(CNN) -- They call it the "coolness factor."
CNN commenters -- clearly energized about the promise of a new, privately developed space shuttle -- are buzzing about winged spacecraft versus capsule-based vehicles like Dragon, which SpaceX used for its historic visit to the space station last month.
A commenter called "gregory" points out the Skylon space plane project in the UK. The theory behind space planes is they would be able to take off from a runway, rocket into low orbit, and then fly to a landing on a runway.
Gregory suggests that space planes are preferable because their engines would be designed to "breathe air like a jet at lower speeds" and then "switch to rocket mode in the high atmosphere." CNN reported on Skylon last year and one insider estimated development cost to be around $10 billion. NASA's program to fund private spacecraft development offers only a fraction of that amount -- less than $400 million awarded so far.
Sierra Nevada's Dream Chaser orbiter, which passed an aerodynamics flight test last month, would launch atop an Atlas V rocket and uses wings to fly back to a runway landing on earth.
"As far as coolness factor -- Skylon wins over Dream Chaser hands down," gregory writes.
Well, yes, experts say privately developed space planes that take off and land independently from runways would be great.
If they existed.
But they don't right now. Why not? It costs a lot of money to develop new technology. For Skylon, a crucial engine test still stands in the way of success, according to reports. Then, down the road, suborbital test flights reportedly could happen as soon as 2016, if all goes well. Virgin Galactic's SpaceShipTwo isn't designed to take off from a runway independently, it has to be launched in flight from a mothership aircraft. It is not intended to achieve orbit.
Dream Chaser -- which aims to reach the space station -- is expected to have its first autonomous flight test in August or September. It's based on well-known design concepts, which saves money on development costs.
Coolness? Aerospace engineers will never choose style over substance.
But the sweeping, sleek design of a winged spacecraft like the Dream Chaser does catch the fancy of a lot of aerospace aficionados who still hold a place in their hearts for NASA's retired shuttle program.
Let's not forget capsules -- such as the Apollo command module -- which traveled to the moon and back.
Yes, they were gumdrop-shaped with less "coolness factor," but they got the job done. More reliable than wings, say supporters, because they're simple and more proven.
As one aerospace insider put it: Sometimes the argument about winged versus capsules "can be almost a religious debate among engineers."
A downside of most capsules: They splashdown in the water, creating water damage, although Russia's Soyuz capsule's system allows it to land safely on solid ground.
As CNN commenter "Dem in Nebraska" points out, "Spashdown requires manpower and equipment to lift the capsule out of the ocean, which requires" lots of expensive logistics and infrastructure. Landing on a runway costs a lot less, Dem suggests.
Right now, the SpaceX Dragon is designed to return to Earth by splashing down.
But the company has plans to develop the Dragon for on-target propulsive landing on solid ground.
All this talk about wings versus capsules goes to a larger point: What's the ultimate goal behind spacecraft like Dream Chaser, Dragon and Boeing's capsule, the CST-100?
Is it to build a vehicle that will take astronauts into low orbit? Or does the design goal take a longer view?
A longer view may be to develop a spacecraft that can travel to low orbit and travel to the moon -- or beyond. This is what SpaceX is looking to do -- develop spacecraft that can be used for different kinds of missions.