Moon ‘Tanks’ and Lunar Combat

United States of America (1958-1967)
Lunar Vehicle Concepts – None Built

Following the defeat of Germany in 1945, the two former allies and ‘superpowers’, the United States and the Soviet Union, began a decades-long confrontation and global competition which became known as the Cold War.

The United States, assisted by its allies, such as Great Britain, had developed a functional nuclear weapon in 1945, and was followed by the Soviet Union in 1949 (post-war, the USA refused to share this technology with the UK, which developed its own nuclear device in 1952).

A year later, in 1950, the newly formed United Nations went to war in Korea with the Chinese and Soviet-backed North Korean forces in a 3-year long conflict which could have escalated into the use of nuclear weapons.

It was clear to the US military that, whilst conventional forces may face off against each other, nuclear weapons may also come to dominate the battlefields of the 1960s and beyond, and also that, in the larger geopolitical rivalry with the Soviet Union, any edge may be decisive.

When, at the end of July 1955, the United States announced its intention to launch artificial satellites into orbit around the Earth, the Soviets saw this as a challenge to their own security. They then began their own space program, culminating in the launch of Sputnik I and II in October-November 1957, the world’s first artificial satellite and the start of what became known as the Space Race. This was a race not just to show some technical superiority over a rival power, but also had the potential to yield dominance of the fourth realm of warfare – space.

Dominance of space would mean control over enemy surveillance satellites, the ability to spy on anyone, anywhere, and also to mount weapons beyond the ability of an enemy to counter strike, but also meant some kind of base would be needed.

This would be a base not in the form of a giant man-made space station orbiting the Earth, but on the greatest natural satellite – the Moon itself. This was made official as a request in early 1958, when the US Secretary of Defense, Neil McElroy, ordered the Advanced Research Projects Agency (ARPA) to take “a close look at the moon”. This was followed on 2nd April 1958 by President Eisenhower declaring the need for establishing a single unified national space agency (the National Aerospace and Space Administration – NASA, was formed on 1st October 1958).

“Last year (1958), Air Force General Homer A. Boushey,… stated that a lunar military base someday will be vital to national security, that in one sense the Moon represents the age-old military advantage of [‘high ground.’] He is one of the many uniformed American leaders seriously thinking in terms of the military relation of outer space to the Earth and human events thereon. While there is perhaps no unified agreement in American military circles on the concept that ‘he who controls the Moon controls the Earth,’ nevertheless, there is well-grounded agreement that vital military keys to our future national defense lie in outer space.”

LTC Robert B Rigg, US Army, 1959

The Moon, Earth’s nearest neighbor, measures some 3,476 km in diameter (equatorial) and orbits the Earth at a distance of between 356,400 km (perigee) to 406,700 (apogee) at an average speed of 1,022 km/s. With a mass of 7.342 x 1022 kg, just 1.2% of the mass of the Earth, it has a surface gravity of just 1.62 m/s2, just 16.5% of Earth’s gravity. The Moon has no functional atmosphere. There are gases to be found on the surface, but the density of molecules is so low as to technically form an exosphere. Whilst minute levels of oxygen, amongst other gases, have been found, the quantities that are so minute as to be of little or no use – certainly not enough for a person to breath or vehicle engine to use.

No atmosphere also means no filtering of the solar and cosmic radiation, with charged particles being attracted to the exterior of any suit or vehicle as a result of the lunar surface being well insulated, building up a charge on anything moving across it. Men or vehicles returning to a base would have to be ‘earthed’ (grounded) to remove this charge – yet another problem to overcome.

If these conditions are not harsh enough, the temperatures range from -130° C to 120° C at the equator and are even colder at the poles. The temperature variation in a small locale can be severe too. The Moon moves around the Earth at just 0.5° per second, meaning not only that days and nights are two-week-long, but also that the area in daylight from the Sun lying next to an area shaded may only be a few centimeters away from each other, but could be over a hundred degrees different in temperature.

The surface is heavily pitted with craters from asteroid and meteorite impacts that struck the crust of the Moon over billions of years. Those impacts led to the surface being covered with a fine dusty material called regolith, which can range in depth from as little as 3 meters deep to around 20 meters deep in places with numerous rocky outcrops. The surface is a difficult and barren zone and any vehicles conducting operations, or any men on the surface, would have to be able to both navigate, survive, and even fight in these conditions – no small feat. Navigation both on foot or by vehicle is, for example, complicated by the fact that the magnetic field is too weak for an effective compass to work (less than 200 nT [nanotesla] compared to Earth’s 22,000 to 67,000 nT) and that a man 1.82 m (6’) tall can see only 2 miles (3.2 km) at best and more usually just 1.5 miles (2.4 km) and could easily become disoriented and lost. Further, the lack of an atmosphere means that radio signals can not be bounced down over the horizon, so radio communication is limited to line of sight only. With this high vacuum, metals in contact with each other can weld themselves together and yet lubrication is complicated by the lubricants boiling off. Any metals should therefore have to consider solid lubricants (which do not sublimate), special surface anti-friction coatings and/or only be in contact with non-metals.

