Papers with "towards X" in the title

Using "towards" in a title is perfectly acceptable, as indicated by the large number of papers that you can find with this word in their title.

I've also used it myself, in just the sort of manner that you are considering, and found no objection from reviewers.

Although I agree with the other answer that "towards" in a title is fine, I don't believe it is acceptable for the as-yet-unsolved major topic to stand alone as the entire title.

In particular, if while working toward a closed-form solution of grasp statics, you publish several papers containing useful partial results, a reader should be able to distinguish them by title and not merely the year of publication.

Most probably once you identify the differentiating factor for this piece of work, you'll still name the major problem, but without using the word "towards". Perhaps something like Separability of force-volume integrals arising in analytic models of grasp statics (I really have no clue about your field, I'm just throwing in some mathematics terms)

In summary: DO name the problem you're working towards, but if possible, make your title descriptive of the portion you've done, and try to avoid the word "towards".