Episode 46: Archimedes Death Ray Revisited
The MythBusters already did their (failed) attempt at an Archimedes Death Ray, so this episode was framed as a contest for other people to make their own attempts. One contest was a "short range" contest to create a mirror that worked at 5 ft and the other was a 100 ft contest. By the end of the episode, the contest had become irrelevant as the contestants were sidelined by the news that MIT's 2.009 (Product Engineering Process) class had ignited a dry boat mockup at 100 feet in 10 minutes using127 glass mirrors. They MythBusters invited the MIT team out to make their attempt.
The MIT team got nothing more than smoke at 150 feet and only achieved ignition once it closed to 75 feet. Perhaps the 2.009 professors should have listened to the 5 minute technical feasibility they had the students do in class: 95% of the 80 students didn't think it would be possible.
The MythBusters really wanted to emphasized the 'bustedness' of this myth, so there were seven reasons given throughout the episode to back up their assessment:
- Compass: Syracuse faced east into the ocean, so Archimedes would have had to use morning rays for his weapon.
- Weather: mirrors only work when the sun is out
- Roman boats were moving: the death ray would have had to work quickly.
- 'Inflammable' sails: sails are difficult to ignite because of their light color and flapping.
- History: It wasn't until 800 years after the battle was that history books mentioned the use of mirrors.
- Scale: It would take quite a lot of people and mirrors to ignite a boat quickly.
- Alternatives: flaming arrows and fireballs are much easier to create, fire, and aim and also use much less manpower.
Myth: At the seige of Syracuse in 212 BC (during the Second Punic Wars), Archimedes built his 'burning mirrors,' which was an arrangement of mirrors that was capable of focusing a ray of sunshine on approaching ships and setting them aflame.
In the MythBusters' own attempt last season, they only got up to 290 degrees, which wasn't enough to ignite their mock Roman trireme.
The episode was initially setup as two challenges: a 5ft death ray and a 100ft death ray. The contestants wereba judged on: * Creative use of materials * Relative to Archimedes myth * Actually sets things on fire * How good they are at making a video
Adam (referring to one of the contestant entries): "I feel like I'm watching something I didn't mean to find"
For the small scale category they accepted two entries: * Carrie and Jess (UCSB engineering students): they lit a piece of balsa wood on fire with a hexagon mirror array. * Brendan Millstein (Lawrence Berkeley) and Stephen Marsh (Harvard): guys who found a parabolic mirror in a box.
They also added their own entry, a giant satellite dish that they converted into a frame for 6000 1" square mirrors.
For the 100ft category they only accepted one entry, which was a NASA guy (Mike Bushroe) who created a variable focus mirror out of steel coated with silvering agent. This contest ended up being a bust at Bushroe's mirror didn't survive transport out to San Francisco (Mike: "Oh no, it's broken"). They showed it resurrected at the end of the episode, but didn't show any results from it.
Small scale contest
The contestants were given materials found in a Roman vessel to ignite: * wood * oakum soaked in pitch * pitch
In round 1, the Brendan and Stephen were allowed to use their parabolic mirror, which toasted all of the materials in nine seconds. The woman's hexagonal array of mirrors fared much worse, taking 2 minutes to ignite the wood and failing to ignite the oakum soaked in pitch.
Round 1 completely ignored their own contest rules, which stated that the material had to be ignited at five feet. With the real requirements re-instituted, they were given 24 hours to create new mirrors. Stephen/Brenden had to completely throw out their parabolic mirror, which had a much closer focal length. They ended up with two designs: plaster spun into a parabola and covered with reflective material and a pressurized drum covered with reflective mylar that was adjustable. Carrie/Jess bent their mirrors and re-aimed in order to meet the new requirements.
Brendan and Stephen were named winners, but neither really succeeded. Brendan/Stephen didn't ignite the wood, but they were able to light the hemp faster than the women.
The MythBusters entry appeared midway through round two, but it turns out that Jamie and Adam didn't pay attention to the rules and couldn't ignite at 5'. They ignited the oakum and pitch, but much closer than 5'.
MIT large scale entry
MIT's setup was the real focus of the episode. As part of the 2.009 Product Engineering Process class, Professor David Wallace and his students had successfully lit a dry mock boat using 127 glass mirrors at 100ft in under 10 minutes as part of a technical feasibility test (more info from the 2.009 web site). The MythBusters invited the class out to San Francisco to recreate their feasibility test, though they made them change the glass mirrors to bronze mirrors to stay accurate to the historical time period. The 2.009 class also would have to ignite a real boat in water, not a fake boat on a roof.
The new setup called for 13 mirror holding stands and 300 bronze mirrors, which the MythBusters prepared.
Grant and Tory converted a boat into a mock Roman trireme using thick timbers coated in tar:
MIT students aimed the mirrors in several minutes. It smoked a black spot into the side of the hull, but it couldn't ignite the hull. They realigned the mirrors to get 400 degrees up to 450 degrees at the focal point, but still no flames. Wallace got the MythBusters to move the boat so that they wouldn't have to readjust the mirrors.
Wallace: "We need a bit of help. What we want you to do is reposition the boat so that we can get another pass at the part we've really charred"
Jamie : "So, what you're saying is that staying still isn't good enough? We actually have to move the boat for you into the line of fire?"
Wallace: "Shutup you lazy Roman pig and do what you're told"
They tried igniting the sail next as many viewers thought that this was more feasible. The sail didn't even smoke as the white reflected much of the heat and it was flapping in and out of the focal point.
The boat was brought within 75 feet for one final shot. Finally, the boat ignited.
For their finale, the MythBusters brought out "The Scorpion," which was Grant's recreation of a known Archimedes weapon (animal sinew replaced with nylon rope springs). The Scorpion is a ballista (torsion catapult) that is effectively a giant crossbow. They shot lit arrows at the boat in what was probably meant to be a spectacular lighting, but Grant's first shot hit water and the next several shots did little to ignite the boat. Tory: "About twenty more of these and that's going up."
Jamie ended it all by dropped a large fireball into the boat to finally set it ablaze. Archimedes was said to be able to launch flaming fireballs 600 ft; Jamie is able to throw flaming fireballs about 20 feet.
Although the Scorpion didn't really work and Jamie tossed his fireball by hand, their point was that Archimedes had much easier means of setting boats aflame that didn't rely on the weather, tremendous manpower, tedious aiming of focal length, time of day, or any of the many other disadvantages of burning mirrors.
Wind knocked over many of their mirrors to finally bring the episode to a close.