable to our understanding of our local universe.”
The Future of Space Conservation and Self-Healing Spacecraft
However, the main challenges for spacecraft billions of miles away are not just physics or software. This is latency in communication. Given the huge distances, commands such as patches could take up to 18 hours to reach Voyager 1 or 2, which is equivalent to the time it would take to provide feedback. Additionally, the ride operates on 1970s technology, which requires modern engineers to think within the constraints of older systems.
While the Voyagers have provided many lessons, they have also hinted at the need for space maintenance in the future.
Newer technology could benefit future spacecraft that can utilize advanced materials that are less susceptible to residue buildup or resistant to the effects of propellants. These materials, born from advanced nanotechnology and polymer research, can significantly extend the life of critical spacecraft components.
One of the important lessons of space exploration is the need for reserves. Future spacecraft designs could include redundant systems, ensuring that if one component fails, another can take over seamlessly. This is especially important for missions where the costs of failure are enormous, both in terms of finances and lost opportunities for discovery.
Incorporating AI and machine learning into spacecraft software could be a breakthrough. Rather than waiting for orders from Earth, spacecraft can diagnose problems on their own, adapt to unexpected challenges, and even predict future problems before they arise. Such a proactive system can extend mission duration and improve data quality.
As NASA stated at its 30th Hubble anniversary regarding spacecraft repairs, “From its beginnings with Skylab, to robotic refueling demonstrations on the International Space Station, service, assembly, and manufacturing in space continues to evolve…Once mature and operational, capabilities it promises to usher in a new era of spaceflight and make what was once thought impossible a reality.”
2023-10-24 11:27:30
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