Unusual conditions required unusual vehicles and Project Horizon certainly had its share of them and this would require some careful planning.

It has also to be borne in mind that in 1959, the exact surface conditions on the Moon were unknown to the extent that a plan in 1959 called for detonating a 500 kiloton nuclear weapon on the surface to analyze the material thrown up and the seismic effects resulting from the blast. Thankfully, the idea of nuking the Moon for science was not carried out and the first actual lunar samples would, in fact, not come back to Earth until 1969 and 1970 with Apollo 11 (USA) and Luna-16 (USSR) respectively.

Planning

Planning for a base of operations on the Moon would start in the first half of 1959 without physical samples of the lunar surface, but with an idea of the conditions based on scientific observation instead. Work on the project began with a feasibility study (Phase I), followed by a detailed development plan including how much it would cost (Phase II) through the rest of 1959 and the first months of 1960. All of the necessary development of technology and hardware needed would begin in 1960 (Phase III) with 4 years of solid work up to the start of lunar base construction in mid-1964. Phase III was to continue through to 1967, with the lunar base construction (Phase IV) finished by the end of 1966 and online (Phase V) by the end of 1967. The final phase, Phase VI, would then follow as capabilities for operations were progressively improved and expanded. All told, it was estimated to take nearly 10 years to have this base fully operational and, by that time (end of 1967), the base would be housing nearly 300 personnel.

The planning for Project Horizon fell to Lt. General Arthur Trudeau, who, at the time, was the Chief of Research and Development. He ordered the Chief of Army Ordnance to draw up the details in a 90-day planning exercise. The experts for this project worked for an agency known as ABMA – the Army Ballistic Missile Agency, and were led by none other than Dr. Wernher von Braun (23/3/1912 – 16/6/1977). Just as Trudeau tasked the Chief of Army Ordnance, who tasked Dr. Braun, Dr. Braun passed the task to Heinz-Hermann Koelle (22/7/1925 – 20/2/2011) as project lead, who brought in Dr. Georg Heinrich Patrick Baron von Tiesenhausen (18/5/1914 – 4/6/2018). Tiesenhausen had been an employee in the German missile program at Peenemünde (from April 1943) during WW2, where he had been a Section Chief in charge of ground support equipment and designed Pruefstand XII for the exhaust deflection system for the Schwimmweste [Eng: ‘life vest’] project (submarine-launched V2 rockets for targeting the USA) and had worked alongside Koelle, Braun, and others. He had not, however, been brought to the USA until 1953. Subsequent to the end of the war in 1945 and prior to being gathered up as part of Operation Paperclip, the Latvian-born scientist had been running a tank collection park for the British and working at a ship winch fabricator. The Project Horizon work was also to bring in every conceivable specialist at some point to have their say or express their views on the potential task at hand. This was an enormous project, despite the very narrow window in which to do it – certainly more than a simple paper exercise in lateral thinking, but a serious discussion over the challenges ahead.

Lt. Gen. Trudeau kicked off the planning work in March 1959 and, by 8th June that year, the report was done and published as ‘Project Horizon: A U.S. Army Study for the Establishment of a Lunar Military Outpost’ – a plan costing US$6 bn. to US$7.7 bn. For reference, US$$6 bn. and US$7.7 bn. in 1959 dollars would be the equivalent of US$53.4 bn. to US$68.8 bn. in 2020 values. Whilst this is a huge sum of money, it is still less than the current US defence budget for 2020, which is US$686 bn., and the costs were going to be spread over a decade. It accounted for just under 1% of the total budget, not to mention this would be money spent by the government within the US on rockets and salaries, etcetera. Maintenance of a lunar base was estimated in 1960 as an immodest US$631m per annum, equivalent to US$5.5 bn. in 2020 dollars – still under 1% of the US annual defense budget. The 1960 viability report by the US Air Force (also considering their own lunar base) on a permanent lunar military outpost pointed out that its total 10-year cost was equivalent to the annual operating costs of the US Farm Subsidy Program; in other words, it was expensive but affordable.

The Project Horizon report would be the outline for how a base could be set up as a critical lunar system, for which a later decision would be taken on exactly how to militarise it and what for. The ability to conduct observations from a fixed platform onto the Earth was obviously valuable, but a base would go further than that, as can be inferred from the ominously titled 1959 report on the base plans “Lunar Based Earth Bombardment System” which could, according to a 1960 report, deliver weapons to Earth with an accuracy of 2 to 5 nautical miles (3.7 to 9.3 km), clearly indicating that nuclear weapons were going to be the weapons of choice.

Getting men, machines, and equipment there, setting up a base, and then protecting it from a potential adversary meant creating a supply system and potential weapons systems. All of this had to be integrated together and work in synergy due to the distance from potential help or resupply. Thus, all of the problems of such an outpost have to be considered together to understand the decisions made.

