Many improvments + install script

install-service.sh

@@ -0,0 +1,202 @@
+#!/usr/bin/env bash
+set -e
+
+# Rocketry Service Installer
+# Installs the React SPA as a systemd service on the system
+
+# Preflight checks
+command -v node  >/dev/null || { echo "Error: node not found"; exit 1; }
+command -v npm   >/dev/null || { echo "Error: npm not found"; exit 1; }
+command -v sudo  >/dev/null || { echo "Error: sudo not found"; exit 1; }
+
+echo "Rocketry Service Installer"
+echo "=========================="
+echo ""
+
+# Port prompt
+read -p "Port to run on [default: 8080]: " PORT
+PORT=${PORT:-8080}
+
+# Validate port
+if ! [[ "$PORT" =~ ^[0-9]+$ ]] || [ "$PORT" -lt 1 ] || [ "$PORT" -gt 65535 ]; then
+  echo "Error: Invalid port number. Must be between 1 and 65535."
+  exit 1
+fi
+
+echo ""
+echo "Building application..."
+npm run build
+
+# Install directory
+INSTALL_DIR="/opt/rocketry"
+echo "Installing to $INSTALL_DIR..."
+sudo mkdir -p "$INSTALL_DIR"
+sudo cp -r dist "$INSTALL_DIR/"
+
+# Write server.js to /opt/rocketry/server.js
+echo "Writing server.js..."
+sudo tee "$INSTALL_DIR/server.js" > /dev/null <<'SERVEREOF'
+#!/usr/bin/env node
+const http = require('http');
+const fs = require('fs');
+const path = require('path');
+
+const PORT = process.env.PORT || 8080;
+const DIST_DIR = path.join(__dirname, 'dist');
+
+const MIME_TYPES = {
+  '.html': 'text/html; charset=utf-8',
+  '.js': 'text/javascript; charset=utf-8',
+  '.css': 'text/css; charset=utf-8',
+  '.svg': 'image/svg+xml',
+  '.png': 'image/png',
+  '.ico': 'image/x-icon',
+  '.woff2': 'font/woff2',
+  '.json': 'application/json',
+};
+
+const server = http.createServer((req, res) => {
+  // Normalize URL
+  let urlPath = decodeURIComponent(req.url);
+  if (urlPath === '/') {
+    urlPath = '/index.html';
+  }
+
+  // Resolve file path
+  const filePath = path.join(DIST_DIR, urlPath);
+
+  // Security check: ensure we're within DIST_DIR
+  if (!filePath.startsWith(DIST_DIR)) {
+    res.writeHead(403, { 'Content-Type': 'text/plain' });
+    res.end('Forbidden');
+    return;
+  }
+
+  fs.stat(filePath, (err, stats) => {
+    if (err) {
+      // File not found; serve index.html for SPA routing (unless it's a file with extension)
+      const ext = path.extname(urlPath);
+      if (ext && ext !== '.html') {
+        // Likely a missing asset file
+        res.writeHead(404, { 'Content-Type': 'text/plain' });
+        res.end('Not Found');
+        return;
+      }
+
+      // SPA fallback: serve index.html
+      const indexPath = path.join(DIST_DIR, 'index.html');
+      fs.readFile(indexPath, 'utf-8', (readErr, data) => {
+        if (readErr) {
+          res.writeHead(500, { 'Content-Type': 'text/plain' });
+          res.end('Internal Server Error');
+          return;
+        }
+        res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
+        res.end(data);
+      });
+      return;
+    }
+
+    if (stats.isDirectory()) {
+      // Try to serve index.html from the directory
+      const indexPath = path.join(filePath, 'index.html');
+      fs.readFile(indexPath, 'utf-8', (readErr, data) => {
+        if (readErr) {
+          // Directory exists but no index.html; fall back to SPA index
+          const mainIndexPath = path.join(DIST_DIR, 'index.html');
+          fs.readFile(mainIndexPath, 'utf-8', (mainErr, mainData) => {
+            if (mainErr) {
+              res.writeHead(404, { 'Content-Type': 'text/plain' });
+              res.end('Not Found');
+              return;
+            }
+            res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
+            res.end(mainData);
+          });
+          return;
+        }
+        res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
+        res.end(data);
+      });
+      return;
+    }
+
+    // Serve file with appropriate MIME type
+    const ext = path.extname(filePath).toLowerCase();
+    const contentType = MIME_TYPES[ext] || 'application/octet-stream';
+
+    fs.readFile(filePath, (readErr, data) => {
+      if (readErr) {
+        res.writeHead(500, { 'Content-Type': 'text/plain' });
+        res.end('Internal Server Error');
+        return;
+      }
+      res.writeHead(200, { 'Content-Type': contentType });
+      res.end(data);
+    });
+  });
+});
+
+server.listen(PORT, () => {
+  console.log(`Rocketry server listening on http://localhost:${PORT}`);
+});
+
+server.on('error', (err) => {
+  if (err.code === 'EACCES') {
+    console.error(`Error: Permission denied. Port ${PORT} may require elevated privileges.`);
+  } else if (err.code === 'EADDRINUSE') {
+    console.error(`Error: Port ${PORT} is already in use.`);
+  } else {
+    console.error('Server error:', err.message);
+  }
+  process.exit(1);
+});
+SERVEREOF
+
+# Make server.js executable
+sudo chmod +x "$INSTALL_DIR/server.js"
+
+# Write systemd unit file
+echo "Writing systemd service file..."
+sudo bash -c "cat > /etc/systemd/system/rocketry.service" <<UNITEOF
+[Unit]
+Description=Rocketry Equation Solver
+After=network.target
+
+[Service]
+Type=simple
+User=nobody
+WorkingDirectory=/opt/rocketry
+ExecStart=/usr/bin/node /opt/rocketry/server.js
+Environment="PORT=$PORT"
+Restart=on-failure
+RestartSec=5
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=multi-user.target
+UNITEOF
+
+# Enable and start service
+echo "Configuring systemd service..."
+sudo systemctl daemon-reload
+sudo systemctl enable rocketry
+sudo systemctl restart rocketry
+
+echo ""
+echo "✓ Rocketry service installed successfully!"
+echo ""
+echo "  Location:  $INSTALL_DIR"
+echo "  Port:      $PORT"
+echo "  URL:       http://localhost:$PORT"
+echo ""
+echo "Service status:"
+sudo systemctl status rocketry --no-pager | sed 's/^/  /'
+echo ""
+echo "Useful commands:"
+echo "  Check status:    sudo systemctl status rocketry"
+echo "  View logs:       sudo journalctl -u rocketry -f"
+echo "  Restart:         sudo systemctl restart rocketry"
+echo "  Stop:            sudo systemctl stop rocketry"
+echo "  Uninstall:       sudo systemctl disable rocketry && sudo rm -rf $INSTALL_DIR /etc/systemd/system/rocketry.service && sudo systemctl daemon-reload"

