Add few functions and scaffold for Δv/T calculus

ksp_toolbox/const.py

@@ -0,0 +1,114 @@
+import typing as t
+from math import pi, sqrt
+
+
+G = 6.67430e-11
+
+
+class Height(t.NamedTuple):
+    apoapsis: float
+    periapsis: float
+
+    @property
+    def a(self) -> float:
+        return 0.5 * (self.apoapsis + self.periapsis)
+
+    @classmethod
+    def circ(cls, h: float) -> "Height":
+        return cls(apoapsis=h, periapsis=h)
+
+
+class Body(t.NamedTuple):
+    name: str
+    radius: float
+    parent: t.Optional["Body"]
+    mass: float
+    apoapsis: float
+    periapsis: float
+    inclination: float
+
+    @property
+    def μ(self) -> float:
+        """Standard grav. parameter"""
+        return self.mass * G
+
+    @property
+    def a(self) -> float:
+        """Semi-major axis"""
+        return 0.5 * (self.apoapsis + self.periapsis)
+
+    def period_at(self, height: Height) -> float:
+        return 2 * pi * sqrt(height.a**3 / self.μ)
+
+    def circ_height_for_period(self, period: float) -> float:
+        return (self.μ * period**2 / (4 * pi**2)) ** (1 / 3)
+
+    def height_for_period(self, period: float, fixed_height: float) -> float:
+        return 2 * self.circ_height_for_period(period) - fixed_height
+
+    def v_circ(self, r: float) -> float:
+        return sqrt(self.μ / r)
+
+    def dv_transfer_ellipse(self, r1: float, r2: float) -> float:
+        """Δv to transfer from circular of radius r1 to elliptical with 2a=r1+r2"""
+        return self.v_circ(r1) * abs(sqrt(2 * r2 / (r1 + r2)) - 1)
+
+    def dv_transfer(self, r1: float, r2: float) -> float:
+        """Δv to transfer from circular of radius r1 to circular of radius r2"""
+        return self.dv_transfer_ellipse(r1, r2) + self.dv_transfer_ellipse(r2, r1)
+
+
+kerbol = Body(
+    name="kerbol",
+    radius=261.6e6,
+    parent=None,
+    mass=1.7565459e28,
+    apoapsis=0,
+    periapsis=0,
+    inclination=0,
+)
+kerbin = Body(
+    name="kerbin",
+    radius=600e3,
+    parent=kerbol,
+    mass=5.2915158e22,
+    apoapsis=13599840256,
+    periapsis=13599840256,
+    inclination=0,
+)
+mun = Body(
+    name="mun",
+    radius=200e3,
+    parent=kerbin,
+    mass=9.7599066e20,
+    apoapsis=12e6,
+    periapsis=12e6,
+    inclination=0,
+)
+minmus = Body(
+    name="minmus",
+    radius=60e3,
+    parent=kerbin,
+    mass=2.6457580e19,
+    apoapsis=47e6,
+    periapsis=47e6,
+    inclination=6,
+)
+eve = Body(
+    name="eve",
+    radius=700e3,
+    parent=kerbol,
+    mass=1.2243980e23,
+    apoapsis=9931011387,
+    periapsis=9734357701,
+    inclination=2.1,
+)
+gilly = Body(
+    name="gilly",
+    radius=13e3,
+    parent=eve,
+    mass=1.2420363e17,
+    apoapsis=48825000,
+    periapsis=14175000,
+    inclination=12,
+)