Approximation results for kinetic variants of TSP

We study the approximation complexity of certain kinetic variants of the Traveling Salesman Problem (TSP) where we consider instances in which each point moves with a fixed constant speed in a fixed direction. We prove the following results: 1. If the points all move with the same velocity, then there is a polynomial time approximation scheme for the Kinetic TSP. 2. The Kinetic TSP cannot be approximated better than by a factor of 2 by a polynomial time algorithm unless P = NP, even if there are only two moving points in the instance. 3. The Kinetic TSP cannot be approximated better than by a factor of 2(Omega(rootn)) by a polynomial time algorithm unless P = NP, even if the maximum velocity is bounded. n denotes the size of the input instance. The last result is especially surprising in the light of existing polynomial time approximation schemes for the static version of the problem.