Getting There

The task of bringing all of the tools, equipment, and men to the Moon was to take 229 flights over a four-year period using the Saturn I and Saturn II rockets. Just getting men into Earth orbit would take 16 flights of the Saturn I and 6 of the Saturn II, with an additional 47 and 71 flights respectively to get the cargo into space. As well as the 300 personnel to be ferried back and forth between the Earth and Moon, using a clever rotation schedule to establish a 12-man outpost, approximately 245 tons of equipment and building materials had to be delivered to the Moon. This does not include the sustaining cost of maintaining the base either. A total of 61 Saturn I and 88 Saturn II launches would be needed over a 28 month period (a rate of 5.3 per month) to get set up, with 64 more to supply the base in year 1 – more than 1 per week. Later, larger and more efficient rockets, including ones propelled by nuclear detonation (predicted to be available from about 1970) would reduce the logistic burden of supplying the base. Bases for launching the Project were planned for either Brazil or Christmas Island, as locations near the equator were desirable.

“to be second to the Soviet Union in establishing an outpost on the Moon would be disastrous to our nation’s prestige and in turn to our democratic philosophy.”

Project Horizon, June 1959

The Base

Buried into the lunar surface, the base would be partially protected from damage by solar radiation and falling meteoroids. It would be built from a series of tubes connected together in much the same manner as many nuclear shelters on Earth, forming functional modules in which work would be conducted. The primary difference would be the source of power, and for this, it was planned to use nuclear reactors to provide sufficient electrical power for all of the heating, lighting, and equipment. An initial 5 kW nuclear reactor would be landed to provide power for the construction camp, followed by a 10 kW unit and a 40 kW nuclear unit for the construction of the rest of the facility. At that time, the 5 kW reactor would be dedicated to just powering the life-support. Lacking radiation shielding (to save weight), these would be placed into craters blasted out from the lunar surface if natural ones could not be found, and then covered with lunar soil to a depth of 12 feet (3.7 m). For normal operations, all power was to come from the 40 kW reactor, with the 10 kW unit held for emergency backup use. Despite the extreme cold in places, spare heat would still have to be released from the reactors and this was to be done with metal radiators fabricated from scrap, such as from cargo containers. Poking out above the surface, these radiators would dump the excess heat through thermal radiation, but also ensure a steady source of radiation on the surface, meaning men would have to stay away. At 50 feet (15.2 m) from the radiator, the dosage for a man within that zone would be 300 millirems per week. For reference, background radiation on Earth is around 100 millirem per year. Such a dose for the soldier within that distance would be just over 3 times the US Nuclear Regulatory Commission (NRC) sets as permissible for someone working around nuclear material. However, this was safe for the lunar surface, as the two plants would be located over 100 meters from the living quarters, about 30 meters apart. A final 60 kW nuclear power unit would also be added later, meaning no less than 4 different nuclear power units for the base to sustain life and conduct its military purposes.

Vehicles – Construction

One of the first vehicles to consider was a construction vehicle which could perform a variety of duties for the initial set-up phase of the outpost. Bearing in mind that gravity on the Moon was just 16.5% of Earth’s, this would, at first, appear to make life easier, as a 1,000 kg load on Earth would weigh just 165 kg on the Moon, but the low gravity created problems for the vehicles as well as the stability of them. On Earth, stability is based in large part on ‘normal’ gravity. With the mass distribution as it is, even if a regular bulldozer could be brought to the Moon, the weight distribution would be incorrect, making the vehicle unstable.

Vehicles would have to be weighted in order to maintain an effective power-to-traction ratio and that weight would not be brought from Earth – it would be added locally on the lunar surface. Much of the lunar vehicle work was to fall to Tiesenhausen and, as a matter of record, it should be noted that he became head of lunar mobility systems at NASA in 1963. Tiesenhausen is also primarily responsible for the lunar rover as it finally appeared as well several years later, but in terms of Project Horizon, there was primarily a concern for a vehicle for construction duties.

Weighing just 4,500 lbs. (2.04 tonnes) as its basic structure, additional mass the vehicle would need to become stable would simply be provided by means of ballasting it with lunar material, bringing its operational weight up to 9,000 lbs. (4.08 tonnes). Operating on four 4’ (1.22 m) open-spoke metal wheels, no tyres were to be used, but the speed would be low – just 1.5 mph up to 5 mph (2.4 to 8.0 km/h) so the cushioning of a rubber tire was not needed. The wheels would have diamond-shaped grousers to gain purchase on the lunar surface, and with a mass of 2,040 to 4,080 kg would, in effect, mean a weight of just 16.5% of that, making traction easier. Powered by a pair of 4 hp electric motors (rechargeable from the nuclear power-generated electricity supply from the outpost), the entire vehicle would be just 15’ (4.57 m) long, 6’ (1.83 m) wide, and 6’ (1.83 m) high and could be controlled directly through a pressurized cab where a man could work without a suit, or via radio (subject to the limits of radio range already discussed). On Earth, such a vehicle would require 20 to 25 hp per ton to operate off-road but, with the reduced gravity of the Moon, the electrical power units (8 hp total) were sufficient to meet the equivalent engine-power on the Moon and provide an operating range of 50-150 miles (81 to 241 km) although, as previously stated, anyone operating that far from a base would run a serious risk of becoming lost.

