1990. Reaching Mars by sailboat

Welcome to the special section “GdV 5th Years.” We are introducing you, day by day, An article from the archives of the Journal of Sailing, starting in 1975. A word of advice, get in the habit of starting your day with the most exciting sailing stories-it will be like being on a boat even if you are ashore.

Appointment on Mars

Taken from the 1990 Journal of Sailing, Year 16, No. 04, May, pp. 46-51.

When it was still science fiction to land the first man on Mars, a group of visionaries in 1990 launched the challenge of the Space Sail Cup, the first space sailing regatta. It was serious, fascinating, with an Italian competitor. A project less crazy than it sounds.

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The challenge of the first Space Sail Cup, the first space sailing regatta, which will kick off in 1992, has been launched. Enrolled in this incredible “regatta” are only spacecraft capable of moving by harnessing the solar wind. As the destination, the planet Mars over 400 million kilometers from Earth, one of the most mysterious and fascinating in our galaxy. At the start of the regatta, which for now has only three competitors, an Italian spacecraft Capitana Italica, which recently won European selections. Born from a design by Aeritalia, Capitana Italica (pictured in the opening computer photo), features incredible technical solutions that have never been tried before. Equipped with a hull, mast and sails, whose surface area will be ten thousand square meters, it will be put into orbit by the Shuttle or an Ariane rocket and will take just over three years to reach the Red Planet.

The news is now known to everyone, thanks to the great prominence given to it by the daily press: theAeritalia, an Italian aerospace company controlled by the Iri Finmeccanica group, has won the selection among European challengers and will represent our continent in the “Columbus 500 Space Sail Cup.” As precisely the name implies, it is a real space “sail race” to be contested on the Earth – Mars route by rounding the Moon“buoy.” When I read the news in the “Corriere della Sera,” I thought that someone must have been brainwashed if they had been able to imagine a sailing ship propelled by the light of the Sun and, what’s more, capable of reaching Mars! Stuff to rival Julius Verne, however, a century late! What if it were possible? Here after not even a minute, the worm of doubt had been triggered and my chronic curious nature had come alive, stimulated in this case also by a certain vein of sadism: but can you imagine the face of Gardini and his multinational corporation set up specifically to win an America’s Cup and suddenly plunged into prehistory? There was enough to try to find out рі more. And so here I am trying to describe a marvelous and fascinating adventure that will see an Italian company,Aeritalia precisely, engaged as a protagonist in a seemingly science-fiction venture. This is not a simple competition, it is about demonstrating the possibility of “building” extremely complex structures in space and sailing to new worlds thanks to a sail propelled by sunlight. But how can light “inflate” a sail and steer a spacecraft?

The solar wind

It is necessary to clarify one thing at once: the “solar wind”, that is, the flow of high-speed protons and electrons emitted by the Sun and cited by several not-very-well-informed sources as the propeller of the “solar sail,” actually plays a minimal role: in fact, its thrust is 1,000 to 10,000 times less than that produced by light. Instead, it is precisely the light emitted by the Sun that will “blow” , very feebly when compared to the Earth’s wind, on the sails of the Space Sail Cup participants. Unfortunately, the concepts of quantum mechanics, which are used to understand the interactions between sunlight and sail, are not so easy to explain. And indeed, there must be a reason why a fellow named Albert Einstein won a Nobel Prize on these theories! Among other things, he established the principle of equivalence between mass and energy, expressing it with the well-known formula E=mc2 where there is the speed of light. Put simply, this means that since light, like all electromagnetic radiation in general, carries an energy (equal to the product of Plank’s constant and its frequency), we can imagine it as consisting of “corpuscles” (photons) that have no mass but are endowed with energy and moving at the speed of light (equal to about 300,000 km/s). When the photons strike the surface of the sail, a physical principle called “conservation of momentum” comes into play. according to which, in the case of “elastic” collision between two bodies (i.e., without either of them undergoing deformation), the mass-velocity product of the system formed by the two bodies remains constant before and after the collision. Beyond the learned enunciation, this principle means that, imagining the sail illuminated by sunlight as being “bombarded” by an infinity of photons, these, on striking its surface are deflected (reflected or absorbed) thus generating real pressure and thus giving rise to thrust. The intensity and orientation of this thrust depend on the inverse of the square of the Sun-sail distance (as the distance from the Sun increases, the force decreases quadratically, with the same sail area of course, for the “thinning out” of photons radially emitted by the Sun), the sail surface, the angle at which the radiation impinges on the sail, and the reflection/absorption characteristics of the sail, if perfectly reflective the “strength” grasped is twice that of a perfectly absorbent surface, (see Figure 1).To get an idea of the smallness of the forces involved, consider that 150,000,000 km from the Sunshine, that is, at the same distance as the Earth from Sunshine, the force exerted by the pressure of light incident perpendicularly on a perfectly reflecting sail of 10,000 square meters (one hectare, equal to a square of 100 m side!) is equal to about 0.09 Newton (9 grams on Earth!). The acceleration with which a spacecraft moves under the action of this force is governed by the law F=mxa and, in the case of a mass of 500 kg, will be equal to 0.18 mm/s2 (about 18 millionths of the acceleration of gravity!). The question that arises is: how is it possible with such a minimal force to reach Mars? And how is it possible to do so in a relatively short time? The answer is quite simple: in space, as is well known, there is no friction and therefore even a small accelerating force is sufficient to achieve continuous increases in speed (which will thus become very high). What is more, the spacecraft certainly does not start from a standstill on its journey to Mars: in fact, at the time of its release into its first orbit, it is moving around the Sun with the same speed as the Earth: 30 km/s, or 108,000 km/h.

