When I mentioned blue-green lasers last week, as a red herring and for the first time since 1987, I little thought that they would recur as a topic only days later. But they have, in the article ‘Lasers ‘powered by sunlight’ could transform space travel, scientists say’, by Nick Forbes, PA Scotland and Alya Zayed, MSN online, 18th November 2024. My connection with it is that in 1996 I was impressed by an article in the Glasgow University graduates’ magazine Avenue, featuring the work of Prof. Neil Isaacs in the Chemistry Dept. I invited him to talk to ASTRA, then Scotland’s national spaceflight society, and he did so as ‘Proteins Structures, Hormones and Sunlight’ on May 31st, 1996, and again on October 26th that year, first to the Astronomy Section at Airdrie Arts Centre and then to the Glasgow Branch at the Glasgow Council for the Voluntary Sector.
Prof. Isaacs’s breakthrough was in the energy-collecting systems of bacteria in the mud at the bottom of ponds, where the only light energy to penetrate was one narrow band in the blue-green part of the spectrum, all that was left after every other form of life had grabbed everything it could use. Under pressure of evolution, those bacteria had become fantastically efficient at catching every available photon and storing its energy for future use. Their efficiency approached that of room-temperature superconductors, then and still a goal of high-energy physics, and indeed their energy-storing molecules resembled the stacked rings of superconducting magnets or multiple supercolliders. Knowing the inefficiency of solar cells at the time, which John Braithwaite and I had studied in Project Starseed (ON, November 20th, 2022) and kept an eye on since, it seemed worth checking up on. Prof. Isaacs agreed that future practical uses couldn’t be ruled out, though the difficulties of growing them outside the lab, let alone in macroscopic structures in space, would be immense.
And yet… The MSN article cited above describes a project with the acronym APACE (not explained), with 4 million euro (£3.34 million) funding from the European Innovation Council and Innovate UK, part of UK Research and Innovation, including researchers from the UK, Italy, Germany and Poland. “The aim is to repurpose the light-harvesting antennae from certain types of photosynthetic bacteria to amplify energy from sunlight, and convert it into laser beams that can transmit that energy across space… using organic materials rather than ‘perishable’ artificial components means the lasers could be effectively re-grown in space’, and ‘unlike conventional semiconductor solar panels, which convert sunlight into electricity, this process would not rely on any electronic components.’ Professor Erik Gauger, from the Institute of Photonics and Quantum Sciences at Heriot-Watt University, said,
“Regular sunlight is usually too weak to power a laser directly, but these special bacteria are incredibly efficient at collecting and channelling sunlight through their intricately designed light harvesting structures, which can effectively amplify the energy flux from sunlight to the reaction centre by several orders of magnitude. Our project will make use of this level of amplification to convert sunlight into a laser beam without relying on electrical components. We already know it is possible to grow bacteria in space, for example through studies on the International Space Station. If our new technology can be built and used on space stations, it could help to generate power locally and even offer a route to sending power to satellites or back to Earth using infrared laser beams.”
Reading between the lines, what is intended is to beam energy to off-planet installations and spaceships, much as the spaceships of the Eagle’s ‘Dan Dare’ were powered by microwave transmissions, ‘impulse waves’ from transmitters on the Earth, Moon and Mars (Eagle, 5th May 1950, reprinted in Dan Dare, Pilot of the Future, The Deluxe Collector’s Edition, Patrick Hawkey Publishing, 1987), but with individual tight beams rather than omnidirectional broadcasts. In either case, the advantage of broadcast power is that the spaceship only has to carry reaction mass for propulsion, not needing an onboard nuclear reactor or big arrays of solar cells, or dangerous chemical propellants. The disadvantage is that the ship is completely dependent on continuously transmitted power from the home planet or orbiters around it. In ‘The Martian Invasion’, the second of Sydney Jordan’s Jeff Hawke stories for the Daily Express in 1954-55, the invasion fleet was powered by microwaves beamed from a huge nuclear reactor on Mars (actually it would have taken three, spaced around the planet, but for dramatic reasons there was only one), which was defended only against nuclear or microwave powered ships and nuclear weapons and was knocked out by a conventional attack just in time. (See ‘Jeff Hawke, Space Rider’, ON, October 8th, 2023.)
