Mars has always held a special fascination for anyone who looked up and wondered about the nature of that reddish star wandering through the night sky. The more we have learned about Mars, the more our longing to explore it has seemed to grow. It has been scrutinized by telescope for centuries, and in past decades has been visited by a host of robotic probes. We know more about Mars today than any other celestial object save our own Moon.
Yet what would it take to send humans to Mars? Most agree that we either already have the technical capability to do so, or that such technology will be available in the near future. But is it worth the cost and effort?
Mars offers a treasure trove of potential scientific discoveries and resources, many of which could justify a manned mission there.
LIFE: Probes sent to the red planet have pointed to Mars being a warmer, wetter world far in the far distant past. Tantalizing hints have also arisen that the world may have harbored microbial life in this ancient period, and there’s a small chance that some of that life may still survive in some hidden environmental niche on the planet. Its the search for evidence of this possible life that has driven many of the recent probes sent to the planet, first to look for the water and chemistry that could support life, and in turn to look for direct signs of that life itself. Astronauts sent to the world could conduct a more intensive and exhaustive search for such than any robotic probe, and settle the question once and for all.
PLANETOLOGY: Studying the geological history and chemical make-up of Mars could greatly facilitate not only our understanding of the greater solar system, but also how our own planet was formed and how it works. Astronauts on Mars could do research along these lines in a way that even an extensive series of probes could not.
HABITATION: Mars is thought to have one of the most friendly environments in the solar system as far as eventual human habitation is concerned. This is not to say that Mars has a pleasant environment, only that the planet harbors many of the right ingredients and conditions that could make a sustained human presence there possible with current or near-term technology. A manned mission could test many of the techniques and devices needed to make such a venture possible.
TECHNOLOGY: A flight to Mars would could also act as a test bed for space travel technologies that could take astronauts further into the solar system. Mars is the most obvious, and currently the most likely, target for any deep space voyage.
RESOURCES: Mars has an abundance of water and carbon dioxide that could allow a manned presence to flourish, giving future martians sources for breathing oxygen, hydrogen for fuel, and carbon for advanced building materials such as graphene. Mars is also rich in other mineral resources, and exploiting these could prove profitable once a transport infrastructure Earth and mars is established.
PHOBOS AND DEIMOS: The moons of Mars could offer not only valuable scientific knowledge, but could also act as staging bases for the exploration of the red planet as well as for excursions further out into space. At least several proposals have been floated that an initial manned mission to the planet shouldn’t bother with a full landing, and instead just explore the planet’s moons.
TERRAFORMATION: Mars is also considered to be the only world in the solar system that can be terraformed using ‘realistic’ (up through Tech Level 15) future technology and transformed into a world that would at least marginally resemble Earth. As such, it could be turned into humanity’s second long-term planetary home. Many enthusiasts and visionaries consider this to be the ultimate goal of any effort involving Mars, and would justify a manned mission as just the first of many excursions to fulfill this goal.
Many difficulties await any astronauts who would journey to the red planet.
DISTANCE: There is nothing between us and Mars. Millions upon millions of miles of nothing. Though not talked about very much publicly by mission planners and pundits, this is in reality the single biggest obstacle to any manned mission: the sheer vast distance to the fourth planet. Even at closest approach, Mars is over 34 million miles away--which is approximately 140 times farther than the Apollo astronauts traveled to the Moon, and subsequently the greatest distance humans have ever traveled from Earth.
A more realistic trajectory for a spacecraft, however, would have to encompass nearly 100 million miles not only cover the distance between the two worlds, but to curve around and catch up to Mars in its orbit around the sun. That’s over 400 times the distance the Apollo astronauts traveled.
To put it another way, if it took the Apollo capsule 3 days to each the Moon, at the same speed (over 100,000 miles a day) it would take over 1200 days to reach Mars--well over 3 years.
Astronauts crammed into an Apollo capsule, Space Shuttle, or any spacecraft past or present would long run out of supplies before they reached their destination. So in order to send humans there, one either has to think of a way to send them faster, using more powerful and advanced engines, or a way to keep them alive longer, with larger and much more robust habitat systems. Most approaches tend to use a combination of both.
