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Large navigation and atmospheric uncertainties have historically driven the need for a mid-lift-to-drag-ratio (mid-L/D) vehicle with (L/D)max of 0.6-0.8 for aerocapture at Neptune. Most planetary entry vehicles flown to date are low-L/D blunt-body aeroshells with L/D less than 0.4. The lack of a heritage mid-L/D aeroshell presents a major hurdle for Neptune aerocapture, as the development of a new entry vehicle incurs significant time and investment. Techniques that may allow Neptune aerocapture to be feasible using heritage low-L/D blunt-body aeroshells are investigated that obviate the need for mid-L/D aeroshells. A navigation study is performed to quantify the delivery errors, and a new guidance algorithm with onboard density estimation is developed to accommodate large atmospheric uncertainties. Monte Carlo simulation results indicate that the reduced navigation uncertainty and improved guidance scheme enable a blunt-body aeroshell with L/D=0.3-0.4 to perform aerocapture at Neptune. The expected heat rate is within the capabilities of existing thermal protection system materials. [ABSTRACT FROM AUTHOR]