On Aug. 5, as nervous JPL engineers watch, the fate of the rover — capable of pulverizing rocks and ingesting soil — will rest on a landing sequence so far-fetched that some scientists were skeptical it could work.Three weeks from tonight, an amiable, whip-smart engineer named Ray Baker will be staring into his computer screen at the Jet Propulsion Laboratory, hopeful and helpless — or, as he puts it, "sweating blood."