Amateur rocket to orbit

[TheEpicSquared]

I think that before going any further, we need to decide on the staging. After all, parallel and Arian stages rocket do work differently. Will we use parallel or serial staging? Both? If serial, 2 or 3 stage design? Have both parallel and serial, like Falcon Heavy? IMO we need to get that sorted before we go any further.

Edited July 9, 2017 by TheEpicSquared

[sevenperforce]

6 minutes ago, TheEpicSquared said:

I think that before going any further, we need to decide on the staging. After all, parallel and Arian stages rocket do work differently. Will we use parallel or serial staging? Both? If serial, 2 or 3 stage design? Have both parallel and serial, like Falcon Heavy? IMO we need to get that sorted before we go any further.

Well, with the requirement that each individual stage MUST be small enough to test, handle, and transport easily, I don't think we can avoid clustering at the very least.

From there it's a small step to parallel staging. I think assuming a parallel+serial approach like Falcon Heavy is a safe bet. Maybe even something like a four-core sustainer with 8 strap-ons, and a single-stick second stage.

I'd be interested in getting a good estimate of stage mass fraction. How heavy will each stage need to be? One advantage is that HTP is very thrusty.

[wumpus]

16 hours ago, sevenperforce said:

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.

http://www.aerotech-rocketry.com/resources.aspx sells high-power ammonium perclorate.  One rather large engine (12.6kg!) appears to have an Isp of 188s (I'm uneasy about my calculation).
http://www.aerotech-rocketry.com/customersite/resource_library/Catalogs_Flyers_Data_Sheets/ldrs-27_prod_data_sheets.pdf (bottom rocket).  Note that adding a vacuum bell might help.

19 hours ago, sevenperforce said:

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

I think the LOHAN project (the one using the weather balloon) had issues even with solid rockets at extreme altitude.  Of course, the solid motors had time to freeze and hit local temps.  Just because it is far easier doesn't mean it is trivial.

27 minutes ago, sevenperforce said:

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.

One description of a rocket is a pipebomb with an opening at one end.  Once you add the HTP* you've basically added the detonator to said explosive.  I'd be much happier having it as a smaller ignition device and using NO₂ (not to mention NTP is likely far more corrosive than LOX, I remember a chemistry teacher claiming it was the worst (most corrosive) chemical he'd ever worked with [of course that was in high school so he might not have dealt with all that much]).  That idea looks great on the launch pad, but getting it there is a nightmare.

If you have NTP, the pressurized NTP+jellied hydrocarbons would make an ideal RCS unit (of course, it could still explode and start the NO2+jellied hydrocarbons making a bigger boom).

* assuming you can obtain it, John Carmack of Armadillo Airspace had serious issues obtaining the stuff.  I think he gave up on HTP all together.  And he is at the extreme end of amature rocket builders.

[sevenperforce]

Unless I recall incorrectly, HTP can be synthesized and distilled with a fairly small lab setup.

Also, to an earlier point -- we should be thinking less about "increasing payload" and more about actually ensuring we can get our rocket into orbit.

What single-stick target TWR should we have? 2? 3?

10 minutes ago, wumpus said:

http://www.aerotech-rocketry.com/resources.aspx sells high-power ammonium perclorate.  One rather large engine (12.6kg!) appears to have an Isp of 188s (I'm uneasy about my calculation).
http://www.aerotech-rocketry.com/customersite/resource_library/Catalogs_Flyers_Data_Sheets/ldrs-27_prod_data_sheets.pdf (bottom rocket).  Note that adding a vacuum bell might help.

White Lightning can go as high as 214 seconds. Definitely a good kick-stage choice.

[sevenperforce]

Thought: to simplify, we could have binary (on/off, no in-between) valves and just have multiple ones in parallel for the things that need to be throttled. Then you only have one actuated control component and you can buy in bulk.

[qzgy]

1 hour ago, sevenperforce said:

HTP can be synthesized and distilled with a fairly small lab setup.

HTP is just concentrated hydrogen peroxide. However, its kinda nasty. Also, there are commercial suppliers of it, but there aren't any open sources I know of or can think of.

