April 2, 2007
If you think shipping freight from Cincinnati to El Paso is challenging, imagine trying to deliver an oxygen generation unit from the Earth to a remote location on the moon.
By 2020, NASA plans to establish a long-term human presence on the moon, potentially centered on an outpost to be built at the rim of the Shackleton crater near the lunar South Pole.
To make such a scenario possible, a reliable stream of consumables such as fuel, food and oxygen, spare parts and exploration equipment would have to make its way from the Earth to the moon as predictably as any Earth-based delivery system. Or more predictably: One missed shipment could have devastating consequences when you can't easily replenish essential supplies.
To figure out how to do that, MIT researchers Olivier L. de Weck, associate professor of aeronautics and astronautics and engineering systems, and David Simchi-Levi, professor of engineering systems and civil and environmental engineering, created SpaceNet, a software tool for modeling interplanetary supply chains. The latest version, SpaceNet 1.3, was released this month.
The system is based on a network of nodes on planetary surfaces, in stable orbits around the Earth, the moon or Mars, or at well-defined points in space where the gravitational force between the two bodies (in this case, the Earth and the moon) cancel each other out. These nodes act as a source, point of consumption or transfer point for space exploration logistics.
"Increasingly, there is a realization that crewed space missions such as the International Space Station or the buildup of a lunar outpost should not be treated as isolated missions, but rather as an integrated supply chain," said de Weck. The International Space Station already relies on periodic visits by the space shuttle and automated, unpiloted Russian Progress re-supply vehicles.
While "supply chain" usually refers to the flow of goods and materials in and out of manufacturing facilities, distribution centers and retail stores, de Weck said that a well-designed interplanetary supply chain would operate on much the same principles, with certain complicating factors.
Transportation delays could be significant--as much as six to nine months in the case of Mars--and shipping capacity will be very limited. This will require mission planners to make difficult trade-offs between competing demands for different types of supplies.
A reliable supply chain will "improve exploration capability and the quality of scientific results from the missions while minimizing transportation costs and reducing risks" to crew members, de Weck said.
SpaceNet evaluates the capability of vehicles to carry pressurized and unpressurized cargo; it simulates the flow of vehicles, crew and supply items through the trajectories of a space supply network, taking into account how much fuel and time are needed for single-sortie missions as well as multiyear campaigns in which an element or cargo shipment might have to be prepositioned by one set of vehicles or crew members while being used by another.
In addition to determining a logical route, SpaceNet also allows mission architects, planners, systems engineers and logisticians to focus on what will be needed to support crewed exploration missions.