Amateur rocket to orbit

[TheEpicSquared]

Well, for the drag problem, if we could find an online wind tunnel simulator, which allowed us to make a model of our rocket, we could get relatively accurate drag models. However, it would be a pain to find a digital wind tunnel simulator...

Another thing I've been wondering about, how are we going to fill up the tanks? We could use the RCS thruster plumbing to pump in air and HTP, but loading the napalm could be a problem. We could load it through the nozzle, but space would be cramped to say the least. 

What propellant would the kick motor be made of? We never really discussed it, IIRC.

[Steel]

34 minutes ago, TheEpicSquared said:

Well, for the drag problem, if we could find an online wind tunnel simulator, which allowed us to make a model of our rocket, we could get relatively accurate drag models. However, it would be a pain to find a digital wind tunnel simulator...

Do you mean CFD (Computational Fluid Dynamics) software? You could run some CFD on a model, you'd only be able to get the drag forces (and so a drag coefficient) at certain velocities and atmospheric conditions, you wouldn't easily (not to say it's impossible, just enormously time consuming) be able to compute an entire ascent. Also with CFD there's always the issue that you can never be 100% sure it's given you the correct answer until you validate it in a windtunnel, for instance:

 

Still, CFD is really the only way to get aerodynamic data in the design stages.

Edited July 16, 2017 by Steel

[Steel]

45 minutes ago, sevenperforce said:

Now that we know a lot of the variables, does anyone have suggestions for modeling drag more accurately, determining volumetric efficiency more concretely, or firming up any of the other "fixed" variables?

I would imagine anything to do with the engines would have to be obtained experimentally, the design is a pretty novel one - hybrid with a non-solid fuel as well as a pretty unique pressure feeding mechanism. I doubt there will be any exisitng models for this kind of thing, unlike for a simple biprop liquid engine.

[kurja]

15 hours ago, TheEpicSquared said:

it would be a pain to find a digital wind tunnel simulator...

duh obviously, you can just build it in KSP and see how she flies!

right?

[Hesp]

15 hours ago, sevenperforce said:

Now that we know a lot of the variables, does anyone have suggestions for modeling drag more accurately, determining volumetric efficiency more concretely, or firming up any of the other "fixed" variables?

CFD. OpenFoam is an open source software.

Missing previous know-how, you will need some iterations to correlate between real object and simulation data.

Anyway you will need to perform also modal and thermostructural analysis with other simulation software before even building a first engine prototype.

 

EDIT: didn't read @Steel 's answer before replying.

Edited July 17, 2017 by Hesp

[sevenperforce]

19 hours ago, TheEpicSquared said:

Another thing I've been wondering about, how are we going to fill up the tanks? We could use the RCS thruster plumbing to pump in air and HTP, but loading the napalm could be a problem. We could load it through the nozzle, but space would be cramped to say the least. 

What propellant would the kick motor be made of? We never really discussed it, IIRC.

I think we could load the napalm pre-assembly. And I was using White Lightning for the kick motor design, but a sugar rocket would work too.

4 hours ago, kurja said:

duh obviously, you can just build it in KSP and see how she flies!

right?

I was going to say, if anyone has RSS and FAR and the know-how to create the hybrid stack, I'd love to see a sim of it.

19 hours ago, Steel said:

I would imagine anything to do with the engines would have to be obtained experimentally, the design is a pretty novel one - hybrid with a non-solid fuel as well as a pretty unique pressure feeding mechanism. I doubt there will be any exisitng models for this kind of thing, unlike for a simple biprop liquid engine.

Well, the one saving grace is that we do have a constant chamber volume, so I think it might be possible to do some preliminary engine dimension calculations with these equations.

[NSEP]

I dont know if amatuers can achieve this feat. But i sure do like the idea of a small and low cost cubesat launcher.

[zeta function]

I'll try to simulate it in RO, but i will have to edit some config files. 

[wumpus]

2 hours ago, sevenperforce said:

I think we could load the napalm pre-assembly. And I was using White Lightning for the kick motor design, but a sugar rocket would work too.

I think you have to load the napalm pre-assembly (which makes transportation a nightmare.  Just how do you declare "napalm" on your hazardous material list without red flags going up everywhere?).  It also makes fueling much more nerve-wracking: leaks are bad.  Leaks when fueling hypergolic fuels are disastrous.

I'd expect you to stick with the White Lightning (or similar off-the-shelf ammonium perchlorite engine).  Sugar rockets are notoriously poor Isp, and it becomes critical at the last stage.  First stage use of sugar rockets makes more sense but would likely require careful ignition tricks (explosive launch bolts/clamps or something like a model rockets guide-pole to keep things straight until all rockets are ignited).