1 hour ago, sevenperforce said:

we should be thinking less about "increasing payload" and more about actually ensuring we can get our rocket into orbit.

Yes. A simple beeping satellite would be good enough. Maybe a piece of paper with all our names on it.

1 hour ago, sevenperforce said:

What single-stick target TWR should we have? 2? 3?

I'm not sure about single stick, but looking at fairly recent models of the black brant, a popular type of sounding rocket, their TWR seems to about 10. I'm not kidding. The nike booster, also used in sounding rockets, has a TWR of 44. It was originally carrying a 14-ton payload, so most of it was dedicated to that. of So maybe a 5-15 TWR would be good for a single-stick. I'm not really sure, but we have to keep in mind the stick also has to carry itself and others up.

 

1 hour ago, sevenperforce said:

Thought: to simplify, we could have binary (on/off, no in-between) valves and just have multiple ones in parallel for the things that need to be throttled. Then you only have one actuated control component and you can buy in bulk.

Also - If we do a simple on/off system, I feel we may come onto the problem of Thrust vectors. Say we have a 4 core sustainer, with cores ABCD

[A]B
[C][D]

If we go to half thrust, that works well. AD or BC can be shut off, and the thrust vector stay in roughly the same place. However, if we want to do 3/4 or 1/4 thrust that doen't work with out changing the average thrust vector. We could just do 3 discrete steps - off, 1/2, and full though. It would have to be a design consideration.

Another benefit of a fully adjustable system is thrust vectoring from the engines, by changing the different relative thrust levels.

Quoting @TheEpicSquared - " I think that before going any further, we need to decide on the staging. After all, parallel and Arian stages rocket do work differently. Will we use parallel or serial staging? Both? If serial, 2 or 3 stage design? Have both parallel and serial, like Falcon Heavy? IMO we need to get that sorted before we go any further. "

As a stage system, what do you feel for using like 8 strap-on solid rocket motors (those white lightnings could work well), an n-core sustainer (core count to be determined,serial staging as necessary), and another single white-lightning as a kicker stage for the final orbit?

Edited July 9, 2017 by qzgy

[qzgy]

double post. Ignore me.

Edited July 9, 2017 by qzgy

[TheEpicSquared]

@qzgy 

A  B

C  D

For your 4-core sustainer, don't you mean that AD or BC can shut down, and the thrust vector would be in the same place? 

And about the staging, I guess it depends on the numbers. It seems reasonable. Maybe have the 8 boosters as the primary thrust source for initial ascent, with the sustainer core at half throttle (having four cores means that they could be differentially throttled for control). When the strap-ons separate the sustainer would throttle back up to full power, until burnout and separation. One of the strap-ons should work as a kick stage for final orbital insertion. However, the TWR might be a bit over-the-top. 

In this configuration, I doubt we would be able to recover the 4-core sustainer though, seeing as its being accelerated to nearly orbital velocities. We could recover the SRBs, but the sustainer is by far the most expensive, it seems. 

[qzgy]

31 minutes ago, TheEpicSquared said:

For your 4-core sustainer, don't you mean that AD or BC can shut down, and the thrust vector would be in the same place? 

Yeah.... Is that not what I said? Oops.

Recovering the sustainer would be nice - if we make it in multiple stages, (let's say for sake of arguement, 3 or 4 stages, plus the kick) we might be able to recover the first one, maybe the second. Kinda depends on what velocities and altitudes are reached by each stage, which depends on A) the SRB used and B) the sustainer core. Both of those affect the possiblility for recovery.

31 minutes ago, TheEpicSquared said:

One of the strap-ons should work as a kick stage for final orbital insertion. However, the TWR might be a bit over-the-top. 

We could probably use a less powerful SRB as the kick stage. That helps with the TWR problem.

 

Also - any thoughts on spin stabilization and/or drag separation?

Edited July 9, 2017 by qzgy

[wumpus]

2 hours ago, sevenperforce said:

Also, to an earlier point -- we should be thinking less about "increasing payload" and more about actually ensuring we can get our rocket into orbit.

