A fast route to a European low cost, reusable, manned launch vehicle.

tahanson43206 · 2023-06-26 18:39:43

This is a follow up to an inquiry at Apogee about RockSim...

Conversation with Brendan Campbell about RockSim...
Hello Tom,
It should be able to handle the first stage just fine. Sadly, nobody in the office knows of a open source package for orbital calculations.
Brendan Campbell
Customer Service
Apogee Components
4960 Northpark Dr.
Colorado Springs, CO 80918
Ph: 719-535-9335
Fax: 719-534-9050
Email: customerservice@apogeerockets.com
Web: www.ApogeeRockets.com
Facebook: http://www.facebook.com/apogeerockets
P.S. Have you tried our Launch Visualizer? Check it out at: https://www.RockSim.com
On 6/26/23 2:05 PM, Tom wrote:
>
> Hi Brendan!
>
> Thanks for getting back to me. I'm not surprised, because the software is offered by a company that makes model rockets.
>
> Would you be willing to ask around the staff, to see if anyone has a suggestion for an Open Source package that can do orbital calculations?
>
> The first stage flight is probably a parabola, and RockSim might be able to handle that, with the payload being a stage instead of a parachute.
>
> Can the software handle mass in the hundreds of tons?
>
> Thanks again for your reply!
>
> (th)
> On 6/26/23 12:28, Apogee Rockets Customer Service wrote:
>>
>> Hello Tom,
>>
>> I'm not sure what exactly you'll need RockSim to do, but it doesn't do any orbital calculations only parabolic flights. We do offer a 30-day free trial if you wanted to look over it and see if it will work for you: https://www.apogeerockets.com/Rocksim/Rocksim_Trial
>>
>> Brendan Campbell
>> Customer Service
>>
>> Apogee Components
>> 4960 Northpark Dr.
>> Colorado Springs, CO 80918
>>
>> Ph: 719-535-9335
>> Fax: 719-534-9050
>> Email: customerservice@apogeerockets.com
>> Web: www.ApogeeRockets.com
>> Facebook: http://www.facebook.com/apogeerockets
>> P.S. Have you tried our Launch Visualizer? Check it out at: https://www.RockSim.com
>> On 6/25/23 10:55 AM, Tom wrote:
>>> Apogee Components
>>> Web Inquiry
>>> From: tahanson43206
>>> Email: tahanson43206
>>> Subject: Inquiry: Inquiry about Rocksim capability for orbital rocket simulation
>>> A group of members of the Mars Society is discussing variations on the EU Ariane rocket. The discussion has progressed beyond hand waving. There is a program called GMAT that might be suitable. I don't know enough about it. Google found your company when I asked for rocket simulation software. Model rockets are important and I'm glad there are folks building them. Hopefully an interest in model rockets will lead to a professional career in some cases. I am a (Junior) Moderator at NewMars.com/forums.
>>> tahanson43206
>>>
>>> Sign up for the Peak of Flight newsletter!
>>>
>>> Apogee Components - 4960 Northpark Drive, Colorado Springs, Colorado, USA
>>>
>>> Copyright (c) 2023 Apogee Components.

(th)

tahanson43206 · 2023-06-26 18:50:21

RockSim appears to be available for $123 as a purchase.

The Pro version is available for a monthly subscription of $30, but there might be a minimum subscription time.

What is important about the Pro version is that it may be of interest for a serious rocket designer:

A. RS-PRO will remain separate from RockSim. RS-PRO is a subscription service (pay by the month), while RockSim will remain a one-time fee program.
RS-PRO picks up where RockSim leaves off. While it retains all of RockSim's design capabilities, its flight simulator is designed to handle rockets that fly at faster speeds (up to Mach 10), and those that fly higher (up to 632 km above sea level).
The second main difference is that RS-PRO predicts flight performance in 6-degrees of freedom, where RockSim is limited to 3-degrees of freedom. This allows it to better predict the flight trajectory of the rocket. You can see this in the Launch Visualizer, which shows you the trajectory.
Finally, RS-PRO is designed to estimate the landing zone (called a splash pattern) where a rocket is most likely to land based on 18 launch uncertainties. The earth is modeled as a rotating oblate spheroid, which is a must on rockets on high sub-orbital flights. Like in real life, a rocket launched straight up will land a bit to the west due to the rotation of the earth underneath it.
RockSim is intended for basic rocket analysis. It has proven itself over and over by thousands of rocketeers that it is a great low-price program for designing rockets and getting a detailed performance analysis. RockSim is here to stay and will be continually upgraded with new design features.

This program is restricted for use by US Citizens and citizens of certain other countries.

(th)

RGClark · 2023-06-26 23:24:29

tahanson43206 wrote:

…
STK (Systems Tool Kit) by AGI (Analytical Graphics Inc.): STK is a widely used software for modeling, analyzing, and visualizing aerospace systems, including rocket trajectories.
FreeFlyer by a.i. solutions: FreeFlyer is another popular software tool for mission planning, analysis, and simulation, which can be used to calculate rocket trajectories.
GMAT (General Mission Analysis Tool) by NASA: GMAT is an open-source software designed for space mission analysis and spacecraft trajectory optimization.
These are just a few examples of software commonly used in the field. If you are looking for a specific software program or have further questions, please provide more details, and I'll do my best to assist you.
…
(th)

I inquired about the three of these. Freeflyer and GMAT can do in-space spacecraft trajectories for changing orbits or flying to other destinations in space. They can not do trajectories from Earth’s surface to LEO.