The receiving ships don’t even need to have their own bacteria-generating tanks, though one suspects larger installations would, if only as backups. The MSN article cited in the first paragraph is illustrated with a blue-green laser, which might suggest that the bacterial products are being used in the transmitting system as well; but the text mentions ‘infra-red lasers’, and of course the electrical energy provided by the amplified sunlight could be used to generate beams at any desired frequency.
I had originally intended to preface this article with a different lead-in. At Christmas last I entered Dan McKay’s Bar in Troon, to be greeted by Alan Martin, the Chairman of the former Astronomers of the Future Club, with the words, “Here’s the man who can settle the question”, in an argument about whether the Moon landings actually took place. I cut straight to the chase by pointing out that our guest speaker at the Club in May 2017 was Prof. James E. Faller, University of Colorado and Honorary Professor, University of Glasgow, the originator and head of the project to put laser retroreflectors on the Moon during the Apollo programme (Fig. 1).
We had seen the astronauts putting those devices into place on live TV (Fig. 2), and since they’re passive reflectors, they’re still up there and are still being used, by the Royal Observatory and other institutions, to track continental drift on Earth and the precise motions of the Moon, for navigational purposes on Earth and in space. If the astronauts didn’t put them there, I asked, who did? The sceptic was good enough to accept defeat and not go over the usual conspiracy theory arguments (‘It could have been done by robots, sent from secret launch sites’, etc…) For the full case, see ‘Yes, We Did Go to the Moon’, ON, October 23rd, 2022, ‘Yes, We Really Did Land on the Moon, Part 2 – On the Moon Itself’, October 30th, 2022, and ‘ Yes, We Really Did Land on the Moon, Part 3 – The Later Missions’, November 6th, 2022.)
Even by the Moon landings in 1969-72, we had come a long way from the initial description of the laser as ‘a solution looking for a problem’, as was said when it was first built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theories of Charles H.Townes and Arthur Leonard Schawlow, as a specialised application of the MASER principle (Microwave Amplification by Stimulated Emission of Radiation). Even MASERS were very new then and the National Geographic Magazine devoted a page to them (Fig. 3) in a comprehensive article about Project Telstar, the first civilian communications satellite (Rowe Findley, ‘Telephone a Star: the Story of Communications Satellites’, May 1962).
It didn’t take long for medical laser applications to be suggested, and in my student days my friend Patrick McNally (later Chief Surgeon at Ayr County Hospital) managed to get us into a Glasgow University lab to see one in operation. After all the preliminary fuss about protective goggles, etc, it has to be said that the dull red spot only a foot or two from its origin was something of an anti-climax; but it was the prelude to much greater things.
Industrial applications quickly began to feature in New Scientist, Tomorrow’s World etc, and it was at least superficially plausible for James Bond to be threatened by one in Goldfinger as early as 1964. Actually the makers couldn’t get a laser whose beam was visible in daylight, and Bond’s peril on the gold slab had to be simulated with a cutting torch from below. (Sean Connery said afterwards that because the torch operator couldn’t see him, it lent a lot to the conviction of his own performance.) Although lasers still had to be precisely built and tuned for particular applications, somehow Goldfinger was able to use the same one to cut through the door of Fort Knox, rather than using a Corporal missile warhead as in the original novel. (See ‘Visitor at Uist’, ON, July 10th 2022).
Initially both MASERS and lasers were extremely pure and highly machined ruby crystals (Fig. 3), working only in red light, but those were expensive and difficult to produce, and it wasn’t long before ways were found to induce ‘lasing’ in suitably doped gases like carbon dioxide, much easier to produce, and giving laser beams (when made visible) in a range of colours including blue-green. Lasers were soon applied to the principle of holography, which had been worked out many years before but lacked a suitable source of coherent light; the prevalent yellow and green tinges made many early holograms unconvincing.
