how to unsubscribe several subscriber in angular 2
<p>I have shareService and subscribe that is in another components :</p>

<pre><code>import { Component, Input, OnDestroy } from '@angular/core';
import { MissionService } from './mission.service';
import { Subscription }   from 'rxjs/Subscription';
@Component({
  selector: 'my-astronaut',
  template: `
    &lt;p&gt;
      {{astronaut}}: &lt;strong&gt;{{mission}}&lt;/strong&gt;
      &lt;button
        (click)="confirm()"
        [disabled]="!announced || confirmed"&gt;
        Confirm
      &lt;/button&gt;
    &lt;/p&gt;
  `
})
export class AstronautComponent implements OnDestroy{
  @Input() astronaut: string;
  mission = "&lt;no mission announced&gt;";
  confirmed = false;
  announced = false;
  subscription:Subscription;

  constructor(private missionService: MissionService) {
    this.subscription = missionService.missionAnnounced$.subscribe(
      mission =&gt; {
        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();

  }
}
</code></pre>

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