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back to article Virgin space rocketship trials 'feather' re-entry system

The SpaceShipTwo suborbital rocketplane, commissioned by beardy biz-lord Richard Branson in order to offer zero-G exoatmospheric joyrides to wealthy customers, has flight-tested its unique "feathering" re-entry mode. VSS Enterprise in feathered descent testing. Credit: Clay Observatory/Virgin Galactic Engage shuttlecock mode, …

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Yag
Flame

And yet ANOTHER one...

Another thing to the credit of Elon Musk : he gave an more original name than this overplayed, bland and annoying "Enterprise" for his spaceship.

Nice engineering feat, but it may be quite... annoying if one of the tails get stuck in the feathering position.

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Vast difference

It might be helpful to provide some information about how vast the energy difference is between a sub-orbital hop and achieving orbit, and therefore why these lower-cost spacecraft without huge rocket booster stacks are never going to be capable of reaching orbit.

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Anonymous Coward

Its basically a high altitude, rocket powered aircraft

I would not pay much to fly in it, you may as well have a go on the Vomit Comet. Much cheaper.

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A question for which I've been wanting an answer...

I've been wondering for a long time why space craft re-enter the atmosphere with such ferocity that they need all that heat shielding... and why no one has though to try taking a bit longer about it. Guess I have my answer. Cheers Lewis

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Since the article doesn't actually answer your question....

Orbital velocity is very very fast indeed, and that speed is scrubbed of during reentry. The kinetic energy needs to go somewhere, and is converted to heat via friction.

SS2 and all other suborbital hops have no translational velocity, and the only KE they need to scrub is what they generate on the way down, vertical. Much less than that of orbital velocity PLUS the height, hence no (or minimal) heat shielding.

Or something like that.

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Because...

...they're going so very fast. Orbital velocity for low earth orbit is around 25,000km/h. In order to go that fast, you need to make your vehicle nearly all fuel. To slow back down again would take an equal amount of fuel, which means lifting it all, which means more take-off fuel. You very rapidly end up launching fuel to get fuel which needs fuel which needs fuel etc. and you no longer have a spacecraft.

Therefore, the only option is to use the atmosphere to slow down. You can do this slowly or quickly, but your limitation is how much heat the spacecraft can absorb. Even with the best insulation in the world, if you spent too long slowing down, the interior would get hot enough to cook the astronauts.

Of course, none of this is a concern for SpaceShipTwo, which only goes 4,200km/h which only generates a small amount of heating. No such suborbital craft would ever need tiles or active cooling or other advanced protection system. The 'feathering' system on SS2 is mostly concerned with maintaining a safe attitude during re-entry, when the air is thin and control surfaces have little effect.

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Silver badge

Its because they re-enter from orbital velocity.

The max speed reached by the Virgin thrill ride is about 2600 mph, by contrast a spacecraft in low Earth orbit is doing close to 16,000 mph.

That speed has to be dumped somehow. There are two ways to do this, powered decent, or aerobraking. Powered decent was used on the Moon because, obviously, there's no atmosphere and the low gravity makes it feasible ( Lunar orbital speed @ 2200 mph). Less speed to dump.

OK, so in order to *be* in orbit around the Earth you must be doing around 16,000 mph. Carrying enough fuel up to do a powered decent is unrealistic, so both the Virgin craft and (for example) the Space Shuttle, use aerobraking.

The difference is the shuttle needs to dump a *lot* more speed. Speed = energy = heat, hence all of the heat shielding.

The Virgin ride is, actually, kind of poor value compared to that $20m Soyuz flight if you take into account the amount of space-time you get per dollar. $200,000 buys you 6 mins, Mark Shuttleworh coughed up 100 times that, but got 11 *days* of flight time.

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Anonymous Coward

not only kinetic

but potential energy has to be dumped. Although usually the potential energy gets converted into kinetic as the thing re-enters :e.g. drop an otherwise stationary brick from height.

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Why so fast?

To complete the answer from the above excellent points. There is a fundamental difference between reaching the edge of space and going into a useful orbit. The energy required to get to the needed altitude it trivial. However the orbit that you are in has a rather unfortunate geometry. Whilst you will technically be in orbit about the centre of the earth's mass, the orbit's path also intersects the surface of the Earth remarkably close to the point where you took off. In order to get your orbit round enough that you get back to your starting point in space without embarrassing terrestrial intersections you need to put a heck of a lot of energy into circularising the orbit. Once you want to come back this same amount of energy has to be dissipated. Whilst you can get rid of some orbital energy slowly (aerobraking has been used for such things as orbital circularisation into Mars orbit from the much faster approach speed from Earth) you are going to find that there will always be a point where you are orbiting inside a thick enough layer of the atmosphere that you have no remaining choice about the rate at which the energy must be got rid off. The answer being: very very quickly.

