1. The Juno Microwave Radiometer (MWR)
Daniel Herr

2. The Juno Mission & Objectives
Second mission in NASA’s New Frontier’s Program [1]
Launched on August 5th, 2011
Flyby of Earth on October 9th, 2013
Inserted into orbit around Jupiter on July 4th, 2016
Planned End of Mission (EOM) on July 30th, 2021 (PJ35)
Overarching goal is to better understand Jupiter’s formation [1].
Determine atmospheric composition below cloud tops, including deep-water abundance
Determine the possible existence and mass of core
Determine structure of internal magnetic field
View of Juno’s trajectory from launch to Jupiter Orbit Insertion (JOI). The trajectory included an Earth flyby (EFB) and two Deep Space Maneuvers (DSMs) [1]

3. Juno’s Scientific Instruments
The Juno spacecraft contains instruments for 9 science investigations [1]
Gravity Science (GRAV)
Magnetometer (MAG)
MicroWave Radiometer (MWR)
Juno Energetic particle Detector Instrument (JEDI)
Jovian Auroral Distributions Experiment (JADE)
Waves
UltraViolet (UVS)
Jovian InfraRed Auroral Mapper (JIRAM)
JunoCam Juno Camera
NASA’s Juno spacecraft and science payload [1]

4. The MWR Objectives Global Water Abundance [2] Atmospheric Dynamics [2]
Chemical ratios in Jupiter’s atmosphere hold information about Jupiter’s formation
Accurate estimation of water understand volatile processing throughout the early solar system.
Atmospheric Dynamics [2]
Explore the subcloud region of Jupiter’s atmosphere
Determine spatial variations in ammonia and water to depths of 100 bars (or > 300km below base of ammonia clouds)
Radiation Belts [2]
Synchrotron emission from relativistic electrons in Jupiter’s radiation belts is a source of contamination for microwave observations of the atmosphere
Observations at multiple frequencies and a wide range of vantage points will help to better understand this phenomena
The MWR Instrument in its flight configuration. A. View of the assembled instrument from the A1 antenna side. B. The Electronics unit (upper left) and Receiver unit (lower right). C. View of the assembled instrument from the A2–A6 antenna side. [2]

5. Juno’s Jupiter Orbit
Juno has a highly eccentric orbit with perijove distance of <8,000 km and apojove distance of ~8,000,000 km [1]
Juno to fly a pattern with overall resulting longitudinal coverage of 11.25° [1]
Jupiter’s radiation belts have proven to be a significant design challenge.
Emit significant electromagnetic radiation in the MWR frequency bands [2]
Radiation is expected to be the main limitation to Juno’s mission lifetime [1]
NASA’s Juno spacecraft takes an orbit over Jupiter’s poles, ducking under the radiation belts, and skimming over the clouds. [1]

6. The MWR System
MWR functional block diagram showing subsystems, left to right respectively: Antennas, Radio Frequency Transmission Lines (RFTLs), Receivers, and Electronics Unit (EU). The receivers and electronics are in a radiation-protected vault on the spacecraft [2]

7. The MWR Antenna’s
The MWR consists of 6 antennas ranging from 0.6 GHz to 22 GHz approximately spaced by octave. These are denoted as A1 to A6 with increasing frequency [2].
A1 and A2 are made of a solid aluminum patch array. Antennas A3 to A5 are a slotted wave-guide topology. And antenna A6 is a horn style antenna [2].
Antenna design and resulting beampattern constrained by overall size, mass, and vibrational requirements [2].
MWR spacecraft configuration. The antennas are located on two sides of the spacecraft, all viewing perpendicular to the spacecraft spin axis. [2]

8. The MWR Antenna Specifications
Nominal MWR characteristics [2]

9. The MWR Dicke Radiometer
Receiver block diagram. R1 and R2 circuits are shown. R3 through R6 are the same except without the extra detector and output [2]

10. Radiometer Performance Specs
Nominal MWR characteristics [2]

11. Weighting Functions
Microwave opacity sources included H2O, NH3, H2, and a liquid water cloud. [2]
Weighting Function [3]
𝑊 T (𝑓,𝜃,𝑧)= 𝜅 a 𝑓,𝑧 𝑒 − 𝜏 0 𝑧,∞ sec(𝜃)
𝜏 𝑧,∞ = 𝑧 ∞ 𝜅 a 𝑓,𝑧′ 𝑑 𝑧 ′ (Np)
Brightness temperature [3]
𝑇 UP 𝑓,𝜃 = 0 ∞ 𝑊(𝑓,𝜃,𝑧)𝑇 𝑧 𝑑𝑧
Contributing Function [2]
𝑇 UP 𝑓,𝜃 = 0 ∞ 𝐶 𝑓,𝜃,𝑧 𝑑 log 𝑝
Contribution functions vs. pressure in a nominal Jupiter atmosphere at the indicated MWR wavelengths [2]

12. Limb Darkening Parameter
Absolute calibration over a wide bandwidth is difficult [2]
The MWR achieves an accuracy of GREATER than 1% despite extensive calibrations
Important spectral features of Jupiter’s atmosphere would lie below the level of uncertainty with this error
Limb darkening parameter is given by [2]
𝑅 𝜃 = 𝑇 𝑏 0 − 𝑇 𝑏 𝜃 𝑇 𝑏 0
The emission-angle dependence is essentially the derivative of the spectrum and contains the same information [2]
It can be measured with greater accuracy (i.e., 1 part in 103)
Capable of discriminating among cases that the spectral measurements cannot

13. Limb Darkening vs Atmospheric Sounding
Absolute nadir brightness temperature spectra for models with different concentrations of NH3 and H2O. The curves indicate the respective model concentrations of each constituent in proportion to the solar abundances. The arrows on the abscissa indicate the MWR wavelengths [2]
Spectra of the limb-darkening parameter as a function of wavelength across the MWR measurement range, for a nominal atmospheric model. The insert shows a blowup of the indicated region of the plot with the currently expected measurement uncertainties for the MWR plotted on the 3 X solar water curve [2]

14. Project Analysis Deliverables
Analysis of Antenna Patterns and Array Factors
Analysis of satellite geometry and antenna footprint vs look angle
Analysis of Jupiter’s atmosphere including brightness temperature and weighting functions*

15. References
[1] S. Bolton et al., "The Juno Mission," Space Science Reviews, Article vol. 213, no. 1-4, pp , 2017.
[2] M. Janssen et al., "MWR: Microwave Radiometer for the Juno Mission to Jupiter," Space Science Reviews, Article vol. 213, no. 1-4, pp , 2017.
[3] F. T. Ulaby and D. G. Long, Microwave Radar and Radiometric Remote Sensing. Ann Arbor: The University of Michigan Press, 2014, pp. xxviii, 984 pages.

16. Perijove & Apojove Rant*
An apsis is an extreme point in the orbit of an object.
Using the prefixes peri- and ap-/apo- we can specify the nearest of farthest point respectively
But hold on, who needs 2 words when you can have 50+! (25+ root words plus 2 prefixes)
*Again, my views as an EE looking into the field of Astronomy
Farthest
Focus
Nearest
Apocenter,
Apoapsis,
Apofocus
Primary
Pericenter, Periapsis,
Perifocus
Aphelion
Sun
Perihelion
Apastron
Star
Periastron
Apogee
Earth
Perigee
Apocynthion,
Apolune
Earth's Moon
Pericynthion,
Perilune
Apojove
Jupiter
Perijove

17. Questions ?