SpaceX is readying a Falcon 9 rocket for launch Friday afternoon to boost a Dragon cargo ship into orbit on a two-day flight to deliver 3.5 tons of supplies and equipment to the International Space Station.
Also on board: an innovative expandable module that will be attached to the lab complex for long-duration tests to find out whether such lightweight components might one day serve as low-cost habitats for deep space missions or commercial space stations.
Liftoff from launch complex 40 at the Cape Canaveral Air Force Station is targeted for 4:43:32 p.m. EDT (GMT-4), roughly the moment Earth's rotation carries the pad into the plane of the station's orbit. Forecasters are predicting a 90 percent chance of good weather.
If all goes well, the Dragon will reach the station Sunday morning when British astronaut Timothy Peake, operating the lab's robot arm, locks onto a grapple fixture. Flight controllers at the Johnson Space Center in Houston then will take over arm operations, pulling the supply ship in for berthing at the Earth-facing port of the forward Harmony module.
This will be the 23rd flight of a Falcon 9 rocket overall and the fourth since a catastrophic second stage failure last June that destroyed the previous station-bound Dragon.
Since then, SpaceX has successfully launched two commercial satellite missions and a NASA science satellite to clear the way for Friday's resumption of station delivery missions. It will be the third resupply mission to reach the station in a little more than two weeks.
As has become commonplace for SpaceX, the first stage of the Falcon 9 is expected to attempt a return to Earth after boosting the second stage and Dragon spacecraft out of the dense lower atmosphere. This time around, the company plans to utilize one of its off-shore drone ships.
SpaceX founder and chief designer Elon Musk believes the only way to significantly lower the cost of putting payloads into space is to recover, refurbish and relaunch spent stages. So far, the company has managed several successful guided re-entries and vertical descents to ocean "splash downs," three partially successful attempts to land on off-shore barges and one successful touchdown at the Cape Canaveral Air Force Station last December.
But the primary goal of the company's eighth operational space station resupply mission is to deliver 1,410 pounds of science gear, 1,205 pounds of crew supplies, 674 pounds of station hardware, 26 pounds of spacewalk equipment, 238 pounds of computer gear and 72 pounds of Russian equipment.
Also on board: 20 mice that are making the trip to space to serve as test subjects in an Eli Lilly experiment to learn more about muscle atrophy and bone loss in space. Other experiments will study plant growth, fungi in space, the growth of microbes on the station and how weightlessness might be utilized for genetics studies.
A wide variety of other research is on board, along with 25 student experiments to replace those lost in the June launch failure. Equally important to NASA, the Dragon will bring back biological samples that have been stored aboard the station when the supply ship returns to Earth around May 11. Of all the supply craft that visit the space station, only the Dragon is designed to bring experiment samples and cargo back to Earth.
"SpaceX is a workhorse for us in bringing up samples we can late load, including live animals, also in bringing home some of our most important samples," said station program scientist Julie Robinson.
"For example, blood and urine samples from the one-year expedition, including (astronaut) Scott Kelly's, will be coming back when this flight returns. These flights are really important to our biological research."
All of the science gear and supplies are housed inside the Dragon's pressurized compartment. Mounted in an unpressurized trunk section is the Bigelow Expandable Activity Module, or BEAM, supplied by Bigelow Aerospace, a Las Vegas company owned by billionaire Robert Bigelow, founder of the Budget Suites of America hotel chain.
Based on designs pioneered by NASA in the 1990s and subsequently developed by Bigelow, the BEAM will be launched in a collapsed state, taking up much less space aboard the Dragon than a rigid module that would otherwise require a much larger rocket to launch.
Once Dragon is berthed at the space station, the lab's robot arm will pull BEAM out of the unpressurized truck second and move it into place for attachment at the trailing port of the Tranquility module. It then will be inflated with internal air tanks, expanding to a length of 13 feet and a diameter of 10.5 feet.
Internal volume will be about 565 cubic feet, "about the size of a small bedroom," said NASA's BEAM project manager Rajib Dasgupta.
"In general, expandable modules require minimal build volume on a rocket, that's their main benefit, and then it expands in space until it's full volume," he said. "In the case of BEAM, it is about four times its packed volume and can potentially provide a comfortable area for astronauts to live and work."
But because the module is being tested in space for the first time, station astronauts will leave the hatch closed during most of BEAM's two-year stay, only entering a few times each year to check on sensors and the module's general health. At the end of its stay, the BEAM will be detached and jettisoned to burn up in Earth's atmosphere.
"By attaching BEAM to the ISS, we'll be able to evaluate our technology, elevate its readiness level and demonstrate we're ready to support humans in space," said Lisa Kauke, BEAM deputy program manager at Bigelow Aerospace. "The astronauts on the ISS will periodically interact with the module, about four times a year, collect the data and most importantly for me, they'll be the first of many astronauts to interact with expandables.
"We know that these modules are robust, because we have experience ourselves with the materials and the assembly, we know they'll open doors to the future because they save on launch volume. Now we get to share that message."
While the idea of an inflatable module might seem counterintuitive given the ever-present threat of impacts with space debris, Kauke said the proprietary material making up the walls of the BEAM, along with micrometeoroid shielding, make the module as tough as more traditional solid-body compartments.
"I'm afraid I can't share too much because it's proprietary," she said of the fabric making up the module's skin. "It's a Vectran-like material that creates the outer structure, it's a load bearing structure, and it's covered by MMOD (micrometeoroid) shield protection. That's also our own proprietary materials, but it's been proven to perform up to the standards of ISS, and we look forward to demonstrating that for you."