# EM launch Or We’re out! What now? T. Vuletić, Institute of physics, Zagreb Višnjan S3++ 2011.

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EM launch Or We’re out! What now? T. Vuletić, Institute of physics, Zagreb Višnjan S3++ 2011

T. Vuletić, Institute of physics, Zagreb Open day 2010 Space elevator Or How do we get out?

C,D: 1 st cosmic velocity V 1 2 /R=g V 1 =7.9 km/s E: 2 nd cosmic velocity V 2 2 /2R=g V 2 =11.2 km/s Earth’s gravity well

Chemical launch: Newton, Jules Verne et al. Gas expansion V=1-4 km/s : insufficient! there’s also the atmospheric drag...

Moon: 1 st cosmic velocity V 1 2 /(R/2)=g/6 V 1 =2.2 km/s 2 nd cosmic velocity V 2 2 /R=g/6 V 2 =3.1 km/s Moon’s gravity well

EM launch: Moon shallow well + there’s no air-drag read... R.A. Heinlein: The Moon is a Harsh Mistress

EM launch: Moon watch... “Moon” by Duncan Jones

read... R.A. Heinlein: The Moon is a Harsh Mistress Logistics orbit: Lagrange points Idea: G.K. O’Neill and his S.S.I. “father” of the particle accelerator

EM gun while we’re still here

Eraser, 1996.

force field force How does it work? Mass Driver: Electromagnets repel or attract and cary the projectile Coilgun: Electromagnet attracts the feromagnetic projectile! Railgun: Rails are shorted by the projectile – current in this circuit forces the project out

EM gun Coil, 30 turns, 4 layers, 1 mm wire Capacitors, 450V, 8.8mF coilgun capacitors railgun solid-state relay

RLC circuit Solving for the Current: damping resonant frequency Damped harmonic oscillator underdamped overdamped critically damped

Capacitance C=8.8 mF Resistance R=0.3  Inductance L=? Damped harmonic oscillator RLC circuit

Inductance Inductance L : Depends on the position of the projectile Force: Force maximum occurs where the inductance variation has a maximum Position: Projectile tip - 5 mm inside coil F= L’·I 2

Force, mass... F=ma~I 2 v=at s= t 2 a2a2

Current, charge Capacitance C=8.8 mF Resistance R=0.3  Inductance L=150  H ~4 Coulombs discharge through the coil ~ kiloAmps in milliseconds! Voltage U=450 V Charge Q=C·U=4 C Energy E=½C·U 2 =900 J

0.5 m 2.5 m V=25m/s V=90km/h 0 msec 20 msec 100 msec 0.0 m Velocity

Energy E= U 2 C2C2 E= v 2 m2m2 Electric ~ 900 J Kinetic ~ 12 J Diminutive efficiency, kein Schwarzenegger... 25 g 

EM gun Machine & electronics shop Institute of physics: I. Čičko, B. Kiš, A. Vojnović Thanks: R. Beuc, Đ. Drobac, B.Erjavec, M. Prester, K. Salamon Take a look: www.youtube.com/user/fizika123 coilgun.info www.powerlabs.org audacity.sourceforge.net Keywords: coilgun, railgun, mass driver, EM launch

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