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Lunar Farside Radio Lab
Acta Astronautica 56 (2005) 629 – 639 www.elsevier.com/locate/actaastro
Academy Transactions Note
Lunar Farside Radio Lab夡 Claudio Maccone∗,1 Via Martorelli 43, I-10155 Torino (TO), Italy Received 31 March 2004; received in revised form 6 August 2004; accepted 14 October 2004 Available online 6 January 2005
Abstract It is proposed that the Farside of the Moon should be protected legally against man-made radio pollution and uncontrolled exploitation. In fact, only by establishing a radiotelescope on the Farside of the Moon it will finally be possible to cope with the Radio Frequency Interference (RFI) that is now increasingly plaguing all of Radioastronomy, Bioastronomy and Search for Extraterrestrial Intelligence (SETI) Searches done from the surface of the Earth. It is suggested to partition the Farside into 3 sectors, each 60◦ wide, to ensure (1) the creation of a future “Lunar Farside Radio Lab” inside crater Daedalus (at 180◦ E) with our planned Radiotelescope (in practice a Phased Array), (2) complete freedom to exploit the Nearside as well as the four Lagrangian points L1, L3, L4 and L5 of the Earth–Moon system by allowing even some International Space Stations to be located there. It is also claimed, however, that (3) the “opposite” Lagrangian point L2 should possibly be kept free of spacecrafts that would flood the Farside by the RFI they produce. Realistically, it might be difficult to comply with the latter request in view of the far-future development of a Space Base located there in order to depart towards the Asteroids and the Outer Planets at very reduced fuel consumption. A more reasonable request about any future space station located at the Earth–Moon L2 point is thus that this future space station should be shielded to prevent its RFI from reaching the Farside of the Moon. (4) A number of further astrophysical, astronautical and technical issues could just be highlighted in this study and deserve much more elaboration. To mention a few: (i) the precise size of the “Quiet Cone” extending into space above the Farside of the Moon. Also, the experimental measurement of how quiet this Cone actually is by letting a radiometer orbit the Moon (see the web site www.rli.it); (ii) the mathematical modelling of the weak ionosphere of the Moon and its possible diffraction effects at very low frequencies. In other words, exploring the radio spectrum below 15 MHz (impossible from Earth) might open up a new era in Cosmology and Astrophysics in general; (iii) last, but not the least, the political problems involved with the future international exploitation of the Moon Farside. The IISL supported this author in this regard, but much more serious action should be undertaken, especially in conjunction with the United Nations. The protection of at least part of the Farside against wild commercial and military exploitation is regarded as the #1 priority of this study. © 2004 Elsevier Ltd. All rights reserved. 夡
Based on a presentation at the IAA “Cosmic studies” Meeting in Paris, March 17th, 2003.
∗ Corresponding author. Tel.: +39 011 2055 387; fax: +39 011 7180 012.
E-mail address: [email protected] (C. Maccone).
1 Member of the IAA and Co-Vice Chair, SETI Permanent Study Group of the IAA.
0094-5765/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2004.10.008
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1. Historical introduction: Jean Heidmann’s (1994) proposal for a SETI base in the Farside Saha Crater Historically, this “IAA Cosmic Study” was started back in 1994 by the French IAA Member Jean Heidmann (1923–2000). He proposed in 1994 that crater Saha on the Moon Farside was selected as location for a Farside radiotelescope. Untimely, Heidmann passed away on July 2nd, 2000, and the author of this paper, who had been appointed “Deputy Study Coordinator” by Heidmann himself, was asked by the IAA to succeed Heidmann as Coordinator of the “IAA Lunar SETI Cosmic Study”. He also was given by the IAA the task of enlarging the horizons of this Study and study all problems involved with setting up a Lunar Farside Radio Lab, rather than just Search for Extraterrestrial Intelligence (SETI) problems. This author appointed as his own deputy Dr. Mike Davis (SETI Institute) who had worked for many years at the Arecibo radiotelescope. Together, they drew a new development plan for this study that, after a meeting held at JPL on November 2nd, 2001, shaped up gradually to the present content. Essentially, all bioastronomical signals currently searched for by radioastronomers fall into two classes: (1) Radio signatures of molecules important to the development of life, like the 22 GHz water maser. (2) SETI signals, narrowband signals possibly broadcast by unknown extraterrestrial civilizations located somewhere in the Galaxy. To detect signals of either type, it is mandatory to reject all the Radio Frequency Interference (RFI) produced in ever increasing amounts by the technological growth of civilization on Earth. RFI pollution has now reached the point that large bands of the spectrum are blinded by all kinds of legal or illegal transmitters. Jean Heidmann repeatedly pointed out [1–3] that Radioastronomy, as it is currently conducted from the surface of the Earth, is doomed to die in a few decades if uncontrolled growth of RFI continues. Advances in modern space technology, however, could bring Radioastronomy to a new life, was it conducted from the Farside of the Moon, that is obviously shielded by the Moon spherical body from all RFI produced on Earth. As already stated, Heidmann proposed that a
radiotelescope should be placed inside the Saha crater, a ∼ 100 km crater located in between 101◦ E and 105◦ E and 2◦ of latitude South, surrounded by a 3000 m high circular rim. An Earth-pointing antenna should also have to be located in the Nearside Mare Smythii plain, linked to Saha “conveniently”. Since 1994, various authors studied in detail the link between Saha and Mare Smythii, and suggested it to be made by either optical fibers (plus a “tether” for the descent-on-the-Moon maneuver) or by a few relay stations to be landed on the Moon surface. The relevant space mission, however, is hard to design at a low cost [4]. Five more papers [5–9] related to the best exploitation of the Moon Farside were published or presented by this author at the IAA sessions in Toulouse (2001), Houston (2002) and Bremen (2003). 2. Terminal longitude on the Moon Farside for radio waves emitted by telecommunication satellites in orbit around the Earth In this section we prove a mathematical formula vital to select any RFI-free Moon Farside Base. We want to compute the small angle beyond the limb (the limb is the meridian having longitude 90◦ E on the Moon) where the radio waves coming from telecommunications satellites in circular orbit around the Earth still reach, i.e. they become tangent to the Moon’s spherical body. The new angle = +90◦ will be called “terminal longitude” of these radio waves. In practice, no radio wave from telecommunication satellites can hit the Moon surface at longitudes higher than this terminal longitude . To find (see Fig. 1) we draw the straight line tangent to the Moon’s sphere from G, the point tangent to the circular orbit having radius R. This straight line forms a right-angled triangle with the Earth–Moon axis EM, right angle at G. Next, consider the straight line parallel to the one above but from the Moon center M, intersecting the EG segment at a point P. Once again, the triangle EPM is right-angled in P, and it is similar to the previous triangle. So, the angle is now equal to the EMP angle. The latter can be found, since (1) The Earth–Moon distance E¯ M¯ = DEarth.Moon is known and we assume its worst case (Moon at perigee): Earth–Moon distance equal to 356,410 km.
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Fig. 1. The simple geometry defining the “terminal longitude, ” on the Farside of the Moon, where radio waves emitted by telecommunication satellites circling the Earth at a radius R are grazing the Moon surface.
