Answer Happy

A spaceship leaves the earth at t = 0 with a constant speed v.
We call the Earth system O and the spaceship system O′. The
spaceship and the Earth communicate with each other by sending
electrons back and forth at very high speed. Electrons are emitted
from the earth at a speed w. This speed must of course satisfy w
> v in order for the electrons to reach the spaceship. The
moment the spaceship departs, the clocks on Earth and on the
spaceship are synchronized, ie if t = 0 then t′ = 0 also applies.
At time te, a packet of electrons is sent from Earth. At t′r, this
package is measured on the spaceship.
Draw spacetime diagrams of the situation, seen from O and from
O′.