I have shareService and subscribe that is in another components :

import { Component, Input, OnDestroy } from '@angular/core';

import { MissionService } from './mission.service';

import { Subscription }   from 'rxjs/Subscription';

@Component({

  selector: 'my-astronaut',

  template: `

    <p>

      {{astronaut}}: <strong>{{mission}}</strong>

      <button

        (click)=confirm()

        [disabled]=!announced || confirmed>

        Confirm

      </button>

    </p>

  `

})

export class AstronautComponent implements OnDestroy{

  @Input() astronaut: string;

  mission = <no mission announced>;

  confirmed = false;

  announced = false;

  subscription:Subscription;



  constructor(private missionService: MissionService) {

    this.subscription = missionService.missionAnnounced$.subscribe(

      mission => {

        this.mission = mission;

        this.announced = true;

        this.confirmed = false;

    })









  }

  confirm() {

    this.confirmed = true;

    this.missionService.confirmMission(this.astronaut);

  }

  ngOnDestroy(){

    // prevent memory leak when component destroyed

    this.subscription.unsubscribe();



  }

}

I want to know if I have 2 subscribers in my constructor, how to unsubscribe twice subscribers in ngDestroy?
I should use subscription2:Subscription;?and in ngDestroy this.subscription2.unsubscribe();?
this is true?