HIGH-PRIORITY OR LOW-PRIORITY, getting to Mars presents major technical challenges. Not only do we need the Orion launch vehicle, we also need a spacecraft capable of supporting astronauts in reasonable comfort during a nine-month-long flight. Then we need to land them on Mars, preferably without broken bones.
Currently, the easiest way to land small probes on Mars is to use air resistance to brake them from interplanetary speed high above the surface, then parachute down using airbags to protect against the thump of landing. This has worked fine for small probes, such as the current Mars rovers. However, with a bigger ship, we can still use the atmosphere for the first step (as we do on Earth for space shuttle descents), but parachutes and airbags alone aren't going to cut it to get us safely down: the atmosphere is just too thin. That probably means we're going to need rockets – and everything we're 'probably' going to need adds unwanted kilos to the spacecraft, which means many more kilos of fuel to get it there, and potentially back again.
But there might be a way to minimise all the heavy lifting. It's a bold plan called 'Mars Direct', championed by the lobby group, Mars Society, and its vocal leader, Robert Zubrin.
Mars Direct means just that: skip the Moon and go straight for the end zone. Furthermore, while many plans for a journey to Mars require a monstrous ship to carry all the required fuel, components and crew – a ship that is so large and complex it would need to be assembled in space – Mars Direct does away with this requirement in a most ingenious way. It does this by splitting the mission across two ships – both of which are kept to a minimum in size, weight and cost by foregoing the fuel necessary for the return trip.
Whoa. But this isn't a one-way mission. No problem, because we're not travelling to a total wasteland; Mars has ample indigenous resources which would allow you to brew your own fuel. "Shipping rocket fuel to Mars is like shipping oil to Saudi Arabia," Zubrin says. "In fact, it's crazier because it's much more expensive to ship rocket fuel to Mars."
The first phase of the mission consists of a robotic craft. It can be launched on a booster comparable to the old Saturn V, and carries the astronauts' return vehicle plus a small nuclear reactor. Once safely on the ground, it sends out a robotic rover, which deploys the nuclear reactor behind a hill, or a pile of rocks – anything that can provide rudimentary radiation shielding. An electrical cable then connects the reactor to the lander. The reactor then fires itself up – and the ship uses the electricity to manufacture rocket fuel by combining hydrogen carried from Earth with carbon dioxide extracted from the Martian atmosphere. The result could be thought of as a sort of nuclear-powered spaceship: the fuel simply serves as a battery to store a year's worth of accumulated nuclear energy.
More importantly, Zubrin says, you get 18 tonnes of rocket fuel for each tonne of hydrogen carried from Earth – a huge advantage since fuel for the return journey is a large fraction of the mass of a conventional carry-everything-with-you mission.
By the time the next Earth-to-Mars launch window opens, two years after the first ship departed, the return vehicle is fuelled and raring to go. Only now do the astronauts launch, again on a relatively small booster. "You don't need a Battlestar Galactica spaceship because the return ride is waiting for you on Mars," Zubrin says.
At the same time, another self-fuelling return vehicle is launched separately, so it can be preparing for a subsequent mission while the astronauts are still on the first.
HOWEVER, NOT EVERYBODY is on-board with Zubrin's vision. Hubbard thinks it's too risky. "I like Bob and applaud his enthusiasm," he says. But, "I think Mars Direct is a bridge too far…Bob's scenario piles a lot of what-if statements on top of each other."
He compares it to climbing Mount Everest without oxygen. We now know this is possible, but Sir Edmund Hillary took bottled gas. "There's taking risk, and taking foolish risk," Hubbard says. If nothing else, he'd like to see the Mars Direct approach tested first, with an unmanned probe, possibly on a sample-return mission. "That sets the stage for knowing what's reasonable."
Even some former Mars Direct believers have re-thought the scheme. One is NASA's Chris McKay. He still thinks Zubrin's self-fuelling lander might be the way to go when the time arrives, but he's reluctantly come to the conclusion that bypassing the Moon just doesn't work unless our only goal is a prove-we-can-do-it 'sprint' mission. If we're going to do more than touch down, look around, and say "far out," he's decided, we can't afford to bypass the Moon.
McKay and others have a whole shopping list of things that need to be done before astronauts will be prepared to leave their boot tracks in Martian dust. One is the boots themselves – and the spacesuits to which they're attached. We need spacesuits we can "wear like coats," he says, day after month after year: something a lot more manageable than the motion-hampering monstrosities of the Apollo era.
Another problem is the dust. Moon dust is nasty stuff, smelling like spent gunpowder, says Harrison Schmitt, one of the last Apollo astronauts, who had to breath it in each time he came back into his lander. Not only are there potential health dangers, but the fine grains also penetrate like graphite lubricant – though of course they don't exactly lubricate. "You have to protect moving parts," he says.
Steven Squyres, principal investigator for NASA's tremendously successful Mars Exploration Rover mission, has noticed the same thing on the Red Planet. "The dust is incredibly fine-grained," he says. "It's clingy stuff that's going to get into everything."
Luckily, it carries a static charge (that's what makes it so clingy), which means it should be possible to develop an electrostatic vacuum cleaner to get rid of it. Thus armed, Moon and Mars dwellers will simply have to be meticulous about dusting themselves off before going indoors. "You learn that in kindergarten," says McKay. "I don't think it will be a fundamental problem."
The durability of rovers is another issue. The timing of launch windows gives astronauts 18 months on the Red Planet before they can return. They're going to want a well-tested and robust rover that's guaranteed to not break down and leave them high, dry and immobile (perhaps something like the MarsCruiserOne, Cosmos 16, p32).
And on a more mundane level: they need a workable, portable drill for taking core samples and looking for fossils and water. "Harrison Schmitt tried to operate a two-metre drill on the Moon and ran into serious problems doing it with a spacesuit," McKay says.
And the list goes on. "I think we're looking at 20 years on the Moon before we have all those things in hand," McKay says.
