NASA will send "organs-on-a-chip" on a lunar flyby in the AVATAR experiment. The AVATAR (Virtual Astronaut Tissue Analog Response) study will use unique "organ-on-a-chip" devices to study the effects of deep-space radiation and microgravity on human health. The chips will contain cells from Artemis II astronauts and will accompany them on their approximately 10-day journey around the Moon. The "organ-on-a-chip" is a miniature device, the size of a USB drive, that will help understand and then predict how a specific body responds to various factors, such as radiation or a new drug. These chips contain living human cells grown to simulate the structure and function of specific organ regions, such as the brain, lungs, heart, pancreas, and liver. The chips can be linked together to simulate the interactions between organs, which is important for understanding how the entire body responds to stressors or treatments. The Artemis II mission will use chips created from hematopoietic stem cells and hematopoietic progenitor cells obtained from blood samples collected by the crew members themselves. These cells are formed in bone marrow, which is one of the most sensitive organs to radiation and plays a key role in hematopoiesis. Therefore, researchers are eager to understand how deep space radiation affects this organ. This research could provide insight into how radiation therapy and chemotherapy drugs used in cancer treatments affect blood cell formation. Therefore, the importance of bone marrow research for both future space missions to the Moon and Mars, as well as for medicine on Earth, makes it an ideal subject for study. Upon return, scientists will perform RNA sequencing of individual cells to determine how gene activity has changed and compare the data with the results of a parallel study on Earth.