The distance hurdle is even more daunting than most people realize. The spacecraft not only has to complete the most colossal journey any human has ever undertaken, but it must also carry all its own supplies, including water, food, air, fuel, tools, and replacement parts. Since there is no chance whatsoever for rescue or assistance once in deep space, it must be made as self-sufficient as possible. Recycling systems for food, water, and air must be as efficient as possible to save on possible mass. Astronauts must have the resources to be able to effect as many repairs on their own as they can.
Some proposals have suggested sending two or more ships flying in tandem in order to handle any unexpected problems, the thought being that if something went catastrophically wrong with one ship, the others could serve as back-up. Others have suggested making the ship unusually large and robust, like NASA’s proposed ISS-sized Nautilus-X, with room for multiple-redundant systems.
AIR: Obviously, no Mars mission would be able to support its crew on such a long journey with just bottled oxygen alone. Advanced air-recycling systems would be an absolute necessity, with near one hundred percent efficiency. However, no air recycling system has functioned for so long without resupply, and advances in such systems would be necessary. Once on Mars, however, the ship can restock itself from resources there, particularly oxygen cracked from Martian water.
CONSUMABLES: Water and food would also have to be recycled, and also with as much efficiency as possible. Water recycling is already fairly well advanced, with systems being tested out on the ISS. Food recycling, creating edible material from organic waste, lags considerably farther behind. Some have suggested that the habitat section of a Mars-bound ship should have a number of cultivated plants, perhaps even a dedicated hyrdoponics section, that would convert waste into food the old-fashioned natural way. Such plants would also help with water and air recycling as well.
RADIATION: One of the more insidious hazards of deep space travel is radiation, both from the Sun and cosmic sources. Heavy shielding would be necessary to help protect astronauts and equipment from this hazard. In addition to more traditional spacecraft shielding, water tanks may be made thin and cylindrical, hugging the outer bulkhead to act as an additional layer of protection. The Mars spacecraft could also take advantage of emerging technologies such as Electromagnetic Shields and Plasma Shields, which are explained more fully in articles linked to at the bottom of this page.
THERMAL REGULATION: One of the more less-publicized potential problems, but significant nonetheless. Spacecraft in Earth orbit have to contend with surface heating on the sunward side that can reach hundreds of degrees, and sub-zero freezing temperatures in their shadows. As a vacuum has no heat convection, this temperature variation can occur within inches of each other, and can lead to both material warping and internal damage if not carefully regulated. Any Mars craft would have to have a smart and robust thermal regulation system, able to adapt itself to a number of conditions, especially if it incorporates any kind of spin gravity system.
IMPACTS: The spacecraft would have to be thickly armored to protect against potential micrometeoroid impacts. In order to reach the fourth planet in any reasonable time frame, the craft would be travelling so fast that impact with even dust-sized grains could wear away the hull and damage structures, especially over months of travel time. The spaceship would have to be heavily armored beyond just the needs of radiation protection, and streamlining the bow of the craft to minimize potential impact damage would also be a plus.
GRAVITY: Lack of gravity for long periods of time can lead to a number of potential medical problems for astronauts. Rigorous exercise and fitness routines can help to minimize this a great deal, but doesn’t eliminate the problem altogether. In order to keep explorers healthy while being exposed to many long months of microgravity, a Mars-bound ship may be equipped to simulate gravity with a spin habitat.
There are several approaches to this. Habitats could be built as pods and set on the end of counter-balanced tethers or booms, and spun like a space-going carnival ride. A ship may also have a full ring habitat, which would also be spun about the ship’s main axis. Finally, the entire habitat portion of the ship can be built as a cylinder and spun.
In order to avoid vertigo, the spin habitats have to be at least 15 meters or so in radius, which is very large as modern and near-future spaceships go. The tether approach is usually cited for a near-term Mars mission, if the artificial gravity angle is considered at all, because it would mass a lot less than other options. Plans for the Nautilus-X, NASA’s proposed deep-space vessel, would have an inflatable ring attached to the main habitat. However, to avoid progressional instability (torque) problems, spaceships with spin habitats would have to be equipped either with a second spin module/ring/cylinder rotating in the other direction, or high speed internal flywheels which would perform the same function.
