SS2 - status

cIclops · 2006-06-12 10:02:52

Flight International has just posted a report from the recent Virgin Galactic presentation in London (this is the real thing BTW)

No images but some basic details were revealed:

SpaceShipTwo (SS2) could have a different rocket fuel, a 140km (87 mile) apogee, increased down range, 7g re-entry loading and reclined passenger seats, SpaceShipOne (SS1) pilot Brian Binnie and Virgin Galactic president Will Whitehorn told last week’s Royal Aeronautical Society space tourism conference.
SS2, which now carries six passengers and two pilots, and its carrier aircraft White Knight 2 (WK2), are under construction. However, neither will be unveiled until late 2007, when flight tests are expected. WK2, with a wingspan expected to be 34-38m (112-124ft), would air launch SS2 1h into the flight. When the new hybrid rocket motor is fired, passengers will experience 4g on the ascent to an apogee of 140km.

cIclops · 2006-09-28 09:37:02

more details to follow ...

SpaceNut · 2006-09-28 10:00:06

Here are a few more story links with other images.

First Images of Virgin Galactic SpaceShipTwo Cabin

Virgin Galactic Unveils SpaceShipTwo Interior Concept

Branson unveils Virgin spaceship

Virgin Galactic reveals VSS Enterprise

Pictures: First pictures of Virgin Galactic SpaceShip2 tourist spacecraft interior unveiled in New York

Rxke · 2006-09-29 00:19:00

From the last linked article by SpaceNut:

WK2 is expected to be unveiled in the third quarter and SS2 in the fourth quarter, when test flights are expected to begin.The space tourism provider also announced its first air miles customer today. Virgin Galactic offers a seat to Virgin Atlantic customers with two million frequent flyer points. Alan Watts, a UK citizen, is the first of 36 people who have that many air miles or close to it and is to fly in 2009. The next such customer would fly in 2010 as the company is limiting air miles customers flights to one a year.

Rxke · 2006-09-29 02:29:22

Interesting (YouTube) Virgin Galactic video about SS2 : http://www.youtube.com/watch?v=XBlifr6EQNU

cIclops · 2007-07-20 21:43:59

Northrop Grumman Buys Scaled Composites

By Brian Berger and Lon Rains
Space News Staff Writers
posted: 20 July 2007
04:27 pm ET
WASHINGTON - Northrop Grumman Corp. agreed July 5 to increase its stake in Scaled Composites - the builder of the Ansari X-Prize Cup-winning SpaceShipOne and a host of record-breaking aircraft - from 40 percent to 100 percent, Northrop Grumman spokesman Dan McClain confirmed July 20.
McClain, who declined to disclose the value of the deal, said the company expects it to close in August pending regulatory approval by the U.S. Department of Justice.
Scaled Composites currently is working with Sir Richard Branson's Virgin Galactic venture on a vehicle designated for now as SpaceShipTwo, which would carry two pilots and six paying passengers into suborbital space for a few minutes of weightlessness. The company also is building a new carrier aircraft, dubbed WhiteKnight2, that will carry SpaceShipTwo to an altitude of 15 kilometers before releasing it to soar to suborbital space.
The two companies last year formed a joint venture called the Spaceship Company to build the new vehicles.
Alex Tai, chief operating officer of Virgin Galactic, declined to comment when asked July 20 how the acquisition would affect his company's dealings with Scaled Composites. "I'm afraid I can't provide you with any comment at this stage and I don't think [Scaled Composites] can either," Tai said.

publiusr · 2007-11-09 11:49:19

I think it is to be named after Fossett.

SpaceNut · 2014-05-16 18:00:26

Seems the hype is coming to an end...

SpaceShipTwo Can’t Reach 100 Km Boundary of Space (62 miles).

So, just how high can this first version of SpaceShipTwo go? Virgin now says the spacecraft will be able to exceed 50 miles. Say its not so...vibrations and oscillations

in the version they used for the first three test flights would have torn the ship apart but engineers have modified SpaceShipTwo with additional tanks to hold helium that will be to dampen out the oscillations and vibrations. However, the additional weight will at least partially offset the extra engine performance. It also will reduce the number of passengers in the back from six to four, sources tell me.

