Amateur rocket to orbit

[sevenperforce]

I wish there was some way to incorporate "orbital" or "orbit" into the name, to underscore that we are targeting LEO and not just suborbital flight.

25 minutes ago, zeta function said:

10% throttling is pretty low (on the core stage)... How are you planning to do that?

Hybrid rockets downthrottle somewhat more easily than bipropellant liquid rockets, but you're right, this is one of the factors that needs to be evaluated. Downthrottling too far may reduce chamber pressure and decrease specific impulse, even if it doesn't choke at the nozzle. This is one of the independent variables that can be altered to a point, but we need to watch carefully.

If we say the minimum throttle is 20% rather than 10%, then total dV (on that initial spreadsheet) drops from 7,130 m/s to 7,118 m/s. So it's not a huge difference. A lot of this is fine-tuning.

If we run into some more advantageous numbers along the way, you can get up over 8 km/s easily even without increasing stage radius. For example, if we use average isp rather than initial isp, if total aerodynamic drag is only 580 m/s, volumetric efficiency goes up to 0.7, White Lightning's propellant fraction goes up to 85%, and we kick naked-stage TWR up to 9, then we end up at 8,028 m/s on a standard 22-cm stage. In contrast, if the fixed independent variables turn out poorly, it gets difficult. If aerodrag is closer to 700 m/s, volumetric efficiency is no better than HEROS-3, White Lightning prop fraction is only 70%, the hybrid's isp is 300/240, and we can only manage a naked-stage TWR of 6, then we'd need each stage to be a full 85% wider to hit 7.8 km/s.

37 minutes ago, TheEpicSquared said:

@sevenperforce Your idea seems quite complex. What if the air-tight chamber isn't air-tight? What if the spring fails? What if the clamps themselves fail? It looks like there are too many failure points, IMO. A few simple explosive bolts with a spring up top seems more reliable.

I think we need to figure out the booster sep mechanism. As you all know, I'm in support of conventional explosive bolts, with a compressed spring up top to push it and the booster away. It's simple, it's been tried and tested, and it should be reliable. 

Pyrotechnic bolts are probably easy enough to self-manufacture. Seems viable to me.

37 minutes ago, TheEpicSquared said:

 

@sevenperforce That's one awesome spreadsheet! I, for one, would love playing around with it. Maybe transfer it to google sheets and upload it that way? And yeah, 10% throttle seems pretty low... 

All right, anyone who wants it -- here you go! Your mileage may vary. Any improvements welcome, and if you find any errors in my formulas, more power to you!

[Steel]

23 minutes ago, sevenperforce said:

 

If we say the minimum throttle is 20% rather than 10%, then total dV (on that initial spreadsheet) drops from 7,130 m/s to 7,118 m/s. So it's not a huge difference. A lot of this is fine-tuning.

I'd say maybe closer to 40% or 50% if we're being realistic. Specialist rocket motor manufacturers can get about 10% minimum with motors specifically designed for deep throttle capability. I highly doubt an amateur designed and produced motor, designed mainly for ease of manufacture and potential reusability, would be able to get anywhere near that, especially in it's first few iterations. Moreover, due to the limited control hardware that will be onboard, the monitoring and fine control to get reliable deep throttling is probably not attainable. I would do the calculation assuming 50% minimum throttle to be on the safe side, then any improvements over this are a bonus.

Also bear in mind that the thrust of a motor does not vary linearly with throttle setting.

Edited July 13, 2017 by Steel

[sevenperforce]

4 minutes ago, Steel said:

I'd say maybe closer to 40% or 50% if we're being realistic. Specialist rocket motor manufacturers can get about 10% minimum with motors specifically designed for deep throttle capability. I highly doubt an amateur designed and produced motor, designed mainly for ease of manufacture and potential reusability, would be able to get anywhere near that, especially in it's first few iterations. Moreover, due to the limited control hardware that will be onboard, the monitoring and fine control to get reliable deep throttling is probably not attainable. I would do the calculation assuming 50% minimum throttle to be on the safe side, then any improvements over this are a bonus.

Also bear in mind that the thrust of a motor does not vary linearly with throttle setting.

Well, linearity of thrust to throttle setting can be handled via software, so that's not a problem. And while I concede your point about deep throttling, the unattainability of the 10% minimum is more a factor of combustion instability in liquid-fueled engines. Hybrids are, by design, able to handle a wider throttle range. But for conservatism, I'll set 40% as the minimum, and see where things go.

[kurja]

Isn't exhaust velocity (and thus delta v per fuel unit) reduced when throttling down? I'd assume thrust per fuel unit spent to be almost nil if oxidizer flow is throttled down to only 10% of what is presumably ideal for the engine.

 

[Steel]

31 minutes ago, kurja said:

Isn't exhaust velocity (and thus delta v per fuel unit) reduced when throttling down? I'd assume thrust per fuel unit spent to be almost nil if oxidizer flow is throttled down to only 10% of what is presumably ideal for the engine.