Living through multiple launches is even more important.  Having a pressurized highly corrosive material inside a container it is hypegolic with gave me the willies.  Can't imagine how you would fabricate/transport the thing remotely safely.  It looks great as a rocket, but how do you get there?

[sevenperforce]

6 hours ago, wumpus said:

Living through multiple launches is even more important.  Having a pressurized highly corrosive material inside a container it is hypegolic with gave me the willies.  Can't imagine how you would fabricate/transport the thing remotely safely.  It looks great as a rocket, but how do you get there?

High-test peroxide isn't corrosive, per se; it's just extremely likely to decompose explosively if there are any heavy metals or imperfections in its container. It'll be entirely benign if encased in simple aluminum. And it's only hypergolic if you decompose it; you can freely mix it with without exploding, as long as the petrol doesn't have any suspended palladium salts or something.

Granted, I certainly don't want to be anywhere near a mixture of HTP and petrol, but that's beside the point.

The high-test peroxide is definitely the most dangerous part of the whole apparatus, I'll give you that. But it's not as bad as it might be. IIRC, Black Arrow got over 300 seconds of specific impulse with mere 85% peroxide.

8 hours ago, qzgy said:

A simple beeping satellite would be good enough. Maybe a piece of paper with all our names on it.

I mean, I'd like to be able to put a Cubesat in orbit. But yeah, we can target our design as merely getting our terminal stage up there. That's the first step, anyway.

Quote

I'm not sure about single stick, but looking at fairly recent models of the black brant, a popular type of sounding rocket, their TWR seems to about 10. I'm not kidding. The nike booster, also used in sounding rockets, has a TWR of 44. It was originally carrying a 14-ton payload, so most of it was dedicated to that. of So maybe a 5-15 TWR would be good for a single-stick. I'm not really sure, but we have to keep in mind the stick also has to carry itself and others up.

Hmmm, very good point. A naked Falcon 9 FT first stage comes in with a pad TWR of only 1.8, which is why I was originally thinking more conservatively, but I guess I really shouldn't be making that comparison.

We may have to factor single-stick pad TWR into our ultimate optimization equation, unfortunately.

Quote

Also - If we do a simple on/off system, I feel we may come onto the problem of Thrust vectors. Say we have a 4 core sustainer, with cores ABCD

[A]B
[C][D]

If we go to half thrust, that works well. AD or BC can be shut off, and the thrust vector stay in roughly the same place. However, if we want to do 3/4 or 1/4 thrust that doen't work with out changing the average thrust vector. We could just do 3 discrete steps - off, 1/2, and full though. It would have to be a design consideration.

Another benefit of a fully adjustable system is thrust vectoring from the engines, by changing the different relative thrust levels.

Sorry, I guess I wasn't clear. I didn't mean simple on-off for each of the cores; I meant that our valve choice should be uniform across the system. So each RCS thruster would have a single valve, each head pressure opening would have 3 or 4 valves, and each HTP injector would have 6 or 7 valves. So, that way you can open a discrete number of valves to give a finite but stepwise throttle range. Remember that even though decomposed HTP is hypergolic with petrol, the design I'm proposing wouldn't be readily restartable, since shutting down oxidizer flow completely would likely result in fuel extrusion.

Quote

Quoting @TheEpicSquared - " I think that before going any further, we need to decide on the staging. After all, parallel and Arian stages rocket do work differently. Will we use parallel or serial staging? Both? If serial, 2 or 3 stage design? Have both parallel and serial, like Falcon Heavy? IMO we need to get that sorted before we go any further. "

As a stage system, what do you feel for using like 8 strap-on solid rocket motors (those white lightnings could work well), an n-core sustainer (core count to be determined,serial staging as necessary), and another single white-lightning as a kicker stage for the final orbit?

I think one of the initial investigations should be precisely how large a White Lightning orbital rocket would need to be. We need to be able to propose a design that outperforms an SRB-based system.

I'm much more inclined to put additional strap-on hybrid rockets on the first stage and just throttle down the sustainer after launch. But an SRB kick stage is probably fine.

