# StarTram.frink

/** This program calculates the drag through the atmosphere of the StarTram
design:

https://en.wikipedia.org/wiki/StarTram
*/

use StandardAtmosphere.frink

getDensity[altitude] :=
{
[temp, pressure] = StandardAtmosphere.getTemperatureAndPressure[altitude]
return StandardAtmosphere.getDensity[altitude, temp, pressure]
}

getDensityVelocitySquaredProduct[altitude, velocity] :=
{
getDensity[altitude] * velocity^2
}

altitude = 6000 m  // Top of evacuated tunnel
v = 8.8 km/s       // Fast enough for orbital velocity (with corrective burn)

mass = 40 tons
Frocket =  0 N     // StarTram is ballistic, no rocket thrust.

target = 350 km
Cd = 0.09
A = pi (1 m)^2    // 33 ft^2

launchAngle = 90 degrees   // We'll call 90 degrees straight up.

timestep = .01 s

t = 0 s
Esum = 0 J
while (altitude < target)
{
density = getDensity[altitude]
Fdrag = 1/2 density v^2 A Cd

weight = G earthmass mass / (altitude + earthradius)^2   // Correct weight for decreasing gravity
Fup = Frocket - Fdrag - weight

a = Fup/mass                                             // Actual upward acceleration

vnew = v + a timestep
vave = (v + vnew) / 2

stepdist = vave * timestep
Esum = Esum + Fdrag * stepdist         // Energy lost this timestep

println[(t->"s") + "\t" + format[altitude,"km", 3] + "\t" + format[v, "mach", 2] + "\t" + format[a,"gee",3] + "\t" + format[Fdrag, "lbf", 5] + "\t" + format[Esum, "MJ", 2]]

v = vnew

// TODO:  Refine this to model changing distance around earth's curve.
altitude = altitude + stepdist sin[launchAngle]

t = t + timestep
}

This is a program written in the programming language Frink.
For more information, view the Frink Documentation or see More Sample Frink Programs.

Alan Eliasen was born 18658 days, 12 hours, 41 minutes ago.