Only 100 km down, the gravitational acceleration would not be reduced by very much. Assuming the Earth is spherical and has uniform density, the probe would only be below ~3% of the mass and would be less than 2% closer in distance. So the acceleration felt by the probe would only vary by a few percent.
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Only 100 km down, the gravitational acceleration would not be reduced by very much. Assuming the Earth is spherical and has uniform density, the probe would only be below ~3% of the mass and would be less than 2% closer in distance. So the acceleration felt by the probe would only vary by a few percent.