Inverting the last equation and making the substitutions described at the points (1), (2) and (4), one gets the terminal longitude of radio waves on the Moon Farside (between 90◦ E and 180◦ E) emitted by a telecommunication satellite circling around the Earth at a distance R = atan
+ . 2 − (R − RMoon )2
R − RMoon 2 DEarth .Moon
Here the independent variable R can range only between 0 and the maximum value that does not make the above radical become negative, i.e. 0 R DEarth.Moon + RMoon . The equation above for shows that the (R) curve becomes vertical for R → (DEarth.Moon + RMoon ) and = 180◦ . Replacing for R the value of the geostationary radius, R = 42, 241.096 km, one finds for the Moon Farside terminal longitude the value =96.525◦ . This is how Heidmann came to select and propose crater Saha: he just used the above (unpublished, but obvious) argument to compute that the longitude of the needed crater had to be higher than the value of 96.525◦ . Then, allowing a little more tolerance of about 5◦ in longitude for further shielding by the Moon’s body, he finally declared in [1] that Saha was the “best” crater to establish a Lunar SETI base. For six years (1994–2000), no one thought of questioning Saha as “best” crater.
3. Selecting crater Daedalus at 180◦ E This author claims that Heidmann was too optimistic in excluding that telecommunications satellites will ever be put into orbits around the Earth higher than the geostationary orbit of 42,165 km. In other words, we feel that the time will come when commercial wars among the big industrial trusts running the telecommunications business by satellites will lead them to grab more and more space around the Earth. This amounts to pushing their satellites into orbits with apogee much higher than the geostationary one, with the result that crater Saha will be blinded as soon as a company decides to go higher than the geostationary orbit. The last remark is important for Bioastronomers. If we, the supporters of Bioastronomy, bet everything on a SETI and Bioastronomy Base located at Saha, then we may loose everything pretty soon! A “safer” crater must be selected further East along the Moon equator. How much further East? The answer is given by the diagram in Fig. 2, based on the above equation for . Terminal longitude on Moon in degrees
¯ = R segment (2) The E¯ P¯ segment equals the E¯ G minus the Moon radius, RMoon . (3) Using Pythagoras’ theorem one finds P¯ M¯ = ¯ ¯ (E M)2 − (E¯ P¯ )2 . (4) The tangent of the requested angle is then given by E¯ P¯ E¯ P¯ tan = = . ¯ ¯ ¯ 2 − (E¯ P¯ )2 PM (E¯ M)
180 170 160 150 140 130 120 110 100 90 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Telecom sat orbital radius in GEO units
Fig. 2. Terminal longitude (vertical axis) on the Moon Farside versus the telecommunication satellites orbital radius R around the Earth (horizontal axis), in units of the Earth’s geostationary radius (42,165 km).
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Fig. 3. An oblique of the crater Daedalus on the Lunar Farside, as seen from the Apollo 11 spacecraft in lunar orbit; the view looks southwest. Daedalus (formerly referred to as I.A.U. Crater No. 308) is located at 179◦ E longitude and 5.5◦ S latitude and has a diameter of about 50 statute miles (∼ 80 km) (photo courtesy NASA).
The vertical trait predicted by our equation for shows up in Fig. 2 as the “upgoing right branch”. This shows that, if we only take the equation for into account (as Heidmann did), the maximum distance from the Earth’s center for these telecommunication satellites is about 8.479 times the geostationary radius, corresponding to a circular orbital radius of about 357,500 km. Was a telecommunication satellite put in such a circular orbit around the Earth, its radio waves would flood Moon longitudes as high as about ∼ 175◦ or more. However, we did not take into account the Lagrangian points yet (see Fig. 4 for a summary about the five Lagrangian points of the Earth–Moon system). If we do, then it plainly appears that it will never be possible to put a satellite into a circular orbit around the Earth at a distance of 357,500 km. In fact, this distance is higher than the distance of 323,050 km of the Lagrangian point L1 nearest to the Earth, and the Lagrangian points are, by definition, the points of
zero orbital velocity in the two-body problem. One is thus led to the question: what is the Moon Farside terminal longitude corresponding to the distance of the nearest Lagrangian point, L1? The answer is provided by Eq. (1.3) upon replacing R = 323, 050 km, and the result is = 154.359◦ . In words, this amounts to the following result: the Moon Farside Sector in between 154.359◦ E and 154.359◦W will never be blinded by RFI coming from satellites orbiting the Earth alone. In other words, the limit of the blinded longitude as a function of the satellite’s orbital radius around the Earth is 180◦ (E and W longitudes just coincide at this meridian, corresponding to the “change-of-date line” on Earth). But this is the antipode to Earth on the Moon surface, that is the point exactly opposite to the Earth direction on the other side of the Moon. And our theorem simply proves that the antipode is the most shielded point on the Moon surface from radio waves coming from the Earth. An intuitive and obvious result, really.
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Fig. 4. The five Earth–Moon Lagrangian points (where Earth and Moon pulls cancel out): (1) Let R denote the Earth–Moon distance, that is 384,400 km. Then, the distance between the Moon and the Lagrangian point L1 equals 0.1596003 × R, i.e. 61,350 km. Consequently the Earth-to-L1 distance equals 0.8403997 × R, i.e. 323,050 km. (2) The distance between the Moon and the Lagrangian point L2 equals 0.1595926 × R, i.e. 61,347 km. (3) The distance between the Earth and the Lagrangian point L3 equals 0.992886 × R, i.e. 381,666 km. (4) The two “triangular” Lagrangian points L4 and L5 are just at distance R from Earth and Moon.
So, where are we going to locate our “Moon Farside Radio Lab” base? Just take a map of the Moon Farside and look. One notices that the antipode’s region is too rugged a region to establish a Moon base. Just about 5◦ South along the 180◦ meridian, however, one finds a large crater about 80 km in diameter, just like Saha. This crater is called Daedalus (Fig. 3). So, this study proposes to establish the first RFI-free base on the Moon just inside crater Daedalus, the most shielded crater of all on the Moon from Earth-made radio pollution!
4. This study’s vision of the Moon Farside for RFI-free Searches Let us replace the simpler value of = 154.359◦ by the simpler value of = 150◦ . This is in agreement with the need for having the borders of the Pristine
Sector making orthogonal angles to the directions of L4 and L5 (Fig. 4). The result is our vision of the Farside of the Moon, shown in Fig. 5. Fig. 5 shows a diagram of the Moon as seen from above its North Pole with the different “colonization regimes” proposed by this study. One sees that (1) The near side of the Moon is left totally free to activities of all kinds: scientific, commercial and industrial. (2) The Farside of the Moon is divided into three thirds, namely three sectors covering 60◦ in longitude each, out of which: (a) The Eastern Sector, in between 90◦ E and 150◦ E, can be used for installation of radio devices, but only under the control of the International Telecommunications Union (ITU-regime).
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Fig. 5. This study’s vision of the Moon Farside with the Daedalus Crater RFI-free Base for Bioastronomy, Radioastronomy and SETI. One or more International Space Stations (ISS) might also be located at the L4 and L5 Earth–Moon points in the future. Only the L2 point should be kept free from RFI-emitting devices, or, alternatively, these devices should be adequately shielded against flooding the Farside by means of their own RFI emissions.
