A few minutes ago, at 11:18pm US Eastern (8:18pm US Pacific, where the Jet Propulsion Lab is), the Juno spacecraft started its 35-minute main engine orbit-insertion burn that’ll slow the ship by about 1200 MPH so that it can get captured by Jupiter’s gravity and drop into a 53-day orbit. As I type these words, Juno is about halfway through the burn, 2800 miles above the cloud tops, and is traveling over 100,000 MPH relative to Jupiter. That 53-day orbit is just for the first couple of orbits. After that, it’ll be trimmed down to 14 days.
Because of how far Jupiter is from Earth, around 500 million miles, it takes light, and more to the point, the radio signals from Juno about 48 minutes to be received on Earth. So, that 11:18 / 8:18 time is the time the signal from Juno about the start of the burn was received on Earth. The burn actually started 48 minutes before.
Keep in mind, with all the heavy gravity, deadly radiation, strong magnetic field, and all manner of rocks being thrown all over the place, this is an incredibly dangerous thing going on. They’ve built in some protections and allowances for some things to go wrong, but if anything major happens, it’s the end of the mission.
Go, Juno, Go!
Live coverage from NASA is here, for your viewing pleasure:https://www.facebook.com/NASA/ and here https://www.nasa.gov/mission_pages/juno/main/index.html