After a 5 year journey, the Juno probe entered orbit around Jupiter in the early hours of this morning (5 July 2016).
Launched on 5 August 2011 (see blog post 8/8/2011), the spacecraft weighed in at about 3.5 tonnes. After a complex journey involving an Earth swing-by and 2 primary deep space manoeuvres, Juno’s Jupiter Orbit Insertion (JOI) burn began at 4.18 BST (3.18 UT) on 5 July 2016 at an altitude of 4,200 km above the 1 bar surface of the giant gaseous planet. Since Jupiter does not have a definite surface, this height is expressed in kilometres above the Jovian atmospheric surface where the pressure is equal to the atmospheric pressure at the Earth’s surface. The burn lasted the planned 35 minutes – the British built thruster performed flawlessly – which slowed Juno’s speed by 480 m/s. This change in speed (delta-V) was sufficient to allow Juno to be captured by Jupiter’s gravity field and inject it into a large and very elongated elliptical orbit. As the mission progresses, the height and shape of this initial orbit will be trimmed by further thruster firings. A consequence of this manoeuvre was that the spacecraft plunged deeper into Jupiter’s trapped radiation belts (analogous to Earth’s Van Allen Belts) than any spacecraft prior. A significant design feature of the spacecraft is that it requires to be heavily radiation-hardened, as the total radiation dose it will receive during the mission will be around 10 Mrad – sufficient to fry the electronics of a typical Earth orbiting spacecraft.
Launched on 5 August 2011 (see blog post 8/8/2011), the spacecraft weighed in at about 3.5 tonnes. After a complex journey involving an Earth swing-by and 2 primary deep space manoeuvres, Juno’s Jupiter Orbit Insertion (JOI) burn began at 4.18 BST (3.18 UT) on 5 July 2016 at an altitude of 4,200 km above the 1 bar surface of the giant gaseous planet. Since Jupiter does not have a definite surface, this height is expressed in kilometres above the Jovian atmospheric surface where the pressure is equal to the atmospheric pressure at the Earth’s surface. The burn lasted the planned 35 minutes – the British built thruster performed flawlessly – which slowed Juno’s speed by 480 m/s. This change in speed (delta-V) was sufficient to allow Juno to be captured by Jupiter’s gravity field and inject it into a large and very elongated elliptical orbit. As the mission progresses, the height and shape of this initial orbit will be trimmed by further thruster firings. A consequence of this manoeuvre was that the spacecraft plunged deeper into Jupiter’s trapped radiation belts (analogous to Earth’s Van Allen Belts) than any spacecraft prior. A significant design feature of the spacecraft is that it requires to be heavily radiation-hardened, as the total radiation dose it will receive during the mission will be around 10 Mrad – sufficient to fry the electronics of a typical Earth orbiting spacecraft.
Details of Juno's payload instruments - Source NASA
Current assumptions about Jupiter's internal structure - Source NASA Juno is not the first spacecraft to orbit Jupiter – the Galileo spacecraft entered orbit in 1995. However, Galileo’s principal mission was to explore Jupiter’s host of moons, which it achieved spectacularly well before plummeting into Jupiter’s atmosphere (deliberately!) in September 2003. Unlike Galileo, Juno’s main mission is the study of Jupiter itself, and to do this it has an array of instruments to accomplish this (see image summarising payload). The primary instruments will investigate the planet’s gravity field, magnetic field, radiation belts and atmospheric composition, as well as imaging the dynamic atmospheric surface below.
One of the main objectives is to study the planet’s internal structure (see image), and this is done indirectly by mapping Jupiter’s gravity field very precisely. The investigators use the spacecraft’s communication system to determine the probe’s orbit to high accuracy. The method, referred to as Doppler ranging (see video), produces a position accuracy of about 1 metre. The short period changes in the spacecraft position and speed allow the gravity field to be mapped, and this in turn reflects the variations in density and structure internally of the planet.
This is just the beginning of the Juno mission – to keep abreast of new developments go to the NASA Juno website: https://www.nasa.gov/mission_pages/juno/main/index.html
This is just the beginning of the Juno mission – to keep abreast of new developments go to the NASA Juno website: https://www.nasa.gov/mission_pages/juno/main/index.html
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