[sevenperforce]

4 minutes ago, zeta function said:

I'll try to simulate it in RO, but i will have to edit some config files. 

Look forward to seeing it!

My suggestion would be to start with an SRB and edit the config files to make it throttleable and to accept both solid fuel and monopropellant as a resource. The monopropellant can represent the HTP and can also be used for RCS.

I think there's a mod that permits differential throttling for SAS; that might be useful too.

2 minutes ago, wumpus said:

I think you have to load the napalm pre-assembly (which makes transportation a nightmare.  Just how do you declare "napalm" on your hazardous material list without red flags going up everywhere?).  It also makes fueling much more nerve-wracking: leaks are bad.  Leaks when fueling hypergolic fuels are disastrous.

Well, we certainly aren't going to be transporting the full rocket post-assembly, so you don't have to load the napalm ahead of time. Napalm loading can be done at the launch site but before assembling the rocket. Then the rocket is assembled and the HTP is loaded once erect.

HTP is not hypergolic with hydrocarbons unless it is first catalytically decomposed, so that's not too terrible of a problem. Of course it IS hypergolic with some ordinary materials like leather...but, fortunately, such fires have a low enough temperature that the HTP will not spontaneously decompose.

2 minutes ago, wumpus said:

I'd expect you to stick with the White Lightning (or similar off-the-shelf ammonium perchlorite engine).  Sugar rockets are notoriously poor Isp, and it becomes critical at the last stage.  First stage use of sugar rockets makes more sense but would likely require careful ignition tricks (explosive launch bolts/clamps or something like a model rockets guide-pole to keep things straight until all rockets are ignited).

Ah, yes...for some reason I was thinking sugar rockets had higher isp, but they don't.

You can't have first-stage use of SRBs, simply because burnout times will vary. If one of the side boosters burns out before the opposite one (and it will), the whole stack starts to cartwheel and then rips itself apart, Challenger-style. The only possible use of a first-stage SRB would be as the core, but that wouldn't help much.

Our hybrid rocket will have all the thrust we need.

[TheEpicSquared]

I don't know about White Lightning for the kick motor. The TWR will be through the roof nearing burnout, and our cubesat might not survive the forces.

We could pre-load the napalm in, but what about when we fill it up again for reuse? It would be difficult to cut the stage in half. 

Also, have we decided on whether we're using a single-stick or quad-stick core?

[sevenperforce]

37 minutes ago, TheEpicSquared said:

I don't know about White Lightning for the kick motor. The TWR will be through the roof nearing burnout, and our cubesat might not survive the forces.

We could pre-load the napalm in, but what about when we fill it up again for reuse? It would be difficult to cut the stage in half. 

Also, have we decided on whether we're using a single-stick or quad-stick core?

We can set the net thrust wherever we want it on the kick motor. White Lightning is not pre-cast, so we can make it lower-thrust. The vehicle is fully suborbital by final staging, so there's no gravity drag loss from using a lower TWR.

As far as refueling and reuse is concerned, I anticipate an interstage (with recovery and guidance hardware) that bolts over the top of the fuel column. So you basically just take the lid off, pour in the napalm (using some sort of insertable mold at the base to ensure the burn area is correct), and then replace the lid.

Unless there are some overly generous assumptions I missed somewhere, I think my spreadsheet demonstrates that we can easily reach orbit with a single-stick core, if we're comfortable going to a 10-12" core instead of an 8" one like HEROS-3.

[TheEpicSquared]

18 minutes ago, sevenperforce said:

We can set the net thrust wherever we want it on the kick motor. White Lightning is not pre-cast, so we can make it lower-thrust. The vehicle is fully suborbital by final staging, so there's no gravity drag loss from using a lower TWR.

Good, a lower TWR would be better.

19 minutes ago, sevenperforce said:

As far as refueling and reuse is concerned, I anticipate an interstage (with recovery and guidance hardware) that bolts over the top of the fuel column. So you basically just take the lid off, pour in the napalm (using some sort of insertable mold at the base to ensure the burn area is correct), and then replace the lid.

That could work. I never thought about loading through the top instead of the bottom. The ablative portion of the nozzle would have to be replaced every flight but that's relatively trivial.

21 minutes ago, sevenperforce said:

Unless there are some overly generous assumptions I missed somewhere, I think my spreadsheet demonstrates that we can easily reach orbit with a single-stick core, if we're comfortable going to a 10-12" core instead of an 8" one like HEROS-3.

Single-stick is good. And a 25-30cm core is fine, with the same diameter for the strap-ons and second stage.

[Steel]

@sevenperforce I've been thinking about your engine concept, and I have a few questions.