It was fitted with a variety of attachments, such as a U-shaped bulldozer blade, robotic arms, a crane boom, and a power take-off for a variety of other equipment which may be needed, such as an auger. This vehicle was calculated to be able to carry up to 480 cu. ft. (13.6 m3) per hour over 250 feet (76.2 m) with its 43 cu. ft. (1.2 m3) front bucket and to bulldoze up to 750 cu. ft. (21.2 m3) in the same time over the same distance. The crane would be able to lift 4,500 lbs. (2,042 kg) up to 2 feet (0.61 m) from the surface at up to 10 feet (3.0 m) from the vehicle. The vehicle would also be suitable to tow heavy loads, such as moving the habitation modules into the trenches dug for them, or supply sleds. Those would be made from leftover cargo containers which would be cut up to form rudimentary supply sleds and also to produce shielding for the habitation modules to protect from radiation and meteorite impacts. The towing capacity of the construction vehicle would be around just 50% of the total vehicle weight, just 2.04 tonnes at best.

Vehicles – Lunar Transport

To avoid the soldiers in suits having to walk around on the surface too much, a transport vehicle was going to be required. Consisting of a skeletonised frame made from light-weight metal, it was going to be compact – just 6’ (1.82 m), square, with the seat and controls exposed – avoiding the need for a cab, although a two-man cab could be used if required. A small load deck, in the manner of a miniature pickup truck, would be at the back. Also electrically powered, this 3-axle vehicle would weigh just 2,000 lbs. (907 kg), and be able to move a load of men and equipment between 50% and 300% of its own weight, depending on the nature of the surface.

Each axle would have a wheel at each end and each would have its own 1 hp electric motor for a total tractive power of 6 hp. Suitable batteries would provide a range of 50 miles (80 km) or 10 hours of operation before needing to be recharged. Interestingly, the prospective design for this vehicle is missing from the available copies of Project Horizon.

A foreign analysis of other types of lunar vehicles was published for the US Air Force in 1967 from an original document by D. St. Andreescu of Romania. Andreescu was a Major General and a member of the Commission on Aeronautics in Romania and the article the US Air Force translated in 1967 was first published in 1963. Andreescu’s work had involved looking at conflict and exploration in space at least as early as 1957, so it is no surprise that his work would garner attention from the US. What is more unusual perhaps and was apparently missed was that Andreescu’s vehicles are taken in part from the art of American Frank Tinsley who drew several of them for the magazine Mechanix Illustrated.

The Foreign Technology Division (the US Air Force Branch responsible for identifying and analyzing foreign technical material) investigated what ‘the other side’ was looking at in terms of potential lunar vehicles. Originally titled ‘Vehicule Lunare’ [English: Lunar Vehicles] in the original Romanian article by Andreescu, the report considered that a Moon-based command post was, just like the USA had concluded, a logical step in the steady conquest and use of space. Andreescu considered a few different types of vehicles and types of power systems for lunar propulsion, including tracks, wheels, a large rolling spherical body, helicoidal screws, rockets, electric motors, walking machines, flying machines, and even leaping or ‘bounding’ vehicles. In doing so, he appears to have been drawing upon ideas or designs which predated this 1963 work, and although it is unclear where he got them from the US Air Force document they are clearly lifted very closely from illustrations in Mechanix Illustrated magazine.

There are, however, two vehicles of particular interest from Andreescu. One, a giant tracked ball virtually identical to the vehicle shown in the Project Horizons plan, and a small tracked lunamobile. Whilst the former vehicle does appear in the Project Horizon report, the second does not – it only appears in a 1967 US Air Force translation of his paper. Of the multiple vehicles Andreescu discussed, therefore, it is those two which are of the most interest in terms of Project Horizons.

Spheres and Tracks

The ‘tank-like’ vehicle ran on wide tracks supported by four large road wheels and a drive or jockey wheel at either end. It is not clear which end the power was supplied to the tracks, as it is not shown in the available image of the vehicle. No supporting rollers are shown. The track is, however, covered across the top by a large dust shield to prevent clouds of regolith being thrown up as it moves. The body of the vehicle is flat-sided, with a shallow sloping front surface, which on a tank would be the ‘glacis’. The rear is more sharply angled. On top of the vehicle is shown what appears to be an exhaust stack for venting gas and/or heat, much like a ship’s funnel over the back end, with a large dome with multiple large rectangular windows at the front of the roof. Inside are shown a trio of astronauts.

Completing the vehicle are a pair of headlamps at the front, a flapped-horizontal slot and a circular feature (perhaps a light) on the ‘glacis’. Projecting from the front, just below those headlamps, are a pair of supporting arms for what appears to be a bulldozer blade.

It would be powered by electric motors running on compressed (pressurized) hydrogen provided by a turbogenerator and recharged by use of nuclear power generators. This power supply would propel the vehicle on the lunar surface at up to 40 km/h for 24 hours of continuous use between recharges. The heat irradiated from the passengers on-board would boil off the hydrogen fuel source and this heat was then recaptured by a lithium hydride recuperator. This power supply would weigh just 1,200 kg – more than 200 kg less than an equivalent diesel engine and without the problems of liquid fuels in a lunar environment.

