Juno Instrument Overview

NASA’s Juno Spacecraft carries a science payload consisting of nine instrument packages to provide unprecedented data on Jupiter’s magnetic environment, its gravitational field, the incredibly dense atmosphere & cloud cover, the interior of the planet and Jupiter’s puzzling aurora.

Juno uses it instruments to look for clues about Jupiter’s formation which will allow scientists to infer details on the solar system’s formation since Jupiter maintained its current state since the early stages of the solar system. Also, the mission sets out to determine whether Jupiter has a solid core, find out how much water is present within the planet’s dense atmosphere, & study winds that can reach more than 600 Kilometers per hour.

Gravity Science – GS

To reveal the interior structure of Jupiter, Juno makes detailed measurements of the planet’s gravitational field which will point to internal structures that are hidden by the planet’s dense atmosphere.

The experiment is a radio science experiment that involves X-Band and Ka-Band ranging from ground stations on Earth to follow the spacecraft in its orbit around the planet and detect even minute changes in the motion of the spacecraft. Local variations in gravity can act on the spacecraft in orbit and cause it to speed up or slow down – those changes in spacecraft motion can be detected using the Doppler Shift in the X and Ka band transponders used by the radio sub-system.

For the gravity experiment, the High Gain Antenna needs to be pointed directly at Earth so that Ka-Band Ranging Signals and X-Band Signals can be sent and received. The Deep Space Network has only one Station capable of providing Ka-Band uplink which is Deep Space Station 25 at DSN Goldstone.

Turnaround ranging using the Deep Space Network involves the DSN station that sends an Ka-Band signal to the spacecraft containing ranging tones that it imposes on a carrier using phase modulation. When the spacecraft receives the tones, it sends them right back via X-Band downlink. The DSN station records the timing of the ranging tones uplink and the timing of the tone’s reception order to calculate the line-of-sight distance to the spacecraft.

After processing of the data taking into account delays by the electronics on the spacecraft and the ground, atmospheric and ionospheric properties, interplanetary plasma, and relativistic effects, the ranging method has an accuracy of about one meter in the outer regions of the solar system.

Magnetometer – MAG

The MAG instrument of Juno measures Jupiter’s magnetic field to create a detailed three-dimensional map of the Gas Giant’s magnetic environment.

Juno uses a fluxgate magnetometer developed at NASA’s Goddard Spaceflight Center that is installed on one of the three solar arrays of the spacecraft to move the instrument as far away from the spacecraft platform to avoid false readings caused by Juno’s own magnetic emissions.

MAG uses dual-fluxgate magnetometers to measure the magnetic field vector and a 3-cell scalar Helium magnetometer sensor provided by JPL is used to measure the strength of the field. An Advanced Stellar Compass provides precise attitude data for each of the sensors.

Two fluxgate magnetometers are installed on the magnetometer boom that is installed on the solar array – one is installed 9.8 meters from the spacecraft structure and the other resides 11.8m from the S/C bus and is rotated 180 degrees relative to the other sensor. The scalar Helium magnetometer is located inboard, 8.8m from the platform.

Jupiter Energetic Particle Detector Instrument

The JEDI instrument will measure energetic particles and their interaction with Jupiter’s magnetic field, investigating Jupiter’s polar space environment with special focus on the physics of the intense Jovian auroras. JEDI measures the energy, spectra, mass species (H, He, O, S), and angular distributions of the higher energy charged particles. The JEDI instrument weighs 6.4 Kilograms including 5 Kilograms of shielding material.

The instrument consists of three nearly identical sensors – each with six ion and six electron views that are arrayed in 12 by 160 degree fans with six 26.7° look directions. Two of those units are installed in a way so that nearly a complete 360-degree coverage normal to the spacecraft spin axis can be achieved in order to get complete pitch angle snapshots. The other sensor is aligned with the spin axis to gather complete sky-views over one spin period of 30 seconds. Each of the JEDI-270/90 units measures 23.3 by 15.9 by 16.1 centimeters while the single JEDI-180 unit is 23.3 by 16.9 by 12.8cm. JEDI sensors are self-contained, they have no additional hardware inside the electronics vault of the spacecraft.