Download or view StarTram.frink in plain text format
/** 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
}
Download or view StarTram.frink in plain text format
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, eliasen@mindspring.com