As part of my ongoing interest and fascination with proposed manned missions to Mars, I finally made my way through Robert Zubrin’s ‘The Case for Mars’. In it, he outlines a plan for a mission called Mars Direct. Coming from the Mars Society, of which Zubrin is president, the mission outlines how we can get astronauts to Mars armed with everything they need for the journey, including a spare return vehicle. The plan was first proposed in the late 1980s; Zubrin’s ‘The Case for Mars’ was first published in 1996. In recent years, the Mars Society has become more forceful in its attempts to see Mars Direct (literally) take off. Zubrin has gone so far as to declare that we are now more prepared to go to Mars than we were to go to the Moon in 1961 when Kennedy pledged the nation to a landing on its surface. I’m not sure I agree. (An artist’s concept of a multi-manned mission after landing on Mars.)
The Mars Direct program gets its name because the project skips a trial run on the Moon. In the wake of Apollo, part of the Apollo Applications Program was the establishment of a manned base on the moon for both continued scientific research as well as a jumping off point for missions to Mars. Recent proposals have taken the same path, testing a crew and all its support systems – environmental, physiological, and psychological – on the Moon where if anything were to go wrong the astronauts could be home in three days. (An artist’s concept of a crew training for a tenure on Mars on the Moon.)
The Mars Society has negated this need by conducting field tests in Mars-like environments on Earth. Specifically, the desert in Utah and the upper Canadian North. In these studies, volunteer ‘astronauts’ spend a period of time living and working as though on Mars. They live and work in the modest crew quarters Mars Direct would send to Mars, only go outside in full simulated pressure suits, conduct field tests, and communicate with ‘mission control’ in Colorado with a 20 minute time delay – the delay of radio communications between Mars and Earth. They also live on a schedule of Martian days called sols, which are 39 minutes longer than days on Earth.
Through field testing, the Mars Society was able to determine what types of crews should be sent to Mars (two mechanics and two field scientists) and what exactly they would need to survive the journey. With strict rationing, a fully stocked and sustainable spacecraft doubling as a habitat is ready to be sent to Mars.
To get to the red planet, the Mars Society proposes launching for Mars when the planets are in conjunction – a time in orbit when Mars and Earth lie on opposite sides of the sun.. This position of conjunction is actually the furthest the two planets get from one another. It was a term first used when the Earth was thought to be central to the solar system, so from an Earth-centred position, the Sun and Mars were in conjunction. (Pictured, a schematic of celestial alignment that results in Mars and Earth being in conjunction at their furthest points from one another.)
Launching at this point in the Earth’s orbit relative to Mars gives a departing spacecraft an extra boost. Not only does it have the momentum from launch, it also has the momentum of the Earth’s orbit. This puts the spacecraft into an elliptical orbit that intersects both Earth and Mars. With a few minor mid-course corrections, the journey to Mars is extremely fuel-efficient.
Conjunction happens roughly once every two years, so the Mars Direct plans calls for a launch every time this alignment presents a favourable launch window. The first launch will send a single Earth Return Vehicle or ERV. The unit’s main cargo is a store of methane. Once on the surface, a pump system sucks Martian atmosphere, which is largely carbon dioxide, into the ERV. The subsequent reaction between the carbon dioxide and the methane produce oxygen, water, and hydrogen. This provides the ERV with fuel. Before the astronauts even get there, a rocket is ready and waiting to take them home.
Two years later, the next launch window will see two spacecraft sent to Mars – a second ERV and a habitat module, complete with residents. Both vehicles will land on Mars at the same point as the first ERV 180 days after launch. If, by chance, the crew misses the landing point, they can drive one of the five rovers they brought with them to the first ERV. (An artist’s concept of a crew on Mars with multiple habitats.)
The second ERV undergoes the same process to derive rocket fuel from the Martian atmosphere, providing the astronauts with a backup way home in case one ERV fails. The crew will have 550 Earth-days on the surface before the planets are properly aligned for the reverse trajectory to take them home. When the crew leaves, they will leave behind one of the fueled ERVs and the habitat module. The next crew to arrive will thus have a larger base already set up with the leftover crew module, the leftover ERV, and the habitat module they flew with.
