Wednesday, September 25, 2013

Io Volcano Observer (IVO)

Io is the innermost of the 4 Galilean moons of Jupiter and it is also the most volcanically active world in the Solar System, with hundreds of active volcanoes scattered over its surface. All that volcanic activity is caused by intense tidal heating from friction generated within Io’s interior as it is pulled between Jupiter and the other 3 Galilean moons - Europa, Ganymede and Callisto. The largest volcanic plumes on Io reach a few hundred kilometres above the surface. With almost no impact craters, Io’s surface is extremely young, and is constantly reshaping itself.

Figure 1: Artist’s impression of Io and Jupiter.

Io Volcano Observer (IVO) is a proposed spacecraft that if selected by NASA, will orbit Jupiter and perform repeated flybys of Io to explore Io’s active volcanism and its impact on the Jupiter system as a whole. The science objectives of IVO are to:
- understand the eruption and emplacement of Io’s currently active lavas and plumes;
- determine the melt state of Io’s mantle and map heat flow patterns to distinguish between shallow and deep-mantle tidal heating;
- determine the state of Io’s lithosphere and understand its tectonic processes via observations of mountains and paterae;
- understand Io’s surface-plume-atmosphere compositions and interactions;
- and understand Io’s mass loss, exosphere, and magnetospheric interactions.

To get to Jupiter, IVO will use a Venus-Earth-Earth Gravity Assist (VEEGA) trajectory. Such a trajectory allows launch opportunities to repeat every couple of years on average. Using the VEEGA trajectory, IVO is expected to arrive at Jupiter 5-6 years after launch from Earth. IVO will insert itself into an elongated orbit around Jupiter and encounters with Io will occur when the spacecraft is near periapse (closest to Jupiter). During each encounter, the spacecraft will gather and return about 20 Gb of science data. IVO will perform 7 flybys of Io over its nominal mission duration of ~2 years. The mission is likely to be extended beyond the minimal duration and following that, the mission will terminate by impacting into either Io or Jupiter.

Since the orbit of IVO is inclined ~45° to Jupiter’s orbital plane, the flybys of Io will occur in a nearly north-south fashion. Such a pole-to-pole flyby geometry is favourable for observations of Io and provides excellent views of the polar regions during approach and departure. To accomplish its science objectives, IVO will carry with it a suite of five instruments - (1) Narrow-Angle Camera (NAC); (2) Wide-Angle Camera (WAC); (3) Fluxgate Magnetometer (FGM); (4) Thermal Mapper (ThM); (5) and the INMS/PIA Package (IPP) consisting of dual Ion and Neutral Mass Spectrometers (INMS) and dual Plasma Ion Analyzers (PIA) with shared electronics.

Figure 2: IVO spacecraft with the 2.1 m high-gain antenna (HGA) for scale. (A. McEwen et al., 2014)

Exploration of the outer Solar System is challenging since power is a major constrain at large distances from the Sun. Instead of solar arrays, IVO will be powered by a pair of Advanced Stirling Radioisotope Generators (ASRGs). Each ASRG has a mass of ~20 kg, a design lifetime of 14 years, produces 140 W of electrical power and uses 0.8 kg plutonium-238. The long design lifetime of the ASRGs allows a 6 year extended mission for IVO. During the extended mission, IVO can use Io’s gravity to pump it into a more elongated orbit around Jupiter. This will allow ~8 additional flybys of Io in ~6 years. In addition, a more elongated orbit may allow for a potential flyby of an outer satellite of Jupiter by IVO, providing extra science returns.

A. McEwen et al., “Io Volcano Observer (IVO): Budget travel to the outer Solar System”, Acta Astronautica Volume 93, January 2014, Pages 539-544