Giant planets There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel.Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Settling the Outer Solar System: The Sources of Power, pp. 158–160, Tarcher/Putnam, 1999, .
Giant planets There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel.Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Settling the Outer Solar System: The Sources of Power, pp. 158–160, Tarcher/Putnam, 1999, .