PSYCHOLOGY: Much has been made over the years of the potential isolation and psychological stress the crew of a Mars should would likely undergo. Estimates of travel time for a Mars mission vary depending on a number of factors, but are usually given at eighteen months to two and a half years. That is a very long time to be cooped up in a relatively small space, in the deeps of the most hostile environment known to man, with the same people for months on end. Psychological breakdowns on such voyages have been gristle for many science fiction stories, and the danger is not a small one. Ongoing studies on isolation have been done over the years, and a number of fixes have been suggested for it, including sending married couples, incorporating cultivated plants in the ship design (which would have other benefits), equipping the ship with extensive virtual reality capabilities, and so on.
Exactly how humans will get to Mars, and how fast, will depend greatly on the propulsion system chosen for the task. A number of possibilities are discussed below. Links to articles with more detailed discussion on these technologies is included at the bottom of this page.
It is assumed that any expedition to Mars would use the advantageous trajectories that open up every two years as Earth catches up to Mars in its orbit. That means that after reaching the red planet, astronauts would have to remain on the world for something like 18 months before they could return to Earth.
All theoretical travel times given below are very broad estimates taken from various sources.
CHEMICAL ROCKETS: Many of the earlier proposals for Mars missions discussed using chemical propulsion. The major problem with this technology is that, while well proven, its very fuel inefficient. Carrying all the fuel necessary for the mission to Mars and back was often considered too cost prohibitive. However, the prospect of manufacturing fuel on-site on the red planet has helped to change this equation. An expedition would only have to carry enough fuel for a one-way trip, then resupply once at Mars from an automated fuel-cracking station.
With chemical rockets, travel time to Mars one way is often quoted at around six to nine months, but is sometimes longer.
ION ROCKETS: These low-acceleration engines don’t have the oomph of chemical rockets, but are very fuel efficient, and over long period of continual firing (a feat chemical rockets aren’t capable of) can often obtain much greater velocities. Ion rockets using xenon as propellant and powered by nuclear reactors or large solar power arrays were mentioned in at least two expedition proposals. Proposed travel times with ion rockets tended to be longer than with most other types of propulsion, from nine to twelve months or even longer one-way.
PLASMA ROCKETS: This is the current favorite of many space exploration pundits and planners after chemical rockets, in the form of the VASIMR engine, which compresses and superheats fuel with the use of powerful magnetic fields. The VASIMR engine would not only be much more fuel efficient, but much faster than any chemical rocket could manage. Travel time to Mars using VASIMR has been estimate to be about 90 days, with some estimates giving as little as 39 days.
FISSION ROCKETS: Manned Mars mission proposals occasionally mention old fission rockets schemes such as NERVA, which heated hydrogen fuel by pushing it through a hot reactor bed. NERVA rocket engines would have both greater fuel efficiency and thrust than chemical rockets, and could make it to Mars anywhere from three to six months, depending on the sophistication and efficiency of the drive. More advanced and powerful fission rockets, such as a gas-core model, could cut that even further.
NUCLEAR PULSE DRIVES: The old Orion Project scheme that envisioned using small nuclear detonations to repeatedly push a spacecraft through deep space. Though the drive would be expensive and controversial in the current political climate, many propulsion experts contend that it would be not only workable but extremely powerful as far as acceleration and endurance. An efficient nuclear pulse drive could theoretically get a crew to Mars in as little as thirty to sixty days.
SOLAR SAILS: Extremely fuel efficient, as in needing no fuel. However acceleration, while constant, would be excruciatingly slow, and estimates of a solar sail reaching Mars can vary up to three years of total travel time. Very impractical for a manned mission. However, they could be used as an economical means to ferry needed equipment to Mars ahead of a manned mission.
VERY ADVANCED PROPULSION: These would include fusion rockets, antimatter rockets, and even more advanced and exotic propulsion schemes discussed in the Deep Space Propulsion section. If the first manned mission to Mars waits until these powerful space technologies are developed, travel time to Mars could be measured in mere weeks.
While advanced propulsion technology is considered a necessity for any practical approach to sending humans to Mars, of equal importance are all the systems that are needed to keep them alive, healthy, and productive along the way. This encompasses a very large array of different disciplines.
In many ways, habitat technology more important to a mission like this than propulsion technology. If a habitat is sufficiently large, robust, and advanced enough to keep explorers alive and functioning for long periods of time, trip length to and from Mars will matter a lot less.
