You’ve probably heard a lot about the New Horizons probe lately, and there’s a good reason for that. Tomorrow, July 14, the probe will fulfill its destiny. After nine and a half years of travel, it will zip past Pluto, madly taking photos and measurements as it goes.
And then—fwoosh!—it will keep going into the depths of space, leaving Pluto behind. The probe will continue its studies of the dwarf planet and its moons, but July 14 is the closest approach. After that, they’re in the rearview mirror.
The first thing any critical person asks when they read that is, “One day of payoff after 9.5 years of travel? Why not drop into orbit and stay there, like Cassini?”
Good question. The first answer is: physics. But the real answer is money.
Here’s the physics part: braking a fast-moving probe—and by fast, I mean “traveling at 32,000 mph”—takes a lot of fuel. You have to rotate it in place and fire thrusters against the direction of travel. Given the speed that must be overcome, that’s a lot of thruster use and a lot of fuel. After braking is accomplished, completing course corrections and maneuvers for orbital insertion takes more fuel.
The money part: launching a probe carrying a big load of fuel is much more expensive than launching a probe carrying a minimum load of fuel. That stuff is heavy. It costs a lot to get it off the ground and into space. And NASA has never been the budgetary favorite of the US Congress.
The New Horizons team had limited funds, so it had to make the same choice that most probe teams are forced to make: give up speed, or give up the duration of study. Now, if you’re studying Mercury or Mars, giving up speed is a good option. They’re not that far away; you can wait a few more months.
But Pluto is way, way, way out there. Several billion kilometers out. Had the New Horizons folks decided to fly slower in order to conserve fuel for braking and an orbital insertion, they might have been retiring by the time the probe arrived.
And that’s why the world’s astronomy geeks are so excited about tomorrow. After 9.5 years, tomorrow is the Big Day.
Now then: imagine you’re on the New Horizons team, and you’ve been waiting since January 2006 for your probe to make its Pluto flyby. And then, ten days before the big event…the probe goes dark. Zzzt. No data, no connection, nothing. For all you know, it hit an asteroid and went kablooey.
That is exactly what happened to these poor scientists. Suddenly, anticipation turned to terror. Their probe was 4.5 hours away for communications purposes. Every command they sent, every query they tried, would take 4.5 hours to arrive at the probe. The probe’s response would take 4.5 hours to come back. The team had a nine-hour lag time for their repair efforts, and a ten-day deadline. If they couldn’t find and fix the problem in that time, then nine and a half years of waiting was down the toilet.
It was, as the mission leader later said, their “Apollo 13” moment. Everyone raced to the office and went into crisis mode, and nobody left until it was resolved. The Mission Operations manager slept on the floor of her office two nights in a row.
The official statement given at a press conference during the crisis was that this was an “anomaly” and a mere “speed bump.” In reality, they were all sweating bullets. But they figured it out. The details of exactly what happened, and how the team debugged their probe’s computer from three billion miles away, makes a great story that you can read at the Washington Post.
Although July 14 is the closest approach, that’s not when the scientists will get their data. New Horizons can only transmit at about one kilobit per second, so it will have to store up its data and trickle it back to Earth over the next two or three months. It will be like a never-ending Christmas.
After whizzing past Pluto, New Horizons will head deeper into the Kuiper Belt to examine one or two of the icy bodies out there. All of this data, from Pluto and any other Kuiper Belt object, is brand new stuff to us. We know next to nothing about this distant region of our solar system.
When New Horizons launched, Pluto was still a planet. The decision to downgrade it to “dwarf planet” occurred eight months after launch—and was made by just 424 astronomers who had stayed for the last day of a meeting of the International Astronomical Union (IAU) in Prague.
New Horizon’s mission leader was quoted as saying, “I’m embarrassed for astronomy. Less than 5 percent of the world’s astronomers voted. This definition stinks, for technical reasons.”
He expected the astronomy community to overturn the decision. He’s still waiting.
When New Horizons launched, there was no such thing as an iPhone. The first iPhone didn’t come out until a year and a half later. That’s how long the little probe has been traveling…and it all comes to fruition tomorrow.