Saturn, the second-largest planet in the solar system after Jupiter but certainly the most beautiful planet because of its rich ring system, has so far been approached by four human spacecraft: Pioneer 11, the two Voyager probes, and Cassini. Unfortunately, while Cassini still has years of work ahead of it, there are no solid plans to send another probe to this planet. The only current outbound probe, New Horizons, passed Saturn’s orbit in 2008, but didn’t pass by Saturn itself.
– 2004-2017: Cassini-Huygens –
As we speak, a single major space probe, Cassini-Huygens, is orbiting Saturn. Launched as a joint project of NASA and the European Space Agency, Cassini is responsible for much of our present-day knowledge about Saturn, and was also the first spacecraft to successfully land a probe on Saturn’s moon Titan, notable because of its methane atmosphere. Cassini’s earlier studies of another moon, Enceladus, created considerable excitement because, like Jupiter’s moons Europa and Ganymede, it seems that Enceladus likely has at least a small underground water ocean.
At present, NASA plans to operate Cassini until 2017, completing hundreds of additional orbits in which it will not only study Saturn and Titan (the two primary targets) but also Enceladus and several other moons. At the end of this mission, it is currently planned to send Cassini into the Saturnian atmosphere to be crushed and burned up, much as NASA ended the life of its Galileo probe on Jupiter several years ago. Cassini is powered by a nuclear power generator than solar probes, so eventually it will have to end its mission; at this point, however, funding as much as power supplies are determining the end date.
– 2015: Saturn Flyby with Probes –
NASA continues to claim that a “Saturn Flyby with Probes” mission will be launched in 2015. If so, this would be the first substantial study of Saturn after Cassini. However, this mission so far lacks both funding and actual discussion of concept vehicles. If it is launched, it almost certainly will not be in 2015. Other “flyby with probes”-type missions, like one to Neptune, have also been effectively cancelled.
– 2020-2030: Titan Saturn System Mission –
Unlike the Saturn Flyby with Probes mission, the Titan Saturn System Mission (TSSM) is a viable concept, although that does not mean it will ever launch. TSSM is an ambitious project which was tentatively scheduled for launch in 2020, arrival in 2029, and then a four-year mission studying Saturn and Titan. The very existence of TSSM owed itself to budget cuts; the probe was, on paper, a combination of the to-be-cancelled Titan probe proposed by NASA, and the Titan/Enceladus probe proposed by the ESA. The combination spacecraft was proposed in 2009; unfortunately, later that same year, it was announced that the Europa-Jupiter probe currently being developed by both space agencies would take priority over the TSSM.
If it is ever developed, the TSSM would consist of an orbital probe and two modular probes, both of which would be dropped on Titan. One would function as a balloon; the other would land, hopefully in a methane ocean. The use of both balloon and lander probes has been done before, although currently, the only successful deployment of a balloon probe to date was a series of Soviet probes on Venus. Beyond arranging for the descent of the Titan probe, the main space probe of TSSM would circle through the Saturn moon system, conducting studies similar to those currently being done by Cassini, except much more advanced.
– Saturn Multiprobes Mission –
NASA has a mission concept for a Saturn spacecraft with multiple probes, which would allow a variety of studies of Saturn itself as well as its most significant moons, especially the atmosphere-possessing Titan.
At present, there are no firm plans to send probes to Saturn, and no apparent plans save those discussed above. In the case of closer planets, especially Mars, interest by third-party space agencies like Russia and Japan has sparked renewed interest by NASA and the ESA. However, for the time being, Russia and Japan probably lack the technical capability to reach Saturn, and have not expressed serious interest in doing so. Saturn will likely remain a secondary target for years to come.
