A common difficulty for Space Settlement Design Competition teams is the business of figuring out the types of space vehicles that are needed to support construction and operations of a space settlement.
In order to get your group thinking about this topic, first think about where they want to go, and the different kinds of vehicles that would be required to get to each place. The Space Settlement Design Competition description of the company Northdonning Heedwell gives some clues. First, we can tell from that description that in the foreseeable future, nobody will develop the Millenium Falcon, the starship Enterprise, the shuttle Galileo, or any ability to teleport or "beam up". We will have to use more conventional methods.
The primary factor in determining the efficiency of an aerospace vehicle is weight. The more an aircraft or spacecraft weighs, the less paying cargo it can carry with the same engine power, or the less distance it can go with the same amount of fuel. When carried to the extreme, an aircraft could be so heavy that it would not be able to get off the ground. The Space Shuttle typically carries up as much as 50,000 pounds to a 150 mile orbit. If it needs to go farther, perhaps to 350 miles, it can only complete the mission with 20,000 pounds or less. If it were flown with no cargo at all, it would not be able to get more than 600 miles above the Earth. Because so much energy is needed to get off of the Earth's surface, most of the Space Shuttle's weight on the launch pad is fuel. On the other hand, satellites or other vehicles that are already in orbit can move to different orbits with relatively little fuel.
We can anticipate that three basic types of transportation vehicles will need to be considered in Space Settlement Design Competition proposals. Although there can be different vehicle designs in each of these major vehicle categories (to account for passenger vs. cargo operations, or different kinds of cargo), the judges will be looking for teams' appreciation of limits imposed by foreseeable technology on vehicle operations:
The space vehicles we are familiar with in real life are launch vehicles. Their job is to get cargo (satellites, experiments, crew, and Space Station supplies) off the Earth's surface, through the atmosphere, and into orbit. Their principal features are huge fuel tanks, engines, and shapes with insulation that enable them to survive a high-speed boost through air. The Space Shuttle Orbiter weighed about 200,000 pounds (empty) at landing, and carried about 50,000 pounds of cargo. As a Space Shuttle stood on its pad just before launch, it weighed 4.5 million pounds--almost 95% of which was fuel, the weight of the tanks that contain the fuel, and the engines that burn the fuel. All launch vehicles have smooth aerodynamic shapes to reduce drag through the atmosphere, and large reusable vehicles like the Space Shuttle need wings, tail(s), landing gear, and thermal protection systems for the mission home; after these vehicles reach 150 miles of altitude, all of this stuff is useless weight, which requires additional fuel to push it around to wherever the vehicle needs to go.
Studies are being conducted on space elevators to do the job now accomplished by launch vehicles. The concept starts construction by deploying counter-balancing ribbons from a terminus in geosynchronous orbit, one down to Earth's surface and the other an equal distance up. A vehicle would climb or descend on the ribbon between the surface and space. The Competition Co-Founders are watching this research; although the physical principles appear sound, no material currently exists that can be manufactured into a cable or ribbon strong enough to withstand the forces induced by this application. On-orbit experience with space tethers also shows that unexpected effects may delay development of this technology. Design Competition proposals that include space elevators will be penalized.
Unless a space settlement is located at about 250 miles of altitude or less, it is not practical to consider routine operations of launch vehicles directly to the settlement. Special on-orbit or orbit transfer vehicles will not need huge fuel tanks, wings, tail(s), thermal protection systems, and most of the other physical features (weight) that distinguish launch vehicles. Most on-orbit vehicles will fire their engines for only a few minutes at a time, and coast through the vacuum of space to their next destination. Indeed, even the engines are smaller; the engines the Space Shuttle uses for its on-orbit maneuvers generate only 6000 pounds of thrust. These vehicles also can be boxy or oddly shaped, since streamlining provides no advantage in the vacuum where they live. Of course, for cargo and passengers to get from the Earth's surface to a space settlement's location, they will need to transfer from a launch vehicle to an on-orbit vehicle, and it can be expected that some sort of Space Station or on-orbit Port facility would provide services to support this operation.
Space vehicles that need to go to destinations outside of Earth orbit, however, will have somewhat different design requirements. The huge distances involved in getting to other destinations in the solar system make it necessary to carry larger fuel tanks than would be needed by Earth-orbit vehicles. Exotic propulsion systems also become interesting, including ion engines (very low thrust engines that operate continuously for long periods of time), solar sails, or perhaps nuclear engines.
Because of huge launch costs for getting materials from Earth, it is expected that some (perhaps most) materials employed in space settlement construction will be acquired from extraterrestrial sources. The Moon is an obvious materials source, and some asteroids with orbits that bring them close to Earth could prove very useful. Every destination will present its own priorities for vehicle design. Lunar landers will need landing gear and engines for landing and ascent. Asteroid mining vehicles will need some means for staying attached to their targets, and for harvesting, processing, and transporting large quantities of ore. For Space Settlement Design Competition scenarios that involve settlements on or near other planets (e.g., Mars), atmospheric and environmental characteristics must be considered in designs of the vehicles that service these communities.