I asked STK by AGI about trajectory simulations for rocket flight to orbit, and they said it could but the links they sent me only showed again in-space trajectories of changing orbits or flying to other destinations in space when you are already in orbit.

Their customer service rep thought the program could do the sims for flight to Earth orbit but admitted he didn’t know of any examples using the program that did.

I think ITAR restrictions limit any programs that can do such sims being publicly available.

Robert Clark

Last edited by RGClark (2023-06-26 23:25:23)

tahanson43206 · 2023-06-27 06:13:32

For RGClark,

The reply from Apogee indicated that their software is ITAR restricted but since you are an American citizen you are able to buy a copy.

Their package can reach 632 km, which should be sufficient for your purposes.

The basic package is available for $130 in a single purchase, and there is no ITAR restriction.

The ITAR restricted package leases for $30 per month. Their package can handle multiple stages.

The problem you are working (as I understand it) is first stage variations, so the "Pro" package may be sufficient.

You can (apparently) do some free testing, to see if the software is potentially useful.

In addition, there may be a community of users who can answer questions.

Remember, you are eligible to acquire ITAR restricted software if you can prove you are a US citizen

(th)

tahanson43206 · 2023-06-27 06:18:09

For RGClark ...

The reusability problem is non-trivial. No entity other than SpaceX has achieved it.

It would seem (to me at least) that the Europeans would do well to reduce costs by developing reusability.

It would take very bright people and inspired, patient leadership to pull that off.

The evidence would appear to be that only one human being on Earth has the leadership skills needed.

(th)

tahanson43206 · 2023-06-27 07:01:51

For RGClark,

If you decide to venture into the exploration of the capabilities of RockSim or RockSim Pro, you have a potential audience here in this forum.

You'd have to ask if anyone is interested in following along as you explore the capabilities of the software. I am hoping that there might be at least two members who would take a more than passing interest if you were to to proceed along this path.

I am ** definitely ** interested.

I'd like to see screen shots via imgur.com, and notes you might take rendered as pdf documents and served from Dropbox.

While I will (most likely) not be asking very useful questions, we have members who definitely ** could ** help you pose questions to the software.

***
I note that Calliban has provided a hint about how to achieve your long term goal of SSTO capability, quite recently. Calliban suggested eliminating the traditional first stage with an acceleration track of some kind. Nothing like that has ever been attempted, beyond the many successful military acceleration tracks for aircraft leaving carriers at sea.

Calliban's suggestion would require equipment capable of accelerating hundreds of tons to something like 500 meters per second.

That would be some impressive engineering.

If an entity built such a system, it would not be mobile, so vessels launched from such a facility would all "enjoy" the same plane.

(th)

RGClark · 2023-06-28 07:46:34

tahanson43206 wrote:

For RGClark,
The reply from Apogee indicated that their software is ITAR restricted but since you are an American citizen you are able to buy a copy.
Their package can reach 632 km, which should be sufficient for your purposes.
The basic package is available for $130 in a single purchase, and there is no ITAR restriction.
The ITAR restricted package leases for $30 per month. Their package can handle multiple stages.
The problem you are working (as I understand it) is first stage variations, so the "Pro" package may be sufficient.
You can (apparently) do some free testing, to see if the software is potentially useful.
In addition, there may be a community of users who can answer questions.
Remember, you are eligible to acquire ITAR restricted software if you can prove you are a US citizen
(th)

Thanks. I’ll give that a try.

Robert Clark

kbd512 · 2023-06-28 08:30:01

tahanson43206,

RGClark is correct. Software simulating trajectories is ITAR-restricted in one way or another. If you have the knowledge, then you can create your own or adapt something that is free.

CamPyRoS - Modules Main Index

CamPyRoS - A 6DOF Rocket Trajectory Simulator
CamPyRoS (Cambridge Python Rocketry Simulator) is a Python package which provides fully featured rocket trajectory simulation including features like:
6 degrees of freedom (3 translational, 3 rotational)
Monte Carlo stochastic analysis
Aerodynamic heating model
Use of live wind data
Variable mass and moments of inertia models

Anything gun-launched is going to be a liquid or powder after it's launched, so this is only useful for launching construction materials. If the acceleration rate is gradual enough for a human to survive it, then the size of the launcher becomes impractically large. In the realm of practical rockets for humans and satellites, we need engines with greater specific impulse, not by tens of seconds, but hundreds to low thousands of seconds for the difference to become great enough to obtain a substantial cost benefit. Otherwise, you're still stuck burning huge quantities of fuel to deliver meager payload mass fractions.

I think 2.5% to 5% payload mass fraction to LEO is a realistically bounded "play area" for various types of pure rocket propulsion schemes to play within. GW and others on this forum have shown why you're not actually going to get much more or less than that and end up with a viable rocket.

As a rule of thumb, the greater the payload mass fraction, the lower the total cost of building and operating the vehicle. That's why the preferred method to transport LNG and crude oil is a super tanker, an example of the square-cube law in action. It takes proportionally less steel to enclose a larger volume of liquid as the storage tank size increases, and less power to propel a given payload mass fraction to its destination by using larger ships. There's no such thing as a practical aircraft that's cheaper than a ship when it comes to transport costs, hence no LNG tanker aircraft, even if you designed an LNG tanker aircraft to fly at 15 knots (like an Airbus Beluga or Boeing Dreamlifter LNG tanker variant that had a wing large enough to remain airborne at the same speed as the super tanker, when in ground-effect, flying just above the wavetops). Even blimps use proportionally more energy to fly in a particular direction at similar speeds, when compared to ocean-going tankers ships.

