  Observations of the early rise and propagation phases of solar eruptive
prominences can provide clues about the forces acting on them through the
behavior of their acceleration with height. We have analyzed such an event,
observed on 13 April 2010 by SWAP on PROBA2 and EUVI on STEREO. A feature at
the top of the erupting prominence was identified and tracked in images from
the three spacecraft. The triangulation technique was used to derive the true
direction of propagation of this feature. The reconstructed points were fitted
with two mathematical models: i) a power-law polynomial function and ii) a
cubic smoothing spline, in order to derive the accelerations. The first model
is characterized by five degrees of freedom while the second one is
characterized by ten degrees of freedom. The results show that the acceleration
increases smoothly and it is continuously increasing with height. We conclude
that the prominence is not accelerated immediately by local reconnection but
rather is swept away as part of a large-scale relaxation of the coronal
magnetic field.
