diff --git a/core/src/main/java/com/rtbishop/look4sat/domain/predict4kotlin/SatPredictor.kt b/core/src/main/java/com/rtbishop/look4sat/domain/predict4kotlin/SatPredictor.kt
new file mode 100644
index 00000000..63920432
--- /dev/null
+++ b/core/src/main/java/com/rtbishop/look4sat/domain/predict4kotlin/SatPredictor.kt
@@ -0,0 +1,201 @@
+package com.rtbishop.look4sat.domain.predict4kotlin
+
+import java.util.*
+import kotlin.math.*
+
+const val speedOfLight = 2.99792458E8
+const val earthRadiusKm = 6378.16
+
+fun Satellite.getQuarterOrbitMin(): Int {
+    return (24.0 * 60.0 / this.tle.meanmo / 4.0).toInt()
+}
+
+fun SatPos.getRangeCircle(): List<Position> {
+    val positions = mutableListOf<Position>()
+    val lat = this.latitude
+    val lon = this.longitude
+    // rangeCircleRadiusKm
+    // earthRadiusKm * acos(earthRadiusKm / (earthRadiusKm + satPos.altitude))
+    val beta = acos(earthRadiusKm / (earthRadiusKm + this.altitude))
+    var tempAzimuth = 0
+    while (tempAzimuth < 360) {
+        val azimuth = tempAzimuth / 360.0 * 2.0 * Math.PI
+        var rangelat = asin(sin(lat) * cos(beta) + cos(azimuth) * sin(beta) * cos(lat))
+        val num = (cos(beta) - (sin(lat) * sin(rangelat)))
+        val den = cos(lat) * cos(rangelat)
+        var rangelon = if (tempAzimuth == 0 && (beta > ((Math.PI / 2.0) - lat))) {
+            lon + Math.PI
+        } else if (tempAzimuth == 180 && (beta > ((Math.PI / 2.0) - lat))) {
+            lon + Math.PI
+        } else if (abs(num / den) > 1.0) {
+            lon
+        } else {
+            if ((180 - tempAzimuth) >= 0) {
+                lon - acos(num / den)
+            } else {
+                lon + acos(num / den)
+            }
+        }
+        while (rangelon < 0.0) rangelon += Math.PI * 2.0
+        while (rangelon > Math.PI * 2.0) rangelon -= Math.PI * 2.0
+        rangelat = Math.toDegrees(rangelat)
+        rangelon = Math.toDegrees(rangelon)
+        positions.add(Position(rangelat, rangelon))
+        tempAzimuth += 1
+    }
+    return positions
+}
+
+fun SatPos.getDownlinkFreq(freq: Long): Long {
+    return (freq.toDouble() * (speedOfLight - this.rangeRate * 1000.0) / speedOfLight).toLong()
+}
+
+fun SatPos.getUplinkFreq(freq: Long): Long {
+    return (freq.toDouble() * (speedOfLight + this.rangeRate * 1000.0) / speedOfLight).toLong()
+}
+
+fun Satellite.getSatPos(date: Date): SatPos {
+    return this.getPosition(stationPos, date)
+}
+
+fun Satellite.getPositions(date: Date, stepSec: Int, minBefore: Int, orbits: Double): List<SatPos> {
+    val positions = mutableListOf<SatPos>()
+    val orbitalPeriod = 24 * 60 / this.tle.meanmo
+    val endDate = Date(date.time + (orbitalPeriod * orbits * 60L * 1000L).toLong())
+    val startDate = Date(date.time - minBefore * 60L * 1000L)
+    var currentDate = startDate
+    while (currentDate.before(endDate)) {
+        positions.add(getSatPos(currentDate))
+        currentDate = Date(currentDate.time + stepSec * 1000)
+    }
+    return positions
+}
+
+fun Satellite.getPasses(refDate: Date, hoursAhead: Int, windBack: Boolean): List<SatPass> {
+    val passes = mutableListOf<SatPass>()
+    val oneQuarterOrbitMin = this.getQuarterOrbitMin()
+    val endDate = Date(refDate.time + hoursAhead * 60L * 60L * 1000L)
+    var startDate = refDate
+    var shouldWindBack = windBack
+    var lastAosDate: Date
+    var count = 0
+    if (this.willBeSeen(stationPos)) {
+        if (this.tle.isDeepspace) {
+            passes.add(nextDeepSpacePass(refDate))
+        } else {
+            do {
+                if (count > 0) shouldWindBack = false
+                val pass = nextNearEarthPass(startDate, shouldWindBack)
+                lastAosDate = pass.aosDate
+                passes.add(pass)
+                startDate =
