The Lunar Orbit Rendezvous was a plan to coordinate the descent and ascent vehicles for a rendezvous in Lunar orbit. This feat required a number of specially designed pieces of hardware and the development of a technique known as the Lunar Orbit Rendezvous. During the late 1960s, the United States produced the Saturn V rocket, which was capable of launching enough mass into orbit required for a single-launch trip holding a crew of three to the surface of the Moon and back again. However, the amount of energy required to transfer material to the surface of Mars is an additional task beyond simply getting into orbit. One helpful aspect is the Mars atmosphere, which allows for aerobraking, meaning less need for using propellant to slow a craft for safe landing. One of the largest issues lies in simply getting to Mars, which means escaping Earth's atmosphere, sustaining the journey to Mars, and finally landing on the surface of Mars. Connecting habitats is useful, as moving between separate structures requires a pressure suit or perhaps a Mars rover. Humans require a pressurized environment at all times and protection from the toxic Martian atmosphere. Significant challenges for Mars habitats are maintaining an artificial environment and shielding from intense solar radiation. Mars habitat design can also involve the study of local conditions, including pressures, temperatures, and local materials, especially water. For example, one idea is to use the locally available regolith to shield against radiation exposure, and another idea is to use transparent ice to allow non-harmful light to enter the habitat. To contend with these constraints, architects have worked to understand the right balance between in-situ materials and construction, and ex-situ to Mars. While the gravity on Mars is lower than that on Earth, there are stronger solar radiation and temperature cycles, and high internal forces needed for pressurized habitats to contain air. One challenge is the extreme cost of transporting building materials to the Martian surface, which by the 2010s was estimated to be about US$2 million per brick. Alternatively, the habitat might be placed underground, which helps solve some problems but creates new difficulties. Mars habitats would have to contend with surface conditions that include almost no oxygen in the air, extreme cold, low pressure, and high radiation. The downside may be minimal shielding for the crew, and two ideas are to use Mars materials, such as ice, to increase shielding, and another is to move underground, perhaps cavesĪ Mars habitat is an hypothetical place where humans could live on Mars. 1990s era NASA design featuring 'spam can' type habitat landers.