(b) The Central Sector, in between 150◦ E and 150◦W, should be kept free from human exploitation, namely kept in its “pristine” radio environment totally free from man-made RFI. This Sector is where crater Daedalus is, a ∼ 100 km crater located in between 177◦ E and 179◦W and around 5◦ of latitude South. (c) The Western Sector, in between 90◦W and 150◦W, could be used for installation of radio devices, but only under the control of the International Telecommunications Union (ITUregime). Also: (1) The Eastern Sector is exactly opposite to the direction of the Lagrangian point L4, and so the body of the Moon completely shields the Eastern Sector from RFI produced at L4. Thus, L4 is fully “colonizable”. (2) The Western Sector is exactly opposite to the direction of the Lagrangian point L5, and so the body of the Moon completely shields the Western Sector from RFI produced at L5. Thus, L5 is fully “colonizable” in this study’s vision, whereas it was not so in Jean Heidmann’s vision. In other words, our study achieves the full bilateral symmetry of the vision itself around the plane passing
through the Earth–Moon axis and orthogonal to the Moon’s orbital plane. (3) It is suggested that L2 should not be utilized at all, since it faces crater Daedalus just at the latter’s zenith. Any RFI-producing device located at L2 would flood the whole of the Farside, and should be ruled out. L2, however, is the only Lagrangian point that should be kept free, out of the five located in the Earth–Moon system. Finally, L2 is not directly visible from the Earth since shielded by the Moon’s body, and that seems to call for “leaving L2 alone”! In case this “no-use” of L2 could not be practically feasible, then our vision requests that the RFI-producing devices to be located at L2 should be adequately shielded against emitting RFI towards the Farside. This concept is expanded in more detail in Section 8.
5. The further two Lagrangian points L1 and L2 of the Sun–Earth system: their “polluting” action on the Farside of the Moon There still is an unavoidable drawback, though. This is coming from the further two Lagrangian points L1 and L2 of the Sun–Earth system (Fig. 6), located along the Sun–Earth axis and outside the sphere of influence of the Earth, that has a radius of about 924,646 km around the Earth. Precisely, the Sun–Earth L1 point is located at a distance of 1,496,557.035 km from the Earth towards the Sun, and the L2 point at the (virtually identical) distance of 1,496,557.034 km from the Earth in the direction away from the Sun, that is toward the outer solar system. These two points have the “nice” property of moving around the Sun just with the same angular velocity as the Earth does, while also keeping at the same distance from the Earth at all times. Thus, they are ideal places for scientific satellites. Actually, the Sun–Earth L1 point has already been in use for scientific satellite location since the NASA ISEE III spacecraft was launched on 12 August 1978 and reached the Sun–Earth L1 region in about a month. On December 2, 1995, the ESA-NASA “Soho” spececraft for the exploration of the Solar Corona was launched. On February 14, 1996, Soho was inserted into a halo orbit around the Sun–Earth L1 point, where it is still librating now (July 2004).
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Fig. 6. In addition to the five Lagrangian points of the Earth–Moon system (already described in Fig. 4) the next two closest Lagrangian points to the Earth are the Lagrangian points L1 and L2 of the Sun–Earth system. These are located along the Sun–Earth axis at the distances of about 1.5 million kilometers from the Earth towards the Sun (L1) and away from it (L2). Spacecrafts located at either of them would flood the Moon Farside by their own emitted RFI for nearly half of the Moon’s synodic period (14.7 days) (drawing courtesy R. Farquhar).
As for the Sun–Earth L2 point, there are plans to let the NASA’s Space Interferometry Mission (SIM) satellite be placed there, as will probably be ESA’s GAIA astrometric satellite as well. So, all these satellites do “pollute” the otherwise RFI-free Farside of the Moon when the Farside is facing them. Unfortunately, the Moon Farside is facing the Sun–Earth L1 point for half of the Moon’s synodic period, about 14.75 days, and it is facing the Sun–Earth L2 point for the next 14.75 days. Really all the time! This radio pollution of the Moon Farside by scientific satellites located at the Lagrangian points L1 and L2 of the Sun–Earth system is, unfortunately, unavoidable. We can only hope that telecommunication satellites will never be put there. As for the scientific satellites already there or on the way, the radio frequencies they use are well known and usually narrowband. This should help the Fourier transform of the future spectrum analyzers to be located on the Moon Farside to get rid of these transmissions completely.
6. The Quiet Cone above the Farside of the Moon The spherical body of the Moon prevents all terrestrial electromagnetic waves from reaching the central part of the Farside, as described in the previous sections. But it does so also for a certain region of space above the Farside itself, that we have come to call the “Quiet Cone”. This definition is appropriate in as much as clearly the radio waves tangent to the
Moon body define a cone, and clearly the apex of such a cone is the closer to the Moon Farside the higher the radius R of the telecommunication satellites around the Earth is. To calculate how far into space the Quiet Cone extends, consider Fig. 2 again. The similarity between the rectangular triangles EGA and MLA (rectangular at G and L, respectively) shows at once that (EM + MA) : EG = MA : ML, i.e. (DEarth.Moon + HApex )/R = HApex /RMoon . Solving for HApex yields the height HApex of the apex of the Quiet Cone above the Moon Farside with respect to center of the Moon: DEarth.Moon RMoon . HApex (R) = R − RMoon A much more elaborated paper about the Quiet Cone was published by this author in 2003 [10]. Two numerical cases are important: (1) For geostationary orbits of 42,165 km, the corresponding apex of the Quiet Cone is located at about 16,000 km outward from the Moon center. In other words, this is how far the Quiet Cone extends into space nowadays, but practically the actual value may be lower in the year 2004 already, for we do not know about military satellites. (2) The lowest possible value of the apex height corresponds to a satellite circling the Earth at the maximum possible distance, namely at the distance of the Langrangian point L1. Thus, the minimal value of the apex is just 2,079 km.
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2.107 yMoon (f) yRelay On Near Side (f) ySETIsat (f_SETIsat)
1.5.107 1.107 5.10
7
0 −5.107 −1.107 −1.5.107 −2.107
−2.10 −1.5.10 −1.10 7
7
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−5.10
7
0
5.10
7
7 7 7 1.10 1.5.10 2.10
xMoon (f), xRelay On Near Side (f), xSETI sat (f_SETIsat)
Fig. 7. The “RadioMoon” space mission in the Moon’s equatorial plane: in the example, the orbiter is at 10,000 km and the Hohmann transfer lets a Phased Array be landed inside crater Daedalus.
7. Proposing “RadioMoon”: a new space mission to robotically set up and operate an RFI-free base inside crater Daedalus A technical difficulty to be faced is the radio link between the Earth and the Base at Daedalus. Because of the large distance of 2730 km between Daedalus and anywhere along the limb, it may be unfeasible to lay down optical fibers or landed data relays linking Daedalus to the Nearside. To solve this problem, we propose a new space mission dubbed “RadioMoon” and described briefly in this section (Fig. 7). RadioMoon is made up by two spacecrafts: one orbiter and one lander. They fly together from the Earth to the Moon and are initially parked in a Moon circular and equatorial orbit having a radius of say, 10,000 km. The orbital period of this single spacecraft around the Moon is 31.641 h (1.3 days). Then, at a time when the spacecraft is just crossing the Earth–Moon axis on the visible side, the lander is released from the orbiter and starts getting down towards the Moon surface along a Hohmann transfer half-elliptical trajectory. By the very definition of this Hohmann transfer, the lander just lands at the longitude of 180◦ E, namely inside crater Daedalus
(slightly different maneuvers there would slow down the spacecraft, to prevent it from crashing). The Hohmann transfer has these parameters: semimajor axis 6378 km, eccentricity 0.742, time to get down from 10,000 km along the half-ellipse 6 h 52.86 min. The lander would be protected by airbags against crashing. We know that such airbags worked out well on July 4, 1997, for the Mars Pathfinder landing on Mars. Since the gravity on the Moon is about a half of the gravity on Mars, there is no reason to doubt that such an airbag-protected landing would work equally well on the surface of the Moon. Finally, after touching down, the lander deploys a flat phased array capable of steering its beam electronically for all RFI-free Searches in Radioastronomy, Bioastronomy and SETI. The orbiter’s task is to gather data from the Phased Array at crater Daedalus when flying above the Farside, and transmit these data back to the Earth when flying above the near side and the other way round for giving the Earth’s instructions to the Phased Array operating at Daedalus, now dubbed the “Lunar Farside Radio Lab”. We contend this is by far the cheaper, easier and safer way to operate a Moon Farside Base.
