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Thought I'd broach the discussion of what, exactly, it would take to get an amateur rocket to orbit.

Obviously I'm not suggesting that anyone attempt to build an orbital rocket in their backyard. This is more a design question -- what would be the simplest, cheapest, most dependable option for getting a rocket into orbit at an amateur level?

Things to consider include:

  • Staging: Serial or parallel?
  • Fuel: Liquid, hybrid, or solid?
  • Guidance: Gimbal, differential thrust, or aerodynamic?

Parallel staging would allow you to light all your engines on the ground, which is nice if you use liquid or hybrid. But it may not be as efficient since crossfeed is not really feasible. Gimbaling is probably well beyond the capacity of amateurs, but differential thrust is a possible guidance mechanism if you use parallel staging with hybrids or liquids. Aerodynamic guidance will work for lower serial stages but you'd probably need spin-stabilization for the upper stage.

If you did go with a liquid or hybrid rocket, what propellants would be used? The kerosene-and-peroxide combination of Black Arrow is promising; both are pretty readily available and there is already a lot of literature on amateur use of peroxide monopropellant for jetpacks. The primary difficulty with a liquid-fueled design is cycle use; pressure-feeding is tricky to get right for an amateur operation, but anything with a turbopump is probably also too complicated. 

A pressure-fed hybrid rocket with something like jellied gasoline and self-pressurizing peroxide is a high-thrust option with respectable specific impulse.

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5 minutes ago, _Augustus_ said:

2 stage solid design with aerodynamic guidance for the first stage and RCS thruster package for the second stage.

I'm not sure at an amateur level you could build two stages large enough to get you to orbit. The smallest orbital rocket that's has ever been attempted [1] has three stages.

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12 minutes ago, Steel said:
21 minutes ago, _Augustus_ said:

2 stage solid design with aerodynamic guidance for the first stage and RCS thruster package for the second stage.

I'm not sure at an amateur level you could build two stages large enough to get you to orbit. The smallest orbital rocket that's has ever been attempted [1] has three stages.

Yeah, with solids you definitely need more than two stages.

What if you used parallel hybrids on the lower stage and then a solid-fueled kick stage for the orbital insertion? Aerodynamic guidance on the core and peroxide monoprop RCS on the payload for upper-stage guidance.

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I saw a video on YouTube by Copenhagen Suborbital where they use vanes in the exhaust to vector the thrust for control.  This could be done fairly easily with some beefy servos , however you might need to make the vanes out of tungsten or something else heat resistant.  I'm curious if a miniature jet engine of the type used on RC aircraft would make sense as a first stage for a small rocket.  If nothing else, it would at least make development a smidgen easier.

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4 minutes ago, Thor Wotansen said:

I'm curious if a miniature jet engine of the type used on RC aircraft would make sense as a first stage for a small rocket.  If nothing else, it would at least make development a smidgen easier.

Probably not, you just wouldn't really get any useful velocity out of it. All you'd get is a rocket at a couple of thousand feet moving at an absolute maximum of about 200 ms-1. Also, the TWR of jet engines is simply not very good for rocketry applications

Edited by Steel
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If you mean by "amateur rockets" as rockets of quite a small size that you don't end up paying significant amount of/for paperwork :

model_pyramid.png

(ref)

Other than that, basically what current small launchers have. Or early launchers where they can only loft a few kg into orbit.

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As we still can't see a tsunami of amateur surface-to-orbit rockets, probably any of listed is unavailable for amateurs.
Either you have to deal will extremal mechanics, or with precise casting, and in any case with specific chemistry.
Unlikely this will change in several years.

Say, twenty years later, probably the cheapest and simplest way will be single-use two-staged "3d-printed" hybrid rocket where one component is solid and easy-to-use, another one is liquid, non-cryogenic and effective.

With partially burnable construction, which probably means that the solid component will be also the stage wall (at least, part of it).
Maybe, not a wall, but a foam made of solid component, filled with the liquid one.
Maybe not a foam but granules made of solid component with the liquid one inside.
Maybe, a stack of flat cylindric sections filled with such foam. "Printed" and stacked as many as you currently need. (Like Shuttle SRB, but more flat and "connectable"), Foam is also a part of construction.

Of course, serial, as parallel complicates both rocket and facility.

Unlikely mechanical fins, as they also complicate, but probably RCS nozzles powered by the main engine pressure.
Afaik, Trident and some other missiles use something like that on the upper stage. Several charges in their chambers, common toroidal or cylindric flue with many openings covered with flaps working as nozzles.
This allows them to use a solid motor for precise maneuvering.
Probably, this is the easiest way to "3d-print" this.

