NASA's Voyager 1 to Make History as First Human-Made Object to Reach One Light-Day

Voyager 1 is expected to be approximately 16.09 billion miles (25.89 billion kilometres) from Earth when it reaches the milestone at 5:16 am EST (3:46 pm IST) on November 18. A light-day represents the distance light travels in 24 hours, approximately 16.09 billion miles (25.9 billion kilometres).

Launched on September 5, 1977, Voyager 1 has been travelling through space for nearly 50 years. Originally dispatched to study Jupiter and Saturn, the spacecraft crossed into interstellar space in August 2012 and has continued transmitting scientific data to Earth.

The milestone will significantly extend the communication delay between the spacecraft and NASA's mission controllers. A radio signal sent from Earth will take approximately 24 hours to reach Voyager 1, and its response will take another 24 hours to return.

“If you want to say 'hello' to Voyager, you send your message and then you go home and you wait two days before you finally get a response,” Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL), said.

The achievement comes just weeks after NASA briefly lost contact with Voyager 1. The agency's Deep Space Network failed to detect signals from the spacecraft during two scheduled communication attempts on October 18 and 19.

Communication was restored on October 20 without engineers having to transmit troubleshooting commands. An investigation revealed that one group of the spacecraft's thrusters had gone offline, triggering its onboard fault protection system. The system automatically activated backup thrusters to maintain the spacecraft's operations.

The exact cause of the incident remains under investigation.

“This is the first time we've seen the spacecraft do something like this, but we are also at a point in the mission where we have to expect the unexpected,” Kareem Badaruddin, Voyager mission manager at JPL, said.

Voyager 1 is currently travelling at approximately 38,000 miles per hour (61,155 kilometres per hour), continuing its journey despite ageing systems and a declining power supply.

The spacecraft relies on radioisotope thermoelectric generators, which convert heat produced by decaying plutonium into electricity. Both Voyager spacecraft lose around four watts of power each year as their plutonium supply declines.

To extend the mission's operational life, NASA engineers completed a power-saving operation in September, switching off three devices aboard Voyager 1 and replacing them with lower-power alternatives.

The operation, known as the 'Big Bang', is expected to help keep the spacecraft's remaining science instruments operational for longer. Without these changes, NASA would have needed to switch off another instrument as early as summer 2027.

Voyager 1 was originally launched with 10 science instruments, several of which have been switched off over the years to conserve power. Despite these limitations, the spacecraft continues to operate in interstellar space, the region beyond the heliosphere, the bubble of particles and magnetic fields generated by the Sun.

It remains the most distant human-made object from Earth. Along with Voyager 2, it is also the only spacecraft to have directly studied the interstellar environment.

Reaching the one-light-day distance will mark another major distance record for Voyager 1, highlighting the continued operation of a nearly five-decade-old spacecraft as it explores the region beyond the Sun's influence.