Bi-Sat Observations of the Lunar 

Atmosphere above Swirls (BOLAS): 

Tethered SmallSat Investigation of Hydration and 

Space Weathering Processes at the Moon 

Tim Stubbs, Michael Collier, Bill Farrell, John Keller, Jared Espley, 

Michael Mesarch, Dean Chai, Michael Choi, Richard Vondrak, 

Michael Purucker, & David Folta (NASA/GSFC)

Ben Malphrus, Aaron Zucherman (Morehead State U.), Robert Hoyt 

(Tethers Unlimited), Michael Tsay (Busek), Jasper Halekas (U. Iowa), 

Tom Johnson (NASA/WFF), Pam Clark (NASA/JPL), Georgiana Kramer 

(LPI), Shahab Fatemi (IRF), Jan Deca (UC Boulder), 

Dave Glenar, Jacob Gruesbeck, & Jason McLain (U. Maryland)

Planetary Science Deep Space 

SmallSat Mission Concepts
The overarching science goal of the BOLAS mission is to determine 

the role of the solar wind in space weathering and the creation of 

water products on the surface of the Moon by investigating crustal 

magnetic fields and the swirl patterns that typically accompany them.

BOLAS Science Targets and Rationale

Primary science:

• Space weathering – regolith exposure to solar wind protons

• Lunar water cycle – role of solar wind in forming OH/water

• Solar wind interaction with crustal fields

Secondary science:

 Crustal magnetism

 Effect of impacts on regional magnetism

 Moon’s global interaction with the solar wind

 Exospheric dust transport

 Lunar ionosphere

Primary target: 

Gerasimovich – amongst strongest crustal magnetic fields with 

extensive swirl patterns. Located on farside around 21°S, 123.5°W
R

D

BOLAS Science – Swirls, Space Weathering and Water

WAC Reflectance (643 nm) Gerasimovich

visibly bright 

“pristine” swirl 

patterns
R

D

Surface OH (Kramer et al. 2011)

BOLAS Science – Swirls, Space Weathering and Water

Surface Magnetic Field [ nT ] (Tsunakawa et al. 2015)

visibly bright 

“pristine” swirl 

patterns

coincide with 

strong crustal 

magnetic fields

coincide with 

absence of OH

indicates that 

crustal fields 

shield surface 

regolith from 

space weathering 

and OH formation 

by the solar wind

Gerasimovich
BOLAS Science – Physical and Chemical Processes

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BOLAS Science – Physical and Chemical Processes

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BOLAS Science – Physical and Chemical Processes

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BOLAS Science – Physical and Chemical Processes

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BOLAS Science – Physical and Chemical Processes

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BOLAS Science – Physical and Chemical Processes

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Results from 3D self-consistent 

hybrid code (Fatemi et al., 2015)

• Uses realistic crustal field 

(Purucker and Nicholas, 2010)

• 10 × 10 km resolution at the 

surface (Y – Z plane)

BOLAS Science – 3D Hybrid Simulation of Gerasimovich

SURFACE
SURFACE

BOLAS Science – 3D Hybrid Simulation of Gerasimovich

10 km resolution 

at the surface 

captures the 

modulation of 

solar wind proton 

flux within crustal 

field region
SURFACE ALTITUDE PROFILE

Altitudes < 20 km 

required to 

observe processes 

responsible for 

decelerating, 

deflecting and 

reflecting solar 

wind protons

BOLAS Science – 3D Hybrid Simulation of Gerasimovich

10 km resolution 

at the surface 

captures the 

modulation of 

solar wind proton 

flux within crustal 

field region

Vertically-aligned, 

dual-point 

measurements 

required to 

determine cause 

and effect
BOLAS Instrumentation

Primary Payload

Ion Spectrometer (Univ. of Iowa)

Incident and reflected proton energies and fluxes

Energetic Neutral Atom (ENA) Imager (GSFC)

Backscattered neutral hydrogen (and ambient electrons)

Mini-magnetometer (GSFC)

Ambient magnetic fields

Plasma Wave System (GSFC)

Electron densities, electric fields and dust impacts

Secondary Payload

Miniaturized Cameras 

Tether diagnostics & surface imaging.

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Leveraging development of miniaturized 

instrumentation for CubeSats with high TRL
BOLAS – Frozen Science Orbit

Low-altitude lunar orbits are 

made difficult by “mascons” –

fuel mass required for stationkeeping is typically prohibitive.

“Frozen” orbits are stable, 

elliptical orbits that can reach low 

altitudes (e.g., LRO) and do not 

require station-keeping.

Stable for > 1 year

• Observe annual cycles and 

occasional events; e.g., 

meteoroid streams and coronal 

mass ejections (CMEs)

• Full local time coverage of 

surface targets every 6 months

Frozen orbit discovered with 30o

inclination – equatorial – and 

mean altitude of 90 km

• Periapsis fixed around 30o S

• Covers all strong crustal fields 

(≳ 300 nT at surface)

• Variable periapsis – minimum 

true altitude = 14.5 km

Periapsis at Gerasimovich –

minimum true altitude = 23.8 km

Frozen orbit not low enough over 

Gerasimovich for science 

requirements (altitude ≲ 20 km)
BOLAS Tethered Microsat Dynamics

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Tethered formation of two microsats enables lower 

spacecraft to obtain measurements closer to the 

Moon, while the center-of-mass of the formation 

follows the stable, frozen orbit.

Collier et al. (2016)

Gravity gradient

aligns and stabilizes 

tethered formation

BOLAS has 25 km-long tether, giving BOLAS-L

• Periapsis true altitude = 2 km

• Gerasimovich periapsis true altitude = 11.3 km

Addresses BOLAS science requirements for 

vertically-aligned, dual-point, low altitude 

(≲ 20 km) measurements at Gerasimovich
BOLAS – Tethered Frozen Science Orbit

BOLAS-L at 

altitudes ≲ 20 km
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Tether – Kevlar yarns braided into multi-line 

“Hoytether” structure to provide redundancy to 

survive meteoroid and exospheric dust impacts

Similar Deployer Tested in 

Microgravity for LOKI Program

3-braid 

100 dTex

Kevlar

1-ply 

100 dTex

Kevlar

10 cm

0.125 mm

BOLAS – Tether and Deployer

Tether Deployer System

Tethers Unlimited, Inc.
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BOLAS Microsat Design

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BIT-3 RF Ion Engines

Light 

Band to 

ESPA

Deployable 

Solar Array

Light Band

Pre-Tether Deployment

Stowed on ESPA ring

Configuration during Spiral Down
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Dimensions 

(H × W × L): 

360 × 260 × 430 mm 

Braided Kevlar 

Tether

Magnetometer 

Boom

PWS 

Antenna 

(rigid)

X-Band 

Antenna 

Patch 

XACT-50 

Star Tracker

BOLAS-L – Post-Tether Deployment
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ACS 

Electrospray 

Thruster Tether Deployer

Magnetometer 

Boom

PWS Whip 

Antenna

Braided Kevlar Tether

BOLAS-H –Post-Tether Deployment
BOLAS Resources

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Microsat BOLAS-L BOLAS-H

Mass [ kg ] 26.7 30.4

Peak power available [ W ] 240 240

Peak power required [ W ] 155 155

Telemetry available [ kbps ] 64 64

Telemetry required for primary 

science * [ kbps ] 39 39

* Assuming: 25% transponder duty cycle (~6 h per day)

10 / 90% split between burst and reduced modes

• Well within ESPA-class mass and volume limits

• Meets power and telemetry requirements

• Orbit-tether-instruments exceed science requirements
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