Slashdot Mirror
Virgin Galactic SpaceShipTwo's Re-entry Tech: the Feather
Dutch Gun writes: When most people think about rocket science, they think of the challenge of getting a spacecraft into space. However, the problem of safely re-entering the atmosphere is a daunting challenge as well. Virgin Galactic introduces us to the concept of "the feather," their term for the combination of fixed-wing and capsule based solutions both used by spaceships in the past, and explain how they believe this hybrid approach to be a superior solution. SpaceShipTwo folds its wings in the initial decent, acting a bit like a badminton shuttlecock, when a capsule decent has the most advantages. In the latter part of the decent, the wings are extended, giving the vehicle the advantages of a glider-like landing.
How can someone misspell descent three times in two sentences?
Before you comment in droves about Samzenpus missing the the edit on the two "descent" fails, please proofread this post.
Happiness in intelligent people is the rarest thing I know.
Ernest Hemingway
you initiate the feather to soon and cause the spaceship to break up.
For those interested, the documentary Black Sky is a must-see on explaining how this concept (and SpaceShipOne in general) works.
SJW's don't eliminate discrimination. They just expropriate it for themselves.
Branson and Virgin did nothing at all except provide funding after the fact to the actual, certified genius aerodynamist and visionary Burt Rutan. /., I will just introduce Rutan to the crowd who might be attracted to the silly clickbait article: Burt has for about
Since it is far outside the knowledge domain of
40 years years been designing outstanding aircraft, some large, most small. He designed for NASA, for Jim Bede, and for thousands of home builders. He pioneered the modern use of canard winds and composite construction. He designed many famous aircraft including SpaceShipOne and its unique tail feathering.
"SpaceShipTwo folds its wings in the initial decent..."
Unfortunately it occasionally folds them during the ascent, too.
I have serious doubts that a feathered reentry would work for anything that has orbital reentry speed. There's a reason we have capsules with heat shields, and it's still tricky. We lost a shuttle over damaged heat shields. I suspect there would be strong vibration issues at orbital reentry speed as well that they haven't had to face yet since all of their flights so far (as well as those actually scheduled) have been sub-orbital. That being said, I wish them luck and hope they continue to innovate.
The feathering mechanism is very clever and effective, and I'm sure that Richard Branson and Virgin Galactic love getting free advertising on Slashdot. But this concept - the mechanism, the shuttlecock behavior, the passive stabilization - was successfully demonstrated when SpaceShipOne won the X-Prize ... in 2004.
So please explain, Oh submitter and editors, why are you cluttering up our lives with old news?
What's the news in this? This has been Virgin's approach for many years now, and it's very interesting, but what brought this to the front page today? Did something change?
If you can actually get your vehicle into space to begin with. Ten years and counting....
First of all, this is really old news. SpaceShip One no longer flies and has been a museum piece for years, and Virgin's burned their bridges with Scaled Composites and thus made it a lot less likely that they will be able to mount a near space effort with the SpaceShip Two design.
Second, this is not an orbital re-entry system, because it's not well-suited for a heat shield and thus can't do the necessary atmospheric braking. It's just a system to get you back from high altitude suborbital flights.
Bruce Perens.
How fast are the virgin ships coming in at? Not sure I'd call it "Re-entry"
However, the problem of safely re-entering the atmosphere is a daunting challenge as well.
Yes this is especially true since they updated Kerbal Space Program manager to 1.02...
Seven puppies were harmed during the making of this post.
Second, this is not an orbital re-entry system, because it's not well-suited for a heat shield and thus can't do the necessary atmospheric braking. It's just a system to get you back from high altitude suborbital flights.
This is exactly correct. Most people don't realize the difference between just going into space and going into orbit.
Google lists the top speed of SS1 as 2,186 mph (lets round it off to about mach 3). That's not slow, and while it's a challenge, it's not too difficult to keep something like that from burning up in the atmosphere.
By contrast, the ISS is moving at 17,150 mph (about mach 22.5). That's over 7 times faster than SS1. A re-entry vehicle leaving ISS (or anywhere in Low Earth Orbit) either needs to slow down significantly before entering the atmosphere and/or survive much more heat as it descends.
This article is not comparing apples to apples, and while SS1 is an engineering feat in it's own right, calling it a 'superior solution' is misleading to say the least.
I thought it was called the SPLAT.
X-Plane.
Rutan's SpaceShip One did it first. And there was a Slashdot article on it.
"Decent" = Well and good.
"Descent" = The "fall" part of a climb/fall profile. Usually accompanied by screaming if gear does not work.
