The Marlet 3E: A Promising but ultimately Unsuccessful Project

In the early days of space exploration, the need for efficient and reliable launch systems became increasingly important. To address this need, the US-Canadian joint project HARP (Heavy-lift Aircraft Rocket Programme) was initiated to develop a multistage rocket capable of placing payloads into orbit. The Marlet 3E was designed to achieve an apogee of 450 kilometers, above the orbiting altitude of the International Space Station, and could carry a payload of up to 25 kilograms. However, this ambitious goal was not achieved due to the challenges in developing a multistage system that could survive the intense forces involved.

The project faced significant technical hurdles, including managing the bureaucracy between three institutions: a university, a government, and a military. Each entity had its own priorities, which made it difficult for the engineers to work towards a common goal. The chief engineer, Gerald Bull, was ultimately left behind as the program ended on June 30th, 1967, before its ambitions could be realized.

Gerald Bull's Post-HARP Career

After leaving Project HARP, Bull continued to work in the field of rocketry, but his career took a dramatic turn. He began selling and smuggling weapons to the South African government, ignoring a United Nations arms embargo. This led to six months in US prison, and upon release, he continued this work, earning him another fine for violating the same embargo. Eventually, Bull moved to Brussels to ply his trade, where he was approached by the Iraqi government, led by Saddam Hussein, with a lucrative offer of $25 million.

Project Babylon: A Hare-Brained Scheme

Bull took the knowledge gained from Project HARP and applied it to develop a new project, Project Babylon. The ultimate goal of this project was to build an artillery weapon capable of firing from Iraq into Israel and Iran. The concept was based on a system that had been proven to be ineffective during World War II, and even less effective in the era of guided missiles. Bull was reportedly aware of the ineffectiveness of this approach but used it as justification to continue his research.

Bull's Assassination

In 1990, Bull was assassinated while placing a key into the door of his Brussels home. He was found lying on the ground with a briefcase containing $20,000 inside. The circumstances surrounding his death remain shrouded in mystery, and speculation has abounded over the years.

Other Projects: Project SHARP and Spinlaunch

After Project HARP, Bull worked on other projects that aimed to overcome some of the limitations he encountered during the Marlet 3E program. One such project was Project SHARP, an even bigger light gas-powered gun that was tested in California in the 1990s. The concept behind this project was to use a light weight hydrogen gas instead of traditional propellants, which could achieve high muzzle velocities.

However, Project SHARP ultimately did not receive the necessary funding, and the system was used to test sub-scale hypersonic scramjet designs. Today, Spinlaunch is attempting to pick up where Project HARP left off, using a completely different form of kinetic launch system to replace large expensive first-stage rockets. The engineering behind these problems needs work, but the physics absolutely check out.

Real Engineering: A Resource for Learning

For those interested in learning more about the science behind rockets and other complex systems, Brilliant offers a free Real Engineering course that dives deep into the subject matter. This course is designed to make learning fun and interesting, with bid-sized interactive lessons that allow users to jump in and out of courses as they please. With their mobile app, learners can access this content anywhere, making it an ideal resource for those looking to learn on the go.

