Space Ship Two - General Thread

[Jason1701]

While the reusable components of RM2 are being integrated with SS2, a different RM2 was used for this test. The test was at Sierra Nevada's facility.

[Garrett]

The report didn't actually say if the motor was in SS2 or not.  I thought there had already been a picture with a caption that the moter was at Scaled and was in the process of being placed into SS2?

I made the assumption that a hotfire test like this would have been performed away from SS2. I may be wrong, but seeing as they need to examine the internal geometry after the test, I strongly suspect that motor was not in SS2.

I do not recall any picture of the motor being at the Scaled Composites site. I do recall a recent quote from a Scaled/VG spokesperson saying that they were working on integrating RM2 into SS2. But "integrating" can mean many things, such as preparing the electrical/electronic connections.

I'm not even sure we know whether the motor has ever been to the Scaled site.

Edit: did not see Jason1701's post before I posted. Thanks Jason for the info, though I'm not sure what you mean by a "different RM2".

[Jason1701]

The report didn't actually say if the motor was in SS2 or not.  I thought there had already been a picture with a caption that the moter was at Scaled and was in the process of being placed into SS2?

I made the assumption that a hotfire test like this would have been performed away from SS2. I may be wrong, but seeing as they need to examine the internal geometry after the test, I strongly suspect that motor was not in SS2.

I do not recall any picture of the motor being at the Scaled Composites site. I do recall a recent quote from a Scaled/VG spokesperson saying that they were working on integrating RM2 into SS2. But "integrating" can mean many things, such as preparing the electrical/electronic connections.

I'm not even sure we know whether the motor has ever been to the Scaled site.

Edit: did not see Jason1701's post before I posted. Thanks Jason for the info, though I'm not sure what you mean by a "different RM2".

There are multiple RM2s being made. One is being integrated with SS2 (oxidizer systems only, my guess), another is being hotfired.

[kkattula]

To understand what they mean by "examination of internal core geometry", I turned to Google, which inevitably led to Wikipedia:
http://en.wikipedia.org/wiki/Solid-fuel_rocket

Solid rocket fuel deflagrates from the surface of exposed propellant in the combustion chamber. In this fashion, the geometry of the propellant inside the rocket motor plays an important role in the overall motor performance. As the surface of the propellant burns, the shape evolves (a subject of study in internal ballistics), most often changing the propellant surface area exposed to the combustion gases.

I'm trying to understand, in my non-rocket specialist mind (but still with my professional engineering/scientist mind), why a rocket company is performing such a fundamental test so late in the program. Surely this is the type of thing they test from the start and compare with computer models?

Whatever the reason, this appears to tell us that the rocket is still not ready for installation into SS2. I'd love to be wrong about that.

It's not a fundamental test.  The shape of the propellant surface varies with the duration of the burn, but you can't examine it at any time unless you stop the burn. Unless you do hundreds of tests, you only have a smallish number of data points and have to extrapolate between them.

So even after the motor is well understood, it makes sense every time you do a test to vary the duration a bit to get another data point to increase confidence in your model.

[Garrett]

So even after the motor is well understood, it makes sense every time you do a test to vary the duration a bit to get another data point to increase confidence in your model.

OK, that makes more sense. So I probably read too much into their statement that the duration of the burn was "chosen to allow examination of internal core geometry". I interpreted that as meaning that the objective of the hotfire was for an internal geometry study, but I can see now that the geometry datapoint is simply a systematic bonus after ever test.
They probably explicitly stated the reasons for the 45 sec duration to allay concerns by outsiders, as their previous hotfire was 58 seconds.

[beancounter]

All this is fine, but when are we going to see an actual firing of the motor in flight?  I think it's been well past SS1 although in fairness, we're looking at 2 different beasties - one experimental while the latest is for actual operations.
Anyone have any real timeline on this?

[Jason1701]

All this is fine, but when are we going to see an actual firing of the motor in flight?  I think it's been well past SS1 although in fairness, we're looking at 2 different beasties - one experimental while the latest is for actual operations.
Anyone have any real timeline on this?

There's nothing about SS2 that, for me, makes it less "experimental" than SS1. I think its flight rate will stay low even after it enters commercial service. I have been hearing doubts about the motor's performance from some industry professionals, which leads me to suspect it will not be flown this year.

Go XCOR!