If the tracked lunamobile is rather mundane as a tracked vehicle, albeit one for the Moon, then it is the spherical vehicle idea from Andreescu which is perhaps the most curious. This was a vehicle with a spherical hull and held upright by means of “hydroscopic” (gyroscopic) stabilisation, ensuring the 3 or 4 men inside would stay correctly orientated in relation to the lunar surface. Running on a single circumferential track, the spherical lunamobile was thought to be useful for exploring the surface due to its shape, which would prevent it from becoming stuck in a crater. A second track that appears to run circumferentially around the vehicle in the horizontal plane, is in fact spare sections of track for the vehicle.

Power was supplied by a large circular solar cell acting like a parasol above the vehicle, which could be angled to receive maximum solar radiation, although no other details are provided by Andreescu or the US Air Force. In the original Mechanix Illustrated magazine article, the vehicle is stated to be inflated using a skin made from rubberised fabric.

The curious matter about this vehicle, described in General Andreescu’s report from 1963, is that this vehicle features at all. It is, in fact, identical to the spherical lunar vehicle seen in Volume III of the Top Secret Project Horizons plan, a plan which was still secret through this time. Looking at the two views of this vehicle in these two reports, it is hard not to see that one party must have known about the other and, as Horizon was 4 years before Andreescu’s report, it would seem at first glance that Andreescu took inspiration from it for that image. The Project Horizon work was, for decades, Top Secret, so it is highly unlikely he could have seen the tracked spherical lunamobile. Instead, the logical conclusion is that the spherical tracked vehicle predated the Project Horizon in some non-classified form from which ABMA and, in due course, Andreescu, drew inspiration and that in fact comes from the distinctly non-secret origins of the front cover of Mechanix Illustrated magazine published in 1958.

The use of the spherical exploration machine in the Project Horizon plan comes up during discussion of combat too, so it is fair to say that where concepts of combat on a lunar surface are concerned- they would, in the eyes of the planners, inevitably involve vehicles and probably tracked ones at that.

Combat

With a very credible Soviet space program and the sense of a race to the Moon, it was part of the planning activities of the program that there was a potential for the base to be attacked by the Soviets. It would, afterall, be a base for nuclear weapons and needed guarding. In considering combat on the lunar surface, the environmental considerations of temperature, pressure (or rather, the lack of pressure), and the low gravity made for a complex combat situation.

“…sole possession of a lunar outpost… would provide a military advantage in case of terrestrial hostilities. Defense must be provided to deter attack to obtain such an advantage”

Project Horizons Vol.I

Development of various elements of equipment to meet the needs of defending the men and equipment on the outpost was going to be divested to the various expert technical agencies. For example, nuclear weapons systems would be left to the Atomic Weapons Laboratories at Picatinny Arsenal, electronic systems would be in the hands of Diamond Ordnance Fuze Laboratory (DOFL), and missile/rocket design would go to the US Army Ordnance Missile Command (AOMC). On the surface of the Moon, vehicles were going to be needed to move around, build facilities, and provide security and these were to be left in the hands of the Ordnance Tank-Automotive Command in Detroit with responsibility for “developing and testing both combat and transport vehicles to meet special requirements”.

“If the moon and other planets are explored and possibly colonized, the world could eventually see a second evolution of weaponry and protection therefrom. Visualise starting with a weapon capable of penetrating thin-skinned vehicles. The vehicles then get thicker skin. The weapons then attain a greater penetrating capability. The vehicles get even thicker skin until the weight and cost thereof becomes insurmountable. The weapons attain longer ranges etc., etc., etc.,. This proceeds through the mortar, howitzer, gun and tank stages until eventually you have missiles, antimissiles and nuclear weapons…..”

US Army Directorate of Research and Development, 1965.

Just as the comment above related to ‘tanks’, it was part of Project Horizon’s initial assessment that the use of vehicles in a potential attack or defense at the outpost was a credible concern. Although they could not carry armor in the sense of a conventional tank due to the difficulties in getting such a vehicle to the Moon, it was certainly conceivable such vehicles may have some ballistic protection beyond just retaining a pressurized atmosphere within the vehicle. Thus, any weapons planned for the outpost should also have had an anti-materiel ability to perforate a vehicle and depressurize it or cripple the automotive parts.

Such a unique combat environment precluded the use of conventional ammunition and weapons like rifles. This is not, as may be thought because the ammunition would not work in an oxygen-free atmosphere. It would work (albeit with some known problems with primer activation in a vacuum) – modern ammunition has its own oxidizer self-contained, so a rifle would indeed work. In fact, the lack of moisture and oxygen actually helps to preserve plastic explosives and prevent corrosion infuses, etcetera, although non-plastic explosives like TNT would degrade with the temperature extremes. Such conventional firearms were, however, designed to fire in Earth-gravity situations, so the sights would be almost useless on the Moon. Add to this that the reduced gravity on the Moon would seriously affect the trajectory of any bullet fired on the surface and that other features of a conventional rifle, like a stock, were not required because a man in a suit would not be able to carry the weapon easily in such a way and what is left is the need for a bespoke weapon – albeit it one which might use conventional-types of ammunition. However, that too involved a lot of weight-wastage through a casing. Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction. In other words – recoil, and this recoil would be harder to manage for the soldier in a low gravity environment. With no effective atmosphere either, any missile fired would not be subject to drag from friction, like it would on Earth, and would increase the range of a projectile by some 6 times or more. The same was also true of the explosive out-gassing behind a recoilless weapon, making them extremely hazardous to friendly vehicles, buildings, or personnel behind. The same applied to explosively producing fragments/debris, as it would travel further and faster than on Earth. Given that penetration is a function of the square of the velocity of the projectile, even bits of regolith kicked up by a blast created an enormous hazard for men and machines.

