Unexpectedly high RASAero estimate for a two-stage rocket.

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There are two really obvious problems which I see here.

The first is that you talk of carbon fibre motor cases and no air frames and 1mm fins to get the performance to back up your idea, so basically a motor with fins. But then talk about using it to launch a multi stage rocket with a payload, so it will have no where near the performance you are using as a baseline, even before the necessary increase in weight to allow for the heavier load on top of the rocket.

Second, you pull these sorts of costs out. Where is the R&D and labour budget? Of course prices look cheap when you just cost up a very basic BOM, but who is going to turn that into a payload lifting machine for not just free, but at their cost once development is allowed for?



It seems strange for a mathematician to apply a linear difficulty scaling for a task that clearly is not.
What about the price of a POXA1328-003 "No Limits" GPS chipset to track it beyond ITAR limitations? Copenhagen Suborbitals claimed it was a $1000 GPS chip and the manufacturer had to export what was essentially military GPS tech with artificial GPS coding limits removed under special clearance by an actual space flight company. The manufacturer of GPS units put significant tweaking time into the GPS unit modifications. There was likely paperwork costs. Then someone smart would have to ground test it with expensive equipment to verify precision.
 
Thanks for the info. I read of some amateurs that tried to reach the Karman line with staging using smaller motors, commercial or homemade, and it seems that the problem was with the staging. So if a team can iron out those problems with staging perhaps an all commercial motor flight to the Karman line is possible. Note also universities have more financial resources than the independent amateur so can essentially make another attempt every year.

I tried doing some tweaks on the design of the OpenRocket sim to see what altitude I could wring out of it. First, I used a slimmer sustainer motor at 75 mm, 3 inches, diameter to reduce drag. I used the M2245 motor.

Next, I gave it more realistic shapes for the booster fins. Note though the reason in the OpenRocket sim I used those exaggerated fins was I was trying to pull back the CP for stability. With the new fins, the CP is disturbingly close to the CG. I didn't get any stability warnings so I let them stay. I also increased the fin thickness to 0.1 cm. For strength of the fins at this slim thickness I chose the fin material as carbon fiber. I also chose carbon fiber for the nose cone and transition.

About the body tube, most rockets meant to get to space, orbital or suborbital, use the rocket tanks themselves as the body of the rocket. So to reduce weight further I chose "Custom" in the selection for the body material and set the density to 0.0.

The nice thing about OpenRocket is that it'll display its estimated altitude as you are making these changes. I was surprised then how much the altitude changed by changing the nose cone shape and length, and how much it was changed by the transition length. The result below:

O8000_to_M2245.jpg



The link to the new OpenRocket sim is here:

https://drive.google.com/file/d/1ybAB9So4x2ngVJzI72h6-CrPC4oLOc-O/view?usp=sharing

Bob Clark
Have you looked at Stability margin bro? Have you looked at airframe heating by total temperature advanced fluid mechanics then computed the oblique shockwave secondary Mach number to determine the highest temperature on airframe in air to determine which epoxy you should pick for that environment by Mach number?
 
The nose cone, which you keep overlooking, is the biggest contributor to the area rule.

The fins, which you keep overlooking, are the second largest contributor to the area rule.
He doesn't understand fluid mechanics how the exposed plate area increases drag. Also the Velocity is squared. So making rocket go faster just adds more drag. More drag force requires components be designed stronger at joints which adds mass. Otherwise he would start with fin span near body tube diameter. The nosecone length to diameter should be 5.8:1 or greater for reduced drag coefficient. He is not engineer. Then he needs to flutter FinSim his designs for Mach 6.57. This will require more fins and smaller span or significant fin geometry or material changes.
 
Have you looked at Stability margin bro? Have you looked at airframe heating by total temperature advanced fluid mechanics then computed the oblique shockwave secondary Mach number to determine the highest temperature on airframe in air to determine which epoxy you should pick for that environment by Mach number?

You know my favorite part about your posts, and Bob's posts? They never lead to any practical application. Will any of these threads lead somewhere?
 