No space habitat system has ever been put to the test of long term isolation away from Earth-based back-up and resupply. The ISS points the way to how it can be done, but isn't yet at that level itself.
The major systems and features would include:
SIZE: One criteria often discussed beyond the essentials for survival would be how large the ship's habitat should be. Proposals have varied from having two Orion capsules linked together (giving the crew about as much space as two joined minivans) to a large ship like the Nautilus-X to the immense, sleek, streamlined craft of science fiction. Smaller ships would be much more economical, both in building fuel costs, but the confined space and lack of redundant systems could put quite a strain on the crew. Larger ships would be more expensive, but would offer the crew much more protection and options in case of emergency, and would also be able to carry more payload and experiments.
POWER: Currently most mission plans call for the vessel to have a nuclear-powered engine, which would at least partially provide for the ship's other systems. A separate nuclear plant may also be included for general power. Modular deployable solar panels are also in almost all mission plans, as are advanced batteries that could run the ship essentials for days or even weeks if necessary on their own. Other possibilities could include solar thermal arrays, which would use mirrors to focus heat on closed-system steam turbines.
MANEUVERING: Thrusters would likely be a separate from the main propulsion system. The current norm in maneuvering thrusters are chemical rockets, but could also take the form of resistojets (steam rockets), ion rockets, small plasma rockets, and more.
SHEILDING: Besides the standard multiple-layer hull shielding against radiation and impacts and thermal extremes, the ship may also use some secondary systems to help build additional barriers between the astronauts and outside hazards. The expedition would carry their water supply in the form of ice, which is easier to handle and store than the liquid form of water. This could be held in shallow, wide tanks hugging the outside of the hull, acting like an additional layer of armor plating in some places. Liquid fuels could also be stored in such a manner. Deployable solar panels could also be designed to be used as directional shields, providing additional cover for the craft, especially in the case of solar storms.
The ship may also take advantage of emerging active electromagnetic shielding technology and plasma shields.
THERMAL REGULATION: Some types of propulsion, such as nuclear rockets or VASIMR plasma rockets, produce vast amounts of heat when firing, so much so that cooling vanes may be needed to prevent this excess heat from melting down the engine or damaging the rest of the ship. They could be designed to be folded down against the hull of the ship while the vessel is coasting, providing an additional layer of shielding.
COMMUNICATIONS: One or more standard large transceiver antennae, like those found on most interplanetary probes, would handle most communications with Earth. Some speculative fiction works have posited somewhat more exotic communications systems between planets, such as laser or meson communicators.
ATMOSPHERE: The ISS currently gets its oxygen from cracking water ice. While this is a proven method and would likely be used in a Mars-bound ship to replenish air lost through general use, the cost of hauling all the ice needed solely to provide air for such a long trip could prove prohibitive. Inevitably, the ship would need a closed air recycling systems that would need to be as close to 100% efficient as possible. While great strides have been made in this direction, no space-bound habitat has yet been able to function that long without getting resupplied from Earth.
It is possible that they could at least partially resupply once they reach Mars and can extract resources from the surface, especially from subsurface ice. Resupply ships could also be sent ahead of the main ship to rendezvous with it at strategic points in its voyage.
Depending on the ship's size and available room, it could also carry a good supply of green plants to help with both air and water recycling. These plants would likely be low-maintenance and hydroponically grown where possible, to save on space.
WATER: Like with the air, the water recycling system on board would have to be as efficient as possible to stretch out the supply throughout the long voyage. These kinds of systems seem to be much further along at present than air recycling systems, at least as far as being able to last in a closed system for eighteen months to three years or more. Yes, that would mean that the astronauts would inevitably have to drink and wash with water in part extracted from their own urine.
Extra water would be stored as ice, and would be fed into the system as water in the system is lost. As mentioned above, green plants may be included in the ship if the design and space allows, aiding in water filtration and recycling.
FOOD: One type of recycling not mentioned for any mission so far is food and solid waste recycling, probably because such systems that currently exist are fairly inefficient and do not yield acceptably palatable results. All the meals the astronauts would need would be prepackaged and stored aboard before the mission is even launched. What food on board plants may provide would actually be negligible and would be there mostly for morale purposes.
