Today is one of celebration for NASA: not only is it Independence Day, but it’s also the day that the agency’s Juno spacecraft puts itself into orbit around Jupiter. After launching in August 2011, the vehicle has been traveling to the gas giant for the last five years and will finally reach its destination later this evening. Once it arrives, the spacecraft will turn on its main engine for 35 minutes to slow itself down by 1,200 miles per hour. If all goes well, the burn will put Juno into a 53-day orbit around the planet.
Juno has only one opportunity to get into Jupiter’s orbit
NASA won’t really be celebrating until that engine burn is successful though. Juno has only one opportunity to get into Jupiter’s orbit. If anything goes wrong during the engine firing and Juno blows past the planet, that’s it for the mission. Because of how crucial this moment is, the Juno mission team is being as cautious as possible. All of the spacecraft’s onboard instruments are powered down so that nothing interferes with orbit insertion.
Fortunately, the Juno mission team has programmed the spacecraft with ways to restart itself if something stops the engine burn. That’s good, because NASA really won’t be in a position to help the spacecraft if any problems arise. It takes about 48 minutes to send a radio signal to Jupiter, and 48 minutes to send one back. If there is an issue, NASA will hear about it an hour later, and by that time it will be way too late for the space agency to send any corrective signals from Earth.
The spacecraft can still get into Jupiter’s orbit after just 20 minutes
NASA doesn’t actually need the engine to burn for the entire 35 minutes to enter Jupiter’s orbit, though. In fact, only 20 minutes will do the trick. Burning for 35 minutes would put Juno into its intended 53-day orbit, but the spacecraft can still get into Jupiter’s orbit after just 20 to 30 minutes. "After it’s been firing for somewhere around 20 minutes to a half hour, we will know it’s been on long enough to put the spacecraft into orbit," Steve Levin, a Juno project scientist at NASA’s Jet Propulsion Laboratory, told The Verge. "So even if something went wrong at that point, we wouldn’t be in the right orbit, but we’d still be orbiting Jupiter, and that’s a very recoverable thing."
NASA will be covering orbit insertion today from the agency's Jet Propulsion Laboratory in Pasadena, California. You can follow along by watching NASA TV or by using NASA’s Eyes on the Solar System app — an interactive module that shows the location of Juno in real time. A timeline of major events for today's mission, courtesy of NASA, is also below. All of the times for Juno’s actions are in Earth Receive Time, or when NASA receives transmission from the craft confirming its status. That means all of the spacecraft’s major milestones will actually occur 48 minutes earlier than the times listed.
Timeline for Jupiter Orbit Insertion
12:00PM ET Pre-orbit insertion mission briefing at NASA’s Jet Propulsion Laboratory.
9:16PM ET Juno turns slowly toward the attitude it needs for orbit insertion.
10:28PM ET The spacecraft makes a faster turn toward its orbit-insertion attitude.
10:30PM ET NASA TV coverage begins.
10:41PM ET Juno switches to the low-gain antenna it will use to communicate with Earth for the insertion. Adjustments are then made to the spacecrafts attitude again.
10:56PM ET To help stabilize the spacecraft, the spinning Juno will rotate faster from 2 revolutions per minute (RPM) to 5 RPM.
11:18PM ET Juno’s engine burn begins.
11:38PM ET The engine has been burning long enough to put Juno into Jupiter’s orbit.
11:53PM ET The 35-minute engine burn ends and Juno is in its intended 53-day orbit.
11:55PM ET Juno start to spin down from from 5 RPM back to 2 RPM.
12:07AM ET Juno begins to adjust its attitude to point toward the Sun.
12:11AM ET The spacecraft switches to its Medium Gain Antenna.
12:16AM ET Juno begins to send more detailed telemetry, but it could take up to 20 minutes to lock onto the spacecraft's signal.
1:00 AM ET Post-orbit insertion mission briefing.