diff --git a/src/body/Earth.ts b/src/body/Earth.ts
index ff1ed43..4fa872f 100644
--- a/src/body/Earth.ts
+++ b/src/body/Earth.ts
@@ -90,8 +90,8 @@ export class Earth {
   );
 
   // / Calculate mean motion _(rad/s)_ from a given [semimajorAxis] _(km)_.
-  static smaToMeanMotion(semimajorAxis: number): number {
-    return Math.sqrt(Earth.mu / (semimajorAxis * semimajorAxis * semimajorAxis));
+  static smaToMeanMotion(semimajorAxis: Kilometers): RadiansPerSecond {
+    return Math.sqrt(Earth.mu / (semimajorAxis * semimajorAxis * semimajorAxis)) as RadiansPerSecond;
   }
 
   /**
diff --git a/src/objects/Satellite.ts b/src/objects/Satellite.ts
index 40e080e..f7664a1 100644
--- a/src/objects/Satellite.ts
+++ b/src/objects/Satellite.ts
@@ -46,6 +46,7 @@ import {
   Radians,
   RaeVec3,
   SatelliteRecord,
+  Seconds,
   TleLine1,
   TleLine2,
 } from '../types/types';
@@ -187,7 +188,7 @@ export class Satellite extends BaseObject {
   toRae(observer: GroundObject, date: Date = new Date()): RAE {
     const rae = this.rae(observer, date);
     const rae2 = this.rae(observer, new Date(date.getTime() + 1000));
-    const epoch = new EpochUTC(date.getTime());
+    const epoch = new EpochUTC(date.getTime() / 1000 as Seconds);
     const rangeRate = rae2.rng - rae.rng;
     const azimuthRate = rae2.az - rae.az;
     const elevationRate = rae2.el - rae.el;
@@ -257,7 +258,7 @@ export class Satellite extends BaseObject {
       const p = pv.position as EciVec3;
       const v = pv.velocity as EciVec3<KilometersPerSecond>;
 
-      const epoch = new EpochUTC(date.getTime());
+      const epoch = new EpochUTC(date.getTime() / 1000 as Seconds);
       const pos = new Vector3D(p.x, p.y, p.z);
       const vel = new Vector3D(v.x, v.y, v.z);
 
diff --git a/src/time/Epoch.ts b/src/time/Epoch.ts
index d07b293..8245eee 100644
--- a/src/time/Epoch.ts
+++ b/src/time/Epoch.ts
@@ -21,7 +21,7 @@
  * SOFTWARE.
  */
 
-import { Seconds } from 'src/main';
+import { Seconds } from '../main';
 import { secondsPerDay } from '../utils/constants';
 
 // / Base class for [Epoch] data.
@@ -30,7 +30,7 @@ export class Epoch {
    * Create a new [Epoch] object given the number of seconds elapsed since the
    * [posix] epoch _(`1970-01-01T00:00:00.000`)_ in the [Epoch] time scale.
    */
-  constructor(public posix: number) {
+  constructor(public posix: Seconds) {
     if (posix < 0) {
       throw new Error('Epoch cannot be negative');
     }
diff --git a/src/time/EpochUTC.ts b/src/time/EpochUTC.ts
index 7e0b0d4..5a6dee5 100644
--- a/src/time/EpochUTC.ts
+++ b/src/time/EpochUTC.ts
@@ -51,7 +51,7 @@ type DateToPosixParams = {
 
 export class EpochUTC extends Epoch {
   static now() {
-    return new EpochUTC(new Date().getTime() / 1000);
+    return new EpochUTC(new Date().getTime() / 1000 as Seconds);
   }
 
   static fromDate({ year, month, day, hour = 0, minute = 0, second = 0 }: FromDateParams) {
@@ -59,17 +59,17 @@ export class EpochUTC extends Epoch {
   }
 
   static fromDateTime(dt: Date) {
-    return new EpochUTC(dt.getTime() / 1000);
+    return new EpochUTC(dt.getTime() / 1000 as Seconds);
   }
 
   static fromDateTimeString(dateTimeString: string): EpochUTC {
     const dts = dateTimeString.trim().toUpperCase().endsWith('Z') ? dateTimeString : `${dateTimeString}Z`;
 