8. The coming “Moon Rush”: trying to protect the Farside of the Moon against wild commercial, astronautical and military exploitation The Farside of the Moon is a unique Natural Preserve of humankind. It still is uncorrupted by manmade RFI. We have the moral duty to keep it so for the centuries to come by preventing any wild commercial, astronautical and military exploitation of the Moon Farside to take place in the future. How can we achieve a legal permanent protection of the Farside? The United Nations appears to be the natural international forum where this matter should be discussed. Also, the International Institute of Space Law (IISL) is the international leading mentor institution to approach the United Nations with the highest hope of success. This legal protection of the Farside, however, might well be just a dream! Reality could be much tougher, as neatly described, for instance, by the Los Angeles reporter Bill Carswell in his April 18, 2002, SpaceDaily article entitled “The
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Fig. 8. Much of the area around the south pole is within the South Pole-Aitken Basin (shown at right in dark on a lunar topography image), a giant impact crater 2500 km (1550 miles) in diameter and 12 km deep at its lowest point. Many smaller craters exist on the floor of this basin. Any water ice at the bottom of the crater could probably exist for billions of years at very low temperatures (Picture courtesy NASA).
Outer Space and Moon Treaties and the Coming Moon Rush” (download from the web site: http://www.spacedaily.com/news/oped-02c.html). In essence, any powerful enough, space-faring country could open up the Moon Rush right now, baffling all international laws, if any. Even if one decided to confine discussions to purely scientific matters, like geology, astrophysics and astrodynamics, there could be some conflicting exploration issues, such as the exploration of the socalled Aitken Basin. In fact, the story is that, on 5 March 1998 it was announced that data returned by the Lunar Prospector spacecraft indicated that water ice is present at both the north and south lunar poles, in agreement with Clementine results for the south pole reported in November 1996. And where is (or would be) this water ice located ? The answer is: within the largest known impact crater in the Solar System: the South Pole-Aitken Basin on the Farside of Earth’s Moon, over 1300 miles across, as shown in Fig. 8. From Fig. 8, it plainly appears that the Southern part of the Central Sector of the Farside would be of exceptional interest for ice hunters, and so this study could hardly ask for any protection of this Aitken Basin by the United Nations or by an international treatise.
In case some hope for legally protecting at least part of the Farside (outside the Aitken Basin) could possibly still exist, next came the news that the Earth–Moon Lagrangian point L2 would be a wonderful starting point for heavy spaceships to explore the Asteroids and Outer Planets. This remark is no less than the core of the IAA Cosmic Study S 1.1 “twin” to this one, namely “The Next Steps in Exploring Deep Space” Cosmic Study of the IAA, led by Drs. Wesley T. Huntress Jr. and Robert W. Farquhar. Academicians may view their wonderful Power Point pages by using the Restricted IAA Access to the web site http://www.iaanet.org/restrict/presentation.pdf. The (hopefully apparent) conflict between the two Cosmic Studies S 1.1 and S 1.2 lies in the question: what shall we put in the far future at the Earth–Moon Lagrangian point L2? Jean Heidmann’s initial answer to this question was just “nothing”, clearly to prevent that RFI made by this L2 Space Station could flood just the whole of the Farside! Wes Huntress and Bob Farquhar, however, convinced all Academicians at the Academy Day in Houston (October 2002) that L2 will be a wonderful space base from which to launch even big spaceships at little gravitational cost towards the Asteroids, Mars and the Outer Solar System Bodies. So, what shall we do?
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Fig. 9. Mandatory RFI Shield in space between a future Space Station located at the L2 Earth–Moon Lagrangian point and the Farside of the Moon. This shield would prevent the RFI produced at L2 from flooding the Farside of the Moon.
The author of this study would answer: we should enforce by law the construction of an “RFI Shield” in space in between the L2 Space Base and the Moon Farside, so as to prevent any RFI reach the Farside surface, as shown in Fig. 9. 9. Conclusions The Farside of the Moon is a unique place, since it is the nearest (and only) place close to Earth to be totally free from man-made RFI. As such, the Farside is just humankind’s natural spot for conducting RFI-free radio explorations of all kinds, ranging from Cosmology to Astrophysics and the radio Contact with alien civilizations in the Universe (SETI). The Farside of the Moon should thus be protected by international agreements against an otherwise too easy and too wild commercial, industrial and military exploitation, unfortunately just a few years ahead. Acknowledgements The author is grateful to Drs. Michael I. Yarymovych, President of the IAA at the time when he took charge of this study, Ed Stone, current President of the IAA, Gerhard Haerendel, former President of COSPAR, and Jean Michel Contant, Secretary General of the IAA, for their encouragement and support. Dr. Mike Davis of the SETI Institute provided the
author with vital information about research done in the USA on many of topics related to this study. The cooperation of the following Jet Propulsion Laboratory current or past employees and leading astronautical experts is gratefully acknowledged: Drs. Macgregor S. Reid, Thomas B. H. Kuiper, Thomas R. McDonough, Dyton Jones, Michael J. Mahoney, Carl Palko. Substantial contributions at the JPL Meeting held on November 2nd, 2001 were also given by Drs. Philip Venturelli of Caltech, Leslie I. Tennen of the Law Offices of Sterns and Tennen in Phoenix, AZ, and Louis D. Friedman, Executive Director of the Planetary Society. Finally, the excellent research work of young and bright Mr. Yuki Takahashi of Japan is greatefully acknowledged, and so is his rich Lunar web site: http://www.astro.gla.ac.uk/users/yuki/.
References [1] J. Heidmann, Saha Crater: a candidate for a SETI Lunar base Academy Transactions Note, Acta Astronautica 32 (1994) 471–472. [2] J. Heidmann, Sharing the moon by thirds: an extended Saha Crater proposal, Advances in Space Research 26 (2000) 371–375. [3] J. Heidmann, Recent progress on the Lunar Farside Crater Saha Proposal, Acta Astronautica 46 (2000) 661–665. [4] C. Maccone, Laydown of a tether from Earth visible location to far side for Lunar SETI, Advances in Space Research 26 (2000) 359–370.
C. Maccone / Acta Astronautica 56 (2005) 629 – 639 [5] C. Maccone, Searching for bioastronomical signals from the Farside of the Moon, First European Workshop on Exo/Astrobiology held at ESRIN, Frascati, Italy, 21–23 May 2001, published by ESA in the relevant Proceedings called ESA SP-496, August 2001, p. 277–280. [6] C. Maccone, The Lunar SETI cosmic study of IAA: current status and perspectives, paper IAA-01-IAA.9.1.05, 52nd International Astronautical Congress, Toulouse, France, 1–5 October 2001. [7] C. Maccone, Planetary defense and RFI-free radioastronomy from the Farside of the Moon: a unified vision, Acta Astronautica 50 (2002) 185–199.
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[8] C. Maccone, The Lunar Farside Radio Lab Study of IAA, paper IAA-02-IAA.9.1.4, 53rd International Astronautical Congress (World Space Congress—2002), Houston, Texas, 10–19 October 2002. [9] C. Maccone, Lunar Farside Radio Lab: a “Cosmic Study” by the International Academy of Astronautics, Paper # IAA.8.3 03, 14th Space Activity and Society Symposium during the 2003 International Astronautical Congress, Bremen, Germany, September 29–October 3, 2003. [10] C. Maccone, The Quiet Cone above the Farside of the Moon, Acta Astronautica 53 (2003) 65–70.
