History of Expandable Spacecraft
The concept of utilizing expandable, or, as referred to in the past, ‘inflatable’ spacecraft and space systems is not a new idea. The history of inflatable space systems goes back to the very beginning of America’s space program. As a matter of fact, the inflatable Echo 1 and Echo 2, the world’s first passive communications satellites, were one of the inaugural projects taken on in 1958 by a new federal agency called NASA. Boasting a diameter close to the height of a 10-story building, the Echo satellites have been described as “perhaps the most beautiful object[s] ever to be put into space.” The challenge that these first NASA engineers faced was how to place such a large structure into the relatively tiny fairing of a Thor-Delta rocket. The ultimate solution was to use an inflatable system, which led to the development of the Echo 1, 1A, and 2, and a brand new substance that the satellite was made out of called ‘Mylar’.
The Echo 2, constructed and launched in the early 1960’s
Even as early as the 1960s, the use of inflatables was not just being limited to communications satellites. With the success of Echo, NASA Langley Research Center wanted to apply the advantages of inflatables’ large, light volumes that would fit within small rocket fairings for crewed operations.
An early 24-foot (7.3m) inflatable space station module from 1961
Of course, in the 1960s, the available softgoods (such as rubber) were not sufficiently advanced to allow for the practical application of inflatables in the context of crewed operations. Thirty years later, in the 1990s, with the advent of Kevlar and similar advanced materials, the concept of an inflatable space station or habitat had become a real possibility. More specifically, in 1992, the President issued National Security Presidential Directive 6, authorizing the Space Exploration Initiative (“SEI”). Under SEI, NASA was to begin work developing plans for a future human mission to Mars. Again faced with the same problem as their predecessors in the 1960s, NASA needed to get a significant amount of volume into space and had only a limited amount of rocket fairing room with which to do so. This led to the idea of using an inflatable crew habitat for the journey to Mars, which was dubbed the ‘Transit Habitat’, more commonly referred to by its abbreviated name, ‘TransHab’.
Like many recent NASA initiatives, SEI was plagued by a lack of budgetary and political support, and was eventually abandoned. However, the idea of an inflatable crew habitat had great merit, and was revived as a crew quarters for the International Space Station (“ISS”). Despite the change in purpose, the original name, TransHab, was retained, and, in 1997, NASA again began focusing its attention on an inflatable habitat.
The advantages of TransHab were clear and numerous. Like all inflatable systems, TransHab offered the potential for a greater amount of on-orbit volume while, relative to a traditional metallic structure, taking up a small amount of rocket fairing space. Additionally, and perhaps most relevant to long-term orbital use, is the enhanced protection from radiation offered by inflatable habitats. Specifically, when exposed to cosmic rays or solar flares, traditional metallic habitats can suffer from damaging secondary radiation wherein the metal that comprises the habitat’s structure creates a scattering effect and/or becomes excited. In contrast, due to their use of non-metallic softgoods as their primary envelope material, inflatables can significantly reduce this dangerous phenomena.
Despite showing great technical promise, after the fact that the ISS program was $4.8 billion over budget came to light, the TransHab/crew habitat program was explicitly canceled by Congress in 2000.
Left – Artist’s conception of Transhab from the 1990’s.
Right – A Transhab test article being placed inside a vacuum chamber at NASA Johnson Space Center.
Although NASA initially developed the concept of inflatable space habitats, any substantial fabrication work was curtailed by Congress in 2000. Therefore, Bigelow Aerospace had to go through the process of re-designing much of what had been done before, developing, and eventually launching the world’s first expandable space habitat prototypes.
This first mission, to construct and test expandable habitat technology in an actual orbital environment, was called the Genesis program, and led to the development of Genesis I, a roughly 3000 lb (1363 kg) spacecraft, 14 feet (4.3 m) long with an 8 foot (2.4 m) diameter in its deployed configuration.