src/App.jsx

@@ -4,6 +4,7 @@ import Solver from './pages/Solver.jsx'
 import EnginePage from './pages/EnginePage.jsx'
 import RocketPage from './pages/RocketPage.jsx'
 import KnowledgebaseFuelsPage from './pages/KnowledgebaseFuelsPage.jsx'
+import KnowledgebaseEquationsPage from './pages/KnowledgebaseEquationsPage.jsx'
 
 export default function App() {
   return (
@@ -89,6 +90,18 @@ export default function App() {
               >
                 Fuels / Oxidisers
               </NavLink>
+              <NavLink
+                to="/knowledgebase/equations"
+                className={({ isActive }) =>
+                  `block px-4 py-2 text-sm transition-colors ${
+                    isActive
+                      ? 'bg-slate-700 text-white'
+                      : 'text-slate-300 hover:bg-slate-700 hover:text-white'
+                  }`
+                }
+              >
+                Equations
+              </NavLink>
             </div>
           </div>
         </nav>
@@ -99,6 +112,7 @@ export default function App() {
         <Route path="/design/engine" element={<EnginePage />} />
         <Route path="/design/rocket" element={<RocketPage />} />
         <Route path="/knowledgebase/fuels" element={<KnowledgebaseFuelsPage />} />
+        <Route path="/knowledgebase/equations" element={<KnowledgebaseEquationsPage />} />
       </Routes>
     </div>
   )

src/components/ErrorBoundary.jsx

@@ -0,0 +1,20 @@
+import { Component } from 'react'
+
+export default class ErrorBoundary extends Component {
+  state = { error: null }
+
+  static getDerivedStateFromError(e) {
+    return { error: e }
+  }
+
+  render() {
+    if (this.state.error) {
+      return (
+        <div className="flex items-center justify-center h-full text-slate-500 text-sm">
+          3D view unavailable
+        </div>
+      )
+    }
+    return this.props.children
+  }
+}

src/engine/engineDesignCalcs.js

@@ -96,10 +96,7 @@ export function calcCooling(thermo, cooling, chamberGeom) {
 
     const { Dt, Dc, Lc } = chamberGeom
     // Simplified Bartz heat flux [W/m²] using typical exhaust gas properties
-    const mu = 6e-5    // Pa·s — typical rocket exhaust dynamic viscosity
-    const cp = 2000    // J/(kg·K)
-    const Pr = 0.7
-    const T_wall = 800 // K — assumed hot-gas-side wall temperature
+    const { mu = 6e-5, cp = 2000, Pr = 0.7, T_wall = 800 } = cooling
 
     const q_est = (0.026 / Math.pow(Dt, 0.2)) *
       (Math.pow(mu, 0.2) * cp / Math.pow(Pr, 0.6)) *
@@ -110,9 +107,9 @@ export function calcCooling(thermo, cooling, chamberGeom) {
     const q_total = q_est * chamberArea
 
     const { channelCount } = cooling
-    const channelArea = channelCount > 0 ? q_total / channelCount : 0
+    const q_perChannel = channelCount > 0 ? q_total / channelCount : 0
 
-    return { method, q_est, q_total, channelCount, channelArea }
+    return { method, q_est, q_total, channelCount, q_perChannel }
   }
 