Academy Transactions Note
Lunar Farside Radio Lab夡 Claudio Maccone∗,1 Via Martorelli 43, I-10155 Torino (TO), Italy Received 31 March 2004; received in revised form 6 August 2004; accepted 14 October 2004 Available online 6 January 2005
Abstract It is proposed that the Farside of the Moon should be protected legally against man-made radio pollution and uncontrolled exploitation. In fact, only by establishing a radiotelescope on the Farside of the Moon it will finally be possible to cope with the Radio Frequency Interference (RFI) that is now increasingly plaguing all of Radioastronomy, Bioastronomy and Search for Extraterrestrial Intelligence (SETI) Searches done from the surface of the Earth. It is suggested to partition the Farside into 3 sectors, each 60◦ wide, to ensure (1) the creation of a future “Lunar Farside Radio Lab” inside crater Daedalus (at 180◦ E) with our planned Radiotelescope (in practice a Phased Array), (2) complete freedom to exploit the Nearside as well as the four Lagrangian points L1, L3, L4 and L5 of the Earth–Moon system by allowing even some International Space Stations to be located there. It is also claimed, however, that (3) the “opposite” Lagrangian point L2 should possibly be kept free of spacecrafts that would flood the Farside by the RFI they produce. Realistically, it might be difficult to comply with the latter request in view of the far-future development of a Space Base located there in order to depart towards the Asteroids and the Outer Planets at very reduced fuel consumption. A more reasonable request about any future space station located at the Earth–Moon L2 point is thus that this future space station should be shielded to prevent its RFI from reaching the Farside of the Moon. (4) A number of further astrophysical, astronautical and technical issues could just be highlighted in this study and deserve much more elaboration. To mention a few: (i) the precise size of the “Quiet Cone” extending into space above the Farside of the Moon. Also, the experimental measurement of how quiet this Cone actually is by letting a radiometer orbit the Moon (see the web site www.rli.it); (ii) the mathematical modelling of the weak ionosphere of the Moon and its possible diffraction effects at very low frequencies. In other words, exploring the radio spectrum below 15 MHz (impossible from Earth) might open up a new era in Cosmology and Astrophysics in general; (iii) last, but not the least, the political problems involved with the future international exploitation of the Moon Farside. The IISL supported this author in this regard, but much more serious action should be undertaken, especially in conjunction with the United Nations. The protection of at least part of the Farside against wild commercial and military exploitation is regarded as the #1 priority of this study. © 2004 Elsevier Ltd. All rights reserved. 夡
Based on a presentation at the IAA “Cosmic studies” Meeting in Paris, March 17th, 2003.
∗ Corresponding author. Tel.: +39 011 2055 387; fax: +39 011 7180 012.
E-mail address: [email protected] (C. Maccone).
1 Member of the IAA and Co-Vice Chair, SETI Permanent Study Group of the IAA.
0094-5765/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2004.10.008
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1. Historical introduction: Jean Heidmann’s (1994) proposal for a SETI base in the Farside Saha Crater Historically, this “IAA Cosmic Study” was started back in 1994 by the French IAA Member Jean Heidmann (1923–2000). He proposed in 1994 that crater Saha on the Moon Farside was selected as location for a Farside radiotelescope. Untimely, Heidmann passed away on July 2nd, 2000, and the author of this paper, who had been appointed “Deputy Study Coordinator” by Heidmann himself, was asked by the IAA to succeed Heidmann as Coordinator of the “IAA Lunar SETI Cosmic Study”. He also was given by the IAA the task of enlarging the horizons of this Study and study all problems involved with setting up a Lunar Farside Radio Lab, rather than just Search for Extraterrestrial Intelligence (SETI) problems. This author appointed as his own deputy Dr. Mike Davis (SETI Institute) who had worked for many years at the Arecibo radiotelescope. Together, they drew a new development plan for this study that, after a meeting held at JPL on November 2nd, 2001, shaped up gradually to the present content. Essentially, all bioastronomical signals currently searched for by radioastronomers fall into two classes: (1) Radio signatures of molecules important to the development of life, like the 22 GHz water maser. (2) SETI signals, narrowband signals possibly broadcast by unknown extraterrestrial civilizations located somewhere in the Galaxy. To detect signals of either type, it is mandatory to reject all the Radio Frequency Interference (RFI) produced in ever increasing amounts by the technological growth of civilization on Earth. RFI pollution has now reached the point that large bands of the spectrum are blinded by all kinds of legal or illegal transmitters. Jean Heidmann repeatedly pointed out [1–3] that Radioastronomy, as it is currently conducted from the surface of the Earth, is doomed to die in a few decades if uncontrolled growth of RFI continues. Advances in modern space technology, however, could bring Radioastronomy to a new life, was it conducted from the Farside of the Moon, that is obviously shielded by the Moon spherical body from all RFI produced on Earth. As already stated, Heidmann proposed that a
radiotelescope should be placed inside the Saha crater, a ∼ 100 km crater located in between 101◦ E and 105◦ E and 2◦ of latitude South, surrounded by a 3000 m high circular rim. An Earth-pointing antenna should also have to be located in the Nearside Mare Smythii plain, linked to Saha “conveniently”. Since 1994, various authors studied in detail the link between Saha and Mare Smythii, and suggested it to be made by either optical fibers (plus a “tether” for the descent-on-the-Moon maneuver) or by a few relay stations to be landed on the Moon surface. The relevant space mission, however, is hard to design at a low cost [4]. Five more papers [5–9] related to the best exploitation of the Moon Farside were published or presented by this author at the IAA sessions in Toulouse (2001), Houston (2002) and Bremen (2003). 2. Terminal longitude on the Moon Farside for radio waves emitted by telecommunication satellites in orbit around the Earth In this section we prove a mathematical formula vital to select any RFI-free Moon Farside Base. We want to compute the small angle beyond the limb (the limb is the meridian having longitude 90◦ E on the Moon) where the radio waves coming from telecommunications satellites in circular orbit around the Earth still reach, i.e. they become tangent to the Moon’s spherical body. The new angle = +90◦ will be called “terminal longitude” of these radio waves. In practice, no radio wave from telecommunication satellites can hit the Moon surface at longitudes higher than this terminal longitude . To find (see Fig. 1) we draw the straight line tangent to the Moon’s sphere from G, the point tangent to the circular orbit having radius R. This straight line forms a right-angled triangle with the Earth–Moon axis EM, right angle at G. Next, consider the straight line parallel to the one above but from the Moon center M, intersecting the EG segment at a point P. Once again, the triangle EPM is right-angled in P, and it is similar to the previous triangle. So, the angle is now equal to the EMP angle. The latter can be found, since (1) The Earth–Moon distance E¯ M¯ = DEarth.Moon is known and we assume its worst case (Moon at perigee): Earth–Moon distance equal to 356,410 km.
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Fig. 1. The simple geometry defining the “terminal longitude, ” on the Farside of the Moon, where radio waves emitted by telecommunication satellites circling the Earth at a radius R are grazing the Moon surface.