On a slightly related note, I have decided not to go through with the LiquidFyre Space Systems Kickstarter after a few moments of consideration revealed massive and glaring fatal flaws in the logic and calculations underlying the business plan.

Bummer, now what am I supposed to do with this extra $5000 I had lying around....
 
You know my favorite part about your posts, and Bob's posts? They never lead to any practical application. Will any of these threads lead somewhere?

Honestly, Andrew is raising some relevant points this time. If Bob Reaally wants to consider this, he'll need to think of them eventuall

I'm just here to watch the explosions :dark:
 
This Bob guy... I don't think he means any harm. He brings up interesting topics. I already know from very limited practical experience that a large to narrow diameter interstage with little casing overhang is doomed to fail by wobble symptoms in minimum diameter rockets even when the rocket is stable in flight. UAH had some paper development of a multistage rocket which covered interstage design on a sounding rocket around a Cesaroni casing. This was a topic myself and other UTC students failed to practically grasp at first. Open rocket itself will not design a successful rocket. I wish I had known about the UAH paper earlier. There are experience related items that lead to why hobby rockets are heavier than OR models for durability reasons real world related. You also need lower accelerations or no one will be able to track it. Too much acceleration can shear tube walls. Try to maximize the sustainer burn time. Add realistic payload masses sized by apogee article sizing your parachute to recover the sustainer and booster stages. Add realistically shock cord and tracker/battery masses. At minimum this guy needs a Raven 3 to ignite the upper stage since its APCP and won't direct ignite. Unlike bob. I've designed two multistage rockets that flew last year granted on L-1 motors. Bob ambitious posts about hypersonic flight as if it's trivial and everyone else screams it doesn't scale. Look up the cost of MA-25S ablative to survive a Mach 7 environment. It's hard to take bob serious when not much effort was it into sim. That MA-25 crap was used on the X-15 and costs more than his budget just so aluminum won't melt. The Mi-15 topcoat by Lockheed Martin goes over the MA-25S to protect it. These are spray on coatings.

I would try as a rule of thumb to overhang the casing on sustainer by a diameter and half or greater. Then ground test for wobbles. Didn't know that at first and my second rocket used that logic which worked.
 
You know my favorite part about your posts, and Bob's posts? They never lead to any practical application. Will any of these threads lead somewhere?
I'm just trying to finish an L-1. The math had practical applications for engineering competitions. You hobbyists still beat our arses so badly at experience it's not funny. There is no substitute for actual flight experience. This community and its members iterative broke 100,000ft which is quite an accomplishment. You will learn what is practically possible and there are less Bob like threads of wanting to push to edge of performance by a humbling realization that certain things physics wise are not doable because of material limitations or regulations. I like to think that somehow Bob's discussions have practical aspect after a bunch of money, time, research, and multiple less ambitious flights are attempted. I do not think all of Bob's goals are achievable in ways he sees them. I do think humanity as a whole is trying to advance space flight and exploration. And that hobby rocketry provides the lowest cost environment to test research systems practically.

The practical application is beyond my budget at this performance range. I do not have L-3 experience or certifications and can not own or fly L-3 motors. I have experimented with nosecone design and supersonic airfoils on L-1 rockets. Flying an L-1 rocket practically is a lot cheaper than renting a wind tunnel to achieve that Mach number. I realized 22,000ft wasn't doable on staged L-1 motors adding up to complex I with the experience I had. I would love to find a group of talented rocketeers and work with them in the future on a 100k ft or beyond project after I graduate this summer and have more disposable income. There are many things beyond my grasp in rocketry. Theoretically supersonic ramjets intrigue me. I think scramjets are thermally too exotic (attrociously high material costs for thermal survival and practical lab tests unaffordable to the many). Conceptually scramjets just bounce and reflect oblique shocks inside the combustion chamber many often times more than three the typical max reflections taught in advance fluid text problems. The practical geometry to make the scramjet work practically exceeded the theory knowledge and requires testing to make it work practically which makes it hard to develop.
 