   if (method === 'film') {

src/engine/equations.js

@@ -16,6 +16,7 @@ export const EQUATIONS = [
     name: 'Fundamental Thrust Equation',
     formula: 'F = ṁ·Vₑ + (pₑ − pₐ)·Aₑ',
     category: 'Thrust',
+    description: 'Calculates total thrust from momentum thrust and pressure thrust. Used when exit conditions and mass flow are known.',
     variables: ['F', 'mdot', 'Ve', 'pe', 'pa', 'Ae'],
     solvers: {
       F:    v => v.mdot * v.Ve + (v.pe - v.pa) * v.Ae,
@@ -40,6 +41,7 @@ export const EQUATIONS = [
     name: 'Thrust from Isp',
     formula: 'F = ṁ·Isp·g₀',
     category: 'Thrust',
+    description: 'Relates thrust, mass flow, and specific impulse. Commonly used when Isp is known instead of exhaust velocity.',
     variables: ['F', 'mdot', 'Isp', 'g0'],
     solvers: {
       F:    v => v.mdot * v.Isp * v.g0,
@@ -55,6 +57,7 @@ export const EQUATIONS = [
     name: 'Effective Exhaust Velocity',
     formula: 'cₑ = F / ṁ',
     category: 'Thrust',
+    description: 'Defines effective exhaust velocity as thrust divided by mass flow. Includes both momentum and pressure thrust effects.',
     variables: ['ceff', 'F', 'mdot'],
     solvers: {
       ceff: v => v.F / v.mdot,
@@ -69,6 +72,7 @@ export const EQUATIONS = [
     name: 'Isp from Effective Exhaust Velocity',
     formula: 'Isp = cₑ / g₀',
     category: 'Specific Impulse',
+    description: 'Converts effective exhaust velocity to specific impulse. Related by the standard gravitational acceleration.',
     variables: ['Isp', 'ceff', 'g0'],
     solvers: {
       Isp:  v => v.ceff / v.g0,
@@ -82,6 +86,7 @@ export const EQUATIONS = [
     name: 'Isp from Thrust & Mass Flow',
     formula: 'Isp = F / (ṁ·g₀)',
     category: 'Specific Impulse',
+    description: 'Directly calculates specific impulse from thrust and mass flow. Fundamental performance metric for rocket engines.',
     variables: ['Isp', 'F', 'mdot', 'g0'],
     solvers: {
       Isp:  v => v.F / (v.mdot * v.g0),
@@ -97,6 +102,7 @@ export const EQUATIONS = [
     name: 'Characteristic Velocity',
     formula: 'c* = p₀·Aₜ / ṁ',
     category: 'Nozzle Performance',
+    description: 'Defines characteristic velocity as a measure of combustion chamber performance. Independent of nozzle expansion.',
     variables: ['cstar', 'p0', 'At', 'mdot'],
     solvers: {
       cstar: v => (v.p0 * v.At) / v.mdot,
@@ -111,6 +117,7 @@ export const EQUATIONS = [
     name: 'c* from Thrust Coefficient & Isp',
     formula: 'c* = Isp·g₀ / Cꜰ',
     category: 'Nozzle Performance',
+    description: 'Relates characteristic velocity to thrust coefficient and specific impulse. Useful for nozzle analysis.',
     variables: ['cstar', 'Isp', 'g0', 'CF'],
     solvers: {
       cstar: v => (v.Isp * v.g0) / v.CF,
@@ -126,6 +133,7 @@ export const EQUATIONS = [
     name: 'Thrust Coefficient',
     formula: 'Cꜰ = F / (p₀·Aₜ)',
     category: 'Nozzle Performance',
+    description: 'Defines thrust coefficient as a dimensionless nozzle performance factor. Typical values are 1.4–1.9 for ideal nozzles.',
     variables: ['CF', 'F', 'p0', 'At'],
     solvers: {
       CF: v => v.F / (v.p0 * v.At),
@@ -141,6 +149,7 @@ export const EQUATIONS = [
     name: 'Tsiolkovsky Rocket Equation (cₑ)',
     formula: 'Δv = cₑ·ln(m₀/mf)',
     category: 'Rocket Equation',
+    description: 'The rocket equation in terms of effective exhaust velocity. Calculates delta-v available from propellant mass ratio.',
     variables: ['dv', 'ceff', 'm0', 'mf'],
     solvers: {
       dv:   v => v.ceff * Math.log(v.m0 / v.mf),
@@ -155,6 +164,7 @@ export const EQUATIONS = [
     name: 'Tsiolkovsky Rocket Equation (Isp)',
     formula: 'Δv = Isp·g₀·ln(m₀/mf)',
     category: 'Rocket Equation',
+    description: 'The classic Tsiolkovsky rocket equation using specific impulse. Foundation of trajectory design and mission planning.',
     variables: ['dv', 'Isp', 'g0', 'm0', 'mf'],
     solvers: {
       dv:  v => v.Isp * v.g0 * Math.log(v.m0 / v.mf),
@@ -170,6 +180,7 @@ export const EQUATIONS = [
     name: 'Mass Ratio',
     formula: 'MR = m₀ / mf',
     category: 'Rocket Equation',
+    description: 'Ratio of initial to final mass. Determines the exponential factor in the Tsiolkovsky equation.',
     variables: ['MR', 'm0', 'mf'],
     solvers: {
       MR: v => v.m0 / v.mf,
@@ -183,6 +194,7 @@ export const EQUATIONS = [
     name: 'Propellant Mass',
     formula: 'mₚ = m₀ − mf',
     category: 'Rocket Equation',
+    description: 'Mass of propellant consumed during burn. Difference between initial (wet) and final (dry) mass.',
     variables: ['mp', 'm0', 'mf'],
     solvers: {
       mp: v => v.m0 - v.mf,
@@ -196,6 +208,7 @@ export const EQUATIONS = [
     name: 'Propellant Mass Fraction',
     formula: 'ζ = mₚ / m₀',
     category: 'Rocket Equation',
+    description: 'Fraction of total mass that is propellant. Higher values indicate more efficient rocket design.',
     variables: ['zeta', 'mp', 'm0'],
     solvers: {
       zeta: v => v.mp / v.m0,
@@ -209,6 +222,7 @@ export const EQUATIONS = [
     name: 'Burn Time',
     formula: 'tᵦ = mₚ / ṁ',
     category: 'Rocket Equation',
+    description: 'Duration of main engine burn. Calculated from total propellant mass and mass flow rate.',
     variables: ['tb', 'mp', 'mdot'],
     solvers: {
       tb:   v => v.mp / v.mdot,
@@ -223,6 +237,7 @@ export const EQUATIONS = [
     name: 'Isentropic Temperature Ratio',
     formula: 'T/T₀ = (1 + (γ−1)/2·M²)⁻¹',
     category: 'Isentropic Flow',
+    description: 'Static to stagnation temperature ratio for isentropic flow. Key relation for compressible flow analysis.',
     variables: ['T', 'T0', 'M', 'gamma'],
     solvers: {
       T:     v => v.T0 / (1 + (v.gamma - 1) / 2 * v.M * v.M),
@@ -241,6 +256,7 @@ export const EQUATIONS = [
     name: 'Isentropic Pressure Ratio',
     formula: 'p/p₀ = (1 + (γ−1)/2·M²)^(−γ/(γ−1))',
     category: 'Isentropic Flow',
+    description: 'Static to stagnation pressure ratio for isentropic flow. Essential for nozzle and intake analysis.',
     variables: ['p_static', 'p0', 'M', 'gamma'],
     solvers: {
       p_static: v => {
@@ -265,6 +281,7 @@ export const EQUATIONS = [
     name: 'Isentropic Density Ratio',
     formula: 'ρ/ρ₀ = (1 + (γ−1)/2·M²)^(−1/(γ−1))',
     category: 'Isentropic Flow',
+    description: 'Static to stagnation density ratio for isentropic flow. Used in continuity equations and flow analysis.',
     variables: ['rho', 'rho0', 'M', 'gamma'],
     solvers: {
       rho: v => {
@@ -287,6 +304,7 @@ export const EQUATIONS = [
     name: 'Speed of Sound',
     formula: 'a = √(γ·R·T)',
     category: 'Isentropic Flow',
+    description: 'Local speed of sound as a function of temperature and gas properties. Used to define Mach number.',
     variables: ['a_sound', 'gamma', 'R', 'T'],
     solvers: {
       a_sound: v => Math.sqrt(v.gamma * v.R * v.T),
@@ -301,6 +319,7 @@ export const EQUATIONS = [
     name: 'Flow Velocity',
     formula: 'v = M·a',
     category: 'Isentropic Flow',