GPS-only guidance, without all that astronavigation, infrared horizons, precise gyroscopes.

(Of course, refurbished second-hand rockets are heresy, though they are great in KSP.)

Edited by kerbiloid
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Well, solid fueled is obviously the cheapest, but IMO (in my relatively non-educated standpoint), to get a "good" amount of payload capacity, a hybrid first stage with one or two solid fueled upper stages would be the best bet. Assuming there are three stages, the first stage could use find and jet vanes, the second stage could use jet vanes and the third stage could use a simple cold gas thruster system for RCS

As you can probably tell, this is serial staging. Seems to me that it's less complicated than parallel staging.

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13 hours ago, Thor Wotansen said:

I saw a video on YouTube by Copenhagen Suborbital where they use vanes in the exhaust to vector the thrust for control.  This could be done fairly easily with some beefy servos , however you might need to make the vanes out of tungsten or something else heat resistant.  I'm curious if a miniature jet engine of the type used on RC aircraft would make sense as a first stage for a small rocket.  If nothing else, it would at least make development a smidgen easier.

As others have said, a jet engine doesn't give you meaningful dV...and honestly a jet engine is probably more complex to build/operate than a hybrid-fueled rocket.

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.

1 hour ago, TheEpicSquared said:

Well, solid fueled is obviously the cheapest, but IMO (in my relatively non-educated standpoint), to get a "good" amount of payload capacity, a hybrid first stage with one or two solid fueled upper stages would be the best bet. Assuming there are three stages, the first stage could use find and jet vanes, the second stage could use jet vanes and the third stage could use a simple cold gas thruster system for RCS

As you can probably tell, this is serial staging. Seems to me that it's less complicated than parallel staging.

The advantages of parallel staging seem dramatic, if you can pull it off. Stage separation is a very dicey maneuver, and doing an air-start of the upper stage engine is an added complication. Parallel staging allows you to use common cores (meaning less testing) and ground ignitions.

Here's a thought. What about a hybrid/vapor pressure-fed rocket using catalyzed HTP as the oxidizer and autogenous pressurant (perhaps with liquid nitrogen as an auxiliary coolant) and jellied petrol as the fuel? The biggest problem with hybrid rockets is getting an even burn surface (combining liquids and solids is hard), but napalm would flow and vaporize rapidly enough that this wouldn't be an issue, and the HTP would decompose and vaporize so you wouldn't have liquid-on-solid at any point. If the napalm used aluminum salts as a gelling agent, you could easily get upwards of 260 seconds of isp. While both napalm and HTP are extraordinarily dangerous, they are well-studied and present no particularly exotic handling requirements. HTP can be manufactured with a fairly inexpensive lab setup and petrol is, of course, widely available. If the rocket was equipped with chutes and peroxide-charged (or nitrogen-charged) airbags, it could be easily recovered and refueled much more simply than typical hybrid rockets, since napalm pours readily.

An alternate option would be to add a powdered oxidizer to the fuel in very low quantities, so the solid/gel fuel would burn on its own. This would ensure a consistent burn but still allow for partial throttling like a typical hybrid. 

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As far as I know, you can buy ammonium perchlorate solid rocket engines (sized similar to black powder engines)[in the US], at what I'm sure is a much steeper price.  This should give you some decent Isp for the upper stages.  Stages beneath that would likely be a hybrid rocket (popular for larger sizes).  I'd recommend aerodynamic fins while possible, leaving the thing spin stabilized (the rotation needed is rather low, it shouldn't interfere with the aero controls, assuming they are raspberry-pi controlled).

I don't know exactly what the goal is (although the name includes "orbiter"), but "the register[.co.uk]" (a tech news/rumor site) is attempting a fairly serious go at such a thing and is presently stalled in bureaucracy (FAA at a New Mexico spaceport).  It uses a first stage powered by weather balloon.  As mentioned  above in the thread, air-ignited stages can be tricky and there were even more problems for the LOHAN crew attempting to ignite rockets at weather balloon altitude.  Also I'd expect that using weather balloons will get you higher much easier than jets, at least for rockets sized for amature builders.

http://www.theregister.co.uk/science/lohan/

Edited by wumpus
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@sevenperforce Makes sense, but I'm assuming it would be extremely difficult to get napalm, especially if the rocket is made just by "some guy" and his team. 

