From the start, SpaceX designed its Dragon capsule to not only fly cargo, but also crew. "Cargo doesn't need windows," Musk quipped before the capsule's first flight to the space station in 2012. Upgrades are underway to add life support equipment, seating and an escape system for crew, but SpaceX has even grander ambitions for its gumdrop shaped Dragon. It is designed to fly people to Mars.

Boeing plans to modify the CST 100 if it wins a second NASA solicitation, currently underway, to fly cargo to the station. Cargo and crew would fly separately.

NASA preceded its so called Commercial Crew development effort with a program to buy flights for space station cargo. supply lines are now running, though one operator, Orbital Sciences Corp, is regrouping after a launch accident last month. The other company flying cargo for NASA is California based Space Exploration Technologies, owned and run by technology entrepreneur Elon Musk.

Whether heading to the International Space Station, which flies about 260 miles above the planet, or other destinations, the journeys begin with rocket rides that have enough muscle to counteract Earth's gravity and get their cargo traveling at speeds of at least 17,500 mph to achieve orbit. fleet, a Delta 4 Heavy, to shoot its Orion deep space capsule as far as 3,600 miles from Earth during a test flight scheduled for Thursday. The key point of the test is to get Orion moving at about 20,000 mph before it slams into Earth's atmosphere to test its heat shield.

PHOTO (top): The Orion capsule is moved at Kennedy Space Center in Florida Nov. 11, 2014. REUTERS/Mike Brown

´╗┐behind modern spaceship design

"I lived through the (space shuttle) Columbia accident in 2003 and one of the conclusions was that that including the payload with the people was not the wisest choice. We think it is a much better approach to have the people and the cargo travel in different vehicles," he said.

In the meantime, Sierra Nevada is pursuing other contracts, including additional station resupply work for NASA that also is drawing bids from SpaceX, Orbital Sciences, Boeing and possibly other contenders.

Boeing, too, chose a capsule design for its planned space taxi, known as the Crew Space Transportation (CST) 100. "The conical shape is inherently stable as we re enter the atmosphere," Chris Ferguson, Boeing director of Crew and Mission Systems, said in an interview with Reuters.

Sierra Nevada already may have landed one customer. Paul Allen's Stratolaunch Systems, which is building a massive airplane to serve as an airborne rocket launching platform, announced last month it is considering buying a smaller version of Dream Chaser for commercial passenger spaceflights. The space plane would be attached to the Stratolaunch mothership for a ride into the atmosphere and then released to fire its own rocket engines and catapult it into space. The system could be used to fly people to and from orbit, as well as for sub orbital hops, including taking off and landing in different locations, so called "point to point" travel. That's a service that Virgin Galactic, another space tourism startup owned by Richard Branson's Virgin Group, would like to offer as well.

So is commercial spaceflight similarly primed?

"We call Dream Chaser a 'space utility vehicle' for a reason. It can accomplish multiple purposes from the same core design, like an AC 130 aircraft. We can do repair missions, change altitudes. Capsules can't do that very easily. We can do construction, like the space shuttle did to build the space station. We can be an independent or co dependent lab and stay in orbit for one year or longer conducting experiments. From the same basic design, we can contemplate all these missions," Sirangelo said.

For now, Virgin Galactic's six passenger, two pilot space plane, called SpaceShipTwo, will be limited to sub orbital flights that originate from and return to the same location. The company's first vehicle was destroyed during a fatal test flight in Mojave, Calif., on Oct. 31. The second vehicle is under construction. Point to point suborbital travel would require a different design, such as a blunter shape to better handle the higher speeds and heat of atmospheric re entry, and a more powerful rocket engine.

As NASA prepares for the debut test flight of the first spaceship in more than 40 years to carry astronauts beyond Earth, a fleet of privately owned vehicles is in development to take over transportation services to and from orbits closer to home.

Like the space shuttle, Dream Chaser is designed for runway, not water, landings, though its small size means it can touch down on most commercial runways anywhere in the world.

Until the accident, SpaceShipTwo was on track to begin the world's first commercial passenger spaceflight service in 2015 11 years after the prototype SpaceShipOne won the $10 million Ansari X Prize for demonstrating private manned spaceflight.

"The long term ambition of SpaceX is to develop the technologies to establish a self sustaining civilization on Mars Wings and runways don't really work if you're going somewhere other than Earth," Musk said at a Massachusetts Institute of Technology symposium in September.

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The capsule, which parachutes to a splashdown in the ocean or a touchdown on land, is intended to improve astronaut safety, added Ferguson, a former NASA space shuttle pilot and commander.

Capsules may be simpler to fly and cheaper to build, but they do have limitations. Sierra Nevada's winged Dream Chaser, for example, resembles a miniature space shuttle, with an aerodynamically shaped body and wings so it can fly back from space, rather than make a ballistic plunge through the atmosphere like capsules.

"We're about 2 gs and most capsules are 4 to 6. That protects returning experiments and crew," Sirangelo said in an interview.

Sierra Nevada currently is protesting NASA's decision to proceed with a final round of development funds and flight services contracts to SpaceX and Boeing. Government Accountability Office is due by Jan. 5. NASA also has an unfunded agreement to work with Jeff Bezos' rocket company, Blue Origin.

"The idea of being able to come home to Ellington Field in Houston with an experiment from the space station for Texas Medical Center and have them take if off the vehicle and get it in their labs in a half hour is very useful," Sirangelo said.

"You put enough humans with brains and eyes and ears and senses in new environments and somebody is going to think of something we haven't thought of. The fashion industry will change. The entertainment industry will change. Something will come out of it that you and I shouldn't even be silly enough to try and forecast," he said.

More diverse are the spacecraft designs the companies have chosen, reflecting not only different technical solutions to the challenges of flying people beyond Earth, but also their alternative visions of the future.

"If you could have had a conversation with that person who bought the first ride and said, 'In your lifetime, you're going to be riding in air conditioned comfort at 35,000 feet, traveling .8 Mach, watching a movie and talking to friends on the ground,' that guy would have said, 'What's a movie?' The telephone, the jet none of that had been invented, but all of it came into being very, very quickly after the airplane," said Stu Witt, the chief executive and general manager of the Mojave Air and Space Port.

"We come back with a significantly lower g force during re entry," said Sierra Nevada Vice President Mark Sirangelo, referring to "gravity force" or a measure of acceleration.

Coincidentally, it was 11 years after Wilbur and Orville Wright flew the world's first powered airplane in 1903 that a paying passenger sat Men Canada Goose Expedition Bonfire Outlet Ireland in the open cockpit of a boat shaped Benoist XIV biplane for a ride across Florida's Tampa Bay, the debut flight of the country's first commercial airliner.

Even suborbital spaceships, such as Virgin Galactic's SpaceShipTwo and XCOR Aerospace's Lynx space place, rely on rocket power to leave the atmosphere, though gravity quickly pulls them back to Earth. They don't necessarily have to launch from land, however.

SpaceShipTwo, for example, is carried by airplane and released mid air to fire its rocket, a design also used by the experimental X 15 space plane in the 1960s. Air launching uses smaller rockets than those needed for similar ground based flights, eliminates the need for expensive launch pads and opens options for launch sites, since the planes can take off from commercial runways.