[QuantumG]

I have been hearing doubts about the motor's performance from some industry professionals

I have been hearing that for years.. none of these industry professionals mentioned the heritage of the rocket, they all seemed to think it was developed for SS1. I've yet to get a straight answer as to Tim Pickens' involvement.. some say he developed the rocket for SS1 from scratch, and that the SS2 rocket is a continuation of that work.. others say there's no relationship between these rockets.

[ChefPat]

Virgin Galactic Granted License Exemption for Spaceflight Experience

[spectre9]

That hybrid motor is scary. 

The big worry is it doesn't have the performance to reach 100km.

To me it just doesn't feel like the right motor for this kind of take the kids/parents along space flight. 

[zaitcev]

We're coming right up on the drops of DreamChaser. Once they are done, testing of SS2 with improvements to the tail should resume. Watch for the shape and area of the tail. Gary was sharp-eyed enough to find the little rump at the back last time. We should be able to see the changes to the tail if we're worth anything as observers.

[Moe Grills]

That hybrid motor is scary. 

The big worry is it doesn't have the performance to reach 100km.

To me it just doesn't feel like the right motor for this kind of take the kids/parents along space flight. 

The question is: Who are the experts on these matters? The people who work directly on the project? Or those posting on this forum?

[Robotbeat]

That hybrid motor is scary. 

The big worry is it doesn't have the performance to reach 100km.

To me it just doesn't feel like the right motor for this kind of take the kids/parents along space flight. 

The question is: Who are the experts on these matters? The people who work directly on the project? Or those posting on this forum?

There are competitors who also don't think it's the right kind of motor, either.

[mr. mark]

We're coming right up on the drops of DreamChaser. Once they are done, testing of SS2 with improvements to the tail should resume. Watch for the shape and area of the tail. Gary was sharp-eyed enough to find the little rump at the back last time. We should be able to see the changes to the tail if we're worth anything as observers.

How do we know that the Dreamchaser drop is going as planned? We have heard nothing about an actual drop date only a vague timeline pointing to sometime around June.

[spectre9]

The uneducated punter getting on SS2 will not know exactly how scary this thing is.

There's also the issues with feathered re-entry of this big heavy vehicle.

It's not just a one man glider like SS1.

That's a lot of weight to be hitting the atmosphere at supersonic speed.

Who wants to be on the flight where the wing locks up after all the vibration from the RM2? 

This is the cheapest way to get into space I guess. 

Good luck to them.

If it's proven very safe I'll eat my words 

[Robotbeat]

It'll work, but I doubt it'll be the cheapest.

[QuantumG]

They're still the furthermost along.. it'll be embarrassing if someone else overtakes them. 

[jabe]

ok..had a thought..they don't happen often so better put it out before i forget it..

they had another motor test and if there are Isp issues, I will be an eternal optimist here and see it as being a bit of a positive.  I have always thought that 6 in the cabin is pretty tight..take 2 seats away to save on mass (lets say 300 kg or so since you need fewer chairs etc) and  you now have only 4 passengers floating around with tonnes of room,  you increase your flight rate by 50% (profit per flight is lower) and a bigger draw since other sub orbital carriers don;t have the room to float around...

motor issues have been debated to death...well sort of

so to take a side track..what are others thoughts on the room issues on SS2?
jb2 

[Kabloona]

I suppose there must be some uncertainty as to how the oxidizer flows over the solid fuel grain.  CFD analysis can only go so far when dealing with combustion, especially if the boundary condition (solid fuel wall) erodes throughout the hot fire.  So it makes a whole lot of sense to me to sample what the fuel grain profile at various stages of the burn.

A fundamental "problem" with hybrids is that the regression rate of the fuel grain can be spatially variable and uneven, depending on the design of the oxidizer injectors, grain geometry, combustion stability, etc. It's very difficult to get uniform regression throughout the grain, because not every area of the grain surface has the same quantity of oxidizer flowing over it, and the gas velocities and thermal characterestics are non-uniform as well. So it's not surprising that they're still trying to characterize the grain regression.

Conventional composite solid propellants like AP/HTPB are not as susceptible to uneven regression, because the oxidizer is incorporated into the fuel matrix, and thus a uniform quantity of oxidizer is available everywhere at the combustion surface. Composites can regress unevenly too, depending on combustion chamber geometry, but the variation is typically not as pronounced as it is in a hybrid.

[savuporo]

Does anyone know if WK1 is still used for anything much ?