On another note, how exactly does one go about programming a rocket? I guess it depends on the guidance computer used. 

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21 minutes ago, TheEpicSquared said:

@sevenperforce Makes sense, but I'm assuming it would be extremely difficult to get napalm, especially if the rocket is made just by "some guy" and his team. 

On another note, how exactly does one go about programming a rocket? I guess it depends on the guidance computer used. 

You'd build all the avionics yourself. Nobody sells dedicated guidance computers. The program itself would either be written in some assembly, or in C if you can find an appropriate compiler.

So, the same way you'd go about programming anything else custom-built around a microcontroller.

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56 minutes ago, wumpus said:

As far as I know, you can buy ammonium perchlorate solid rocket engines (sized similar to black powder engines)[in the US], at what I'm sure is a much steeper price.  This should give you some decent Isp for the upper stages.  Stages beneath that would likely be a hybrid rocket (popular for larger sizes).  I'd recommend aerodynamic fins while possible, leaving the thing spin stabilized (the rotation needed is rather low, it shouldn't interfere with the aero controls, assuming they are raspberry-pi controlled).

I don't know exactly what the goal is (although the name includes "orbiter"), but "the register[.co.uk]" (a tech news/rumor site) is attempting a fairly serious go at such a thing and is presently stalled in bureaucracy (FAA at a New Mexico spaceport).  It uses a first stage powered by weather balloon.  As mentioned  above in the thread, air-ignited stages can be tricky and there were even more problems for the LOHAN crew attempting to ignite rockets at weather balloon altitude.  Also I'd expect that using weather balloons will get you higher much easier than jets, at least for rockets sized for amature builders.

http://www.theregister.co.uk/science/lohan/

Balloon launched doesn't actually sound that crazy when you start thinking about it.

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2 hours ago, TheEpicSquared said:

@sevenperforce Makes sense, but I'm assuming it would be extremely difficult to get napalm, especially if the rocket is made just by "some guy" and his team. 

On another note, how exactly does one go about programming a rocket? I guess it depends on the guidance computer used. 

The "real" stuff, Napalm B, is impossible to procure outside of military contracting, but napalm is shorthand for any form of jellied petrol. "Some guy and his team" would need to purchase a suitable gelling agent and mix it with gasoline themselves...it's not terribly dangerous as long as you don't accidentally ignite it. In which case it's still less dangerous than HTP.

The nice thing about HTP is that decomposes catalytically and, if cooled with a small tank of liquid nitrogen, the decomposition gasses can be used as the pressurant to push the liquid through the larger catalytic bed and into the combustion chamber. 

 

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On 7/6/2017 at 3:15 PM, sevenperforce said:

The advantages of parallel staging seem dramatic, if you can pull it off. Stage separation is a very dicey maneuver, and doing an air-start of the upper stage engine is an added complication. Parallel staging allows you to use common cores (meaning less testing) and ground ignitions.

Here's a thought. What about a hybrid/vapor pressure-fed rocket using catalyzed HTP as the oxidizer and autogenous pressurant (perhaps with liquid nitrogen as an auxiliary coolant) and jellied petrol as the fuel? The biggest problem with hybrid rockets is getting an even burn surface (combining liquids and solids is hard), but napalm would flow and vaporize rapidly enough that this wouldn't be an issue, and the HTP would decompose and vaporize so you wouldn't have liquid-on-solid at any point. If the napalm used aluminum salts as a gelling agent, you could easily get upwards of 260 seconds of isp. While both napalm and HTP are extraordinarily dangerous, they are well-studied and present no particularly exotic handling requirements. HTP can be manufactured with a fairly inexpensive lab setup and petrol is, of course, widely available. If the rocket was equipped with chutes and peroxide-charged (or nitrogen-charged) airbags, it could be easily recovered and refueled much more simply than typical hybrid rockets, since napalm pours readily.

An alternate option would be to add a powdered oxidizer to the fuel in very low quantities, so the solid/gel fuel would burn on its own. This would ensure a consistent burn but still allow for partial throttling like a typical hybrid. 

Idk about parallel staging. I can see the advantages of ground ignition, but if a stage is being lit at sea level and is meant to get to orbit, it seems that the stage would have to be quite large to accommodate the propellant burned. which would be difficult for an "amateur" (relatively speaking, of course). This could be avoided by having a throttleable liquid engine, but manufacturing a liquid-fueled engine would be vastly more complex and expensive than a solid or hybrid.

