Rockets in Ursa Major

It is the early twenty-first century. Humans are seeking signs of life elsewhere in the universe, but all exploratory ships have been lost without a trace—except for DSP 15. Thirty years after leaving Earth, and given up for lost, DSP 15 suddenly appears on radar screens at the space station at Mildenhall, England. Her crew has been frozen to prevent aging, and as the ship settles to a landing, Dr. Richard Warboys eagerly waits with other scientists for word of what DSP 15 has found. But there is no crew, only a message scratched into a metal surface, signed by the captain: "If this ship returns to Earth, then mankind is in deadly peril—God help you."