No, for $3000 you have a rocket that will destroy itself before it reaches 1% of the target altitude. A simulation program does not handle strength of materials, fin flutter, or a multitude of other dynamic limitations.

Your optimistic cost estimate - and cartoon-like design - does not include onboard electronics for staging or tracking, or a place to carry them.


A more accurate estimate of the weight and cost can be obtained by comparing to the original FourCarbYen.

83148a.jpg


You can see there is quite a significant length beyond that of the fins for the carbon fiber airframe. Then we can calculate the weight of the portion that would only consist of the length of the fins to serve as the fin can. Since there is also much less carbon fiber required we can estimate what would be the saving in cost.

Note also since the stages would not be recovered for this suborbital space shot, the parachute and recovery equipment would also be removed, though retaining GPS altimeters and GoPro camera in the nose cone. Without this equipment the rocket would also be shorter compared to the original, further reducing air drag, weight, and cost:

83148.jpg



Bob Clark
 
You know my favorite part about your posts, and Bob's posts? They never lead to any practical application. Will any of these threads lead somewhere?

I'm hardly saying anything new. Suborbital and orbital rockets don't use airframes. For the FourCarbYen rocket the airframes weighed more than the dry weight of the motors. That is a significant weight that wouldn't be used for an actual space rocket.

Note that the Princeton attempt at the Karman line also won't use airframes:

https://rockets.princeton.edu/spaceshot/

They may give you access to their sims showing their rocket can exceed the Karman line with commercial motors by not using an airframe if you contact them. The Princeton team also did structural and aerodynamic simulations beyond just using altitude simulators such as OpenRocket or RASAero. They are very open to discussing their design so they'll probably discuss this with you also if you inquire.


Bob Clark
 
Honestly, Andrew is raising some relevant points this time. If Bob Reaally wants to consider this, he'll need to think of them eventuall

I'm just here to watch the explosions :dark:

Actually, I don't have to do it. Several university teams are already doing it to make their own attempts at the Karman line this year. The method and techniques have been well known for decades, so it is not surprising university teams would be making the attempt.

It is notable as well though looking at the university teams descriptions of their designs that this is something that can be emulated by independent amateurs.

Bob Clark
 
Actually, I don't have to do it. Several university teams are already doing it to make their own attempts at the Karman line this year.
Fine, we get it. I'm not sure what you're trying to accomplish by endlessly rehashing the same arguments here.
 
Bob. This is why hobby rockets have all that draggy useless airframe or nosecone length. It's to store a required by safety codes "recovery device". Clever use of recovery equipment mass allows you to not need a mass counterweight to obtain a CG you want. Try to size the parachute as round for your rocket. Use the sea level density if you want. You can take the sustainer mass without motor for example. This chute will have a pack length of several tube diameters (3-6) before a shock cord is added. The smallest chute I've heard on an N flying case sub minimum diameter is 18" with an idiotic high descent rate that could arguably harm something.

https://apogeerockets.com/education/downloads/Newsletter149.pdf

You need to understand limitations of regulations prohibit your idea from actual testing. Unless you really want an unguided MLRS with an ITAR export controlled GPS without a warhead but enough kinetic energy to cause significant harm which will not look okay in the face of any civil space program or amatuer event even if you call it a sounding rocket people with authority may argue how stupid and not well thought out this plan is and they won't care of any 100km no recovery rocketry records. They may view you as bad person. This is more than drop fifty pound anvil from 100km, it has immense forward kinetic energy, that could like crater something or someone if your not careful. Wallops could probably do it, but doesn't make it easy for average joe. Then it's going to be a pissing contest if the airframe or interstage design of a sub minimum diameter rocket can take thousands of pounds of thrust force and not permanently deform for staging. It's hard enough to make it work for amatuer rocketry. Telling me saving a chute mass and possibly killing something isn't a pro con thing I want to weigh, it's an obvious no. You couldn't fly your design at any sanctioned TRA/NAR launch. FAR would likely say no without a chute. Your talking about accepting total liability and insuring it if it's even insurable for a castrophic loss of life type event or property damage. You can't just lobb stuff Suborbital without a chute. People will care. They might start lobbing fanged explody things back...
 
