The next-generation system of space vehicles at the National Aeronautics and Space Administration has been called "Apollo on steroids" because of its resemblance to vehicles from the early days of the United States space program. The resemblances aren't all superficial; the upper stages of the Ares I and Ares V rockets in the new system will be powered by descendants of the J-2 engine that powered the upper stages of the Saturn I and V rockets of the Apollo program. In this photograph, core components of the new engine, known as J-2X, are readied for testing at NASA's Stennis Space Center near Bay St. Louis, Mississippi.

The Orion capsule used in the Constellation program looks like the capsules from the Apollo program, but it is a much bigger beast. The Apollo capsules that went to the moon carried three astronauts; Orion can hold as many as six. In this photograph, a mock-up of the Orion capsule is moved into a hangar at NASA's Langley Research Center in Hampton, Virginia.

The first test flight of the Ares rockets will come next year. That initial flight, called Ares I-X, will involve a dummy upper stage for the rocket. In this photo, segments for the simulated upper stage are being prepared at NASA's Glenn Research Center in Ohio.

Segments for the "upper stage simulator" in the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida, which will be used in the Ares I-X test flight scheduled to take place next year. The Ares I could initially take astronauts to the International Space Station, but may eventually be used with the heavy-lift Ares V to take crew and equipment to the Moon, to near-earth Asteroids and even to Mars.

The Ares I will have an escape tower that will pull the Orion capsule away from the rocket in case of emergencies that require an abort during launching. Technicians at Alliant Techsystems inspect an inert escape rocket abort motor on its test stand in Promontory, Utah .

The Ares V rocket, while much taller than the current space shuttle system, will use liquid-fueled engines and two solid-rocket motors, a configuration that resembles the current shuttle. In this photo, wind-tunnel tests of a scale model of the vehicle at the Marshall Space Flight Center in Huntsville, Alabama shows the air flow around the components at four and a half times the speed of sound.

In this artist's concept illustration, the first and second stages of the Ares V heavy-lift vehicle separate after launching. The image evokes earlier photographs and film from the days of the Apollo program.

An artist's rendering shows the Orion capsule in an abort flight test, with parachutes slowing the descent toward White Sands Missile Range in New Mexico, where the test would take place.

As the Constellation program has moved from proposal to computer screen and into development, many changes have been forced by factors like budgets and physics. Initial plans called for the Orion capsule to return to Earth and land on land, like the Russian Soyuz capsule does. But the airbag system required for a return to land added so much weight to the capsule that NASA is now focused on an Apollo-style splashdown in the ocean.

As NASA winds down the space shuttle program, getting people and equipment to the International Space Station is becoming a pressing issue. The Russian Soyuz craft will be the sole vehicle for getting people to and from the station, and cargo ships have been developed by the European Space Agency and are under development by the Japanese space agency. NASA is also counting on cargo services from two private companies, Space Exploration Technologies of Hawthorne, California and Orbital Sciences Corp. of Dulles, Va. In this illustration, SpaceX launches a demonstration flight of its Falcon 1, a single-engine precursor to the nine-engine rocket that it will use for station cargo flights.

A test of the nine-engine Falcon 9 rocket by SpaceX in McGregor, Texas. The company plans its first flight of the rocket from Florida in 2009. The company hopes to take astronauts to the International Space Station aboard Falcon 9 rockets as well, though NASA has not signed on to finance the development of crew transport.