The very small may lead us to the very large. Payload sizes, for one thing, can be shrunk as we increasingly master the art of miniaturization, giving us far more bang for the buck. In that sense, we can think about tiny interstellar probes that may one day be sent, as Robert Freitas has envisioned, in waves of exploration, each of them no larger than a sewing needle, but armed with artificial intelligence and capable of swarm-like behavior. Mastering the tiny thus enables the longest of all journeys.
But thinking about small payloads also makes me ponder much larger constructs. Suppose in a hundred years we can work at the atomic level to build structures out of the abundant raw material available in the asteroid or Kuiper belts. It’s possible to imagine enormous arcologies of the kind discussed by Gerard O’Neill that may one day house substantial human populations. In this way nanotech opens the door to renovation in the realm of gigantic colony worlds.
And if one of these colony worlds, eventually exploring ever deeper into the Solar System, becomes so taken with life off-planet that it continues its outward movement, perhaps we’ll see nearby stars explored in millennial time-frames, harvesting Oort Cloud materials and their counterparts among nearby stars. For that matter, could nanotech one day help us build the kind of lens structures Robert Forward envisioned to focus laser beams on departing interstellar craft containing humans? Using these technologies, Forward could work out travel times in decades rather than millennia. The art of the small may work in both these directions.
Image: Don Davis produced this image of a toroidal-shaped space colony for NASA, emphasizing not only its size but its closed ecosystem. Credit: Don Davis / NASA Ames Research Center.
The Next Hundred Years
Closer to our own time, virtual reality enabled by miniaturization and microsatellites may play a large role in how we explore Mars. Robotic bodies, as Emily Lakdawalla points out in a Nautilus essay called Here’s What We’ll Do in Space by 2116, have no need for the mammalian necessities of water and shelter. Putting robots on the Martian surface that serve as avatars for humans in Mars orbit would allow us to map and explore vast areas with minimal risk to life. Now we’re talking building up infrastructure of the sort that may eventually fill the Solar System.
A ‘virtual Mars’ from orbit is one Elon Musk would dislike, given his intention of walking the Martian surface one day, and given the growth of commercial space, it’s possible that private companies will be on the surface before a NASA or ESA-led robotic effort of the kind Lakdawalla imagines might be attempted. But surely there’s a rational mix between human and robotic to be found here. We’ll never tame the questing spirit that drives some to push for manned missions — nor should we — but the advantages of robotics will surely play a huge role in the creation of a human presence around and on whatever bodies we explore in the coming century.
I’m much in favor of Lakdawalla’s ideas on what happens next:
Most of the planets that we’ve discovered beyond the solar system are Neptune-sized, so it would behoove us to understand how this size of world works by visiting one with an orbiter. Uranus is closer, so quicker and easier to get to; but because of its extreme tilt, it’s best to visit near its equinox, an event that happens only once in 42 years. The last equinox was in 2007; I will be sorely disappointed if we do not have an orbiter at or approaching Uranus in 2049. But we may choose to orbit Neptune before we travel to Uranus, because Neptune has an additional draw: its moon Triton, likely a captured Kuiper belt object, and a world where Voyager 2 saw active geysers.
Image: Hubble observations of Uranus, among the first clear images, taken from the distance of Earth, to show aurorae on the planet. Imagine what we could learn with an orbiter in place here. Credit: NASA, ESA, and L. Lamy (Observatory of Paris, CNRS, CNES).
Triton may prove irresistible, especially given what we’ve seen at Pluto, but so too are Kuiper Belt objects like Haumea. This is an interesting place, a fast-spinner (about once every 3.9 hours) that is orbited by two moons, one of them (Hi’iaka) a whopping 300 kilometers in diameter. The scientific interest here is quickened by the belief that Haumea’s oblong shape resulted from a collision, perhaps giving us an opportunity to deeply investigate its composition. In any case, its highly reflective surface seems to be covered with water ice, so perhaps there is some form of cryovolcanism going on here. Triton again comes to mind.