-    return new EpochUTC(new Date(dts).getTime() / 1000);
+    return new EpochUTC(new Date(dts).getTime() / 1000 as Seconds);
   }
 
   static fromJ2000TTSeconds(seconds: Seconds): EpochUTC {
-    const tInit = new EpochUTC(seconds + 946728000);
+    const tInit = new EpochUTC(seconds + 946728000 as Seconds);
     const ls = DataHandler.getInstance().getLeapSeconds(tInit.toJulianDate());
 
     return tInit.roll(-32.184 - ls as Seconds);
@@ -85,11 +85,11 @@ export class EpochUTC extends Epoch {
     // Add day - 1 days in milliseconds to the epoch.
     const dts = new Date(`${year}-01-01T${timeField}Z`).getTime() + (day - 1) * MS_PER_DAY;
 
-    return new EpochUTC(dts / 1000);
+    return new EpochUTC(dts / 1000 as Seconds);
   }
 
   roll(seconds: Seconds): EpochUTC {
-    return new EpochUTC(this.posix + seconds);
+    return new EpochUTC(this.posix + seconds as Seconds);
   }
 
   toMjd(): number {
@@ -103,20 +103,20 @@ export class EpochUTC extends Epoch {
   toTAI(): EpochTAI {
     const ls = DataHandler.getInstance().getLeapSeconds(this.toJulianDate());
 
-    return new EpochTAI(this.posix + ls);
+    return new EpochTAI(this.posix + ls as Seconds);
   }
 
   toTT(): EpochTT {
-    return new EpochTT(this.toTAI().posix + 32.184);
+    return new EpochTT(this.toTAI().posix + 32.184 as Seconds);
   }
 
   toTDB(): EpochTDB {
     const tt = this.toTT();
     const tTT = tt.toJulianCenturies();
     const mEarth = (357.5277233 + 35999.05034 * tTT) * DEG2RAD;
-    const seconds = 0.001658 * Math.sin(mEarth) + 0.00001385 * Math.sin(2 * mEarth);
+    const seconds = 0.001658 * Math.sin(mEarth) + 0.00001385 * Math.sin(2 * mEarth) as Seconds;
 
-    return new EpochTDB(tt.posix + seconds);
+    return new EpochTDB(tt.posix + seconds as Seconds);
   }
 
   toGPS(): EpochGPS {
@@ -168,7 +168,7 @@ export class EpochUTC extends Epoch {
     return EpochUTC.dayOfYearLookup_[dex][month - 1] + day - 1;
   }
 
-  private static dateToPosix_({ year, month, day, hour, minute, second }: DateToPosixParams): number {
+  private static dateToPosix_({ year, month, day, hour, minute, second }: DateToPosixParams): Seconds {
     const days = EpochUTC.dayOfYear_(year, month, day);
     const yearMod = year - 1900;
 
@@ -181,6 +181,6 @@ export class EpochUTC extends Epoch {
       Math.floor((yearMod - 1) / 100) * 86400 +
       Math.floor((yearMod + 299) / 400) * 86400 +
       second
-    );
+    ) as Seconds;
   }
 }
diff --git a/test/objects/__snapshots__/Satellite.test.ts.snap b/test/objects/__snapshots__/Satellite.test.ts.snap
index 72cf2fc..5e2e7bf 100644
--- a/test/objects/__snapshots__/Satellite.test.ts.snap
+++ b/test/objects/__snapshots__/Satellite.test.ts.snap
@@ -25,26 +25,26 @@ Object {
 
 exports[`Satellite should calculate and return Geodetic coordinates when given a date 1`] = `
 Geodetic {
-  "alt": 405.17244322847,
-  "lat": 0.1099327125671112,
-  "lon": 0.2809557331563047,
+  "alt": 409.48725329355693,
+  "lat": -0.48221646502840027,
+  "lon": 1.2198848056557416,
 }
 `;
 
 exports[`Satellite should calculate and return ITRF coordinates when called 1`] = `
 ITRF {
   "epoch": EpochUTC {
-    "posix": 1705109326817,
+    "posix": 1705109326.817,
   },
   "position": Vector3D {
-    "x": 6478.244529235784,
-    "y": 1869.552512878403,
-    "z": 739.5500168212324,
+    "x": 2068.607191044621,
+    "y": 5650.9777806539605,
+    "z": -3130.036328555523,
   },
   "velocity": Vector3D {
-    "x": 2.366559347644857,
-    "y": -7.704390508005883,
-    "z": -1.227328372730736,
+    "x": -5.491548321368525,
+    "y": -0.6798748760128108,
+    "z": -4.863052489363518,
   },
 }
 `;
@@ -64,7 +64,7 @@ RAE {
   "elRad": -1.2837885129141846,
   "elRateRad": -0.03103994353789119,
   "epoch": EpochUTC {
-    "posix": 1705109326817,
+    "posix": 1705109326.817,
   },
   "rng": 12650.301530537545,
   "rngRate": 1.8799097918581538,