JoshNH4H · 2014-05-16 23:01:24

It seems rather odd to me that this is something they're having such trouble with. The delta v requirements are quite small, and given their reasonably high exhaust velocities it should be pretty easy to boost up to suborbital speed. If you're starting at 16 km with 100 m/s of velocity it gets even easier, especially since you can use engines much closer to a vacuum environment.

GW Johnson · 2014-05-17 08:11:14

That's the first I'd heard of a vibration problem. I knew they'd bumped into an unanticipated radiant-heating problem on the tail booms from the rocket plume a couple of years ago. That's where the silvery coating on the insides of the tail booms came from. Although, they should have anticipated it: it's pretty easy to see the carbon in the plume, which always glares very brightly.

If you're moving about Mach 3 at about 70,000 feet more or less vertical, you should coast up to near 60 miles. The air thins pretty rapidly up there. As Josh said, it's not a serious challenge delta-vee-wise. Unless you start adding ballast. And why helium? Wouldn't simple water do?

The article linked seems to indicate the vibrations are coming from the engine, which suggests rough burning (mild combustion instability). Adding liquid ballast to damp out the vibration response of the vehicle is the same idiot solution that NASA used for the 5-segment Ares instability problem. Head-in-sand does not solve stick-up-ass problems.

The real solution is to "cure" the instability in the motor. When they scaled it up from SS1 size to SS2 size, they ran afoul of a resonance somewhere (analogous to NASA going to 5 vs 4 segments and triggering one). This has already been seen in test and ignored. Now the chickens have come home to roost.

The correct procedure is to identify the oscillation mode, then try the family or families of internal geometry changes that might de-stimulate it, based on your acoustical resonance theory and analysis. Usually a computer code. But, that's more engine development and re-engineering, which politically and PR-wise is something they may not be able to admit in public.

They need to talk to a solid rocket outfit who has used acoustic mode analyses on smaller motors. That would be a tactical motor outfit with a "can-do" reputation. Not many are left any more. The one I used to work for was one of those, but got closed decades ago by its parent corporation, for nothing but ugly corporate politics.

That solid motor stability physics is pretty close to the kind of physics going on inside their hybrid. Very little of the acoustic instability experience with liquids applies here, most of the physics are different. And none of the big solid motor outfits (really just ATK these days) actually do that kind of analysis, as I have pointed out in another thread.

GW

RGClark · 2014-05-17 09:59:47

It was an unfortunate, though understandable, choice to use hybrids. It was understandable because SpaceShipOne had successfully accomplished the Ansari challenge using hybrids. There was also the belief that hybrids were safer than liquid engines. However, the accident at Scaled belies that view.
If they had used liquids they would have been flying suborbitally years ago.

Bob Clark

GW Johnson · 2014-05-17 15:26:10

I'm not sure I agree with your implied statement that liquids are safer than hybrids. I think theirs is hypergolic ignition. With only one liquid to pump-iup to pressure and transfer, the machinery is simpler and therefore inherently more reliable. The solid component has all the simplicities of solids, but not the critical disadvantage: cannot stop once started.

The only real problem with hybrids is inexperience. Almost no one has actually tried them. That means not all the pitfalls have been identified yet. That's the real risk.

I no longer remember what I might have read about their their engine test accident. I'm not at all sure the cause was ever reported publicly.

Whatever it was, they certainly screwed up (they killed somebody). I'd bet the same mistake would have obtained with a liquid bipropellant system, in my ignorance. There's just not much to go wrong with the solid component of a hybrid. Not even cracks in the propellant bother it, unlike true solids. First place to look is a mistake handling the liquid component.

The problem being discussed here is an unaddressed combustion instability. There is no good reason for Scaled to make the same mistake NASA did, dealing with such an instability. They need to deal effectively with it, and ballast just ain't the answer.

GW

SpaceNut · 2014-05-17 18:27:12

With harmonic resonance change where the frets are in the chamber ( think Guitar) not changing the length of the chamber or exit port thrust....

