ClayD
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What Are Our Motors "Missing"?
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cjl
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Sims agree - even not accounting for the velocity at motor ignition, my design shows >200kft of additional altitude just from the N5800 alone if lit at 50,000 feet.
Cool. So if the O25,000 can get your N5800 rocket up there fast enough for it to stay straight, you'd have yourself your own space shot using just 2 commercial motors (one of which would have to be flown as a manufacturer's demo) :fly:
Details like FAA approval, recovery from that altitude, getting one of those O25,000 motors, etc. are minor details that would have to be worked out, of course.
cjl
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Cool. So if the O25,000 can get your N5800 rocket up there fast enough for it to stay straight, you'd have yourself your own space shot using just 2 commercial motors (one of which would have to be flown as a manufacturer's demo) :fly:
Details like FAA approval, recovery from that altitude, getting one of those O25,000 motors, etc. are minor details that would have to be worked out, of course.
It kind of seems that way. I'm almost starting to think that with an appropriate 98mm booster, this might have a shot at getting to space. If my N shot at BALLS next year is successful, maybe that could be a good future project (though the FAA approval could be interesting). It really does look (from preliminary numbers at least) like a purely class 2 rocket (O impulse in total) could reach space though.
MClark
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The performance that was achieved in Arcas, Loki and other systems of the day is amazing. The engineers that designed them really knew what they were doing and had the opportunity to do it.
The technology is over 50 years old and many of the materials used are now considered obsolete and have been replaced with "modern and better" stuff. If we could replace some of the parts of, say an Arcas, with today's materials that really are better it could be made to even higher performance. Nose cones and payload section tube could be made of newer, lighter stuff and certainly the electronic payload could be made lighter.
Launching a rocket into space is a great goal but it is not a realistic one in the near future for rocketeers asking the questions that come up on these forums. This year at BALLS we had rockets being launched with the goal of 100,000 feet and a fist full of cash from the Carmack Prize. Although two met the altitude the other rules were not met with a good GPS and recovery of the entire rocket intact.
Space is generally said to start at 100 kilometers, which would be about 330,000 feet or over three times what the Carmack Prize entries were shooting for. The number of places an amateur rocket can be launched into space is very limited. A goal of 100,000 feet still extremely limits the launch locations and opportunities, probably to the same list as space. Realistic goals are required for a project to be successful.
Mark
The technology is over 50 years old and many of the materials used are now considered obsolete and have been replaced with "modern and better" stuff. If we could replace some of the parts of, say an Arcas, with today's materials that really are better it could be made to even higher performance. Nose cones and payload section tube could be made of newer, lighter stuff and certainly the electronic payload could be made lighter.
Launching a rocket into space is a great goal but it is not a realistic one in the near future for rocketeers asking the questions that come up on these forums. This year at BALLS we had rockets being launched with the goal of 100,000 feet and a fist full of cash from the Carmack Prize. Although two met the altitude the other rules were not met with a good GPS and recovery of the entire rocket intact.
Space is generally said to start at 100 kilometers, which would be about 330,000 feet or over three times what the Carmack Prize entries were shooting for. The number of places an amateur rocket can be launched into space is very limited. A goal of 100,000 feet still extremely limits the launch locations and opportunities, probably to the same list as space. Realistic goals are required for a project to be successful.
Mark
ClayD
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But... Mark,, you could just stage a couple cti motors... :marshmallow:
CJL and ADRIAN have the details on the table..
(really i am just horsing around, i know they are talking about the motor having the performance, not foolhardy that launching and successfully staging from a O25000 is a feat of an accomplishement all in its own right.)
As a severe dyslexic, theres a different learning curve to life... i read this to mean you suggest changing your ULTIMATE goals to what seems achievable.... which is kind of backwards... When really you shoud be setting pace to make your un-real goal a reality itself... why achieve something that is already in reach(or realistic)
Long term goals need Zero reality.. the shorter the goal term, the more :"reality": you have to have. Sometimes even if you dont get that ultimate goal, the short term achievements change the world... (Velcro)..
Clay
cjl
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Agreed, but I think with the appropriate aerodynamic design and careful planning, a fully commercial N to N would have a shot at >250k (possibly even space). I'm not saying it would be easy by any stretch of the imagination, but I do think that it would be possible. I will say though that I haven't fully run the sims through on the possible booster scenarios, so this is based on some very extensive sims of single stage performance on an N5800 plus some educated guesswork on what a booster could add. I could definitely be wrong about the available performance.
Don't get fall into the trap of picking a booster that doesn't have enough thrust, though. With the long delays you need for this, vertical flight is key, and even the best simulators tend to be too optimistic about the flight angle. I wouldn't go any lower than the N5800, the N10000 Vmax or the Aerotech N4800. If the N10000 has enough impulse, that seems like an excellent candidate.
