Amateur rocket to orbit

[TheEpicSquared]

21 hours ago, sevenperforce said:

A hybrid rocket addresses both of these problems, actually. Hybrids are throttleable because you can control the flow of the oxidizer. And since hybrids are pressure-fed by definition, they are already going to be built much stronger than the liquid stages we are typically used to, with plenty of margin.

Oh, well that's the structural problem solved then.

21 hours ago, sevenperforce said:

I'm thinking a 4-core arrangement, with three strap-on boosters around a central core and the payload mounted on top. Each of the strap-on boosters would be fitted with a single tailfin for passive aerodynamic stability and roll cancellation on ascent, and they could be differentially throttled for yaw and pitch control. All would ignite and fire at full throttle on the pad, but the core would throttle down shortly before Max-Q and remain throttled down until booster burnout (similar to a Delta IV Heavy). At booster burnout, they would separate and the core would be throttled back up.

The payload could be fitted with a simple HTP monoprop RCS system, providing guidance for the core during the terminal portion of the burn. It would also probably make sense to give the payload a small COTS solid-fueled kick stage for final circularization.

Alright, but even with throttling the center core down after liftoff, it would still have to be bigger than a serial staging first stage. However, if an amateur team can fabricate a stage big enough, then I don't see why it wouldn't work. 

However, I think the fins on the three boosters should be actively controlled, seems like it would be more precise than differential throttling. Also, if the core stage had jet vanes, that could do away with a monoprop RCS system on the payload, and instead have it on the stage for control while coasting. This would give more flexibility to payload as well.

21 hours ago, sevenperforce said:

Hybrid casings have to be strong enough to hold combustion pressures, so they are plenty strong enough to survive being chuted down. Since all four cores are essentially identical, this makes the testing process much simpler since they would be readily reusable.

One cool addition would be an ablative nozzle that reshapes over the course of the burn. It could be machined out of something as simple as ordinary wood (cork, pine, or oak) and allow the nozzle expansion ratio to increase to compensate for change in pressure and thus maximize specific impulse.

I'm assuming that only the three boosters would be recovered, as the core would get all the way to orbit. But yeah, drogues and main chutes could fit in the nosecones of the boosters. 

Speaking of the boosters, I'm assuming a separation motor would be needed at the top to push away the spent core. That seems relatively easy, however, to accomplish. This would, however, require additional heat shielding on the core where the separation motor plume would hit the core.

The ablative nozzle idea is interesting. It would need a lot of testing, but if it can be done by amateurs, then it could be quite beneficial.

23 hours ago, sevenperforce said:

 Solid oxidizers have much lower specific impulse than liquid oxidizers, so that's one of the issues there. That's the biggest reason why solid-fueled rockets have notoriously low specific impulse: solid oxidizers have high density and low specific energy. And the solid oxidizers that do exist do not vaporize well at all, in comparison to hydrocarbon-based solid fuels which vaporize, mix, and burn readily.

Well, that's probably why reverse hybrids aren't used widely. So I guess standard hybrids are the way to go. Which brings me to my next question, which would be the better oxidizer for jellied petrol, HTP or LOX? I'm assuming the one which results in a higher Isp would be the one to go with.

[sevenperforce]

36 minutes ago, TheEpicSquared said:

Even with throttling the center core down after liftoff, it would still have to be bigger than a serial staging first stage. However, if an amateur team can fabricate a stage big enough, then I don't see why it wouldn't work. 

I don't think the individual cores would be larger than a serial first stage. Falcon Heavy could still take a reasonable amount of payload to orbit even without its upper stage, and its cores are the same size as the F9 first stage. And here we'd be dealing with three boosters instead of two.

That being said, a kick stage (maybe made from a cluster of separation motors) for the final push into orbit is still probably a good idea.

36 minutes ago, TheEpicSquared said:

However, I think the fins on the three boosters should be actively controlled, seems like it would be more precise than differential throttling. Also, if the core stage had jet vanes, that could do away with a monoprop RCS system on the payload, and instead have it on the stage for control while coasting. This would give more flexibility to payload as well.

If we were dealing with low-energy propellants, fins might work...but with medium-energy propellants like HTP and jellied petrol, specific impulse is high enough that you'd run out of aerodynamic control authority before the boosters ran out of propellant. And the vanes are a REALLY complex metallurgical problem.