Military applications quickly turned up in fiction, but took longer in practise. It was said of the first laser rifle produced by the US Army that if you could get close enough to hurt someone with it, you might as well hit them over the head with it. Nevertheless they continued to feature in Bond films, and in Moonraker (1979), US forces fight a battle in space with Hugo Drax’s followers, both sides using lasers whose beams are visible not just due to smoke and dust in air, but in hard vacuum, as plainly as the unexplained ones in Star Wars. ‘Laser rifles’ might be more effective than conventional guns in weightlessness, unless you were firmly anchored against recoil, as Professor Quatermass’s friend Pugh found out the hard way in Quatermass II (1955). But as David Langford pointed out in War in 2080 (David & Charles, 1981), most conflict in space is likely to be hand-to-hand and swordplay might be equally useful – his comment was ‘And then, Athos, I pricked him thrice i’ the oxygen regulator’.
Military space lasers gained a new lease of life with the Strategic Defence Initiative (‘Star Wars’ to its detractors), in which the first element of the ‘missile shield’ was to consist of laser ‘battle stations’ firing at enemy missiles during the boost phase. Unfortunately it was illustrated by an animation showing the destruction of a Soviet rocket – in military green, admittedly, but bearing an escape tower which showed it was a manned vehicle. The apparent act of murder led to objections that such a ‘defensive’ system could be used by any nation possessing it to achieve domination in space, stopping any civilian or commercial launch which they saw as against their interests. I haven’t managed to find that image in recent years, but I did find one showing the USA’s F-15 antisatellite system being deployed against a European, civilian Ariane V launch (Fig. 4), which shows how some segments of right-wing opinion view competition in space.
Battle stations would need highly powered x-ray lasers to be effective, and although prototypes were build and fired successfully, at least against drone aircraft, they filled two-storey buildings and were not going to be deployed in large numbers, without a great deal of further development. Proponents of SDI were fond of asserting that the Soviet Union was far ahead in those areas: a US spy satellite had been temporarily blinded years before, and that was ascribed to a prototype super-laser, but there were no further instances and the general conclusion was that the satellite had chanced to spot the burn-out of a meteor. A mysterious facility in the Soviet nuclear testing area of Semipalatinsk was alleged to be a test-bed for beam weapons powered by tactical nuclear explosions; I suggested instead that the energy flow through the structure might be in the opposite direction, and the aim might be to trigger pulsed fusion using high-energy lasers or electron beams, as proposed for propulsion in the British Interplanetary Society’s Project Daedalus. I did at least get a hearing for that from SDI advocates, unlike the ‘escape tower’ animation above, but I’ve heard nothing more about the Semipalatinsk structure since.
Nevertheless, in some right-wing circles to this day it is argued that on the first launch of the Energia super-booster, near the end of the Cold War, the payload was a 100-ton ‘laser cannon’ called ‘Polyus’, intended to threaten or destroy Western spacecraft. I take leave to doubt it, partly because it seems unlikely that anything as big and expensive would be entrusted to the first launch of an untried rocket. In the event, the first Energia yawed wildly on takeoff, but managed to recover and climb out. But also the weapon was supposed to be a 1-megawatt carbon dioxide laser, and I’ve yet to hear what the power source would be – the only artwork I’ve seen shows very small solar panels (Fig. 5), compared for example with the huge arrays on the International Space Station which deliver only kilowatts, not megawatts. But more tellingly, to me the black object on the side of the Energia (Fig. 6) looks a lot more like an aerodynamic engineering model of the Buran space shuttle, which was launched successfully on the second Energia flight (Fig. 7). On my tour of the Atlas-Convair plant outside San Diego in 1984, I was shown a similar dynamic model of the Galileo Jupiter Orbiter, which I had seen at the Jet Propulsion Laboratory three days earlier. The model looked nothing like the spacecraft, but was designed to behave identically in vibration tests and other simulations. (As a physics lecturer at Glasgow University said during the Profumo Affair, to great applause, ‘It doesn’t matter what a model looks like, as long as it behaves properly’.) It seems a much more sensible thing for Polyus to have been, and I note that the Wikipedia article on it says. ‘This article needs additional citations for verification’, where currently there are only four.
