But although it meets the definition of outer space, the atmospheric density within the first few hundred kilometers above the Kármán line is still sufficient to produce significant drag on satellites. Most artificial satellites operate in this region called low Earth orbit and must fire their engines every few days to maintain orbit.[citation needed] The drag here is low enough that it could theoretically be overcome by radiation pressure on solar sails, a proposed propulsion system for interplanetary travel.[citation needed] Planets are too massive for their trajectories to be significantly affected by these forces, although their atmospheres are eroded by the solar winds. COUNT 4
QSN1 Where do most satellites operate? ANS1 low Earth orbit QSN2 What system could possibly be used for interplanetary travel? ANS2 solar sails QSN3 why do satellites need to fire engines every few day to keep orbit? ANS3 atmospheric density QSN4 above what line location in outer space to satellites orbit? ANS4 Kármán line