Space Ship Two - General Thread

[Borklund]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

[Lars_J]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

Lots of people say that, but have they actually pointed out something that is wrong or false in the account given??

[docmordrid]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

Lots of people say that, but have they actually pointed out something that is wrong or false in the account given??

Reminds me of the old politics of personal destruction question "So, when did you stop beating your wife?"

An obvious hit piece, pure and simple.

[Lars_J]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

Lots of people say that, but have they actually pointed out something that is wrong or false in the account given??

Reminds me of the old politics of personal destruction question "So, when did you stop beating your wife?"

An obvious hit piece, pure and simple.

Saying it over and over doesn't make it true. Not a flattering piece - for sure - but given the history of SS2 development (& promises), can you point out something wrong in the article?

[Lar]

Why is this discussion in an update thread?

Because if we start a discussion thread it gets deleted.

Looking into that.

I think there's been enough about the book, people have differing opinions about it. Further back and forth won't do much good in my view.

[Kabloona]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

Lots of people say that, but have they actually pointed out something that is wrong or false in the account given??

Yes, here, in what seems to be an evenhanded critique of the Branson book:

www.newspacejournal.com/2014/01/26/new-branson-bio-examines-delays-and-other-problems-with-virgin-galactic/

The article points out some factual errors and the asks the valid question,
If the author can't even get public domain facts correct, what else has he gotten wrong?

[docmordrid]

Looks more like character assassination than a technical history of Virgin Galactic, yes.

Lots of people say that, but have they actually pointed out something that is wrong or false in the account given??

Reminds me of the old politics of personal destruction question "So, when did you stop beating your wife?"

An obvious hit piece, pure and simple.

Saying it over and over doesn't make it true. Not a flattering piece - for sure - but given the history of SS2 development (& promises), can you point out something wrong in the article?

That list is in Foust's article, and that's a partial list. We already know that the "nylon is new" contention is extremely iffy, myself and others pointing out public references back to 2009.

I also have a problem with the tone of the premise, especially considering the authors previous anti-Branson work. I'm not saying Branson is an angel, but too often we see these yellow journalism hit pieces from the anti-pick_your_victim crowds on all sides. This guy seems to be filling his 401k at Branson's expense.

[Elmar Moelzer]

Why is this discussion in an update thread?

Because if we start a discussion thread it gets deleted.

Either way, I don't like it on this thread. I find the book in bad taste and the discussion about Branson's character annoying.

[parabolicarc]

When Virgin Galactic is ready to fly passengers then they will bring all their websites and leaflets up to date.  Until then the sites will say whatever the author was told on the day he wrote it.  Different authors may have been told different things on different days.

Nothing to worry about there.  Just do not believe everything you read in the newspapers (or websites).

This isn't about worrying whether their website is up to date. It's about trying to understand what's going on with SS2 and whether parabolicarc's reports of a "new" nylon hybrid to replace the "existing" rubber hybrid are correct or not. The whole question of the current hybrid's (whatever it is) performance has been a big issue on this thread. If VG has been testing (and now flying) a nylon hybrid all along, instead of just starting to test fire a nylon hybrid relatively recently, as reported by parabolicarc, then at least some of his information is incorrect, and, given the controversy here over his posts, that would be rather a big deal to some people.

They have flown three times with a rubber-nitrous oxide engine. Those burns were for 16, 20 and 20 seconds apiece.

My sources indicate that is as far as they can go with that version of the engine. Burn it longer, you get oscillations that are dangerous to the crew, passenger and ultimately the ship.

An alternative nylon-nitrous engine has been in the works for quite some time. Whitehorn mentioned it some years ago. However, it never received a lot of publicity, and the VG website includes information about the rubber engine. Information about the nylon engine's emissions was submitted to FAA as part of the application for an experimental permit. If you look at the FAA's final environmental impact statement released in May 2012, you will find emissions figures for the nylon engine alongside those for the rubber one.