The size and mass of the x-ray laster installations was no barrier to ground-launched laser propulsion, for purposes other than SDI, and the prospect aroused considerable enthusiasm at conferences I attended in the the USA, 1985-86. At the 1985 Space Development Conference in Washington D.C., Dr. Arthur Kantrowitz, founder and CEO of the Avco Everett Research Laboratory, told his audience, “The government is building the transport line to space – I don’t want you to tell them!”
By 1987, however, there was a programme to evaluate the possibilities with experimental launches held at White Sands Missile Range, New Mexico (Fig. 8), and it had already reached the second round of funding, with emphasis on ‘new ideas and innovative approaches to the laser propulsion field’ (Fig. 9). Dr. Kantrowitz had been thinking primarily of discus shaped-vehicles, perhaps to be lifted by balloon and then rocket to a height where laser propulsion would become effective, but direct launch by laser propulsion from ground level had also been proposed and was already under test (Fig. 10).
It was described by the late Jerry Pournelle and featured in his story ‘High Justice’ (Analog, October 1974), with a cover by Kelly Freas (Fig. 11), as well as in his collection of non-fiction essays A Step Further Out, (Baen Books, 1979).
The late Dr. Robert Forward had suggested using similar lasers to propel ‘Starwisp’ lightsail probes out of the Solar System, and an expanded system to launch fleets of them to the nearer stars forms the basis of Breakthrough Starshot, founded by Prof. Stephen Hawking and venture capitalist Yuri Milner (Fig. 12). The fleet of lightsails would be parked beyond the orbit of the Moon (Fig. 13), to be sent on their way by massed lasers on Earth (Fig. 14), taking 20 years to reach Alpha Centauri at 20% of lightspeed.
The return signal would be sent by phased array (Fig. 15), similar to the much larger system suggested by my friend Dr. Gerry Nordley for interstellar communication (see ‘Unbuild Your Own Solar System’, ON, 13th August 2023). The programme has stimulated multiple studies, including the option of a multiple flyby of Alpha Centauri A and B as well as Proxima Centauri, taking 141 years in total (Fig. 16).
Bob Forward had proposed a much more ambitious project to send a crewed mission to Barnard’s Star and back (Fig. 17), or even Epsilon Eridani (Fig. 18), taking a full human lifetime, with a starship of concentric lightsails to be propelled from Earth throughout. When I say ‘more ambitious’, it envisaged a launch from the near vicinity of the Sun, and laser propulsion by a beam focussed by a Fresnel lens in space which would be larger in diameter than the Sun itself. It formed the basis of his novel The Flight of the Dragonfly (1984), first published in Analog as Rocheworld, 1982, and perhaps is the most ambitious proposal for laser propulsion to date.
Nearer to home, lasers have been suggested as means to deflect asteroids and comets away from Earth. In 1986 Gordon Ross of ASTRA designed a parabolic solar sail called ‘Solaris’ for the task (Fig. 19), and that was one of the major concepts in the discussion project leading to my book Incoming Asteroid! What Could We Do About It? (Springer, 2013). We shared our work with Prof. Max Vasile of Strathclyde University, who in turn shared his with us, eventually proposing a fleet of such sails called ‘mirrorbees’. But the Optics Department at Glasgow University concluded that a parabolic sail couldn’t focus sunlight sufficiently for the desired effect, at a safe distance from the target, and Max challenged our group to come up with an answer. It took Gordon Ross, Chris O’Kane and the late John Braithwaite only days to do so, and at the final seminar of the book project they produced a working model which was demonstrated in the Bridie Library of Glasgow University Union (Fig. 20).
With a small handheld parabola powering a miniature laser, and using only the sunlight from a narrow gap in the curtains, they were able to produce a spot of light on the other side of the room which had to be kept moving, because it was bright enough to ignite paper. It was much more dramatic than the faint red spot which Pat McNally and I had seen in the early 60s, and demonstrating it in a library was perhaps not the best idea (I didn’t know it was coming), but then, Prof. Jim Faller had proposed to demonstrate the principle of corner retroreflectors by getting the audience to hold up burning petrol lighters, until I pointed out that the venue had an overhead sprinkler system. In space, Gordon and Chris reckoned that existing rockets could launch enough of the lightsails to deflect even objects 1 km in diameter, given six years to do it (Fig. 21), and John Braithwaite’s modified design could resolve several other technical problems which Max had raised.
