A SpaceX Dragon cargo capsule loaded with more than 5,800 pounds of supplies and experiments is due to dock with the International Space Station at 11:20 a.m. EDT (1520 GMT) Saturday, delivering a NASA instrument to study the content in minerals from dust storms and several small CubeSats.
The unmanned supply ship launched Thursday evening from NASA’s Kennedy Space Center in Florida atop a Falcon 9 rocket. Since then, the spacecraft has performed a series of propellant burns to refine its approach to the space station, culminating in the final automated rendezvous sequence on 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 under the station, passing approximately 1,300 feet (400 meters) directly below the compound before positioning itself 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 to the space station.
After reaching a waypoint approximately 720 feet (220 meters) ahead of the station, the Dragon spacecraft will dock with the Harmony module at 11:20 a.m. EDT, using its Draco thrusters to control the rate of closure and alignment with the mooring. corridor.
A brief hold is expected approximately 66 feet (20 meters) from the station before the final approach for docking. NASA astronauts Jessica Watkins and Bob Hines on the space station will monitor the rendezvous and docking of the Dragon spacecraft, ready to send hold or abort commands if something goes wrong.
Mission controllers from NASA’s Johnson Space Center in Houston and SpaceX’s headquarters in Hawthorne, Calif., will oversee the rendezvous and docking.
The Cargo Dragon will contact the International Docking Adapter with a soft capture ring, which will bring the capsule for a hard mate with a series of hooks to secure the spacecraft to the station. Cargo Dragon also features a set of rotating spring shock absorbers to lessen the shock of contact with the station.
Data and power cables will also robotically connect inside the docking mechanism to connect the Dragon spacecraft to the space station.
Once Dragon is firmly attached to the station, the station’s astronauts 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. An additional 1,199 (544 kilograms) of cargo is stowed inside the Dragon’s unpressurized rear cargo hold, or trunk.
Supplies inside the spacecraft’s pressurized section 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 sausages are on board — and equipment to support around 40 research projects.
There are also spare parts for the space station toilets, a spare catalytic reactor and ion exchange bed for the station’s water recycling system, and processor assembly bladders of brine to recover additional water from urine, thus improving the water-harvesting capacity of the research laboratory.
The Dragon spacecraft will also deliver five NASA-sponsored CubeSats to the space station for deployment via Japan’s Kibo laboratory module.
Other experiments on the CRS-25 mission will study how the immune system changes in microgravity, the growth of cultures in space, and a study of an alternative to concrete that could be used to build structures on the moon or Mars. .
There’s also a spare battery charge/discharge unit for the station’s power system in the Dragon Vault, the next Earth Surface Mineral Dust Source, or EMIT, survey instrument from The NASA. Like EMIT, the battery charge/discharge unit will be robotically extracted from the Dragon’s rear cargo bay and placed in a stow 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 around the world entire.
The data collected by the instrument will help scientists learn more about the impact of dust thrown into the atmosphere by deserts on terrestrial ecosystems and human health.
Dust storms can spread from the mainland, where they can cause temperatures to rise or fall, form clouds, provide nutrients to ocean and land organisms, restrict visibility and pose a health risk to people.
“This is an important cycle in the Earth system,” said Rob Green, EMIT Principal Investigator and JPL Principal Investigator.
The EMIT instrument will be removed from the trunk of the Dragon spacecraft after docking by the space station’s Canadian-made robotic arm, and placed on a mounting bracket on the lab’s port beam. EMIT will measure the mineral composition of desert soils with a visible and short-wave infrared spectrometer.
Green said EMIT will “fill a gap in knowledge about the mineral dust source regions of our planet.” A NASA spokesperson said the EMIT instrument, part of the agency’s Earth Venture program, is designed for a 12-month primary mission.
“At present, our knowledge is based on approximately 5,000 mineral analyzes where minerals have been collected and analyzed. When EMIT completes its mission, we will have one billion direct observations of the mineral composition of Earth’s drylands,” Green said.
The space station’s orbit will take the EMIT instrument over most of the world’s deserts, including the Sahara Desert in Africa, the Middle East and the deserts of Asia, Australia and the Western Americas. .
“Whether it’s an iron oxide, much like rust, a carbonate or a clay, these different mineral molecules leave fingerprints in the light that we get to measure,” said Green.
The CRS-25 mission was supposed to launch in early June, but officials grounded the Dragon spacecraft after discovering a leak in the ship’s propulsion system. SpaceX detected “high vapor readings” of monomethylhydrazine, or MMH, fuel in an “isolated region” of the Dragon spacecraft’s propulsion system during propellant loading before launch in early June, NASA said in a statement.
The Dragon spacecraft carries hydrazine and nitrogen tetroxide thrusters to power its Draco thrusters for in-orbit maneuvers, including rendezvous burns to approach the space station and deorbit burn at the end of the mission to return to Earth.
Benji Reed, SpaceX’s senior director of human spaceflight programs, said the steam leak in the Dragon propulsion system was caused by “imperfections in the sealing surface where a valve connects to the system.”
Technicians replaced the valve and confirmed the leak had stopped, allowing CRS-25 launch preparations to resume at Cape Canaveral. SpaceX’s ground crew also replaced the four main parachutes already stowed on the capsule “out of an abundance of caution,” Reed told reporters Wednesday.
Read more about the leak in our mission preview story.
“This is going to be a very busy mission for us,” said Dana Weigel, NASA’s deputy space station program manager. “It is full of a lot of science. The expected duration is approximately 33 days.
The Dragon spacecraft’s return to Earth is scheduled for mid-August, when the cargo capsule detaches from the station and heads for splashdown off the coast of Florida.
A SpaceX recovery boat will be in position to retrieve the capsule from the sea and bring it back to Cape Canaveral for unpacking and refurbishment.
The cargo due to be returned to Earth on the CRS-25 mission in mid-August includes a spacesuit worn by European astronaut Mattias Maurer during a spacewalk in March. Astronauts found water inside Maurer’s spacesuit helmet after it was safely returned inside the station, a problem similar to the issue that caused a spacewalk emergency in 2013 when European astronaut Luca Parmitano had to cut short a spacewalk due to a water leak.
Parmitano struggled to breathe and lost vision as water filled his helmet, but he escaped injury in one of the most dangerous spacewalking incidents in the history of the modern space.
Maurer didn’t notice his water leak until he was back inside the station. But NASA officials don’t want to hold any non-emergency spacewalks until they complete an investigation into the water leak.
“We need to take this costume home and look at it as part of the investigation to really try to figure out what happened to the costume, and that will be part of what we need for our assessment of our possible readiness when we’re looking at going back to nominal EVAs (spacewalks),” Weigel said.
The next spacewalks on NASA’s schedule are scheduled for later this year, when the next SpaceX Dragon cargo mission delivers a new set of solar arrays to the station. Astronauts will help install the new solar panels, requiring at least two spacewalks to complete the job.
Email the author.
Follow Stephen Clark on Twitter: @StephenClark1.