A coming Voyager 1 milestone puts radio delays in perspective
· BehindLines newsroom
NASA is drawing attention to the next milestone in Voyager 1’s journey: according to its light-day page, the spacecraft is expected to be one light-day from Earth on November 18. In its skywatching guide published November 2, the agency highlighted this anticipated point for the most distant human-made object ever sent into space. That distance is about 25.9 billion kilometers.
A light-day is a measure of distance: how far light travels in twenty-four hours. Radio communications follow the same rule. At that distance, a command sent from Earth will take about one day to reach Voyager 1. The return signal will take just as long: radio propagation will therefore take about two days for a round trip, with processing and scheduling delays possibly adding more time.
Launched in 1977, Voyager 1 is already traveling through interstellar space. It crossed the heliopause in 2012, the boundary of the region dominated by the solar wind. November’s milestone measures how far it is from Earth.
To keep its observations going, engineers must manage a declining supply of electrical power. In early September, they switched off three devices and activated three lower-power alternatives. The changes had to happen at the same time to preserve the distribution of heat. According to NASA’s October 29 update, these energy savings are intended to keep the science instruments operating longer.
The mission remains vulnerable to incidents. NASA’s communications network did not detect Voyager 1’s signal during two scheduled contact sessions on October 18 and 19. The signal reappeared on October 20. Engineers found that the spacecraft had automatically switched to backup thrusters; the cause of the interruption was still being investigated in that update.
In its November guide, NASA also links the milestone to a public participation activity. That event is separate from the crossing, which remains a forecast. As the mission approaches its fiftieth anniversary, it makes one constraint of distant exploration easy to grasp: information travels fast, but a round trip can take about two days.