Eventually, after a decade or so of the same missions, astronauts will have the beginnings of a colony set up. There will be sufficient space to house a much larger crew and more resources available for the astronauts. Future missions will be able to stay longer and begin trying to live off the land.
The Mars Direct plan was first considered by NASA in 1989 after President Bush tried to spark a Mars program on the 20th anniversary of Apollo 11’s landing on the moon. Issues of feasibility with 1980s technology aside, the proposal was deemed prohibitively expensive. The program was predicted to cost in the vicinity of $450 billion. To put that in perspective: NASA spent $25 billion on the Apollo program between 1962 and 1972. Adjusted for inflation, that puts Apollo close to $171 billion. The proposed Mars Direct price tag adjusted for inflation comes out to around $781 billion. (An artist’s concept of a mission launching from Mars for Earth.)
In recent years, the Mars Society has adjusted the program’s cost to reflect technological advances. The price per launch is now estimated to be one-quarter the cost of a $450 million Shuttle launch – $112.5 million per launch. In comparison with the Shuttle, this is appealing. For a quarter the cost we can get a lot more bang for our buck.
The proposal not only sounds doable, it sounds easy. The grunt work of planning the route to Mars, what to take, who to send, and how to keep them alive has been done. There are certain redundancies like the backup ERVs to ensure crew safety. The cost per launch is not outlandish for NASA’s current position. But there’s one glaring oversight. The proposal doesn’t mention how any pieces of the Mars Direct will land on the red planet. It is described vaguely as being entirely automated using a combination of aerobraking and retrorockets.
The mission’s landing system is likely glossed over because the Mars Society doesn’t know how to land on Mars. The fact is, no one knows how to land a manned spacecraft on Mars.
Mars is not an easy planet to land on, and none of the landings methods that have delivered landers and rovers to its surface are viable for Mars Direct. Previous missions have used a combination of three means. First, aerobraking that uses the Martian atmosphere to slow a falling spacecraft. The second is retrorockets that produce thrust opposite the spacecraft’s fall to slow its descent. Third is airbags that form a protective cocoon around a spacecraft allowing it to bounce and roll before coming to a stop on the Martian surface. (An artist’s concept of the Mars Pathfinder Lander – carrying Rover Sojourner – as it lands and bounces off the surface on its airbags.)
Mars Direct’s main problem, and indeed the problem with any Mars mission at this point, is weight. None of these methods work for a payload heavier than the Mars Exploration Rovers Spirit and Opportunity. This is why the upcoming Mars Science Laboratory is using the Sky Crane system. It is a possible solution to the problem of heavy payloads reaching Mars intact.
It turns out that landing on Mars is a lot harder than landing on the Moon. This may be surprising to some; that we’ve landed men on the Moon is often considered enough relevant experience to land men on Mars. The difficulty of landing on Mars may be completely expected to others. Mars isn’t the Moon and it isn’t Earth. It’s somewhere in between. It has too much atmosphere to use exclusively retrorockets like the system the Apollo lunar module used to land on the Moon, and has too little atmosphere to land with a gliding profile like the shuttle does on Earth. (Left, Apollo 12 LM Intrepid. November 1969.)
This is one important aspect of a lunar mission NASA had worked out in 1961. In fact, most of the pieces of the lunar mission were in place. The necessary technologies and delicate manoeuvres needed to be tested and practised in space before the mission was a ‘go’, but the pieces were all there.
The preliminary technologies that would send Apollo to the moon were under development in the late 1950s. As Mercury began to take shape and NASA began firmly consolidating all research centres and necessary people, Apollo began to take shape as well.
The preliminary efforts came together 1961 as the race between the US and Soviet Union to put a man in space intensified. In February, studies on different ways Apollo could get to, and land on, the Moon (referred to as the mission mode) were presented and discussed at an inter-centre meeting in Washington. As part of the meeting, the group from the Langley research centre presented a breakdown of lunar orbit rendezvous mode that was eventually selected. This presentation included the basic idea of how the lunar module would land – without an atmosphere, engineers were able to confidently propose a landing method.
