A year from now, a new decade will begin, and with it will open a whole new stream of ideas for NASA missions, some closer — like Mars, some away. Some very distant. Some people expect that the era of robotic travel to worlds that are not just millions — billions of kilometers away will open for us. Among them are Uranus and Neptune (the planets we visited in 1986 and 1989, respectively), as well as hundreds of ice bodies outside the area known as the Kuiper belt.
The Kuiper belt is home to Pluto and thousands of other worlds of various sizes. Most of the bodies there are made up of building blocks of our Solar system, long ago escorted to distant icy edges. A visit to the Kuiper belt can reveal clues to how our planet and its neighbors formed, why there is so much water and other mysteries.
On the borders of the Solar system
Uranus and Neptune also contain lots of puzzles all by themselves. The more we learn about planetary systems, the more we see that most worlds are not as big as Jupiter and not as small as Earth. Many of them tend to be close in size to Uranus and Neptune, the “ice giants” that have been named for the exotic state of water ice that lies deep beneath the cloud layers. The study of Uranus and Neptune will not only help us understand the planets of our Solar system — it will help us understand the planets that orbit other stars.
Many of these missions depend on time. The upcoming decade Survey — NASA’s “ten-year review” of when the Agency send spacecraft in the 2020s and 2030s-could create or disrupt these far — reaching plans to explore the outer Solar system.
Decade Survey: how the ten-year review will take place
Starting in 2020, a team from the National Academy of Sciences (with the participation of several stakeholders from the space community) will assemble and compile a list of priority research objectives. Scientists will offer their options in the form of prescribed recommendations, known as” white papers ” (read: technical document).
From these recommendations, there will be a General consensus on what the priorities should be. These goals serve as guidelines for the proposals of middle-class missions in the new Frontiers category (New Horizons and Juno were in this category). NASA first collects a list of proposed missions, and then narrows them down gradually to one or two finalists. Once the finalist gets the green light, the team behind him can start planning and designing — and that takes years.
All this can make it difficult to get into a specific window in which you can explore Uranium or Neptune, as well as look to the object from the Kuiper belt. That’s why accurate charts are risky.
A visit to an ice giant
One group, in particular, considered the option of a mission to visit Uranus and Neptune at the same time. The last iteration includes the flyby of Uranium and the orbit of Neptune. Under the leadership of Mark Hofstadter and Amy Simon, scientists plan to look to the other side of Uranium, different from the one Voyager 2 observed in 1986, and study Neptune and its largest satellite, Triton. Triton rotates backwards, which may be due to the fact that it was once the largest object of the Kuiper belt-before Neptune pulled Triton to itself, throwing many of its original satellites.
Simon says these missions should be deployed within 15 years, including travel time and research. This is due to how long individual parts of the spacecraft can remain in space with relative confidence. While the spacecraft may live longer, 15 years is the minimum during which you can be sure that the mission will complete its scientific tasks to the full extent But how to make sure that the journey does not consume too many resources in the current phase of research? One way to disperse a spacecraft is to use the gravitational force of the planet to disperse it.
“Usually, to get there in less than 12 years, resort to flying around the planets, usually including Earth and Venus,” says Simon. In such scenarios, you dive into the planet’s gravity well, hoping for a slingshot effect that will accelerate your vehicle and save maximum fuel. “The best of the options also use Jupiter, because it is the most massive and can greatly accelerate the spacecraft.”
New horizons, for example, used Jupiter’s help to reach Pluto. Cassini used four separate overflights to accelerate with Saturn after launching from Earth, gaining acceleration from Venus twice, returning to Earth, and finally the final jump from Jupiter.
Simon says that in order to get to Uranus in a short time, one could use a flyby of Saturn — for example, in the window between 2024 and 2028 to catch the gas giant in the right place in its 29-year orbit. Such a mission will require a quick consideration by NASA standards — usually missions planned ten years before launch, then planned, designed and launched within five years — so you have to count on the next window, the flight of Jupiter in the period from 2029 to 2032, followed by access to Neptune. The next chance will appear not earlier than in ten years.
