Amateur rocket to orbit

[TheEpicSquared]

2 hours ago, Steel said:

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.

Well, probably not for supersonic speeds, but we could get reliable data for the subsonic portion of the flight.

[wumpus]

20 hours ago, sevenperforce said:

While this looks great, just how are you going to convince a gel to maintain that particular shape, much less convince the convince the oxidizer to mosy over to the fuel and ignite with it.  It looks like some sort of baffle (extreme high melting point) will be needed, with a (mostly downstream) carefully engineered design to regroup the combustion pressure outward.

The hybrids I've seen are long and similar to SRBs, with nearly all the combustion happening in a tube.  I'm curious why you abandoned this design for something with much more drag.

[sevenperforce]

3 minutes ago, wumpus said:

While this looks great, just how are you going to convince a gel to maintain that particular shape, much less convince the convince the oxidizer to mosy over to the fuel and ignite with it.  It looks like some sort of baffle (extreme high melting point) will be needed, with a (mostly downstream) carefully engineered design to regroup the combustion pressure outward.

The hybrids I've seen are long and similar to SRBs, with nearly all the combustion happening in a tube.  I'm curious why you abandoned this design for something with much more drag.

As I show in another mockup, the burn region will be much longer than shown. Also note that this is just the engine end; the whole rocket extends vertically quite a distance.

[Steel]

25 minutes ago, TheEpicSquared said:

Well, probably not for supersonic speeds, but we could get reliable data for the subsonic portion of the flight.

Which, unfortunately, won't cover much of the flight for a small vehicle like this. Likelihood is that it'll be supersonic in well under 30 seconds or so from liftoff ( @sevenperforce what do your initial calculations say about how quickly it might break the sound barrier?)

Edited July 19, 2017 by Steel

[TheEpicSquared]

Just now, Steel said:

Which, unfortunately, won't cover much of the flight for a small vehicle like this. Likelihood is that it'll be supersonic in well under 30 seconds or so from liftoff ( @sevenperforce what do your initial calculations say about how quickly it might break the sound barrier?)

Yeah, that's a problem. On the bright side though, we get good numbers for the few seconds that we are supersonic.  

[Steel]

3 minutes ago, TheEpicSquared said:

Yeah, that's a problem. On the bright side though, we get good numbers for the few seconds that we are supersonic.  

To be completely honest, the aerodynamics of rocket like this are not really that important. All rockets are pretty similar in design, so at most it will be a difference of a few hundred ms^-1 of dV. If the calculations budget in a "worst case scenario" number that's based on rockets of a similar design with a +10% safety factor, then you can't go too far wrong.

Edited July 19, 2017 by Steel

[sevenperforce]

11 minutes ago, Steel said:

Which, unfortunately, won't cover much of the flight for a small vehicle like this. Likelihood is that it'll be supersonic in well under 30 seconds or so from liftoff ( @sevenperforce what do your initial calculations say about how quickly it might break the sound barrier?)

The rocket will be supersonic between 10 and 20 seconds after liftoff.

[TheEpicSquared]

So, are we going to make a whitepaper on this or something? @sevenperforce You said something about it.

Edited July 21, 2017 by TheEpicSquared

[sevenperforce]

5 hours ago, TheEpicSquared said:

So, are we going to make a whitepaper on this or something? @sevenperforce You said something about it.

That's the plan! Let's see, what else do we need to figure out?

[Steel]

Sorry to interject more of my thoughts, but I'm going to interject another of my thoughts:

Since the rocket engine proposed here is quite complex, with complex burn face geometries, head pressures that need to be monitored and controlled as well as a complete lack historical data and experience to suggest whether this design would actually work or not, is it not actually easier just to design a liquid bi-prop, pressure-fed, HTP/Kerosene engine? That way you have 60 years worth of design experience, existing guides on how to go about designing all aspects of the engine, all the technical literature you could ever want and, perhaps most importantly, data and models that can give reasonably accurate performance numbers before construction and test firing?