7 hours ago, TheEpicSquared said:

@qzgy

In this configuration, I doubt we would be able to recover the 4-core sustainer though, seeing as its being accelerated to nearly orbital velocities. We could recover the SRBs, but the sustainer is by far the most expensive, it seems. 

All the more reason to make the strap-ons the same cores as the sustainer.

7 hours ago, qzgy said:

Also - any thoughts on spin stabilization and/or drag separation?

Drag separation maybe, though that only works on lower stages, unless you're dealing with a LOT of stages. Spin stabilization on the terminal stage, maybe, but I prefer a vernier-oriented RCS attitude control system.

[wumpus]

I wouldn't count on high TWR off a pad unless you had some particular reason to ignore the atmosphere (like mountain or balloon launch).  It might not be a bad idea to have plenty of SRBs (sugar+KNO₃?) to get close to mach1 or something (even if they don't directly add much delta-v).  In small rockets aero losses are higher relatively than big rockets, and the big boys don't do the obvious steps to minimize gravity losses, so I'd think in terms of mountain/balloon launch before going all out with high TWR.

Don't underestimate the issues of finding a place to launch.  LOHAN has quite a bit of sponsorship, but is still waiting for the FAA to give them permission to fly.  I'd have to wonder if someplace like Jamaica or even "sea launch in international water" would make more sense (especially for balloon launches where you don't need a completely flat platform).  Does anybody play KSP in Ecuador?  Some of those mountains are ideal for rocket launches (high, equatorial, and a few with roads near the top).

[TheEpicSquared]

@sevenperforce I'm not sure I follow your valve idea. Even if you have 6 or 7 valves one after the other, closing just one would shut off the flow, rendering the other valves redundant.

[rudi1291]

6 minutes ago, TheEpicSquared said:

@sevenperforce I'm not sure I follow your valve idea. Even if you have 6 or 7 valves one after the other, closing just one would shut off the flow, rendering the other valves redundant.

You could put them in paralell. Which is probably what @sevenperforce meant. Like, poke a lot of holes into a tank and put a valve into each hole. And you don´t need that many valves. 6 would give you the ability to throttle in steps of ~1.5%...

[sevenperforce]

Just now, rudi1291 said:

15 minutes ago, TheEpicSquared said:

@sevenperforce I'm not sure I follow your valve idea. Even if you have 6 or 7 valves one after the other, closing just one would shut off the flow, rendering the other valves redundant.

You could put them in paralell. Which is probably what @sevenperforce meant. Like, poke a lot of holes into a tank and put a valve into each hole. And you don´t need that many valves. 6 would give you the ability to throttle in steps of ~1.5%...

Precisely. The base of the HTP tank would have, say, 7 openings (one in the center and the others arranged in a hexagonal pattern) with an on-off valve in each one.

Although the steps wouldn't be as fine as 1.5%; it would be in 17% increments. And it's very possible that 17% might be below minimum possible throttle for stable combustion, in which case you might only have five throttle settings: 33%, 50%, 67%, 83%, and 100%. But, still, that's a reasonable degree of control.

The point of having multiple binary valves rather than finely throttleable valves is, again, cost reduction. The HTP tank valves need much more flow capacity than, say, RCS thrusters. But it will almost definitely be cheaper to purchase a dozen small binary valves than it would be to purchase small binary valves for the RCS thrusters and one big throttleable valve for the HTP tank. Plus, that's only one wiring configuration to worry about.

Another thought I had last night: we don't actually need a separate pressurant tank. We can just take a page from OTRAG's playbook and fill the HTP tank 75% full, then top off the rest with air at 600 psi or so. Actually really ridiculously simple:

The vertical spacing between the catalyst bed opening and the nozzle throat is very important. The chamber pressure is a direct function of the burn surface area. As the jellied petrol burns away, the surface area must decrease so that chamber pressure decreases and the jellied petrol can flow down. This ensures the correct feedback loop; otherwise you are trying to compensate by constantly varying pressure and you end up with runaway problems.