The nylon engine is one of several alternatives that have been tested due to performance problems with the rubber hybrid. The alternative development has been going on for quite some time now, very quietly, in Mojave. Nobody will talk about it for the record, although these tests are widely known here in Mojave. For example, I witnessed hot fires on the same test stand in December 2012 and January 2013 of different alternative engines. I saw the results of a nylon-nitrous test that exploded in May 2013 on a different test stand. 
 

[rpapo]

They have flown three times with a rubber-nitrous oxide engine. Those burns were for 16, 20 and 20 seconds apiece.

My sources indicate that is as far as they can go with that version of the engine. Burn it longer, you get oscillations that are dangerous to the crew, passenger and ultimately the ship.

Were these oscillations discussed earlier, or on another thread?

[parabolicarc]

They have flown three times with a rubber-nitrous oxide engine. Those burns were for 16, 20 and 20 seconds apiece.

My sources indicate that is as far as they can go with that version of the engine. Burn it longer, you get oscillations that are dangerous to the crew, passenger and ultimately the ship.

Were these oscillations discussed earlier, or on another thread?

I don't know. I know they have always been the biggest problem with scaling up the SpaceShipOne hybrid. Sources I have noticed them on video of engine tests that Virgin released back in 2009. They are still a problem, and there are several efforts underway to find a solution. It's possible they will this year. But, we'll have to wait and see.

[Elmar Moelzer]

If Scaled has such problems with the hybrid, wouldn't SNC have the same with the engines for the DC?
I am pretty sure they stated that their engine development is complete and does not have any problems.

[Kabloona]

The oscillations parabolicarc referred to, if true, could be due to combustion instability, which can be a thorny problem because it depends on a multitude of variables and is difficult to solve analytically.

This paper, though old, gives a summary of hybrid rocket combustion instability in Section 6.0.
http://www.dtic.mil/get-tr-doc/pdf?AD=AD0754769

Solving combustion instability in their case, if that is indeed their problem, may be difficult or impossible without extensive modification of the grain design and/or fuel type, which could be why they're switching to nylon, if parabolicarc's sources are in fact correct.

As for the DC engines, presumably they are (or will be) different enough (in grain geometry, thrust, fuel formulation, injector pattern, etc, etc) that they avoid combustion instability. Since combustion instability is analytically quite difficult to predict, sometimes you get lucky and sometimes you don't. Apparently they got unlucky with the SS2 engine design.

(disclaimer: this is just my speculation as to what might be behind the "oscillation" problem referred to by parabolicarc, if true.)

[parabolicarc]

Read this story by Alan Boyle on the Newton engines VG is developing for LauncherOne:

http://www.nbcnews.com/science/hello-newton-virgin-galactic-unveils-its-other-rocket-engine-2D11922691

Now, notice all the details that VG is willing to disclose. Pounds of thrust, burn times....the works. It sounds great!

Now, notice the lack of details in the story about the RM2 engine for SpaceShipTwo. Nearly 10 years into the project, we don't know how long it's going to burn, how many lbs of thrust it can produce, how long it's been tested for lately, how high its going to take the spaceship, or even if it's going to burn rubber or nylon. There's nothing specific in the story; the Scaled test logs are equally useless.

Also note this carefully worded written response in the story from VG's vice president for special projects on the status of the hybrid engine.

"We and our contractors at Scaled Composites and Sierra Nevada are continuing to develop ways to improve the motor design by making them easier to manufacture and install, or by further improving their handling characteristics and performance," Pomerantz said in an email.

Tells you everything you need to know right there.  Spaceflight is right around the corner, but they can't explain what they're flying with.

[QuantumG]

Now, notice all the details that VG is willing to disclose. Pounds of thrust, burn times....the works. It sounds great!

Now, notice the lack of details in the story about the RM2 engine for SpaceShipTwo.

As VG has told you every time you've asked: that's not their information to disclose.

When you asked SNC at NewSpace to disclose any issues with RM2, you got given the inverse answer. As I said to you then: you keep asking the wrong questions. They've told you they can't answer those questions. Ask something different, or at least ask the question differently.

