Like every year, Elsevier professional astronautics and planetary science journals are offering their first issue of the year free for download
Acta Astronautica
Icarus
Still to come
Advances in space research
Planetary and Space Science
as usual, lots of interesting infos

Hmmm... no free full text articles

EDIT: I was wrong: http://www.sciencedirect.com/science/journal/00191035 ; and even more

The first issue of Acta Astronautica for 2010 is online and freely accessible.
Not much UMSF-related except for
The Dawn project's transition to mission operations: On its way to rendezvous with (4) Vesta and (1) Ceres
and
Lunette: A low-cost concept enabling multi-lander lunar science and exploration missions

The 2010 first issue of Planetary and Space Science, a dedicated BepiColombo issue is available for free!

The November 2010 issue of Planetary and Space Science "Surfaces and atmospheres of the outer planets, their satellites and ring systems: Part VI" is currently available for free download

As usual, the first issue of 2011 of Elsevier journals is free to access (only Acta Astronautica and Planetary and Space Science are available at the moment, see the links above)
Unfortunately, only the html version of the papers is freely accessible, and not the pdf