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Silver badge
Headmaster

MPH?

Oh, how quaint.

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Paris Hilton

Balls of steel

Test pilots Pete Siebold and Clint Nichols must have balls of steel. Or a stronger-than-steel composite.

Paris icon - because I'm sure she likes men with balls of steel.

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Blimey

" the VSS plunged rapidly and "almost vertically" through nearly 20,000 feet in just over a minute before un-feathering at 33,500 feet"

I need a new pair of trousers just reading that, and I'm only on the first floor.

"3 miles a minute, vertically, you say? The first manned test, you say? Oh, I've got to take the goldfish to the vet that day, best get a temp in!"

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Bronze badge

Work it out...

This doesn't even need a pocket calculator to get a rough figure.

Just over 5000 feet to a mile, so about 4 miles in a minute, so 4 * 60 miles per hour.

That's 240mph, plus any forward component. It's fast compared to your drive to work, but a Spitfire could fly faster in level flight.

That's the sort of rough calculation you need when you use a slide rule. Somewhere around 200 knots true air speed. Indicated air speed is what matters, because that takes into account air density, but if you can call the environment "space" things have gotten fuzzy.

Oh, and a rough estimate would be an IAS of 120 knots. This is not a high-speed maneuver.

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From the figures

it's a rapid change in vertical altitude, dropping from some 50,000ft to 30,000ft in a minute- the best part of a third of their altitude.

No, it's not rocket propelled flight downwards, but it's still a 'kin fast plummet to be doing with brand new technology. So yeah, sorry I'm not displaying the right amount of blasé, but I remain impressed.

Also, I'm clearly not a pilot. IAS means nothing to me in this context, so why would I try and work out a unit I've absolutely no frame of reference for? You'd derive exactly the same look of blank 'and?' if you were to give me the speed in terms of olympic pool lengths.

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Bronze badge

You missed the point

A Spitfire could fly faster in a Controlled Level flight

This is Straight down in a virtually untested craft.

I would like to of seen your response if you were asked to go along.

I would say No to the Test and Yes to the spitfire.

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Not friction heating

[[... and is converted to heat via friction.]]

It is my understanding that friction is not responsible for re-entry heating.

http://en.wikipedia.org/wiki/Aerodynamic_heating

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Silver badge

Interesting...

Read the Wiki article a couple of times and still don't understand it - it doesn't really explain how the KE of the gas is converted in to heat. Perhaps there is a pressure change at the surface, so we get P1TV1/T1 = P2V2/T2 involved. Bernoulli and Boyle must be involved somewhere!

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Boffin

Mr

http://en.wikipedia.org/wiki/Aerodynamic_heating

"When fluid flow slows down its kinetic energy is converted to heat"

OK, but how? Maybe by.... friction???

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I'll give it a try..

Here's my (admittedly poor) understand of it: After reading the Wiki article, I got the impression that heat gets generated because the relative speed of the air around the craft is getting slowed down to (almost?) zero, and the kinetic energy stored in the air is released as heat. This is the same thing that happens if an object dropped from altitude hits the ground, all the energy of the falling motion must "go somewhere". Try dropping a solid metal bar onto ice. If the Ice doesn't crack, you will notice that some of it has melted upon impact.

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Bronze badge

Friction heating

The aerodynamic heating at re-entry is a form of friction heating. Kinetic energy is transformed to heat, just as if you were using your feet for brakes. But the friction (fluid friction) is in the air around the spaceship, not on the surface of the spaceship. There is negligable friction at the surface because the air is so fluid -- some of the air moves with the space ship, bouncing against the next bit of air, bouncing against the next bit of air, etc.

That wikepedia article is a bit confusing because it assumes fluid is flowing against a stationary structure, rather than the other way around, but it works out the same.

The energy transfered back from the hot air to the spaceship is only a fraction of the kinetic and potential energy lost by the spaceship, because most of the hot air gets left behind.

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Black Helicopters

Aerobraking

Some of the orbital probes sent to Mars used aerobraking (even with the tenuous atmosphere of Mars!) to help dissipate inter-planetary speed, to allow less fuel to be carried for orbital insertion.

