The Affordable Care Act’s second act begins Saturday.

After a rocky start in October 2013, when glitches plagued the website, the ACA’s health insurance marketplace’s enrollment period for 2015 opens on Saturday. Consumers can sign up for 2015 coverage through Feb. 15.

Maine’s health specialists say it’s difficult to know how the ACA’s sequel will go, or even how to measure success.

“It’s kind of like throwing darts,” said Mitchell Stein, a Cumberland-based independent health policy analyst.

The second year that people can purchase marketplace insurance is expected to make a further dent in the rolls of the uninsured. Many of those eligible to buy subsidized insurance – people who earn between 100 and 400 percent of the federal poverty limit, or about $90,000 for a family of four – are self-employed, work part time, or are contract workers who can’t obtain coverage through an employer.

About 44,000 Mainers purchased insurance on the marketplace for 2014, beating federal expectations.

But for 2015, state health industry experts are not making a prediction, because it’s unclear how many people are still uninsured, and how many of them will be willing to pay a penalty rather than sign up for health benefits.

Nationally, 7.1 million people gained insurance through the marketplace in 2014, and the U.S. Department of Health and Human Services this week estimated an additional 2 million to 3 million will sign up in 2015. The federal government did not release state-by-state estimates.

“If I gave you a number (for Maine), I would be making it up,” said Jake Grindle, health services navigator at Western Maine Community Action in East Wilton. Grindle coordinates Maine’s navigators – the federally funded workers, located in every county in the state, who help people sign up for insurance.

Also declining to make projections were the Maine Health Access Foundation and Consumers for Affordable Health Care, both statewide nonprofits that are helping in the effort to sign people up for insurance.

Grindle said it’s hard to know how many people who are open to purchasing insurance have actually learned how affordable it can be. Many of the 44,000 who signed up for 2014 were people motivated to purchase insurance, such as those with chronic health conditions. But Grindle said no one knows what percentage were already motivated and how many were persuaded to buy insurance by a marketing campaign or an acquaintance.

“It’s hard to say how far we’ve reached into that second pool (of persuadable enrollees),” Grindle said.

The remaining uninsured may be reluctant to purchase insurance or don’t realize that subsidies can greatly reduce the costs, Grindle said. While premium costs vary greatly depending on the plan chosen, a typical plan might cost about $150 per month, with a subsidy.

Premium costs will be about the same as last year for most plans, according to the Maine Bureau of Insurance. Consumers will have an additional insurance company to choose from, as Harvard Pilgrim has joined Maine Community Health Options and Anthem Blue Cross Blue Shield on the Maine marketplace.

Maine Community Health Options, a new cooperative operating with a federal loan, captured more than 80 percent of the market this year.

Emily Brostek, executive director of Consumers for Affordable Health Care, said they will let people know about the affordability of most plans, and that the penalty for not purchasing insurance – the individual mandate – is going up. People who are eligible to purchase insurance but who refuse to do so will have to pay $325, or 2 percent of their income, whichever is higher, for refusing to sign up in 2015, and the penalty will increase further in 2016.

For this year, those who declined coverage paid a $95 penalty, or 1 percent of their income.

“The big message we are giving people is that they should understand their options. Many people just assumed that they couldn’t afford it last year,” Brostek said.

Maine is also ramping up its efforts for the enrollment period.

Grindle said a federal grant to pay for navigators increased from $475,000 in 2014 to $520,000 for 2015, because the number of federal navigators is rising from 69 to 78. Also, hospitals and other nonprofit groups are boosting their efforts to help sign up people, Grindle said, joining the community health centers that were a major part of the grassroots effort for the 2014 enrollment period.

Alyson Cummings, spokeswoman for Maine Health Access Foundation, said the nonprofit is spending about $500,000 on marketing efforts for 2015 sign-ups, similar to what it spent for this year.

“We are targeting young adults this year,” Cummings said. “They are a tough nut to crack.”

In Maine, which has the highest median age in the nation, only 22 percent of ACA marketplace enrollees in 2014 were in the 18-34 age group, according to the U.S. Department of Health and Human Services. That was below the national average of 28 percent.

Gary Briggs, 62, of Falmouth, said he’s signing up for marketplace insurance for the first time for 2015 because his former employer eliminated health coverage for retirees. Although Briggs is retired, he’s not old enough to receive Medicare, which kicks in at age 65. Briggs said his subsidized monthly premium will be about $400, which is less expensive than if he had to buy individual insurance without a subsidy.

“I’m barely able to get by, but I’m appreciative that this insurance is available,” Briggs said.