The part of your current tack that offends my practical side the most is the "Explorer 1 was just another stage on a suborbital rocket" part.

Sure, the Redstone SRBM was a "suborbital rocket". But it was an SRBM- it could lob 3 tons of nuke 200 miles, and was only a few m/s short of orbit on its own. Even then, the Baby Sergeant motor used for the final kick is essentially what you're proposing- an optimized O8000WT (it's a 98% O6700) and they needed 15 of them in 3 tiers to get the payload into a barely-acceptable orbit. I realize that instruments, etc. have gotten smaller since then, but the tyranny of the rocket equation still wins out in the long run.
 
Fine, we get it. I'm not sure what you're trying to accomplish by endlessly rehashing the same arguments here.
I think he wants a low mass sub minimum diameter airframe with optimized volumetric loading. It worries me he wants an ITAR export controlled GPS and no chute. Usually people want to recover rockets. Because they are expensive and cause a lot of damage if not recovered correctly.
 
Your fourcarb yen file has a cardboard nosecone which doesn't work at Mach 5.2. Airfoils of carbon fiber 1mm thick are not design for manufacturable meaning there is not a way to produce that. (machining tolerances)
 
Your fourcarb yen file has a cardboard nosecone which doesn't work at Mach 5.2. Airfoils of carbon fiber 1mm thick are not design for manufacturable meaning there is not a way to produce that. (machining tolerances)

If you do the “Modified FourCarbYen” sim I posted even with a 0.3 cm fin thickness, it still exceeds the Karman line.

Anyway, you would be using the same thickness fins used on the original FourCarbYen but without an airframe, only a fin can.

Bob Clark
 
Fine, we get it. I'm not sure what you're trying to accomplish by endlessly rehashing the same arguments here.

The proof is in the pudding, as the saying goes. Making the von Karman line is a non-trivial task for a university team. But of course they’ll make more attempts if their first attempts do not succeed.

My opinion, they will ultimately succeed. Then it is an interesting fact that their designs are ones that can be emulated by independent amateurs to also make successful flights beyond the von Karman line.

Bob Clark
 
The proof is in the pudding, as the saying goes. Making the von Karman line is a non-trivial task for a university team. But of course they’ll make more attempts if their first attempts do not succeed.

My opinion, they will ultimately succeed. Then it is an interesting fact that their designs are ones that can be emulated by independent amateurs to also make successful flights beyond the von Karman line.

Bob Clark
You offer no proof, no pudding, then restate your assertion. Please stop, it's exhausting.
 
The proof is in the pudding, as the saying goes. Making the von Karman line is a non-trivial task for a university team. But of course they’ll make more attempts if their first attempts do not succeed.

My opinion, they will ultimately succeed. Then it is an interesting fact that their designs are ones that can be emulated by independent amateurs to also make successful flights beyond the von Karman line.

Bob Clark

You haven't really shown anyone here why your opinion is worth much so far bob. Its not that there is some test you need to pass to post on here, but the only thing you've really proven on here or in your posts on reddit is that you have an impressive ability to ignore everything that people take their time to try and explain to you. Well that and that you have no idea how to operate the simulation software that you rely on for your arguments, and that you don't understand the value or limitations of simulation.
The only thing that really makes since is that you are a troll, which would explain the nonsense you post on /r/the_donald, if you are not a troll you should possibly conciser taking a few steps back and learning the basics of rocketry, and not leaning them vicariously through university blog posts because that really is not working so far. Like actually going and building something. Maybe after that you might begin to understand why people on here are rejecting the ideas you are suggesting.
 
Wouldn't be fun if RGClark, Andrew_ASC, and nickcodybarrett were all at the same university?

