How will landing on Mars work?

The challenges of a Mars landing are numerous, although researchers are planning and working hard to figure out exactly how we'll pull it off. Assuming people are able to arrive in the vicinity of Mars, there are a few elements to consider when it comes to landing. Scientists and engineers are already throwing around different processes and design ideas. Considerations are being given to the shape of the vehicle, the type of fuel it will use, the location of its engines and the size of its payload. Another question is whether propulsive maneuvers, performed in the form of short thruster burns, will be accompanied by parachutes during landing. There is also the issue of how best to accommodate astronauts during interplanetary missions ... the list goes on.

One of the main issues with landing humans on Mars is figuring out how to slow down so the vehicle landing doesn't smash into the ground. The problem is Mars' thin atmosphere. This issue doesn't affect the Mars rovers' landings because those machines are lightweight. If humans land on Mars, they'll need to bring quite a bit of luggage and, without a dense atmosphere to provide friction, it'll be very difficult to slow this heavier payload.

The way friction helps slow moving objects can be seen in your everyday life. For example, think of a time when you saw a driver slam on his brakes to come to a stop quickly. Also, airplanes -- much like spacecraft -- use the air's friction to decrease speeds and land safely.

The landing situation is further complicated by other factors affecting the density of Mars' atmosphere. The season, weather, latitude and even the time of day can change the atmosphere's density. For example, almost 8 million metric tons of carbon dioxide leaves and re-enters Mars' atmosphere seasonally. That's comparable to nine inches (23 centimeters) of dry ice (solid carbon dioxide) [source: Encyclopaedia Brittanica]. Researchers are working on modeling Mars' atmospheric changes so the astronauts can land within a sufficiently dense portion that still provides enough visibility. Planners are considering whether the arriving spacecraft should immediately proceed to the surface (possibly easier from an operational standpoint), or park in orbit before landing. Parking in orbit gives the astronauts more flexibility in case a dust storm strikes, similar to when airplanes circle the airport in bad weather.

Now that we've had a look at some of the challenges that mission planners face, let's look at some of the possible solutions that are being tossed around on the next page.

Landing on Mars isn't going to be a walk in the park, but it also might not be as tricky as first thought. Although ideas are still being hammered out, here are some details of what a prospective mission plan to Mars could entail.

Planners must decide if the landing should be done in stages, by sending payloads down separately, or all at once. Landing a large mass could probably be achieved, but astronauts might be restricted to landing on portions of the planet with low elevations, and they might be able to carry only a small amount of supplies for a short visit of limited scope.

One idea put forth by aerospace expert Robert Zubrin in his book, "The Case for Mars" involves sending a cargo-carrying spacecraft prior to the habitat spacecraft that contains the human crew. This cargo vehicle could provide enough supplies to increase the length of the astronauts' stay and already be fueled and ready for the return trip (discussed below). The astronauts can leave the habitat spacecraft they originally arrived in behind, in order to begin the development of an infrastructure on Mars.

The key to Zubrin's plan is that the fuel for the return voyage is manufactured on Mars. The atmosphere of Mars (unlike the moon's) has an abundance of carbon dioxide that may come in handy to future astronauts. For example, by mixing about six metric tons of hydrogen (a surplus of hydrogen could be taken aboard for this reason) with carbon dioxide, a chemical processor could create enough methane and oxygen to propel the vehicle during liftoff and the trip back to Earth. From these same basic building blocks, the processor could also generate the oxygen, water and fuel our astronauts would require during an extended stay on Mars, as well as the flight home, saving outbound cargo space.

Planners are also studying whether to leave a portion of the spacecraft in orbit, or bring it all down to the surface. But knowing the spacecraft (what remains of the original that blasted off from Earth) is able to land on Mars is an important factor in the mission plan's design. That remaining portion is sometimes referred to as the Earth return vehicle (ERV), and it's what astronauts would use to eventually travel back to Earth. Being able to land the entire ERV -- as opposed to just a lander -- could allow for longer visits and avoid complications related to complex orbital maneuvers [source: Zubrin]. But these sorts of technical decisions are still being debated.

It looks like we're ready to descend to the surface, so let's take a closer look at what we're riding in. Currently, a spacecraft heading toward Mars is slated to resemble the old Apollo program -- along the lines of the new Constellation program, which is planned to take humans back to the moon.

The ERV (or whatever portion of the spacecraft will be landing) will likely end up looking a bit like a gumdrop. A large, dish-shaped aeroshell (or heat shield) will help increase the amount of friction created when the craft cuts into the atmosphere, thus slowing it down [source: Zubrin].

A likely scenario is that after the craft makes an initial pass through the atmosphere to reduce its speed, it returns to an orbital position. At the selected time, the aeroshell is again employed -- possibly with a parachute -- to make the final pass through the atmosphere toward Mars' surface. Small thrusters can then be fired to ensure a smooth landing. To learn more about landing maneuvers, read How Space Shuttles Work.

­Now that we've examined some of the unknown aspects surrounding a Mars landing, let's discuss the other questions about the mission.

Manned missions are still a long way off as many of the details of landing on Mars must be addressed. The U.S. plan is to return to the moon by 2020 and eventually build a permanent base there. Estimates on when we'll take that next step and journey to Mars are tentative. According to the British National Space Centre, the goal is for an international cooperative effort to launch astronauts to Mars by 2030.

The price tag for sending humans to Mars will vary greatly depending on the final spacecraft and mission plan design. Utilizing technology similar to what's already been developed helps keep costs more manageable. For example, the Constellation rockets are based on the Saturn Vs, making use of some design elements of the Space Shuttle program. Another money saver that might be employed is making use of the Martian atmosphere to generate fuel, oxygen and water (like we read about on the previous page).

There is the possibility that preliminary voyages could send people into Mars' orbit without actually setting down on the surface, although many in the field argue it's pointless to explore if you're not going to get up close and personal with the surface of the planet. It's like driving to the beach and spending the whole afternoon watching the ocean from your car. This could, however, help fix some of the kinks of long-distance space travel and enable explorers to receive real-time reports from robots on the surface of the planet, without the risk and cost of a landing. Robotic vehicles that can return from Mars with samples are also in the works.

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Alas, once the dust has settled around the landed spacecraft and astronauts can take those first incredible steps onto Mars' surface, they also open a whole new can of worms for scientists to solve -- mainly, how will the astronauts survive the harsh and uncompromising Martian climate, and how will they spend their time while they're there? We'll save those questions for another day.

For more information about Mars and the future of space exploration, visit the links on the next page. ­

It makes me sad that in the time since I wrote this article, the Shuttle Program has ended and the Constellation Program has been cancelled. Public and private space exploration is a constantly shifting field of diverse international players, but it's my hope that others will pick the mantle of taking us back to the moon and on to Mars.

I loved writing this article, and reading Robert Zubrin's book in particular. Many people have proposed ways we could conduct manned interplanetary missions, but Zubrin's strategy seemed to me the most elegant and practical. His plan involves using the resources of the Red Planet to fuel a sequence of manned and unmanned missions to build an infrastructure that would allow us to truly explore our celestial neighbor firsthand, while at the same time creating a redundancy in case any equipment or spacecraft malfunctioned.

Sources

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