How to use the tar.o.ApA function in tar

calculateDeltaV: function(data){
    var radiusOfBody = data["b.radius["+ this.vessel.orbitingBody.id +"]"]
    var r1 = data['o.ApA'] + radiusOfBody
    var r2 = data['tar.o.ApA'] + radiusOfBody
    var mu = data["b.o.gravParameter["+ this.vessel.orbitingBody.id +"]"];

    var factor1 = Math.sqrt(mu/r1)
    var factor2 = Math.sqrt((2 * r2)/(r1 + r2))

    this.deltaV = factor1 * (factor2 - 1)

    // console.log("delta V1: " + this.deltaV)
  },

getVesselAndTargetInfo: function(data){
    if(this.isnoTarget(data)){return}
    this.targetBody = this.datalink.getOrbitalBodyInfo(data['tar.name'])
    this.targetBody.orbitingBody = this.datalink.getOrbitalBodyInfo(data['tar.o.orbitingBody'])
    this.targetBody.periapsis = data['tar.o.ApA']
    this.vessel.orbitingBody = this.datalink.getOrbitalBodyInfo(data['v.body'])
    this.vessel.periapsis = data['o.ApA']
    this.vessel.altitude = data['v.altitude']
    this.vessel.orbitalVelocity = data['v.orbitalVelocity']

    this.datalink.subscribeToData([
      "b.o.gravParameter["+ this.vessel.orbitingBody.id +"]",
      "b.radius["+ this.vessel.orbitingBody.id +"]",
      "b.o.phaseAngle["+ this.targetBody.id +"]"
    ])
  },

window.requestAnimationFrame(function(){
      this.fields.vesselBody.update(data['v.body'])
      this.fields.targetBody.update(data['v.body'])

      this.fields.vesselAltitude.update(DataFormatters.distanceString(data['v.altitude']))

      this.fields.vesselApoapsis.update(DataFormatters.distanceString(data['o.ApA']))
      this.fields.targetApoapsis.update(DataFormatters.distanceString(data['tar.o.ApA']))

      this.fields.vesselPeriapsis.update(DataFormatters.distanceString(data['o.PeA']))
      this.fields.targetPeriapsis.update(DataFormatters.distanceString(data['tar.o.PeA']))

      this.fields.vesselTimeToApoapsis.update("-" + TimeFormatters.durationString(data['o.timeToAp']))
      this.fields.targetTimeToApoapsis.update("-" + TimeFormatters.durationString(data['tar.o.timeToAp']))

      this.fields.vesselTimeToPeriapsis.update("-" + TimeFormatters.durationString(data['o.timeToPe']))
      this.fields.targetTimeToPeriapsis.update("-" + TimeFormatters.durationString(data['tar.o.timeToPe']))

      this.fields.vesselInclination.update(DataFormatters.degreeString(data['o.inclination']))
      this.fields.targetInclination.update(DataFormatters.degreeString(data['tar.o.inclination']))

      this.fields.vesselEccentricity.update(data['o.eccentricity'].toFixed(3))
      this.fields.targetEccentricity.update(data['tar.o.eccentricity'].toFixed(3))