Ever since NASA successfully accomplished the seemingly impossible task of landing humans on the moon, space leaders have set Mars as a goal. When that proved to be too difficult, dangerous and expensive, NASA opted for a mostly reusable transportation system (the space shuttle) and a human-occupied International Space Station in low Earth orbit that could become a place to assemble missions back to the moon or to Mars.

Hoping to regain the glory of Apollo, President Barack Obama in 2010 called for a human trip to Mars by 2035. Five years later, NASA is projecting success and spending nearly all its $4 billion annual budget for human space exploration on the Space Launch System and Orion capsule, supposedly built for Mars trips. Incredibly, NASA still does not have a feasible mission design or a credible overall cost estimate for the first human trip to Mars. However, there is enough known about the mission and required equipment to provide a ballpark estimate of its cost.

The most critical element needed for a trip to Mars is also the most expensive. A new vehicle must safely sustain the crew for two to three years without resupply and embody all the functions of the current ISS and be a lot better. These requirements include an environmental control and life support system that monitors and controls partial pressures of oxygen, carbon dioxide, methane, hydrogen and water vapor. It must filter out particulates and microorganisms, provide thermal control with external cooling loops and pumps, and distribute air. This system for Mars also must provide potable water and perform habitation functions, such as food preparation and production, hygiene, collection and stabilization of metabolic waste, laundry services and trash recycling. Waste management systems safeguard crew health, controlling odors and retarding the growth of microbes.

Other critical systems include electric power generation and control, communications and navigation, attitude control (control moment gyroscopes), exercise equipment, propulsion to dodge foreign objects, puncture repair kits, fire suppression equipment, medical equipment for first aid and continuing care of potentially sick or disabled crew, airlock, spacesuits for extravehicular activity, manipulator arm and control station, and food, extra supplies of oxygen, nitrogen, fuels and other expendables. Long-term exposure to space radiation in excess of levels encountered on the ISS will require significantly enhanced protection for the crew.

Manned spaceship in Mars orbit
Concept of a manned spaceship in Mars orbit. Credit: European Space Agency and AEOS – Medialab
Concept of a manned spaceship in Mars orbit. Credit: European Space Agency and AEOS – Medialab

Every one of these systems must operate without resupply for the duration of the mission and do so with several times the reliability of its corresponding system on the ISS. They must be repairable in flight in the event of minor malfunctions. The National Research Council recently reported that U.S. and Russian systems on ISS demonstrate rates of hardware failures that would be unsustainable on a Mars mission.

Finally, to underscore the difficulty and danger, there would be no possibility of crew rescue during a human mission to Mars.

This extraordinary vehicle could rightly be called a Traveling Space Station, or TSS.

The most applicable cost analog for a TSS is the existing ISS, which was built in sections and assembled over a period of 20 years. Total cost of the ISS was about $100 billion in 2015 dollars, including contributions from international partners, but excluding shuttle, Soyuz and other transportation costs. It has been difficult to get reliable cost data from our main partner, Russia.
The requirement for greatly improved reliability calls for extensive redundancy and lengthy and expensive testing. Thus a ballpark total cost for one TSS could be at least 30 percent greater than the ISS, bringing the cost of the first single TSS to about $130 billion.

The overall cost of a Mars mission must also include SLS and Orion, $5 billion before 2010, plus $4 billion for each of the past five years, plus a likely $4 billion a year for at least 20 years leading to a first trip in 2035, assuming that date holds. These figures include SLS and Orion project costs plus their share of NASA fixed cost overhead. Transportation costs alone could total over $100 billion before the first Mars mission in 2035.

A ballpark cost of the first Mars mission in 2035 would total $230 billion. Second and subsequent missions, occurring at three-year intervals, would cost about $142 billion each including SLS and Orion costs. An expendable lander for the first and subsequent missions is not included in these estimates.

A return from Mars would hit Earth’s atmosphere at nearly 52,000 kilometers per hour. We would have no way of protecting a very large TSS from the heat of entry. Every piece of equipment except the crew capsule would be expended on each mission. A new TSS, several new SLS vehicles and probably a new Orion capsule would be required for each subsequent Mars mission.

We sent nine Apollo crews to the moon (six landed); if we send nine crews to Mars, the total bill would be in the neighborhood of $1.5 trillion.

The NASA administrator recently was quoted as advocating a crew-tended base on Mars (“pioneering”) extending indefinitely into the future. The overall total for pioneering Mars could easily grow beyond $2 trillion.


Still, that program is not totally out of the question if we really, really want to do it. NASA’s annual budget would need to be increased gradually to about $54 billion (in 2015 dollars) per year for the first trip to Mars and to continue at that level to support one mission per three years. Yes, $54 billion appears high compared with the current 2016 budget request of $18 billion, but that is still less than 1.5 percent of the federal budget. Participation by international partners could help a great deal. Efficiencies brought about by NASA purchasing hardware and services from commercial suppliers could also make a large difference. It only requires continuing leadership by presidents and Congresses and the sustained will of the American people to make it happen.

If for some reason we decide not to send astronauts to Mars in the next 30 to 50 years, SLS and Orion become a very low priority for operations in cislunar space, particularly when it is known that currently available commercial launchers (Delta 4 Heavy versions and Falcon 9 Heavy, available starting in about a year) and commercial capsules can perform functions equivalent to SLS/Orion for less than one-half the cost. SLS/Orion funding could be phased over to higher-priority activities closer to home and the moon.

One attractive option could be to aim for a lunar base on an incremental go-as-you-can-pay basis, supported by international partners and using efficient commercial procurement methods. That base could be functional in about 20 years with NASA’s overall budget remaining constant in 2015 dollars. The objective would be to explore, occupy and exploit resources of the moon, with resupply and rescue only four days away.

The building of a resource utilization facility on the moon to extract water and create rocket propellant from it (liquid oxygen and hydrogen) would help create a permanent spacefaring infrastructure, one that could support a variety of missions throughout cislunar space and eventually, to Mars and other deep-space destinations.

O. Glenn Smith is former manager of shuttle systems engineering at NASA’s Johnson Space Center. Paul D. Spudis is a staff scientist at the Lunar and Planetary Institute in Houston.