Space Ship Two - General Thread

[Danderman]

What is confusing everyone is that Virgin Galactic is claiming that they have successfully fired a rubber hybrid for "full duration". I saw the video and didn't notice any major chunks blowing out of the nozzle, so unless I read this thread, my opinion would be that the rubber hybrid problems were solved.

[parabolicarc]

What is confusing everyone is that Virgin Galactic is claiming that they have successfully fired a rubber hybrid for "full duration". I saw the video and didn't notice any major chunks blowing out of the nozzle, so unless I read this thread, my opinion would be that the rubber hybrid problems were solved.

Yes, that is confusing. So are the continued engine tests that followed earlier this month. It's a complex situation.

[Go4TLI]

What is confusing everyone is that Virgin Galactic is claiming that they have successfully fired a rubber hybrid for "full duration". I saw the video and didn't notice any major chunks blowing out of the nozzle, so unless I read this thread, my opinion would be that the rubber hybrid problems were solved.

Maybe not so much.  They probably have fired an engine at full duration.  On a test stand it is much easier to accommodate for the oscillations supposedly being encountered.  It's not as easy in flight where that could have much more sever effects on both the vehicle and crew.   My guess is that is where the focus is, not on if the engine can fire the whole duration or not. 

[Lurker Steve]

Yes, that is confusing. So are the continued engine tests that followed earlier this month. It's a complex situation.

I'm not sure why the engine tests are confusing ?

Do you expect them to stop all R&D ??

For instance, Dream Chaser has a milestone : "Main Propulsion and RCS Risk Reduction and TRL Advancement Testing". It would seem that SNC,  Scaled, and Virgin are all interested in learning everything they can about these hybrid engines, and improving them where necessary.

I wouldn't be surprised if they were even playing with the fuel / oxidizer mixture or trying different shaped fuel grains.

[Kabloona]

At some point engineering development has to "downselect" into a single design for production. Until they can get out of engineering development mode, and so far it looks like they haven't yet, there won't be any commercial flights.

So no one expects them to stop "R&D" for future vehicle improvements, but if they can't even get to a stable engine configuration, then it's a big problem. And from what parabolicarc is saying, so far they haven't been able to do so.

For DC, they may well be testing different grain configurations, etc, and that's to be expected at this point in the DC program. But SS2 was supposed to be flying a long time ago, and from what parabolicarc is saying there's no end in sight.

[parabolicarc]

Yes, that is confusing. So are the continued engine tests that followed earlier this month. It's a complex situation.

I'm not sure why the engine tests are confusing ?

Do you expect them to stop all R&D ??

For instance, Dream Chaser has a milestone : "Main Propulsion and RCS Risk Reduction and TRL Advancement Testing". It would seem that SNC,  Scaled, and Virgin are all interested in learning everything they can about these hybrid engines, and improving them where necessary.

I wouldn't be surprised if they were even playing with the fuel / oxidizer mixture or trying different shaped fuel grains.

I guess what I was trying to get across is that there are multiple paths that have been pursued to deal with the engine issues by Sierra Nevada, Virgin and Scaled. It's difficult to get a full overview of exactly what is going on. I know a fair amount, but I don't have a full picture.

They designed this thing backwards. Instead of figuring out the engine (the long pole in the tent), and then designing the ship around it, they designed the ship first. So, they've had engine problems, and then come up with solutions and it's, "Oh, that looks promising." And the answer is, "Yes, but...." You're trying to make something work in a constrained shape and space.

[a_langwich]

I keep thinking Scaled ought to look at air augmentation for Spaceship Two.  It may be too late in the development program, but then the same comment would probably have been made ten years ago, too. 

Air augmentation, as in grabbing incoming air, maybe compressing it a bit like a ramjet, then mixing it with the rocket exhaust to get further heated and sped up.  Rather like a high speed version of bypass flow for a turbofan.  There might be a minor benefit from mixing in extra oxidizer in the form of air, but there's no additional combustor.  More pointedly, the intake does not have to be designed to protect combustion; that will take place in the combustion chamber regardless.