On 10/07/2017 at 4:24 PM, sevenperforce said:

 

1. With this design, will you not have to very accurately control the "head pressure" so that it matches the chamber pressure? Since you have a liquid rather than solid fuel, if your chamber pressure is less than the head pressure the propellant will be forced into the combustion chamber area, reducing the size of this area and potentially stopping combustion altogether. On the ther hand, if the chamber pressure is higher than the head pressure then the propellant will be forced back up the motor, increasing the size of the chamber and the burn area, which sounds to me like it's potentially explosive. This problem will only get more challenging with the addition of throttling, where the head pressure and chamber pressure would have to change in sync to avoid any problems.

2. Can you guarantee that the burn surface of the propellant will remain in the shape you intend? With the napalm being a liquid (albeit a highly viscous one) will it necessarily flow in a way that maintains the shape of the combustion chamber or will it just flow via the path of least resistance - which may or may not be the desired shape. Needless to say, a combustion chamber that changes geometry during flight is not something you want.

Edited July 18, 2017 by Steel

[monophonic]

Sorry to interrupt, but did you know napalm can be made to a consistency of rubber? Of course I only know this because towards the end of my service a warrant officer ordered me to help him train the rookies to handle themselves with the stuff. He got a phone call while a batch was cooking and it was on for quite some time. I have no idea what the ratio of gas to other ingredients was in the end though, but the blob did burn just as well as the runny stuff and much longer. Clearly that's no good for weapon use, but as hybrid rocket fuel it might work.

Oh, here's my coat, bye!

[Steel]

1 hour ago, monophonic said:

Sorry to interrupt, but did you know napalm can be made to a consistency of rubber? Of course I only know this because towards the end of my service a warrant officer ordered me to help him train the rookies to handle themselves with the stuff. He got a phone call while a batch was cooking and it was on for quite some time. I have no idea what the ratio of gas to other ingredients was in the end though, but the blob did burn just as well as the runny stuff and much longer. Clearly that's no good for weapon use, but as hybrid rocket fuel it might work.

Oh, here's my coat, bye!

But if it has the consistency of rubber it won't flow, so the whole pressure feed concept won't work.

Still interesting to know though!

Edited July 18, 2017 by Steel

[sevenperforce]

6 hours ago, Steel said:

@sevenperforce I've been thinking about your engine concept, and I have a few questions.

1. With this design, will you not have to very accurately control the "head pressure" so that it matches the chamber pressure? Since you have a liquid rather than solid fuel, if your chamber pressure is less than the head pressure the propellant will be forced into the combustion chamber area, reducing the size of this area and potentially stopping combustion altogether. On the ther hand, if the chamber pressure is higher than the head pressure then the propellant will be forced back up the motor, increasing the size of the chamber and the burn area, which sounds to me like it's potentially explosive. This problem will only get more challenging with the addition of throttling, where the head pressure and chamber pressure would have to change in sync to avoid any problems.

2. Can you guarantee that the burn surface of the propellant will remain in the shape you intend? With the napalm being a liquid (albeit a highly viscous one) will it necessarily flow in a way that maintains the shape of the combustion chamber or will it just flow via the path of least resistance - which may or may not be the desired shape. Needless to say, a combustion chamber that changes geometry during flight is not something you want.

Good questions!

The trick with this particular plan is to have geometry such that the available burn surface area will decrease if the propellant flows/burns upward and increase if it flows/burns downward, providing negative feedback rather than a positive feedback loop. This can be achieved by making the base of the oxidizer tank and catalyst bed injector assembly an upward-opening cone, so that the cross-sectional area of the fuel "tank" decreases as you go up:

As you can see, the surface area of the exposed fuel is greatest in the depicted geometry. Should that surface regress upward (either due to increased burn rate or increased chamber pressure), the available surface area will decrease, lowering combustion rate and chamber pressure.

Recall as well that head pressure is not the only determining factor; the entire weight of the annular fuel column is pushing down on the chamber, and moreso under acceleration. This is why the hybrid likely would not be restartable; once flow begins, you need positive chamber pressure or the fuel column will creep out of the nozzle.

During an active burn, the fluid dynamics will probably look something like this:

8 minutes ago, Steel said:

1 hour ago, monophonic said:

Sorry to interrupt, but did you know napalm can be made to a consistency of rubber? Of course I only know this because towards the end of my service a warrant officer ordered me to help him train the rookies to handle themselves with the stuff. He got a phone call while a batch was cooking and it was on for quite some time. I have no idea what the ratio of gas to other ingredients was in the end though, but the blob did burn just as well as the runny stuff and much longer. Clearly that's no good for weapon use, but as hybrid rocket fuel it might work.