RGClark's general idea of creating a lighter and therefore cheaper Ariane-6 launcher seems like it should work, but it needs to be a lot bigger if it's going to be purely LH2-fueled. Weight / cost / complexity goes up as the giant propellant tank becomes even bigger, not down. The tank needs to get wider, unless Kourou's high bay gets taller. Without the solids taking up space on the pad, that should be doable. It'll need to hold almost 50% more propellant, so it requires proportionally more engine power to maintain the acceleration rates of the original vehicle due to drag and weight, but also to provide engine-out capability as the number of engines increases to push more propellant and payload downrange.

If this was me trying to solve this problem, and I was intent on using liquids, I would design a booster stage that uses RP-1 or LCH4. Thrust is pretty good, though not quite as good as solids, and specific impulse is significantly better. Take the average of the thrust and specific impulse from Ariane-6, adjust for weight relative weight of propellants when compared to to RP-1 or LCH4, and what you realize is that solids plus LH2 looks an awful lot like pure RP-1 or LCH4 propulsion. I would keep the LH2-fueled upper stage, as-is. That would be my primary advantage over a Falcon-9. My booster performs the same as Falcon-9, but my upper stage is quite a bit more performant.

At 5.4m diameter, I don't need to adjust the size of the core stage too greatly for LCH4, although the empty weight will certainly go up to contain the heavier propellant. It may even be the case that the aero loads on the tank dictate the mass of Aluminum required, above any beyond what is strictly necessary to support the propellant weight. I would look into a larger balloon tank, since that seems to permit the propellant mass fraction of the RL-10 powered Centaur upper stages to be even lighter than Aluminum while using much cheaper sheet steel.

Calliban · 2023-06-28 08:52:20

Kbd512, the steam powered launch gun is not intended to reach orbital speeds, but to provide an initial vertical 500m/s boost. This allows effective elimination of a lower stage, because something like 1/3 of the propellant needed to reach orbit is used in accelerating the vehicle to an initial 1000mph. So this is a plausible route to achieving an SSTO. If we limit acceleration to 10g, then the barrel must be 1.25km long. Acceleration takes about 5 seconds. I take 10g to be about the maximum acceleration that humans can sustain without injury, for brief periods.

The capital cost of the gun will be high, because it will involve drilling a 10m diameter hole some 1.25km into the Earth, inserting a low alloy steel tube and filling the gaps with fine grain concrete. But ultimately the gun should reduce the marginal cost of reaching orbit. That is assuming that barrel wear can be kept to a minimum. I think this will probably be the case, as the propellant will be steam heated to <300C, the barrel will be smooth bore and the sabot can be lined with a soft material. To minimize corrosion and erosion, we could coat the interior of the barrel with grease or graphite powder.

Last edited by Calliban (2023-06-28 08:53:14)

RobertDyck · 2023-06-28 10:06:33

Modern fighter pilots must prove they can withstand 9 Gs of acceleration for 15 seconds. To do this they wear a g-suit that use air bladders to squeeze their legs. They also use a "high maneuver" which means holding your breath while grunting, using your muscles to delineately increase blood pressure. All to ensure sufficient blood to the brain to prevent blackout. Not all pilots pass. Some fail, they blackout in the chair in the centrifuge. Those that fail often are assigned to support aircraft instead of primary air superiority fighters because the support aircraft only require 3 Gs.

One test pilot demonstrated a new G-suit that included a.vest to squeeze his chest as well. He survived 12.Gs without blacking out. In a centrifuge. But that was just one individual.

NASA limits launch vehicle acceleration to 3 Gs when there are humans onboard.

kbd512 · 2023-06-28 11:44:39

As someone who has been in NASA's g-simulator, as well as flown maximum performance turns with a CFI monitoring what I'm doing, without blacking out, thankfully, I can confirm that at 3g it's somewhat difficult to perform basic tasks, such as maintaining the turn without losing or gaining any altitude, paying attention to your instruments, and what's going on outside the cockpit (looking for other aircraft so you don't accidentally have a mid-air collision).

In NASA's g-simulator, they give you a bunch of basic math problems to complete while they take the centrifuge up to speed. IIRC, they also did manual dexterity tasks that involved reaching above your head and flipping some switches in a specific sequence, and reading off some values on a screen (simulating communicating with mission control). The g-simulator was "just for fun". Flying around in a Cessna while performing a series of hard turns (up to the limit of what the aircraft was capable of without damage or loss of airspeed / altitude) was an actual instructional flight intended to show what the aircraft was capable of, if need be. My CFI called them "pylon turns". It's amazing how tightly those little aircraft can turn. Pick a fixed point on the ground to look at, and it almost looks like you're not actually going anywhere. I modestly exceeded 3g in those sustained turns, maybe as much as 3.5g, and my bank angle was about 60 degrees (much more than we normally use). At no time did we exceed 4g. We never did loops or barrel rolls. I was definitely shoved down into my seat in the turns. The hardest part was keeping my hand on the throttle, because my arm was outstretched. If I adjusted my seat forward, it wasn't comfortable on the rudder pedals or reading the instruments. It was a minor workout, since we kept doing various different kinds of turns for a half hour or so. We also did "slow flight" on that hop. It was a lot of fun. We only did that a couple of times. Most of the training was about everything but flying- fundamentals of flight, navigation, weather, talking to ATC, instrument flight practice for IFR conditions, learning how to get a "quick read" about what was going on with the plane and paying attention to what was most important, and a lot of emphasis on emergency procedures. I can't know what other CFIs taught, but mine was very big on memorizing emergency procedures, paying close attention to how weather affected your flying, and also on making good decisions about your limitations. Every flight included a, "This just happened to your aircraft, now what are you going to do?" scenario. He went on to get his ATP rating and flew for an airline services about a year later.

