by Luke Colby
As we all look forward and dream of manned missions to Mars, we will face many challenges both technical and political if we are ever to set foot on the red planet. Of those many challenges, one is lifting heavy cargos into low earth orbit, and beyond. Before we can go anywhere outside the confines of Earth orbit we must revive or re-invent the equivalent of the mighty Saturn V rocket. A frightening fact that we must come to grips with is that no country in the world today possesses a working launch system that has the power to send humans beyond Earth orbit. Sadly, the production lines for the Saturn V and the Russian Energia (similar in power to the Saturn V) were shut down just as we were beginning to realize the potential that these powerful rockets possessed.
I mention all these troubling facts because they must be understood in order to see the problems we must overcome before we can even think about going to Mars or back to the Moon. Fortunately, the situation is not as grim as one might at first suppose from the facts above. There are in fact several alternatives to re-incarnating the Saturn V, which utilize components of existing launch systems with only slight modifications. This article discusses two such possibilities derived from the current space shuttle launch vehicle.
Ever since the space shuttle program was started back in the late 70’s – early 80’s, engineers recognized the fact that we would eventually need powerful launch systems that could lift cargoes into space that were too heavy for the space shuttle. As a result, while designing the space shuttle launch system, several concepts were created that would allow the shuttle’s external tank and solid rocket boosters to be used as a booster for cargoes other than the space shuttle. One such design was the “Shuttle C” which was essentially the space shuttle booster with the orbiter replaced by a cargo container with retrievable engines on the bottom (see figure below).
This elegant, simple, and practical design could be used to lift much larger cargoes into orbit. Unfortunately, the draw back to the design is that the interior diameter of the cargo container is not much greater than the orbiter cargo bay. This requires the habitats, cargo containers, etc. to be long narrow containers - a rather limiting scenario.
Not to worry though - another possibility exists. Heavy lift boosters can be made out of existing production rockets by putting the cargo on top of the space shuttle’s big external tank, similar to the way cargo is carried on the smaller Titan IV, which is used for lifting large satellites into high orbits (see figure on right). This design is perhaps the most promising for modifying the space shuttle, because it allows the cargo faring to be even bigger than the diameter of the large external tank, which is already 27.6 feet in diameter. In fact, when Dr. Zubrin, who is best known for his revolutionary “Mars Direct” plan, was working at Martin Marietta (now absorbed by Lockheed, hence the new name Lockheed Martin) he and his colleagues designed a modification of the space shuttle booster stack that could carry a tuna can shaped Mars habitat module and upper stage booster into low earth orbit (LEO). This modified booster, Ares, could lift 121 metric tons into LEO or 45 metric tons on a Mars trajectory - enough for the large habitat that would be needed for the long trip to Mars. Further, without great modifications, this booster could carry the Earth Return Vehicle (ERV) in its payload bay as well. So, all the launches to Mars could be made with one vehicle that, once developed, would provide us with a powerful booster based on proven technology, which would be cost effective. While there are a few technical issues that would have to be worked out with this design, such as how to retrieve the engine pod (that must be reusable to be cost effective) without damage, much of what is holding back the construction of this simple design is politics and financial issues. At this time, NASA is spending large fractions of its budget (about 70%) on keeping up the aging fleet of space shuttles and building the International Space Station. However, there are already plans underway to devote money to designing new launch systems, including a heavy lift launch vehicle. These funds are meant to be distributed to private companies which will conduct the R&D.
The two booster designs I have mentioned are only two out of many possibilities for a heavy lift booster capable of taking us beyond Earth orbit, but they are two of the most probable because they require the least new technology and research, which translates into less cost, which in the end is what governs much of the aerospace industry.