Space Ship Two - General Thread

[QuantumG]

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

Exactly. There's many differences though: scale, airframe, oxidizer. It's a system. Many things have to work together.

[Lee Jay]

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

Exactly. There's many differences though: scale, airframe, oxidizer. It's a system. Many things have to work together.

How are the oxidizers different?

[QuantumG]

How are the oxidizers different?

The last I heard, Dreamchaser won't be using VaPak nitrous oxide like SS2. They'll have a compressed gas pressurization system.

[parabolicarc]

The SSOne hybrid proved to be difficult to scale up for SpaceShipTwo. Vibrations and oscillations were apparent in the videos of the first engine tests they released nearly five years ago. The vibrations and oscillations are not good for the pilots, the passengers or the ship. They are still trying to solve those problems today.

I believe, based on what I have heard, that they have gone as far as they can with the engine they used for the first three powered flights. Those tests were designed to expand the flight envelope of the ship and to show progress in the program and to buy them time while ground testing continued to find a better solution.

It feels like I've said this 500 times already. I'll say it another 500 times until it sinks in.

[Andy USA]

It feels like I've said this 500 times already. I'll say it another 500 times until it sinks in.

Not here you won't. Use your own site for that.

[Robotbeat]

Yeah, as I keep saying, the inevitable switch to full liquid rockets is inevitable.

The sooner they get it done, the better!

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

I've never seen Dream Chaser outfitted with hybrids except in models.

I just think hybrids are an inferior choice for propulsion on this scale. They're no safer than liquids and aren't nearly as high performance, plus they aren't as flexible or as capable of gas and go. You /will/ see virgin galactic transition their passenger vehicle to liquids eventually.

[baldusi]

Yeah, as I keep saying, the inevitable switch to full liquid rockets is inevitable.

The sooner they get it done, the better!

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

I've never seen Dream Chaser outfitted with hybrids except in models.

I just think hybrids are an inferior choice for propulsion on this scale. They're no safer than liquids and aren't nearly as high performance, plus they aren't as flexible or as capable of gas and go. You /will/ see virgin galactic transition their passenger vehicle to liquids eventually.

This is the SpaceShipTwo thread.
But the Dream Chaser use two RocketMotorOne, the same of SpaceShipOne. Those work and are demonstrated. I still believe they would be better to also transition to liquids. But that for evolving is they ever reach that stage.

[QuantumG]

But the Dream Chaser use two RocketMotorOne, the same of SpaceShipOne. Those work and are demonstrated. I still believe they would be better to also transition to liquids. But that for evolving is they ever reach that stage.

Citation needed.

Last I heard, the Dream Chaser's two motors produce about six times as much thrust as RocketMotorOne. That is, about 45,000 lbf each.

The SpaceShipTwo motor is about 60,000 lbf.

[Danderman]

With the SS2 only pushing 2.5 Gs for the ascent burn with the current hybrids, that's not too bad for their passenger list.

Apart from the issue that the current hybrids - as described here - can't actually meet the required performance, there is a second issue - safety. The hybrid design lends itself to incomplete combustion, which permits chunks of unburned propellant to separate from the binding and end up, at best, out through the nozzle. This behavior was observed during flights of SS1, and was the cause of great consternation and worry. I assumed that this chunking would be fixed within 10 years, but was wrong.

BTW, Lockheed received a contract from the Feds some years ago to design and test a 250,000 lb thrust hybrid, which seems to have disappeared from history.

[Lar]

Thread trimmed.

[Nomadd]

Yeah, as I keep saying, the inevitable switch to full liquid rockets is inevitable.

The sooner they get it done, the better!

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

I've never seen Dream Chaser outfitted with hybrids except in models.

I just think hybrids are an inferior choice for propulsion on this scale. They're no safer than liquids and aren't nearly as high performance, plus they aren't as flexible or as capable of gas and go. You /will/ see virgin galactic transition their passenger vehicle to liquids eventually.

I imagine you're right. The fact that people would be a lot more likely to pay for 10 minutes of air swimming that 4 minutes is probably a factor too. Safety was suppose to be a big factor for the hybrid, but that oxidizer tank failing would kill the spacecraft just as dead as any other tank. And I have to think a tank of liquid will always be more predictable than a giant pencil eraser. I just don't see where all this belongs in the update thread. (yet)

[Danderman]

For the record, there is no one here actively promoting the Official Story from VG that "everything is OK", there are just people reacting to the stories that VG releases, and who assume from the sparse data that indeed everything is OK.