For a space launch, you're effectively "just another observer" who's merely along for the ride. With the correct seating arrangement (basically flat on your back, relative to the direction of acceleration) and lots of support gear like g-suits and neck supports, I could envision sustaining 10g for 5 seconds. But in a space suit? I'm not so sure about that. Maybe. In a fighter jet, or pretty much any other aircraft, you're in a seated position, which is less than ideal for maintaining blood flow to your brain, but you're not wearing a pressure suit. You do have the weight of a helmet on your head, though.

The early capsule programs had 7g accelerations using military test pilots only, and NASA did extensive g-simulation. I'm having a hard time with taking someone without lots of training and subjecting them to 7g+. I think significant training will be required, being in peak physical condition, and doing regular g-simulations to ensure that all potential crew members are ready for the kind of stress they'll be subjected to during a real mission. The moment we acquiesce on high acceleration launches, engineers will want to do high acceleration reentries as well, and those are unlikely to go nearly as well as a 5-second high-g launch. If I'm honest with myself, 5 seconds at 10g is doable. It'll hurt, but it won't kill me. 7g at 20+ seconds during reentry is going to be a much greater hurdle, though.

Calliban · 2023-06-28 12:54:47

At 7g, the length of the barrel increases to 1.8km for a 500m/s exit velocity, which is a tad over 1 mile. This is deep, but still substantially shallower than the deepest mines, which are 4km deep. The deepest gas wells go down 40,000', which is 12.3km. But these wells are no more than 1' in diameter. And pressure and temperature at the bottom of these wells is horrific. Rocks at these depths have plastic properties!

If we assume linear acceleration, then V^2 = 2AS. So for a constant acceleration of 7g, v is proportional to the square root of barrel length.

The cost of drilling is a non-linear function of depth. I have seen crude estimates of cost being proportional to the square of depth. So there is going to be an engineering trade-off here, between exit velocity, acceleration effects on humans and equipment and capital cost of the gun. For satellites and inert payliads, we have different problems. Most satellites are relatively fragile. A high g launch requires that payloads be engineered for those conditions. It also requires that the upper stage be engineered to survive the boost phase. An upper stage that is engineered for high-g acceleration will be heavier. Again, there are engineering trade-offs to be made.

I think this is a worthwhile project. If we can eliminate the need for a lower stage, then we cut the long-term cost of space launch by 50%. That is over and above the launch cost reductions that Elon musk is talking about with a conventional two-stage Starship.

As the gun is a fixed capital asset, its marginal cost is an inverse function of its use rate. If we can reuse the sabot, then the ultimate cost driver will be the cost of electricity needed to charge the hot water tank. Starship upper stage weighs 1350te, fully fuelled with a 150te payload. At 500m/s, its kinetic energy will be 168.75GJ. If we assume the gun is 30% efficient at converting thermal energy into KE, then we need 563GJ (156.25MWh) to launch a Starship upper stage to 500m/s. Assuming an electricity cost of $100/MWh, that will cost $15,625 per launch, or about $0.1/kg lifted to LEO. That is peanuts compared to a realustic LEO delivery cost.

Last edited by Calliban (2023-06-28 13:07:21)

RobertDyck · 2023-06-28 14:37:22

One of Heinlein stories had a craft thrown off the top of Pikes Peak, Colorado. I think it was some sort of rail. Linear magnetic accelerator? Doesn't matter; it was just a story. But I don't think anyone has proposed a cannon for humans since "Le Voyage dans la Lune" (1902).

Mars_B4_Moon · 2023-06-30 04:39:10

Vega C Return to Flight Delayed After Z40 Test Failure

https://europeanspaceflight.com/vega-c- … t-failure/

GW Johnson · 2023-07-01 10:02:12

I looked this one up. Vega C is a four stage launcher of small satellites (a bit over 1-ton class). The lower 3 stages are solids, the 4th stage is a liquid (which is how you get the most precise trajectory results (a technique pioneered in the 1960's with the Minuteman ICBM).

The flight failure prompting the revision had to do with a nozzle throat insert failure in the second stage. The "verification" static firing also failed, but not due to the revised throat insert. The article does not say what that failure was.

This probably has more to do with lax or inadequate design methods than with anything to do with solids fundamentally. I've seen this before. At the plant where I worked, proper design analyses were done of everything, and verified in various tests, before a motor design was considered "ready" for anything. Our corporate masters had other plants doing solids, one of which did really big ones.

That one doing big solids did not like to spend the up-front money on design analyses verified in tests. Instead, they used the same design process that produced the Titanic: just rescale one you already did before. It had a similar disastrous result, when a 10-foot diameter motor blew up on a USAF test stand, destroying that part of a USAF facility. The corporation had to take a billion-dollar write-off the year they had to replace the USAF's facility.