Another issue, particularly if we are considering air-start of hybrid upper stages, is ullage. Ullage is never a problem in KSP, but since we are dealing with liquid HTP rather than compressed nitrous or another gas, there must be an acceleration vector when the throttle valves open or it will have very big problems. The RCS thrusters need to be angled down, like Verniers. If we end up air-starting, then we would need to start firing the upper-stage RCS thrusters before separation, while lower-stage acceleration is still holding the HTP at the bottom of the tank. This will ensure that HTP is forced up through the uptake lines.

Note that there would also be a smaller catalyst bed in front of each of the RCS valves, though it's not shown here.

28 minutes ago, wumpus said:

I wouldn't count on high TWR off a pad unless you had some particular reason to ignore the atmosphere (like mountain or balloon launch).  It might not be a bad idea to have plenty of SRBs (sugar+KNO₃?) to get close to mach1 or something (even if they don't directly add much delta-v).  In small rockets aero losses are higher relatively than big rockets, and the big boys don't do the obvious steps to minimize gravity losses, so I'd think in terms of mountain/balloon launch before going all out with high TWR.

With core-throttling asparagus staging (like Delta IV Heavy), you have the benefit of moderately high TWR off the pad AND moderately high TWR at staging because you've already burned a lot of your core's fuel. So TWR issues (whether we have too much or too little) can always be handled by MOAR BOOSTERS, of the hybrid-rocket variety.

SRBs are fine for a serial kick stage, but I am hesitant to use them as parallel boosters, because of combustion inconsistencies. A hybrid rocket can be throttled in real-time, but SRBs cannot, and amateurs don't have the resources to cast perfectly identical SRBs that ignite at exactly the same instant and burn at exactly the same rate and burn out at exactly the same altitude. 

One thing we absolutely need to model (probably iteratively) is the ideal TWR curve and ascent profile for very small orbital rocket. It's not a simple problem. Instantaneous drag forces are hard enough to calculate without wind tunnel testing, but we are dealing with parallel stages, which add an entirely new set of parameters.

I think our best option is to look at something like the Japanese SS-520-4, which was a serially-staged, pure-solid-fueled attempt at launching a single 3-kg cubesat. We could also look at the successful Lambda 4S, which was similar but had two strap-on SRBs. The L4S first stage is a solid-fueled sounding rocket motor pushing 215 seconds of specific impulse at sea level, a little better than White Lightning. Unfortunately, it's still very big for being the smallest successful orbital vehicle:

Spoiler

Despite its size, this represents the minimum size for a solid-fueled orbital ELV. So this is what our hybrid parallel-and-serial rocket needs to beat. As a starting point, we should really look at the dV budget of each stage for the Lambda 4S, since it will give us a good idea of what we need to be able to field for a hybrid-fueled PRLV.

1 hour ago, wumpus said:

Don't underestimate the issues of finding a place to launch.  LOHAN has quite a bit of sponsorship, but is still waiting for the FAA to give them permission to fly.  I'd have to wonder if someplace like Jamaica or even "sea launch in international water" would make more sense (especially for balloon launches where you don't need a completely flat platform).  Does anybody play KSP in Ecuador?  Some of those mountains are ideal for rocket launches (high, equatorial, and a few with roads near the top).

From our position, we'd need to include a survey and analysis of launch site options. If you go international then you have to worry about exporting what are essentially munitions. We should field a design which is capable of reaching orbit even from sea level, though; that way we can simply note increased payload margins with alternate launch sites.

EDIT: Another consideration is the potential for boosting our first stage performance with air augmentation:

If the lower stage(s) need(s) a mounting point for stabilizing fins, then it might make sense to make that mounting point a shroud that can help increase thrust and specific impulse, at least on the parallel boosters.

[mikegarrison]

I think the basic problem here is that you seem to be defining "amateur" as "under-funded". After all, isn't Blue Origin amateur (so far), but with a lot of funding?

[qzgy]

2 hours ago, sevenperforce said:

Another consideration is the potential for boosting our first stage performance with air augmentation:

Looking at the wiki, it seems like a good idea to increase rocket performance. However, we have to also consider that the intake has to be designed and integrated with the rest of the rocket. That might be difficult, especially at high altitudes and velocities.

