The NASA New Horizons spacecraft is less than a day away from Pluto, having received final commands for its close encounter Tuesday with the dwarf planet, which is rapidly revealing itself as a dynamic, geologically complex little world.
An image released over the weekend showed what scientists said were linear features that might be cliffs, as well as what appeared to be a large impact crater. Meanwhile, images of Charon, Pluto’s unusually large moon, showed a gash in the surface larger than the Grand Canyon.
The speedy spacecraft is on track to pass about 7,800 miles from Pluto at 7:50 a.m. Eastern time Tuesday — or, to be NASA-precise, at 7:49:58.
Whatever New Horizons does at this point, it’ll do on its own. Pluto is 3 billion miles from Earth, and New Horizons can’t be joy-sticked from Mission Operations at the Johns Hopkins University Applied Physics Laboratory. A one-way message to New Horizon takes 4.5 hours even at the speed of light.
That means the spacecraft is flying autonomously, going through an elaborate set of pre-programmed maneuvers in which it will pivot and whirl its way through the Pluto system, studying not only the dwarf planet but three of its moons, including Charon.
The spacecraft doesn’t have to be absolutely perfect in these maneuvers, but it has to be very good. The mission designers have built in some redundancy, with multiple observations and some slight wiggle room on the timing.
But New Horizons, launched in 2006, doesn’t have the computing power to correct itself if it’s aiming in the wrong direction. One inevitable feature of exploring the outer solar system is that the technology is relatively ancient by the time the spacecraft gets there.
“In some ways, these are technologies from the ’90s,” project manager Glen Fountain of APL told reporters assembled at the media center of the laboratory.
This is a one-shot deal, with time so precious that for nearly 22 hours, from late Monday to late Tuesday, New Horizons won’t communicate with Earth. The team on Earth will receive its last bulletin from the spacecraft at 11:17 p.m. Monday. Then everyone will wait, and hope.
The antenna on board is rigid, meaning the whole spacecraft has to turn to Earth to send a message. The team has decided to let that be Pluto-observation time even if that means everyone at Mission Operations is left in a state of suspense.
The team on Earth won’t know if the spacecraft is healthy until 8:53 p.m. Eastern time Tuesday, when Mission Operations expects to receive a brief bulletin, relayed from a huge radio dish in Madrid,with basic information about spacecraft operations. That is the moment everyone will be waiting for.
Silence would be distressing, though mission operations manager Alice Bowman said that wouldn’t necessarily mean that something had gone disastrously wrong. There are benign reasons the radio link might not work, and the team would listen in again eight hours later. In the meantime, New Horizons would be continuing with its intensive examination of the Pluto system.
“We’re out there on the frontier. You know?” Bowman said. “Things can happen. And things do happen. And we have to be prepared for that. If we don’t get the signal, then eight hours later we should have another opportunity to get that signal.”
The team has already endured a July 4 weekend scare when the spacecraft’s workhorse computer became overloaded and forced the spacecraft to hunker down for three days in a “safe mode” with the backup computer in charge. The spacecraft went into a controlled spin initially, a configuration that would have made the main scientific objectives impossible. On Tuesday, three days after the computer glitch, the team managed to get the spaceship prepared anew for the encounter.
But that has also left the team in a conservative mood, with Fountain saying Sunday he didn’t want to send any commands to the spacecraft that weren’t absolutely essential.
“Any time you send anything to the spacecraft, there’s some chance something may go wrong, however small,” he said.
He wants his team to enjoy the ride, tense though it may be.
“It’s a wonderful time to be alive and to be aware of what’s going on,” Fountain said.