There were plenty of excited scientists at New Horizons’ Mission Control room Wednesday afternoon following the probe’s successful Jupiter flyby, but it was an altogether different story during the planetary pass itself. 

New Horizons made its closest approach by Jupiter at about 12:43 a.m. EST (0543 GMT) Wednesday, but mission controllers at Maryland’s Johns Hopkins University Applied Physics Laboratory had the night off, folks at the operations center tell me. 

“I slept well last night,” New Horizons mission operations manager Alice Bowman told me just after the probe’s Wednesday flyby. 

The reason is simple: New Horizons wasn’t phoning home during the flyby and Mission Control’s line was disconnected. 

Due to spacecraft design and orbital mechanics, New Horizons can either face its instruments at fun stuff like Jupiter’s volcanic moon Io [image 1, image 2], or turn its antenna towards Earth to send funky images of the same back home via the Deep Space Network. But it can’t do both at the same time.   

Because of that, and the fact that the one way travel time for a signal is upwards of 45 minutes (much too long to say, ‘Wait, go back! I think you missed something!” to a probe flying 52,000 miles per hour (83,600 kph)), mission managers decided to pre-program the entire six-month Jupiter flyby. That meant preparing some 42,000 separate commands and sending them to the probe on time.

“The memory on the spacecraft can’t hold that much, and we have to load it up in pieces,” Bowman said, adding that uploading the third chunk of the probe’s Jupiter rendezvous instructions early Tuesday was actually the most nerve-wracking period for her and her team. “We had to have perfect contact with Canberra [tracking] station and the spacecraft in order to meet that deadline.” 

So probe lost contact with Earth Tuesday night at about 8:30 p.m. as planned, then silently hurtled ever-closer to Jupiter, made the closest approach, and began the long journey away from the planet with nary a peep to or from mission control. It began reassuring mission controllers of its successful Jupiter flyby data at 11:55 a.m. on Wednesday.

You can read more about it – and see some neat pictures – by clicking here.