Oh, here's my coat, bye!

But if it has the consistency of rubber it won't flow, so the whole pressure feed concept won't work.

Eh, not necessarily. There is a complex interplay of possible fluid dynamics across a range of pressures and temperatures. Depending on the combination of gelling agents used, the napalm can be a shear-thinning fluid, a shear-thickening fluid, or a Maxwell fluid. It can flow in response to heat, thicken in response to pressure, or basically exhibit any other range of behaviors, all based on composition and chemistry.

Edited July 18, 2017 by sevenperforce

[DerekL1963]

13 minutes ago, sevenperforce said:

The trick with this particular plan is to have geometry such that the available burn surface area will decrease if the propellant flows/burns upward and increase if it flows/burns downward, providing negative feedback rather than a positive feedback loop. This can be achieved by making the base of the oxidizer tank and catalyst bed injector assembly an upward-opening cone, so that the cross-sectional area of the fuel "tank" decreases as you go up:

In theory.  It remains to be seen if the theory is correct.  Especially since "decreasing burn area" != "burn quenching".
 

14 minutes ago, sevenperforce said:

During an active burn, the fluid dynamics will probably look something like this:

What those fluid dynamics look like to me is "there's no mixing, so most of the oxidiser mass is wasted and there's a lot of combustion in the nozzle and even so most of the fuel is wasted".  And that's setting aside the extraordinary difficulty of matching fuel pressure to chamber pressure.

[sevenperforce]

Just now, DerekL1963 said:

In theory.  It remains to be seen if the theory is correct.  Especially since "decreasing burn area" != "burn quenching".
 

Decreasing burn area decreases the available fuel flow, which decreases burn rate.

Just now, DerekL1963 said:

What those fluid dynamics look like to me is "there's no mixing, so most of the oxidiser mass is wasted and there's a lot of combustion in the nozzle and even so most of the fuel is wasted".  And that's setting aside the extraordinary difficulty of matching fuel pressure to chamber pressure.

Nozzle vs oxidizer injector geometry is not necessarily to scale.

[DerekL1963]

5 minutes ago, sevenperforce said:

Decreasing burn area decreases the available fuel flow, which decreases burn rate.

You already said that in the portion of your previous message that I quoted.  Repeating it does not address the issue I raised.
 

6 minutes ago, sevenperforce said:

Nozzle vs oxidizer injector geometry is not necessarily to scale.

Again, scale isn't the issue here - lack of mixing is.

[Steel]

18 minutes ago, DerekL1963 said:

Again, scale isn't the issue here - lack of mixing is.

That's a good point, traditional hybrid engines use thin channels to make sure no oxidiser is too far away from the fuel grain and also to take advantage of turbulent boundary layers to improve mixing. With a chamber of the size and geometry you're suggesting a lot of the oxidiser will just being injected in and fly straight out of the nozzle without getting anywhere near a wall.

[sevenperforce]

41 minutes ago, Steel said:

That's a good point, traditional hybrid engines use thin channels to make sure no oxidiser is too far away from the fuel grain and also to take advantage of turbulent boundary layers to improve mixing. With a chamber of the size and geometry you're suggesting a lot of the oxidiser will just being injected in and fly straight out of the nozzle without getting anywhere near a wall.

The throat will be much smaller than depicted and the "chamber" will have a longer characteristic length, permitting higher chamber pressure.

Also, the HTP injector and catalyst bed should probably be conical and pointed outward.

[TheEpicSquared]

@Steel Yes, I do mean CFD software. We could use that for preliminary testing and when we have some numbers, a scale model could be built and put in a real wind tunnel to confirm the numbers.

[Steel]

6 minutes ago, TheEpicSquared said:

@Steel Yes, I do mean CFD software. We could use that for preliminary testing and when we have some numbers, a scale model could be built and put in a real wind tunnel to confirm the numbers.

Provided, of course, that you can find a supersonic wind tunnel (which are somewhat difficult to come by!). Realistically, for an amateur project CFD is the best you're going to get before flight testing.

Edited July 19, 2017 by Steel

[DerekL1963]

17 hours ago, sevenperforce said:

Also, the HTP injector and catalyst bed should probably be conical and pointed outward.

Which, with the current throttling scheme, will virtually guarantee combustion instability - while still not solving the problem of ensuring complete mixing of fuel and oxidizer.  Figuring out some way of evening out the flow (without causing too much backpressure into the cat pack) will go a long ways towards solving both issues.  You absolutely need an even feed across the entire face of the oxidizer injector.

Seriously, as you've already shown the performance of this design is marginal.  You can't afford to have any significant amount of propellant go unburned if you hope to get anywhere near the theoretical performance of these propellants.