Edited July 21, 2017 by Steel

[wumpus]

1 hour ago, Steel said:

Sorry to interject more of my thoughts, but I'm going to interject another of my thoughts:

Since the rocket engine proposed here is quite complex, with complex burn face geometries, head pressures that need to be monitored and controlled as well as a complete lack historical data and experience to suggest whether this design would actually work or not, is it not actually easier just to design a liquid bi-prop, pressure-fed, HTP/Kerosene engine? That way you have 60 years worth of design experience, existing guides on how to go about designing all aspects of the engine, all the technical literature you could ever want and, perhaps most importantly, data and models that can give reasonably accurate performance numbers before construction and test firing?

If you go that route you might as well end up replacing HTP with LOX (assuming you are confident in ground lighting, less sure about the second stage).  While I'm not confident in saying LOX is safer than HTP, it is quite more available.  I'd also consider LOX+Alcohol: lose a few Isp for a ~1000C temperature difference.  If you switch to LOX, I can't say whether HTP (+catalyst) would make a good igniter, I don't think it is commonly used.  On the other hand, I suspect that professional igniters are out there in the "I do not work with these chemicals*" fame.

* http://blogs.sciencemag.org/pipeline/archives/category/things-i-wont-work-with <- recommended for most who enjoyed 'Ignition!'.

[Steel]

7 minutes ago, wumpus said:

If you go that route you might as well end up replacing HTP with LOX (assuming you are confident in ground lighting, less sure about the second stage).  While I'm not confident in saying LOX is safer than HTP, it is quite more available.  I'd also consider LOX+Alcohol: lose a few Isp for a ~1000C temperature difference.  If you switch to LOX, I can't say whether HTP (+catalyst) would make a good igniter, I don't think it is commonly used.  On the other hand, I suspect that professional igniters are out there in the "I do not work with these chemicals*" fame.

* http://blogs.sciencemag.org/pipeline/archives/category/things-i-wont-work-with <- recommended for most who enjoyed 'Ignition!'.

Im not sure, I'd still go with HTP because it (A) is not cryogenic and (B) can still be decomposed and used as monoprop for the RCS and potentially to pressurise the tanks (not 100% whether that can be done in practice). Switching to LOX would mean having to design plumbing and tanking to deal with cryogenic temperatures as well as having to carry an additional tank of nitrogen or helium to pressurise the tanks. 

Edited July 21, 2017 by Steel

[shynung]

57 minutes ago, Steel said:

Im not sure, I'd still go with HTP because it (A) is not cryogenic and (B) can still be decomposed and used as monoprop for the RCS and potentially to pressurise the tanks (not 100% whether that can be done in practice). Switching to LOX would mean having to design plumbing and tanking to deal with cryogenic temperatures as well as having to carry an additional tank of nitrogen or helium to pressurise the tanks. 

I agree with this. Also, decomposed HTP (hot steam+ GOX) is practically hypergolic with most fuels. Switching to LOX would mean designing a starter system, which is another system that can fail at the worst moment.

Also, since we're talking about gelled propellants, I'd like to copy some relevant text from the late John D. Clark's Ignition! on gelled propellants, page 184:

Quote

Assuming, however, that the storage problems have been coped with, somehow, the operational problems remain. The first of these is that of forcing the fuel out of its tank. If a metallized gel is pressurized—that is, high pressure gas is let into the tank to force the fuel out —a sort of tunneling process takes place. The gas simply blows a hole for its own passage down through the gel to the outlet, and leaves most of the fuel untouched and sitting quietly around the sides of the tank, instead of flowing, as it should, through the feed line to the motor. The fuel has to be completely enclosed, as in a flexible bladder (to which the expulsion pressure is applied), or a large fraction of it simply won't leave the tank.

 

Edited July 21, 2017 by shynung

[DerekL1963]

10 minutes ago, shynung said:

I agree with this. Also, decomposed HTP (hot steam+ GOX) is practically hypergolic with most fuels. Switching to LOX would mean designing a starter system, which is another system that can fail at the worst moment.