Why do I think this fits Spaceship Two? 
1. - more performance from the engine.  The Russian designer Shavyrin got 550s Isp from an air-augmented solid.  Would the extra performance be enough to balance out the extra weight of the augmentation system?  That would have to be settled by detailed tests and analysis and tradeoffs.

2.  SS2 has had problems with engine vibration issues.  It might be adding in the extra reaction mass would dampen some of the oscillation.  Even if it didn't, the air augmentation would provide the most boost early in the flight profile, while tapering off later.  This matches well with the decreasing weight of the vehicle, which is most sensitive to accelerations later in the profile.  It might also allow the hybrid to use a better (smoother) throttle setting.

3.  The aerodynamics of air augmentation are tremendously simplified by SS2's flight profile:  Mach 0.6-3.0, starting at high altitude.  That's a well studied, well understood range, certainly compared to hypersonic speeds.   

4.  Scaled's expertise was in aerodynamic structures, like this, rather than rocket engine development.  No need to hire, or train.  Just make it work.

5.  Once they make it work, it doesn't much matter if they change to a different hybrid fuel, or even to a liquid bi-prop, or a solid. 

Downsides:

1.  The additional inlet and cowling add weight, some drag, and change the aerodynamics of the vehicle.  How much would be traded against performance increases.

2.  Air-augmentation hasn't been implemented often.  They would likely have to become experts rather than find and hire experts.  On the other hand, look at the shuttle-cock design, or the asymmetric Boomerang:  unconventional is in their company DNA.  An untapped area might hold great rewards, too, besides the obvious risk.

3.  The most obvious downside is that this is a major developmental change (see 1) at what should be near the end of the testing program.  True.  Only Scaled/VG/TSC are in the position to know whether they can finish without such a change.  Even if they are considering early flights short of 100 km or with fewer than 6 passengers, though, this would make a natural incremental boost, a v1.1 or SS2.1 program.  Consider:  same engine, same airframe with some additional structure, same cabin, same flight profile. 


(hat tip to simonbp for the pointers to air augmentation and Gnom program)

[Chris Bergin]

Converted this into a general thread as there's very few updates and a whole lot of grandstanding.

[Kabloona]

Thanks, Chris. Nature abhors a vacuum. ;-)

[Occupymars]

How DiCaprio is single-handedly wiping out clean air gains by Ford http://www.turlockjournal.com/section/26/article/23874/

"The little sight-seeing trip will generate 30 tons of carbon dioxide based on the Federal Aviation Administration’s environmental assessment of Richard Branson’s planned space excursion"

"Based on examples of carbon footprint equivalents found on the carbonfund.org site, DiCaprio will be creating the carbon footprint equivalent of driving 2,700 Chevy Suburbans 12,000 miles a year during his two-hour excursion.

I'm no expert on carbon dioxide production rates from different fuels but I find it hard to believe that one SS2 flight will produce the same amount of carbon dioxide as burning about 30,000 tonnes of gasoline. Very lazy journalism.

[pippin]

Well, it's a rocket engine so they can't emit more than they are carrying along and SS2 certainly doesn't carry 30,000t of fuel.
Then it has more than one seat... Probably a factor of 1,000 getting lost somewhere like in the old joke with the beer and the calories.

[smoliarm]

Yes, the math in the article is about 3 orders off.
Assuming the initial FAA number is correct  -  30 tonnes of CO2 per flight:
Most of this CO2 (~90%) comes from White Knight, and only 10% (may by even less) comes from SS2.
With avia-kerosene, the chemistry and math are easy 
30 tonnes of CO2 -->  8.18  tonnes of carbon --> 9.66  tonnes of Kerosene
Which is equivalent to 10.57  tonnes of Gasoline (gas has lower carbon percentage)

13.21       - m3 of Gas
13210.2   - liters of Gas
3490.2     - gallons of Gas
52352.3   - mileage @ 15 mpg
4.4   # of Chevy-Sub at 12,000 miles per year

So, it's 4.4, not 2700 

But, I think it's better to compare jets with jets, not with Chevys:
***  30 tonnes of CO2 -->  9.66  tonnes of Kerosene  ***
Well, IIRC, 10 tonnes of Kerosene is a normal fuel load for a 737 flight from say NY to Chicago -- just one flight.
Indeed, White Knight is just a jet, very peculiar and fancy-looking, but the engines are REGULAR. Why it should be so much worse in CO2 emission?

