One Step Back,
One Giant Leap Forward

The Apollo project ended a long time ago. About half of all Americans were not yet born when Gene Cernan closed the hatch on lunar module Challenger and the astronauts of Apollo 17 left the moon.

When President George W. Bush visited NASA in 2004 and announced a new vision for space exploration that would return humans to the moon by 2020 in preparation for future exploration of Mars, he addressed a far more mature space agency compared to the one that designed and implemented the Apollo program.

Despite recent funding cuts that have left the future of many NASA projects in doubt, the agency in recent years has launched robotic spacecraft bound for all corners of our solar system, and operated a human spaceflight program that included the largest-ever space station assembled in Earth orbit and the world's only reusable spacecraft.

In 2005, prior to the aforementioned funding challenges, NASA administrator Mike Griffin challenged a handpicked group of engineers and managers to design a mission architecture that would accomplish the next phases of the vision—returning humans to the moon and pushing on to Mars. "Architecture" is NASA-speak for the combination of spacecraft, launch vehicles, orbital mechanics, and operations required to accomplish a space mission.

"Rocket science" is the art of managing velocity changes that are dictated by physics. Leaving Earth orbit on a three-day trans-lunar traverse requires a velocity increase of 3,100 meters per second; capturing into a preferred lunar orbit requires a velocity decrease of 1,100 m/s; and descending to the lunar surface requires a further decrease of 1,900 m/s. Returning to Earth requires the same basic velocity changes again—in reverse order.

With the help of past lunar missions, NASA reduced the mission design problem to a fundamental question: Are dockings or undockings performed in Earth orbit or lunar orbit?

After analyzing various scenarios, especially the level of risk and probability of losing the mission or crew, NASA selected a dual-rendezvous mission powered by a heavy-lift launch vehicle taking a lunar lander and Earth departure stage (EDS) into Earth orbit. This launch would be followed by a small launch vehicle to lift the crew exploration vehicle (CEV) and crew into Earth orbit, where it would rendezvous with the EDS.

The EDS then performs a translunar insertion burn and is expended. The remaining CEV-lander stack performs the four-day cruise to the moon and is inserted into lunar orbit by the descent stage of the lunar lander. The crew transfers from the CEV to the lander and descends to the lunar surface, leaving the CEV in lunar orbit. The crew can spend up to a week anywhere on the surface, performing science investigations, resource utilization experiments and technology demonstrations that begin the preparation for a Mars mission.

To return, the crew fires engines on the ascent stage of the lander and docks with the CEV. The ascent stage is jettisoned and the service module of the CEV fires a trans-Earth injection burn to pull out of lunar orbit and return to Earth.

NASA scientists working on this new mission architecture are seeking to build upon previous spacecraft designs, but also seek to distinguish their work from the familiar icons of NASA's past successes. After all, they grew up with Star Trek, Star Wars, and model rockets—and while Apollo was their parents' space program, they want the next lunar mission moon to be distinctly theirs.

We naturally thought this moon mission would look far more advanced, perhaps something like the Millennium Falcon. But a funny thing happened on the way back to the moon: physics and technology intervened. Physics, or at least our current understanding of it, dictates the velocity changes needed to travel through space, and puts Sir Issac Newton in the designer's chair.

Technology has improved some since Apollo, and our missions will therefore be more capable, but we still haven't developed hyperdrive. With physics the same and technology improved only incrementally, it's no surprise that the current solution looks a lot like Apollo. It isn't due to lack of imagination on the part of this new generation of engineers, but rather to the fact that the Apollo engineers understood the problems as well as we do today.

[Adapted from “One Step Back, One Giant Leap Forward," by John F. Connolly, NASA Johnson Space Center, for Mechanical Engineering, May 2006.]
 

We naturally thought this moon mission would look far more advanced, perhaps something like the Millennium Falcon.