No space probe has visited Uranus or Neptune since the Voyager 2 flew by both Ice Giants in the late 20th Century. A group of researchers from NASA and a number of universities have issued a report detailing four proposals for returns to Uranus or Neptune sometime in the 2030s according to the New Scientist.

Four missions, three orbiters, and a flyby, proposed for Uranus or Neptune

The report suggests a possible four missions. Two would orbit either Uranus or Neptune and would include an atmosphere probe that would drop into one or the other planets.

One probe would go to Uranus but would eliminate the atmosphere probe for a suite of 15 extra instruments.

The flyby would be the cheapest option and would go past Uranus. The most have instruments for any of the proposed missions would be a narrow-angle camera, a doppler imager, and a magnetometer. Some of the additional instruments would include plasma detectors, infrared and UV imaging, dust detection, and microwave radar capability.

Why go to the ice giants?

Unlike Jupiter and Saturn, which have been extensively explored thanks to the Galileo, Cassini, and Juno missions. Uranus and Neptune have hardly been looked at. An orbiter that explores either planet and its extensive system of moons and rings for a decade and a half would garner a treasure trove of scientific knowledge.

The Neptune mission would also concentrate on its moon Triton, thought to be a captured Kuiper Belt object. The search for exo-planets has discovered that Neptune-sized planets are the most plentiful. Finding out why this might be is a priority for scientists.

Launch windows

Because of the size of the NASA budget, likely only one of these missions are likely to start anytime soon.

A Neptune mission would have a good chance for departure in 2030 while 2034 is best for a voyage to Uranus, thanks to the position of Jupiter to provide a gravity assist. The journey would take 14 years and would require nuclear power similar to that carried by Galileo, Cassini, and New Horizons.

Could advanced propulsion technology help matters?

On the other hand, the addition of better propulsion technology could shorten the voyage to one of the ice giants and widen the launch windows. The heavy lift Space Launch System is already being contemplated for the Europa Clipper, scheduled to depart in the early 2020s. Either the SLS or a commercially available heavy lifter such as the Falcon Heavy or the New Glenn could do a similar service for an ice planet mission. Add a nuclear electric propulsion system, and the voyage could be shortened even more.