They had done something stupid with a tube-slot grain design: put the slots forward to get the center of gravity that they needed, when all other such designs put the slots aft (and for very good reason). Had they done the design analyses, those analyses would have predicted the explosion. They did not. They just turned the drawing around, built it, and blew up a USAF test cell.

The design analyses that we at McGregor always did would have included an interior ballistics model that included compressible flow effects down the bore, erosive burning effects, and geometry changes due to propellant deflections under the internal pressure distributions, among many other things. Our analyses also coupled in the effects of thermal-structural design of all the case and nozzle components, too. Which is why our failure rates in production were under 1 in a million.

Basically their motor choked inside, at the aft end of the bore, because of all the upstream slot surfaces producing too much flow rate to go through that bore. The too-high bore flow speeds produced erosive burning, which amplified the effect. The propellant was structurally too compliant, and deflected in a way that closed the aft bore diameter further, under the dramatic pressure drop down the bore. That amplified the effect further. The motor was improperly designed and blew up. A static test before giving one to USAF would have revealed that, but they did not do it, thinking reversing the slots to forward was an inconsequential change.

The lesson here is do it "right" and verify in test at each step. Taking shortcuts to increase profit is the way to lose that profit.

GW

Last edited by GW Johnson (2023-07-01 10:04:51)

tahanson43206 · 2023-07-01 11:45:31

For GW Johnson re analysis of design for a solid fuel rocket ...

The design analyses that we at McGregor always did would have included an interior ballistics model that included compressible flow effects down the bore, erosive burning effects, and geometry changes due to propellant deflections under the internal pressure distributions, among many other things. Our analyses also coupled in the effects of thermal-structural design of all the case and nozzle components, too. Which is why our failure rates in production were under 1 in a million.

Hod did the team perform that analysis?

Computers were coming along by then, so they might have been enlisted to perform some of the computations, but I'll bet that the work could have been done by folks with calculators.

Related question ... slots ...

I assume (just guessing) these are longitudinal cuts into the meat of the solid, to facilitate combustion at a desired rate.

If you have an image to show what those are, I'd be interested in seeing them.

Mars_B4_Moon put this report into RGClark's liquid fueled replacement for solid rocket boosters topic.

(th)

GW Johnson · 2023-07-01 15:16:20

At the McGregor rocket shop, most of the design analyses, especially the earlier ones in the process, were done pencil-and-paper using slide rules early on, and later using scientific calculators (which were very expensive back then). We had a couple of home-grown finite-element analyses we typically ran as the design gelled, one doing 2-D or axisymmetric structural analysis, and the other doing 2-D or axisymmetric thermal analysis (complete with time variations). It was a lot easier to set up realistic models for 2-D/axisymmetric than for 3-D, but still harder than just doing the pencil-and paper stuff. That’s why the early investigations were all pencil-and-paper.

For truly 3-D problems in structural, we had purchased a copy of NASTRAN. We also had a home-grown interior ballistics code JCBALL, which did the compressible flow, and the erosive burning stuff. We also had one of the predictive codes for combustion instability, purchased somewhere, but I no longer remember which one it was. We had both AFRISP and NASA-ODE as mainframe codes for thermochemicals (and of the two AFRISP was easier to use and gave just as good data).

All these codes were card batch input on a mainframe. Turn around time was 3 hours to 3 days. And the accountants and managers were all angry with the engineers when we “delayed payroll” by using the mainframe. It mattered not to them that what we were doing is what made the products reliable, which in turn is where all the revenues derived.

Tactical rocket vehicle trajectories could be as easily simulated with the ramjet vehicle trajectory code. These models required very large effort to set up. We obtained a series of these ramjet cycle analysis and trajectory codes from what was then the Aero Propulsion Laboratory at WPAFB (people like Ken Watson and John Leingang). These were AB, ABTRAJ, RJ, RJTRAJ, and finally ZTRAJ. ZTRAJ had been re-written from RJTRAJ to run on a desktop instead of card batch on a mainframe. (My second tenure was when I finally began writing my own ramjet cycle codes, in Fortran IV, later BASIC.)

I wrote a code my first year there (about 2000 statements) that modeled tests in our ramjet ground test direct-connect facility, for purposes of test data reduction. Initially, data was recovered from oscillograph paper manually, at selected time points, and fed into this analysis, along with the fuel flow rates coming from "traditional" hand-calculated ballistic analysis of the solid gas generators. Later on, after automated data reduction became available, this same program got re-written to run directly on digital data, using a desktop computer. Although, it still required a "traditional" gas generator analysis to determine the fuel flow rates.

Typical rocket tests have only 4 data channels to reduce: 2 Pc channels for redundancy, and 2 thrust channels for redundancy. The ramjet tests were different, requiring a lot more data channels to reduce. Initially, we had 16 pressure and force channels plus 8 thermocouple channels. Later, after digital data acquisition became available, we pretty much took about 100 channels.

Early on there were still photos and movie film at 24 frames per seconds of tests, including if desired high-speed film at 5000 frames/second. These usually took a week or two to come back from the developer. Video cameras were big, over a hundred pounds, and tens of thousands of dollars in the early days, so we did not have any.

To get real time information, I stood outside and watched the tests with my own senses, in order to know what really happened, sometimes crucial in analyzing the reduced test data. This was especially true of the ramjets. Over the course of 8 early years, I watched about 120 ramjet tests standing 75 feet from the thrust stand loaded with class 1.3 explosives, and no place to go if there was a problem. It truly was a 5-sense experience.

