As the sun rose on Friday over the lunar plateau where India’s Vikram lander and Pragyan rover sit, the robotic explorers remained silent.
The Indian Space Research Organization, India’s equivalent of NASA, said on Friday that mission controllers on the ground had sent a wake-up message to Vikram.
The lander, as expected, did not reply. Efforts will continue over the next few days, but this could well be the conclusion of Chandrayaan-3, India’s first successful space mission to the surface of another world.
India is only the fourth country to complete an intact landing on the moon, after the United States, the Soviet Union and China. Vikram, which arrived a month ago, was also the first spacecraft to set down in the moon’s south polar region, which has become an area of intense scientific curiosity in recent years.
Soon after landing, the small rover, Pragyan, rolled down a ramp and started driving around. Over the next week and a half, as the sun moved across the sky, the two solar-powered spacecraft studied their surroundings, measuring underground temperatures, identifying elements in the lunar soil and listening for moonquakes.
As the sun began to set, ISRO officials sent commands to put Vikram and Pragyan to sleep. Their batteries were fully charged, and Pragyan’s solar panels were pointed to where the sun would rise again.
The hope was that when sunlight again warmed the solar panels, the spacecraft would recharge and revive. But that was wishful thinking. Neither Vikram nor Pragyan were designed to survive a long, frigid lunar night when temperatures plunge to more than a hundred degrees below zero, far colder than the electronic components were designed for. The spacecraft designers could have added heaters or used more resilient components, but that would have added cost, weight and complexity.
Even if the spacecraft do not revive, the mission, named Chandrayaan-3, was a success for ISRO, assuaging the disappointment of four years ago when its first attempt to land on the moon ended in a crash during the Chandrayaan-2 mission.
Undeterred, ISRO built a copy of the failed lander — fixing shortcomings in the original design — and tried again. This time, on Aug. 23, the landing proceeded without a glitch. With Prime Minister Narendra Modi watching via a video link, the control room erupted in cheers when Vikram’s safe arrival was confirmed.
“Chandrayaan-3’s triumph mirrors the aspirations and capabilities of 1.4 billion Indians,” Mr. Modi said afterward, describing the event as “the moment for new, developing India.”
The mission’s science observations included a temperature probe deployed from Vikram that pushed into the lunar soil. The probe recorded a sharp drop, from about 120 degrees Fahrenheit at the surface to 10 degrees just three inches down. Lunar soil is a poor conductor of heat.
The poor heat conduction could be a boon for future astronauts; an underground outpost would be well-insulated from the enormous temperature swings at the surface.
Another instrument on Vikram, a seismometer, detected on Aug. 26 what appeared to be a moonquake.
Pragyan traveled more than 300 feet in all. As it drove around, it fired laser pulses into rocks and soil, allowing it to identify elements based on colors of light emitted from the vaporized material. The instrument confirmed the presence of elements such as aluminum, calcium, iron and titanium. In a bit of a surprise, it also found sulfur.
Traces of sulfur have been measured in lunar soil and rock samples brought back to Earth by NASA’s Apollo astronauts and Soviet robotic spacecraft decades ago. The Pragyan measurement suggests that concentrations of sulfur might be higher in the polar regions. Sulfur is a useful element in technologies like solar cells and batteries, as well as in fertilizer and concrete.
Before it went to sleep earlier this month, Vikram made a small final move, firing its engines to rise about 16 inches above the surface before softly landing again. The hop shifted Vikram’s position by 12 to 16 inches, ISRO said.
“Hoping for a successful awakening for another set of assignments!” ISRO posted on X, the social network formerly known as Twitter, on Sept. 2. “Else, it will forever stay there as India’s lunar ambassador.”