"This is a launch we've been waiting for for quite some time, because it's really important to our overall ISS research program," said Julie Robinson, chief scientist for the ISS, during a conference call with reporters last week. "It has about 2,000 kilograms of research equipment and supplies. The big driver on that amount of mass, which is really high compared to our average, is that we have about 1,400 kilograms for the BEAM module itself."

Though BEAM represents a large portion of Dragon's cargo haul, it's incredibly light when compared to other ISS modules like Tranquility, which has a mass of about 19,000 kilograms. When filled with air, BEAM expands to about four times its packed size. Its total, inflated volume is 16 cubic meters—the size of a small bedroom.

BEAM represents an important private sector partnership for NASA, which dabbled in inflatable modules in the 1990s before the program was canceled due to a lack of funding. The Las Vegas-based firm Bigelow Aerospace licensed the technology and launched two, uncrewed expandable habitat modules in 2006 and 2007 called Genesis I and II. Both were just slightly smaller than BEAM.

"These two spacecraft outperformed all expectations," said Lisa Kauke, BEAM's deputy program manager for Bigelow. Kauke said the Genesis project showed the technology was ready for the next step: human occupancy.

"The main difference in the case of BEAM is that the module is certified to human-rated standards," said Rajib Dasgupta, NASA's project and technical integration manager for the project. "What that means is that some of the structural factors of safety for human-rated conditions are generally higher than what you'd get for a non-human rated module."

After launch, BEAM will spend at least five days getting acclimated to the vacuum of space. NASA flight controllers at the Johnson Space Center in Houston, Texas will unpack the module with the station's robotic arm in mid-April, and attach it to Tranquility. BEAM will be inflated around the end of the month or beginning of May.