BioSentinel

BioSentinel is a planned low-cost CubeSat spacecraft on an astrobiology mission that will use yeast to detect, measure, and compare the impact of deep space radiation on DNA repair over long time beyond low-Earth orbit.

Selected in 2013 for a 2019 launch, the spacecraft will operate in the deep space radiation environment throughout its 18-month mission. This will help scientists understand the health threat from cosmic rays and deep space environment on living organisms and reduce the risk associated with long-term human exploration, as NASA plans to send humans farther into space than ever before.

Background
BioSentinel is one of thirteen low-cost CubeSat missions selected as secondary payloads for the first test flight of NASA's Space Launch System called Exploration Mission 1. The spacecraft will be deployed in cis-lunar space. The BioSentinel mission will be NASA's first time since Apollo 17 in 1972, to send living organisms to deep space (beyond low Earth orbit).

Objective
The primary objective of BioSentinel is to develop a biosensor using a simple model organism (yeast) to detect, measure, and correlate the impact of space radiation to living organisms over long durations beyond low Earth orbit (LEO) and into heliocentric orbit. While progress has been made with simulations, no terrestrial laboratory can duplicate the unique space radiation environment.

Biological science
The BioSentinel biosensor uses the budding yeast Saccharomyces cerevisiae to detect and measure double-strand breaks (DSBs) on DNA that occur in response to ambient space radiation. This yeast strain was selected because its DSB repair mechanisms are well studied and are very similar to those in human cells. The biosensor consists of specifically engineered yeast strains and nutrient selection strategies that ensure that only cells that can repair their DSBs will grow in specialized media. Therefore, culture growth and metabolic activity of yeast cells directly indicate a successful DSB-and-repair event.

After completing the Moon flyby and spacecraft checkout, the science mission phase will begin with the wetting of the first set of yeast-containing wells with specialized media. Multiple sets of wells will be activated at different time points over the 18-month mission. One reserve set of wells will be activated in the occurrence of a solar particle event (SPE). Approximately, a 4 to 5 krad total ionizing dose is anticipated. Payload science data and spacecraft telemetry will be stored on board and then downloaded to the ground.

Biological measurements will be compared to data provided by onboard radiation sensors and dosimeters. Additionally, three identical BioSentinel payloads will be developed for comparison reference, one of them will be exposed at low Earth orbit outside the International Space Station (ISS), where there is a comparatively low-radiation environment due to Earth's magnetic field protecting the space station.

Spacecraft
The Biosentinel spacecraft will consist on a 6U CubeSat bus format, with external dimensions of 10×20×30 cm and a mass of about 14 kg. At launch, BioSentinel resides within the second stage on the launch vehicle from which it is deployed to a lunar flyby trajectory and into an Earth-trailing heliocentric orbit.

Of the total 6 Units volume, 4 Units will hold the science payload, including a radiation dosimeter and a dedicated 3-color spectrometer for each well; 1U will house the ADCS (Attitude Determination and Control Subsystem) and 1U will house the attitude control thruster assembly, which will be 3D printed all in one piece: cold gas (DuPont R236fa) propellant tanks, lines and seven nozzles. The use of 3D printing also allows the optimization of space for increased propellant storage (165 grams ). The thrust of each nozzle is 50 mN, and a specific impulse of 31 seconds. The attitude control system is being developed and fabricated by the Georgia Institute of Technology.

Electric power will be generated by deployable solar panels rated at 30W, and telecommunications will rely on the Iris transponder at X band.

The spacecraft is being developed by NASA Ames Research Center, NASA Jet Propulsion Laboratory, NASA Johnson Space Center, NASA Marshall Space Flight Center, NASA Headquarters, Loma Linda University Medical Center, and the University of Saskatchewan in Canada.