+    description: 'Flow velocity as Mach number times local speed of sound. Relates Mach number to actual velocity.',
     variables: ['v_flow', 'M', 'a_sound'],
     solvers: {
       v_flow:  v => v.M * v.a_sound,
@@ -315,6 +334,7 @@ export const EQUATIONS = [
     name: 'Nozzle Expansion Ratio',
     formula: 'ε = Aₑ / Aₜ',
     category: 'Nozzle Geometry',
+    description: 'Ratio of exit area to throat area. Determines the degree of expansion in the nozzle divergent section.',
     variables: ['eps', 'Ae', 'At'],
     solvers: {
       eps: v => v.Ae / v.At,
@@ -328,6 +348,7 @@ export const EQUATIONS = [
     name: 'Isentropic Area Ratio (supersonic)',
     formula: 'ε = (1/Mₑ)·[(2/(γ+1))·(1+(γ−1)/2·Mₑ²)]^((γ+1)/(2(γ−1)))',
     category: 'Nozzle Geometry',
+    description: 'Relates exit area ratio to exit Mach number for isentropic supersonic flow. Critical for nozzle design.',
     variables: ['eps', 'Me', 'gamma'],
     solvers: {
       eps: v => areaRatioFromMach(v.Me, v.gamma),
@@ -340,6 +361,7 @@ export const EQUATIONS = [
     name: 'Choked Throat Mass Flow',
     formula: 'ṁ = Aₜ·p₀·√(γ/(R·T₀))·(2/(γ+1))^((γ+1)/(2(γ−1)))',
     category: 'Nozzle Geometry',
+    description: 'Mass flow through a choked throat condition. Maximum mass flow for given stagnation conditions.',
     variables: ['mdot', 'At', 'p0', 'gamma', 'R', 'T0'],
     solvers: {
       mdot: v => {
@@ -380,6 +402,7 @@ export const EQUATIONS = [
     name: 'Nozzle Exit Pressure',
     formula: 'pₑ = p₀·(1 + (γ−1)/2·Mₑ²)^(−γ/(γ−1))',
     category: 'Nozzle Geometry',
+    description: 'Static pressure at the nozzle exit. Calculated from chamber pressure and exit Mach number.',
     variables: ['pe', 'p0', 'Me', 'gamma'],
     solvers: {
       pe: v => {
@@ -402,6 +425,7 @@ export const EQUATIONS = [
     name: 'Nozzle Exit Temperature',
     formula: 'Tₑ = T₀ / (1 + (γ−1)/2·Mₑ²)',
     category: 'Nozzle Geometry',
+    description: 'Static temperature at the nozzle exit. Lower than stagnation temperature due to expansion.',
     variables: ['Te', 'T0', 'Me', 'gamma'],
     solvers: {
       Te:    v => v.T0 / (1 + (v.gamma - 1) / 2 * v.Me * v.Me),
@@ -416,6 +440,7 @@ export const EQUATIONS = [
     name: 'Nozzle Exit Velocity',
     formula: 'Vₑ = Mₑ·√(γ·R·Tₑ)',
     category: 'Nozzle Geometry',
+    description: 'Actual exhaust velocity at nozzle exit. Product of exit Mach number and local speed of sound.',
     variables: ['Ve', 'Me', 'gamma', 'R', 'Te'],
     solvers: {
       Ve:    v => v.Me * Math.sqrt(v.gamma * v.R * v.Te),
@@ -432,6 +457,7 @@ export const EQUATIONS = [
     name: 'Thrust-to-Weight Ratio',
     formula: 'TWR = F / (mᵥ·g₀)',
     category: 'Performance',
+    description: 'Ratio of thrust to vehicle weight. Values > 1 allow acceleration and ascent.',
     variables: ['TWR', 'F', 'm_vehicle', 'g0'],
     solvers: {
       TWR:       v => v.F / (v.m_vehicle * v.g0),
@@ -446,6 +472,7 @@ export const EQUATIONS = [
     name: 'Total Impulse',
     formula: 'J = F·tᵦ',
     category: 'Performance',
+    description: 'Total impulse as integrated thrust over burn time. Used for classification and performance assessment.',
     variables: ['J', 'F', 'tb'],
     solvers: {
       J:  v => v.F * v.tb,
@@ -459,6 +486,7 @@ export const EQUATIONS = [
     name: 'Isp from Total Impulse',
     formula: 'Isp = J / (mₚ·g₀)',
     category: 'Performance',
+    description: 'Calculates specific impulse from total impulse and propellant mass. Alternative method for performance analysis.',
     variables: ['Isp', 'J', 'mp', 'g0'],
     solvers: {
       Isp: v => v.J / (v.mp * v.g0),
@@ -474,6 +502,7 @@ export const EQUATIONS = [
     name: 'Oxidiser/Fuel Ratio',
     formula: 'O/F = ṁₒₓ / ṁf',
     category: 'Propellant',
+    description: 'Mass flow ratio of oxidiser to fuel. Optimum value depends on propellant pair and design parameters.',
     variables: ['OF', 'mdot_ox', 'mdot_f'],
     solvers: {
       OF:      v => v.mdot_ox / v.mdot_f,
@@ -487,6 +516,7 @@ export const EQUATIONS = [
     name: 'Total Mass Flow',
     formula: 'ṁ = ṁₒₓ + ṁf',
     category: 'Propellant',
+    description: 'Total propellant mass flow is sum of oxidiser and fuel mass flows. Used in bipropellant engines.',
     variables: ['mdot', 'mdot_ox', 'mdot_f'],
     solvers: {
       mdot:    v => v.mdot_ox + v.mdot_f,
@@ -500,12 +530,70 @@ export const EQUATIONS = [
     name: 'Mass Flow Split from O/F',
     formula: 'ṁ_f = ṁ/(1+OF),  ṁ_ox = ṁ·OF/(1+OF)',
     category: 'Propellant',
+    description: 'Splits total mass flow into oxidiser and fuel flows given their mass ratio. Used for injection design.',
     variables: ['mdot', 'OF', 'mdot_f', 'mdot_ox'],
     solvers: {
       mdot_f:  Object.assign(v => v.mdot / (1 + v.OF),        { requires: () => ['mdot', 'OF'] }),
       mdot_ox: Object.assign(v => v.mdot * v.OF / (1 + v.OF), { requires: () => ['mdot', 'OF'] }),
     },
   },
+
+  // ── Chamber Characteristic Length ──────────────────────────────────────
+  {
+    id: 'chamber_characteristic_length',
+    name: 'Chamber Characteristic Length',
+    formula: 'L* = Vᶜ / Aₜ',
+    category: 'Nozzle Performance',
+    description: 'Characteristic chamber length relates chamber volume to throat area. Typical range 0.5–1.5 m for liquid rockets.',
+    variables: ['Lstar', 'Vc', 'At'],
+    solvers: {
+      Lstar: v => v.Vc / v.At,
+      Vc:    v => v.Lstar * v.At,
+      At:    v => v.Vc / v.Lstar,
+    },
+  },
+
+  // ── Specific Gas Constant from Molar Mass ─────────────────────────────
+  {
+    id: 'specific_gas_constant',
+    name: 'Specific Gas Constant',
+    formula: 'R = R̄ / Mₘ',
+    category: 'Isentropic Flow',
+    description: 'Specific gas constant for a particular gas, derived from the universal gas constant and molar mass. R̄ = 8.314 J/(mol·K).',
+    variables: ['R', 'Mm'],
+    solvers: {
+      R:  v => 8.314 / v.Mm,
+      Mm: v => 8.314 / v.R,
+    },
+  },
+
+  // ── Vehicle Mass Identity ─────────────────────────────────────────────
+  {
+    id: 'vehicle_mass_identity',
+    name: 'Vehicle Mass (Wet Mass)',
+    formula: 'mᵥ = m₀',
+    category: 'Performance',
+    description: 'Identity relation: vehicle mass equals initial (wet) mass for TWR calculation.',
+    variables: ['m_vehicle', 'm0'],
+    solvers: {
+      m_vehicle: v => v.m0,
+      m0:        v => v.m_vehicle,
+    },
+  },
+
+  // ── Subsonic Area Ratio ───────────────────────────────────────────────
+  {
+    id: 'area_ratio_mach_subsonic',
+    name: 'Isentropic Area Ratio (subsonic)',
+    formula: 'ε = (1/Mₑ)·[(2/(γ+1))·(1+(γ−1)/2·Mₑ²)]^((γ+1)/(2(γ−1)))',
+    category: 'Nozzle Geometry',
+    description: 'Isentropic area ratio as a function of Mach number (subsonic branch). Used for intake and subsonic flow analysis.',
+    variables: ['eps', 'Me', 'gamma'],
+    solvers: {
+      eps: v => areaRatioFromMach(v.Me, v.gamma),
+      Me:  v => machFromAreaRatio(v.eps, v.gamma, false),
+    },
+  },
 ]
 