GW Johnson · 2014-05-18 08:57:15

In solids, it's usually a tangential or radial mode that offends, not a longitudinal mode, although all those responses interact with each other. The situation is truly 3-D, as the grain bore geometry changes as the propellant burns, impacting massflow generation, erosive burning, and the compressible-flow conditions. There is usually also change in bore geometry down the length, as well as exposed volumes at each end where there is no propellant.

In hybrids, the situation is quite similar, with a perforated fuel grain. The differences are that the burn rate is entirely by the erosive-burning-type mechanism, and massive massflow injection at the forward end (the oxidizer). That mass injection would tend to amplify compressible-flow effects, and is the prime driver for the fuel surface regression rate.

Another difference is that in solids, the chemistry is mostly completed in the massively-blown boundary layer at the surface of the propellant. In hybrids, the bulk of the chemistry takes place in the flow down the bore, far from where any particular surface patch where the fuel flow is generated. That difference provides a very much stronger coupling between the chemical energy release and the compressible flow conditions in the bore, than exists in the solid. I suspect that is the source of the rough-burning or mild instability experienced so often with hybrids.

What has to be cleaned-up is the wakes or separated zones that exist at the internal-surface geometry changes inside the engine. Those are the location of shed vortices, which can very easily flip-flop around. That kind of physical motion can interact with the chemistry of heat release, and with the natural vibration modes (in 3-D) inside the engine space. That's where instability comes from.

Because of the enhanced links for interaction, I suspect that hybrids are more prone to instability than solids, but solids can be bad enough, as the NASA 5-segment SRB variant so eloquently proved.

Getting rid of step or steep changes in grain geometry would be a good first step in curing the rough-burning problem.

It's different in liquids. The droplet vaporization takes place co-located with the chemistry releasing all the heat, with turbulent eddies all around, which tend to explode randomly as they mix reactants. Unsteady vaporization processes act just like unsteady reactant injection rates, except that it happens very much faster, and with far greater amplification of effects. That's where most of the instability in liquids takes place. All you need is a natural mode that resonates with your chemistry-vaporization phenomena's frequency, and there you go: boom! For liquids, it's all about how you spray, which controls evaporation rates, and how far down the chamber it occurs.

That difference is why the liquid guys' experiences are of little use to the solid guys, and probably of very limited use to the hybrid guys.

GW

SpaceNut · 2014-05-18 11:06:34

http://hyperphysics.phy-astr.gsu.edu/hb … tring.html

With regards to fuel geometry and buring that is the PSI in the chamber which is the same as string tension. With the psi in the chamber effecting how loud the tone will be.
This is the same as church organ Pipe...Acoustic resonance

music7.1.gif

The feul mass that remains after burning is the mass of the string in the equations.
The length of the stack is the string length.
The thrust of the exhaust is the wave velocity.

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

http://www.vibrationdata.com/Newsletter … 008_NL.pdf

The thrust oscillation frequency of the Ares I five-segment booster is 12 Hz (compared with 15 Hz for the Shuttle's four-segment version).

http://www.nasaspaceflight.com/2008/11/ … tion-data/
Modelling carried out on the Ares I vehicle predicts two major structural resonances at about 10 Hz and 12 Hz.

GW Johnson · 2014-05-18 13:16:42

Odd that a longitudinal mode in 10 Hz range should be the trouble in a solid. As I said, in most solids, it's usually a radial or tangential mode at several hundred to a few thousand Hz, depending on the size.

But it's a low frequency problem in the 5 segment motor, OK. Having a structural vibration mode in the vehicle that matches a rough-burning frequency in the motor is a recipe for disaster. As I said, ballast is no real fix. You change either the excitation (eliminate that noise source in the motor), or you eliminate that response mode in the vehicle. Those are fixes.

GW

RobertDyck · 2014-05-20 15:59:03

GW Johnson wrote:

You change either the excitation (eliminate that noise source in the motor), or you eliminate that response mode in the vehicle. Those are fixes.