We had a really good track record in experimental gas generator-fed ramjet tests like that, only 4 blew up. I saw every one of those explosions standing out there. With heavyweight hardware designed not to throw shrapnel, it was safe enough. But you will “say it, do it, then turn and run”, every single time! I know I did! But, those observational experiences let me know more about what was really going on inside those ramjets, than any other ramjet worker anywhere in the country. And some of my friends at the Aero Propulsion Lab knew that. Tom Curran was one. His dissertation supported the coaxial dump combustor flameholder used in ASALM-PTV.

My second 8 year tenure, we had video and digital data. The hardware was not heavyweight, so it could throw shrapnel. I no longer stood outside. But by then, I was experienced enough to get what I needed from the sight and sound of the video. And by the way, the design process was the same: pencil-and-paper supported by calculators, plus those mainframe codes, some converted to run on desktops.

We could watch some rocket firings from outside (and I did), but you had to be about a football field or more away to do it safely. That was true all through both my 8-year tenures there.

Slots are cavities shaped like fins. Some are full length off the bore, but most are not. Those that are not full length lead to boost-sustain behavior. Initially there is lots of surface with the bore plus the slots, leading to lots of pressure and thrust. Later, there is only the lower surface of the bore left, with lower pressure and thrust.

GW

tahanson43206 · 2023-07-01 16:36:23

For RGClark ... we are no longer close to the theme of your topic.

We can move this new direction, or we can leave it here.

You are the topic manager, so it is your call.

Mars_B4_Moon dropped a link into your topic that is "sort of" related ... it has one liquid stage and three solids.

Your goal, as I understand it, is to eliminate the solids.

The discussion with GW Johnson is going to be about solids, so a move would seem appropriate if you request it.

***
For GW Johnson ...

Thanks for the history of your experiences and observations working with solid fuel rockets, and with various computing methods.

Is your code proprietary? If not, and if you still have it hanging around somewhere, are you willing to share it?

Because RGClark and kbd512 have both expressed concerns about ITAR (which dates to 1974), are there any ITAR issues to worry about?

It seems to me that it doesn't make a lot of sense to raise ITAR issues for basic physics, but government bureaucrats may not know one kind of knowledge from another, so the safe thing to do is to clamp a lid on everything.

I read somewhere that ItAR workers impounded a wooden desk, because it had been used by a scientist/engineer to perform some calculations. That is the level of mentality that goes with (or ** has ** gone with) ITAR enforcement.

(th)

kbd512 · 2023-07-02 16:41:37

tahanson43206,

It's ITAR-regulated because software-based tools used to calculate rocket trajectories can also be used to launch ICBMs at the US. It's pretty silly at this point, because anyone with a degree in physics or math can figure out how to put a rocket on a ballistic trajectory to another country, and all the equations to do that are printed in numerous textbooks. A physics or math grad, working with a computer science grad or even a talented programmer right out of high school, can put together a computer program to do the math required.

Devising control systems for the rocket, creating reliable rocket engines, and the development of a nuclear warhead to do some real damage, would all require a much more involved inter-disciplinary education. That said, anyone who graduates from our university system with a PhD in nuclear physics has to "prove" that they can design and build a working nuclear reactor or nuclear weapon.

tahanson43206 · 2023-07-02 17:49:15

This topic is (at least in part) about the Ariane spacecraft family ... Here is a report about a planned static test of a mockup of the vehicle. the article shows the assembly building rolling away from the rocket, which is a procedure I've not seen before.

https://www.msn.com/en-us/news/technolo … 66aa&ei=49

(th)

kbd512 · 2023-07-02 19:08:18

Going back to the original premise of this thread, what engines does ArianeGroup have to work with?

Merlin-1D weighs 470kg for 835kN of sea level thrust.
Vulcain 2.1 weighs 1,650kg and produces 935kN of sea level thrust.
On a kilo-for-kilo basis, Merlin-1D is producing 2.7X greater thrust than Vulcain 2.1.

Is there any reason why an engine like Vulcain 2.1, that only produces a little more thrust than a Merlin, and uses the same gas generator technology to feed propellants to the injectors, should cost ESA $10M per copy and weigh more than 3X more than Merlin-1D?

Is there a way to overcome that issue, or is it the result of using such a light fuel?

Does ArianeGroup have any RP-1 or LCH4-fueled engine designs sitting on the shelf or under active development?

We need sea level thrust for the proposed alternative design booster. Regardless of the propellant used, boosters are giant and heavy gas cans that we have to lug uphill to get to the point where the more efficient LH2-fueled upper stage can perform its specific impulse magic.

Can we expect all LH2-fueled booster engines to have such paltry thrust for the engine weight required?

