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Juno switched to autopilot mode for Jupiter final approach

Artist's concept of the Juno spacecraft at Jupiter. Credit: NASA/JPL-Caltech
Artist’s concept of the Juno spacecraft at Jupiter. Credit: NASA/JPL-Caltech

Four days out from arriving at the solar system’s biggest planet, NASA’s Juno spacecraft received a final uplink of commands Thursday governing the robotic probe’s high-velocity braking maneuver Monday to steer into orbit around Jupiter.

Juno will run on autopilot for the rest of its approach, counting down to a series of tightly-choreographed maneuvers Monday leading to a 35-minute ignition of the craft’s main engine to slow its speed by 1,212 mph (541.7 meters per second), just enough to be captured in orbit by the firm grasp of Jupiter’s gravity.

Before uploading the final command sequence, ground controllers stationed at NASA’s Jet Propulsion Laboratory and at a control center run by Lockheed Martin, the spacecraft’s builder and operator, prepared the engine for Monday’s critical burn.

“Ten days ago, we opened the main engine cover so that the engine would be ready to fire when we get to July 4, and a couple of days ago we pressurized the whole system, so that the engine is ready to go, (and) all the propulsion, all the piles and valves are all ready to fire,” said Ed Hirst, Juno mission manager at JPL.

Engineers transmitted the final command file, dubbed “ji4040,” to Juno around 3:15 p.m. EDT (1915 GMT) Thursday via an antenna in NASA’s Deep Space Network located in Goldstone, California.

“Once those commands are sent, it will be hands-off from the team here on the ground,” Hirst told reporters Thursday before sending the order for Juno to launch its Jupiter arrival sequence. “We’ll continue to monitor the spacecraft and make sure everything is executing as we expect to execute, but the spacecraft is on its own, and it’s designed to take care of itself with all the command sequences that we’ve sent it.”

Scott Bolton, an astrophysicist from the Southwest Research Institute in San Antonio who leads the Juno science team, said Thursday he has mixed emotions as the spacecraft zips toward Jupiter.

“Yeah, I’m nervous,” Bolton said.

Bolton’s team proposed the $1.1 billion Juno mission to NASA in February 2004, and it beat out a competing concept to return samples from South Pole-Aitken basin on the far side of the moon, winning the space agency’s backing in June 2005.

Juno launched Aug. 5, 2011, from Cape Canaveral on top of the most powerful version of United Launch Alliance’s Atlas 5 rocket, and the probe returned to Earth’s vicinity in October 2013 for a gravity assist, slingshotting it toward Jupiter.

“I’m excited with anticipation, of course, because we’re finally arriving, but I also have tension and nervousness because there’s a lot riding on what happens July 4,” Bolton said.

Engineers expect to receive confirmation that Juno’s main engine, burning a mix of liquid hydrazine and nitrogen tetroxide propellants, has started its 35-minute burn at 11:18 p.m. EDT Monday (0318 GMT Tuesday).

Radio tones broadcast by Juno will be picked up by an array of huge dish antennas on the ground. Each tone comes in at a slightly different frequency, serving as confirmation

Artist's concept of Juno's Leros 1b main engine during the orbit insertion burn. Credit: NASA/JPL-Caltech
Artist’s concept of Juno’s Leros 1b main engine during the orbit insertion burn. Credit: NASA/JPL-Caltech

Juno’s high-gain antenna will not be pointed toward Earth during the insertion burn, eliminating any chance engineers will receive detailed telemetry on the progress of the engine firing.

Instead, controllers will listen for tones at the start and end of the burn, and watch for a subtle fluctuation in the radio signal coming from Juno caused by the Doppler shift, a variation in the frequency of the spacecraft’s transmission as its velocity changes.

The Doppler effect is similar to the change in pitch of an emergency siren as an ambulance passes.

Juno will begin configuring itself for the make-or-break engine firing shortly after 9 p.m. EDT Monday (0100 GMT Tuesday), when the spacecraft will begin turning to face the right direction for the burn.

The pointing maneuver will turn Juno’s three huge solar array wings, each stretching nearly 30 feet (9 meters) long, away from the sun, forcing the probe to drain power from its batteries. Juno is the first spacecraft to travel to Jupiter’s distance, where the sun is 25 times dimmer than it is at Earth, and rely solely on solar power.

The power-efficient space probe can run all its systems and scientific instruments on enough juice to power five 100-watt light bulbs.

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Follow Stephen Clark on Twitter: @StephenClark1.

Source: You’ll find lots of information about the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Also we have facts about the space station, ISS, SpaceX launch, space program, and outerspace. Space Flight

Juno switched to autopilot mode for Jupiter final approach

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