Editor's note: SpaceX has successfully launched the Dragon CRS-21 cargo mission for NASA and landed its Falcon 9 rocket. Read our launch wrap story here.

CAPE CANAVERAL, Fla. The next SpaceX resupply launch to the International Space Station, scheduled for Sunday (Dec. 6), will carry a host of science gear to the astronauts living and working on the orbiting laboratory.

The robotic flight, called CRS-21, marks the 21st mission for SpaceX under its commercial cargo resupply services contract with NASA. Launch is scheduled for 11:17 a.m. EST (1617 GMT) on Sunday from NASA's Kennedy Space Center in Florida, and you can watch the action live here at Space.com, courtesy of NASA. You can also watch directly via NASA TV or SpaceX.

SpaceX initially aimed to launch the CRS-21 cargo mission for NASA on Saturday (Dec. 5), but foul weather prompted a delay. "Due to poor weather in the recovery area for todays attempt, now targeting Sunday, December 6 at 11:17 a.m. EST for launch of CRS-21," SpaceX wrote in an update early Saturday morning. SpaceX plans to recover the mission's Falcon 9 booster for later reuse.

The upgraded Dragon cargo capsule that will launch atop a veteran SpaceX Falcon 9 rocket is filled with 6,400 lbs. (2,903 kilograms) of supplies and science investigations. The research gear will support a variety of experiments in the life sciences, regenerative medicine and many other fields.

Related: How SpaceX's Dragon space capsule works (infographic)

Saturday's flight will mark the first time SpaceXs upgraded Dragon spacecraft will carry cargo. (Up until now, the advanced Dragon variant has solely carried astronauts.) The vehicle is a modified version of the Crew Dragon spacecraft that lacks the systems necessary for human missions, such as seats, cockpit controls and a life-support system, as well as the SuperDraco thrusters that provide a special emergency escape system that's only used if a problem occurs during launch.

This new Dragon allows more science to ride skyward. Costello explained that the interior of Dragon can now support more powered payloads, which is a huge benefit for the life sciences as it allows for more cold storage and other types of investigations. It also allows for the crew to store some of the powered payloads onboard Dragon while the craft is on orbit.

Several of the payloads on Dragon feature a unique piece of hardware called a tissue chip. Human cells and tissue grow on the chip scaffold, creating a 3D structure in microgravity that researchers can observe to learn more about how fundamental processes work in space, including aging and bone and muscle loss.

One such investigation, run by the University of Florida, will study how muscles atrophy in space. Sixteen samples of skeletal muscle will be sent to the space station, where the bundles of muscle tissue will be observed in microgravity. Half of the muscle samples were donated by younger, active individuals while the other half are from older, more sedentary volunteers.

Half of the samples in each group will be subjected to electric stimuli to see how the muscles contract in the absence of gravity. Researchers will use this experiment as a starting point for future research that will eventually test therapies to see if muscle degradation can be prevented.

Another payload will look at brain organoids created using stem cell technology. This investigation seeks to understand how microgravity affects the survival and function of brain cells, which could lead to advances in treatments for autism and Alzheimers disease, researchers said.

"Space travel mimics the effects of aging we see on Earth, only in a much shorter time span, making it easier to examine the processes that are taking place," Bill McLamb, chief scientist at Kentucky-based company Space Tango, told Space.com. "Its hard to study human brains in space, which is why these types of experiments are so beneficial."

The investigation will take stem cells and convert them into brain cells that will form three-dimensional structures called brain organoids. Stored in a special container called a well, these types of mini organs are able to mimic both the cellular variety and the function of the developing human brain.

This type of research could help NASA and its partners prepare for crewed missions to distant destinations such as Mars, which will expose astronauts to the rigors of space for long stretches, and also help combat degenerative brain disease here on Earth, researchers said.

A team of researchers from Stanford University will be looking at how engineered heart tissue behaves in microgravity. The Cardinal Heart investigation will send tissue samples that consist of cardiomyocytes, endothelial cells and cardiac fibroblasts to study how changes in gravity affect the heart at the cellular level.

Researchers know that microgravity causes changes in the workload and shape of the human heart, but it's still unknown if these changes could become permanent if a person lived for long periods of time in space.

The project's tissue bundles will be affixed to tissue chips. The experiment's results could help identify new treatments and support development of screening measures to predict cardiovascular risk prior to spaceflight, team members said. Follow-on investigations will include therapies that could treat heart disease.

The HemoCue investigation will look at how white blood cells react in space. Here on Earth, doctors use the total number of white blood cells, as well as the various types observed, to diagnose illness. HemoCue will debut a new type of technology that will allow users to do white blood cell counts on orbit.

The goal is to test how well the device works in microgravity. If effective, it could be a valuable tool in an astronauts medical kit, researchers said.

Another payload called Micro-14 looks at how yeast, in particular Candida albicans, responds to the space environment. C. albicans is an opportunistic pathogen, capable of causing severe and even life-threatening illness in immunocompromised hosts. Micro-14 will evaluate how the yeast responds to microgravity, looking for changes at the cellular and molecular levels.

Since astronauts can become immunocompromised during spaceflight, researchers are especially interested in how best to predict the health risks from this organism. Previous research has shown that many microbes exhibit increased virulence in a microgravity environment, but more research is needed on this particular pathogen.

NASAs Jet Propulsion Laboratory in Southern California is spearheading a project that will take swab samples from various locations within the station to look at the relationship between bacteria and their metabolites (chemicals produced by bacterial growth). The project will help researchers better understand the distribution of microbes and metabolites within closed environments and how this distribution affects human health. The research could aid administrators of hospitals and nursing homes, where residents are often immunocompromised.

Related: SpaceX rocket launches for record 7th time, nails landing at sea

Sunday's launch marks the 101st flight overall for SpaceXs workhorse two-stage Falcon 9 rocket. The liftoff is expected to feature a veteran Falcon 9 first stage, designated B1058, that already has three flights under its belt. This frequent flyer previously launched SpaceX's Demo-2 mission, which sent two NASA astronauts to the space station this past summer, well as a communications satellite for the South Korean military and a batch of the companys own Starlink satellites.

Flying previously flown boosters has become commonplace for SpaceX, as the company continues to prove the Falcon 9's reliability. In fact, CRS-21 marks the 24th flight of 2020 for SpaceX, with the majority of those missions having flown on veteran rockets rather than brand-new ones.

To date, SpaceX has successfully landed its first-stage boosters 67 times. Now that the company has two fully operational drone-ship landing platforms "Of Course I Still Love You" and "Just Read the Instructions" in Florida, its able to launch (and land) more rockets. "Of Course I Still Love You" is already at the recovery zone waiting for its turn to catch B1058 when it returns to Earth shortly after liftoff.

Weather was a concern for SpaceX going into the weekend. Forecasts predicted iffy weather for a Saturday launch attempt, with the 45th Weather Squadron predicting a 50% chance of favorable conditions for liftoff. The primary concerns were thick clouds and cumulus clouds. The backup attempt on Sunday looks much better, with the forecast improving to 70% favorable on that day.

If all goes as planned, the Dragon will arrive at the station and dock at the Harmony modules space-facing port just over 24 hours after it blasts off.

Editor's note: This story was updated at 8:22 a.m. EST to include SpaceX's launch delay to Sunday, Dec. 6, due to bad weather.

Follow Amy Thompson on Twitter @astrogingersnap. Follow us on Twitter @Spacedotcom or Facebook.

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Tissue chips and organoids: SpaceX is launching lots of science to space for NASA on Sunday - Space.com