A SpaceX Dragon cargo capsule loaded with more than 5,800 pounds of supplies and experiments is set to dock with the International Space Station at 11:20 a.m. EDT (1520 GMT) Saturday, delivering fresh food, a climate research payload, spare parts, and several small satellites to the complex.
The unpiloted supply ship launched Thursday evening from NASA’s Kennedy Space Center in Florida on top of a Falcon 9 rocket. Since then, the spacecraft has completed a series of thruster burns to fine-tune its approach to the space station, culminating in the final automated rendezvous sequence Saturday morning.
The mission will mark SpaceX’s 25th cargo delivery to the space station under two multibillion-dollar Commercial Resupply Services contracts with NASA. This flight, known as CRS-25, will be the third arrival at the space station for this particular reusable Cargo Dragon spacecraft.
The Cargo Dragon will approach from behind and below the station, passing about 1,300 feet (400 meters) directly below the complex before swinging into position directly in front of the outpost to line up with the forward docking port of the Harmony module.
The spacecraft uses thermal and laser ranging sensors, coupled with a relative GPS navigation system, to navigate toward the space station.
After reaching a waypoint about 720 feet (220 meters) in front of the station, the Dragon spacecraft will proceed in for docking with the Harmony module at 11:20 a.m. EDT, using its Draco thrusters to control the closure rate and alignment with the docking corridor.
A brief hold is planned about 66 feet (20 meters) from the station before final approach for docking. NASA astronauts Jessica Watkins and Bob Hines on the space station will monitor the Dragon spacecraft’s rendezvous and docking, ready to send hold or abort commands in the event of a problem.
The Cargo Dragon will make contact with the International Docking Adapter with a soft capture ring, which will bring in the capsule for a hard mate with a series of hooks to secure the spacecraft to the station. Cargo Dragon also has a set of rotary spring dampeners to lessen the shock of contact with the station.
Data and power cables will also robotically connect inside the docking mechanism to link the Dragon spacecraft with the space station.
Once Dragon is firmly attached to the station, astronauts on the station will open hatches to begin unpacking cargo inside the craft’s pressurized compartment.
The Dragon spacecraft is loaded with 5,881 pounds (2,668 kilograms) of cargo, including 4,682 pounds (2,124 kilograms) of equipment inside the pressurized cabin. Another 1,199 (544 kilograms) of cargo is stowed inside Dragon’s unpressurized rear cargo bay, or trunk.
The supplies inside the pressurized section of the spacecraft include fresh food for the seven astronauts and cosmonauts living on the station — NASA says apples, oranges, cherry tomatoes, onions, baby carrots, garlic, tahini, cheese, and dried sausage are on-board — and equipment to support around 40 research investigations.
There are also spare parts for the space station’s toilet, a spare catalytic reactor and ion exchange bed for the station’s water recycling system, and brine processor assembly bladders to recover additional water from urine, enhancing the research lab’s water reclamation capability.
The Dragon spacecraft will also deliver five NASA-sponsored CubeSats to the space station for deployment though the Japanese Kibo lab module.
Other experiments on the CRS-25 mission will investigate how the immune system changes in microgravity, crop growth in space, and a study looking at an alternative to concrete that could be used to construct structures on the moon or Mars.
There’s also a spare battery charge/discharge unit for the station’s power system in the Dragon trunk, next NASA’s Earth Surface Mineral Dust Source Investigation, or EMIT, instrument. Like EMIT, the battery charge/discharge unit will be robotically extracted from the Dragon’s rear cargo bay and placed in a stowage position outside the station.
Developed at NASA’s Jet Propulsion Laboratory, the $118 million EMIT instrument will measure the mineral content of the world’s desert regions, the source of global dust storms that can impact climate and weather worldwide.
Data collected by the instrument will help scientists learn more about how dust lifted into the atmosphere from deserts impact Earth’s ecosystems and human health.