RCS allows replication of the HTP injection system and allows attitude control even while the engine is off.

40 minutes ago, TheEpicSquared said:

OI guess standard hybrids are the way to go. Which brings me to my next question, which would be the better oxidizer for jellied petrol, HTP or LOX? I'm assuming the one which results in a higher Isp would be the one to go with.

LOX is definitely higher-isp, but it is harshly cryogenic and eats anything it touches. It's also not self-pressurizing since it isn't a monopropellant like HTP. Finally, since the impulse density of jellied petrol is lower than most hybrid rockets, the higher impulse density of HTP helps. You can also synthesize HTP yourself...can't do that with LOX, not in any significant quantities.

[qzgy]

For at least lower stage attitude control, have vernier thrusters been considered? Something like on the R-7 family?

It might add unnecessary weight, cause an integrated RCS system might, if good enough, be able to already perform this job.

 

Also, I just joined this thread, but what kind of payload are we thinking of launching? Something similar to an integrated satellite/upper kick stage like Explorer 1?

Edited July 8, 2017 by qzgy

[sevenperforce]

4 minutes ago, qzgy said:

For at least lower stage attitude control, have vernier thrusters been considered? Something like on the R-7 family?

It might add unnecessary weight, cause an integrated RCS system might, if good enough, be able to already perform this job.

Also, I just joined this thread, but what kind of payload are we thinking of launching? Something similar to an integrated satellite/upper kick stage like Explorer 1?

Vernier thrusters for a hybrid rocket would need to be their own whole hybrid rocket engines, which seems like a large complication when differential throttling on the parallel cores can do the trick. Though I would imagine angling the integrated RCS so every puff pushes at least a little bit prograde.

As far as payload, I'm thinking just getting a guidance and comm system into orbit would suffice to win the "first amateurs to orbit" trophy.

[TheEpicSquared]

6 minutes ago, sevenperforce said:

I don't think the individual cores would be larger than a serial first stage. Falcon Heavy could still take a reasonable amount of payload to orbit even without its upper stage, and its cores are the same size as the F9 first stage. And here we'd be dealing with three boosters instead of two.

That being said, a kick stage (maybe made from a cluster of separation motors) for the final push into orbit is still probably a good idea.

Fair point. However, a kick stage would resurface the problem of air-ignitions, which we were trying to avoid by using parallel staging. I guess it's impossible robber rid of completely. You'd still need to light the separation motors in the air.

6 minutes ago, sevenperforce said:

If we were dealing with low-energy propellants, fins might work...but with medium-energy propellants like HTP and jellied petrol, specific impulse is high enough that you'd run out of aerodynamic control authority before the boosters ran out of propellant. And the vanes are a REALLY complex metallurgical problem.

RCS allows replication of the HTP injection system and allows attitude control even while the engine is off.

Yeah, I agree that jet vanes would be hard to produce, seeing that it would have to withstand huge temperatures and all of that. I guess differential throttling is the way to go, if it's precise enough.

Another possibility for first stage control (could be complicated though) is secondary injection thrust vector control, which is injecting a liquid from separate tank into the nozzle of the boosters, thus producing more thrust on one side, causing the rocket to rip over the other way. The PSLV uses it for lower stage control, but as I said, this system would be relatively complex. Differential throttling seems much more attractive.

I'm not disputing the addition of an RCS system. It's definitely necessary. I just don't think it should be part of the payload, it should be part of the rocket itself. And I don't see why HTP wouldn't work.

17 minutes ago, sevenperforce said:

LOX is definitely higher-isp, but it is harshly cryogenic and eats anything it touches. It's also not self-pressurizing since it isn't a monopropellant like HTP. Finally, since the impulse density of jellied petrol is lower than most hybrid rockets, the higher impulse density of HTP helps. You can also synthesize HTP yourself...can't do that with LOX, not in any significant quantities.

Good point.

12 minutes ago, qzgy said:

For at least lower stage attitude control, have vernier thrusters been considered? Something like on the R-7 family?

It might add unnecessary weight, cause an integrated RCS system might, if good enough, be able to already perform this job.

Verniers only would work effectively on liquid fuel engines, whereas the rocket @sevenperforce and I are discussing would be hybrid.