Thrust-to-Weight Ratio for various booster engines:
P-120C (HTPB): 3:1
5-Segment SLS SRB (PBAN): 7:1
RL-10 (LH2): 37:1
RS-68A (LH2): 48:1
J-2X (LH2): 54:1
RS-25D (LH2): 60:1
RD-180 (RP1): 71:1
Rutherford (RP1): 73:1 *cheating because it doesn't include the weight of the Lithium-ion batteries to drive the turbopumps
RD-171 (RP1): 76:1
F-1 (RP1): 82:1
Vulcain 2.1 (LH2): 85:1
YF-20 (UDMH): 105:1
NK-33 (RP1): 125:1
Raptor 2 (LCH4): 146:1
Merlin-1D (RP1): 214:1
LR87 (Aerozine-50): 231:1

Blue Origin doesn't list an engine weight for their LCH4-fueled BE-4, which is why it didn't make the list, but thrust is 550Klbf. Highly experimental engines which have never flown to space aren't listed, either. All the engines on this list have significant firing experience or are under active development and intended for current use or were historically used in significant numbers. All the active Russian engines have TWRs in the 70:1 to 80:1 regime, so not a lot of difference for our workhorse engines. They clearly good engines, but nothing to write home about. Hypergolics are not as well-represented on this list because they're dangerous to use and they're starting to fall out of favor in Russia and China, the last major users of hypergolic booster propellant technology. Merlin-1D is clearly the standout competitor. LR-87 looks very impressive until you realize you're losing 30 seconds of specific impulse to the Merlin-1D at all altitudes for an oxidizer/fuel combo that eats flesh for breakfast and both engines are gas generators. Basically, no total impulse, weight, or payload performance improvement over fancy jet fuel, aka "RP-1", but LR87's TWR is top notch.

This means Vulcain 2.1 does considerably better than the most powerful solids and the RS-68A or RS-25D in the TWR department. If it's not already best-of-breed, it has to be pretty close. Amongst the liquid engines, Vulcain 2.1's TWR appears to be very middle-of-the-road, and not much better than legacy Russian RP-1 engine technology.

Is Vulcain 2.1 already at the limit of what's achievable with a LH2-fueled gas generator?

I noticed a definitive trend here. The higher the specific impulse of any given engine, the lower its TWR. The same trend seems to apply to the solids. P-120C has a higher Isp than the 5-segment SLS SRBs, but considerably lower TWR. There must be something unavoidable here. Maybe GW can tell us why. Raptor 2 is full-flow staged combustion using a fuel with a slightly higher Isp but lighter exhaust product, yet compares rather poorly to Merlin-1D in the TWR department. This can't be a coincidence because I looked at some historical engines as well.

That said, Vulcain 2.1 already appears to be best-of-breed when stacked up against all other LH2-fueled engines, at least in terms of TWR. It does considerably better than all of its peers which underwent final development around the same time (uprated RS-25D / E for SLS, J-2X for Ares I / Ares V, RS-68A for the final versions of Delta-IV Heavy).

Merlin-1D produces bat guano crazy thrust from a cheap fuel, when compared to its weight, regardless of which other kind of engine we're talking about. Since we intend to delete the solids and cluster more liquid engines into the booster to produce the required thrust, TWR is very important to get the show on the road.

GW Johnson · 2023-07-03 07:45:38

The "engine" thrust/weight for the solids has the entire propellant and case in its weight. The liquids do not have the tanks and propellants in their weight. The comparison is not fair.

What you want is to compare the thrust to the entire stage weight. You need the tanks plus propellant weights for the liquids. You will find that the tank weight for a given propellant weight is higher with lower density propellants, precisely because you need more material surface to contain the larger volume.

And that does not address the drag penalty of having the larger tank volume affecting air flow about the vehicle with the lower density propellants. Because upper stages are intrinsically lower-mass items, you can get away with low density propellants in upper stages better than in lower stages (where high density propellants offer better tank/propellant mass ratios, amplified by the very large stage masses involved).

GW

Last edited by GW Johnson (2023-07-03 07:46:08)

RGClark · 2023-07-03 08:44:07

GW Johnson wrote:

The "engine" thrust/weight for the solids has the entire propellant and case in its weight. The liquids do not have the tanks and propellants in their weight. The comparison is not fair.
What you want is to compare the thrust to the entire stage weight. You need the tanks plus propellant weights for the liquids. You will find that the tank weight for a given propellant weight is higher with lower density propellants, precisely because you need more material surface to contain the larger volume.
And that does not address the drag penalty of having the larger tank volume affecting air flow about the vehicle with the lower density propellants. Because upper stages are intrinsically lower-mass items, you can get away with low density propellants in upper stages better than in lower stages (where high density propellants offer better tank/propellant mass ratios, amplified by the very large stage masses involved).
GW

That is a valid point. However, another consideration is the comparison between adding solid side boosters to just adding additional core engines. The solid boosters do require also adding their propellant weight so that requirement comes into play when considering the T/W ratio comparison.
On the other hand just adding the engines to the core, and not additional liquid-fueled boosters, means just the added engine weight.
For that reason, it can in fact be the better option just to add the additional core engines, even if it requires to add some fairings around the engines because the nozzles stick out a bit outside the core stage diameter. Remember this was done around the F-1 engines on the Saturn V first stage:

When the engines are comparatively low cost such as the Vulcain in comparison to the boosters that becomes a major advantage for the engines. Note, this is particularly a disadvantage for the Ariane 6 solid’s because their large size make them high cost.

However, this won’t always work to just add core engines. Note the large size of the Delta IV and Atlas V core engines means it would be impractical to add additional copies of those to the core. Plus, the major factor their side boosters are so small, 1/10th the core size, and low cost for the Delta IV and Atlas V case make them the optimal solution for that case.

