Active Stabilization with the help of Thrust Vector Control (TVC)

plugger said:

In all seriousness Wallace I don't consider this an argument. It's a discussion, nothing more. I doubt I've offended Jim, but if I have that wasn't my intention. Jim's raised points I've not thought about regarding the distance a rocket travels from a cylinder perspective and that's not something I've ever considered. And yes, Jim's had more than one high alt staging flight whereas I've not. But Jim doesn't have a monopoly on those rarefied altitudes; other people have gone as high and higher than he has. And yet Jim's the only one in that small club that's even leveraged active stabilisation in his successful attempts (at least to my knowledge). So there is evidence to highlight that active stabilisation isn't a requirement for high altitude staging despite being used successfully in that realm.

And I still remain unconvinced in the net benefit of such systems when it comes to a peak altitude AGL perspective. Even Jim wrote above "That's why I use stabilization, and at some angle, it helps on altitude too." which meshes quite well with my earlier comment of "I know this would be a sliding scale in terms of the less vertical a non-guided flight is and how that corresponds to the guided system from an active guidance perspective."

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It's pretty hard to offend me (possible, but difficult). For those of us that fly at Blackrock, and for Balls anyway, there is a 15 nm radius for the COA. Strickly speaking, it is illegal to fly a rocket outside of that radius. Just for fun, try running some simulations where you allow staging to occur at different angles. You will be very surprised at how low the angle is where you land outside of that radius. Then, add a jet stream.

Each year, we report back to the FAA on the results of the high altitude flights and where they landed. For flights outside of the waiver, we report on what happened and why. If there are an increasing number of flights over 100K or much higher, you have to wonder what the response of the FAA will be when those rockets start regularly landing outside of the waiver. Over the last few years, most of those attempts have not been successful. More people will try, though, and this will become an issue.

Up to the present time, there has been a technical issue that contributes to the above problem. Specifically, the methods used for tilt detection have an amount of drift in the gyros that is on the order of the setting that would be required to stay within the waiver. It is really tough to use a tilt value that actually would control dispersion when the result of doing that would be to have a perfectly good flight inhibited due to gyro drift.

This year, I'm hoping to fly a rocket over 300K. Who knows, it could happen. This particular flight can't use the stabilization system. However, I will be using gps to determine the actual trajectory, rather than an inertial system, so at least if the flight is inhibited, it will be at an angle where I truly don't want to fire the sustainer. This is a really important capability.

Jim

TonyL said:

plugger,
You are correct that one does not have to use active stabilization to reach high altitudes, however it sounds like you have never had to do a dispersion analysis? [the statistical estimation of potential flight trajectories due to rocket/launcher/environment variations]

Anything on the rocket I think should be there for a purpose. Jim's stated intent has been to reduce landing dispersion [sounds good to me], and it has been demonstrated successfully.

If one is going for maximum altitude, one can always do the university style 'hail-mary' shot and eventually one of them will likely work [or not].

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You're correct Tony, I've never had to do a dispersion analysis. Down here if we are looking to do a high altitude flight the standard process is we submit a High Altitude Flight form as well as a sim file and the High Altitude Review Committee does a dispersion analysis.

TonyL said:

A vertical autopilot on the booster is the very best place for it [all else being equal] as controlling the rockets initial direction will maximize vertical delta-V. Correcting direction after direction errors have been allowed to accumulate is very unlikely to be as efficient [assuming the same control system] as there is no free lunch when it comes to drag. Correcting under boost can be harder, so compromise in order to improve likelihood of success is always a candidate.

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But is anyone actually doing this? Up thread Jim mentions

the system provided roll control from launch and then roll and vertical control during the coast period.

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Given that Jim's the only person I'm aware of that's leveraging active stabalisation on high altitude staging attempts and during boost he's only leveraging roll control, not vertical control, seems to imply that no one is currently doing what you mention above. Also I do believe many if most of the people flying their own active stabilisation systems are parking them during boost/at high Mach. I'm happy to be proven wrong though.

TonyL said:

You are correct to consider that the added mass will potentially reduce the maximum achievable altitude, but you are neglecting flight trajectory dispersion, which will limit the probability of actually reaching the theoretical altitude. We have seen many flights with very high theoretical altitudes that were never realized.

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Agreed, but as I mentioned up thread there are other dumber ways of optimising verticality during the booster burn. Also, I think you're almost implying here that off trajectory flights are the primary cause as to why staging shots have a low probability of reaching their theoretical altitude. I'm not sure I agree with that.

TonyL said:

The much fewer number that have been successful are there through a combination of hard work and luck. The right answer is the the one that is expected to meet one's objectives.

One will always have the highest theoretical altitude from the most minimized/optimized design, however realizing it is another matter

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Can't argue there either. I'd go as far as to say any 100k' + shot is a combination of hard work and luck.

When you look at Curt's PHX4 flight where he hit roughly 250k' MSL and consider he didn't use any active stability system and still recovered the sustainer 6.36 miles from the launch point I think we can both agree that there is still a lot of room for people to attempt high altitude two stage flights, stay within cylinder, and still achieve quite incredible results.

JimJarvis50 said:

It's pretty hard to offend me (possible, but difficult).

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That's what I expected and I appreciate you stating that. As mentioned I'm not out to offend anyone and I really enjoy the fact that given your accomplishments you're still available (for lack of a better term) to people in the hobby like myself.

I've got to run and go cut some wood for the fireplace as it's bloody cold down here but I'll respond to you soon. Thanks again for the response.