If a realistic simulation shows it's possible for a 2-stage rocket with commercial motors to achieve 330,000 feet, and if there is a realistic path for the FAA approval, then it's a realistic goal. Not that it would be easy, or inexpensive, but I think it's within the capability of the people discussing this on this forum as long as it's not legally prohibited. The rocket tilt meter or equivalent could be used to limit the ignition conditions to ones that would result in acceptable footprints, which should help with the FAA approval.
Most of the hard parts related to these extreme altitudes (deployment charges, motor ignition, aeroheating) will be tested at Balls 2012. The sustainer heating would be significantly less than what Chris is planning to run into next year if he goes through with igniting an optimized N5800 at ground level. (I think that's actually a more difficult technical problem, and I don't know if he has a plan for it). Here's a brainstorming list of conditions that are beyond what we will have tested at the end of BALLS next year, if all goes according to plan:
-Radio range to 100 km
-Motor ignition at >20,000 feet
-Rocket tilt meter use that late into a flight
...and I'm coming up blank after that. I don't see any of those as show-stoppers. What else am I missing that makes this unrealistic?
Rocketman248
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I don't think the N10,000 would be a very good booster for those kinds of projects. While very powerful, it's still just barely an N. It's only a couple hundred Ns over an M. My Ultimate Wildman only did about 12,000ft on it. Granted, it's a 6" diameter rocket, so it has a lot more drag than a minimum diameter rocket. Even so, I don't think it would have enough impulse to really push a two stager up there.
ClayD
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While were talking reality...
Why, and what is the thinking behind 330k, being obtained by N-N staging....
Or even O - N staging being realistic at all...
I am not naysaying... but what makes what you would build that much differnent than Jim's rocket that was N-N this year... And, 3 times the altitude...
I think the prooving ground you will have to make up with your officials to get a COMPLEX flight to 300k Approved, will be as big of a mountain as the rocket itself...
It may not be realistic, but its years away............ and i would like to see it happen, i just dont think any part of it is at all easy.
Well-proven RASAero sims showing the benefit of longer ignition delays. Also, the sustainer motor would be bigger than what Jim used. Based on past history, I believe what RASAero tells me. I'm not sure if it would need the O25000 as a booster, because I haven't done the sims myself yet, but if RASAero tells me an N-N would get there using an achievable ignition altitude, I will believe it.
Agreed, and possibly worse. To me that's the biggest unknown, how much credit could we get from officials for ignition inhibits from a Rocket Tiltmeter or something like it.
Ironically, given where this thread started, there is one part of this that would be easy, and that's the motors. Just buy and assemble.
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Dynamic stability optimization is required for high-performance flights. It's not a trivial problem to understand or solve. Simulations will be "garbage-in, garbage out" if you guess at this, giving you false hope for high max altitudes. Problems with dynamic stability will also put extra stress on the rocket during flight, leading to a high angle-of-attack, and failure. We see this a lot at BALLS.
One common feature in all professional unguided rockets is spin stabalization. As part of this, the rocket and payload are balanced (using some expensive test equipment) before flight.
I don't agree with the notion that commercial motors can reach 200Kft. They are optimized for re-use and reliability, not performance. It's not the same as engineering a rocket whose airframe is the motor, and the mass fraction is improved by trading off other factors... such as reloadable, easy to assembly, easy to manufacture, etc. All this is part of the engineered system, made for a specific purpose but not optimized for other purposes (a good point that Bob made a few messages ago).
One common feature in all professional unguided rockets is spin stabalization. As part of this, the rocket and payload are balanced (using some expensive test equipment) before flight.
I don't agree with the notion that commercial motors can reach 200Kft. They are optimized for re-use and reliability, not performance. It's not the same as engineering a rocket whose airframe is the motor, and the mass fraction is improved by trading off other factors... such as reloadable, easy to assembly, easy to manufacture, etc. All this is part of the engineered system, made for a specific purpose but not optimized for other purposes (a good point that Bob made a few messages ago).
I've been through the school of hard knocks on that one already. And if I haven't, Chris and I certainly will next year at BALLS. I was asking about things that will be beyond our experience base after BALLS 2012.
Thanks, John. That's just the sort of response that adds a little more satisfaction to eventual success. Kinda like, a 3" motor can't set an L record, or a long-burning 29mm F will never outperform a fast-burning 24mm F.