For a look at a Haumea mission concept, see Fast Orbiter to Haumea and Haumea: Technique and Rationale, based on ideas Joel Poncy (Thales Alenia Space, France) presented at the Aosta interstellar conference back in 2009. But in weighing outer system missions, keep in mind as well the search for the putative Planet 9, the discovery of which would doubtless fuel speculation on the kind of technologies that might reach it. Lakdawalla mentions the possibility but, noting that the world would be ten times further out than Pluto, says that it would take a revolution in spacecraft propulsion to get to it in less than a hundred years.
The FOCAL Mission’s Allure
True enough, but the very presence of this intriguing object poses yet another driver for the development of technologies to reach it. So does a target with an equally compelling justification, the Sun’s gravitational lensing focus beginning at 550 AU. A spacecraft sent out from our system in such a trajectory that it would observe gravitational lensing of its target — on the other side of the Sun — could yield huge returns, given the vast magnifying power of the lens. Bear in mind that the focal line in a gravitational lens runs to infinity, so as the spacecraft receded, continuing observations could be made across a wide range of wavelengths.
FOCAL is the name of the mission, given Claudio Maccone’s championing of the concept and the name dating back to the early 1990s, and you can see the design of such a mission in his book Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer, 2009). We continue to explore sail missions with gravity assist and, further in the future, beamed laser or microwave methods to reach the needed velocities.
Meanwhile, FOCAL’s allure is bright: As Michael Chorost writes in The Seventy Billion Mile Telescope, “For one particular frequency that has been proposed as a channel for interstellar communication, a telescope would amplify the signal by a factor of 1.3 quadrillion.” SETI anyone?
Then again, suppose Pale Red Dot, now working hard on Proxima Centauri using the HARPS spectrograph at ESO’s 3.6-meter telescope at La Silla, turns up an interesting planet in the habitable zone. Or perhaps David Kipping will find something in the MOST data he is currently working on. As we learned more about such a planet (and other possibilities around Centauri A or B), the idea of turning a FOCAL-like lens upon the stars would become irresistible.
Image: Beyond 550 AU, we can start to take advantage of the Sun’s gravitational lens, which may allow astrophysical observations of a quality beyond anything we can do today. Credit: Adrian Mann.
With all this in mind, though, we can’t forget not only how far we have to go before we’re ready for FOCAL, but how many things we can accomplish much closer to home. Lakdawalla writes:
Some people have suggested floating balloons under the Venusian sulfuric-acid cloud deck to search for active volcanoes, or sending similar balloons under the smog of Saturn’s moon Titan to watch its methane rivers flow and possibly even touch down in a Titanian ethane lake. We’ve dreamed of touring the populations of icy worlds that float ahead of and behind the giant planets in their orbits; many of these worlds have binary companions, and some of them have rings. We’ve suggested setting up lunar bases on polar crater rims where the Sun always shines, and sending rovers into crater bottoms where the Sun never does, where water ice may have been preserved over the age of the solar system.
All true, and I still love the AVIATR concept (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance), a 120 kg airplane fueled by Advanced Stirling Radioisotope Generators (ASRG), which demand less plutonium-238 than earlier RTGs and produce less waste heat. AVIATR could stay airborne in Titan’s benign conditions (benign, that is, because of a dense atmosphere and light gravity) for a mission lasting as long as a year, exploring the moon by powered flight. See AVIATR: Roaming Titan’s Skies for background on the concept. There has been no shortage when it comes to intriguing concepts for exploring Titan.
My belief is that an interplanetary infrastructure will one day lead to our first interstellar missions, but just when those will occur is impossible to know. In any case, building the infrastructure will be so fraught with discovery that every step of the way is cause for celebration, assuming we have the sense to continue the push outwards. That, of course, is an open issue, and I suspect there will never be a time when expansion into space is anything but controversial. As always, I fall back on Lao-Tzu: “You accomplish the great task by a series of small acts.”