# 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.