How fast is the Earth traveling through space?
Velocity is a vector. Speed is its magnitude. Earth's velocity vector rotates through
The averaging here is like averaging relative speed of Moon with respect to the Earth The Moon is ahead of the Earth in about a fortnight and behind the Earth (in regression) for the next fortnight..
Likewise, the Earth is ahead of the Sun in a half year behind for the next half, relating to the orbit of the Sun about the center of Milky Way. There is no preferred space in space, All motion is relative to one another.
Algebraically, there is a maximum and a minimum for the speed of the Earth relative to the center of the Milky Way. Yet, the angular speed 2.5 E-08 radian/year of the Sun about MW center is quite small compared to the angular speed 6.28 radian/year of the Earth about the Sun
Contribution of the speed of the recession of Milky Way in space to the Earth's speed in space is much smaller in magnitude.
So, there is reason to state that the 4-sd approximation 29,78 km/sec to its average speed about the Sun is the average speed of the Earth in space. The other contributions are insignificant. .