Vision based velocity estimation for soft landing of spacecrafts

Soft landing means to land a spacecraft on a surface by gradually reducing its velocity to within 0-5m/s. In order to land the spacecraft accurately at the desired landing spot the descent velocity of the spacecraft have to be determined. This paper introduces a vision based velocity estimation of a lander during soft-landing on an alien planet or a satellite. The method estimates the velocity by taking a series of images of the landing surface as the lander descents. Using two consecutive pictures estimate how much vertical and horizontal motion is there which gives an estimate of the lateral velocity. First, the vertical motion is calculated and then it is cancelled in the second image to bring the two images to same scale. Then from the resulting two images the horizontal velocity is estimated.