EM launchOr

We’re out! What now?

T. Vuletić, Institute of physics, ZagrebVišnjan S3++ 2011

T. Vuletić, Institute of physics, ZagrebOpen day 2010

Space elevatorOr

How do we get out?

C,D:1st cosmic velocityV1

2/R=g V1=7.9 km/s

E:2nd cosmic velocityV2

2/2R=g V2=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:1st cosmic velocityV1

2/(R/2)=g/6 V1=2.2 km/s

2nd cosmic velocityV2

2/R=g/6 V2=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 gunwhile

we’re still here

Eraser, 1996.

force

fieldforce

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 railgu

n

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 oscillatorRLC circuit

position (mm)

-10 0 10 20 30

L ( H

)

-200

-150

-100

-50

0

50

100

150

200

250

L' (

H/m

)

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

position (mm)

0 10 20 30 40

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’·I2

Force, mass...

F=ma~I2

v=at

s= t2a 2

0

500

1000

1500

Coil center

0

5

10

15

0

10

20

30

time (s)

100 101 102 103 104 105 10610-1

100

101

102

103

104

Coil mouth

Coil current

Projectile acceleration

Projectile velocity

Distance covered by the projectile

s (

mm

)v

(m

/s)

a (x

1000

m/s

2 )I

(k

A)

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·U2=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= U2

C 2

E= v2m 2

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/fizika123coilgun.infowww.powerlabs.orgaudacity.sourceforge.net

Keywords:coilgun, railgun, mass driver, EM launch