diff --git a/src/lib/shipDux/index.js b/src/lib/shipDux/index.js
index cbe4fde..e03e866 100644
--- a/src/lib/shipDux/index.js
+++ b/src/lib/shipDux/index.js
@@ -3,6 +3,7 @@ import u from 'updeep';
 
 import propulsion from "./propulsion/index.js";
 import identification from "./identification.js";
+import { calculateDriveReqs } from './propulsion/drive.js';
 
 const dux = new Updux({
   subduxes: {
@@ -19,4 +20,6 @@ const dux = new Updux({
 
 dux.setMutation( 'setShipMass', mass => u({reqs: {mass}}) );
 
+dux.addReaction( calculateDriveReqs );
+
 export default dux;
diff --git a/src/lib/shipDux/propulsion/drive.js b/src/lib/shipDux/propulsion/drive.js
index ec9ca64..f165e7d 100644
--- a/src/lib/shipDux/propulsion/drive.js
+++ b/src/lib/shipDux/propulsion/drive.js
@@ -1,5 +1,6 @@
 import { Updux } from "updux";
 import u from "updeep";
+import { createSelector } from "reselect";
 
 import reqs from "../reqs.js";
 
@@ -18,6 +19,18 @@ const dux = new Updux({
 dux.setMutation("setDrive", (changes) => u(changes));
 dux.setMutation("setDriveReqs", (reqs) => u({ reqs }));
 
+// needs to be at the top level
+export const calculateDriveReqs = store =>
+  createSelector(
+    [
+      (ship) => ship.reqs.mass,
+      (ship) => ship.propulsion.drive.rating,
+      (ship) => ship.propulsion.drive.advanced,
+    ],
+    (ship_mass, rating, advanced) =>
+      store.dispatch.setDriveReqs(calcDriveReqs(ship_mass, rating, advanced))
+      );
+
 export function calcDriveReqs(shipMass, rating, advanced = false) {
   const mass = Math.ceil(rating * 0.05 * shipMass);
   const cost = mass * (advanced ? 3 : 2);