A small fleet of privately developed spacecraft will head into orbit in the next few years–assuming that current levels of public and private funding can be sustained. If it happens, this will mark a new chapter in space exploration and research, as NASA comes to rely more on private companies for the technology to put manned and unmanned vehicles in space.

Progress reports from several private space companies at the American Institute of Aeronautics and Astronautics’s Space 2010 conference, in Anaheim, CA, reveal new details of spacecraft design as well as testing and flight schedules.

To develop their new spacecraft, these companies have received financial assistance from NASA for reaching various milestones under the so-called Commercial Orbital Transportation Services and Commercial Crew Development programs, which are oriented toward getting commercial providers to deliver cargo, and eventually crews, to the International Space Station. But since supplying the ISS is a somewhat limited market, and subject to the funding whims of Congress, the manufacturers hope to bring in additional revenue by opening up new markets for their vehicles.

Furthest along in developing a viable spacecraft is SpaceX, headquartered in Hawthorne, CA, and founded by Internet millionaire and energy entrepreneur Elon Musk. SpaceX is developing a reusable spacecraft, called Dragon, and a launch vehicle, the Falcon 9. The Falcon 9 had a successful test flight in June. It went into orbit at 250 kilometers. The Dragon spacecraft, which resembles an Apollo capsule, successfully completed a high-altitude drop test using its reentry parachutes three weeks ago.

Orbital tests of the spacecraft are expected to begin later this year, prior to its first resupply mission to the ISS in 2011. Although the Dragon will initially just transport cargo, it is being designed with human passengers in mind, and should require minimal modifications before it can ferry crews to and from orbit. Beyond missions to the ISS, SpaceX plans to fly refurbished Dragon spacecraft under its DragonLab program, offering scientific or engineering researchers pressurized and unpressurized environments for experiments they want conducted in zero gravity or in the vacuum of space.

Not far behind is Virginia-based Orbital Sciences, which is focusing on building an expendable, cargo-only vehicle. Unlike SpaceX, which prides itself on designing and building many components in-house, including the Falcon 9’s engines and the Dragon’s heat shield, Orbital is using as many commercially available components as possible to minimize the development risk.

For example, the pressurized cargo module of the company’s Cygnus spacecraft is being supplied by French firm Thales Alenia, which also builds pressurized compartments for the European Space Agency’s cargo supply spaceship, the ATV. Orbital Sciences is also building a new launch rocket, the Taurus II, again using many off-the-shelf components. The first stage of the Taurus II is equipped with modified Russian engines originally built for the Soviet Union’s ill-fated manned lunar program.

The plan is for both the Taurus II and Cygnus to have their first launches in 2011, with the first resupply mission to the ISS in 2012. Orbital believes the modular design of the Cygnus will allow it to adapt the spacecraft for a number of uses, including flying experiments in its pressurized compartment, or using the propulsion and navigation module as part of a satellite.

Sierra Nevada Corporation of Sparks, NV, is developing a spacecraft called Dream Chaser that incorporates two hybrid engines similar to those the company is supplying to Virgin Galactic for the suborbital SpaceShipTwo. The basic structure of the first Dream Chaser has been built, and Sierra Nevada plans to begin orbital flights in 2014, launching atop the workhorse Atlas V rocket. Sierra Nevada’s executive vice president and chairman, Mark Sirangelo, says the company hopes to use the Dream Chaser to service satellites, with astronauts conducting space walks to perform maintenance.

Aerospace giant Boeing, headquartered in Chicago, is building the CST-100, a space capsule designed to fly on a Falcon 9, Atlas V, or Delta IV rocket. It features a new type of launch escape system that uses rocket engines mounted beneath the spacecraft to send it clear of danger. Similar spacecraft typically use an escape tower attached to the nose of the capsule to pull it to safety in an emergency. These escape towers must be jettisoned once the spacecraft is under way. The new pusher system doesn’t have to be jettisoned, and so could be reused, reducing costs. Test flights are due to begin in 2013; Boeing claims the CST-100 could be operational by 2015. On the exhibition floor, Boeing is displaying an ambitious model of a private space station made of inflatable modules (built by Las Vegas-based Bigelow Aerospace) that could be serviced by CST-100 spacecraft.

Finally, there’s Blue Origin, a Kent, WA, company founded by Jeff Bezos, CEO of Amazon.com. Blue Origin began testing a suborbital spacecraft design, called New Shepard, in 2006 as a precursor to an orbital vehicle, currently known only as the Blue Origin Space Vehicle Concept. Some hardware for this new vehicle has been built, including the escape system, which uses a design similar to Boeing’s CST-100 system.