Space station benefits from a wide opening

James Oberg NBC News space analyst

HOUSTON - Anybody on Earth who’s ever moved into a new apartment and jammed a sofa into a too-narrow doorway appreciates the value of having a passageway that's big enough for your stuff. And that goes double in space, where the option of going outside and looking for another entrance isn’t practical.

Aboard the international space station, astronauts are now unloading several tons of supplies and equipment from the Leonardo cargo module, which was brought up on the space shuttle Discovery. They're also transferring a year’s worth of trash and recyclable equipment into the module's vacated slots.

In the process, they're using a particular element of the space station that usually gets overlooked amid all the attention to more sexy features such as solar panels, air locks and oxygen generators. It’s called the “hatch,” and it just doesn’t get any respect — despite the fact that its 4-foot-plus width gives the international space station capabilities that are unprecedented in 30 years of orbital operations, going back to NASA's Skylab and Russia's earliest outposts.

“The large hatch truly is an unsung hero of the ISS design!” said now-retired space station astronaut Dan Bursch, co-holder of the U.S. record for longest-ever space mission.

“I must say that I don't remember getting any bumps or scrapes from hitting the hatch or frame of the ISS hatch design,” he said in an e-mail to MSNBC.com, “but I sure do remember getting bumps and scrapes from the smaller ones!”

The transfer advantage
The benefit goes beyond mere comfort and convenience. “The ability to transfer that much big hardware has been a big advantage,” noted David McCann, the leader of the Boeing Co.’s Structures and Mechanical Systems Group at NASA's Johnson Space Center in Houston.

McCann said a smaller hatch would have had a negative impact on the design — and capability — of all the space station's internal equipment. Without it, “we couldn’t have built the [science] racks the way we did, or outfitted the space station the way we did,” he told MSNBC.com.

NASA French cosmonaut Claudie Haignere and Russian cosmonauts Victor Afanasyev and Konstantin Kozeyev wave to the camera through a port between their Soyuz spacecraft and the international space station during a 2001 visit. The station's Soyuz tunnel is smaller than the American hatches.

Former astronaut Don Thomas, now chief scientist for the station program, said the 4-foot-wide hatch makes it possible to bring in equipment as big as a standard-size refrigerator with ease. “Without the large hatch that ISS provides, we would be limited to flying much smaller experiments, which would limit what we have been able to achieve on the ISS,” he said.

The hatch is part of what is formally called the Common Berthing Mechanism, a device installed at each end and often around the waist of U.S. modules such as the Unity connecting node and the Destiny laboratory.

The doorway is square, 51 inches (130 centimeters) on each side. This compares with the round tunnels from docking vehicles such as the Soyuz (31 inches, or 80 centimeters) and the space shuttle (42 inches, or 107 centimeters), whose docking tunnels must be tucked into rugged mating mechanisms. In terms of actual cross-sectional area, the shuttle tunnel has twice the area of the Soyuz tunnel, and the Common Berthing Mechanism's door has twice again the area of the shuttle tunnel.

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