WASTE: Recycling systems are never completely 100% efficient, and some of what is recycled (water, air) is inevitably lost due to various factors. On the ISS, the end result of air and water recycling yields worn filters beyond reuse and a chemically-laden sludge that has to be disposed of. And Mars vessel would also run into this limitation, and would have to deal with both unrecyclables and solid waste in some way. On the trip between worlds, its unlikely that the waste would just be carelessly dumped out an airlock, for fear of it creating a navigational hazard for the ship (it would be traveling at the same velocity and direction as the spacecraft.) Rather, they'd save it for orbit around Earth or Mars, where they can jettison it into an orbit where the waste is guaranteed to burn up upon re-entry.
Once they actually reach Mars, what are our explorers expected to do?
Where to land would have been determined long before the expedition ship is even assembled. The site would likely be chosen as much for ease of landing and getting the astronauts down safely than for pure scientific interest, such as a wide open plain or a very large crater. It would also likely be scouted out by a robotic lander or rover beforehand as well. Only after landing techniques are proven would they send expeditions further afield to more risky but scientifically fertile locations, such as to martian highlands or one of the poles.
First and foremost, the astronauts would have to set things up on the surface to facilitate their own survival on the planet. Unless they're using very advanced and speedy propulsion, they will have to wait things out until the orbital positions of the planets realign to facilitate an optimal trajectory back to Earth. Depending on various factors, the period on-planet is generally assumed to last anywhere from three to eighteen months.
Their lander would be able to function as a habitat for them for a while, but may not be designed to endure as such for their entire stay on the planet. Their first order of business would be constructing a more durable habitat.
The size and character of this habitat may vary from mission plan to mission plan greatly depending on length of stay, size of the landing party, available technology, whether it could be sent ahead of the main expedition and assembled via robot, and more. Most modern visions usually have a main inflatable habitat module, mostly pre-assembled and brought from Earth, with supplementary buildings being assembled from prefabricated materials and kits as needed. The buildings and the lander would all be clustered closely together and may be connected by special inflatable tunnels, to give the astronauts easy access to each without having to don excursion suits. A separate article detailing martian bases will address what necessities such a habitat would have to include.
Simultaneous to setting up that first habitat will be setting up its power supply. Like the habitat itself, it could either have been brought along by the main expedition or been sent on ahead and be waiting for the astronauts when they land. A compact nuclear fission plant or a wide array of advanced solar cells or a combination of the two would likely be the habitat's main source of power.
Most modern schemes call for the expedition to include a fuel production station, that would combine an onboard supply of hyrdogen with the carbon dioxide in the atmosphere to produce methane. Alternately, the hydrogen could also be cracked from martian permafrost. One of the explorers' first priorities would be to get this fuel plant working or, if was sent ahead of the expedition, to secure it and its fuel. After all, without it, their chances of returning home would look pretty dim.
Other initial necessities may include the mining of permafrost to replenish their water supply, or setting up a hydroponics facility to supplement the water and air recycling.
Only after the essentials for long-term survival were established would the expedition be able to focus more completely on the science for the duration of their stay. Investigations into the Martian soil and geology and weather and possibilities of ancient life could be conducted on a much more extensive scale with humans on the spot than with remote landers and rovers. Between tending experiments, expeditions to nearby spots of interest, and maintaining the base and all its systems, the astronauts' time on the red planet would likely be quite full and active for their entire stay.
At least one scheme for a Mars expedition posited using the base set up by the first expedition to help supplement that by a second expedition, which would land in the same spot. The second expedition would also include a habitat module and other supplementary buildings to be assembled, and would add them to the cluster from the first expedition. A third expedition would do the same, and so on, slowly building up a true outpost on the red planet that would eventually be able to handle much larger number of astronauts.
The following are the more notable schemes for sending astronauts to the Red Planet that have been proposed by various space agencies and experts over the years.
INTERNATIONAL COOPERATION: One of the primary features of many recent Mars exploration proposals is that the mission be a joint venture among the prominent space faring nations. These usually include the US and Russia, but some visions also include the Europeans, Chinese, Japanese participating. This would not just be a political and public relations consideration. The countries taking part can share resources, technology, and help to mitigate the cost to any one participating member.
