  Recently, Hoang et al. (arXiv:1608.05284) reported analysis of the
interaction of relativistic spacecrafts with interstellar medium (ISM, i.e. gas
atoms and dust particles) relevant for the Breakthrough starshot initiative
(https://breakthroughinitiatives.org/Initiative/3). The main conclusion is that
dust pose much greater threat to the starship than gas atoms. However, analysis
used to treat interaction of the spaceship with gas atoms is based on the
incorrect use of the Szenes model. Only by proper treatment of the Szenes model
can be found if the conclusion remains valid - or not. In the following, the
main comments we have raised about the paper are listed. Present text is based
on the v2 version of the above mentioned paper [0] that was accepted for
publication in Astophysical Journal.
