Alien Attack

Contact with the bases on Mars is lost, then a mysterious attacker destroys all the space stations, the space telescopes and finally a space shuttle. All communications on Earth are also down as the satellites in Earth orbit are jammed. America decides to send the Research vessel Discovery to Mars to investigate, on a suicide mission, for their enemy must be far in advance of Earth to cross interstellar space. It is armed though; hypersonic nuclear missiles and hypersonic cruise missiles are installed within the hanger bay. Before it sets off from the Moon, the enemy are sighted, their mothership is a massive asteroid and it is spotted behind Mars, but why have they not followed up their initial attack.