Inverting the last equation and making the substitutions described at the points (1), (2) and (4), one gets the terminal longitude of radio waves on the Moon Farside (between 90◦ E and 180◦ E) emitted by a telecommunication satellite circling around the Earth at a distance R = atan
+ . 2 − (R − RMoon )2
R − RMoon 2 DEarth .Moon
Here the independent variable R can range only between 0 and the maximum value that does not make the above radical become negative, i.e. 0 R DEarth.Moon + RMoon . The equation above for shows that the (R) curve becomes vertical for R → (DEarth.Moon + RMoon ) and = 180◦ . Replacing for R the value of the geostationary radius, R = 42, 241.096 km, one finds for the Moon Farside terminal longitude the value =96.525◦ . This is how Heidmann came to select and propose crater Saha: he just used the above (unpublished, but obvious) argument to compute that the longitude of the needed crater had to be higher than the value of 96.525◦ . Then, allowing a little more tolerance of about 5◦ in longitude for further shielding by the Moon’s body, he finally declared in [1] that Saha was the “best” crater to establish a Lunar SETI base. For six years (1994–2000), no one thought of questioning Saha as “best” crater.
3. Selecting crater Daedalus at 180◦ E This author claims that Heidmann was too optimistic in excluding that telecommunications satellites will ever be put into orbits around the Earth higher than the geostationary orbit of 42,165 km. In other words, we feel that the time will come when commercial wars among the big industrial trusts running the telecommunications business by satellites will lead them to grab more and more space around the Earth. This amounts to pushing their satellites into orbits with apogee much higher than the geostationary one, with the result that crater Saha will be blinded as soon as a company decides to go higher than the geostationary orbit. The last remark is important for Bioastronomers. If we, the supporters of Bioastronomy, bet everything on a SETI and Bioastronomy Base located at Saha, then we may loose everything pretty soon! A “safer” crater must be selected further East along the Moon equator. How much further East? The answer is given by the diagram in Fig. 2, based on the above equation for . Terminal longitude on Moon in degrees
¯ = R segment (2) The E¯ P¯ segment equals the E¯ G minus the Moon radius, RMoon . (3) Using Pythagoras’ theorem one finds P¯ M¯ = ¯ ¯ (E M)2 − (E¯ P¯ )2 . (4) The tangent of the requested angle is then given by E¯ P¯ E¯ P¯ tan = = . ¯ ¯ ¯ 2 − (E¯ P¯ )2 PM (E¯ M)
180 170 160 150 140 130 120 110 100 90 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Telecom sat orbital radius in GEO units
Fig. 2. Terminal longitude (vertical axis) on the Moon Farside versus the telecommunication satellites orbital radius R around the Earth (horizontal axis), in units of the Earth’s geostationary radius (42,165 km).
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Fig. 3. An oblique of the crater Daedalus on the Lunar Farside, as seen from the Apollo 11 spacecraft in lunar orbit; the view looks southwest. Daedalus (formerly referred to as I.A.U. Crater No. 308) is located at 179◦ E longitude and 5.5◦ S latitude and has a diameter of about 50 statute miles (∼ 80 km) (photo courtesy NASA).
The vertical trait predicted by our equation for shows up in Fig. 2 as the “upgoing right branch”. This shows that, if we only take the equation for into account (as Heidmann did), the maximum distance from the Earth’s center for these telecommunication satellites is about 8.479 times the geostationary radius, corresponding to a circular orbital radius of about 357,500 km. Was a telecommunication satellite put in such a circular orbit around the Earth, its radio waves would flood Moon longitudes as high as about ∼ 175◦ or more. However, we did not take into account the Lagrangian points yet (see Fig. 4 for a summary about the five Lagrangian points of the Earth–Moon system). If we do, then it plainly appears that it will never be possible to put a satellite into a circular orbit around the Earth at a distance of 357,500 km. In fact, this distance is higher than the distance of 323,050 km of the Lagrangian point L1 nearest to the Earth, and the Lagrangian points are, by definition, the points of
zero orbital velocity in the two-body problem. One is thus led to the question: what is the Moon Farside terminal longitude corresponding to the distance of the nearest Lagrangian point, L1? The answer is provided by Eq. (1.3) upon replacing R = 323, 050 km, and the result is = 154.359◦ . In words, this amounts to the following result: the Moon Farside Sector in between 154.359◦ E and 154.359◦W will never be blinded by RFI coming from satellites orbiting the Earth alone. In other words, the limit of the blinded longitude as a function of the satellite’s orbital radius around the Earth is 180◦ (E and W longitudes just coincide at this meridian, corresponding to the “change-of-date line” on Earth). But this is the antipode to Earth on the Moon surface, that is the point exactly opposite to the Earth direction on the other side of the Moon. And our theorem simply proves that the antipode is the most shielded point on the Moon surface from radio waves coming from the Earth. An intuitive and obvious result, really.
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Fig. 4. The five Earth–Moon Lagrangian points (where Earth and Moon pulls cancel out): (1) Let R denote the Earth–Moon distance, that is 384,400 km. Then, the distance between the Moon and the Lagrangian point L1 equals 0.1596003 × R, i.e. 61,350 km. Consequently the Earth-to-L1 distance equals 0.8403997 × R, i.e. 323,050 km. (2) The distance between the Moon and the Lagrangian point L2 equals 0.1595926 × R, i.e. 61,347 km. (3) The distance between the Earth and the Lagrangian point L3 equals 0.992886 × R, i.e. 381,666 km. (4) The two “triangular” Lagrangian points L4 and L5 are just at distance R from Earth and Moon.
So, where are we going to locate our “Moon Farside Radio Lab” base? Just take a map of the Moon Farside and look. One notices that the antipode’s region is too rugged a region to establish a Moon base. Just about 5◦ South along the 180◦ meridian, however, one finds a large crater about 80 km in diameter, just like Saha. This crater is called Daedalus (Fig. 3). So, this study proposes to establish the first RFI-free base on the Moon just inside crater Daedalus, the most shielded crater of all on the Moon from Earth-made radio pollution!
4. This study’s vision of the Moon Farside for RFI-free Searches Let us replace the simpler value of = 154.359◦ by the simpler value of = 150◦ . This is in agreement with the need for having the borders of the Pristine
Sector making orthogonal angles to the directions of L4 and L5 (Fig. 4). The result is our vision of the Farside of the Moon, shown in Fig. 5. Fig. 5 shows a diagram of the Moon as seen from above its North Pole with the different “colonization regimes” proposed by this study. One sees that (1) The near side of the Moon is left totally free to activities of all kinds: scientific, commercial and industrial. (2) The Farside of the Moon is divided into three thirds, namely three sectors covering 60◦ in longitude each, out of which: (a) The Eastern Sector, in between 90◦ E and 150◦ E, can be used for installation of radio devices, but only under the control of the International Telecommunications Union (ITU-regime).
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Fig. 5. This study’s vision of the Moon Farside with the Daedalus Crater RFI-free Base for Bioastronomy, Radioastronomy and SETI. One or more International Space Stations (ISS) might also be located at the L4 and L5 Earth–Moon points in the future. Only the L2 point should be kept free from RFI-emitting devices, or, alternatively, these devices should be adequately shielded against flooding the Farside by means of their own RFI emissions.
(b) The Central Sector, in between 150◦ E and 150◦W, should be kept free from human exploitation, namely kept in its “pristine” radio environment totally free from man-made RFI. This Sector is where crater Daedalus is, a ∼ 100 km crater located in between 177◦ E and 179◦W and around 5◦ of latitude South. (c) The Western Sector, in between 90◦W and 150◦W, could be used for installation of radio devices, but only under the control of the International Telecommunications Union (ITUregime). Also: (1) The Eastern Sector is exactly opposite to the direction of the Lagrangian point L4, and so the body of the Moon completely shields the Eastern Sector from RFI produced at L4. Thus, L4 is fully “colonizable”. (2) The Western Sector is exactly opposite to the direction of the Lagrangian point L5, and so the body of the Moon completely shields the Western Sector from RFI produced at L5. Thus, L5 is fully “colonizable” in this study’s vision, whereas it was not so in Jean Heidmann’s vision. In other words, our study achieves the full bilateral symmetry of the vision itself around the plane passing
through the Earth–Moon axis and orthogonal to the Moon’s orbital plane. (3) It is suggested that L2 should not be utilized at all, since it faces crater Daedalus just at the latter’s zenith. Any RFI-producing device located at L2 would flood the whole of the Farside, and should be ruled out. L2, however, is the only Lagrangian point that should be kept free, out of the five located in the Earth–Moon system. Finally, L2 is not directly visible from the Earth since shielded by the Moon’s body, and that seems to call for “leaving L2 alone”! In case this “no-use” of L2 could not be practically feasible, then our vision requests that the RFI-producing devices to be located at L2 should be adequately shielded against emitting RFI towards the Farside. This concept is expanded in more detail in Section 8.