When evaluating failure modes, that it will fail is practically irrelevant - and a statement such as "can fail at the worst moment" is an appeal to emotion, not engineering.  A proper evaluation considers the likelihood of failure, which in this case is damn near zero for a properly designed and tested igniter system.

That being said, I'm with @Steel.  This engine is way too complex for an amatuer effort.

[sevenperforce]

23 minutes ago, Steel said:

Sorry to interject more of my thoughts, but I'm going to interject another of my thoughts:

Since the rocket engine proposed here is quite complex, with complex burn face geometries, head pressures that need to be monitored and controlled as well as a complete lack historical data and experience to suggest whether this design would actually work or not, is it not actually easier just to design a liquid bi-prop, pressure-fed, HTP/Kerosene engine? That way you have 60 years worth of design experience, existing guides on how to go about designing all aspects of the engine, all the technical literature you could ever want and, perhaps most importantly, data and models that can give reasonably accurate performance number before construction and test firing?

Hmm, good idea.

The biggest problem with going bipropellant instead of hybrid is that you have to start worrying about chamber cooling, and regenerative cooling is tough. Ablative chambers are a possibility, but we're already doing an ablative nozzle.

I like geometric 

1 hour ago, Steel said:

1 hour ago, wumpus said:

If you go that route you might as well end up replacing HTP with LOX (assuming you are confident in ground lighting, less sure about the second stage).  While I'm not confident in saying LOX is safer than HTP, it is quite more available.  I'd also consider LOX+Alcohol: lose a few Isp for a ~1000C temperature difference.  If you switch to LOX, I can't say whether HTP (+catalyst) would make a good igniter, I don't think it is commonly used.  On the other hand, I suspect that professional igniters are out there in the "I do not work with these chemicals*" fame.

Im not sure, I'd still go with HTP because it (A) is not cryogenic and (B) can still be decomposed and used as monoprop for the RCS and potentially to pressurise the tanks (not 100% whether that can be done in practice). Switching to LOX would mean having to design plumbing and tanking to deal with cryogenic temperatures as well as having to carry an additional tank of nitrogen or helium to pressurise the tanks. 

Agreed; even if HTP is hard to get, handling of LOX is outside what amateurs can do. Plus, HTP has far more thrust than LOX even if isp is a little low.

I can't think of a good way to get HTP decomposition to actually pressurize the tanks without triggering runaway decomposition. Can anyone else?

46 minutes ago, shynung said:

Decomposed HTP (hot steam+ GOX) is practically hypergolic with most fuels. Switching to LOX would mean designing a starter system, which is another system that can fail at the worst moment.

Entirely hypergolic, in fact.

49 minutes ago, shynung said:

Since we're talking about gelled propellants, I'd like to copy some relevant text from the late John D. Clark's Ignition! on gelled propellants, page 184:

Quote

Assuming, however, that the storage problems have been coped with, somehow, the operational problems remain. The first of these is that of forcing the fuel out of its tank. If a metallized gel is pressurized—that is, high pressure gas is let into the tank to force the fuel out —a sort of tunneling process takes place. The gas simply blows a hole for its own passage down through the gel to the outlet, and leaves most of the fuel untouched and sitting quietly around the sides of the tank, instead of flowing, as it should, through the feed line to the motor. The fuel has to be completely enclosed, as in a flexible bladder (to which the expulsion pressure is applied), or a large fraction of it simply won't leave the tank.

 

Hmm, interesting! I didn't think much had been done with gelled propellants.

One difference here is that we are eschewing the entire outlet/feed line; rather, the entire fuel column is pressed downward. Don't know if that will make a difference or not.

45 minutes ago, DerekL1963 said:

When evaluating failure modes, that it will fail is practically irrelevant - and a statement such as "can fail at the worst moment" is an appeal to emotion, not engineering.  A proper evaluation considers the likelihood of failure, which in this case is damn near zero for a properly designed and tested igniter system.

I think the difference was talking about on-pad failure vs in-flight failure. If an ignition fails on the pad, you can shut down the other engines and try again the next day. If S2 ignition fails, you're boned.

