Exploring MarsPathfinder Rover

Electrostatic Charging

October 8th 2002Joseph Kolecki

.

Preliminary Activities

1. What surface conditions prevail on Mars?a.Cold, dry, dustyb.Warm, dry, dustyc.Cool, wet, crustyd.All of the above

 2.How might the surface conditions on

Mars be related to ambient electrical activity?a.Conduciveb.Not conducivec.A little conducived.Conditionally Conducive

3.Which surface element on Mars would you think most likely to develop and carry charge?a.Rocksb.Dustc.Duracrustd.Volcanic glass

 4.What charging mechanisms do you

believe are operational on Mars?a.Collisional chargingb.Triboelectric (frictional) chargingc.Photoelectric effectd.None of the above

5.What are some issues associated with surface vehicle and astronaut charging?a.No issuesb.Charge is harmlessc.Charge could impact operationsd.Charge could produce fatal

conditions

Mars

Mount Olympus

“Old” Surface - Mantle

North Pole

Tarsus

Mariner’s Valley

Northern Desert

Cirrus Clouds

Tarsus

Mount Olympus

Mariner’s Valley

Martian arroyos as seen from orbit…

Fossil Martian Nano-Bacteria?

~100 nm

Why go to Mars???

Most earth-like planet

Reachable via present day technology

Possible future colonization

…

Simple curiosity – It’s there!!!

Why Send Robots to Mars???

Robots are “more durable”/less expensive than humans.

Robots can accomplish almost as much as humans.

Robots can help us to learn as much as we can about the Martian

environment before we send humans.

Environmental Issues at Martian Surface

Radiation environment

Chemistry

Toxicity

Electrical charge

Biology (?)

Electrical Charging in the Martian Environment

++++++++++

----------

Why expect charging on Mars?

Cold, dry climate – good for charging things up

Seasonal winds – good for stirring things up

Dust storms – good for keeping things stirred up in a variety of ways

What physical mechanisms might be involved?

Collisional charging due to turbulent motion in dust clouds & dust storms

Triboelectric charging due to vehicle or astronaut motion across the

surface

Photoelectric charging due to solar UV at the surface

Collisional Dust-Charge Exchange Mechanism

+

-e-

Effects of Collisional Charging in a Martian Dust Cloud

Paschen’s Curve

Pressure-Distance Product

Ele

ctr

ic P

ote

nti

al

Diff

ere

nce

Paschen Curve Minimum

Pressure-Distance Product

Ele

ctr

ic P

ote

nti

al D

iffere

nce

10

0V

5 X 10-5 atm-m

Sojourner Rover:

Triboelectric charge = Frictionally generated electric charge

Rover Charging Scenario

Each wheel rolls over surface dust bearing down with 1/6 of rover

weight.

Dust beneath wheels becomes compressed.

Grains rub together liberating charge.

Large grains (-)

Small grains (+)

Small grains cling to wheel charging rover.

Large grains remain behind as charged wheel track.

Dust collection in laboratory

+

-

+ 150 V

- 150 V

Clogged wheel

Wheel track

Clogged Wheels!

Theory:

Predicts charging

Laboratory:

Confirms prediction

Pathfinder:

Similar to laboratory

Mars:

Does charging actually occur??

Conclusions

Because of mass constraints on rover, no instruments were carried to

measure charge.

Instruments will be carried on future landers and rovers to better characterize Mars’ electrical

environment.

Some Issues Remaining to be Solved

What is the nature of Martian surface electricity?

Do electrical discharges accompany dust storms? Dust devils?

Can these storms be detected by radio static?

Does triboelectric charging pose a hazard to future large rovers? To

future astronauts?

joseph.c.kolecki@grc.nasa.gov