5. The further two Lagrangian points L1 and L2 of the Sun–Earth system: their “polluting” action on the Farside of the Moon There still is an unavoidable drawback, though. This is coming from the further two Lagrangian points L1 and L2 of the Sun–Earth system (Fig. 6), located along the Sun–Earth axis and outside the sphere of influence of the Earth, that has a radius of about 924,646 km around the Earth. Precisely, the Sun–Earth L1 point is located at a distance of 1,496,557.035 km from the Earth towards the Sun, and the L2 point at the (virtually identical) distance of 1,496,557.034 km from the Earth in the direction away from the Sun, that is toward the outer solar system. These two points have the “nice” property of moving around the Sun just with the same angular velocity as the Earth does, while also keeping at the same distance from the Earth at all times. Thus, they are ideal places for scientific satellites. Actually, the Sun–Earth L1 point has already been in use for scientific satellite location since the NASA ISEE III spacecraft was launched on 12 August 1978 and reached the Sun–Earth L1 region in about a month. On December 2, 1995, the ESA-NASA “Soho” spececraft for the exploration of the Solar Corona was launched. On February 14, 1996, Soho was inserted into a halo orbit around the Sun–Earth L1 point, where it is still librating now (July 2004).
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Fig. 6. In addition to the five Lagrangian points of the Earth–Moon system (already described in Fig. 4) the next two closest Lagrangian points to the Earth are the Lagrangian points L1 and L2 of the Sun–Earth system. These are located along the Sun–Earth axis at the distances of about 1.5 million kilometers from the Earth towards the Sun (L1) and away from it (L2). Spacecrafts located at either of them would flood the Moon Farside by their own emitted RFI for nearly half of the Moon’s synodic period (14.7 days) (drawing courtesy R. Farquhar).
As for the Sun–Earth L2 point, there are plans to let the NASA’s Space Interferometry Mission (SIM) satellite be placed there, as will probably be ESA’s GAIA astrometric satellite as well. So, all these satellites do “pollute” the otherwise RFI-free Farside of the Moon when the Farside is facing them. Unfortunately, the Moon Farside is facing the Sun–Earth L1 point for half of the Moon’s synodic period, about 14.75 days, and it is facing the Sun–Earth L2 point for the next 14.75 days. Really all the time! This radio pollution of the Moon Farside by scientific satellites located at the Lagrangian points L1 and L2 of the Sun–Earth system is, unfortunately, unavoidable. We can only hope that telecommunication satellites will never be put there. As for the scientific satellites already there or on the way, the radio frequencies they use are well known and usually narrowband. This should help the Fourier transform of the future spectrum analyzers to be located on the Moon Farside to get rid of these transmissions completely.
6. The Quiet Cone above the Farside of the Moon The spherical body of the Moon prevents all terrestrial electromagnetic waves from reaching the central part of the Farside, as described in the previous sections. But it does so also for a certain region of space above the Farside itself, that we have come to call the “Quiet Cone”. This definition is appropriate in as much as clearly the radio waves tangent to the
Moon body define a cone, and clearly the apex of such a cone is the closer to the Moon Farside the higher the radius R of the telecommunication satellites around the Earth is. To calculate how far into space the Quiet Cone extends, consider Fig. 2 again. The similarity between the rectangular triangles EGA and MLA (rectangular at G and L, respectively) shows at once that (EM + MA) : EG = MA : ML, i.e. (DEarth.Moon + HApex )/R = HApex /RMoon . Solving for HApex yields the height HApex of the apex of the Quiet Cone above the Moon Farside with respect to center of the Moon: DEarth.Moon RMoon . HApex (R) = R − RMoon A much more elaborated paper about the Quiet Cone was published by this author in 2003 [10]. Two numerical cases are important: (1) For geostationary orbits of 42,165 km, the corresponding apex of the Quiet Cone is located at about 16,000 km outward from the Moon center. In other words, this is how far the Quiet Cone extends into space nowadays, but practically the actual value may be lower in the year 2004 already, for we do not know about military satellites. (2) The lowest possible value of the apex height corresponds to a satellite circling the Earth at the maximum possible distance, namely at the distance of the Langrangian point L1. Thus, the minimal value of the apex is just 2,079 km.
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2.107 yMoon (f) yRelay On Near Side (f) ySETIsat (f_SETIsat)
1.5.107 1.107 5.10
7
0 −5.107 −1.107 −1.5.107 −2.107
−2.10 −1.5.10 −1.10 7
7
7
−5.10
7
0
5.10
7
7 7 7 1.10 1.5.10 2.10
xMoon (f), xRelay On Near Side (f), xSETI sat (f_SETIsat)
Fig. 7. The “RadioMoon” space mission in the Moon’s equatorial plane: in the example, the orbiter is at 10,000 km and the Hohmann transfer lets a Phased Array be landed inside crater Daedalus.
7. Proposing “RadioMoon”: a new space mission to robotically set up and operate an RFI-free base inside crater Daedalus A technical difficulty to be faced is the radio link between the Earth and the Base at Daedalus. Because of the large distance of 2730 km between Daedalus and anywhere along the limb, it may be unfeasible to lay down optical fibers or landed data relays linking Daedalus to the Nearside. To solve this problem, we propose a new space mission dubbed “RadioMoon” and described briefly in this section (Fig. 7). RadioMoon is made up by two spacecrafts: one orbiter and one lander. They fly together from the Earth to the Moon and are initially parked in a Moon circular and equatorial orbit having a radius of say, 10,000 km. The orbital period of this single spacecraft around the Moon is 31.641 h (1.3 days). Then, at a time when the spacecraft is just crossing the Earth–Moon axis on the visible side, the lander is released from the orbiter and starts getting down towards the Moon surface along a Hohmann transfer half-elliptical trajectory. By the very definition of this Hohmann transfer, the lander just lands at the longitude of 180◦ E, namely inside crater Daedalus
(slightly different maneuvers there would slow down the spacecraft, to prevent it from crashing). The Hohmann transfer has these parameters: semimajor axis 6378 km, eccentricity 0.742, time to get down from 10,000 km along the half-ellipse 6 h 52.86 min. The lander would be protected by airbags against crashing. We know that such airbags worked out well on July 4, 1997, for the Mars Pathfinder landing on Mars. Since the gravity on the Moon is about a half of the gravity on Mars, there is no reason to doubt that such an airbag-protected landing would work equally well on the surface of the Moon. Finally, after touching down, the lander deploys a flat phased array capable of steering its beam electronically for all RFI-free Searches in Radioastronomy, Bioastronomy and SETI. The orbiter’s task is to gather data from the Phased Array at crater Daedalus when flying above the Farside, and transmit these data back to the Earth when flying above the near side and the other way round for giving the Earth’s instructions to the Phased Array operating at Daedalus, now dubbed the “Lunar Farside Radio Lab”. We contend this is by far the cheaper, easier and safer way to operate a Moon Farside Base.
