Alberto Carrasco Gallardo

The Submillimetre Wave Instrument (SWI) onboard the Jupiter Icy Moons Explorer (Juice) spacecraft consists of a 29 cm off-axis paraboloid antenna and two double-sideband heterodyne receivers operating in the frequency ranges of 530–638 and 1066–1286 GHz. This instrument is designed to study Jupiter's atmosphere and the exospheres of the Galilean moons. We used the Lunar-Earth-Gravity-Assist (LEGA) data from August 2024 to characterise this antenna using several SWI observations pointing towards the Earth. The data analysis of the LEGA observations dedicated to the antenna beam allows us to characterise the antenna beam Full Width at Half Maximum (FWHM), sidelobes, absolute pointing and receiver coalignement. Moreover, an estimate of the calibration efficiency factor has been obtained from an optical model simulation.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On 19 August 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km s ⁻¹ relative to the Sun. On 20 August 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km s ⁻¹ relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 µm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Jupiter Icy Moons Explorer (Juice) embarked in 2023 on a 8-year interplanetary journey to Jupiter and its icy moons. The Submillimetre Wave Instrument (SWI) is one of the ten science instruments aboard the spacecraft. SWI is a sophisticated and first-of-its-kind payload visiting the outer solar system, featuring dual-band tunable receivers, two independent pointing mechanisms, and spectrometers capable of high resolution (up to a resolving power of 10 ⁷ ). It is designed to support the diverse science objectives of the Juice mission targeting Jupiter's middle atmosphere, icy-moon's exospheres as well as near sub-surface thermophysical properties. For this purpose the Juice mission adopts a complex trajectory tour within the Jovian system, which further necessitates a sophisticated, mission-driven operations concept for SWI. This presents significant planning, operations and commanding challenges which are described in this paper in the context of the Lunar and Earth Gravity Assist (LEGA). After the development and ground calibration of the instrument, the SWI Team has designed a comprehensive calibration strategy applicable during the Cruise Phase of Juice. Among the various opportunities for calibration, including the Near-Earth Commissioning Phase and more than ten Payload Checkout Windows, the LEGA offers the means not only to improve the calibration of the instrument, but also to validate the operational strategy of future icy moon flybys.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using 20 both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On August 19, 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km/s relative to the Sun. On August 20, 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km/s relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 μm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using 20 both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On August 19, 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km/s relative to the Sun. On August 20, 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km/s relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 μm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using 20 both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On August 19, 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km/s relative to the Sun. On August 20, 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km/s relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 μm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Submillimetre Wave Instrument (SWI) onboard the Jupiter Icy Moons Explorer (Juice) spacecraft consists of a 29 cm off-axis paraboloid antenna and two double-sideband heterodyne receivers operating in the frequency ranges of 530–638 and 1066–1286 GHz. This instrument is designed to study Jupiter’s atmosphere and the exospheres of the Galilean moons. We used the Lunar-Earth-Gravity-Assist (LEGA) data from August 2024 to characterise this antenna using several SWI observations pointing towards the Earth. The data analysis of the LEGA observations dedicated to the antenna beam allows us to characterise the antenna beam Full Width at Half Maximum (FWHM), sidelobes, absolute pointing and receiver coalignement. Moreover, an estimate of the calibration efficiency factor has been obtained.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using 20 both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On August 19, 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km/s relative to the Sun. On August 20, 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km/s relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 μm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Jupiter Icy moons Explorer (Juice) was the first spacecraft ever that performed a combined gravity assist using 20 both the Moon and Earth in succession. The double flyby required highly precise navigation to succeed. The LEGA allowed Juice to make a shortcut through the inner solar system on its way to Jupiter, using less fuel than would have been otherwise required. On August 19, 2024, Juice had its closest approach to the Moon. This first part of the manoeuvre accelerated the spacecraft by approximately 0.9 km/s relative to the Sun. On August 20, 2024, the spacecraft swung past Earth. This second part of the manoeuvre reduced the spacecraft's speed by 4.8 km/s relative to the Sun. This was a unique opportunity for its payloads to observe the Moon and Earth from a close distance as both calibration and science targets. The Submillimetre Wave Instrument (SWI), a dual channel heterodyne spectrometer observed both targets in two far-infrared bands around 500 and 250 μm wavelength in order to characterize and calibrate the overall performance of the instrument, including its receiver frontend, spectrometer backend and telescope mechanisms. In addition, the commanding pipeline and operations processes of the instrument were also tested close to its full range of flexibility using the relevant pipelines. In this paper we provide a contextual description of physical and functional characteristics of SWI, its operational principles and in-flight calibration activities during LEGA.

The Jupiter Icy Moons Explorer (Juice) embarked in 2023 on a 8-year interplanetary journey to Jupiter and its icy moons. The Submillimetre Wave Instrument (SWI) is one of the ten science instruments aboard the spacecraft. SWI is a sophisticated and first-of-its-kind payload visiting the outer solar system, featuring dual-band tunable receivers, two independent pointing mechanisms, and spectrometers capable of high resolution (up to a resolving power of 10⁷). It is designed to support the diverse science objectives of the Juice mission targeting Jupiter's middle atmosphere, icy-moon's exospheres as well as near sub-surface thermophysical properties. For this purpose the Juice mission adopts a complex trajectory tour within the Jovian system, which further necessitates a sophisticated, mission-driven operations concept for SWI. This presents significant planning, operations and commanding challenges which are described in this paper in the context of the Lunar and Earth Gravity Assist (LEGA). After the development and ground calibration of the instrument, the SWI Team has designed a comprehensive calibration strategy applicable during the Cruise Phase of Juice. Among the various opportunities for calibration, including the Near-Earth Commissioning Phase and more than ten Payload Checkout Windows, the LEGA offers the means not only to improve the calibration of the instrument, but also to validate the operational strategy of future icy moon flybys.