PARIS — The Australian government’s satellite broadband project is confronting a spike in projected demand that will stretch its satellites’ capacity and force strict bandwidth limits on customers, the company managing the project said.

In a May 7 report on what remains the most ambitious broadband rollout of any of the world’s large nations, NBN Co. said it will incur substantial new costs as it moves customers scheduled for satellite service onto terrestrial wireless technologies and prepares to fund the additional terrestrial towers.

The “Fixed Wireless and Satellite Review,” compiled at the request of the Australian government and conducted with the Boston Consulting Group, highlights a phenomenon well known to the two U.S. satellite broadband providers, ViaSat Inc. of Carlsbad, California, and Hughes Network Systems of Germantown, Maryland.

After initially forecasting satellite broadband would be most popular in rural regions, the two U.S. companies have had to adjust as demand from the suburbs and other areas with terrestrial alternatives exceeds expectations.

With fixed beams over these areas, ViaSat and Hughes have had to manage a situation in which beams in one area fill up while beams in less-populated rural areas are far from saturated.

ViaSat and Hughes are commercial enterprises. NBN Co., on the other hand, is under a government mandate to provide broadband connections to every Australian by 2021.

Most Australians will be served by NBN’s rollout of terrestrial fiber. But 3.5 billion Australian dollars ($3.2 billion) was reserved for fixed wireless and satellite technologies between 2012 and 2021. Given what it is finding out about demand for the services, the company has concluded it will need another 1.3 billion Australian dollars to complete the work.

NBN has contracted with Space Systems/Loral of Palo Alto, California, to build two large Ka-band high-throughput satellites for delivery in 2015 in a deal valued at 620 million Australian dollars and signed in February 2012. Each satellite will have 101 spot beams — 75 for highly populated areas and 26 larger beams for rural regions.

Europe’s Arianespace consortium will launch both on Ariane 5 heavy-lift rockets under a separate contract. ViaSat is providing the ground network and consumer premises equipment.

The two satellites were scheduled to be launched within six months of each other, but NBN is now concerned that six months will be insufficient time to test the satellite system and correct any issues on the second. The company is likely to ask that the second launch occur a year after the first, the NBN report said.

In recent months, NBN has determined that far more people will sign up for the government-subsidized satellite service than had been forecast two years ago.

The new assessment concludes that NBN must impose firm limits on how much bandwidth a given satellite customer gets in the regions most likely to be saturated — along Australia’s west and east coasts, where the population is concentrated.

The most recent assessment follows the experience of NBN’s Interim Satellite Service, provided by Optus Satellite of Australia and Thailand’s Thaicom IPStar Ku-band satellite. Gilat Satellite Networks of Israel is providing the ground terminals for that service.

The interim service reached a subscriber count of 44,000 much faster than forecast and has been forced to refuse new customers in some areas as its satellite capacity is full, NBN said.

Exacerbating the problem has been the fact that some satellite service retailers have offered customers essentially all-you-want bandwidth packages. This has caused other subscribers to quit the service in frustration for lack of bandwidth.

ViaSat officials have reported the same issue in the United States, saying retailers have on occasion oversold the satellite service. ViaSat has criticized the previous owner of one of its satellites for having packed it with so many subscribers that service quality suffered, giving satellite broadband a bad reputation from which it is only now recovering.

NBN evaluated several possible solutions to the beam saturation issue, including ordering a third satellite and purchasing third-party capacity, which may not have been immediately available.

The company has tentatively decided to install fixed wireless towers in areas that up to now had been identified as satellite-service regions to take pressure off the beams most likely to be crowded. NBN said it is also likely to extend the Interim Satellite Service well beyond the arrival of its own satellites.

One of the complexities of the NBN project is that it has assigned geographic zones a given technology. Some will get fiber, others fixed wireless and others a satellite service. But for reasons of local geography, this results in a hodgepodge in which satellite, terrestrial wireless and fiber customers will live a few hundred meters from one another.

One effect of this finely tuned distribution of technologies by geographic location is that 6,000 of the 44,000 Interim Satellite Service subscribers are in areas where they will not be offered NBN’s satellite service. One reason for extending the interim service to 2017, and perhaps longer, is to give NBN time to transition these customers to fixed wireless.

Australian Communications Minister Malcolm Turnbull and Finance Minister Mathias Cormann said in response to the report that the cost increase for the satellite and fixed-wireless deployment is not out of line and will not affect the government’s equity investment of 29.5 billion Australian dollars in NBN.

Follow Peter on Twitter: @pbdes

Peter B. de Selding was the Paris Bureau Chief for SpaceNews.