They should get together and do a build thread. That way I can read the words "Karman line" for the 100th time since Tuesday of this week alone... :)
 
It seems like every so often the world produces a new Sim Ninja who is going to set the Rocket Community ablaze with his unique blend of skills. These skills always seem to be the best combination of RockSim manipulation, the ability to ask the illogical question and ignore logical responses and the willingness to piss everyone that ever came before them. We just happen to be lucky enough to live in rare times when three of them chose to grace us with their presence at once. How lucky we are...how lucky we are.
 
Farbeit from me to douse a good pile on, but it's worth remembering that at least two of them will have some chance of naturally outgrowing it.
 
You haven't really shown anyone here why your opinion is worth much so far bob. Its not that there is some test you need to pass to post on here, but the only thing you've really proven on here or in your posts on reddit is that you have an impressive ability to ignore everything that people take their time to try and explain to you. Well that and that you have no idea how to operate the simulation software that you rely on for your arguments, and that you don't understand the value or limitations of simulation.
The only thing that really makes since is that you are a troll, which would explain the nonsense you post on /r/the_donald, if you are not a troll you should possibly conciser taking a few steps back and learning the basics of rocketry, and not leaning them vicariously through university blog posts because that really is not working so far. Like actually going and building something. Maybe after that you might begin to understand why people on here are rejecting the ideas you are suggesting.

The university teams ARE building their own rockets to attempt to reach the von Karman line.

That's the important thing. An actual successful demonstration supersedes any logical or mathematical argument.

If and when they succeed, the arguments on this forum will rapidly transition from explaining why it won't work, to describing their own proposals to duplicate the university teams successful launches.

The Princeton team has provided a link to the technical documentation describing the development of their work:

Princeton Spaceshot: Technical Documentation.
https://rockets.princeton.edu/spaceshot-technical-documentation


Bob Clark
 
The university teams ARE building their own rockets to attempt to reach the von Karman line.

That's the important thing. An actual successful demonstration supersedes any logical or mathematical argument.

If and when they succeed, the arguments on this forum will rapidly transition from explaining why it won't work, to describing their own proposals to duplicate the university teams successful launches.

The Princeton team has provided a link to the technical documentation describing the development of their work:

Princeton Spaceshot: Technical Documentation.
https://rockets.princeton.edu/spaceshot-technical-documentation


Bob Clark

Speaking as a university student, we are all working with amateur rocket technology. Sure, many student groups have larger budgets than all but the most dedicated amateurs, but that doesn't mean that any particularly advanced research is taking place among college rocket teams. The Princeton rocket isn't any more likely to succeed than the extreme altitude attempts made by amateurs at events like BALLS in the past, and its success hinges on many factors including wind. If people here had the resources to build rockets the size of USC's, they would. No one here will be surprised if Princeton, USC, or other amateurs cross the Karman line, and no one is suddenly going to acquire a many-thousand dollar filament winder and a 60 quart mixer as a result. It has been done before (CSXT) and all that was shown is that the investment required was significant.

What bothers most people in this community that you have tormented for the past year across multiple platforms is your insistence that "Orbital rockets are now easy", which is one of the least informed opinions I have ever seen on this forum. Only a dozen COUNTRIES have ever placed an object into orbit. Claiming that your bogus simulation results prove anything is laughable, because people here have flight data from similar rockets that they have actually built. You seem to think that you discovered something new, and you disagree with everyone, including actual aerospace engineers, who points out any issues with your "plan", which is based entirely on the slippery slope fallacy.

As a member of one of the university teams that you attempt to give advice to, I think you need to stop pretending that you have knowledge that anyone here doesn't. I agree with slaak and will only be checking on this thread later for entertainment.
 
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The t value of R/L is squared in the drag coefficient of slender bodies. The profile determined the constant affecting this t value. So if the radius is smaller than length significantly the theory drag coefficient decreases. There's less famous math dorks out there from the fifties with some radical nosecone equations for hypersonic flight. Usually falls into wind tunnel lab tests before Project XYZ where XYZ are replaced by different numbers then Google refuses it's existence. People here are awfully mean to Bob. Math guys don't physically do anything "practical" with building physical objects, but without certain equations they develop; the "practical" improvements in performance would be unknown by engineers.
 
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