Gas giants and their moons

The Galileo atmospheric probe was part of NASA’s 1989 Galileo mission to Jupiter. As part of the mission, a 337kg probe was deployed from the spacecraft tasked with collecting data from the Jovian atmosphere. The probe endured a maximum deceleration of 228g and temperatures in excess of 16,000°C but was still able to transmit useful data for 58 minutes before ultimately succumbing to the intense pressures of Jupiter’s atmosphere.

The probe used a two-stage parachute system to control its descent into the Jovian atmosphere. Shortly after atmospheric entry, once the vehicle had passed the period of maximum heating and deceleration, having burnt off over 100kg of ablator material from the heat shield, the parachute system was activated. First, a pilot chute was deployed from the top of the vehicle using a mortar system. This pilot chute was used to pull off the vehicle's back cover, deploying the 2.47m projected diameter conical ribbon main parachute. This parachute was designed to help control the vehicle's descent rate through the atmosphere rather than to allow the vehicle to land. Finally, the heat shield was jettisoned, exposing the vehicle's sample analysis instruments to the atmosphere and allowing the probe to start transmitting the data it had collected to the orbiter. In order to survive the harsh conditions on Jupiter, the main parachute canopy and suspension lines were made from the temperature-resistant polymer, Dacron, with the parachute riser made from the aramid, Kevlar.

Although the Galileo Jupiter Atmospheric Probe’s mission was relatively short, it gathered a lot of valuable data about Jupiter’s atmosphere. It gave an insight into the composition of the atmosphere and detected winds in excess of 640m/s. [12]

When landing on Triton, the Triton hopper would be landing on a moon in a retrograde orbit around its parent planet about 30 AU from the Earth (1AU=distance Earth-Sun). This retrograde orbit is most likely because Triton is a captured object from the Kuiper Belt. Making the Triton hopper the first human-made object to land on a Kuiper belt Object when it would land in 2040 [99].

The vehicle would land using propulsion since the atmosphere on Triton is only 14-40 microbar (~1 Pa), mainly consisting of Nitrogen. To get to the point, a landing can be attempted, the entire system would first be inserted with a solid stage into a 200km parking orbit around Triton. Then the lander would separate and, using a bi-propellant stage would descend to an altitude of 250m, where the hopper would make its first hop to the surface [99].

The Triton Hopper is estimated to have a dry weight of 325kg and 450kg when fully fuelled with Nitrogen. The engine used for hopping would use Nitrogen, which is sourced after the first hop from the atmosphere and surface of Triton because the atmosphere is made mostly of Nitrogen. The hops it would make will be 1.3 km high and 5.2 km downrange, during which it will gather data on the atmosphere of Triton. Besides this, it will take along a wide range of sensors and cameras to analyse and photograph Triton [99].

The spacecraft has a launch mass of 7,235 kg and a dry mass of 2,756 kg. It includes an orbiter payload of 60.5 kg and an atmospheric probe payload of 19.7 kg. The power source is 735 W from three Next-Generation Radioisotope Thermoelectric Generators.

Key science questions focus on Uranus's origin, interior, and atmosphere, studying atmospheric circulation, 3D structure, formation, evolution, and composition. The mission also investigates the magnetosphere and the internal structures, geological history, compositions, and formation processes of Uranus's satellites and rings.

The atmospheric probe will study the vertical distribution of cloud-forming molecules, thermal stratification, and wind speed as a function of depth. It will carry four scientific instruments: a double focus mass spectrometer, an atmospheric structure instrument, an ortho-para H2 detector, and a radio science experiment. This mission aims to enhance our understanding of Uranus and its system.