Aerographite has been suggested in a recent paper as a possible candidate for interstellar photon sailing. This paper begins by presenting known properties of this extremely low density, light absorptive, material. After a review of analytical tools, a number of possible interstellar missions are then considered. The first confirms that a thin-film Sun-accelerated probe deployed at the 0.4-AU perihelion of an initially parabolic solar orbit could reach Proxima/Alpha Centauri after a voyage duration of about two centuries. The next case examined is a thin-film probe accelerated to about 0.033 c by an in-space laser array. Finally, it is shown that a combined aerographite-graphene hollow-body solar-photon sail may have significant advantages in accelerating a generation ship to an interstellar cruise velocity in excess of 900 km/s. Some of the unknowns regarding this substance that must be addressed before this material can be applied to interstellar sail application, including the closest feasible perihelion distance and aerographite performance in the space environment, are also discussed. Keywords: Aerographite, Graphene, Photon Sailing, Interstellar Travel

Solar sails enable missions to observe the solar environment from unique vantage points, such as sustained observations away from the Sun-Earth line; sub-L1 station keeping; high inclination solar orbits; Earth polar-sitting and polar-viewing observatories; fast transit missions to study heliosphere to interstellar medium transition, as well as missions of interest across a broad user community. Recent and planned demonstration missions make this technology ready for use on near-term science missions.

A near-term possibility for utilization of Breakthrough Initiatives Project Starshot technology is application of the sun diving maneuver as a replacement for laser acceleration of highly miniaturized photon sails to interstellar velocities. This possibility was discussed during the June 2022 Breakthrough Discuss meeting in Santa Cruz California. Here, we consider application of statite-type photon sail probes to achieve rectilinear trajectories to explore outer solar system and near-interstellar destinations. Statite-Type solar photon sails are sufficiently thin and reflective that solar radiation pressure force on the sail exactly balances the solar gravitational force. In such a force-free environment, the spacecraft exits the solar system at its pre-sail-deployment solar-orbital velocity. Here we consider departures from a circular 1 AU solar orbit, the perihelion of a 0.7-1 AU elliptical solar orbit and the perihelion of a 0.3-1 AU solar orbit. Possible outer-solar system destinations of possible interest to Breakthrough Initiatives extraterrestrial-life/artifact -search researchers include Europa, Titan, Enceladus, Methone, and Arrokoth. More distant possible objectives are ‘Oumuamua and the Sun’s inner gravitational focus. To achieve a rectilinear trajectory, the sail must be oriented normal to the Sun and spacecraft areal mass thickness is 1.46 × 10-3 kg/m2. Current sail technology is reviewed to determine whether it can achieve the required areal mass thickness.

The Solar-Electric Sail accelerates by reflecting positively charged solar wind ions. If it is used to propel an interstellar migration mission, its interstellar cruise velocity relative to the home star cannot exceed the solar wind velocity. In an effort to analytically determine interstellar cruise velocity for a 107 kg generation ship, a constant solar wind velocity within the heliosphere of a Sun-like star of 600 km/s is assumed. The solar wind proton density at 1 AU is also considered constant at 10 protons per cubic centimeter. Solar wind density is assumed to decrease with the inverse square of solar distance. It is shown that, to maintain sufficient acceleration to achieve an interstellar cruise velocity about 70% of the solar wind velocity, the radius of the sail’s electric field is enormous—greater than 105 km. Because the solar wind velocity and density are not constant, field strength must be varied rapidly to compensate for solar wind variation. Although not competitive with the ultimate theoretical performance of solar-photon sail propelled migrations departing from Sun-like stars, the solar-electric sail might be superior in this application for migration from dim K and M main sequence stars. Such migrations conducted during close stellar encounters might have durations < 1000 terrestrial years. If only a tiny fraction of M dwarf stars host star-faring civilizations, a significant fraction of Milky Way galaxy planetary systems may have been inhabited, even if no major advances over currently postulated interstellar transportation systems are postulated. SETI theoreticians should consider this when estimating the effects of interstellar colonization.

A Von Neumann probe is a self-reproducing intelligent device with interstellar capabilities. A space-faring civilization could conceivably use such constructs to occupy much or all of the Milky Way galaxy and perhaps the entire universe. This paper presents several reasons that a civilization might decide to produce and deploy Von Neumann probes. Physically possible interstellar propulsion methods for such devices are discussed, as is a launch strategy minimizing the duration of an interstellar transfer. Various solar system locations could be investigated to determine whether Von Neumann probes are present in our vicinity.

