diff --git a/src/utils/functions.ts b/src/utils/functions.ts
index 13b3294..7ee3d81 100644
--- a/src/utils/functions.ts
+++ b/src/utils/functions.ts
@@ -8,6 +8,7 @@ import {
   DifferentiableFunction,
   JacobianFunction,
   Radians,
+  SpaceObjectType,
 } from '../types/types';
 
 /**
@@ -618,3 +619,38 @@ export function toPrecision(value: number, places: number): number {
 export function sign(value: number) {
   return value >= 0 ? 1 : -1;
 }
+
+const spaceObjTypeStrMap = {
+  [SpaceObjectType.UNKNOWN]: 'Unknown',
+  [SpaceObjectType.PAYLOAD]: 'Payload',
+  [SpaceObjectType.ROCKET_BODY]: 'Rocket Body',
+  [SpaceObjectType.DEBRIS]: 'Debris',
+  [SpaceObjectType.SPECIAL]: 'Special',
+  [SpaceObjectType.BALLISTIC_MISSILE]: 'Ballistic Missile',
+  [SpaceObjectType.STAR]: 'Star',
+  [SpaceObjectType.INTERGOVERNMENTAL_ORGANIZATION]: 'Intergovernmental Organization',
+  [SpaceObjectType.SUBORBITAL_PAYLOAD_OPERATOR]: 'Suborbital Payload Operator',
+  [SpaceObjectType.PAYLOAD_OWNER]: 'Payload Owner',
+  [SpaceObjectType.METEOROLOGICAL_ROCKET_LAUNCH_AGENCY_OR_MANUFACTURER]:
+    'Meteorological Rocket Launch Agency or Manufacturer',
+  [SpaceObjectType.PAYLOAD_MANUFACTURER]: 'Payload Manufacturer',
+  [SpaceObjectType.LAUNCH_AGENCY]: 'Launch Agency',
+  [SpaceObjectType.LAUNCH_SITE]: 'Launch Site',
+  [SpaceObjectType.LAUNCH_POSITION]: 'Launch Position',
+  [SpaceObjectType.LAUNCH_FACILITY]: 'Launch Facility',
+  [SpaceObjectType.CONTROL_FACILITY]: 'Control Facility',
+  [SpaceObjectType.GROUND_SENSOR_STATION]: 'Ground Sensor Station',
+  [SpaceObjectType.OPTICAL]: 'Optical',
+  [SpaceObjectType.MECHANICAL]: 'Mechanical',
+  [SpaceObjectType.PHASED_ARRAY_RADAR]: 'Phased Array Radar',
+  [SpaceObjectType.OBSERVER]: 'Observer',
+  [SpaceObjectType.BISTATIC_RADIO_TELESCOPE]: 'Bi-static Radio Telescope',
+  [SpaceObjectType.COUNTRY]: 'Country',
+  [SpaceObjectType.LAUNCH_VEHICLE_MANUFACTURER]: 'Launch Vehicle Manufacturer',
+  [SpaceObjectType.ENGINE_MANUFACTURER]: 'Engine Manufacturer',
+  [SpaceObjectType.NOTIONAL]: 'Notional',
+  [SpaceObjectType.FRAGMENT]: 'Fragment',
+};
+
+export const spaceObjType2Str = (spaceObjType: SpaceObjectType): string =>
+  spaceObjTypeStrMap[spaceObjType] || 'Unknown';
diff --git a/src/utils/utils.ts b/src/utils/utils.ts
index f07fb93..658e858 100644
--- a/src/utils/utils.ts
+++ b/src/utils/utils.ts
@@ -42,7 +42,7 @@ class Utils {
     return <Kilometers>Math.sqrt((pos1.x - pos2.x) ** 2 + (pos1.y - pos2.y) ** 2 + (pos1.z - pos2.z) ** 2);
   }
 
-  static dopplerFactor(location: EciVec3, position: EciVec3, velocity: EciVec3): Kilometers {
+  static dopplerFactor(location: EciVec3, position: EciVec3, velocity: EciVec3): number {
     const mfactor = 7.292115e-5;
     const c = 299792.458; // Speed of light in km/s
 
@@ -60,8 +60,17 @@ class Utils {
     };
 
     const rangeRate = (range.x * rangeVel.x + range.y * rangeVel.y + range.z * rangeVel.z) / distance;
+    let dopplerFactor = 0;
 
-    return <Kilometers>(1 + (rangeRate / c) * sign(rangeRate));
+    if (rangeRate < 0) {
+      dopplerFactor = 1 + (rangeRate / c) * sign(rangeRate);
+    }
+
+    if (rangeRate >= 0) {
+      dopplerFactor = 1 - (rangeRate / c) * sign(rangeRate);
+    }
+
+    return dopplerFactor;
   }
 }
 
diff --git a/test/utils/utils.test.js b/test/utils/utils.test.js
index c36dd5e..acacd1a 100644
--- a/test/utils/utils.test.js
+++ b/test/utils/utils.test.js
@@ -74,7 +74,7 @@ describe('Doppler factor', () => {
     };
     const dopFactor = Utils.dopplerFactor(observerEcf, positionEcf, velocityEcf);
 
-    expect(dopFactor).toBeCloseTo(1.0000107847789212, numDigits);
+    expect(dopFactor).toBeCloseTo(0.9999892152210788, numDigits);
   });
 
   test('if negative range rate works', () => {