LIVERPOOL, England – Small-satellite builder Surrey Satellite Technology Ltd. (SSTL) remains hopeful that it will find a least one nation willing to purchase a fourth DMC-3 satellite to add to the three launched July 10 aboard India’s PSLV rocket.

That was the idea when SSTL contracted with 21AT of China in 2011 for the first three DMC3 satellites: 21AT purchased all the capacity on these spacecraft for seven years, a commitment that SSTL used to pay for the satellites’ construction, launch and insurance.

The Guildford, England-based company then thought that the certainty of the first three would be enough to lure a customer to purchase a fourth satellite whose capacity would be used by 21AT to provide in-orbit backup, and by the satellite’s owner, which would gain access to the full constellation.

SSTL competitors in this small-satellite segment of the optical Earth observation market – Airbus of Europe, Deimos of Spain, ImageSat of Israel – are using the same strategy:

Buy a satellite from us and you’ll get immediate access to a constellation, which your satellite will join to the benefit of you and the constellation’s current owners.

The first trial of the strategy for SSTL was in Peru, where Airbus won the Perusat-1 competition.

Luis Gomes, SSTL’s director for Earth observation, said that despite the lack of success so far, the fact that the company now can point to three satellites that are in orbit and – by October – fully operational is a strong sales argument.

“Until the satellites are launched, they remain abstract for some customers,” Gomes said in a July 14 interview here at the UK Space Conference. “What we would like is to have DMC3 become a constellation of six satellites. With six, you get a very nice look angle – no more than 20 degrees off-pointing – and reduced image degradation. People are interested in this.”

SSTL has purchased hardware for a fourth DMC3 and could have it completed in six months or less, Gomes said. Further models would take as long as two years to put into service.

The DMC3 satellites launched July 10 have contracted design lives of seven years, although SSTL expects them to remain operational for more than 10 years. Finding a second customer after 21AT would not only reduce periods between overflights of DMC3 over any given territory and improve the look angle, it would also begin what SSTL hopes will be a long-term constellation-refresh process.

Under the SSTL-21AT contract, the Chinese company may send image requests to the satellites directly when the targets are on the Chinese mainland. For images outside China, SSTL has a right of review that Gomes declined to detail but said will not undermine 21AT’s ambitions to expand beyond China.

The DMC3 satellites have a ground resolution of 1 meter in black-and-white, and 4 meters in color. Each satellite has about 300 gigabytes of on-board storage, and can deliver imagery to the ground at a speed of 400 megabits per second, Gomes said.

The July 10 launch put the DMC3 program some seven months behind the schedule originally agreed to when the contract was signed in mid-2011. Gomes said that while 21AT was not happy about the delay – caused by SSTL-ordered validation of the satellites’ performance – the Chinese customer understood the reasoning and did not protest.

The PSLV launch carried an all-SSTL payload including two technology research satellites in addition to the three DMC3 spacecraft.

PSLV enjoys a good reputation among commercial customers for its reliability and the environmental conditions under the fairing as the rocket climbs through the atmosphere.

Schedule transparency has not been a PSLV strong suit, numerous customers have said. Gomes said that, in this case, the Indian Space Research Organisation and its commercial arm, Antrix, demonstrated maximum flexibility.

When SSTL informed the Indian launch-service provider that the satellites would be delayed by several months, the PSLV team agreed to go on standby and to be ready when SSTL gave the word.

“We were very open with Antrix and they were very accommodating,” Gomes said. “Our concern was that we did not want our delay to put our launch behind several Indian government launches scheduled for the PSLV this year. So we knew we needed to keep the July date.”

Industry officials have said PSLV is not the least-expensive vehicle on the commercial market. Gomes agreed, but said the vehicle’s reliability is such that SSTL was willing to put all three DMC3 satellites on a single launch.

Peter B. de Selding was the Paris bureau chief for SpaceNews.