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"WEBVTTKind: captionsLanguage: enIn 1966, on the south eastern coast of Barbados,the US Army in partnership with the CanadianGovernment, began the earth shuddering testsof this massive artillery gun.A 36 metre long barrel constructed by weldingtwo 16 inch naval guns together end to end.Loaded with over half a metric tonne of blackpowder, the barrel needed rings of stiffeningreinforcement along its length to withstandthe immense pressure developed inside.Long white straightening rods needed to carefullyadjust the barrel to shoot straight and true.Its white paint gives away its true purpose.This was no military gun painted in drab olivecamouflage.This was a scientific instrument.A space cannon.A gun capable of launching a projectile toan altitude of 180 kilometres.Nearly half way to the orbiting altitude ofthe international space station, and the altitudeof the lowest orbiting satellite everThis gun was undeniably a space gun.Holding the record of highest altitude projectileever launched.The history of this bizarre science projectis a fascinating story.From the advances in ballistic science neededto achieve this extraordinary feat, to thereasons Barbados, a small island in the Caribbeanwas chosen for the gun's location.A tale that ends with bureaucratic sabotageand the assassination of the lead scientist.The remnants of these experimental guns remainhere on the beaches of Barbados.Laying idle since their final launch in 1966.Rusted relics of a bygone era, that you cancatch a glimpse of while taking off from runway09 of Grantley Adams International AirportBut why here, why on this beach off the southeasterncoast of Barbados?Project Harp was a joint effort from the CanadianGovernment, funding research at McGill Universityand the US Army’s Ballistics Research Laboratory,who were seeking more data on upper atmosphereconditions, in the same decade the SR-71 madeits debut this data was highly valuable,butgathering that data with sounding rocketswas expensive.Canada, not short on wide open spaces, couldhave located suitable sites near the university’shometown of Montreal.However, the dean of McGill, Donald Mordell,had higher ambitions than just gathering upperatmosphere data.A vision of a low cost space launch system,capable of launching satellites into orbitfor a fraction of the cost.Barbados was selected for these reasons.The most eastern of all the Caribbean islands.Firing from the south eastern shore at a fixedfiring angle over the sea, there was essentiallyunlimited fallout area.With plenty of space for debris from the launchesto fall into the ocean.Located along the launch path of Cape Canaveral,the infrastructure needed to track the launchesalready existed nearby.And, critically, located just 13 degrees northof the equator, Barbados would benefit fromthe increased rotational speed at the equatorand require lowered launch energies as a result.Barbados also came with the added benefitof being a region of extreme atmospheric researchinterest, the nursery of hurricanes that surgethrough the gulf of mexico every year.Barbados of the 1960s was a low income country,highly dependent on sugar exports, yet tomake the transition to a relatively high incometourism country independent from the Britishempire.The potential of a burgeoning space launchindustry on the tiny island was met with enthusiasmby the country's government.Striking a deal with McGill UniversityTo meet its objective Project Harp neededan extremely powerful gun, with a delicatecontrol over the explosive power pushing thepayload towards space.Projectile design is the first area of concern.This graph shows the relationship betweenshot weight and muzzle velocity for the harpgun system.A lower mass projectile will have a highermuzzle velocity.We need to balance this with the ballisticcoefficient, which is a measure of the projectile'sability to resist air resistance and maintainits velocity.Found by dividing the mass of the projectileby the drag coefficient multiplied by thecross-sectional area.Creating a narrow and dense projectile, essentiallya dart, can maximize ballistic coefficient.This is why Project Harp utilized sabot rounds.A saboted round is much narrower than thegun barrel, allowing it to minimize its crosssection and maximize it’s ballistic coefficient.However we need a method of creating a sealwith the gun barrel, allowing the propellantspressure to act on the projectile.There are several design options for sabots,but as we saw, projectile weight affects muzzlevelocity, and these sabots increase the effectiveprojectile weight, despite falling away uponleaving the barrel.So it’s vital to keep these plates as lightas possible.The main body of a pusher plate is made fromlightweight aluminum, but the aluminum isquite soft and the base of the missile hasa low area.With the immense pressure pushing on the finsfrom below, they can begin to sink into thealuminum.To counteract this a high strength steel insertis often added for the projectile to sit upon.We then need some method of keeping the projectilealigned in the barrel.This often was as simple as placing laminatedplywood cutouts between each fin.Finally we need a soft material that won’tscratch the barrel to form a tight seal betweenthe sabot and the barrel, for this ProjectHarp used polyethylene.The altitude reached is ultimately decidedby the velocity of the projectile exitingthe barrel, the muzzle velocity.From here pressure from the guns barrel willno longer be acting on the projectile andatmospheric drag will begin to sap away thekinetic energy imbued to it.Using gunpowder as an energy source is a challenge.Produce too much energy too quickly, and thebarrel of the gun will be over pressured.At best this damages the gun, at worst itcreates a bomb.The key to ballistic performance is this graph.The gun pressure distribution (page 171 ofbook).On the x-axis we have the distance from thebreech face, and on the y-axis we have pressure.Which