[Steel]

3 hours ago, wumpus said:

There's nothing in the definition of hybrid that requires pressurization, just that at amature levels you can expect exclusively pressure-fed engines.  Turbopump-fed hybrids (even using NO₂) might well be useful engines that require being able to dwell in space and possibly allow multiple burns (just don't expect to see them without NASA-sized budgets).

1.  You want a CNC instead of a 3d printer.  This allows you to use the material of your choice (likely forged aluminum for weight or possibly a strength/high melting point metal.  Possibly even titanium depending on your CNC machine).  While building a CNC machine out of a dremel tool is a major undertaking itself, you can probably get access to one a lot easier than even a mid-ranged industrial 3d printer.

2. The batteries needed for an electric turbopump should scale the same as the Rutherford engine rocket labs uses.  The key is likely LiFePO₄ batteries (they can pump out their power faster than most batteries) and having them all wired in parallel (or as close as possible to all discharge along with the stage*).  Also while such design might not be "amature electronics", many EEs are familiar enough with power supply design and can presumably figure out much of the differences involved (turbines are *slow* compared to modern power supplies.  Expect to get away with "obsolete" things like iron core inductors to reduce weight).  I suspect a team capable of reaching orbit would have no difficulty recruiting someone capable of designing such a system.

* if the batteries are a significant part of the weight of the booster, you've just discovered a great way to do asparagus staging: switching between battery sources should be trivial [for switching in values of time measured in microseconds].

While your standard DIY 3-axis dremel CNC machine is fine for a small-scale hobbyist, if we're talking high-performance rocketry turbopumps you're going to struggle. Firstly I can't imagine a dremel tool has the power to cut billet titanium or forged alumiuium, and secondly due to the complexity of turbopump parts, you'd probably need a 4- or 5- axis CNC manchine. I'd say designing in-house and paying for external manufacture is the only way to go without shelling out potentially hundreds of thousands of dollars for CNC machines. That way you can design it and then pick the manufacture method that suits the design best (be that 3D printing, CNC or something else).

Everything you're saying about batteries is true, but since there's next to zero knowledge about electric turbopump rocketry in the public domain (or indeed outside Rockcetlab) then it's a bit of a stretch to suppose an amateur team should tackle it while the technology is still in it's infancy.

After all, moving from pressure-fed to a turbopump set-up is an enormous amount of work and only gives you a small amount of extra performance, you can still get to orbit with pressure fed engines.

Edited July 8, 2017 by Steel

[Kerbart]

On 7/6/2017 at 9:15 AM, sevenperforce said:

Exhaust vanes will work well enough if they're tungsten, but that's expensive and the servos would definitely be heavy and very very expensive. Aerodynamic fins are cheaper, simpler, and easier to work with.

Carbon is cheap and heat resistant; I've heard that people who were building their liquid fueled rockets long before it became a mainstream hobby had good success with it.

[sevenperforce]

3 hours ago, Kerbart said:

Carbon is cheap and heat resistant; I've heard that people who were building their liquid fueled rockets long before it became a mainstream hobby had good success with it.

I'm worried less about the actual material itself and more about the actuating mechanism. It would be complex, heavy, and fragile, and the cost reduction of chuting down the otherwise-sturdy spent stages is substantial for an amateur approach.

[sevenperforce]

3 hours ago, TheEpicSquared said:

Fair point. However, a kick stage would resurface the problem of air-ignitions, which we were trying to avoid by using parallel staging. I guess it's impossible robber rid of completely. You'd still need to light the separation motors in the air.

Air-ignitions for solid rockets aren't as much of a problem. It's just a liquid or hybrid rocket that is difficult.

My ideal design is very strongly influenced by the Atlas rocket that put John Glenn in orbit. Parallel/drop staging, MECO just short of orbit, solids for circularization.

3 hours ago, TheEpicSquared said:

Verniers only would work effectively on liquid fuel engines, whereas the rocket @sevenperforce and I are discussing would be hybrid.

I mean, technically you could use a tiny hybrid rocket and plumb it from the main stage's HTP tank, but since HTP is a monopropellant it is MUCH easier to just use that. Plus, with Verniers you're still doing differential throttling.

[qzgy]

13 minutes ago, sevenperforce said:

My ideal design is very strongly influenced by the Atlas rocket that put John Glenn in orbit. Parallel/drop staging, MECO just short of orbit, solids for circularization.

