Mars for Less
Mars for Less (MFL)  is a proposal for a near-term human Mars expedition that involves the use of existing Evolved Expendable Launch Vehicles (EELVs, or alternatively, Medium-Lift Launch Vehicles, MLLVs). The MFL plan claims that the barrier to entry for a manned Mars mission can be lowered significantly by avoiding development costs in launch vehicles, particularly heavy lift launch vehicles (HLLVs) that many think are required for human space exploration. While more complex than many other mission proposals, Mars for Less has strong economic arguments, including avoiding launch vehicle development costs, and offering the prospect of an anchor tenant for the currently over-supplied launch vehicle market, which could result in reduced launch costs and incentives to develop reusable launch technology. The MFL plan was developed by aerospace engineer Grant Bonin in 2003 when he was a student at Carleton University.
The Mars for Less mission is heavily based on Robert Zubrin's Mars Direct mission design, in which two different spacecraft are used for a single human expedition. One spacecraft (called the Earth Return Vehicle, or ERV) is sent to Mars unmanned on a trajectory similar to a Hohmann Transfer Orbit before the crew. This vehicle lands and fuels itself using a Sabatier process, creating methane/oxygen rocket fuel (bipropellant) out of carbon dioxide obtained from the Martian atmosphere and a relatively small amount of hydrogen imported from Earth. Once the ERV is fuelled, the crew is launched to Mars on a free return trajectory. The crew arrives after about 180 days and lands in the proximity of the ERV. They spend about 500 days on the surface exploring, then return to Earth in the ERV.
The Mars for Less plan is different from Mars Direct in that it uses multiple launches of existing launch vehicles, instead of a few launches of heavy lift boosters. In the MFL plan, separate components are launched individually to low-Earth orbit, where they are mated together over the course of about half a year. Each component is itself autonomous, so that only an orbital assembly, and not construction, would ideally be required. By avoiding the development of a heavy lift launch vehicle like NASA's proposed Ares V, such a mission could theoretically be undertaken today.
In January 2006 MFL author Grant Bonin wrote an economic argument to complement the technical discussion of MFL, titled "The Case for Smaller Launch Vehicles in Human Space Exploration". Bonin cites high flight rates of existing launch vehicles as a key driver in cost reduction, increased confidence, and in motivating the development of smaller, reusable launch systems instead of bigger expendable ones. Part 1 of this article appeared in The Space Review on January 3, 2006, and Part 2 appeared on January 9, one week later.
Small vs. large launch vehicles
Mars for Less addresses the issue of whether heavy-lift launch vehicles are needed for human space exploration. Whereas Robert Zubrin has long advocated the development of a new heavy launcher for any Mars expedition, Bonin's work rejects such notions. This issue is still hotly debated among space advocates.
While Bonin maintains that better economics result from high launch rate, smaller, currently flying vehicles, Zubrin claims that the cost per kilogram for launching payloads is lowest with bigger systems today. On the other hand, Bonin cites the importance of high launch volumes and an anchor tenant for the launch industry as being key to driving such costs down, and to promoting better systems instead of bigger ones. Bonin also cites the critical issue of redundancy, maintaining that a larger number of smaller boosters reduces risk, whereas a program based on a single big vehicle puts its eggs in one basket.
There are other arguments that walk a middle ground, advocating a mixed fleet approach and/or the use of orbital propellant transfer to separate the issue of launch from the in-space aspects of a given mission. In such scenarios, spacecraft may be launched with a big launch vehicle to avoid orbital assembly, and then have fuel transferred to them by smaller launches.
Near term viability
Critics contend that plans like Mars for Less neglect the issue of landing larger masses, i.e. atmospheric entry, descent and landing, since proven technologies do not scale well for larger payloads. Mars expeditions with humans may therefore need new technology development for the descent process. At Space Vision 2006, Bonin acknowledged this fact, stating that either Mars for Less or its parent plan Mars Direct would have to be recalculated because their original figures were overly optimistic with regard to aerocapture.
Mars for Less was first published in the September/October 2005 issue of the Journal of the British Interplanetary Society. A modified version of the proposal was presented at the International Space Development Conference and SpaceVision in 2006. Mars for Less was also an early mission design advocated by the space advocate group Marsdrive. Mars for Less has also been released as an add-on for the Orbiter Space Flight Simulator.