On July 4, millions of miles above the fireworks — if “above” were really a relevant concept — NASA’s Juno Spacecraft will complete a five-year, nearly two-billion mile journey by entering Jupiter’s orbit. Or it won’t. The end of the trip to our solar system’s fifth planet has been billed as a sort of nerdy Independence Day celebration, but the truth is that it’s going to be a suspense-filled holiday for NASA scientists. If Juno doesn’t slide gracefully into orbit — as the mathematical models suggest it will — it will rocket into space out towards Neptune, the Kuiper Belt, and the big, immeasurable beyond.

NASA scientists launched Juno towards the sun on August 11, 2011, using the star’s gravity (and Earth’s) to discuss throwing the basketball court-sized spacecraft toward outer orbit. This gravity assist maneuver added some 8,800 miles per hour to Juno’s already blistering pace and limited the amount of fuel necessary to make the flight.

At around 11:30 p.m. Eastern time on July 4, as the sparklers burn out, Juno will arrive at its target. For Steve Levins, a Juno project scientist working out of NASA’s Jet Propulsion Laboratory, it all comes down to this maneuver. He stressed that this may be the hardest part of the whole mission. At a lecture he gave last year, he said: “You have to make the spacecraft fire the main engine at the right time so that you slow down and enter Jupiter’s orbit.”

The precise burn calculations are already programmed into Juno’s mission parameters, but if it misses its mark, even by a half-an-hour, the mission is as good as over; there are no second chances. Principal investigator for the mission, Scott Bolton, reiterated the importance of this initial slowdown burn at a press conference held on June 16, saying that the margin for error is, in celestial terms, negligible.

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As if there weren’t enough pressure, any communication to or from Juno take at least 40 minutes to arrive on either end. As a result, scientists won’t know if the slowdown burn was successful or not until after its already too late, and they have no backup plan. The sweating and the preparation will happen on July 4. The excitement or disappointment will happen on July 5. The tweets will come a little later and the headlines will hit front pages a little after that.

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Data will take longer to arrive.