The race course and tactics

We can distinguish the path of the spacecraft into 3 basic stages:

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1) in the first phase, the goal is to reach lunar orbit–the first “buoy” of the race–in the shortest possible time and pass as close to our satellite as possible, partly to take advantage of its gravitational field for propulsive purposes.
2) the immediate next goal will be to place the spacecraft into interplanetary orbit around the Sun, thereby disengaging it from Earth’s gravitational field.
3) The third phase will be the actual navigation to Mars.

Phases 1 and 2 are undoubtedly the most critical, as the spacecraft will be orbiting the Earth and will have to increase its rotational speed by ensuring that the thrust imparted by the sail is the maximum possible along the route. To do this will require continual maneuvering of the sail, which will come to be in some sections “against the sun” and in others with the “Sun aft” (see Figure 2). This will require sophisticated and continuous trim control, to allow the sail to be in a condition of maximum useful thrust at all times (see figure 3). Phase 3, on the other hand, will be possible to accomplish with 2 different “‘tactics.” A first tactic, which is simpler because it does not require attitude adjustments, is of the same type as that implemented to reach the Moon. This time, however, as the ship’s rotation is directly around the sun, the sail trim will be constant and such as to maximize total energy storage. With this tactic it is planned to reach Mars in about 4.8 years, describing the “spiral” (see Figure 4). The second possible tactic starts from the physical assumption that an elliptical orbit has the same energy content as a circular orbit having a radius equal to the semi-major axis of the ellipse itself. It is therefore possible, by following an elliptical orbit, to reach a single point in the orbit of Mars with less energy than that required by the first tactic. In this way, Mars could be reached in “only” 3.5 years (see figure 5), with consistent related difficulties, however, due to: the need to continuously adjust the sail to make the ship’s orbit elliptical around the Sun; and the navigational precision required to find oneself at the rendezvous with Mars at a very precise point in its orbit (see figure 6).

Aeritalia Project to “sail” to Mars

Why the name of “Capitana Italica”. Capitana was the first name of Christopher Columbus‘ flagship, renamed Santa Maria upon departure to propitiate the graces of heaven and the Catholic Queen of Spain. Capitana Italica is the name chosen byAeritalia to christen its ship (see Figure 7). It is a name laden with meanings that go beyond a simple Columbian commemoration and underscoresAeritalia ‘s leading role as an Italian, European, and global space industry. And better than that the adventure could not have begun. Capitana Italica indeed won the European selections by defeating 2 British, 2 French and no less than 4 projects submitted by the Soviet Union and snatching the following verdict from Klaus Heiss, creator of the Space Sail Cup: “Aeritalia presented the most complete, spectacular and realistic proposal. It is the most impressive project among those presented in Europe and, in several respects, also in comparison with those in the United States.” But let’s see in some detail what it looks like. It basically consists of three parts: the Sail, the Mast, and the actual Ship.

The sail – Constructed of 5-micron-thick Mylar and subjected to an “aluminization” treatment on the 2 faces to increase its reflective power, it has a surface area of 10,000 square meters. Its shape is square with a side of 100 meters. In order to make it possible to stow the entire spacecraft inside a standard container transportable by the Shuttle or an Ariane rocket, it was necessary to devise a very “daring” structure capable of unfolding itself once launched from the carrier. The idea is both very simple and ingenious: 4 inflatable spars hinged to the center of the sail and arranged according to the diagonals of the sail itself. These spars are real inflatable “tubes” like those of pneumatic dinghies, made of Kevlar fabric pre-impregnated with a special resin that can polymerize by the heat of the sun and the catalyst contained in the inflation gas. The sequence of sail opening is rap- presented in its four main stages on the opposite page. The total weight of the sail and support spars is only 126 kg! To make the most experienced sailmaker envious.

The mast-It consists of a carbon-fiber lattice structure that can extend telescopically and reach the operational length of about 10 meters.

The ship – It is the “brain” of the system. It contains the on-board computers, telecommunications equipment, facilities for scientific experiments, solar panels for generating the electricity needed to power the satellite services, and sail controllers.

by Paul Damia