 

2 hours ago, sevenperforce said:

. Unfortunately, it's still very big for being the smallest successful orbital vehicle:

  Reveal hidden contents

Despite its size, this represents the minimum size for a solid-fueled orbital ELV. So this is what our hybrid parallel-and-serial rocket needs to beat. As a starting point, we should really look at the dV budget of each stage for the Lambda 4S, since it will give us a good idea of what we need to be able to field for a hybrid-fueled PRLV.

A delta-v check would be good, actually on both the SS-540-4 and the lambda. The Lambda carried a 26 kg payload. I think, at most we would be consider a 3 kg payload. Not much of a difference, but still a difference. Probably reduces the Delta-v by a bit.

Also, what is the energy density of the lambda launch vehicle? Why should also try to focus on increasing that to the best of our abilities.

[sevenperforce]

1 hour ago, mikegarrison said:

I think the basic problem here is that you seem to be defining "amateur" as "under-funded". After all, isn't Blue Origin amateur (so far), but with a lot of funding?

I suppose there is some degree of difficulty in precisely defining "amateur".

For reference, this is what the world-record-holding amateur hybrid rocket launch looks like:

Dry mass of 75 kg, wet mass of 163 kg, single 10 kN N2O+paraffin hybrid rocket motor. Max velocity was Mach 2.3. Some analysis here. Specific impulse was 198-217 seconds, probably giving an effective dV of around 1500 m/s, but Mach 2.3 is only about 720 m/s. Gravity drag on a 15-second burn period comes to about 150 m/s, so for this particular design we're looking at roughly 600 m/s of aerodynamic drag losses. That's with a launch TWR of just over 6:1.

This is instructive, since at least the initial launch phase will be very similar for our vehicle. We may go with a slightly lower TWR to decrease drag losses, though this in turn increases gravity drag. There's a whole optimization problem there.

A useful exercise would be to use the parameters of the HEROS-3 hybrid rocket and determine how many serial stages it would take to get this vehicle into orbit, using the OTRAG bundled-stage approach. Then compare to the Lambda 4S vehicle for reference.

32 minutes ago, qzgy said:

Looking at the wiki, it seems like a good idea to increase rocket performance. However, we have to also consider that the intake has to be designed and integrated with the rest of the rocket. That might be difficult, especially at high altitudes and velocities.

Air-augmentation shrouds do need to be integrated, but if you need a fin mounting place anyway, then you're already planning for some structural mass. Modeling is a lot cheaper than building, that's for sure. Note that air augmentation at these specific impulses will be useless above 2.5 km/s, but by that time I hope we'd be well out of the atmosphere anyway.

32 minutes ago, qzgy said:

A delta-v check would be good, actually on both the SS-540-4 and the lambda. The Lambda carried a 26 kg payload. I think, at most we would be consider a 3 kg payload. Not much of a difference, but still a difference. Probably reduces the Delta-v by a bit.

Also, what is the energy density of the lambda launch vehicle? Why should also try to focus on increasing that to the best of our abilities.

We cannot come near the energy density of orbital-grade solid-rocket fuel, but we can get the impulse density quite high with jellied petrol and HTP. Higher than kerolox for sure.

I'll try to put together a dV check on the Lambda.

[sevenperforce]

Okay, the Lambda 4S had 509 m/s of net dV from launch to side-booster burnout, 932 m/s of net dV from side-booster jettison to first-stage burnout, 1,849 m/s of net dV on the second stage, 2,209 m/s of net dV on the third stage, and 3,915 m/s of net dV on the fourth stage. It also had a launch TWR of around 8.

[qzgy]

Just now, sevenperforce said:

Okay, the Lambda 4S had 509 m/s of net dV from launch to side-booster burnout, 932 m/s of net dV from side-booster jettison to first-stage burnout, 1,849 m/s of net dV on the second stage, 2,209 m/s of net dV on the third stage, and 3,915 m/s of net dV on the fourth stage. It also had a launch TWR of around 8.

So about 8700 m/s net. How much is lost to drag and gravity?

[sevenperforce]

2 minutes ago, qzgy said:

So about 8700 m/s net. How much is lost to drag and gravity?

