NASA ended its space shuttle program in 2011, in part to focus on other goals such as putting humans in deep space and on Mars. But the agency still needs a reliable and cost-effective way to get astronauts to and from the International Space Station (ISS). For the past several years it has been paying Russia to do just that. But soon, it will no longer have to do so.

Since 2010 private companies have been competing for a lucrative opportunity: to provide routine transport of American astronauts and cargo to the ISS as well as deliver other low Earth orbit payloads. Now three companies are closing in on that goal; NASA will be announcing the winner or winners later this year. With only a couple months left in a four-year-long race, two well-known spaceflight heavy hitters—SpaceX and Boeing—have been joined by a seeming underdog: Sierra Nevada Corp., a 51-year-old company with spaceflight cred that includes supplying the Virgin Galactic SpaceShipTwo engine.*

In 2010 NASA announced the Commercial Crew Program, with a goal of developing a “safe, reliable and cost-effective crew transportation to low Earth orbit,” says Stephanie Martin, the program’s spokesperson. This strategy takes advantage of the flexibility, efficiency and adaptiveness of private companies in making competitive technologies that respond to a growing space-related business marketplace while reducing taxpayer expenses. According to the Space Foundation’s 2014 Space Report, the space economy is globally valued at about $314.2 billion, a figure that includes everything from telecommunications to weather forecasting to navigation to launches of military satellites. Other organizations would also benefit from the commercial development of more vehicles capable of reaching space at lower costs. “Researchers might want to have access to low Earth orbit to do experiments,” Martin says. Space tourism is another possibility; one consulting firm estimated that space tourism could be worth over a billion dollars by 2021.

NASA awarded five companies a total of nearly $50 million through the first round of funding in 2010 to develop spacecraft, launch systems and support equipment, including Blue Origin, Paragon Space Development Corp. and United Launch Alliance as well as those involved in manned vehicle development like Boeing and Sierra Nevada. Over the subsequent rounds of funding SpaceX entered the fray whereas other companies dropped out or, in some cases, entered into “unfunded Space Act Agreements,” allowing the firms to continue working with NASA scientists but without receiving more funding.

The latest round of the competition, awarded in 2012, gave $10 million to Sierra Nevada for the recently completed safety testing of its vehicle, called Dream Chaser. In July the company completed another milestone by successfully testing several of Dream Chaser’s major systems, including life-support as well as environmental and thermal controls. Earlier in the month it also tested the vehicle’s main propulsion system.

With the completion of this latest safety-testing milestone of key systems, Mark Sirangelo, corporate vice president of Space Systems at Sierra Nevada, says that this stage of the Dream Chaser program, before NASA announces a winner, is “90 to 95 percent complete,” with at least one more landing flight test and tests of the thrusters remaining. The company has a November 1, 2016, date set for the first unmanned launch of its spacecraft into orbit. If all goes as planned, it would stage a second launch about six months later and would then apply to NASA to certify the Dream Chaser as ready to take a crew to the ISS, Sirangelo says.

Sierra Nevada’s crew transportation vehicle design differs markedly from that of Boeing or SpaceX. Although all three designs use a traditional vertical launch rocket to get their vehicles into space, Sierra’s competitors are building capsules that are designed to land back on Earth using either parachutes and airbags (in the case of Boeing’s CST-100) or thrusters (SpaceX’s Dragon capsule). But the Dream Chaser uses a lifting-body design—essentially, it is a space plane that resembles a small version of the space shuttle and, like it, can land on a runway. The design is based on a spacecraft, the HL-20, that NASA developed in the 1980s and ’90s but decided not to pursue. Sirangelo says that the lifting-body design is ideal, because it can land with a lower g-force than a capsule; instead of plummeting back to Earth slowed by parachutes or thrusters, it glides. That’s useful in a number of scenarios, according to Sirangelo. A higher g-force, such as what could be experienced in a returning capsule, could cause problems if a delicate experiment was being returned from the ISS or if an astronaut were sick or injured. The space plane design is also more quickly accessible when it returns, as it can land on any commercial runway large enough for a Boeing 737 airplane, Sirangelo says, unlike a capsule landing in a potentially remote area. This past October Sierra Nevada tested the automated landing system by dropping the Dream Chaser from a helicopter; the vehicle’s approach to the runway was spot-on, although a mechanical malfunction prevented one of the wheels from deploying, sending the vehicle skidding off the runway. Nevertheless, both Sierra and NASA deemed the test a success.

NASA hopes to have astronauts flying on the winning vehicle by 2017. Later this summer or early this fall the agency plans to announce the competition winner(s), which will eventually involve transportation of astronauts to the ISS. NASA’s Martin says it is possible that the agency may choose more than one design for crew transportation. “We do look forward to continuing to work with all of our partners,” even those that don’t receive the next contract, she says—down the road NASA may want the option of having multiple transportation vehicles to choose from.

Of course, Sierra Nevada may end up on that also-ran category. Roger Handberg, professor of political science at the University of Central Florida and an expert on space policy, for one, is dubious about the company’s chances. SpaceX, which he thinks is the current favorite, has already completed several successful missions to and from the ISS with an unmanned version of its Dragon capsule whereas the Dream Chaser has not yet been in orbit. “It’s hard to beat something with nothing,” he says. “Until you fly, you’re going to have that problem.” Sierra has also received less funding than its competitors; to date the Commercial Crew Program has awarded the company more than $363 million whereas during the same time period Boeing has received $621 million and SpaceX $545 million. These discrepant figures are due in part to the fact that Sierra Nevada had “the most significant amount of risk reduction and technology development work to do,” according to a statement by NASA when it awarded the latest round of funding in 2012.

Complicating matters, both the Boeing and Sierra designs rely on Atlas 5 rockets to get to orbit, which in turn rely on Russian-made RD-180 engines, Handberg notes. In May Russia announced that the U.S. could no longer use Russian-made engines for military launches; it is not clear whether that includes voyages to the space station. Sierra’s Sirangelo, however, does not think that the recent tensions with Russia will affect future space missions. Martin agrees: “We’ve had great cooperation with Russia,” she says. “We’ll always continue to work with them on the International Space Station.”

*Correction (8/14/14): This sentence was edited after posting to correct the age of Sierra Nevada Corp.