[wumpus]

19 minutes ago, sevenperforce said:

I think the difference was talking about on-pad failure vs in-flight failure. If an ignition fails on the pad, you can shut down the other engines and try again the next day. If S2 ignition fails, you're boned.

You then need either launch clamps or TWR such that TWR of N-1 engines <=1 (which might do wonders for aerodynamics, but I have to wonder if low TWR is remotely efficient for pressure fed rockets).  I don't think that launch clamps are so much an issue as strengthening the structure such that they can hold the force in the opposite direction as the typical case.

[Steel]

34 minutes ago, sevenperforce said:

Hmm, good idea.

The biggest problem with going bipropellant instead of hybrid is that you have to start worrying about chamber cooling, and regenerative cooling is tough. Ablative chambers are a possibility, but we're already doing an ablative nozzle.

I think an ablative chamber would be the way to go, by far and away the simplest option. SpaceX used it for their Kestrel 2nd stage engine on Falcon 1 (maybe not the most ringing endorsement, but shows it can be done). The AJ-10 used a chamber coated in Tungsten-Carbide from what I have read. TR-201 used on the second stage of Delta launches 1972-1988 also used an ablative chamber.

34 minutes ago, sevenperforce said:

I can't think of a good way to get HTP decomposition to actually pressurize the tanks without triggering runaway decomposition. Can anyone else?

Probably not possible (especially if it's hypergolic), was just spit-balling to come up with other positives.

34 minutes ago, sevenperforce said:

Hmm, interesting! I didn't think much had been done with gelled propellants.

One difference here is that we are eschewing the entire outlet/feed line; rather, the entire fuel column is pressed downward. Don't know if that will make a difference or not.

I think the same principle might apply. When releasing a high pressure gas on top of a viscous gel, its usually more energetically favourable for gas to force it's way through a tunnel in the gel than for it to force the gel downwards I guess.

Edited July 21, 2017 by Steel

[DerekL1963]

14 minutes ago, sevenperforce said:

I think the difference was talking about on-pad failure vs in-flight failure. If an ignition fails on the pad, you can shut down the other engines and try again the next day. If S2 ignition fails, you're boned.

If anything in the second stage propulsion system fails, you're boned.  The real question here is more one of development risk (at the program level) than one of flight risk.   A complex engine about which virtually nothing is known, vs. a simple igniter which is well characterized.  It's silly to pretend the latter is a source of greater concern.
 

20 minutes ago, sevenperforce said:

One difference here is that we are eschewing the entire outlet/feed line; rather, the entire fuel column is pressed downward. Don't know if that will make a difference or not.

It doesn't make a difference.  If you've got gas pressing on a gel and an outlet for the pressure, tunneling is a potential concern.
 

22 minutes ago, sevenperforce said:

The biggest problem with going bipropellant instead of hybrid is that you have to start worrying about chamber cooling, and regenerative cooling is tough.

Regenerative cooling is tough, but well understood.  The proposed engine is even tougher, and a complete mystery. 

[shynung]

1 hour ago, DerekL1963 said:

When evaluating failure modes, that it will fail is practically irrelevant - and a statement such as "can fail at the worst moment" is an appeal to emotion, not engineering.  A proper evaluation considers the likelihood of failure, which in this case is damn near zero for a properly designed and tested igniter system.

34 minutes ago, sevenperforce said:

I think the difference was talking about on-pad failure vs in-flight failure. If an ignition fails on the pad, you can shut down the other engines and try again the next day. If S2 ignition fails, you're boned.

This is what I was trying to say. Even if the individual igniters are reliable, in serially staged rockets in which each individual engines have their own igniters, the probability of one engine failing to fire, resulting in a jeopardized launch, rise considerably.

Consider an igniter that has a failure rate of 1 in 10 (exaggerated to simplify calculations). If a two-stage rocket uses that igniter, one in each stage, and a single ignition failure means failure to reach orbit, that means the rocket would have a failure rate of about 1 in 5.

Which is why I don't recommend any propellant combination that isn't hypergolic, at least for S2 and above; if we need the performance, we can use a non-hypergolic S1 and ignite it externally.