It might be a better idea to looks at a Japanese Lambda or SS-520-4 kind of system. I'm just suggesting this as these two things, especially the SS-540-4 system was designed to be a small payload into orbit, unlike the Atlas launch system.

From what I have found, it has 3 stages, in a dropping sequence. I'm not sure what kind of rocket motor it is, but judging from the text on this site (http://space.skyrocket.de/doc_lau/s-520.htm) I think it might be solid propellant.

Also, (I might be wrong about this, I'm not highly qualified or anything), I think it might be easiest to have to payload and upper stage integrated. In all likelihood, the upper stage is probably going to be a kicker SRB, so that would probably stay in orbit (until orbital decay happens). Why not just leave the satellite on the upper stage?

As a final note - has anyone actually considered the legal requirements for doing this kind of thing? Like, we don't want to chuck something into orbit and have it hit something important.

[sevenperforce]

2 hours ago, qzgy said:

It might be a better idea to looks at a Japanese Lambda or SS-520-4 kind of system. I'm just suggesting this as these two things, especially the SS-540-4 system was designed to be a small payload into orbit, unlike the Atlas launch system.

From what I have found, it has 3 stages, in a dropping sequence. I'm not sure what kind of rocket motor it is, but judging from the text on this site (http://space.skyrocket.de/doc_lau/s-520.htm) I think it might be solid propellant.

Yes, it's all-solid. Hobby-class solid rocket motors are small enough that handling is not dangerous, and stuff like combustion instability, burn rate, thrust curve, and propellant grain never really come up. But when you move into larger SRBs, these things all become problematic. Building solid-fueled first and second stages large enough to get a cubesat-sized payload into orbit is just a little beyond what amateurs can really reasonably attempt, even if the upper stages would be more manageable.

Parallel staging with a high-impulse-density hybrid fuel allows all the stages to be of a reasonable size but have a stack with potentially enough energy to actually reach orbital speeds.

Quote

Also, (I might be wrong about this, I'm not highly qualified or anything), I think it might be easiest to have to payload and upper stage integrated. In all likelihood, the upper stage is probably going to be a kicker SRB, so that would probably stay in orbit (until orbital decay happens). Why not just leave the satellite on the upper stage?

Oh, I would definitely say yes about keeping the solid kick stage attached to the payload. No reason to bother with the added weight of a payload deployment system.

Quote

As a final note - has anyone actually considered the legal requirements for doing this kind of thing? Like, we don't want to chuck something into orbit and have it hit something important.

There would definitely be a lot of permitting involved, but starting with the right propellant choice helps a little. There are some permitting costs that are unavoidable but the idea is to drive down overall costs.

This is just a pipe dream, but it REALLY would be cool for a bunch of video game nerds on a game forum to actually design (and perhaps publish?) plans for an orbital rocket that amateurs could reasonably construct. I certainly don't have the time, space, or funds to actually build something like this, but we could definitely come up with the designs, do the math, simulate it, investigate permitting, and all that stuff.

[qzgy]

2 minutes ago, sevenperforce said:

Parallel staging with a high-impulse-density hybrid fuel allows all the stages to be of a reasonable size but have a stack with potentially enough energy to actually reach orbital speeds.

Ahh, ok. Out of curiosity,  what is the actual energy density increase of a hybrid system rather than a solid one? Like, is it significant enough to justify the extra work in making it a hybrid system?

4 minutes ago, sevenperforce said:

This is just a pipe dream, but it REALLY would be cool for a bunch of video game nerds on a game forum to actually design (and perhaps publish?) plans for an orbital rocket that amateurs could reasonably construct. I certainly don't have the time, space, or funds to actually build something like this, but we could definitely come up with the designs, do the math, simulate it, investigate permitting, and all that stuff.

Agreed. This is wishful thinking, but perhaps if a design is agreed upon and is simulated to work and all that kind of stuff, it may be possible to reach out to some other group to actually build the rocket (and crowdsource it maybe?) I too, don't have the time, resources, skill, or money to build one.

[sevenperforce]

9 hours ago, qzgy said:

Ahh, ok. Out of curiosity,  what is the actual energy density increase of a hybrid system rather than a solid one? Like, is it significant enough to justify the extra work in making it a hybrid system?

