Artist's rendering of the BOLAS concept. Vertical separation by the tether allows for a quasi-stable orbit and an extraordinary reduction in propellant requirement
|Mission duration||≥ 1 year (proposed)|
|Spacecraft type||Two CubeSats|
|BOL mass||~15 kg each|
|Power||2 deployable solar arrays|
|Peri||10 km |
Bi-sat Observations of the Lunar Atmosphere above Swirls (BOLAS) is a spacecraft mission concept that would orbit the Moon at very low altitude in order to study vital aspects of the lunar surface. The concept, currently under study by NASA, involves two small identical CubeSat satellites connected vertically above the lunar surface by a 25 km long tether. The mission goal is to understand the hydrogen cycle on the Moon, dust weathering, and the formation of lunar swirls. The team from NASA's Goddard Space Flight Center was selected in August 2017 to further mature the concept.
BOLAS is a mission concept under study at NASA, with the goal of understanding the cycle of hydrogen on the Moon and to determine the formation mechanism of the lunar swirls. The mission would involve two small CubeSat satellites connected with a 25 km (16 mi) long space tether. The lower CubeSat would orbit at an altitude of 10 km (6.2 mi) above the surface. Without a tether system, a comparable low-altitude mission would need prohibitive amounts of fuel to maintain its orbit. The two tethered spacecraft would be placed at a 30° orbit inclination and will be stable for more than one year.
The two CubeSats are 6 units each and would be equipped with nearly identical miniaturized instruments. The mission will use the subsystems developed by Kentucky's Morehead State University, which is leading NASA's Lunar IceCube mission.
A bolas is a type of throwing weapon used by South American gauchos made of weights on the ends of interconnected cords. Its application in aerospace is called space bolas or momentum exchange tether.
The BOLAS mission would investigate the lunar hydrogen cycle by determining the mechanisms and dynamics of lunar hydrogen implantation, and their dependence on surface composition, regolith properties, local topography, plasma conditions, time-of-day, and crustal magnetic fields.  The second main objective is to understand the role that magnetic anomalies and space weathering could play in the formation of lunar swirls — enigmatic features found across the Moon's surface. The mission would also study regolith, local topography, plasma conditions, and magnetic fields within the crust.
Scientists think the lunar swirls form as a result of magnetic fields in the lunar crust, which protect the lighter-colored regolith either by diverting solar wind, or through the interaction with electric fields.
The two CubeSats are 6 units each, measuring 10×20×30 cm, not including their deployable solar panels. The higher satellite is called BOLAS-H, and the lower one is BOLAS-L. Both would operate independently and possess their own propulsion featuring two Busek BIT-3 RF ion engines each. They would also feature an attitude control system (ACS), and an X-band transponder for communication.
The two CubeSats are 6 units each and would be equipped with nearly identical miniaturized instruments: 
- ion spectrometers for measuring protons (H+)
- energetic neutral atom (ENA) imager to detect neutralized solar wind protons backscattered from the Moon. To be placed only on the lower BOLAS satellite (BOLAS-L).
- magnetometer to measure local magnetic fields
- plasma wave system (PWS) for measuring electron concentrations, electric fields, and dust impacts.
- Lunar IceCube, a planned lunar CubeSat mission
- Lunar Polar Hydrogen Mapper, a planned lunar CubeSat mission
- Tethered satellites could see the moon's weird swirls up close. Leah Crane, New Scientist. 9 August 2017.
- Jenner, Lynn (8 August 2017). "NASA Studies Tethered CubeSat Mission to Study Lunar Swirls". NASA. Retrieved 10 September 2018.
- Bi-Sat Observations of the Lunar Atmosphere Above Swirls (BOLAS): Tethered SmallSat Investigation of Hydration and Space Weathering Processes at the Moon. (PDF) Stubbs, T. J.; Malphrus, B. K.; Hoyt, R., etal. 49th Lunar and Planetary Science Conference; 19-23 March, 2018 at The Woodlands, Texa, USA.
- A Miniature Lunar Sky Crane Could Help Solve the Mystery of the Moon's 'Tattoos'. Calla Cofield, Space.com. 3 September 2017.
- L. L. Hood & G. Schubert (1980). "The Moon: Lunar magnetic anomalies and surface optical properties". Science. 208: 49–51. Bibcode:1980Sci...208...49H. doi:10.1126/science.208.4439.49.
- Steigerwald, Bill (28 April 2016). "Lunar Tattoos: New Clues". NASA. Retrieved 10 September 2018.