Thus, Jupiter is the largest reservoir of metallic hydrogen in the solar system, and free flight in the atmosphere of Jupiter is possible only in the upper layer with a depth of no more than 1500 kilometers. The state of aggregation of this substance and physical characteristics are still difficult to imagine, a review of modern hypotheses is given in this MIPT review. With a high probability, liquid metallic hydrogen can be saturated with free electrons and therefore have the strongest conductivity along with magnetic properties. Therefore, it is unlikely that it will be possible to control any metal “vessel” and use conventional electronics.
According to Leif Fletcher from the University of Leicester, the ideal apparatus for deep penetration into the atmosphere of gas giants should indeed be in the form of a bullet. In addition, the apparatus must be constructed from chemically inert, thin and light materials. In the mid-2010s in this capacity considered carbon nanotubes, but so far they do not reach the required length and thickness, not only for the full-fledged execution of the carbon case, but also for enclosing electronics in a carbon frame. For greater stability and “buoyancy” of the device, another design is also possible, proposed at the NASA Jet Propulsion Laboratory in 2015:
This design is called a “windbot” and, presumably, could not only stay in the atmosphere of a gas giant for a long time, but also extract energy from it. Back in 2004, NASA designed a rover that could move on the surface of the planet. like a tumbleweed. Such an idea was logical given the windy conditions on Mars, but as the simulations showed, a rolling rover should wear out too quickly. But in the atmosphere of a gas giant, this design is much more convenient. As part of the NIAC program, a robotic probe was proposed that could work for a long time both without wings and without a balloon. The windboat should automatically catch the wind and determine turbulence zones, and ideally use the wind as a source of energy. It would be easier to protect such a device from radiation and other electromagnetic effects, as well as quickly correct the course (the device would not have to “turn around”). In addition, windbots could be distributed in the atmosphere, forming a mobile network, and, if necessary, docked into larger forms, similar to the way I described here.
Apparently, because of the obstacles described above, a manned expedition to the atmosphere of a gas giant will never be possible. However, the satellites of the gas giants, such as Titan, are priority targets for extraterrestrial colonization, so some permanent presence in the atmospheres of these planets is most likely indispensable. Probes can be not only research, but also meteorological, which would make it possible to prepare for magnetic storms on the giant, protecting the electronics of the entire colony. In addition, if metallic hydrogen is promising rocket fuel and liquid superconductor, then its extraction on gas giants according to the “scooping” principle may turn out to be more profitable (even from an energy point of view) than synthetic production. Finally, our Jupiter and Saturn are probably significantly different in physical properties from hot Jupiters. Apparently, the atmosphere of hot Jupiters is much more sparsethan those of Jupiter and Saturn and is theoretically better suited for a through flight.