We describe an extension of special relativity characterized by {\it three}
invariant scales, the speed of light, c, a mass, κ and a length R.
This is defined by a non-linear extension of the Poincare algerbra, A,
which we describe here. For R→∞, A becomes the Snyder
presentation of the κ-Poincare algebra, while for κ→∞ it
becomes the phase space algebra of a particle in deSitter spacetime. We
conjecture that the algebra is relevant for the low energy behavior of quantum
gravity, with κ taken to be the Planck mass, for the case of a nonzero
cosmological constant Λ=R−2. We study the modifications of
particle motion which follow if the algebra is taken to define the Poisson
structure of the phase space of a relativistic particle.Comment: 13 page