PRELIMINARY MISSIONS: Many proposals posit sending missions first to the Moon or to nearby asteroids, not only for the scientific value of such missions in their own right, but to test technologies and techniques for eventually sending astronauts to Mars. If this path is chosen, the road to Mars may prove to be quite circuitous, as the agencies involved first concentrate on these nearby targets. Each would likely consume at least a decade of development and planning on their own. Mars espeditions would commence only after at least the first such missions are carried out, delaying that first manned voyage to the red planet by decades longer than need be otherwise.
However, this would also likely would be the surest and safest means of ultimately staging a Mars mission, as most of the needed technology would not only be fully developed but field tested as well.
THE VON BRAUN PROPOSAL: Wernher von Braun was the first to create a detailed technical study of a mission to Mars in the late 1940s and 50s, most famously condensed into a series of articles of Collier's magazine in 1952. This scheme featured over 400 launches to assemble ten spacecraft in Earth orbit, intended to carry a total of 70 astronauts to the red planet. In 1956 he scaled down his plan to a two-ship, 12-crew mission, and in the 1960s he revised it again to take advantage of then-off-the-shelf technology such as the Saturn V launch vehicle.
COLD WAR SCHEMES: Both the US and the USSR fielded speculative studies about sending explorers to Mars during the 60s and 70s. The most prominent US version posited using eight Saturn-V launches to assemble a Mars ship in low Earth orbit. The Soviet plan, in preliminary development until 1971, was to use a single launch to place a craft in low earth orbit, with separate launches to bring it fuel and crew. The USSR Mars ship would not have touched down on Mars, but rather would have been a three-year flyby mission to deliver probes.
THE CASE FOR MARS: A series of conferences held thought out the 1980s and into the mid-90s, the plans featured updates of the earlier US Cold War Era scheme. These conferences were significant in that they introduced in situ resource utilization as a viable strategy, particularly the idea of manufacturing fuel for the return trip on-planet. It also advocated a return to the Moon and expeditions to nearby asteroids as preliminary steps to going to Mars.
MARS DIRECT: A proposal by Robert Zubrin and David A. Baker, whose main feature was in stripping down the mission parameters, particularly crew and payload mass, to the bare minimum and to utilize resources on Mars to manufacture fuel for the return voyage. This was all meant to reduce costs as much as possible and make such a mission more attractive to both Congress and the public at large. A main feature of the plan was to send an Earth Return Vehicle (ERV) and fuel-production station ahead of a manned mission, where they would be waiting for the human explorers when they landed over a year later. The manned expedition would carry its own ERV but use the one already waiting for it on the surface, with theirs ready to use for the next epedition. This would be repeated for all subsequent missions, to provide the safety feature of always having a back-up ERV in case of emergency. Updated versions of this plan are still backed by the civilian space advocacy group the Mars Society.
NASA DESIGN REFERENCE MISSIONS: From the 1990s onward, NASA on an almost annual basis creates a new "reference" mission plan while consulting its many different field offices and divisions. The idea is to use the premise of a manned mission to Mars to explore alternative approaches and innovations. These can save money and increase the performance and efficiency of not just an eventual Mars expedition, but the ideas propagated during these brainstorming conferences can be applied to other missions and endeavors as well. Some of the later DRM mission proposal have included using Ares launch vehicles and Orion space capsules joined together as part of the mission plan.
MARPOST: Short for Mars Piloted Orbital Station, this was a Russian proposal from 2000, using technologies developed for the International Space Station and a nuclear reactor to power an electrical ion engine as the primary means of propulsion. Designed at the time to be the next step for Russia after the ISS's completion, the plans were to be finalized by 2012, and the ship itself to be completed in 2021. It was later re-envisioned as a reusable interplanetary exploration craft, and may have been the conceptual precursor to NASA's proposed Nautilus-X vehicle.
MARS TO STAY: A radical shift in strategy, backed by, among others, Apollo 11 astronaut Buzz Aldrin. This posits that any astronauts sent to Mars should be sent there to stay permanently, with each mission being outfitted extensively to be as self-sufficient as long as possible, and frequent follow-up missions from Earth sending fresh supplies and crew as needed. The idea is to not waste a single resource on anything but what many see as the most important long-range goal for Mars exploration, namely establishing a permanent manned presence on fourth planet. The strategy of using an initial ever-expanding base built from landers and inflatable habitats would probably form the core of this scheme.
GENERAL MARS EXPLORATION
POSSIBLE LANDING SITES