may look something like this.Over the centuries there have been many waysof assessing the pressure along points inthe barrel, with some of the earliest beingsimple copper or lead plates placed insidethe gun barrel that would deform accordingto the pressure they experienced,but the piezoelectric crystal sensor revolutionisedthe science.This sensor, which uses a piezoelectriccrystal, could measure a varying pressureover time, providing a real time measurementof pressure, not a single maximum pressurepoint provided by a metal deformation plate.Piezoelectric means a material, typicallya crystal, generates an electric current whenmechanical stress is applied, a current whichcan be measured to generate a pressure reading.These sensors can be placed at the bottomof rounds to develop optimised pressure gradients.Allowing scientists to test new methods.With the ultimate goal of maximising the areaunder this curve, that’s the total energyreleased, without exceeding the maximum pressurethe gun can handle.Project HARP used some clever methods to achievethis.First, the most obvious, extending the lengthof the barrel.The longer the barrel the more time the pressurehas to act on the projectile.However as the propellant continues to burn,and the volume behind the projectile increases,the pressure behind it continually diminishes.Eventually aerodynamic drag and friction betweenthe projectile and the barrel will equal thepressure behind the projectile and no furthergains in velocity are possible.So we need to figure out what the optimalbarrel length for a given charge and projectilewill be.Next we need to maximise the energy releasedfrom our propellant.To increase muzzle velocity Project Harp neededblack powder, A LOT of black powder.They used huge 50 kilogram propellant bagsthat were rammed into the barrel with a hydraulicpress behind the projectile.Stacked directly on top of each other, eachhaving ignition charges sewn into the backof each bag facing the primer.These ignition charges only worked when theinitial flame front from the primer reachedthem with sufficient temperatures.Finally a large air gap between the finalbag and the sabot base was included.But tests using this configuration did notend as expected.This is a typical pressure-time diagram outputby the pressure sensors inside the barrelsfor these early tests.The peak pressure here is a lot higher thanthe scientists predicted and the muzzle velocityalso came in lower than expected.Clues to the cause began to emerge upon inspectingthe polyethylene disk from the bottom of thesabot.Grains of unburnt black powder were lodgedin the soft white plastic.Unburnt black powder means the total energypotential of the propellant was not released,but also indicates a larger problem.This is what was theorised to be happening.The primer ignites the first black powderbag, creating a pressure front which forcesthe column of bags towards the sabot base,while hot gas flows around the edges towardsthe projectile.The flame front begins marching forward ata slower rate than the pressure front, whilethe pressure front compresses the bags preventingfurther gas from flowing around them, impedingthe flame front further.The column impacts the sabot at high speed,the force of this impact was at times largeenough to cause damage to the sabot and projectile.At this time the flame front catches up, anda high pressure region is created in the compactedzone, which travels backwards towards thebreech, wasting precious kinetic energy.Testing new methods with the only 16 inch120 foot long gun in the world was not feasible,so interior ballistics tests were performedwith this.A massive instrumented barrel on rails thatrecoil backwards down the rails with eachfiring, allowing the researchers to developnew ignition methods in relative safety.Although it was called the HARP Flyer becauseit would frequently fly off its mountingswhen tests overpressured it.A solution to the black powder bags racingahead of the flame front was devised by placinglight wooden spacers between the bags.These spacers prevented the movement of thebags, but also helped the bags further alongthe barrel to ignite as hot gas could reachthem in the air gaps provided by the spacers.Using the HARP flyer, ballistic performancegraphs comparing the two methods were created,and they looked like this.With peak pressure lowering and the area underneaththe curve being larger for the spaced charges.This did not solve the issue completely andthe final configuration included electricallyfired squids to simultaneously fire all bagstogether.The projectiles themselves took many formswith different payloads and designs.One fascinating payload came in the form oftri-methyl-aluminium, or TMA, a liquid chemicalthat was loaded into the inside of the missile,but this was not a propellant.The liquid was pumped from the rocket witha piston driven by compressed nitrogen gas,triggered by a timer.Once outside the rocket the TMA began to reactwith oxygen in the ozone layer, forming aluminescent tracer cloud.A cloud that glowed in the dark.Allowing ground observers to easily see it.This tracer was used to analyse wind sherein the upper atmosphere, vital data in anera of intense aerospace development.Project Harp provided a cheap and reliablemethod of studying the upper atmosphere whencompared to sounding rocket alternatives,and the US Army’s funding was tied to thisobjective, but the Canadian leadership ofProject Harp had loftier ambitions,centred around a massive gun capable of launchingsatellites to space.A gun with twice the bore diameter of ProjectHarps largest gun, at 32 inches, with thicksolid steel walls to withstand the expectedincrease in barrel pressure.However the real challenge would be in thedevelopment of a multistage, high mass fractionrocket system capable of firing from the gunand accurately placing a satellite into orbit.The Martlet 4 was designed for this purpose.A full bore design, removing the need fora sabot, only the polyethylene disk