The effect on-target of the projectile or directed energy device differed substantially from terrestrial combat too, as substantial damage could be done to a target simply by exposing it to the vacuum of space, piercing the suit or vehicle skin.

An attack on the outpost from the Soviets could not come without warning. Either the launch would be detected or the launched-craft picked up by Earth-based monitoring. If a craft could be landed secretly, the outpost would also have a short-range radar set with a range of up to 2 miles (3.2 km) and backed up by an active infra-red system with a range of 400 – 500 yards (366 – 457 m) range.

Planning assumption for outpost defense related to a roughly platoon-sized attacking force, but defense had to consider combat in 4 situations:

1. Space-suited personal combat
2. Lunar surface vehicle combat
3. Moon-orbiting space vehicles
4. Non-orbiting space vehicles

Project Horizon considered various modes of killing or incapacitating an enemy force approaching the perimeter of the outpost (scenarios 1 and 2 above). This perimeter defense had to be able to provide adequate means of killing both suited men and also vehicles and should be fireable directly or remotely. Options for such a weapon were considered and evaluated for both performances but also whether they were technically feasible.

These included

1. Beamed electromagnetic radiation
2. Flamethrower
3. Blast weapons
4. Fragmentation weapons
5. Radiant energy

Defending against orbiting craft was more complex than a surface defense and, whilst an orbiting enemy could be tracked using Hercules, Zeus, or Hawk radar, it would be difficult to engage as available surface to air (or in this case surface to orbit) missiles were well beyond the 1,000 lb. (454 kg) weight limit imposed and a new bespoke weapon was needed. This would be expensive and with a long development time. An electron accelerator-based weapon was considered and would work by directing beams of gamma and/or neutron radiation at a craft to kill the crew and damage the craft. Just like the missile idea, however, this was far too heavy, 6,000 lbs. (2,722 kg) on Earth for such a system and still over 1,000 lbs. (454 kg) equivalent for a lunar-based system. In conclusion, Project Horizon rationalized that no effective defense could be provided against an orbiting enemy vehicle and the men on the outpost could, at best, dig into the surface to obtain protection until a suitable missile defense system became light enough to install there.

Personal Combat

With a set of unique problems from the environment (lack of atmosphere and exposure to solar radiation), equally unique weapons would be needed for troops to use if combat was to take place between US soldiers and a (presumably Soviet) force landing there.

Spacesuits would have to include an element of armor protection, along with the ability to self-seal following perforation, as a simple weapon that made even a small hole in a suit could prove lethal. More holes meant a greater chance of killing the opponent with the environment rather than the terrestrial method of killing the opponent by means of trauma. Weapons that optimized the delivery of high-velocity fragments were therefore considered the most desirable.

The suit proposed by Project Horizon included a hard suit for the body, made from titanium approximately 4 mm thick for standard protection and up to nearly 10 mm thick for maximum protection covering the stomach and chest, with a composite inner layer for resisting radiation. The same would go for a vehicle, with a titanium metal structure of approximately the same thickness to provide some resistance to fragments and also to maintain pressurization. Later, in analyzing how much protection 3.70 – 9.25 mm of titanium could actually provide on the lunar surface, it was calculated that a simple 6 grain (0.38 gram) fragment at 3,800 ft/s (1,158 m/s) or a 17 grain (1.10 gram) fragment at 2,400 ft/s (732 m/s) could pierce the suit or vehicle.

In terms of personal firepower, Project Horizon considered the various options and limitations which had to be considered, such as having to be self-sustaining.

The assessment was clear that the best weapon for defeating an enemy force either suited on-foot or in a vehicle of any description would be a Claymore-type mine. The standard Army type coming into service was the T48E1 mine, weighing just 1.36 kg and containing 675 5.56 mm diameter steel balls in a plastic resin. Once detonated, these balls, which were arranged in a slightly concave shape, would be fired out at a speed of 3,700 to 3,900 fps (1,128 to 1,189 m/s) across a 60-degree arc. On Earth, the mine’s effective lethal radius was around 200 feet (61 m), but on the Moon, with no atmosphere to slow down the balls and low gravity, the effective lethal range was increased to 2,500 feet (762 m), although the spread of the balls at that range would be extreme.

The Claymores could be set as a perimeter defense to be triggered upon command or by a tripwire, but they could also be handheld. This was not as hazardous as it may sound as, due to the vacuum of space, there was no blast hazard to the man detonating it on the end of a pole 5 to 6 feet (1.52 to 1.83 m) long. With a suitable shield surrounding the back of the mine to prevent mine fragments from being fired at the soldier wielding this weapon, in total, it was under 1 kg in weight. This made it simple, cheap, and easy to use for all combat purposes against men or machines.