Also, parallel staging would mean the center core would need to be significantly strengthened, which would be yet another added complication to worry about. Good example of this is the Falcon Heavy. 

Provided that napalm could be obtained, and HTP could be produced in adequate amounts, I like your idea for a hybrid. I can see how jelly would allow for more contact between the oxidizer and the fuel.

 Another thing that I'm wondering about for a hybrid: reverse hybrids. Having a liquid fuel and a solid oxidizer instead of the other way around. There isn't a lot of information on the web, but immediately I can see a few advantages. I think the biggest is that you could do away with toxic/poisonous liquid oxidizers like HTP or nitric acid, and the problems of cryogenics like LOX. You could use fuels like petrol, which is widely available and much easier to work with. A standard solid oxidizer like ammonium perchlorate could be used, but I'm not sure how available that would be. Probably quite expensive though, because military and all that. 

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5 minutes ago, TheEpicSquared said:

Idk about parallel staging. I can see the advantages of ground ignition, but if a stage is being lit at sea level and is meant to get to orbit, it seems that the stage would have to be quite large to accommodate the propellant burned. which would be difficult for an "amateur" (relatively speaking, of course). This could be avoided by having a throttleable liquid engine, but manufacturing a liquid-fueled engine would be vastly more complex and expensive than a solid or hybrid.

Also, parallel staging would mean the center core would need to be significantly strengthened, which would be yet another added complication to worry about. Good example of this is the Falcon Heavy.

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.

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.

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.

43 minutes ago, TheEpicSquared said:

Another thing that I'm wondering about for a hybrid: reverse hybrids. Having a liquid fuel and a solid oxidizer instead of the other way around. There isn't a lot of information on the web, but immediately I can see a few advantages. I think the biggest is that you could do away with toxic/poisonous liquid oxidizers like HTP or nitric acid, and the problems of cryogenics like LOX. You could use fuels like petrol, which is widely available and much easier to work with. A standard solid oxidizer like ammonium perchlorate could be used, but I'm not sure how available that would be. Probably quite expensive though, because military and all that. 

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.

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7 hours ago, RedKraken said:

The engineering approach to amateur sub-orbitals : http://watzlavick.com/robert/rocket/index.html

...

Maybe change pressure-fed to electric turbopumps that are 3d printed?

...

Several enormous problems to overcome with this approach as an amateur:

1. unless you access to industrial standard metal 3D printers theres no way you could make turbopumps of the necessary strength and tolerances.

2. Moving to an electric turbopump set-up on a rocket that's not designed for it is probably a bad idea. Firstly you add in a whole lot of complexity in the form of both high-power (power) and low-power (control) electronics, which in itself bring with it a whole new range of potential failure points. Secondly you also add in tens, possibly hundreds, of kilograms of batteries or supercapacitors (which are both extremely expensive) which also have to be prepared in order to discharge huge amount of energy very quickly. You're suddenly moving well outside th realms of amateur electronics.

 

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There are services that provide metal printing. Although they have their own limitations.

Maybe sometime in the future they would be capable of doing what we need. But if you're talking about amateur, turbopumps are basically out of the question. Pressure fed all the way. It's not that bad, actually. And it may be possible to use other types of pumps instead.

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20 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.

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).

6 hours ago, Steel said:

Several enormous problems to overcome with this approach as an amateur:

1. unless you access to industrial standard metal 3D printers theres no way you could make turbopumps of the necessary strength and tolerances.

2. Moving to an electric turbopump set-up on a rocket that's not designed for it is probably a bad idea. Firstly you add in a whole lot of complexity in the form of both high-power (power) and low-power (control) electronics, which in itself bring with it a whole new range of potential failure points. Secondly you also add in tens, possibly hundreds, of kilograms of batteries or supercapacitors (which are both extremely expensive) which also have to be prepared in order to discharge huge amount of energy very quickly. You're suddenly moving well outside th realms of amateur electronics.

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 LiFePObatteries (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].

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3 minutes 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).

Fair point about turbopumping the oxidizer, but I was more thinking about tank pressure. Hybrids and solids, like pressure-fed liquid rockets, have to have a body that can contain pressures equal to or greater than combustion pressures, since the combustion takes place in the "tank". This makes mass fraction higher, but it also means going asparagus certainly wouldn't be a strength problem.

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I figure there will be rutherford engine clones being worked on in just about every university aerospace shop on the planet.

The kids working on this stuff will be keen to see their projects fly.

And those designs and expertise will filter thru to the amateur space.

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