Perhaps Scaled Composites can strap together several of the rubber-laughing gas rockets to achieve orbital speed, and then devise a cunning method to use aerobraking to gradually slow the craft for reentry.

Since aerobraking will likely take many orbits to achieve the speed reduction, a side benefit is that they can sell extended space orbiting as a special feature!

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Stop

Unlikely.

Even for a pathetic little suborbital toy like they're playing with, the rocket motor is big. It takes up the entire rear third of the vehicle. I've not been able to find out how much it masses, but some of the early test versions used 4 tonnes of oxidiser, and given the size of the tank on the flight model I doubt they're using much less to fly with.

It would take 50 such engines to get a craft like spaceshiptwo to orbit. Probably closer to 70 once you take into account the structure needed to bolt all the extra engines on. Add another 100 engines for a first stage booster, because you're certainly not going to be able to drop all of that weight from beneath their tiddly little carrier plane.

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So is the VMS ship nicknamed "Mary"?

It is, after all, the Virgin Mother Ship.

Mine's the one with the rosary in the pocket.

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Thumb Up

Eight Miles High and Falling Fast

"The spaceship is a joy to fly and the feathered descent portion added a new, unusual but wonderful dynamic to the ride," said Siebold after changing his underpants

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Silver badge
Stop

Reentry *from orbit* explained...

...ping from orbit.

17,500 mph. BRAKE!! BRAKE!! BRAKE!! Ouch.

17,400 mph. BRAKE!! BRAKE!! BRAKE!! Ouch, brakes are hot.

17,300 mph. BRAKE!! BRAKE!! BRAKE!! Ouch. brakes are fried.

17,200 mph. BRAKE!! BRAKE!! BRAKE!! Ouch. Scrubbing off 100 mph hurts.

17,100 mph. BRAKE!! BRAKE!! BRAKE!! Ouch. Darn G-force.

17,000 mph. BRAKE!! BRAKE!! BRAKE!! Damn, This is going to take a while...

etc.

etc.

etc.

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Bronze badge
Stop

Gliding reentry

The space shuttle actually uses its shape for lift during reentry, allowing it to remain higher that it otherwise could while shedding speed. It also does sweeping s-turns, probably to afford control over the distance traveled during the reentry. The g's and heating rate are much less than with a capsule descent but the heating time is a lot longer.

BTW, the energy ratio between a 'popup' flight like with SpaceShipTwo and a true flight to orbit is about 12:1, thus no huge fuel strapons and engines to match. Calling this thing a 'spaceship' is a bit like describing an obscene call as 'phone sex.'

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The title is required, and must contain letters and/or digits.

>> It also does sweeping s-turns, probably to afford control over the distance traveled during the reentry.

The Shuttle needs to be banked so that the lift (= drag, stopping force, heat, etc.) is not applied too strongly or quickly. When banked, the vertical component of the lift vector is smaller, but there is now a sideways component which causes the orbiter to change course while re-entering. To stay on course they need to turn and bank the other direction some of the time, hence "S" curves.

As you said, this banking ability also provides the "cross range" capability, i.e., to land in the same place it took off, after just one orbit, as frequently mentioned in this website's articles about the X-37B.

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This is not a title

"the feathered descent portion added a new, unusual but wonderful dynamic to the ride,".

Translation - it scared the crap out of us.

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Joke

Ahhh the prospects of going to space with a big VIRGIN sign on your back

A subject is needed^^

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Headmaster

Spaceship 'of a sort'?

Excuse me?

Are you claiming that The first two Mercury flights, Freedom 7 and Liberty Bell 7, were NOT spaceships as they only went suborbital?

Are you claiming the Alan Shepherd and Gus Grissom are NOT astronauts as they only went suborbital?

Would you want to go as high as the SS1 / VSS craft go in something that WASN'T rated as some form of spacecraft?

Would you like to step outside? (at 150,000 ft...)

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Pint

"...Alan Shepherd ...only went suborbital?"

"Only" ? Apollo 14. The fricken Moon. Whacking golf balls for "miles and miles."

Your basic point is still correct. An Astronaut is appointed, and this designation becomes indisputable upon reaching a certain arbitrary altitude that varies by era and opinion.

PS: I have a book Shepherd signed. And books signed by Bean and Duke. I'm just saying... :-)

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Pint

So, have there been any bids on the golfball?

If we do go back to the moon, surely someone would be willing to pay MONEY for it.

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