Well, again, it comes down to the difference between amateur-level rocketry and professional rocketry. Solid-fueled rockets with reasonably high specific impulse are possible -- the Shuttle SRBs have a vacuum isp of 269 seconds -- but high-energy solid rocket fuel is ridiculously dangerous, difficult to handle, hard to cast, and chemically complex. Solid fuel available to amateurs is much less energetic; commercial Estes hobby rockets have isp ranging from 60 to 90 seconds, and the sugar+KNO3 rockets I've made range from 100 to 130 seconds. 

In contrast, a HTP+jellied petrol hybrid rocket should be able to push at least 250 seconds at sea level and as high as 300 seconds in vacuum specific impulse. And unlike some other hybrid-fuel oxidizers, HTP is exceedingly dense.

9 hours ago, qzgy said:

Agreed. This is wishful thinking, but perhaps if a design is agreed upon and is simulated to work and all that kind of stuff, it may be possible to reach out to some other group to actually build the rocket (and crowdsource it maybe?) I too, don't have the time, resources, skill, or money to build one.

Definitely! You could also get corporate sponsorships for high-profile amateur work. 

First step, I think, is doing some optimization to figure out what staging combination will result in the smallest overall LV size. Gross vehicle size, more than any other single factor, is going to be the greatest determiner of overall project cost.

[TheEpicSquared]

It's a bit ambitious, I know, but I really think we might be on to something here. IMO, we should settle on an idea (right now I like @sevenperforce's HTP+napalm idea) and start designing. 

Edited July 9, 2017 by TheEpicSquared

[Bill Phil]

I highly suggest basing our design on OTRAG.

[sevenperforce]

20 minutes ago, TheEpicSquared said:

It's a bit ambitious, I know, but I really think we might be on to something here. IMO, we should settle on an idea (right now I like @sevenperforce's HTP+napalm idea) and start designing. 

At the very least, we could show what the minimum threshold for an amateur shot at orbit would be. 

The primary concern I have about using jellied petrol is fuel stability. In this video of a LOX+wax hybrid rocket, imperfections in the wax casting cause a chunk of the wax to break off and be forced out through the nozzle; the LOX burns through the exposed motor casing a second or so later.

From what I've read, the biggest challenge with hybrid motors is getting fuel that is "wet" enough to vaporize consistently, but still solid enough to retain its shape throughout the burn. Napalm is, of course, much closer to a liquid than to a solid, so the main problem is making sure the fuel stays inside the chamber. 

It's not an insurmountable problem -- after all, we're just designing, not building, so we can skip over some of the engineering challenges. But we do need to make sure we have a viable approach. It might be worth proposing/investigating some alternate shapes that would ensure combustion pressure keeps the fuel inside rather than forcing it out (e.g., blurring the line between a hybrid engine and a pressure-fed liquid engine). The traditional cylindrical fuel casting has some advantages, like thermally insulating the motor casing, so those issues would need to be considered.

For example, here's a possibility: 

In this design, the pressurant (which could be liquid nitrogen, as shown here, or even really high-pressure air for additional oxidization potential) and the HTP tank are stacked inside the motor where you'd typically have the combustion area. A large lower valve on the pressurant tank forces the HTP down, through a catalyst bed, while a smaller upper valve produces head pressure on the napalm. In this way, the napalm column burns from the bottom, but undergoes plastic deformation and flow under head pressure and acceleration, so that the burn surface remains at the same point, and combustion pressures prevent it from flowing out the nozzle. So it's basically a pressure-fed liquid bipropellant rocket, but with the fuel being stored and "injected" in gel phase rather than in liquid phase. Shouldn't be substantially harder to build than a standard hybrid rocket.

9 minutes ago, Bill Phil said:

I highly suggest basing our design on OTRAG.

Agreed. Clustering and parallel staging is inherently more challenging than serial staging due to the potential for differences in combustion rates, but if you are using throttled hybrid rockets then you can compensate. 

It may be that we find a 10 or 15-core cluster is what's required. 

[qzgy]

3 minutes ago, sevenperforce said:

For example, here's a possibility: 

In this design, the pressurant (which could be liquid nitrogen, as shown here, or even really high-pressure air for additional oxidization potential) and the HTP tank are stacked inside the motor where you'd typically have the combustion area. A large lower valve on the pressurant tank forces the HTP down, through a catalyst bed, while a smaller upper valve produces head pressure on the napalm. In this way, the napalm column burns from the bottom, but undergoes plastic deformation and flow under head pressure and acceleration, so that the burn surface remains at the same point, and combustion pressures prevent it from flowing out the nozzle. So it's basically a pressure-fed liquid bipropellant rocket, but with the fuel being stored and "injected" in gel phase rather than in liquid phase. Shouldn't be substantially harder to build than a standard hybrid rocket.