 // Equation presets: named groups that seed the workspace with a useful set of variables

src/engine/units.js

@@ -115,6 +115,12 @@ export const UNIT_FAMILIES = {
       { id: '—', label: '—', toSI: v => v, fromSI: v => v },
     ],
   },
+  molar_mass: {
+    units: [
+      { id: 'g/mol',  label: 'g/mol',  toSI: v => v * 0.001, fromSI: v => v * 1000 },
+      { id: 'kg/mol', label: 'kg/mol', toSI: v => v,         fromSI: v => v },
+    ],
+  },
 }
 
 export function getUnitsForFamily(familyId) {

src/engine/variables.js

@@ -92,6 +92,20 @@ export const VARIABLES = {
     unitFamily: 'area',
   },
 
+  Lstar: {
+    id: 'Lstar', symbol: 'L*', name: 'Characteristic Chamber Length', units: 'm',
+    description: 'Characteristic length of the combustion chamber: L* = Vᶜ/Aₜ. Higher values indicate larger chambers.',
+    category: 'Nozzle Performance',
+    unitFamily: 'length',
+  },
+
+  Vc: {
+    id: 'Vc', symbol: 'Vᶜ', name: 'Chamber Volume', units: 'm³',
+    description: 'Total volume of the combustion chamber',
+    category: 'Nozzle Performance',
+    unitFamily: 'volume',
+  },
+
   // ── Tsiolkovsky Rocket Equation ───────────────────────────────────────
   dv: {
     id: 'dv', symbol: 'Δv', name: 'Delta-v', units: 'm/s',
@@ -155,6 +169,13 @@ export const VARIABLES = {
     category: 'Isentropic Flow',
     unitFamily: 'spec_gas',
   },
+
+  Mm: {
+    id: 'Mm', symbol: 'Mₘ', name: 'Molar Mass', units: 'kg/mol',
+    description: 'Molar mass of the exhaust gas mixture. Used to calculate specific gas constant: R = R̄/Mₘ',
+    category: 'Isentropic Flow',
+    unitFamily: 'molar_mass',
+  },
   T: {
     id: 'T', symbol: 'T', name: 'Static Temperature', units: 'K',
     description: 'Local static temperature at a cross-section',

src/hooks/useEngineDesign.js

@@ -19,7 +19,7 @@ export function useEngineDesign() {
   const [chamber, setChamber]       = useState({ Lstar: 1.0, contractionRatio: 8, convAngleDeg: 30 })
   const [nozzle, setNozzle]         = useState({ type: 'conical', divAngleDeg: 15 })
   const [injector, setInjector]     = useState({ type: 'doublet', N: 20, dpFraction: 0.2, Cd: 0.7, rhoFuel: 800, rhoOx: 1140 })
-  const [cooling, setCooling]       = useState({ method: 'regenerative', channelCount: 40, filmFraction: 0.05 })
+  const [cooling, setCooling]       = useState({ method: 'regenerative', channelCount: 60, mu: 6e-5, cp: 2000, Pr: 0.7, T_wall: 800, filmFraction: 0.05 })
   const [feedSystem, setFeedSystem] = useState({
     type: 'pressure_fed', feedFactor: 1.3,
     rhoFuel: 800, rhoOx: 1140, pressurantR: 2077, pressurantT: 300,

src/pages/EnginePage.jsx

@@ -9,6 +9,7 @@ import {
 } from '../engine/engineExportImport.js'
 import DesignSection from '../components/engine/DesignSection.jsx'
 import EngineModel3D from '../components/engine/EngineModel3D.jsx'
+import ErrorBoundary from '../components/ErrorBoundary.jsx'
 import { formatValue } from '../engine/format.js'
 import { getUnitsForFamily } from '../engine/units.js'
 import { ENGINE_FIELD_INFO } from '../engine/engineFieldInfo.js'
@@ -524,6 +525,7 @@ export default function EnginePage() {
               infoKey="coolingMethod"
             />
             {cooling.method === 'regenerative' && (
+              <>
                 <NumInput
                   label="Channel Count"
                   value={cooling.channelCount}
@@ -531,6 +533,40 @@ export default function EnginePage() {
                   infoKey="channelCount"
                   step="1"
                 />
+                <NumInput
+                  label="Dynamic Viscosity (μ)"
+                  value={cooling.mu}
+                  onChange={v => setCooling(c => ({ ...c, mu: v }))}
+                  units="Pa·s"
+                  step="1e-5"
+                  placeholder="6e-5"
+                />
+                <NumInput
+                  label="Specific Heat (cₚ)"
+                  value={cooling.cp}
+                  onChange={v => setCooling(c => ({ ...c, cp: v }))}
+                  units="J/(kg·K)"
+                  step="100"
+                  placeholder="2000"
+                />
+                <NumInput
+                  label="Prandtl Number (Pr)"
+                  value={cooling.Pr}
+                  onChange={v => setCooling(c => ({ ...c, Pr: v }))}
+                  units="—"
+                  step="0.05"
+                  placeholder="0.7"
+                />
+                <NumInput
+                  label="Wall Temperature (T_wall)"
+                  value={cooling.T_wall}
+                  onChange={v => setCooling(c => ({ ...c, T_wall: v }))}
+                  unitFamily="temperature"
+                  defaultUnitId="K"
+                  step="50"
+                  placeholder="800"
+                />
+              </>
             )}
             {cooling.method === 'film' && (
               <NumInput
@@ -593,7 +629,9 @@ export default function EnginePage() {
 