Whilst the attack scenarios involving orbiting were complex, the judicious use of detonating a nuclear weapon nearby was possible. Detonating a 10MT nuclear device in space, launched from the outpost for protection would, for example, have a lethal radius of around 320 km, although it did mean having to station nuclear weapons there and obviously accepting the risk of killing yourself with your own weapon’s radiation (unlike a detonation in Earth’s atmosphere, a nuclear blast in a vacuum primarily produces intense radiation rather than blast or thermal energy release). Even should the outpost detonate a weapon in lunar orbit to defend against an attacking craft, the lack of atmosphere on the surface meant that there would be no attenuation of the intense radiation, creating a hazard for the outpost.

Proximity to the blast was one of the notable flaws of the Army’s new M-28 ‘Davy Crockett’ nuclear weapon system. Often referred to as a recoilless rifle system, the M-28 was, in fact, a type of spigot mortar (120 mm) that could throw the 23 kg Mk.54 nuclear warhead around 2 km. With a yield of 0.01 to 0.03 kT of TNT, the warhead on Earth would cause severe damage over a 10 m radius and moderate blast damage out to around 500 m (surface detonation), and up to a kilometer as an airburst. On the Moon, with no atmosphere to attenuate the explosion, damage could spread a lot further but so could the potential range of the warhead.

The Davy Crockett, fired at a maximum angle of 45 degrees, could, from the Moon, reach a lunar altitude of just over 1,200 m – high enough to be a threat to a descending enemy craft but not high enough to engage an orbital target and both with serious personal safety issues.

An alternative to the M-28 was also considered, one which was more accurate, lighter, and simpler, but with a shorter range. This was the Dumbo II, which was still on the drawing board and consisted of little more than a launching tray on legs with a rocket-propelled bomb loaded into it. On the lunar surface, this device would have a range of just 4,400 yards (just over 4,000 m) with an accuracy of 40 yards (37 m). It was, in the understatement of the decade, “desirable” to increase the range. With a range improvement to 17,700 yards (just over 16,000 m), it would increase the weight from 130 lbs. (59 kg) to 160 lbs. (72.6 kg).

In 1965, this subject of lunar personal weapons was examined once more by the US Army in the unusual title report “The Meanderings of a Weapon Oriented Mind When Applied in a Vacuum such as on the Moon”.

With the problems of cold welding over close-fitting and non-low friction metal parts, no lubricants, the temperature extremes in which it would have to operate and the issue of recoil from conventional-type weapons, solutions to a projectile weapon were perhaps harder to overcome in some regards than for a vehicle. The laser (‘Light Amplification by Stimulated Emissions of Radiation’), a concept of creating a focussed and intense beam of light, had been theorized for some time but did not exist before May 1960, when Theodore Maiman made the first laser (a ruby-laser) at the Hughes Research Laboratory in California. To theorize a laser weapon was beyond the ability of engineering in 1965 when the paper was written. It was not until 1967, with Co2 lasers of over 1,000 watts, that the first lasers were powerful enough to cut through even a sheet of steel 1 mm thick (TWI- The Welding Institute Cambridge, England), and the US Army paper actually suggested a lead time of at least 20 years. Although proposed in 1965, therefore, as a solution, laser-based systems were just pie in the sky, leaving recoilless weapons or very-low recoil weapons as the next best probable alternative.

Projectiles considered were rockets of various descriptions, balls (spheres), flechettes, and even rocks, which, based on the low gravity environment, would travel 2.73 times further than on Earth. For example, fired from the shoulder of a 6’ (1.8 m) tall man 5’ (1.5 m) from the ground at 3,000 f/s (914 m/s), a projectile would go 8,190 feet (2,500 m) when fired horizontally. Rather hazardously, however, was that due to the lack of atmosphere, if the projectile were fired upwards above the horizontal plane, it could go enormous distances. At 45 degrees, for example, a projectile launched at 3,000 f/s (914 m/s) (well short of the escape velocity of 2,400 m/s), would travel 320 miles (515 km), having reached an altitude of 80 miles (129 km) above the lunar surface.

The lack of ‘drop’ on the round added the severe hazard of projectiles in flight for large distances and long periods of time but had one significant advantage – the lack of anything other than the most rudimentary of sights being required. This is because a projectile would drop just 60 mm or so for every 100 m. Given a maximum line of sight engagement range of maybe 1.5 km, a projectile would, at worse, drop just 90 cm.

The lack of atmosphere also meant that wind resistance was effectively zero, so the shape of the projectile did not matter in terms of an efficient ballistic shape. Although ‘armor’ was not probable, it was objectively going to be easier for a spacesuit to resist perforation by a blunt object than a pointed one. Considering that vehicles were also a possibility, a pointed projectile with a high sectional density was preferred to aid in perforating the skin on those as well. The report concluded with a series of prospective weapon types summarised below. Noteworthy is that none of them are as expensive or perhaps simple and dangerous to men and vehicles as the Claymore-on-a-stick proposed in Project Horizon.