RASAero has been right on the money on all my high-performance flights so far, up to Mach 2.5 and 32,000 feet. So unless the density vs. altitude model inside the program is way off at the higher altitudes, I think it's quite reasonable to believe it for a flight to 200,000 or 300,000 feet, too.
mikec
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After the MIT three-stage that ignited horizontal and ended up "20 to 35 miles" downrange at BALLS this year, I'm wondering how the analysis is done for multistage flights. I find it hard to believe that 35 miles was inside the dispersion ellipse for the flight's waiver.
Agreed.
Here's a thread on having fun simulating this thought experiment:
https://www.rocketryplanet.com/forums/showthread.php?p=189142#post189142
The bottom line is that it looks like yes, an N-5800 to N-5800 combination can get an optimized rocket to space, if it has good enough heat tolerance.
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By stating that, I think you've missed my point. The air density model is realtively simple. So is playing with staging delay. So is static stability margin. But what happens to your dynamic stability as the motor burns and as the rocket passes through various velocities and air densities? How will the rocket respond to disturbances (internal or external) under these ranges of conditions? How fast will it correct and at what maximum angle of attack? Will the angle of attack not recover enough (or at all) and end up turning the rocket, losing significant altitude, or stressing it to destruction?
It's worthwhile and necessary to work through everything else, such as material selection, thermal issues, reliable staging, recovery, etc. I'm just pointing out the most commonly ignored aspect that comes after all those are solved. And the solution does not scale from smaller high-performance rockets.
There are solid fuel rocket propellant formulas that you and me would never be allowed to possess much less launch.
Crap that is so volatile that it has to be kept super-cooled before ignition and so toxic that it can only be fired far from any civilian populations.
I dont know if this is the stuff being used in these sounding rockets or if it is only being used in experimental military ordinance.
Crap that is so volatile that it has to be kept super-cooled before ignition and so toxic that it can only be fired far from any civilian populations.
I dont know if this is the stuff being used in these sounding rockets or if it is only being used in experimental military ordinance.
cjl
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That's the thing though - there really isn't any solid fuel formula that delivers any better than about 300s (vacuum) ISP, and that's only a tiny bit better than highly aluminized, well-expanded APCP. Many of the experimental military propellants are aimed more at goals such plume minimization, not extra performance.
I understand about dynamic stability, and you're right, it doesn't scale from high-performance rockets. Smaller rockets are more difficult. If you're flying a 12" G rocket with moderate static stability and 50 Gs of acceleration, it takes only a mm or two of lateral mass offset to send it cartwheeling (ask me how I know). Yet you can hang a big camera off the side of a large camera rocket, and the time constant for that disturbance to affect the flight angle is so long, that the rocket has generated plenty of vertical velocity and fin restoring force by that time. Granted, the bending forces on a large rocket going through wind shear or moderate angles of attack are much, much larger than they are for a small rocket, which is why coupler failures and airframe tube bending failures are so common on high performance flights of large rockets. I've looked into some of these failures in some depth with the owners.
The solution is a straightforward combination of careful attention to symmetry (both in lateral CG and aero symmetry), extra margin in the bending strength, and, most importantly, extra stability margin using additional fin area. Extra-large fins dramatically reduce the magnitude of the excursions and the resulting bending moments. This is a key design feature that IMO is often overlooked. A little extra margin there covers up a multitude of errors. My 3" L record attempt rocket had 2 of its fins visibly tweaked out of alignment during the fillet curing process, and yet the rocket flew marvelously straight because the fins and stability margin were huge by record attempt standards (about 15% of the rocket length). I had some extra weathercocking because the wind was somewhat over my usual 10 mph design assumption, but not enough to keep it from hitting 32,000 feet.
Attaching everything but the nosecone directly to the end of the motor, and using the motor as the coupler for the extended nosecone, makes the rocket much stronger than traditional designs. That just leaves the nosecone airframe extension as the driving case for rocket bending failures, and a little bit of axial carbon fiber there goes a long way. It's not hard to make it stronger in bending than the motor that it's overlapping.
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Current sounding rockets do not use any of those energetic propellant ingredients. Even the historic ones we've used here as examples don't use anything special.
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Both are difficult. Larger is not easier, just a different region of the problem space. Larger high-performance rockets have higher moments of inertia, and are overdamped. It isn't as simple as "careful attention to symmetry ... and extra stabiity margin". A small disturbance is less likely to cause a rapid pitch oscillation, but a static imbalance or a large disturbance will start a pitch rotation that may not correct (or recover at all). The method used to minimize the magnitude of the response in any one direction is to induce a spin (from the launcher or from fin angle or tabs). Responses to disturbances are confined within a 'cone' with a much smaller average pitch angle, and the response doesn't build up in a single direction. Some energy is used to impart the spin, but the flight stays vertical, reaching a higher altitude.
