In 1989, the then President of the United States, George H. W. Bush, called upon NASA to define a Space Exploration Initiative, involving a space station in Earth orbit, a return to the Moon, and human missions to Mars. NASA undertook a study of what was required, and produced what is known as the "90-Day Report", reflecting the length of time spent in producing it. The price tag for the whole package would be about $450 billion dollars, and be spread over several decades. In 1994 Robert Zubrin and David Baker proposed a much simpler plan, which they called Mars Direct. Many of the key elements of the Mars Direct plan have since been incorporated into the mission designs at NASA.
NASA 90-Day Report
Concentrating on the part of the report dealing with Mars exploration, after calculating the mass of the supplies and fuel that would be needed to ferry the crew to Mars and back, it was clear that the spacecraft would be far too massive for it to be launched from Earth. Therefore first of all a vast infrastructure would have to be built as a spacedock in orbit around Earth. This dock would be used to build the spacecraft in space. This would take about thirty years, and would also involve the development of new technologies and materials. The estimated cost was deemed to be completely unaffordable, and so the idea of going to Mars was shelved.
Mars Direct Mission
Robert Zubrin introduced this radical new approach while he was a senior engineer at Martin Marietta Astronautics, with the collaboration of his colleague David Baker. The key difference is that instead of transporting to Mars all of the rocket fuel needed for the return journey, that fuel is manufactured on Mars. This approach leads to a large reduction in the mass that has to be shipped from Earth. So great a reduction, that there is no longer any need for any spacecraft to be built in orbit – everything can be taken on board a heavy-lift vehicle.
Hardware for Mars Direct Mission
The hardware required for the mission to Mars consists of three main vehicles:
- A heavy-lifting booster: This would have the capability of launching 40 tonnes directly to Mars. At the moment the USA does not have a heavy-launch vehicle, but one is being planned by NASA: the Ares V. No new technology is needed in building the Ares V – it can be built using four rocket engines and two solid fuel rockets of the type used for many years to launch the Space Shuttle.
- The Earth Return Vehicle (ERV): This would be a two-stage vehicle, sent to Mars uncrewed. It would have living quarters and supplies for the crew to use on the journey back to Earth. The fuel it would need will be manufactured on Mars.
- The Habitat Unit: This unit would consist of up to three decks of working and living space. There would be individual sleeping quarters, a common mess area, and also in the lowest deck, laboratory facilities. The habitat unit would thus function as a crewed spacecraft for the journey to Mars, and as living and working quarters while the crew members carry out their mission on the surface of Mars.
Mars Mission Schedule
As the first step, the Ares V would be used to launch an ERV to Mars, via an orbit which would take about 8 months. After landing, the nuclear generator would be used to power the chemical plant. Carbon dioxide, which is abundant in the atmosphere of Mars, would be reacted with several tonnes of hydrogen shipped from Earth, to produce methane and water, via the Sabatier reaction. The water would be split by electrolysis into hydrogen and oxygen, with the hydrogen being recycled to produce more methane and water. Together with the oxygen, the methane can be used as fuel to power the engines in the ERV for the journey back to Earth. There will be surplus fuel that the crew can use in rover vehicles.
Generating the fuel will take several months. Once fuelling is complete a second ERV will be launched to Mars, again taking 8 months to arrive. A second booster will launch a habitat unit with its crew on board, with a journey time of six months. One of their first tasks will be to confirm that the waiting ERV is correctly fuelled and in a state ready to take them home. If not the second ERV will be directed to land nearby, and the crew will use it as their vessel home, once it has completed generating fuel. If the second ERV is not needed, it can be directed to a completely different landing site, where it will be use by a subsequent crew.
While the crew are on the surface (for about 500 days) their home will be the living space in the habitat. They will be able to do scientific studies in the laboratory, and explore the surrounding terrain using a methane-fuelled rover.
On completion of their mission, the crew will set off on their return journey in the ERV, taking 180 days to get to Earth.
The Way to Mars
In 2003 a joint NASA / European Space Agency study showed that within ten years or so and for an initial cost of about $35 billion dollars, a mission such as Mars Direct was achievable.
Robert Zubrin, founder of the Mars Society, and author of The Case for Mars (Simon & Schuster, ISBN 978-0684835501) has been responsible for changing the way that a Mars mission is viewed, moving it from an impossible and unaffordable dream, to an achievable and realistic goal. Now it needs to be put into operation.
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