         {/* ── Centre: 3D Model ── */}
         <div className="flex-1 relative border-r border-slate-700 bg-slate-950/50">
+          <ErrorBoundary>
             <EngineModel3D chamberGeometry={cg} nozzleGeometry={ng} />
+          </ErrorBoundary>
         </div>
 
         {/* ── Right: Results ── */}
@@ -647,7 +685,7 @@ export default function EnginePage() {
                     <ResultRow label="Est. Heat Flux"      value={cr.q_est}        unit="W/m²" infoKey="q_est_result"        />
                     <ResultRow label="Total Heat Load"     value={cr.q_total}      unit="W"    infoKey="q_total_result"      />
                     <ResultRow label="Channel Count"       value={cr.channelCount} unit="—"    infoKey="channelCount_result" />
-                    <ResultRow label="Channel Area (each)" value={cr.channelArea}  unitFamily="area" defaultUnitId="mm²" infoKey="channelArea_result" />
+                    <ResultRow label="Heat load / channel" value={cr.q_perChannel}  unit="W" infoKey="q_perChannel_result" />
                   </>
                 )}
                 {cr.method === 'film' && (

src/pages/Home.jsx

@@ -23,9 +23,12 @@ export default function Home() {
             <h2 className="text-xl font-semibold text-white mb-2 group-hover:text-blue-400 transition-colors">
               Equation Solver
             </h2>
-            <p className="text-sm text-slate-400">
+            <p className="text-sm text-slate-400 mb-3">
               Drag-and-drop rocketry variables. Enter known values and unknowns solve automatically using constraint propagation.
             </p>
+            <p className="text-xs text-slate-500 mb-3">
+              Includes: thrust, Isp, c*, thrust coefficient, Tsiolkovsky, mass/burn-time, isentropic flow, nozzle geometry, exit conditions, TWR, total impulse, O/F ratio
+            </p>
             <div className="mt-4 text-sm text-blue-400 font-medium">Open solver →</div>
           </Link>
 
@@ -43,14 +46,33 @@ export default function Home() {
             <div className="mt-4 text-sm text-blue-400 font-medium">Open designer →</div>
           </Link>
 
-          <div className="p-6 rounded-xl border border-slate-800 bg-slate-900/50 opacity-60 cursor-not-allowed">
-            <div className="text-3xl mb-3">📊</div>
-            <h2 className="text-xl font-semibold text-slate-500 mb-2">Trajectory Plotter</h2>
-            <p className="text-sm text-slate-500">
-              Simulate flight trajectories with drag and gravity losses.
+          <Link
+            to="/design/rocket"
+            className="group block p-6 rounded-xl border border-slate-700 bg-slate-900 hover:border-blue-500 hover:bg-slate-800 transition-colors"
+          >
+            <div className="text-3xl mb-3">🛸</div>
+            <h2 className="text-xl font-semibold text-white mb-2 group-hover:text-blue-400 transition-colors">
+              Rocket Designer
+            </h2>
+            <p className="text-sm text-slate-400">
+              Design and configure multi-stage rockets. Visualize your design in 3D with mass budget and delta-v calculations.
             </p>
-            <div className="mt-4 text-sm text-slate-600 font-medium">Coming soon</div>
-          </div>
+            <div className="mt-4 text-sm text-blue-400 font-medium">Open designer →</div>
+          </Link>
+
+          <Link
+            to="/knowledgebase/fuels"
+            className="group block p-6 rounded-xl border border-slate-700 bg-slate-900 hover:border-blue-500 hover:bg-slate-800 transition-colors"
+          >
+            <div className="text-3xl mb-3">📚</div>
+            <h2 className="text-xl font-semibold text-white mb-2 group-hover:text-blue-400 transition-colors">
+              Fuels & Oxidisers
+            </h2>
+            <p className="text-sm text-slate-400">
+              Browse a comprehensive database of rocket propellants with chemical properties, performance data, and specifications.
+            </p>
+            <div className="mt-4 text-sm text-blue-400 font-medium">View database →</div>
+          </Link>
         </div>
       </div>
     </div>

