diff --git a/src/layers/satellites/catalog.js b/src/layers/satellites/catalog.js
index 25eaf9b2c..fd136c82d 100644
--- a/src/layers/satellites/catalog.js
+++ b/src/layers/satellites/catalog.js
@@ -1,5 +1,6 @@
 import * as Cesium from 'cesium';
 import { twoline2satrec } from 'satellite.js';
+import { noradIdFromSatnum } from '../../sources/tle.js';
 import {
   DENSE_REFRESH_FRAMES,
   DENSE_GROUP_PATH,
@@ -113,7 +114,7 @@ export function createCatalog({ state: layerState, services, parts, source }) {
           const entry = entries[i];
           const satrec = twoline2satrec(entry.line1, entry.line2);
           if (!satrec || satrec.error !== 0) continue;
-          const noradId = Number(satrec.satnum);
+          const noradId = noradIdFromSatnum(satrec.satnum);
           if (layerState._catalog.has(noradId)) continue; // core catalog keeps priority
           const pos = parts.orbits.propagatePosition(satrec, now);
           if (!pos) continue;
diff --git a/src/layers/satellites/ingestion.js b/src/layers/satellites/ingestion.js
index 7fb36bb00..14e464892 100644
--- a/src/layers/satellites/ingestion.js
+++ b/src/layers/satellites/ingestion.js
@@ -1,5 +1,6 @@
 import { twoline2satrec } from 'satellite.js';
 import * as Cesium from 'cesium';
+import { noradIdFromSatnum } from '../../sources/tle.js';
 import { CATALOG_GROUPS, ISS_NORAD, POINT_STYLES } from './policy.js';
 
 export function createIngestion({
@@ -108,7 +109,7 @@ export function createIngestion({
           const satrec = twoline2satrec(entry.line1, entry.line2);
           if (!satrec || satrec.error !== 0) continue;
 
-          const noradId = Number(satrec.satnum);
+          const noradId = noradIdFromSatnum(satrec.satnum);
           if (seen.has(noradId)) continue;
           seen.add(noradId);
 
diff --git a/src/layers/satellites/orbits.js b/src/layers/satellites/orbits.js
index 32bb57cf9..0e4461e85 100644
--- a/src/layers/satellites/orbits.js
+++ b/src/layers/satellites/orbits.js
@@ -8,7 +8,7 @@ import {
   twoline2satrec,
 } from 'satellite.js';
 import { findNextSatellitePass } from '../../data/satellitePass.js';
-import { parseTleText } from '../../sources/tle.js';
+import { noradIdFromSatnum, parseTleText } from '../../sources/tle.js';
 import { ORBIT_PATH_STEPS, ISS_NORAD } from './policy.js';
 
 export function createOrbits({ state: layerState, services, parts, source }) {
@@ -284,7 +284,7 @@ export function createOrbits({ state: layerState, services, parts, source }) {
     const current = propagatePosition(satrec, referenceDate);
     if (!current) return null;
     return {
-      noradId: Number(satrec.satnum),
+      noradId: noradIdFromSatnum(satrec.satnum),
       name: String(name || '').trim(),
       current,
       periodSec: orbitalPeriodSeconds(satrec),
diff --git a/src/sources/tle.js b/src/sources/tle.js
index ac7aedc2c..f5fad48bd 100644
--- a/src/sources/tle.js
+++ b/src/sources/tle.js
@@ -21,8 +21,50 @@ export function parseTleText(text) {
   return result;
 }
 