Dust storms can spread from continent, where they can cause temperatures to rise or fall, form clouds, provide nutrients to ocean and land organisms, restrict visibility, and pose a health hazard to people.
“This is an important cycle in the Earth system,” said Rob Green, EMIT’s principal investigator and a senior research scientist at JPL.
The EMIT instrument will be removed from the trunk of the Dragon spacecraft after docking by the space station’s Canadian-built robotic arm, and placed on a mounting bracket on the lab’s port-side truss. EMIT will measure the mineral composition of desert soils with a visible and shortwave infrared spectrometer.
Green said EMIT will “close a gap in knowledge about mineral dust source regions of our planet.” A NASA spokesperson said the EMIT instrument, which is part of the agency’s Earth Venture program, is designed for a 12-month primary mission.
“Right now, our knowledge is traced to abut 5,000 mineral analyses where minerals have been collected and analyzed. When EMIT completes its mission, we will have a billion direct observations of the mineral composition fo the Earth’s arid land,” Green said.
The space station’s orbit will take the EMIT instrument over most of the world’s deserts, including the Sahara Desert of Africa, the Middle East, and deserts of Asia, Australia, and the western Americas.
“Whether it’s an iron oxide, kind of like rust, or a carbonate, or a clay, those different mineral molecules leave fingerprints in the light we get to measure,” Green said.
The CRS-25 mission was scheduled for launch in early June, but officials grounded the Dragon spacecraft after finding a leak in the ship’s propulsion system. SpaceX detected “elevated vapor readings” of monomethyl hydrazine, or MMH, fuel in an “isolated region” of the Dragon spacecraft’s propulsion system during propellant loading ahead of the launch in early June, NASA said in a statement.
The Dragon spacecraft carries hydrazine and nitrogen tetroxide propellants to power its Draco thrusters for in-orbit maneuvers, including rendezvous burns to approach the space station, and the deorbit burn at the end of the mission to return to Earth.
Benji Reed, SpaceX’s senior director of human spaceflight programs, said the vapor leak in the Dragon propulsion system was caused by “imperfections in the sealing surface where a valve connects into the system.”
Technicians replaced the valve and confirmed the leak stopped, allowing preparations for the CRS-25 launch to resume at Cape Canaveral. SpaceX’s ground team also replaced the four main parachutes already stowed on the capsule “out of abundance of caution,” Reed told reporters Wednesday.
Read more about the leak in our mission preview story.
“This is going to be a really busy mission for us,” said Dana Weigel, NASA’s deputy space station program manager. “It’s packed with a lot of science. The planned duration is about 33 days.”
The Dragon spacecraft’s return to Earth is scheduled in mid-August, when the cargo capsule will undock from the station and head for splashdown off the coast of Florida.
A SpaceX recovery boat will be in position to retrieve the capsule from the sea and return it to Cape Canaveral for unpacking and refurbishment.
The cargo slated for return to Earth on the CRS-25 mission in mid-August includes a spacesuit worn by European astronaut Mattias Maurer on a spacewalk in March. Astronauts found water inside Maurer’s spacesuit helmet after he safely returned inside the station, a similar issue to the problem that caused a spacewalk emergency in 2013 when European astronaut Luca Parmitano had to cut short a spacewalk due to a water leak.
Parmitano had trouble breathing and lost visibility as water filled his helmet, but he escaped injury in one of the most dangerous spacewalk incidents in modern space history.
Maurer didn’t notice his water leak until he was back inside the station. But NASA officials don’t want to stage any non-emergency spacewalks until completing an investigation into the water leak.
“We’ve got to get that suit home got take a look at it as part of the investigation to really try to understand what happened to the suit, and that’ll be part of what we need for our assessment for our eventual readiness when we look at returning back to nominal EVAs (spacewalks),” Weigel said.
The next planned spacewalks on NASA’s calendar are scheduled late this year, when the next SpaceX Dragon cargo mission will deliver a fresh set of solar arrays to the station. The astronauts will help install the new solar arrays, requiring at least two spacewalks to finish the job.
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