src/pages/KnowledgebaseEquationsPage.jsx

@@ -0,0 +1,225 @@
+import { useState, useMemo, useRef } from 'react'
+import React from 'react'
+import { EQUATIONS } from '../engine/equations.js'
+import { VARIABLES } from '../engine/variables.js'
+
+export default function KnowledgebaseEquationsPage() {
+  const [search, setSearch] = useState('')
+  const [categoryFilter, setCategoryFilter] = useState('All')
+  const [activeVariableFilter, setActiveVariableFilter] = useState([])
+  const equationRefs = useRef({})
+
+  // Get all unique categories
+  const categories = ['All', ...new Set(EQUATIONS.map(eq => eq.category))]
+
+  // Apply all three filters
+  const filteredEquations = useMemo(() => {
+    const q = search.toLowerCase().trim()
+
+    return EQUATIONS.filter(eq => {
+      // Category filter
+      if (categoryFilter !== 'All' && eq.category !== categoryFilter) return false
+
+      // Text search
+      if (q) {
+        const nameMatch = eq.name.toLowerCase().includes(q)
+        const formulaMatch = eq.formula.toLowerCase().includes(q)
+        const descMatch = eq.description.toLowerCase().includes(q)
+        const varMatch = eq.variables.some(varId => {
+          const v = VARIABLES[varId]
+          return v?.name.toLowerCase().includes(q) || v?.symbol?.toLowerCase().includes(q)
+        })
+        if (!nameMatch && !formulaMatch && !descMatch && !varMatch) return false
+      }
+
+      // Variable filter — equation must have ALL active variables
+      if (activeVariableFilter.length > 0) {
+        const hasAllVars = activeVariableFilter.every(varId => eq.variables.includes(varId))
+        if (!hasAllVars) return false
+      }
+
+      return true
+    })
+  }, [search, categoryFilter, activeVariableFilter])
+
+  // Toggle variable in active filter
+  const toggleVariableFilter = (varId) => {
+    setActiveVariableFilter(prev =>
+      prev.includes(varId)
+        ? prev.filter(v => v !== varId)
+        : [...prev, varId]
+    )
+  }
+
+  // Remove variable from filter
+  const removeVariableFilter = (varId) => {
+    setActiveVariableFilter(prev => prev.filter(v => v !== varId))
+  }
+
+  // Scroll to equation
+  const scrollToEquation = (eqId) => {
+    equationRefs.current[eqId]?.scrollIntoView({ behavior: 'smooth', block: 'start' })
+  }
+
+  return (
+    <div className="flex flex-1 overflow-hidden">
+      {/* ── Left panel ────────────────────────────────────────────────────── */}
+      <div className="w-72 shrink-0 flex flex-col border-r border-slate-700 bg-slate-900">
+        {/* Search */}
+        <div className="p-3 border-b border-slate-700">
+          <input
+            type="text"
+            placeholder="Search equations…"
+            value={search}
+            onChange={e => setSearch(e.target.value)}
+            className="w-full px-3 py-1.5 rounded-md bg-slate-800 border border-slate-600 text-sm text-slate-100 placeholder-slate-500 focus:outline-none focus:border-blue-500"
+          />
+        </div>
+
+        {/* Category filter pills */}
+        <div className="px-3 pt-2 pb-2 border-b border-slate-700 flex flex-wrap gap-1">
+          {categories.map(cat => (
+            <button
+              key={cat}
+              onClick={() => setCategoryFilter(cat)}
+              className={`px-2 py-0.5 rounded text-xs font-medium transition-colors ${
+                categoryFilter === cat
+                  ? 'bg-blue-600 text-white'
+                  : 'bg-slate-700 text-slate-300 hover:bg-slate-600'
+              }`}
+            >
+              {cat}
+            </button>
+          ))}
+        </div>
+
+        {/* Equation list */}
+        <div className="flex-1 overflow-y-auto">
+          {filteredEquations.length === 0 && (
+            <p className="px-4 py-6 text-sm text-slate-500 text-center">No equations match your filters.</p>
+          )}
+          {filteredEquations.map(eq => (
+            <button
+              key={eq.id}
+              onClick={() => scrollToEquation(eq.id)}
+              className="w-full text-left px-3 py-2 border-b border-slate-800 text-sm hover:bg-slate-800 transition-colors"
+            >
+              <div className="font-medium text-slate-100 truncate">{eq.name}</div>
+              <div className="text-xs text-slate-500 mt-0.5 truncate">{eq.category}</div>
+            </button>
+          ))}
+        </div>
+      </div>
+
+      {/* ── Right panel ───────────────────────────────────────────────────── */}
+      <div className="flex-1 flex flex-col overflow-hidden bg-slate-950">
+        {/* Active variable filter strip */}
+        {activeVariableFilter.length > 0 && (
+          <div className="px-4 py-3 border-b border-slate-700 bg-slate-900/50 flex items-center gap-3 flex-wrap">
+            <span className="text-xs text-slate-400">Active filters:</span>
+            {activeVariableFilter.map(varId => {
+              const v = VARIABLES[varId]
+              return (
+                <div
+                  key={varId}
+                  className="inline-flex items-center gap-1.5 px-2.5 py-1 rounded-full bg-blue-900/30 border border-blue-700/50 text-xs text-blue-200"
+                >
+                  <span>{v?.symbol} · {v?.name}</span>
+                  <button
+                    onClick={() => removeVariableFilter(varId)}
+                    className="ml-1 text-blue-400 hover:text-blue-200 transition-colors text-sm leading-none"
+                  >
+                    ×
+                  </button>
+                </div>
+              )
+            })}
+            <button
+              onClick={() => setActiveVariableFilter([])}
+              className="text-xs text-slate-400 hover:text-slate-200 transition-colors ml-auto px-2 py-1 rounded hover:bg-slate-800"
+            >
+              Clear filters
+            </button>
+          </div>
+        )}
+
+        {/* Equations grid */}
+        <div className="flex-1 overflow-y-auto p-4">
+          <div className="space-y-4 max-w-5xl">
+            {filteredEquations.length === 0 ? (
+              <div className="text-center text-slate-500 py-12 text-sm">
+                No equations match your filters.
+              </div>
+            ) : (
+              filteredEquations.map(eq => (
+                <EquationCard
+                  key={eq.id}
+                  eq={eq}
+                  activeVariableFilter={activeVariableFilter}
+                  onToggleVariable={toggleVariableFilter}
+                  ref={el => equationRefs.current[eq.id] = el}
+                />
+              ))
+            )}
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+const EquationCard = React.forwardRef(function EquationCard({ eq, activeVariableFilter, onToggleVariable }, ref) {
+  return (
+    <div ref={ref} className="rounded-xl border border-slate-700 bg-slate-900 overflow-hidden">
+      {/* Card header */}
+      <div className="px-4 pt-3 pb-2 flex items-start justify-between">
+        <div className="flex-1 min-w-0">
+          <div className="flex items-center gap-2 mb-1">
+            <span className="font-semibold text-slate-100 text-sm">{eq.name}</span>
+            <span className="text-[10px] font-medium text-slate-400 bg-slate-800 border border-slate-700 px-1.5 py-0.5 rounded">
+              {eq.category}
+            </span>
+          </div>
+        </div>
+      </div>
+
+      {/* Formula */}
+      <div className="mx-4 mb-3 rounded-lg bg-slate-950 border border-slate-700 px-4 py-2.5">
+        <div className="font-mono text-sm text-amber-300 text-center leading-relaxed">
+          {eq.formula}
+        </div>
+      </div>
+
+      {/* Description */}
+      <div className="px-4 mb-3">
+        <p className="text-slate-300 text-sm">{eq.description}</p>
+      </div>
+
+      {/* Variable chips */}
+      <div className="px-4 pb-3">
+        <div className="flex flex-wrap gap-2">
+          {eq.variables.map(varId => {
+            const v = VARIABLES[varId]
+            const isActive = activeVariableFilter.includes(varId)
+            return (
+              <button
+                key={varId}
+                onClick={() => onToggleVariable(varId)}
+                className={`px-2.5 py-1.5 rounded-lg text-xs font-medium transition-colors border ${
+                  isActive
+                    ? 'bg-blue-900/50 border-blue-600 text-blue-100'
+                    : 'bg-slate-800 border-slate-600 text-slate-300 hover:border-blue-500 hover:text-slate-100'
+                }`}
+              >
+                <span className="font-mono font-bold">{v?.symbol}</span>
+                {' · '}
+                <span>{v?.name}</span>
+                {v?.units && <span className="text-slate-500"> ({v.units})</span>}
+              </button>
+            )
+          })}
+        </div>
+      </div>
+    </div>
+  )
+})

src/pages/RocketPage.jsx

@@ -3,18 +3,30 @@ import { PropellantModal } from '../components/PropellantModal.jsx'
 import { useRocketDesign } from '../hooks/useRocketDesign.js'
 import DesignSection from '../components/engine/DesignSection.jsx'
 import RocketModel3D from '../components/rocket/RocketModel3D.jsx'
+import ErrorBoundary from '../components/ErrorBoundary.jsx'
 import { formatValue } from '../engine/format.js'
+import { getUnitsForFamily } from '../engine/units.js'
 import { exportRocketJSON, parseRocketImport, downloadBlob } from '../engine/rocketExportImport.js'
 