Actually 9,414 m/s net dV. The final orbit was a 322 x 2414 km eccentric orbit with perigee velocity of 8,217 m/s, so that's 1,197 m/s in aerodynamic and gravity drag losses.

[TheEpicSquared]

@sevenperforce 

About the valves, wouldn't having 7 valves+piping significantly increase mass, and cost as well? Legitimate question, does a finely-moving valve really cost that much? 

If it does, then I'd say reducing the number of valves from 7 to 4. One in the middle with theee around. This gives us 25% throttle increments, so we'd have 25% (if possible), 50%, 75% and 100%. That seems good, I'd say. The strap-ons would fire at 100% while the sustainer would throttle down to 50% or even 25% if that deep throttling is possible. 

Your air augmentation idea seems nice, but I'd have to agree with @qzgy, it does seem to be quite difficult.

Also, do you use MS Paint for your diagrams? 

@mikegarrison I think by "amateur" we mean "an educated guy who doesn't have a few million / billion to invest in a rocket or three".  

So, I guess the basic design is a 4-core design, with 3 strap-ons and 1 sustainer, possibly with a solid kick motor for final orbital insertion. This configuration seems ideal. We could use differential throttling for control until strap-on jettison, at which point we could start using the HTP monopropellant RCS system.

I'm also thinking, in the event of a kick motor, an RCS system would take up a lot of mass. How feasible would a system of reaction wheels be? After all, with a ~3kg payload, the kick motor could be quite small. Since the motor only needs to be used for a short period of time, de-spinning the wheels would not be necessary. The wheels themselves wouldn't need to be that big, given the low mass of the motor+payload. Also, we could orient the craft to release the payload facing a certain way, if necessary.

Another thing, as per @sevenperforce's idea of having the HTP tank integrated into what would be the combustion chamber, what type of length reduction and diameter increase are we looking at? Decreased length always is a good thing, obviously, but a wider rocket body of course means more drag.  

Edited July 10, 2017 by TheEpicSquared

[mikegarrison]

47 minutes ago, sevenperforce said:

I suppose there is some degree of difficulty in precisely defining "amateur".

For reference, this is what the world-record-holding amateur hybrid rocket launch looks like:[...]

To my point, however, the video claims that is the world record for altitude of a "student" hybrid rocket. Not an "amateur" rocket of any kind.

"Student" is a somewhat ambiguous term, but it can be generally understood to mean people enrolled in a formal school. "Amateur", on the other hand, is a term that has been abused in many fields but typically means "not professional" or "not being paid to do the work". One could argue that SpaceX, for instance, is professional because they are paid by others to provide launches, but Spaceship One was amateur. However, the distinction is fuzzy. The people who actually built Spaceship One were professionals. But the people who build sailboats for amateur boat racing are usually professionals too, and yet we still consider the racing itself to be amateur.

7 minutes ago, TheEpicSquared said:

@mikegarrison I think by "amateur" we mean "an educated guy who doesn't have a few million / billion to invest in a rocket or three".  

So as I suggested, you mean "underfunded".

Edited July 10, 2017 by mikegarrison

[sevenperforce]

1 hour ago, TheEpicSquared said:

@sevenperforce 

About the valves, wouldn't having 7 valves+piping significantly increase mass, and cost as well? Legitimate question, does a finely-moving valve really cost that much? 

If it does, then I'd say reducing the number of valves from 7 to 4. One in the middle with theee around. This gives us 25% throttle increments, so we'd have 25% (if possible), 50%, 75% and 100%. That seems good, I'd say. The strap-ons would fire at 100% while the sustainer would throttle down to 50% or even 25% if that deep throttling is possible. 

My assumption was that a high-pressure valve's flow rate scales roughly with its weight, so the number of valves required would be less about throttling range and more about the flow requirements. If the max flow into the combustion chamber is 4 times as high as flow into each individual RCS thruster, then you'd want 1 valve per RCS thruster and 4 valves in the main chamber. If flow is 8 times higher, then you'd use 8 valves in the main chamber, and so forth. 