 

Ideally, as long as there's choking at the throat of the nozzle you should get the same exhaust velocity (in practice you'd probably see a small decrease), you're just getting a greatly reduced mass flow rate.

Edit: originally in the above I stated "as long as there's no choking at the throat" but in fact choked flow is of course required in a de Laval nozzle.

Edited July 13, 2017 by Steel

[sevenperforce]

If you set minimum throttle at 40% thrust and calculate ascent phase dV based on average isp rather than start isp, then you can get to 7800 m/s at a 13% diameter increase and a naked-stage TWR uprating to 9:1. This does require that you launch with the core at 40% and the second booster pair at 68% thrust, and throttle the latter down to 40% as well after just 8 seconds, though the higher thrust rating means takeoff thrust is still over 4.5:1.

14 minutes ago, Steel said:

Ideally, as long as there's no choking at the throat of the nozzle you should get the same exhaust velocity (in practice you'd probably see a small decrease), you're just getting a greatly reduced mass flow rate.

Precisely.

Edited July 13, 2017 by sevenperforce

[Vanamonde]

Some posts have been trimmed from this thread. Keep the discussions on-topic, please. 

[qzgy]

At the moment, are we going to assume we have infinitely variable throttle control? I'm a bit unsure...

[Steel]

2 hours ago, qzgy said:

At the moment, are we going to assume we have infinitely variable throttle control? I'm a bit unsure...

That's also a good point. To have fine throttle control you're going to need to have an entire computer in order to constantly monitor chamber pressures and propellant pressures simultaneously across all (is is 8 first stage engines now?) engines, making adjustments to valves if necessary, as well as the ability to throttle the whole stack independently of the ideal throttle position in case one or more engines run in instability. On this note, you also need some pretty expensive micro-adjustable valves.

What might be more realistic is for each engine to have two, three or maybe four pre-determined throttle settings (maybe 100%, 80%, 60% and then minimum, whatever that may be). This way, the valve settings can be pre-determined on a test stand as well as the way to get between each setting controllably.

Edited July 14, 2017 by Steel

[TheEpicSquared]

@Steel I think we're hoping for a 5 stick design (4 strap-ons and 1 core), but if that doesn't have enough Dv we are thinking of an 8 stick design (4 strap-ons and a quad-stick core). And I agree that it would be simpler to have pre-determined throttle settings. Maybe those could be deduced through testing. But does a micro-adjustable valve really cost that much? I searched "micro-adjustable valve" on google and a site came up selling a 5-pack for just $3.49. Granted, those are meant for garden sprinklers, but still...

When looking at @sevenperforce's spreadsheet (just the images posted, I haven't had time to download it yet), it looks like somewhere around 8km/s of Dv is the max, with favorable drag and gravity losses, fuel fractions, etc. If we can't find a way to optimize the design, a quad-stick core design seems the most viable. However, I'll  download the spreadsheet when I can and play around with it.

[Steel]

13 minutes ago, TheEpicSquared said:

@Steel I think we're hoping for a 5 stick design (4 strap-ons and 1 core), but if that doesn't have enough Dv we are thinking of an 8 stick design (4 strap-ons and a quad-stick core). And I agree that it would be simpler to have pre-determined throttle settings. Maybe those could be deduced through testing. But does a micro-adjustable valve really cost that much? I searched "micro-adjustable valve" on google and a site came up selling a 5-pack for just $3.49. Granted, those are meant for garden sprinklers, but still...

Unfortunately there's a big difference between a micro-adjustable valve for low pressure garden sprinklers and a computer-controlled micro-adjustable valve for a high pressure HTP system. For the former "micro-adjustable" just means the ability to have a few more positions than just on or off. For the latter it means the ability to make minute adjustments to carefully control the flow. Also because you're working with gas (and high pressure gas at that) the precision of manufacture and the quality of seals e.t.c has to be orders of magnitude higher.

Edited July 14, 2017 by Steel

[Hesp]

Just a quick note regarding HTP...

Propellant-grade hydrogen peroxide is available to qualified buyers. In typical circumstances, this chemical is sold only to companies or government institutions that have the ability to properly handle and utilize the material.

Maybe I missed in the discussion HOW you plan to retrieve, store and handle fuels and oxidizers, but anything good enough to fuel an hybrid rocket is equally good enough to make a bomb.

[DerekL1963]

4 hours ago, Hesp said:

Just a quick note regarding HTP...

Propellant-grade hydrogen peroxide is available to qualified buyers. In typical circumstances, this chemical is sold only to companies or government institutions that have the ability to properly handle and utilize the material.

Maybe I missed in the discussion HOW you plan to retrieve, store and handle fuels and oxidizers, but anything good enough to fuel an hybrid rocket is equally good enough to make a bomb.