Suits

Exo-activity on the lunar surface (or even in space, as a ‘space-walk’) had not been done in 1959, so some of the suit-ideas and the science of space-suits were not fully developed by the time. There were, however, clear goals for a practical suit and the advantage of the low gravity meant that a 300-pound (136 kg) spacesuit would weigh just 50 pounds (22.7 kg) equivalent on the lunar surface.

Nonetheless, wearing a suit is a tiring task and normal wear would be limited to just 8 continuous hours, although 12 hours was acceptable. With a degree of caution, a man may operate in his suit for up to 24 hours and, in a dire emergency, 72 hours.

Referred to as a “metallic body conformation suit”, the outer surface was to be shiny (like all good 1950’s sci-fi) in order to reflect heat, but tough enough to resist the impact of micro-meteorites.

Any combat taking place in such a suit would be awkward and obvious to any attacker.

Termination

In 1959, there was a serious lack of crucial data on which to make some decisions – such as where to even put the base. Earth-based observations of the Moon could show the ‘seas’ – large flattish areas with few impacts, but the best available map being made by the Army Map Service at the time was just 1:5,000,000 scale and the contours were 2,000 feet (610 m) apart, meaning what looked flat could actually be quite a steep slope and landing on a cliff was ill-advised. An improved version of the map, due in around 1960 using better methods of stereo-image analysis, would be 1:1,000,000 scale with contours just 300 meters apart, with the aim of getting accuracy on surface features down to 150 or even 100 m by 1962. It is obvious, therefore, that with so little known, any outpost might find itself on impossible terrain. Any such landing without a better idea of the terrain was impossible in practical terms.

This was a fundamental part of the death knell for such ideas. It had not been the costs that killed Project Horizons perhaps as much as politics and practicality. It was not seen as being unfeasible or even unaffordable but perhaps just not necessary. The idea of launching at least one new Saturn rocket a week for years on end was one thing the Army could live with, but with the formation of NASA in October 1958, the writing was on the wall for the Army. NASA would take over all of the space work from the Army and Project Horizon, in particular, was handed over to their control by General John Medaris in March 1960. NASA had no interest in this project and it was thus left to die. The rest of the Army’s role in space was also handed over by the first half of that decade and the Army regained its terrestrial focus.

No weapons base on the Moon meant no need for weapons against men and machines, no lunar combat, and no ‘Moon-tanks’.

In 1967, with the signing through the United Nations of the Outer Space Treaty (OST), all signatories (including the USA and the Soviet Union) agreed not to place nuclear weapons in space (Article IV) either in orbit or on a celestial body (like the Moon), and that the Moon, in particular, was to be used exclusively for peaceful purposes. It also prohibits the establishment of military bases, installations, and fortifications on the Moon (Article IV), although military facilities for peaceful purposes were not prohibited. The treaty did not end ideas for a Moonbase, like Project ARES in the 1990s, but it did preclude space-based nuclear weapons. A further treaty, known as the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (‘The Moon Treaty’) signed in 1979 and effective from 1984, added to the Outer Space Treaty by prohibiting the creation of military bases although neither the United States nor the Soviet Union (or now Russia) have ratified that treaty.

“Article IV
State Parties to the Treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner.

The Moon and other celestial bodies shall be used by all State Parties to the Treaty exclusively for peaceful purposes. The establishment of military bases, installations, and fortifications, the testing of any type of weapons, and the conduct of military maneuvers on celestial bodies shall be forbidden. The use of military personnel for scientific research or for any other peaceful purposes shall not be prohibited. The use of any equipment or facility necessary for peaceful exploration of the Moon and other celestial bodies shall also not be prohibited.”

United Nations Office for Disarmament Affairs: Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies 1967. Underlining added by the author. Full text at http://disarmament.un.org/treaties/t/outer_space/text

“No national sovereignty rules in outer space. Those who venture there go as envoys of the entire human race. Their quest, therefore, must be for all mankind. And what they find should belong to all mankind.”
President Lyndon Johnson in ‘The President’s News Conference
at the LBJ Ranch (29th August 1965).
Collected in Public Papers of the
Presidents of the United States:
Lyndon B. Johnson: 1965 II (1966), 944-945.

Project Horizon was, perhaps, more of an embarrassment just a few years after it had been completed. The new NASA-controlled program was not interested in nuclear weapons on the Moon and the Defense Department fought to prevent its release to the public. In a 3 year struggle (1959-1962), the project was subject to numerous requests for release and, after no less than 10 separate security reviews by 3 different intelligence agencies, it was finally revealed at the end of the year. The project was effectively obsolete before it had even been finished, regardless of future changes, but it can be said that the project did form an important mental step in the long process of getting men to the Moon and, for Tiesenhausen – for what would eventually convey astronauts on the lunar surface with the Apollo 15 mission in July 1971.

Tiesenhausen’s work finally reached its fruition in the form of the lunar rover (Lunar Roving Vehicle – LRV) on the Apollo 15 mission. It took the simple option of tires over tracks. Source: NASA

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