Most people simply believe some part of what Branson says, or believe that VG is just going through the usual process of missing deadlines, there is no one here pushing the VG line.

In fact, most people here do not take Branson's statements at full face value.

The real problem, in this sense, is the media which serves as a stenographer for Branson. 

[R7]

The hybrid design lends itself to incomplete combustion, which permits chunks of unburned propellant to separate from the binding and end up, at best, out through the nozzle.

Eww. What if it does not fit through the throat fast enough and possibly knocked loose more chunks on it's way there. IIRC certain solid motor tests have failed quite spectacularly this way. Granted hybrid engine might not have so violent positive feedback (pressure increases temp which increases combustion rate which increases pressure) but still a bad day.

[R7]

Safety was suppose to be a big factor for the hybrid, but that oxidizer tank failing would kill the spacecraft just as dead as any other tank

50+bar NOX BLEVE would be a lot more violent than 2-3bar LOX tank pop.

[Lee Jay]

Yeah, as I keep saying, the inevitable switch to full liquid rockets is inevitable.

The sooner they get it done, the better!

I'm confused by the pessimism around the hybrids.  These motors, as I understand it, are close cousins to the ones in Dream Chaser, and those have passed all their testing milestones.  Isn't that so?

I've never seen Dream Chaser outfitted with hybrids except in models.

That's not a reason.  The hybrids have been tested and there was a milestone passed for that.

I just think hybrids are an inferior choice for propulsion on this scale. They're no safer than liquids and aren't nearly as high performance, plus they aren't as flexible or as capable of gas and go. You /will/ see virgin galactic transition their passenger vehicle to liquids eventually.

DC uses ethanol + N2O for RCS.  Would it be possible to build a pressure-fed ethanol/N2O engine that generates as much thrust in the same size as the hybrids do?  They need all that thrust for pad aborts, and SS2 needs a good fraction of it to reduce gravity losses on the climb.

[Robotbeat]

Safety was suppose to be a big factor for the hybrid, but that oxidizer tank failing would kill the spacecraft just as dead as any other tank

50+bar NOX BLEVE would be a lot more violent than 2-3bar LOX tank pop.

BLEVE is unlikely if the liquid is kept chilled.

[R7]

BLEVE is unlikely if the liquid is kept chilled.

Sufficient self-pressurization too.

[Lar]

It feels like I've said this 500 times already. I'll say it another 500 times until it sinks in.

Not here you won't. Use your own site for that.

I have, Andy. Many times.

It would be more productive if you directed your ire at those who have spent years obfuscating the truth about this program instead of those who have tried the pierce the fog that surrounds it.

But, that's up to you. It's your forum. It's Bergin's site. You guys run it the way you want.

Personally, I find your posts valuable when they bring new info forward. Some editorializing with them at the same time is not bad. But this thread shouldn't descend into bashing or religion. So let's not go there?

What I've concluded is that there are serious concerns about the engines of SS2 in the minds of many. Which may or may not include the SS2 folk themselves... but outward appearances certainly make it seem that way ...  THAT said, there is no rush here as long as no one is being defrauded of more than they can afford to lose, let them proceed at their own pace. And if they overstate things, well, welcome to earth, we all do from time to time.  Keep them honest by presenting independent data and perspectives. Just not 500 times in a row without adding anything new.

I'm a new mod and I may be all wet so take that with a grain of salt. If I'm modding incorrectly I am sure Chris will let me know.

[mr. mark]

I guess it's a question of belief or priorities. Why would Virgin Galactic continue to operate a system that was underperforming and had no end game? Why would Virgin Galactic continue to assert that the system is just fine and will do the job. Why would Virgin Galactic continue to use the engine to expand SS2's flight envelope? So it comes down to who you believe. The company who is developing the product and whose reputation is on the line or others who for whatever reason may dissagree with that development plan.

[Borklund]

I guess it's a question of belief or priorities. Why would Virgin Galactic continue to operate a system that was underperforming and had no end game? Why would Virgin Galactic continue to assert that the system is just fine and will do the job. Why would Virgin Galactic continue to use the engine to expland SS2's flight envelope? So it comes down to who you believe. The company who is developing the product and whose reputation is on the line or others who for whatever reason may dissagree with that development plan.

I can see that point of view, but I can also see the opposite point of view - why hasn't SS2 flown to space? why hasn't there been a full duration burn of the current iteration of the SS2 engine?