Space Initiatives will receive a NAIC grant for interstellar exploration. Tiny gram-scale interstellar probes propelled by laser light are probably the only technology capable of reaching another star during this century. The availability by mid-century of a laser beamer powerful enough (about one hundred gigawatts) to boost a few grams to relativistic speed is assumed as are laser sails strong enough to survive launch and terrestrial light buckets (about four tenths of a square mile each) big enough to catch optical signals from Proxima b.
The proposed representative mission, around the third quarter of this century, is to fly by the nearest stellar neighbor, the potentially habitable world Proxima b, with a large autonomous swarm of thousands of tiny probes.
Given extreme constraints on launch mass (grams), onboard power (milliwatts), and coms aperture (centimeters to meters), it was determined in during work over the last three years that only a large swarm of many probes acting in concert can generate an optical signal strong enough to cross the huge distance back to Earth. The eight-year round-trip time lag eliminates any practical control by Earth. Therefore, the swarm must possess a very high degree of autonomy in order to prioritize which data is returned to Earth. Coordinating the swarming of individuals into an effective whole is the dominant challenge for this representative mission to Proxima Centauri b. Coordination rests on establishing a mesh network via low-power optical links and synchronizing probes’ on-board clocks with Earth and with each other to support accurate position-navigation-timing (PNT).
This representative mission begins with a long string of probes launched one at a time to about two tenths of the speed of light. After launch, the drive laser is used for signaling and clock synchronization. It will provide a continual time signal like a metronome. Initial boost will be modulated so the tail of the string catches up with the head (“time on target”). Exploiting drag imparted by the interstellar medium (“velocity on target”) over the twenty-year cruise will keep the group together once assembled. An initial string of hundreds to thousands of astronomical units long will dynamically coalesce itself over time into a lens-shaped mesh network one hundred thousand kilometers across. This will be sufficient to account for ephemeris errors at Proxima, ensuring that at least some probes pass close to the target.
A swarm whose members are in known spatial positions relative to each other with state-of-the-art microminiaturized clocks to keep synchrony, can utilize its entire population to communicate with Earth. It can periodically build up a single short but extremely bright contemporaneous laser pulse from all of them. Operational coherence means each probe sends the same data but adjusts its emission time according to its relative position. In this way, all pulses can arrive simultaneously at the receiving arrays on Earth. This effectively multiplies the power from any one probe by the number of probes in the swarm, allowing orders of magnitude greater data return.
A swarm could tolerate significant attrition enroute, thus mitigating the risk of “putting all your eggs in one basket,” and enabling close observation of Proxima b from multiple vantage points. Fortunately, swarming techniques can be explored and tested now in a simulated environment, which is what is proposed in this work. The innovations required for this mission should have a profound effect on space exploration, complementing existing techniques and enabling entirely new types of missions. Picospacecraft swarms could cover all of cislunar space, or could instrument an entire planetary magnetosphere. There could be a number of such missions well before mid-century, starting in Earth or lunar orbit, but in time extending deep into the outer Solar system. Such a swarm could explore the rapidly receding interstellar object 1I/’Oumuamua or the solar gravitational lens. These could be precursors to the ultimate interstellar mission, but also scientifically valuable in their own right.