This is the crew for the last shuttle mission, STS-135, next to their ride: The mighty Atlantis. They are about to launch in the last mission of the Space Shuttle program.
They are Commander Christopher Ferguson, Pilot Douglas Hurley, Mission Specialist 1 Sandra Magnus and Mission Specialist 2 Rex Walheim. The four were—in fact, they still are—the crew of the STS-335 rescue mission, which would be launched in the case there is a major malfunction on Endeavour.
The four are the smallest crew in a space shuttle since STS-6, launched on April 1983. Yes, there were space shuttles flying even before there were Macs. Think about that twice and marvel at the amazing technological feat that these machines represent.
Endeavour's STS-134 was supposed to be the last mission of the space shuttle program. It was the last one to get funding from the government. However, and here comes the trick, every shuttle mission since the Columbia disaster calls for a rescue mission. They are called Launch On Need missions and they are designated STS-3xx. Chances are that there will not be any need for such a mission, but the money is already allocated for it.
As a result, NASA decided to launch Atlantis anyway and make good use of all those resources. It will carry the Multi-Purpose Logistics Module Raffaello and a Lightweight Multi-Purpose Carrier. Wouldn't they need a rescue mission too, you ask? No, not really. The ISS has enough space now to support a full shuttle crew for 80 days, and the astronauts could return to Earth on board a couple of Soyuz spacecraft anyway.