was includedto protect the bottom of the rocket from thehot gas inside the barrel.This is a massive challenge.During launch the rocket would be under extremecompressive load.This would cause the rocket to bulge outwardscreating friction with the barrel.On one test the fibreglass rocket actuallygot stuck inside the barrel and the gas pressureburstthrough the middle of the rocket blowing theinternals of the rocket out of the muzzlelike a giant buckshot cannon.Developing the system required numerous testswith inert propellant stand ins.Longitudinal stripes were painted onto testprojectiles to examine friction wear aftereach shot.For these tests the gun was moved to an iceand snow covered lake north of McGills MontrealCampus.Here they could fire the projectiles in ahorizontal position, landing on the snow andice and slowly decelerating to be recoveredby the researchers for analysis.Another design, the Martlet 3C was designedto be slightly smaller than the gun bore,and the space between the barrel and the rocketcasing was filled with a dense fluid thatwould travel with the rocket in bore and preventfriction on the rocket casing.It was ultimately decided after testing thata full bore rocket made from fibreglass witha teflon coating was the best option.When it came time to test active propellantthe propellant grain layers were laminatedtogether in a hydraulic press around a starshaped mandrel.When dried an inhibitor coating was applied,the end casings, including the nozzle werefitted and the fibreglass casing was simplywrapped around the solid propellant and cured.This was an extremely cheap method of construction.Structural issues were assessed with thismethodand when completed flip out stabilisationfins were incorporated and the single stageMarlet 3E was born.Capable of placing 25 kilogram payload toan apogee of 450 kilometres.Above the orbiting altitude of the ISS.However this was not orbit, without the necessaryhorizontal velocity these payloads would simplyfall back to earth.To achieve orbit a multistage system was needed.The Marlet 4.However scaling a system like this up wouldbe extremely difficult.G hardened guidance and control systems neededto be developedFeeding into a central computer that controlledcold gas thrusters.High acceleration tests proved these systemswere capable of surviving up to 5000 gs, wellabove the launch acceleration.The staging would necessitate gradual decreasingof diameter, and so the previous method offluid support was revisited.This optimised staging method was provingdifficult to develop with the time pressureon the program.The joint US-Canadian program was time limitedto 3 years, and the engineers at project harppursued unguided multistage rockets basedon earlier saboted systems.Ultimately the program ended, on June 30th,1967, before its ambitions could be realized.Managing the bureaucracy between 3 institutions,a university, a government and a militaryproved too difficult.Each having their own priorities.Leaving the chief engineer behind ProjectHARP Gerald Bull, lost in the wind.Seeking a new patron from this expertise hewrote his own demise.Beginning by selling and smuggling weaponsto the South African government, ignoringa United Nations arms embargo and earninghimself 6 months in US prison.Upon release he continued selling arms tothe South African government and got caughtand fined again.Eventually moving to Brussels to ply his tradethere.In 1981 he was approached by the Iraqi government,led by the now infamous Saddem Hussain.With a 25 million dollar paycheck, Bull tookthe knowledge he gained during project harpto Iraq to begin a new project, Project Babylon.A project with the ultimate goal of buildingan artillery weapon capable of firing fromIraq into Israel and Iran.A hare-brained scheme, that was proven tobe completely tactically useless during WorldWar 2, and would be even less effective inthe era of guided missiles.Bull was supposedly aware of how ineffectivethis would be as a weapon and used this asjustification to continue his research, butthe Israeli government didn’t see thingsthat way and Mr Bull was assassinated as heplaced the key into the door of his Brusselshome.He was found by police lying on the groundwith a briefcase containing 20 thousand dollarsinside.Other projects like Project SHARP, an evenbigger light gas powered gun was tested inCalifornia in the 90s.No projectile can exceed the velocity of thepropellant pushing it, and Project SHARP realisedthis and began using light weight hydrogengas instead.Capable of achieving a muzzle velocity of7 km/s, but the estimated 1 billion dollarfunding needed to scale it up never arrived,and the system ultimately was used to testsubscale hypersonic scramjet designs.Today Spinlaunch is attempting to pick upwhere Project Harp left off, using a completelydifferent form of kinetic launch system toreplace large expensive first stage rockets.The engineering behind these problems needwork, but the physics absolutely check outand you can test that for yourself with ourReal Engineering course on brilliant thatdives deep into the science behind rockets,including orbits and centripetal acceleration.It’s powerful knowledge to obtain, and youcan complete this course for free by signingup at brilliant.org/realengineering.Getting started on your first course is completelyfree for the first 30 days, but the first500 people that sign up with our link willget 20% off Brilliant's annual premium subscription.Brilliant makes learning fun and interestingwith bized-sized interactive lessons thatmake it easy to jump in and out of courses,so you can learn on your own time, and it’seven easie00 r with their mobile app, so youcan learn the fundamentals of computer scienceon your morning commute to work or school.And when you are done with that you can moveonto more advanced computer science courseslike their intro to neural networks.Brilliant includes interactive elements tohelp you quickly 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