This paper provides an overview of Alpha, a rapidly developed, low-cost CubeSat mission to verify the performance of a highly retroreflective material for light-sail propulsion. Designed, integrated, and tested by students of the Space Systems Design Studio at Cornell University, this mission demonstrates a number of key technologies that enable next-generation capabilities for space exploration. In particular, this paper focuses on the novel application of ChipSats (gram scale spacecraft-on-a-chip technology) as a means of verifying Alpha's sail orbit and attitude dynamics. Other innovations include an entirely 3D-printed structure to enable quick and inexpensive prototyping, an onboard Iridium modem that bypasses the need for ground-station radio equipment, retroreflective sail material that provides more deterministic thrust from laser illumination, and an attitude-control subsystem that provides full attitude and angular-rate control using magnetorquers only. In addition to these near-term technology demonstrations, Alpha is among the first exhibitions of holography in space, a medium that shows longer-term promise in several roles for interstellar travel.

The metaphysical concept of panpsychism defines a field of proto-consciousness that is present at all levels in the universe. An observational indication that this concept might be correct is self-organization on all levels from the molecular to the galactic. In 2011, an investigation into the validity of author Olaf Stapledon’s concept that a portion of stellar motion is volitional led to a consideration of an observational stellar kinematics anomaly dubbed Parenago’s Discontinuity. Data available at the time indicated that cooler, less massive stars (such as the Sun) revolve a bit faster around the center of the Milky Way galaxy than hotter, more massive stars, at least in a sphere with a radius of ~260 light years centered on the Sun. The spectral signature of this discontinuity becomes evident at about the point in the stellar population where molecules can form in stellar photospheres, which supports a published model of molecular consciousness. A mechanistic explanation for Parenago’s Discontinuity requires interaction between star fields and dense diffuse nebulae that might drag less massive stars faster than more massive stars. Reference to three major catalogs of deep-sky objects reveals that nebulae large enough to drag stars over a radius of ~260 light years are very rare. In 2016, the European Space Agency (ESA) released the first data set from the Gaia space observatory. It now appears clear that Parenago’s Discontinuity is a non-local phenomenon. An unexpected and provocative aspect of the reduced Gaia observations is an indication that stars within >500 light years of the Sun apparently accelerate in the direction of their galactic revolution as they age. Other published supporting work includes a demonstration that certain binary stars are similar in many respects to biological organisms. A well-developed model of quantum consciousness supports the concept that neutron stars are conscious. It has been noted that spiral galaxies such as our Milky Way retain their shape after absorbing smaller satellite galaxies, which also supports panpsychism or self-organization at the highest levels. Another research team has reported that the apparent fractal arrangement of galaxy clusters and voids is also in congruence with some form of universe self-organization. The work of two separate researchers who are contemplating methods of communicating with stellar-level consciousness indicates that experimental astro-panpsychism may be possible as well as observational astro-panpsychism. It is becoming evident that panpsychism may be moving from the realm of metaphysics to the domain of observational astrophysics.

We discuss a possibility to survey many Kuiper Belt Objects (KBO) with a single launch using a few smallscale spacecraft, each equipped with solar sails, which could be unfurled from a single interplanetary bus at the perihelion of that craft's solar orbit. Each small-scale spacecraft would carry a scientific payload and would be directed to intersect one or more KBOs. The proposed scenario is the following: the sails are carried as a payload to a relatively small heliocentric distance (0.1 - 0.3 AU). Once at the perihelion, the sails are deployed. Besides electromagnetic propulsion due to the solar radiation, another mechanism could be convenient: thermal desorption, a physical process of mass loss which can provide additional thrust as heating liberates atoms, embedded on the surface of a solar sail. Therefore, the sails experience additional propulsive force due to the thermal desorption that dramatically increases the distance that sails travel per year.

Hyperthin solar sails deployed as close to the Sun as possible are the only currently feasible approach to extrasolar solar exploration and interstellar travel. This paper quantifies and investigates the effects of timing errors in the unfurlment (or inflation) of solar sails at the perihelion of parabolic solar orbits upon the spacecraft's trajectory direction. Methods of correcting such aim errors include on-board solar-, radioisotope-, or nuclear-electric thrusters, electromagnetic thrustless turning, application of electric or magnetic sails, and a new application of toroidal magnetic ion scoops.