55 minutes ago, sevenperforce said:

One difference here is that we are eschewing the entire outlet/feed line; rather, the entire fuel column is pressed downward. Don't know if that will make a difference or not.

Clarke's text was talking about tank pressurization. I think we'll run into the same problem unless we use bladders of some sort.

58 minutes ago, sevenperforce said:

The biggest problem with going bipropellant instead of hybrid is that you have to start worrying about chamber cooling, and regenerative cooling is tough. Ablative chambers are a possibility, but we're already doing an ablative nozzle.

I don't see why we shouldn't go with both ablative chambers and nozzles in one rocket. If the heat load on each part is different, we can vary the ablative material thickness to match cooling requirements.

1 hour ago, sevenperforce said:

I can't think of a good way to get HTP decomposition to actually pressurize the tanks without triggering runaway decomposition. Can anyone else?

This is where a turbopump would be needed. I know it's complicated machinery, but it's the only way to transfer pressure between liquid without mixing them together.

I was about to say 'use bladders', but then we're using decomposed HTP (=hot GOX) as pressurant. It'd eat through the bladder material anyway.

[sevenperforce]

2 minutes ago, wumpus said:

You then need either launch clamps or TWR such that TWR of N-1 engines <=1 (which might do wonders for aerodynamics, but I have to wonder if low TWR is remotely efficient for pressure fed rockets).  I don't think that launch clamps are so much an issue as strengthening the structure such that they can hold the force in the opposite direction as the typical case.

All five engines should have a low enough throttle range that they can be ignited and then held at low throttle with vehicle TWR < 1; once ignition is verified on all five engines, throttle up to launch.

4 minutes ago, Steel said:

I think an ablative chamber would be the way to go, by far and away the simplest option. SpaceX used it for their Kestrel 2nd stage engine on Falcon 1 (maybe not the most ringing endorsement, but show it can be done).

Ablative chambers are less reusable, so that's an issue.

I wonder if you could place the entire biprop liquid combustion chamber inside the oxidizer tank. HTP has a ridiculously good heat capacity so it can suck up all the heat from the chamber without decomposition. Plus then you can make the chamber lighter because it doesn't have to deal with internal pressure (the tank pressure is higher than the combustion pressure). 

6 minutes ago, Steel said:

32 minutes ago, sevenperforce said:

I can't think of a good way to get HTP decomposition to actually pressurize the tanks without triggering runaway decomposition. Can anyone else?

Probably not possible (especially if it's hypergolic), was just spit-balling to come up with other positives.

 

13 minutes ago, shynung said:

This is where a turbopump would be needed. I know it's complicated machinery, but it's the only way to transfer pressure between liquid without mixing them together.

Well, the hypergolicity of HTP isn't the issue here; it's the spontaneous decomposition. HTP decomposes if heated above its boiling point of 150.2 degrees Celsius. Thankfully, it has a very high enthalpy of vaporization, so we can use it as a coolant if we want, but progressive in-tank decomposition to maintain pressure seems like a nightmare. Decomposing HTP self-heats to greater than the boiling point of HTP, so it's very problematic.

54 minutes ago, DerekL1963 said:

It doesn't make a difference.  If you've got gas pressing on a gel and an outlet for the pressure, tunneling is a potential concern. 

A potential concern, yes, but if the outlet area is larger than the inlet area, the tunneling concern maybe somewhat...less.

A lot depends on the density and cohesion of the jellied propellant. If it is very high it will stick together; if it is very low it won't stick to the walls as easily. So it should be solvable.

[shynung]

1 minute ago, sevenperforce said:

Well, the hypergolicity of HTP isn't the issue here; it's the spontaneous decomposition. HTP decomposes if heated above its boiling point of 150.2 degrees Celsius. Thankfully, it has a very high enthalpy of vaporization, so we can use it as a coolant if we want, but progressive in-tank decomposition to maintain pressure seems like a nightmare. Decomposing HTP self-heats to greater than the boiling point of HTP, so it's very problematic.