Interesting. Fuel change. My guess is rough burning is caused by uneven mixing of fuel. More finely ground powder, and better blending before pouring, may help. May have to look at settling; are fuel components separating before solidifying? Creating layers of material? If one batch separates, say aluminum sinking to the bottom of liquid rubber in a barrel, before pouring into the casing, that may cause each pour to have layers of greater/lesser concentration of aluminum. Or some other component. How grannular is solid fuel?

Found an article about ATK's new booster. It's over a year old, but...
http://www.nasaspaceflight.com/2013/01/ … d-for-sls/

Some of the characteristics of the Advanced Booster include features that have been identified by NASA as important for the next-generation booster are: an energetic propellant to improve performance and reduce cost,
...
As listed, the increased operating pressure, improved propellant, tailored thrust profile, increased expansion ratio all combine to provide a 15.1mT boost to the SLS’ payload capability.

Their claim of "energetic propellant" and "increased operating pressure" make me leary. But would this propellant help?

SpaceNut · 2014-05-20 17:38:36

SpaceShipTwo in its first powered flight over Mojave. Sparks, NV, April 29, 2013.

http://www.bbc.com/news/science-environment-22344398

The hybrid rocket motor is termed "green” oxidizer (N2O) and the fuel is Hydroxyl-terminated polybutadiene (HTPB) which is the same as SpaceShipOne rocket motor.

JoshNH4H · 2014-05-20 18:36:40

They might want to consider changing oxidizer to LOX. They would get a lot more energy out of it, though at the cost of cryogenics.

RobertDyck · 2014-05-20 20:56:54

In the 1970s a German company called OTRAG developed a rocket intended for commercial satellite launch. They used commercial grade kerosene, not RP-1. For oxidizer they used a mixture of nitric acid and N2O4. That fuel mixture had a major problem with oscillation. NASA had experimented with it previously, but found the engine always exploded. But OTRAG developed a set of baffles that damped the oscillation. Could something dampen the oscillation for SS2?

JoshNH4H · 2014-05-20 21:46:46

Probably, but the process of finding out what would probably be expensive.

RGClark · 2014-05-25 08:05:14

Virgin Galactic appears to have acknowledged that SpaceShipTwo will not be
able to reach the full altitude of 100 km considered to be space:

SpaceShipTwo Can’t Reach 100 Km Boundary of Space.
http://www.parabolicarc.com/2014/05/15/ … ary-space/

It is unfortunate that VG decided to use hybrid engines for SS2. If they had
used liquid engines, then they would already be flying suborbitally:

Transitioning SpaceShipTwo to liquid fueled engines: a technology driver to
reusable orbital launchers.
http://exoscientist.blogspot.com/2014/0 … iquid.html

Bob Clark

Tom Kalbfus · 2014-05-25 18:41:26

Of course if it could reach suborbital space in one stage, if they use the second stage, the could have a longer suborbital flight and since they already have that vehicle, they might as well.

SpaceNut · 2014-05-25 20:19:14

New Fuel to Boost SpaceShip Two

Virgin Galactic is switching to an alternate plastic-based (polyamide-based grain) rocket motor fuel for its SpaceShipTwo (SS2) commercial space vehicle to improve performance over the original rubber-based fuel grain propellant. Work on the alternate fuel has been underway in parallel with the baseline hydroxyl-terminated polybutadiene (HTPB) rubber-based system for some time, slightly more powerful than the baseline HTPB-fueled RM2 hybrid rocket motor made by Sierra Nevada, the switch to the alternate fuel does not require additional structural reinforcement or major systems changes says Whitesides.

GW Johnson · 2014-05-27 10:38:35

You have to be careful talking about hybrids. In a true hybrid, oxidizer and fuel are completely separated. Usually the fuel is a solid plastic or rubber, and the oxidizer any of several liquids. In these, if you stop the oxidizer flow, the motor goes out.

Some hybrids have what are really underoxidized solid propellants as their "fuel". Usually, these don't go out when you stop the oxidizer flow. That puts you back to the the main disadvantage of a true solid: no way to stop the burn.

BTW, HTPB rubber is very similar to the rubber most street shoe soles are made of.

GW

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Re: SS2 - status

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