The United States has recently declared an intention to return U.S. astronauts to the Moon by the year 2020. This has been spurred by a number of factors, perhaps the main one being a perceived need to regain public enthusiasm for space exploration. Implicit in this statement is a view that a permanent manned presence in low Earth orbit aboard the ISS is not considered sufficiently exciting! I'm sure that motivation has also been provided by the declarations of other nations that have similar intentions. For example, the Chinese space agency have set 2017 as the date for a manned lunar landing, despite the relatively newness of the Chinese manned space program. Another influential feature is the retirement of the Space Shuttle fleet in 2010, forcing major change and new development in the U.S. space program. Although it is important to realize that the U.S. is not the only player in this field, nevertheless I will focus on American plans for a return to the Moon simply because they are sufficiently advanced to give a flavor of how it might be achieved.
The most striking thing about the new NASA plan is that it combines the huge experience gained in the Apollo and Space Shuttle eras of the American space program. The manned vehicle that will replace the shuttle looks very Apollo-like. Initially called the Crew Exploration Vehicle, but now renamed Orion, this spacecraft looks like the Apollo command and service modules (Fig. 10.4). However, it is about three times larger, accommodating four astronauts for the trip to the moon. To launch Orion, a new man-rated launch vehicle is being developed, called Ares 1, using existing components derived from the Space Shuttle and Apollo launch systems. The theory is that this will allow NASA to use tried-and-tested rocket components, and also to benefit from an experienced work force familiar with the manufacture and integration of these components. It is hoped that this will allow a smoother transition to the new operation once the shuttle fleet is retired.
To land on the Moon, however, requires other equipment, not least of which is a lunar lander spacecraft. NASA proposes developing a separate heavy lift launcher, again composed of Space Shuttle and Apollo components, capable of lifting a payload of the order of 125 metric tonnes into low Earth orbit. This launch vehicle, called Ares 5, will be used to lift the lander spacecraft and a propulsion stage into orbit. It's worth pointing out that although the Ares 1 and 5 launchers are discussed here in the context of the return-to-the-moon program, NASA envisages a wider role for these launch systems involving manned space missions to destinations other than the moon.
So, let's have a look at how all of this new infrastructure to take people back to the Moon fits together, and the way it does is strikingly similar to the Apollo moon landings. The heavy lift Ares 5 launcher blasts off first, taking the unmanned cargo—the lander spacecraft and the propulsion stage—into Earth orbit. Then sometime in the following 30 days the crew takes off in the Orion spacecraft as the payload of the Ares 1 launch vehicle. This new man-rated launch system is much simpler than the Space Shuttle, and as such it is hoped to be more reliable. Once in Earth orbit, the Orion spacecraft will rendezvous and dock with the lander and propulsion stage. After checkout, the propulsion stage rocket engines are fired to boost the whole assembly into a lunar trajectory. Once this maneuver is completed, the propulsion stage is discarded, leaving the Orion spacecraft and the lander docked together for a 3-day cruise to the Moon.
On arrival at the Moon, the main engine of the Orion spacecraft is ignited to take the assembly into a low Moon orbit (Fig. 10.5). The four astronauts
then transfer to the lander spacecraft, and undock from Orion, allowing the lander descent engines to fire to take the crew down to the surface. Initially, it is planned that the astronauts will spend 7 days on the surface, while the Orion spacecraft is monitored and controlled robotically in its orbit above. On conclusion of the surface exploration, the crew returns to orbit in the lander ascent module, and then rendezvous and dock with the waiting Orion spacecraft. After transfer of the crew, and the jettisoning of the lander, the main engine of the Orion vehicle is fired to take the astronauts on a trajectory back to Earth. Finally, an atmospheric entry and a parachute descent bring the crew safely home on American soil, probably in California.
Although I personally find the prospect of this shift back to space exploration (as opposed to space applications) exciting, the question of why we should return to the Moon should be addressed. Scientists will always be able to come up with ideas about the scientific exploitation of the unique properties of a lunar base, but do they justify the cost? The price tag for this U.S. initiative is estimated to be about the same as that for the ISS, around $100 billion at least. The opponents of manned spaceflight are hard at work once again bringing criticism to bear on the return-to-the-Moon initiative and claiming how much better value there would be in unmanned, robotic exploration of the Moon.
Another criticism leveled at the new plan is that it has the appearance of a one-shot moon landing program, similar to Apollo, with no prospect of a lasting legacy, such as the establishment of a longer-term manned presence on the Moon. In answer to this, NASA claims the possibility of building some form of semipermanent lunar base using the new launcher and spacecraft infrastructure. Presumably the cargo lofted by the heavy lift launch vehicle can be modified to take components of such a base to the lunar surface. I think this is perhaps the key to justifying the expenditure: the development of a manned lunar outpost in the long-term for exploration of the Moon and to support manned missions to Mars. In addition to the scientific return that this project would give, the Moon can also serve as a proving ground for a broad range of space operations and processes, including the idea of learning to live off the land—in other words, learning the techniques of self-sufficiency that will be useful in establishing future manned bases in other places in the solar system.
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