Some examples:

How big is the hybrid rocket on the Dream Chaser?  (no reason they couldn't answer that one)
What's the advantage of going with two rockets instead of just the one on the Dream Chaser?
What potential problems did you avoid by going with the size of hybrid rockets you did on the Dream Chaser?
If you had to, how long would it take you to upgrade to bigger hybrid rockets on the Dream Chaser?

I think you get the idea. Ask questions they can actually answer and you might have a chance of getting answers they can actually give.

[Lars_J]

Now, notice all the details that VG is willing to disclose. Pounds of thrust, burn times....the works. It sounds great!

Now, notice the lack of details in the story about the RM2 engine for SpaceShipTwo.

As VG has told you every time you've asked: that's not their information to disclose.

I don't think he meant to imply that they had to release the information - Just that the willingness to share so much about one engine and not the other might be an indication of the confidence they have in the respective engines. Just sayin'.

[Kabloona]

Also note this carefully worded written response in the story from VG's vice president for special projects on the status of the hybrid engine.

"We and our contractors at Scaled Composites and Sierra Nevada are continuing to develop ways to improve the motor design by making them easier to manufacture and install, or by further improving their handling characteristics and performance," Pomerantz said in an email.

Tells you everything you need to know right there.  Spaceflight is right around the corner, but they can't explain what they're flying with.

It sure doesn't sound like a ringing endorsement of the current motor design. More like the Beatles' line "It's getting better all the time!"

[craigcocca]

Perhaps this question might seem a bit amateurish, but why not equip SS2 with three or four smaller HTPB motors instead of a single large one?  If a smaller engine burns more evenly and avoids the thrust oscillation issues that the larger engine is having, then it would seem that bundling a few smaller engines could be a workable solution to get SS2 into space sooner rather than later.

The tail end of SS2 would looks something like the business end of the Bell X-1:
http://www.militaryimages.net/photopost/data/792/bell_x-1_engine_nozzles.jpg

[Kabloona]

Perhaps this question might seem a bit amateurish, but why not equip SS2 with three or four smaller HTPB motors instead of a single large one?  If a smaller engine burns more evenly and avoids the thrust oscillation issues that the larger engine is having, then it would seem that bundling a few smaller engines could be a workable solution to get SS2 into space sooner rather than later.

The tail end of SS2 would looks something like the business end of the Bell X-1:
http://www.militaryimages.net/photopost/data/792/bell_x-1_engine_nozzles.jpg

Four smaller hybrids in the same volume as the one larger hybrid would have even worse performance due to added inert mass (cases, nozzles, etc) and less fuel mass. So even if that approach cured the "oscillations," it wouldn't get the vehicle where they want it to go.

[parabolicarc]

Also note this carefully worded written response in the story from VG's vice president for special projects on the status of the hybrid engine.

"We and our contractors at Scaled Composites and Sierra Nevada are continuing to develop ways to improve the motor design by making them easier to manufacture and install, or by further improving their handling characteristics and performance," Pomerantz said in an email.

Tells you everything you need to know right there.  Spaceflight is right around the corner, but they can't explain what they're flying with.

It sure doesn't sound like a ringing endorsement of the current motor design. More like the Beatles' line "It's getting better all the time!"

The problem is that there's not one RocketMotorTwo, there are multiple ones whose hots fires are all jumbled in together as part of Scaled's hot fire summaries. There's a rubber-nitrous version they have been flying with on SpaceShipTwo. Sierra Nevada has been working to dampen the oscillations on that. Scaled Composites is working on an alternative hybrid that burns nitrous and nylon. Other motor designs have been tested.

Virgin Galactic is working on a bi-prop liquid replacement, which Branson has mentioned publicly. I'm pretty sure testing of that is not included in the RM2 logs on the Scaled site.

Virgin wants to fly this year, but they can't fly with the version of the hybrid they've been using. They're still trying to make that work and testing alternatives.