8. The coming “Moon Rush”: trying to protect the Farside of the Moon against wild commercial, astronautical and military exploitation The Farside of the Moon is a unique Natural Preserve of humankind. It still is uncorrupted by manmade RFI. We have the moral duty to keep it so for the centuries to come by preventing any wild commercial, astronautical and military exploitation of the Moon Farside to take place in the future. How can we achieve a legal permanent protection of the Farside? The United Nations appears to be the natural international forum where this matter should be discussed. Also, the International Institute of Space Law (IISL) is the international leading mentor institution to approach the United Nations with the highest hope of success. This legal protection of the Farside, however, might well be just a dream! Reality could be much tougher, as neatly described, for instance, by the Los Angeles reporter Bill Carswell in his April 18, 2002, SpaceDaily article entitled “The
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Fig. 8. Much of the area around the south pole is within the South Pole-Aitken Basin (shown at right in dark on a lunar topography image), a giant impact crater 2500 km (1550 miles) in diameter and 12 km deep at its lowest point. Many smaller craters exist on the floor of this basin. Any water ice at the bottom of the crater could probably exist for billions of years at very low temperatures (Picture courtesy NASA).
Outer Space and Moon Treaties and the Coming Moon Rush” (download from the web site: http://www.spacedaily.com/news/oped-02c.html). In essence, any powerful enough, space-faring country could open up the Moon Rush right now, baffling all international laws, if any. Even if one decided to confine discussions to purely scientific matters, like geology, astrophysics and astrodynamics, there could be some conflicting exploration issues, such as the exploration of the socalled Aitken Basin. In fact, the story is that, on 5 March 1998 it was announced that data returned by the Lunar Prospector spacecraft indicated that water ice is present at both the north and south lunar poles, in agreement with Clementine results for the south pole reported in November 1996. And where is (or would be) this water ice located ? The answer is: within the largest known impact crater in the Solar System: the South Pole-Aitken Basin on the Farside of Earth’s Moon, over 1300 miles across, as shown in Fig. 8. From Fig. 8, it plainly appears that the Southern part of the Central Sector of the Farside would be of exceptional interest for ice hunters, and so this study could hardly ask for any protection of this Aitken Basin by the United Nations or by an international treatise.
In case some hope for legally protecting at least part of the Farside (outside the Aitken Basin) could possibly still exist, next came the news that the Earth–Moon Lagrangian point L2 would be a wonderful starting point for heavy spaceships to explore the Asteroids and Outer Planets. This remark is no less than the core of the IAA Cosmic Study S 1.1 “twin” to this one, namely “The Next Steps in Exploring Deep Space” Cosmic Study of the IAA, led by Drs. Wesley T. Huntress Jr. and Robert W. Farquhar. Academicians may view their wonderful Power Point pages by using the Restricted IAA Access to the web site http://www.iaanet.org/restrict/presentation.pdf. The (hopefully apparent) conflict between the two Cosmic Studies S 1.1 and S 1.2 lies in the question: what shall we put in the far future at the Earth–Moon Lagrangian point L2? Jean Heidmann’s initial answer to this question was just “nothing”, clearly to prevent that RFI made by this L2 Space Station could flood just the whole of the Farside! Wes Huntress and Bob Farquhar, however, convinced all Academicians at the Academy Day in Houston (October 2002) that L2 will be a wonderful space base from which to launch even big spaceships at little gravitational cost towards the Asteroids, Mars and the Outer Solar System Bodies. So, what shall we do?
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Fig. 9. Mandatory RFI Shield in space between a future Space Station located at the L2 Earth–Moon Lagrangian point and the Farside of the Moon. This shield would prevent the RFI produced at L2 from flooding the Farside of the Moon.
The author of this study would answer: we should enforce by law the construction of an “RFI Shield” in space in between the L2 Space Base and the Moon Farside, so as to prevent any RFI reach the Farside surface, as shown in Fig. 9. 9. Conclusions The Farside of the Moon is a unique place, since it is the nearest (and only) place close to Earth to be totally free from man-made RFI. As such, the Farside is just humankind’s natural spot for conducting RFI-free radio explorations of all kinds, ranging from Cosmology to Astrophysics and the radio Contact with alien civilizations in the Universe (SETI). The Farside of the Moon should thus be protected by international agreements against an otherwise too easy and too wild commercial, industrial and military exploitation, unfortunately just a few years ahead. Acknowledgements The author is grateful to Drs. Michael I. Yarymovych, President of the IAA at the time when he took charge of this study, Ed Stone, current President of the IAA, Gerhard Haerendel, former President of COSPAR, and Jean Michel Contant, Secretary General of the IAA, for their encouragement and support. Dr. Mike Davis of the SETI Institute provided the
author with vital information about research done in the USA on many of topics related to this study. The cooperation of the following Jet Propulsion Laboratory current or past employees and leading astronautical experts is gratefully acknowledged: Drs. Macgregor S. Reid, Thomas B. H. Kuiper, Thomas R. McDonough, Dyton Jones, Michael J. Mahoney, Carl Palko. Substantial contributions at the JPL Meeting held on November 2nd, 2001 were also given by Drs. Philip Venturelli of Caltech, Leslie I. Tennen of the Law Offices of Sterns and Tennen in Phoenix, AZ, and Louis D. Friedman, Executive Director of the Planetary Society. Finally, the excellent research work of young and bright Mr. Yuki Takahashi of Japan is greatefully acknowledged, and so is his rich Lunar web site: http://www.astro.gla.ac.uk/users/yuki/.
References [1] J. Heidmann, Saha Crater: a candidate for a SETI Lunar base Academy Transactions Note, Acta Astronautica 32 (1994) 471–472. [2] J. Heidmann, Sharing the moon by thirds: an extended Saha Crater proposal, Advances in Space Research 26 (2000) 371–375. [3] J. Heidmann, Recent progress on the Lunar Farside Crater Saha Proposal, Acta Astronautica 46 (2000) 661–665. [4] C. Maccone, Laydown of a tether from Earth visible location to far side for Lunar SETI, Advances in Space Research 26 (2000) 359–370.
C. Maccone / Acta Astronautica 56 (2005) 629 – 639 [5] C. Maccone, Searching for bioastronomical signals from the Farside of the Moon, First European Workshop on Exo/Astrobiology held at ESRIN, Frascati, Italy, 21–23 May 2001, published by ESA in the relevant Proceedings called ESA SP-496, August 2001, p. 277–280. [6] C. Maccone, The Lunar SETI cosmic study of IAA: current status and perspectives, paper IAA-01-IAA.9.1.05, 52nd International Astronautical Congress, Toulouse, France, 1–5 October 2001. [7] C. Maccone, Planetary defense and RFI-free radioastronomy from the Farside of the Moon: a unified vision, Acta Astronautica 50 (2002) 185–199.
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[8] C. Maccone, The Lunar Farside Radio Lab Study of IAA, paper IAA-02-IAA.9.1.4, 53rd International Astronautical Congress (World Space Congress—2002), Houston, Texas, 10–19 October 2002. [9] C. Maccone, Lunar Farside Radio Lab: a “Cosmic Study” by the International Academy of Astronautics, Paper # IAA.8.3 03, 14th Space Activity and Society Symposium during the 2003 International Astronautical Congress, Bremen, Germany, September 29–October 3, 2003. [10] C. Maccone, The Quiet Cone above the Farside of the Moon, Acta Astronautica 53 (2003) 65–70.