That's quite an elegant solution. The problems I immediately see here are

A) How consistent will the pressure feeding be? For instance, we don't want one side accidentally burning more than the other, causing funny stuff to happen inside the combustion chamber

B) What if it is throttled too low, that the chamber pressure from ignition is not high enough to keep the napalm from flowing in uncontrollably?

Also - this still has to be controlled, so I would guess there has to be some form of cable tunnel or something similar to control the valves necessary for control, right?

[Steel]

16 minutes ago, sevenperforce said:

In this design, the pressurant (which could be liquid nitrogen, as shown here, or even really high-pressure air for additional oxidization potential) and the HTP tank are stacked inside the motor where you'd typically have the combustion area. A large lower valve on the pressurant tank forces the HTP down, through a catalyst bed, while a smaller upper valve produces head pressure on the napalm. In this way, the napalm column burns from the bottom, but undergoes plastic deformation and flow under head pressure and acceleration, so that the burn surface remains at the same point, and combustion pressures prevent it from flowing out the nozzle. So it's basically a pressure-fed liquid bipropellant rocket, but with the fuel being stored and "injected" in gel phase rather than in liquid phase. Shouldn't be substantially harder to build than a standard hybrid rocket.

A really interesting proposition! I reckon you'd need to do a lot of simulation work to ensure that the materials act as you've said here. High temperatures and pressures often result in behavior that goes completely against what you would expect.

Edited July 9, 2017 by Steel

[sevenperforce]

22 minutes ago, qzgy said:

That's quite an elegant solution. The problems I immediately see here are

A) How consistent will the pressure feeding be? For instance, we don't want one side accidentally burning more than the other, causing funny stuff to happen inside the combustion chamber

B) What if it is throttled too low, that the chamber pressure from ignition is not high enough to keep the napalm from flowing in uncontrollably?

Also - this still has to be controlled, so I would guess there has to be some form of cable tunnel or something similar to control the valves necessary for control, right?

The chamber would be annular, that is, cylindrical. So the pressure and flow rate would be constant around the cross-section. 

There would definitely be a minimum throttle settling, though that's typical of any real-world throttleable rocket engine. It probably would not be restartable (though restarting would be outside the range of what we would try to do anyway). 

Cabling could run to the pressurant chamber without difficulty since it would not be a high-temperature region; the pressurant would necessarily come out quite cold due to expansion. The valve leading to the catalyst bed could be passively pressure-actuated; all throttling could be controlled from the pressurant tank. You could even vary the mixture ratio, within certain limits.

[sevenperforce]

Added/clarifying thought:

In terms of engine design, the goal is to have stable, quasi-steady-state combustion (like a bipropellant liquid engine) while still having the fuel surface serve as a flameholder and chamber wall+casing insulator (like a hybrid rocket). This avoids the complexity of active cooling on the combustion chamber. As discussed above, the nozzle can be ablatively cooled with relatively inexpensive materials. A secondary goal for engine design is reasonably rapid reusability, another advantage of napalm over paraffin or rubber.

There are solid+solid rockets (standard SRBs), liquid+solid rockets (LOX hybrids), vapor-solid rockets (nitrous hybrids), liquid-liquid rockets (standard liquid rockets), vapor-liquid rockets (FRSC and ORSC), and vapor-vapor rockets (FFSC), but I don't think I've ever seen a vapor-gel rocket.

In terms of staging design, the goal is to have individual rocket cores which are small enough to be handled, filled, and transported easily but large enough that you don't need dozens and dozens of them in parallel.

It may be that we end up with a stage size where a single-stick can do high-altitude atmospheric sounding, a 1+3 parallel arrangement can do suborbital flight, and a two- or three-layer asparagus system with a sugar-rocket kick stage can reach orbit.

For those unfamiliar with OTRAG, it's a modular pipe-based pressure-fed liquid rocket system with an ablative nozzle, using differential thrust for pitch and yaw control.