+/**
+ * The catalog number an Alpha-5 field stands for, or null for any other field.
+ *
+ * Since the catalog passed 99999 (July 2026) a TLE writes the numbers above it
+ * in Alpha-5: a letter A–Z, skipping I and O, stands for 10–33 in the
+ * ten-thousands place, so 100000 is "A0000" and 339999 is "Z9999".
+ */
+function alpha5CatalogNumber(field) {
+  const letter = field[0];
+  if (
+    letter >= 'A' &&
+    letter <= 'Z' &&
+    letter !== 'I' &&
+    letter !== 'O' &&
+    /^\d{4}$/.test(field.slice(1))
+  ) {
+    let tens = letter.charCodeAt(0) - 65 + 10;
+    if (letter > 'I') tens -= 1;
+    if (letter > 'O') tens -= 1;
+    return tens * 10000 + Number(field.slice(1));
+  }
+  return null;
+}
+
+/**
+ * NORAD catalog number of a satrec as a number.
+ *
+ * satellite.js keeps the TLE's five-character field verbatim in
+ * `satrec.satnum`, and `Number("A0000")` is NaN, so every Alpha-5 satellite
+ * would share one NaN key. An Alpha-5 field decodes to its number; a
+ * five-digit field is unchanged; anything else stays NaN.
+ * @param {string} satnum
+ * @returns {number}
+ */
+export function noradIdFromSatnum(satnum) {
+  const field = String(satnum ?? '').trim();
+  return alpha5CatalogNumber(field) ?? Number(field);
+}
+
 /** The NORAD catalog number from TLE line 1, or null. */
 export function tleCatalogNumber(line1) {
-  const number = Number.parseInt(String(line1).slice(2, 7), 10);
+  const field = String(line1).slice(2, 7);
+  const alpha5 = alpha5CatalogNumber(field);
+  if (alpha5 !== null) return alpha5;
+  const number = Number.parseInt(field, 10);
   return Number.isInteger(number) ? number : null;
 }
diff --git a/src/tools/queries/space.test.mjs b/src/tools/queries/space.test.mjs
index f6c2a8df8..5ff267ce1 100644
--- a/src/tools/queries/space.test.mjs
+++ b/src/tools/queries/space.test.mjs
@@ -1,7 +1,12 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
+import { twoline2satrec } from 'satellite.js';
 import { composeCatalog, coreTools } from '../index.js';
-import { parseTleText, tleCatalogNumber } from '../../sources/tle.js';
+import {
+  noradIdFromSatnum,
+  parseTleText,
+  tleCatalogNumber,
+} from '../../sources/tle.js';
 
 // Element sets published for 1 January 2024.
 const TLE = `ISS (ZARYA)
@@ -51,6 +56,51 @@ for (const missingLine of [1, 2]) {
   });
 }
 
+test('Alpha-5 catalog numbers decode, skipping I and O', () => {
+  for (const [field, id] of [
+    ['A0000', 100000],
+    ['A0404', 100404],
+    ['H9999', 179999],
+    ['J0000', 180000],
+    ['N9999', 229999],
+    ['P0000', 230000],
+    ['T0449', 270449],
+    ['Z9999', 339999],
+  ]) {
+    assert.equal(noradIdFromSatnum(field), id, field);
+    assert.equal(tleCatalogNumber(`1 ${field}U`), id, field);
+  }
+});
+
+test('every other catalog field reads as it did before', () => {
+  assert.equal(noradIdFromSatnum('25544'), 25544);
+  assert.equal(noradIdFromSatnum('00404'), 404);
+  assert.equal(noradIdFromSatnum(''), 0); // as Number('') did
+  for (const field of ['I0000', 'O0000', 'a0404', 'A00']) {
+    assert.ok(Number.isNaN(noradIdFromSatnum(field)), field);
+    assert.equal(tleCatalogNumber(`1 ${field}U`), null, field);
+  }
+});
+
+test('a satellite numbered above 99999 keeps its number and is found by it', async () => {
+  // The ISS set with its catalog field in Alpha-5: A0000 is 100000.
+  const text = TLE.replaceAll('25544', 'A0000');
+  const [iss] = parseTleText(text);
+  const { satnum } = twoline2satrec(iss.line1, iss.line2);
+  assert.ok(Number.isNaN(Number(satnum))); // what the catalog builders used
+  assert.equal(noradIdFromSatnum(satnum), 100000);
+  const catalog = composeCatalog({
+    tools: coreTools,
+    services: { satellites: satellites(text), clock: CLOCK },
+  });
+  const result = await catalog.call('next_satellite_pass', {
+    location: { lat: 40.7, lon: -74 },
+    satellite: '100000',
+  });
+  assert.equal(result.data.satellite, 'ISS (ZARYA)');
+  assert.equal(result.data.norad, 100000);
+});
+
 test('the next pass defaults to the ISS and reports times, peak and direction', async () => {
   const catalog = composeCatalog({
     tools: coreTools,