Another proposal we discussed was Prof. Colin McInnes’s idea to deflect asteroids by direct impacts. This has now been tried with the DART mission to the dual asteroids Didymos and Dimorphos, and Europe’s Hera mission is now on its way there to assess the effects. We proposed launching the impactors from a mass driver in Low Earth Orbit (Fig. 22), and the late Andy Nimmo then asked whether its multiple solar panels (only a few of which can be seen in Fig. 22 could be used to power a super-laser to generate the same effect. It turned out that such deflection had been studied in a project of Profs. Philip M. Lubin and Gary B. Hughes, of the University of Santa Barbara, in a project called DE-STAR which could deflect or even vaporise asteroids up to 500 metres in diameter, given time (Fig. 23). That may prove more effective than brute force impacts, come the day (and it will come, some day).
Back when lasers were still ‘a solution looking for a problem’, in 1961 R.N. Schwartz and C.H. Townes, one of the inventors of the laser, had suggested that a 200-inch telescope could focus a narrow band laser emission sufficiently for it to be read, and taken down by hand (!), by an observer at the eyepiece of a similar telescope on a planet of another star. (‘Interstellar and Interplanetary Communication by Optical Masers’, Nature, 190, 205 (1961), reprinted in A.G.W. Cameron, ed., Interstellar Communication, Benjamin, New York, 1963.) In 1959, Prof. R.N. Bracewell of Stanford University had suggested that the mysterious long-delayed radio echoes of the 1920s might have been an attempt by an interstellar probe to contact us (also in Interstellar Communication), and James Strong of the British Interplanetary Society had suggested the probe might be located at either the L4 or L5 Earth-Sun Lagrange points, equidistant from the Earth and Moon (Flight to the Stars, Temple Press, 1965). It turned out that both points were sources of LDEs, and I suggested that the probe might have split into two elements, to read and send signals more clearly by interferometry. Gavin Roberts produced two paintings on the subject, one of which (Fig. 24) became the last plate in my book Man and the Stars (Souvenir Press, 1974). The view of the Earth in it is based on a photograph taken by Neil Armstrong, outbound from Earth on Apollo 11. (See ‘The Earth from Space’, ON, 7th May 2023.) For a more full account of the ‘space probe affair’, see ‘Epsilon Boötis, Clyde Tombaugh, Black Knight and STS-88’, ON, June 12th, 2022.
At the current state of development, lasers in space are used mostly for dockings with the International Space Station, and we can expect to see a lot more of that with the deployment of the Lunar Gateway station, and the commercial stations which are intended to replace the ISS by the end of the decade. Laser altimeters are now in general use on lunar probes, and their failures have been showing just how difficult lunar landings in rough terrain can be, but outright failures like the one on the Odyssey lander in February are to be avoided, and should be, when lasers provide much better accuracy than the radar on which the Apollo astronauts had to rely.
The first successful two-way laser communication with a spacecraft was with NASA’s LADEE lunar orbiter, launched in September 2013 and deorbited in April 2014 (Fig. 25).
The current record for it is a two-way link to the Lucy probe, on its way to the Trojan asteroids in the orbit of Jupiter (Fig. 26), which was achieved at the end of April 2024 over a distance of 140 million miles. Also in April 2024 the White House officially directed NASA to establish a lunar time zone, for use in a future Lunar Internet and particularly for lunar GPS (Scott Alan Johnstone, ‘The Moon Will Get Its Own Time Zone’, Universe Today, online, 4th April 2024.). In sorting out the issues that operations in the Moon’s lumpy gravitational field will involve, we can expect the expansion of space laser capabilities to be so rapid that surveys of the field, in single articles like this one, will no longer be possible.
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