Though the World Trade Center rebuilding effort has been marred by delays and bitter disputes, the National September 11 Memorial, which will take up half of Ground Zero, is well on its way to completion, with its opening date still on schedule for next year’s 10th anniversary of the terrorist attacks. The memorial, for which 90 percent of the contracts have been awarded, 99 percent of the steel has been installed and 60 percent of the concrete has been poured, is expected to draw between 5 and 7 million visitors per year — making it the biggest attraction in the city — and could even be finished a few months early. The museum below the eight-acre memorial space is slated to open the following year, and construction for the 125,000-square-foot space is slated to get underway in the next few months. The $700 million construction project got half its funding from the government and half from corporations and the public. Officials in charge of the memorial estimate that it will cost $50 million a year to run.