Robert Clark

Last edited by RGClark (2023-07-03 08:47:22)

RGClark · 2023-07-03 09:20:24

tahanson43206 wrote:

For RGClark ... we are no longer close to the theme of your topic.
We can move this new direction, or we can leave it here.
You are the topic manager, so it is your call.
Mars_B4_Moon dropped a link into your topic that is "sort of" related ... it has one liquid stage and three solids.
Your goal, as I understand it, is to eliminate the solids.
The discussion with GW Johnson is going to be about solids, so a move would seem appropriate if you request it.
…
(th)

The underlying basis of my proposal to dispense with the SRB’s on the Ariane 6 was their high cost made the Ariane 6 pricing and non-reusability just as bad as the pricing and non-reusability on the ULA launchers, the Delta IV and Atlas V, which put ULA on the brink of bankruptcy. Any variation of the topic of cost/capability of solids vs. liquids is perfectly fine.

Actually, small solids as addendum to the liquid-fueled core engines could be quite cost effective. BUT they have to be small and serve as an addendum to the thrust of the core engines, not provide the major portion of the thrust of the rocket.

So in my all-liquid version of the Ariane 6 I spent quite a bit of effort to find ways the two Vulcains would have sufficient thrust for lift-off, chiefly by using an upper stage 1/3rd the size of the current version of the Ariane 6 and also by assuming the Vulcain thrust could be ramped up 9%. But if small side boosters 1/10th the size of the current Ariane 6 SRB’s were used that would be cost effective as addendum to the two Vulcains thrust. That way, we could use the original large size upper stage and thereby get larger payload. The side boosters now being normal sized, 1/10th the core stage size, they would now also be low cost. Instead of adding €40 million($44 million) to the cost launcher cost, they would add only €4 million($4.4 million) to the cost.

With the side boosters now being normal sized, and normal priced, you could have variations on the configuration of the Ariane 6 launcher: without SRB’s, with two small SRB’s, or with four small SRB’s. Like is the case with the Delta IV and Atlas V.

However, as I mentioned the primary reason why ESA wants to use the large sized boosters is politics, and not to be cost effective. The ESA member states making the SRBs want them to be high cost, because that way they get high revenue returned to them with each launch. It is extremely dubious they would sign off on a non-SRB Ariane 6 for that reason, but these are two of the most powerful ESA states that make the SRB’s. Even the scenario with 1/10th the SRB size is also doubtful for the same reason, the greatly reduced revenues they would get with each launch.

Anyone who has lived in the world to adulthood knows politics stupefies everything. (Yes, I know that is not the proper usage of “stupefy” but it gets the point across.)

Robert Clark

Last edited by RGClark (2023-07-03 10:09:17)

kbd512 · 2023-07-03 09:25:00

GW,

I can subtract the 10t of weight from the P-120C, but the TWR still doesn't change by more than 1. I get 3.3:1 for P-120C without the casing vs 3.08:1 with the casing. Rounding to the nearest whole number, my TWR figure remain unchanged. My assessment is quite fair, because the stage mass, minus the engine, is never more than a few percentage points of the total wet mass for a liquid stage, whereas solid stages have much higher inert mass, to the tune of about 10% or so. P-120C is 9.3%, for example. If we're talking about the inert mass of Ariane-6's core stage or empty P-120C casings, there's not a dime's worth of difference between the two. The booster's core stage imparts just over 52% of the total impulse, and the pair of solid motors impart 48% of the energy delivered, but the inert mass fraction is 2X greater for the pair of solids. RP-1 or LCH4 or hypergolics would be a different story. Falcon-9 is proof of that.

Moreover, there is no such thing as a solid rocket motor without its casing. I can shrink or grow the size of the propellant tanks for a liquid engine, but the engine's TWR doesn't change one iota. You cannot simply "make a booster-sized solid motor shorter or longer". Thrust, thrust profile, and host of other variables change dramatically when you do that. It's basically an entirely different motor, but you already know that.

The drag penalty is small, regardless of propellant selection, because someone on the team is an aerodynamicist who ensures that drag remains a minor penalty. I think you're trying to over-sell solids. You're partial to them. I love what solids do in the thrust department when you really need thrust like it's going out of style. However, looking at the overall efficiency of solids vs RP-1 or LCH4, for rockets of the size we're interested in, and it's pretty clear that certain design choices are made for reasons other than improving the overall capability of the rocket, for the lowest total program cost. There is not one solid motor in the world that can replace a Falcon-9 performance class booster for less money spent. Whether that's because solid rocket companies are greedy, their manufacturing processes are not optimized, or whatever, it is indeed the case if we look at historical precedent.

I have enough info to realize that what RGClark wants is a completely redesigned rocket, that no money will be saved by doing that, and the most probable outcome is that the new rocket ends up costing even more money. He acts like building rockets is like building Legos. Subtract this engine over here, add that one over there, and voila! We have a more capable rocket. Nope. That doesn't work, either.

What you want is to compare the thrust to the entire stage weight.

This is where we ultimately have to go to design a functional rocket, but if 1 engine weighs 1/3rd of what the next one weighs while producing similar thrust, and we're intent on clustering a bunch of them together for our booster, that will significantly affect inert mass, won't it?

Here's what I think:

For a total cost similar to a Falcon-9, the booster is going to be remarkably similar to a Falcon-9's booster stage. It won't use solids or LH2 as fuel. That was a compromise solution intended to produce a specific outcome favorable to the military industrial complex. Solids could add extra total impulse, but if the core isn't using RP-1 or LCH4, then it's going to have non-competitive performance and cost. The booster on the Falcon-9 is no more costly than a single P-120C motor. If it was me and I had the option, I would design my core stage to accept 2 to 4 P-120C motors in case I needed extra booster performance. The upper stage would use the Vulcain engine to exceed the performance of a single Merlin.

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