implement nature::jupiter_altitude_to_pressure()

doc/research.md

@@ -82,6 +82,7 @@ Based on Figure 27 from SRC1, and Figure 28 using the middle of the 3 temperatur
 - 350km-850km: `p[bar](a[km]) = e^(-8.0920583983 - 0.0066339143 * a)`
 - 50km-350km: `p[bar](a[km]) = e^(-0.969198983 - 0.027000953 * a)`
 - -125km-50km: `p[bar](a[km]) = e^(0.0626589359 - 0.0473755348 * a)`
+- <-125km: `p[bar](a[km]) = -715.5577817531 * a - 89044.7227191413` (low-effort linear regression assuming p(-70000km) = 5e7 bar)
 
 ### Designing the in-game atmosphere
 

src/nature.rs

@@ -271,3 +271,18 @@ pub fn format_seconds_to_hour_min(seconds: f64) -> String {
         (seconds % 3600.0) / 60.0
     );
 }
+
+pub fn jupiter_altitude_to_pressure(altitude: f64) -> f64 {
+    // See doc/research.md
+    let a = altitude - JUPITER_RADIUS;
+    if a >= 1e6 {
+        return 0.0;
+    } else if a >= 350e3 {
+        return (-8.0920583983 - 0.0066339143 * a).exp();
+    } else if a >= 50e3 {
+        return (-0.969198983 - 0.027000953 * a).exp();
+    } else if a >= -125e3 {
+        return (0.0626589359 - 0.0473755348 * a).exp();
+    }
+    return -715.5577817531 * a - 89044.7227191413;
+}