So, the author of this 'Chevy Suburbans' calculation -- he definitely fooled himself with "carbon footprint equivalents" 

[belegor]

Well, it's a rocket engine so they can't emit more than they are carrying along and SS2 certainly doesn't carry 30,000t of fuel.

It's more complicated than that:
http://en.wikipedia.org/wiki/Global_warming_potential
http://en.wikipedia.org/wiki/Carbon_dioxide_equivalent

[pippin]

Well, the article wasn't talking about CO2 equivalents, it was talking about tons of CO2.
Equivalents might be different, indeed, especially considering the altitudes involved.

[Elmar Moelzer]

Sorry, I just cant see how commercial space travel would have any relevant impact on global warming compared to any of the other modes of transportation, not at those flight rates. The worst offenders are cargo ships, IIRC.

[pippin]

No, that's pollution, not warming. CO2 wise cargo ships are actually pretty good, problem is they burn all that dirty oil we don't want in our car fuel anymore.
I think CO2 is essentially plain old power plants, heating, cooking and cars.
But this is really OT.

[Elmar Moelzer]

Either way, commercial spaceflight wont even make a dent in the statistics.

[parabolicarc]

Virgin Galactic has officially responded to claims made in Tom Bower's book that were in The Sunday Times.

Dear Sir:

Tom Bower’s claims in extracts from his new book on Richard Branson that Virgin Galactic has “no licence” and “no rocket” to go to space (“Lost in space” and “The sun lizard fading into exile”, News Review, last week) misrepresent the facts and use old information to create a story. Indeed the recent progress of the Galactic programme, including the latest rocket powered flight, renders Bower’s main claims false.

The company’s rocket motor has burned for the full duration and thrust multiple times, and the company released video footage of one such test in December. Bower also fails to note that the team has an experimental permit from the Federal Aviation Administration for the test flight programme phase.

The company applied for a commercial licence in 2013 as planned and to coincide with the latter stages of the test flight programme. It expects to receive that licence well in advance of commercial service later in 2014.

Most seriously, Bower attempts to cast doubt on Virgin Galactic’s absolute commitment to safety, particularly by suggesting that any potential lessons that could have been learnt by the tragic 2007 industrial accident at Scaled Composites were somehow brushed under the carpet. The opposite is true. The company supported the full independent enquiry and accepted all the resulting recommendations in terms of system re-design along with their costs and time implications. The end result is a system that will be significantly safer.

Bower also claims that Richard no longer owns any of the principal Virgin businesses and that the company has ceased to innovate. Among others, Virgin Galactic is majority owned by Richard Branson and it certainly innovates. Richard’s empire has not shrunk and his work, through his foundation and companies, is creating a real impact.

Yours sincerely

George Whitesides
CEO, Virgin Galactic


I've analyzed the response here:

http://www.parabolicarc.com/2014/02/03/whitesides-responds-bowers-allegation-spaceshiptwos-engine/

In short, Whitesides' response is far less specific than Bower's claims. Bower says Virgin Galactic lacks an engine that can get it to space (Karman line -- 100 km/62 miles). Whitesides merely points to progress in powered flights and ground tests without addressing the matter directly.

Whitesides is correct. They probably will get a commercial license far in advance of commercial operations starting.

[Kabloona]

@parabolicarc, thanks for posting that response. Yes, there may be some unintended irony in the statement that the FAA license will be received well before commercial flights start.

On your website response to the VG letter, the first comment is by Carolynne Campbell in which she discusses the safety of nitrous oxide with what sounds like firsthand knowledge. I Googled her name and came up with this story. Is this in fact that Carolynne Campbell?

http://www.dailymail.co.uk/sciencetech/article-1082652/Rocket-woman-builds-300mph-jet-car-garden.html

Since she has apparently built her own nitrous-hybrid-rocket-powered car, I expect she is quite well informed on the subject and speaks with some authority.

[Star One]

Worth having a look at the comments under this article as well as the article itself.

http://www.theguardian.com/media/greenslade/2014/jan/31/richard-branson-ipad