 /* ── Tiny input / result primitives (self-contained, no unit dropdown) ── */
 
-function NumInput({ label, value, onChange, units, step, placeholder }) {
-  const display = value == null ? '' : value
+function NumInput({ label, value, onChange, units, step, placeholder, unitFamily, defaultUnitId }) {
+  const unitList = unitFamily ? getUnitsForFamily(unitFamily) : null
+  const [selectedUnitId, setSelectedUnitId] = useState(
+    () => defaultUnitId ?? unitList?.[0]?.id ?? null,
+  )
+
+  const selectedUnit = unitList?.find(u => u.id === selectedUnitId) ?? unitList?.[0] ?? null
+
+  const displayValue = value == null
+    ? ''
+    : selectedUnit ? selectedUnit.fromSI(value) : value
 
   function handleChange(str) {
     if (str === '') { onChange(null); return }
-    const n = parseFloat(str)
-    if (!isNaN(n)) onChange(n)
+    const typed = parseFloat(str)
+    if (isNaN(typed)) return
+    onChange(selectedUnit ? selectedUnit.toSI(typed) : typed)
   }
 
   return (
@@ -22,14 +34,27 @@ function NumInput({ label, value, onChange, units, step, placeholder }) {
       <label className="text-xs text-slate-400 w-44 shrink-0">{label}</label>
       <input
         type="number"
-        value={display}
+        value={displayValue}
         step={step ?? 'any'}
         placeholder={placeholder ?? ''}
         onChange={e => handleChange(e.target.value)}
         className="flex-1 min-w-0 w-24 px-2 py-1 bg-slate-800 border border-slate-600 rounded text-sm text-slate-100
                    focus:border-blue-500 focus:outline-none placeholder-slate-600"
       />
-      {units && <span className="text-xs text-slate-500 shrink-0 whitespace-nowrap">{units}</span>}
+      {unitList && unitList.length > 1 ? (
+        <select
+          value={selectedUnit?.id ?? ''}
+          onChange={e => setSelectedUnitId(e.target.value)}
+          className="px-1 py-0.5 bg-slate-700 border border-slate-600 rounded text-xs text-slate-300
+                     focus:outline-none cursor-pointer shrink-0"
+        >
+          {unitList.map(u => <option key={u.id} value={u.id}>{u.label}</option>)}
+        </select>
+      ) : unitList?.[0] ? (
+        <span className="text-xs text-slate-500 shrink-0">{unitList[0].label}</span>
+      ) : units ? (
+        <span className="text-xs text-slate-500 shrink-0 whitespace-nowrap">{units}</span>
+      ) : null}
     </div>
   )
 }
@@ -235,10 +260,11 @@ export default function RocketPage() {
           <DesignSection title="Vehicle Geometry">
             <NumInput
               label="Outer Diameter"
-              value={displayRadius != null ? parseFloat((displayRadius * 2000).toPrecision(6)) : null}
-              onChange={v => setOuterRadius(v != null ? v / 2000 : null)}
-              units="mm"
-              step="10"
+              value={displayRadius != null ? displayRadius * 2 : null}
+              onChange={v => setOuterRadius(v != null ? v / 2 : null)}
+              unitFamily="length"
+              defaultUnitId="mm"
+              step="0.01"
               placeholder={suggestedRadius ? `${(suggestedRadius * 2000).toFixed(0)}` : 'e.g. 300'}
             />
             {suggestedRadius && !outerRadius && (
@@ -292,7 +318,8 @@ export default function RocketPage() {
               label="Fuel Density (ρ_f)"
               value={propDensities.rhoFuel}
               onChange={v => setPropDensities(p => ({ ...p, rhoFuel: v ?? 800 }))}
-              units="kg/m³"
+              unitFamily="density"
+              defaultUnitId="kg/m³"
               step="10"
               placeholder="800"
             />
@@ -300,7 +327,8 @@ export default function RocketPage() {
               label="Oxidizer Density (ρ_ox)"
               value={propDensities.rhoOx}
               onChange={v => setPropDensities(p => ({ ...p, rhoOx: v ?? 1140 }))}
-              units="kg/m³"
+              unitFamily="density"
+              defaultUnitId="kg/m³"
               step="10"
               placeholder="1140"
             />
@@ -308,8 +336,9 @@ export default function RocketPage() {
               label="Burn Time"
               value={structure.burnTime}
               onChange={v => setStructure(s => ({ ...s, burnTime: v }))}
-              units="s"
-              step="1"
+              unitFamily="time"
+              defaultUnitId="s"
+              step="0.1"
               placeholder={engineData?.inputs?.burnTime ?? '30'}
             />
             {effectiveBurnTime != null && !structure.burnTime && (
@@ -324,16 +353,18 @@ export default function RocketPage() {
               label="Payload Mass"
               value={payload.mass}
               onChange={v => setPayload(p => ({ ...p, mass: v ?? 0 }))}
-              units="kg"
+              unitFamily="mass"
+              defaultUnitId="kg"
               step="1"
               placeholder="0"
             />
             <NumInput
               label="Payload Bay Length"
-              value={payload.bayLength != null ? parseFloat((payload.bayLength * 1000).toPrecision(6)) : null}
-              onChange={v => setPayload(p => ({ ...p, bayLength: v != null ? v / 1000 : 0 }))}
-              units="mm"
-              step="10"
+              value={payload.bayLength}
+              onChange={v => setPayload(p => ({ ...p, bayLength: v ?? 0 }))}
+              unitFamily="length"
+              defaultUnitId="mm"
+              step="0.001"
               placeholder="0"
             />
           </DesignSection>
@@ -352,7 +383,9 @@ export default function RocketPage() {
 
         {/* ── Centre: 3D Model ── */}
         <div className="flex-1 relative border-r border-slate-700 bg-slate-950/50">
+          <ErrorBoundary>
             <RocketModel3D geometry={geometry} />
+          </ErrorBoundary>
 
           {/* Requirements checklist — shown when model can't render */}
           {!geometry && engineData && (