Which is why. Self pressurization of HTP tank would mean either in-tank decomposition or spraying decomposed HTP (hot steam + oxygen gas) into HTP tank. Both are risky business.

10 minutes ago, sevenperforce said:

I wonder if you could place the entire biprop liquid combustion chamber inside the oxidizer tank. HTP has a ridiculously good heat capacity so it can suck up all the heat from the chamber without decomposition. Plus then you can make the chamber lighter because it doesn't have to deal with internal pressure (the tank pressure is higher than the combustion pressure). 

Peroxide rate of decomposition increases with rising temperature. It's best to keep it away from anything hot, IMO. That, or use it immediately after being heated in, say, a regeneratively-cooled chamber.

[sevenperforce]

1 minute ago, shynung said:

Which is why. Self pressurization of HTP tank would mean either in-tank decomposition or spraying decomposed HTP (hot steam + oxygen gas) into HTP tank. Both are risky business.

The latter is fine as long as the outlet is above the level of the liquid; even a tiny bit of expansion will cool it plenty. The trouble is the pressure loop. Since the gaseous portion of the chamber is the highest pressure in the vessel, there's no way to pressure-pump anything into it, which means you'd need everything to take place inside the chamber.

1 minute ago, shynung said:

Peroxide rate of decomposition increases with rising temperature. It's best to keep it away from anything hot, IMO. That, or use it immediately after being heated in, say, a regeneratively-cooled chamber.

Right.

[DerekL1963]

1 hour ago, sevenperforce said:

A lot depends on the density and cohesion of the jellied propellant. If it is very high it will stick together; if it is very low it won't stick to the walls as easily. So it should be solvable.

On the other hand, if the density and cohesion is high - you'll increase the difficulty of feeding the propellant into the chamber.  This will require higher gas pressure, thus likely bring back the problem of tunneling.  TANSTAAFL.  You can't consider only one variable in isolation.  (And getting the propellant to inject, vaporize, mix, and burn is already going to be difficult enough.)
 

2 hours ago, shynung said:

Consider an igniter that has a failure rate of 1 in 10 (exaggerated to simplify calculations). If a two-stage rocket uses that igniter, one in each stage, and a single ignition failure means failure to reach orbit, that means the rocket would have a failure rate of about 1 in 5.

Which is why I don't recommend any propellant combination that isn't hypergolic, at least for S2 and above; if we need the performance, we can use a non-hypergolic S1 and ignite it externally.

You don't recommend using any combination that isn't hypergolic...  based on what exactly?  The near zero failure rate of igniters?  The even lower failure rate if you use redundant igniters?  Seriously, igniters are cheap, bone simple, lightweight, and well understood.  To convince me that we should toss all that in favor of the operational expense and complications of using hypergolics you're going to have to do better than that.

[sevenperforce]

45 minutes ago, DerekL1963 said:

On the other hand, if the density and cohesion is high - you'll increase the difficulty of feeding the propellant into the chamber.  This will require higher gas pressure, thus likely bring back the problem of tunneling.  TANSTAAFL.  You can't consider only one variable in isolation.  (And getting the propellant to inject, vaporize, mix, and burn is already going to be difficult enough.)

Well, still, you're not really feeding it into a chamber. It is the chamber.

45 minutes ago, DerekL1963 said:

You don't recommend using any combination that isn't hypergolic...  based on what exactly?  The near zero failure rate of igniters?  The even lower failure rate if you use redundant igniters?  Seriously, igniters are cheap, bone simple, lightweight, and well understood.  To convince me that we should toss all that in favor of the operational expense and complications of using hypergolics you're going to have to do better than that.

HTP has advantages over LOX, period. Being hypergolic is just an added benefit.

[DerekL1963]

1 hour ago, sevenperforce said:

Well, still, you're not really feeding it into a chamber. It is the chamber.

Well, no.  Unless the fuel tank is completely open to the chamber, which I had presumed you wouldn't do because it's monumentally stupid.
 

1 hour ago, sevenperforce said:

HTP has advantages over LOX, period.

HTP has disadvantages over LOX, period.   That pendulum swings both ways.