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Also, do you use MS Paint for your diagrams? 

Yeah, it's fast. I can do more complicated stuff but for this kind of thing, it's hard to beat MS Paint for speed.

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So, I guess the basic design is a 4-core design, with 3 strap-ons and 1 sustainer, possibly with a solid kick motor for final orbital insertion. This configuration seems ideal. We could use differential throttling for control until strap-on jettison, at which point we could start using the HTP monopropellant RCS system.

I'm also thinking, in the event of a kick motor, an RCS system would take up a lot of mass. How feasible would a system of reaction wheels be? After all, with a ~3kg payload, the kick motor could be quite small. Since the motor only needs to be used for a short period of time, de-spinning the wheels would not be necessary. The wheels themselves wouldn't need to be that big, given the low mass of the motor+payload. Also, we could orient the craft to release the payload facing a certain way, if necessary.

Ehh, I don't know. Reaction wheels are expensive, heavy, and require rather complex electronic controls. Better to use the last puffs of HTP in the terminal hybrid stage to spin up just before separation. Spin-stabilization works well enough.

I'm not confident that a 4-core design would be enough to get to orbit, but I'll see.

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Another thing, as per @sevenperforce's idea of having the HTP tank integrated into what would be the combustion chamber, what type of length reduction and diameter increase are we looking at? Decreased length always is a good thing, obviously, but a wider rocket body of course means more drag.  

Fineness ratio is really important for small launch vehicles. We want it to be as narrow as possible without running into bending-moment problems.

Just how narrow we can get is going to depend on how thick the HTP tank walls will need to be. That, in turn, will depend on what kind of combustion pressures we are dealing with. Recall that the head pressure in the HTP tank needs to be higher than combustion pressure all the way to burnout; that's the challenge with pressure-fed rockets. By PV=nRT, the ratio of pressurant volume to total tank volume must be equal to the ratio of liftoff pressure to combustion pressure, since the pressurant will need to expand to fill the whole tank. So this means the HTP tank walls need to be thick enough to contain that kind of pressure. You want a large diameter so that you maximize tank volume for a given tank wall area, but not so large that your fineness ratio drops too low.

(I wish there was a way to decompose a small flow of the HTP inside the tank in order to maintain tank pressure, as this would mean the tank would only need to hold slightly higher pressures than the combustion region rather than 5-10x greater, but I can't think of a way to do it. HTP decomposition is heat-catalyzed; if one gram of HTP decomposes inside the tank, the whole tank instantly decomposes. I suppose you could try to do something with liquid nitrogen to keep the tank temperature low enough to prevent runaway decomposition but that seems ridiculously complicated and rather heavy.)

Edited July 10, 2017 by sevenperforce

[Steel]

1 hour ago, mikegarrison said:

To my point, however, the video claims that is the world record for altitude of a "student" hybrid rocket. Not an "amateur" rocket of any kind.

"Student" is a somewhat ambiguous term, but it can be generally understood to mean people enrolled in a formal school. "Amateur", on the other hand, is a term that has been abused in many fields but typically means "not professional" or "not being paid to do the work". One could argue that SpaceX, for instance, is professional because they are paid by others to provide launches, but Spaceship One was amateur. However, the distinction is fuzzy. The people who actually built Spaceship One were professionals. But the people who build sailboats for amateur boat racing are usually professionals too, and yet we still consider the racing itself to be amateur.

So as I suggested, you mean "underfunded".

I think in most fields these days (and in pretty much every sport) an amateur is someone who is not employed full-time to do whatever it is they're an amateur at. To qualify as an amateur rocket (at least in my eyes) everyone working on it is doing it outside of an employment setting. Thus, SpaceX, whoever did SpaceshipOne (was it Scaled Composites?), Blue Origin e.t.c are all professional rocketeers because there were paid engineers working on them.

Your sailboat analogy doesn't quite work, because equally the baseball bats used by amateur players are made by professionals, but they are still amateur players. In rocketry, the rocket is "the player" in a sense, rather than the tool used by the player (like a sailboat or a baseball bat).

Edited July 10, 2017 by Steel