Also, SpaceShip Two can not reach orbital velocity. It is a strictly ballistic craft, with limited thermal protection, and has an essentially vertical up/vertical down flightpath with limited atmospheric shock interaction. Eggers Blunt Body Theory does not apply. Pretty much everything is supersonic aerodynamics, which does scale up/down. Aerobody(Size =W, Shape =X, Speed=Y, Altitude=Z) will behave exactly the same as Aerobody (Size=2W, Shape =X, Speed = Y, Altitude =Z). This is why NASA, Boeing, and other aerospace groups have this things called "Wind Tunnels" and "Sub-scale test vehicles."
Getting into space (crossing the Kaman line) is relatively "easy" compare to getting into orbit - which requires a huge amount of energy to generate the forces required to maintain that orbit. It's all that energy (speed) that must be dumped that makes orbital vehicle reentry so spectacular.
When Burt Rutan (a brilliant aero guy) decided to go for the X-Prize, he did something all the other would-be competitors did not do: he read the rules and did not automatically presume those rules included some pre-determined self-imposed notion that the winning scheme had to have something in common with actual spaceflight. Everyone else, dreaming of boots on Mars, stupidly designed rockets - and thus failed to fly anything. Rutan noted that there was nothing about orbital speeds, so he built an airplane (his area of expertise) that met all the rules but had nothing to do with trips to other worlds or even to Low Earth Orbit.
THE problem with a flaming-hot "reentry" is horizontal velocity, NOT altitude, NOT "space", NOT what most people think and NOT what "feathering" solves; there's no layer of extreme heat high up at the edge of space. The heat of reentry comes from [1] the compression of air molecules ahead of a vehicle as that vehicle punches through the air at (in the case of the Shuttle) about Mach 25 and [2] that heat radiating through the boundary layer. The thin boundary layer of air forms between the compression shockwave ahead of the vehicle and the vehicle's body, and while it IS hot, it's cooler that the plasma outside the boundary layer. The shuttle's tiles were designed to withstand the boundary layer heat but could not have withstood full exposure to the compression temps beyond it, which is why the operators of the shuttles were always so careful about "tripping the boundary layer" (causing turbulence in that thin layer of smooth air which would let the hotter plasma get though and touch the tiles). NASA was so concerned about tripping the boundary layer, that they did a famous space walk to put an astronaut under the belly of an orbiter in space to pull a little plastic "gap filler" out from between two tiles so it would not be a risk during reentry. On the last flights of the orbiters, NASA placed test tiles with varying height bumps in carefully-selected spots under the orbiter to intentionally "trip" it to generate solid scientific data on the effect (an effect not fully-understood back when shuttles were designed due to lack of data and computing power at the time). The locations chosen were places of the undersides of the wings where any resulting TPS failure and possible burn-through would not destroy any vital components or structures. Many people mistakenly think the re-entry heat is from "friction" (because it was presented that way to the public in the 60's as a simplification) but most of the general public think the heat is just from some location high up between space and the top of the sky.
For the X-Prize, Rutan avoided the entire thermal issue of reentry. His Space Ship One (and the follow-on Space Ship Two) never approaches orbital speed (of well over 14000+mph) at all... they go like a German V-2 from WWII (steeply up out of the atmosphere under rocket power, then coasting upward bleeding-off all the velocity to zero, then falling back down accelerating to terminal velocity by force of gravity) which also needed no real thermal protection. The "feathering" of the Rutan design is only designed to reduce the falling speed, which from such a height would indeed be supersonic and therefore a complex aero hassles but would never approach an orbital speed and therefore require a real thermal protection system. Feathering helps Space Ship One (and Two) stay well below the speeds of the fastest runs of the X-15 which had required thermal protection while going less than a quarter of the speed of the shuttles. The "feathering" would do no good whatsoever on any real spacecraft returning to Earth from Orbit or from any other location in space.
I hate it when people who should know better (often journalists whose JOB is to ask questions and learn the facts and then inform the public) push this sort of misleading marketing to a gullible and distracted public, who then presume that anybody using thermal protection on a spacecraft (or designing a spacecraft unlike the one in the article) is some sort of a backward idiot who is wasting money.
It reminds me of Branson crowing about how environmentally friendly and efficient their hybrid motor is. "We have reduced the [carbon emission] cost of somebody going into space from something like two weeks of New York’s electricity supply to less than the cost of an economy round-trip from Singapore to London."
Never mind that spaceflight would have to scale up many orders of magnitude to be a meaningful contributor to carbon emissions, that there are few rockets that emit as much carbon for their performance as their hybrid, or that they produce fewer emissions simply because they aren't doing anywhere near as much.