In 2011, I was invited to participate in a symposium at the London headquarters of the British Interplanetary Society. The subject of the symposium was the contributions of philosopher/science-fiction-author Olaf Stapledon. Instead of concentrating on the many technological projections in Stapledon’s masterwork Star Maker , I elected to investigate whether there is any evidence to support his core metaphysics—that the universe is in some sense conscious and that a portion of stellar motion is volitional (as an alternative to Dark Matter). Stars do not possess neurons or tubules, but the spectral signatures of cooler stars such as the Sun reveal the presence of simple molecules. A universal proto-consciousness field congruent with vacuum fluctuations could interact with molecular matter via the contribution of the Casimir Effect to molecular bonds. Surprisingly, there is observational evidence that cooler stars move somewhat faster around the galactic center than their hotter sisters. This velocity difference, called Parenago’s Discontinuity, occurs in the stellar temperature distribution where molecular spectral lines become apparent. Data from Allen’s Astrophysical Quantities and the European Hipparcos space observatory reveal that Parenago’s Discontinuity is found in main sequence stars as far as ~260 light years from the Sun and in giant stars at distances greater than 1,000 light years. As discussed in the paper, local explanations for Parenago’s Discontinuity seem inadequate. Gaia, a successor to Hipparcos, is currently on station observing positions and motions of ~1 billion stars in our galaxy. If the Discontinuity is a galaxy-wide phenomenon, the volitional star hypothesis will be advanced. One way that a minded star could alter its galactic trajectory is by the emission of a uni-directional jet. Such jets have been observed in young stars. Future work will hopefully show how uni-directional jets correlate with star temperature and distance from the galactic center. It is therefore not impossible that panpsychism can emerge from philosophy to become a subdivision of observational astrophysics.

Rockets move spacecraft around in space from one destination to another. Solar sails also move spacecraft around in space from one destination to another. That is just about the only similarity between these two methods of spacecraft propulsion—commonality of function. Once you get to the next level and begin to describe how they work, their processes and support systems, and the mission-level requirements they each possess, the similarity ends—with a vengeance. In this chapter, characteristics peculiar to solar sails are in italics.

Chapters 1 to 4 discussed the importance of the rocket propulsion in the first 50 years of spaceflight, and its limitations with respect to what space-faring nations (augmenting in number and quality) would want to accomplish in the solar system and beyond. Chapter 5 discussed the concept of sailing, first on Earth seas with conventional sailboats, then by extending the concept to space; there, the first similarities and differences between sea sailcraft and space sailcraft were emphasized. Chapter 6 detailed the principles of space sailing. Now we discuss what a space sail actually means through the great impact it can have on the design of the different systems, which is not as obvious as it might seem.

The single most important characteristic of a solar sail is its power source— the Sun. The Sun supplies a continuous source of sunlight, providing the gentle push that makes a solar sail such a useful propulsion system. Unfortunately, the Sun is also the limiting factor in the overall usefulness of a solar sail. When a spacecraft gets far from the sun, there is simply not enough light available to provide additional propulsion. Recall the "inverse square law" discussed previously. In deep space, the Sun is essentially a point source, with sunlight radiating away from it in all directions forming an ever-expanding sphere of light. Since the total amount of light from the Sun is the same when the expanding light sphere reaches the orbit of Mercury, Venus, or Earth, we are not “losing” sunlight. What we are doing, however, is reducing its intensity. The amount of sunlight may be the same, but the surface area of the sphere is much larger the farther you get from the Sun. The only way that the amount of sunlight can remain constant, which we intuitively know it must, yet cover a much larger area, is for the amount of sunlight per unit area to decrease.

Although the rockets described in the previous chapter have opened the solar system to preliminary human reconnaissance and exploration, there are severe limitations on rocket performance. This chapter focuses on these limits and what we may ultimately expect from rocket-propelled space travel.

We are nearing the end of this introductory book on solar sailing. We saved one of the most intriguing topics—trajectory design—for last. However, it is beyond the scope of this book to delve deeply into mathematics and the related physical aspects. So after a very short presentation of the sailcraft motion equations, we discuss the class of trajectories (and missions) via several technical plots. Some trajectories have been designed in past decades, some were investigated in the first years of this century, and some have been calculated specifically for this book by means of modern (and very complex) computer codes. This chapter discusses sailcraft motion equations in their simple form, using no additional mathematics; presents generalized Keplerian orbits that only sailcraft can draw; describes interplanetary transfer by solar sailing; describes some of the new striking features solar-sail propulsion offers, such as the possibility of designing orbits that differ from the Keplerian ones significantly, which allows a mission designer to move beyond the limits of conventional spacecraft; discusses the behavior of a sailcraft under the gravitational influence of more than one celestial body; highlights the so-called artificial equilibrium points; explains the high nonlinear feature of very low sail-loading sailcraft.

In the previous chapters, we described the space rocket engines, how they work, their role in past and current spaceflight, and their limitations. We have also shown that the rocket is not the only propulsion type that could be employed in space. Among the types of space propulsion currently under investigation, one is particularly promising: the solar sail. This propulsion mode is not conceptually new, even though only recent technology gives it a good chance to make a quality jump in spaceflight. Its principles and how to efficiently use a sail vehicle could be understood better by reviewing what happened about four millennia ago on the seas and by referring to the progress of physics in the 19th and 20th centuries.