In March, the future of manned spaceflight looked sufficiently promising that the Space Science Board of the National Academy of Science urged President Kennedy to formally make the scientific exploration of the Moon and planets NASA’s ultimate goal for the foreseeable future. It was deemed important at the time to create a sense of national leadership resulting from bold and imaginative US space activities. (Left, the Saturn V’s first two stages undergo testing. 1961.)
Also in March, a report on the feasibility and potential of the proposed Apollo program determined that it was indeed feasible with current technologies. Preliminary and ongoing testing suggested that the hardware and computer systems that the lunar program needed would be complete before the end of the decade. A likely schedule was that an Apollo spacecraft could be tested in Earth orbit as early as 1966 or 1967.
In April, the bulk of Apollo elements came together. During the month, various groups met as part of the Apollo Technical Liaison meetings to determine the status of each element of the spacecraft and its systems.
The group in charge of human factors discussed problems of shielding astronauts from radiation. Those in charge of instrumentation and communication determined instrument requirements and dealt with problems of environmental control, spacecraft recovery, antenna placement on the spacecraft and tracking, as well as telemetry display on the onboard digital computer. Live broadcasts from the Moon were also planned this early on – there was never a thought of missing a PR opportunity.
Onboard propulsions representative worked out the problems of storing cryogenic fuels and how to decrease the hazards of possible booster explosion. Those charged with constructing the spacecraft determined that it was too soon in the process to decide what materials would be used to build the spacecraft. They did, however, talk about what possible materials they could use to protect the astronauts from meteoroids, heat, and radiation.
The unclear specifications of the Apollo spacecraft, its size and weight, prompted the telemetry engineers to urge NASA to create a panel devoted to determining the expected weight and volume of the Apollo spacecraft so its trajectory could be definitively planned. Mechanical engineers made decisions on reaction controls, spacecraft heating, and the source of Apollo’s electricity. The group in charge of navigation settled issues of guidance and control. (Right, the Saturn V’s first stage F-1 undergoes testing. 1961.)
As the systems that powered Apollo came to life, the rocket that would launch the astronauts to the moon was also well on its way. The rocket that would make up the first ‘C’ stage of the Saturn V, which used five powerful F-1 engines to provided the stage’s more than 7 million pounds of thrust, had already proved its power during ground tests earlier in the year. By April, the future rocket was deemed feasible for the first aspect of the launch to the moon. The second stage was declared feasible as well. Additionally, the circumference of the growing rocket were deemed acceptable to carry the size and weight of the Apollo spacecraft.
In the beginning of May, NASA Associate Administrator Robert C. Seamans established the Ad Hoc Task Group for a Manned Lunar Landing Study. This consolidated all ongoing efforts that supported the development and eventual flight of Apollo.
When Kennedy declared that America would land a man on the Moon and return him safely within nine years, the program was truly feasible. It was a promise he could reasonably make. Not to mention, Congress was behind the plan and Apollo had the funding it needed to keep progressing. Mars Direct is in the opposite position. More of the mission details are worked out, but the vehicles and systems that will actually take the missions from Earth to Mars have yet to be seen past the point of prototypes and blueprints. These are the things that require substantial funding, and without a known way to actually land the system on Mars, the project is unlikely to get all the funding and support it needs.
It’s been 50 years and a month since Kennedy’s historic lunar declaration. It doesn’t seem likely that we’ll repeat the same feat and get a man on Mars within nine years.
Suggested Reading/Selected Sources
Robert Zubrin “The Case for Mars”. Simon & Schuster. 1996.
Paul Davies ed “A One Way Mission to Mars: Colonizing the Red Planet”. Journal of Cosmology, Cosmology Science Publishers. 2010.
Ivan D. Ertel and Mary Louise Morse. “The Apollo Spacecraft: A Chronology”. NASA. 1969.