HORIBA Jobin Yvon gratings equip two JUNO instruments



Copyright: Artist view - ESA/ATG medialab

In Greek and Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter's wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiter's true nature. The JUNO spacecraft will also look beneath the clouds to see what the planet is up to, not seeking signs of misbehavior, but helping us to understand the planet's structure and history.

JUNO is a NASA space probe currently orbiting the planet Jupiter. It was launched from Cape Canaveral on August 5, 2011, and entered Jupiter orbit on July 4, 2016. The spacecraft will orbit 37 times around Jupiter during 20 months, it is the second time in history than a satellite will orbit Jupiter.

Some of the best space organisations were involved in this JUNO space mission, including NASA, JPL, SWRI, Lockeed Martin from USA and LATMOS, SELEX (FINMECCANICA), HORIBA Jobin Yvon (HJY) from Europe.

8 scientific instruments were on board, among which two spectrometers, both integrating HJY gratings : First one is the Ultraviolet Spectrograph (UVS), designed to observe and characterize Jupiter’s far-ultraviolet auroral Jovian emissions in the 70 to 205 nm spectral range. Light entering the entrance slit is dispersed by a HJY toroidal holographical grating with 1600 grooves per millimeter, low stray light value and TRL9 space qualified. UVS achieves a spectral resolution of 0.4 to 0.6 nanometers in point-source operation and 1 to 1.2 nm in extended source operation. The instrument has a spatial resolution of 0.1 degree, equivalent to 125 Kilometers at a distance of 1 Jupiter radius.

The second spectrometer called Jupiter Infrared Aural Mapper (JIRAM) is dedicated to probe the upper layers of Jupiter’s atmosphere using an imager and a spectrometer. Covering a spectral range of 2 to 5 µm JIRAM observes the absorption maxima of water at 2.7 and 2.9 µm and methane around 2.3 and 3 µm. Using the 4-5 µm band, JIRAM can observe clouds in the upper regions of Jupiter’s dense atmosphere as well as auroral emissions at 3.4 µm and Hot Spots at the upper end of JIRAM’s range at 5 µm. The JIRAM instrument is equiped with a HJY ruled diffraction grating that is 60x32mm in size and has 30gr/mm. The grating has a high efficiency of 90% with low stray light values and provides an interesting efficiency level on an ultra-broad spectral range.

Thanks to its scientific instruments, JUNO will be able to :

  • Determine how much water is in Jupiter's atmosphere, which helps determine which planet formation theory is correct (or if new theories are needed)
  • Look deep into Jupiter's atmosphere to measure composition, temperature, cloud motions and other properties
  • Map Jupiter's magnetic and gravity fields, revealing the planet's deep structure
  • Explore and study Jupiter's magnetosphere near the planet's poles, especially the auroras – Jupiter's northern and southern lights – providing new insights about how the planet's enormous magnetic force field affects its atmosphere.

The JUNO mission is the second spacecraft designed under NASA's New Frontiers Program. The first is the Pluto New Horizons mission, which flew by the dwarf planet in July 2015 after a nine-and-a-half-year flight and which was also integrating a HJY grating in its space spectrometer.

Juno spacecraft and its science instruments.
Image credit: NASA/JPL

Ultraviolet Spectrograph UVS
Image credit: SwRI

Jovian Infrared Auroral Mapper – JIRAM
Image credit: ASI/IFSI