The Uranium mission can use traditional fuel and engines to get to the acceleration points faster — whether it’s an Atlas V rocket or a Delta IV Heavy. But because Neptune is so far away and the exact trajectory doesn’t line up as perfectly as we’d like, the mission to this planet will rely on the Space Launch System, the next-generation NASA missiles with increased payload (and it hasn’t even flown yet). If she won’t be ready in time, we’ll have to rely on other next-generation technology: solar electricity, which uses solar energy for the ignition of the ionized gas to accelerate the movement of the vehicle. So far, it has only been used on the Dawn spacecraft in missions to West and Ceres and in two missions to small asteroids.
“Even in the case of solar electricity, chemical engines are still needed, in case solar energy is no longer effective, as well as for braking in orbit,” says Simon.
Thus, the schedule is quite tight. But if we move more actively, both of these missions can serve another purpose: to get to the unknown worlds of the Kuiper belt.
The big unknown
Another work, written by three members of The new horizons team, looks at the possibility of returning to the Kuiper belt after a successful probe walk to Pluto. “We saw how interesting it was and wanted to know what else was out there,” says Tiffany Finley, chief engineer at the Southwest research Institute (SWRI) and co-author of an article published in the Journal of Spacecraft and Rockets.
The Kuiper belt contains ice remains from the formation of the Solar system, and the objects in it include a huge variety of different materials. Pluto, for example, slightly more Eris. But Pluto is made of ice, so it has less mass. Eris consists of rocks for the most part, so it is more dense. Some worlds appear to consist of methane, while others contain a lot of ammonia. Somewhere in the margins of our Solar system, there are many dwarf planets and small worlds that hold key points for our understanding of how planets appear — and whether other planetary systems may be similar to ours.
Scientists used narrow restrictions: they limited the mission to a 25-year period and examined the 45 brightest objects of the Kuiper belt, comparing them with respect to different scenarios of planetary flights. Jupiter, surprisingly, opened most of the targets in the list. But Jupiter’s window opens once every 12 years, making missions with his participation time-dependent. Simple flights of Saturn provide quite a good list of targets from the Kuiper belt.
But when you pair these worlds with Uranus or Neptune, you get a chance to discover new facts about our mysterious, most distant planets and even some dwarf planets in one fell swoop.
Get to these worlds will help the effect of a slingshot, first from Jupiter, and then from another planet. Each of these planets aligns with Jupiter in a narrow window in the 2030s, and neatly fits into different parts of this decade. For example, to go to the list of worlds on the way with Neptune, you need to get to Jupiter in the early 2030s, and get to the Kuiper belt through Uranus will require a launch in the mid-2030s. Jupiter and Saturn are aligned just for the “slingshot” to the Kuiper belt in the late 2030s.
The list of goals promises many interesting features. Varuna, an oblong world that has gained such shape due to the fast speed of rotation, is perfectly suited to fly around Jupiter-Uranus. Neptune, as already mentioned, provides an opportunity to look at Eris. A mission through Jupiter-Saturn will allow you to observe Sedna, a large dwarf planet with an orbit that can point the way to the still undiscovered tenth planet. Jupiter-Saturn will make a stop at one of the most interesting dwarf planets: Haumea.
Like Varuna, Haumea is egg-shaped, while most large dwarf planets in the Kuiper belt are usually round. But Haumea received this form because of the ancient collision that gave her two moons, the ring system and the tail of debris. When asteroids have a similar composition, they are called the “collision family”. Haumea produced the only known family of collisions in the Kuiper belt.
“Haumea, of course, the coolest object. Everyone wants to Haumea”, say scientists.
Whatever we choose, we won’t have much time. Therefore, if we want to see the rings of Haumea or even the red, alien light of Sedna, the work should begin in the near future. These worlds are so small that there is only one way to know their secrets: to get to them.