Emissaries - The Canta Libre Trilogy, #1

Aliens. First contact was a surprise when it came. A silly, childish message of peace and friendship from a place so far away only Earth's newest prototype spaceship, the Canta Libre, could reach it - or so people thought. The UN-led team that went out to represent humanity was mostly scientists and soldiers, led by General Ramirez, and carrying Ambassador Hartmann to the most momentous meeting in human history.
But they were not alone. Other teams went too; one led by Petrov, a gang boss with dreams of technological riches and power beyond measure, the other crewing an ancient ark ship the rest of the world had long since forgotten, its mission changed by an unscrupulous government, its half-human captain, Ken Lee, bitter and heartbroken. Some, like young Kitty Hamilton and drug designer Mike McBain, were dragged into the race for first contact against their will.
Others, like Geoffrey Cejka and physicist Susan Iverson were eager participants. But none of them - not even the military robot - would complete the mission unscathed or unchanged. Some wouldn't complete it at all. Yet, though the struggle to answer the call of the enigmatic aliens would challenge the hapless travellers to the limits of their endurance, and the struggle to be the first to represent humanity would be vicious and deadly, for the survivors, the real struggle was still to come.