text: // @flow
  export default class Rocket {
      country: string;
      year:    number;
      name:    string;
  
      constructor (country: string, name: string, year: number) {
          this.country = country;
          this.name    = name;
          this.year    = year;
      }
  
      launch (payload: number) {
          if (payload < 0 || payload > this.maxPayload)
              return 'We have a problem!';
  
          return 'Rocket launched succesfully!';
      }
  
      maxPayload: number = 6900;
  }
  
  