+                    Date(pass.losDate.time + (oneQuarterOrbitMin * 3) * 60L * 1000L)
+                count++
+            } while (lastAosDate < endDate)
+        }
+    }
+    return passes
+}
+
+private fun Satellite.nextDeepSpacePass(refDate: Date): SatPass {
+    val satPos = getSatPos(refDate)
+    val id = this.tle.catnum
+    val name = this.tle.name
+    val isDeep = this.tle.isDeepspace
+    val aos = Date(refDate.time - 24 * 60L * 60L * 1000L).time
+    val los = Date(refDate.time + 24 * 60L * 60L * 1000L).time
+    val tca = Date((aos + los) / 2).time
+    val az = Math.toDegrees(satPos.azimuth)
+    val elev = Math.toDegrees(satPos.elevation)
+    val alt = satPos.altitude
+    return SatPass(id, name, isDeep, aos, az, los, az, tca, az, alt, elev, this)
+}
+
+private fun Satellite.nextNearEarthPass(refDate: Date, windBack: Boolean = false): SatPass {
+    val oneQuarterOrbitMin = this.getQuarterOrbitMin()
+    val calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC")).apply {
+        clear()
+        timeInMillis = refDate.time
+    }
+    val id = this.tle.catnum
+    val name = this.tle.name
+    val isDeep = this.tle.isDeepspace
+
+    var elevation: Double
+    var maxElevation = 0.0
+    var alt = 0.0
+    var tcaAz = 0.0
+
+    // wind back time 1/4 of an orbit
+    if (windBack) calendar.add(Calendar.MINUTE, -oneQuarterOrbitMin)
+    var satPos = getSatPos(calendar.time)
+
+    if (satPos.elevation > 0.0) {
+        // move forward in 30 second intervals until the sat goes below the horizon
+        do {
+            calendar.add(Calendar.SECOND, 30)
+            satPos = getSatPos(calendar.time)
+        } while (satPos.elevation > 0.0)
+        // move forward 3/4 of an orbit
+        calendar.add(Calendar.MINUTE, oneQuarterOrbitMin * 3)
+    }
+
+    // find the next time sat comes above the horizon
+    do {
+        calendar.add(Calendar.SECOND, 60)
+        satPos = getSatPos(calendar.time)
+        elevation = satPos.elevation
+        if (elevation > maxElevation) {
+            maxElevation = elevation
+            alt = satPos.altitude
+            tcaAz = Math.toDegrees(satPos.azimuth)
+        }
+    } while (satPos.elevation < 0.0)
+
+    // refine to 3 seconds
+    calendar.add(Calendar.SECOND, -60)
+    do {
+        calendar.add(Calendar.SECOND, 3)
+        satPos = getSatPos(calendar.time)
+        elevation = satPos.elevation
+        if (elevation > maxElevation) {
+            maxElevation = elevation
+            alt = satPos.altitude
+            tcaAz = Math.toDegrees(satPos.azimuth)
+        }
+    } while (satPos.elevation < 0.0)
+
+    val aos = satPos.time.time
+    val aosAz = Math.toDegrees(satPos.azimuth)
+
+    // find when sat goes below
+    do {
+        calendar.add(Calendar.SECOND, 30)
+        satPos = getSatPos(calendar.time)
+        elevation = satPos.elevation
+        if (elevation > maxElevation) {
+            maxElevation = elevation
+            alt = satPos.altitude
+            tcaAz = Math.toDegrees(satPos.azimuth)
+        }
+    } while (satPos.elevation > 0.0)
+
+    // refine to 3 seconds
+    calendar.add(Calendar.SECOND, -30)
+    do {
+        calendar.add(Calendar.SECOND, 3)
+        satPos = getSatPos(calendar.time)
+        elevation = satPos.elevation
+        if (elevation > maxElevation) {
+            maxElevation = elevation
+            alt = satPos.altitude
+            tcaAz = Math.toDegrees(satPos.azimuth)
+        }
+    } while (satPos.elevation > 0.0)
+
+    val los = satPos.time.time
+    val losAz = Math.toDegrees(satPos.azimuth)
+    val tca = Date((aos + los) / 2).time
+    val elev = Math.toDegrees(maxElevation)
+    return SatPass(id, name, isDeep, aos, aosAz, los, losAz, tca, tcaAz, alt, elev, this)
+}