Edited July 9, 2017 by sevenperforce

[TheEpicSquared]

@sevenperforce That's quite an interesting idea. There are some limitations, like @qzgy said, but those seem work-around-able. How would it be ignited though? An ignition plug at the bottom of the HTP tank would be subject to extremely high temperatures. 

Would electric spark ignition work? Two wires with a battery (doesn't have to be big, maybe could be as small as an AAA) at a point of lower stresses, and the wires would contact each other in a way that would produce a spark when the circuit is completed. At the very least, this would eventually heat up the metal (and plastic insulation) of the wire, and could possibly ignite the propellant. 

And another thing, how would separation of the strap-ons work? You could use explosive bolts, but that involves even more complex events. One idea I had is as follows:

So you have a "claw" of sorts, attached to the center core, which holds on to a rod that is attached to the strap-on. Between these two "claw" arms is a very compressed spring, attached another to the center core. The idea is that when its time for separation, the "claw" opens, releasing the booster. This allows the spring to push the spent booster away from the center core. Combined with a separation motor at the top, this theoretically should allow for strap-on separation without the need for explosive bolts. 

I drew a quick diagram (the separation system and the stages are not to scar relative to each other, of course)

Obviously, the "claw" arms, the attachment point, and the rod hat connects to the strap-on would have to be incredibly strong to withstand the forces of launch. In the diagram, I only drew two arms, but in reality 4 or 6 or even 8 (or more) would be better, as it would hold the rod from every angle. 

Thoughts? 

[qzgy]

5 minutes ago, TheEpicSquared said:

And another thing, how would separation of the strap-ons work? You could use explosive bolts, but that involves even more complex events. One idea I had is as follows:

I think explosive bolts are actually easier than the mechanical system you propose. An explosive bolt is one part, your system consists of more parts, each of which could fail and go horribly wrong. Sure, an explosive bolt has other complications, but with your system, you have to trust a much weaker attachment system (friction or something similar) as opposed to a nut and a bolt, which are quite strong.

Also - Has NOX been considered as an oxidizer? I'm not sure of its advantages/disadvantages, but it is another option, and probably less nasty than LOX. The downside is that we would still need an RCS system, probably from HTP monoprop system.

 

[sevenperforce]

45 minutes ago, qzgy said:

I think explosive bolts are actually easier than the mechanical system you propose. An explosive bolt is one part, your system consists of more parts, each of which could fail and go horribly wrong. Sure, an explosive bolt has other complications, but with your system, you have to trust a much weaker attachment system (friction or something similar) as opposed to a nut and a bolt, which are quite strong.

Also - Has NOX been considered as an oxidizer? I'm not sure of its advantages/disadvantages, but it is another option, and probably less nasty than LOX. The downside is that we would still need an RCS system, probably from HTP monoprop system.

Do you mean nitrous oxide? Nitrous has higher specific impulse but much lower impulse density. Since we need a head pressurant for the fuel, its self-pressurizing capabilities don't help us much. 

One major advantage to HTP that I didn't note before is that once it is decomposed, it is hypergolic with kerosene and gasoline, and likely jellied petrol as well. So we need no ignition system. In fact, we could even consider an air-start if all you have to do is open a valve.

For stage separation (both parallel and serial), what about using the RCS monoprop for a pneumatic sep?

 

[TheEpicSquared]

@sevenperforce Gasoline and petrol are the same thing, so I don't see why it wouldn't work with jellied petrol. And that's another problem solved! And with the air-start problem solved, I once again think serial staging is better. It also allows for modularity: there is enough space in the first stage to add SRBs or even common cores, to increase payload capacity. 

Now that I think of it, my mechanical separation idea does have some drawbacks. I think a pneumatic/hydraulic pusher system to push the second stage away from the first stage would be best, using the monopropelant HTP.

On another note, how exactly are first and second stages connected? I'm assuming it uses explosive bolts that disconnect at separation or something, but I don't know exactly.

[sevenperforce]

I was thinking about it, and the separation system could be even simpler than I thought. You've got a high-pressure nitrogen (or other pressurant) tank, after all. So, once you reach stage burnout, you just vent remaining pressure into the separation module, forcing open the clamps holding the stages together. The venting then serves to push the spent stage away without the need for a separation motor.

You can do both serial and parallel staging. Common cores ARE what I'm proposing, after all; just with throttle control to allow the core to act as a sustainer. We can look at the range of hobby rocket systems to see what possibilities there are for serial staging arrangements.