I'm on a private [very serious] amatuer rocketry mailing list (I.E. actual builders and operators) and the difficulty of obtaining HTP is a frequent topic of discussion, to the point where no design that uses it is regarded as viable.

[wumpus]

30 minutes ago, DerekL1963 said:

I'm on a private [very serious] amatuer rocketry mailing list (I.E. actual builders and operators) and the difficulty of obtaining HTP is a frequent topic of discussion, to the point where no design that uses it is regarded as viable.

I'm curious to know if enough would be available to use as an igniter.  The whole engine appears to be designed in such a way as you could replace the N₂ with NO₂ and simply remove the HTP.  You would still need an igniter, where HTP would work.  This becomes even more important in the second stage where air ignition would likely be a big deal.

Are "launch clamps" viable in amatuer rocketry?  I'd expect them to be built around explosive bolts holding the thing down, but it would reduce most of the ignition issues of the first stage.

[zeta function]

Hydrogen peroxide is synthesis-able using the anthraquinone process. It might be doable at home. Or one could heat hydrogen peroxide (low concentration, from medicine stuff) to 105 degrees Celsius to let the water boil off.

[sevenperforce]

3 hours ago, Steel said:

That's also a good point. To have fine throttle control you're going to need to have an entire computer in order to constantly monitor chamber pressures and propellant pressures simultaneously across all (is is 8 first stage engines now?) engines, making adjustments to valves if necessary, as well as the ability to throttle the whole stack independently of the ideal throttle position in case one or more engines run in instability. On this note, you also need some pretty expensive micro-adjustable valves.

What might be more realistic is for each engine to have two, three or maybe four pre-determined throttle settings (maybe 100%, 80%, 60% and then minimum, whatever that may be). This way, the valve settings can be pre-determined on a test stand as well as the way to get between each setting controllably.

These are definitely all elements that need to be determined (or at least examined) during the planning phases, because it's something we can figure out and incorporate into whatever we post/publish.

From a sampling perspective, virtually everything we need to know can be determined by sampling HTP tank head pressure and napalm column head pressure in conjunction with onboard telemetry to that point. In fact, we could even write the control program now. But there are things that need to be considered: not just throttle fineness, but throttle response time. It's fine if our throttle can't make fine adjustments, because we can just vary the throttle setting in pulses, as long as throttle response time is rapid enough. We don't want to be stuck with a throttle that takes a second or two to move between positions.

It would be nice if we could get away from differential throttling entirely, but we simply can't. There will always be slight inconsistencies in burn time, and with any sort of clustering (or parallel staging, as we are using), those inconsistencies make fire-and-forget LVs wholly unrealizable.

3 hours ago, TheEpicSquared said:

@Steel I think we're hoping for a 5 stick design (4 strap-ons and 1 core), but if that doesn't have enough Dv we are thinking of an 8 stick design (4 strap-ons and a quad-stick core). And I agree that it would be simpler to have pre-determined throttle settings. Maybe those could be deduced through testing. But does a micro-adjustable valve really cost that much? I searched "micro-adjustable valve" on google and a site came up selling a 5-pack for just $3.49. Granted, those are meant for garden sprinklers, but still...

Not only do we need high-pressure, high-sensitivity valves, but they have to be capable of electronic control. This is an additional research and investigation topic; how do we control the valves? Do they have individual batteries that receive adjustment signals over a small wire, or do they receive power through a larger carrier wire that provides signals? Is the temperature and pressure well within allowances for the valve, the valve control mechanism, and the wiring? 

What if a valve fails mid-flight? Do we use redundant valves? Is it more likely to fail-open or fail-closed? Are any valve failures recoverable?

3 hours ago, TheEpicSquared said:

When looking at @sevenperforce's spreadsheet (just the images posted, I haven't had time to download it yet), it looks like somewhere around 8km/s of Dv is the max, with favorable drag and gravity losses, fuel fractions, etc. If we can't find a way to optimize the design, a quad-stick core design seems the most viable. However, I'll  download the spreadsheet when I can and play around with it.

Oh, 8 km/s is by no means the maximum; that's just the target I was aiming for. Remember that I've already accounted for aerodrag, gravity drag, and isp losses, so 8 km/s should be plenty to get to orbit. And you can simply increase stage diameter to pretty much instantly add as much dV as you need. Of course, that only holds true up to a point; once you go too thick, the drag assessment is no longer valid. I would have tied the drag number to fineness ratio if I had a good way to model the drag coefficient, but I don't, not for a clustered arrangement. Anyway, if you use slightly more generous assumptions then you can push up to nearly 9 km/s with only a 5% increase in stage diameter:

5 hours ago, Hesp said:

Just a quick note regarding HTP...

Propellant-grade hydrogen peroxide is available to qualified buyers. In typical circumstances, this chemical is sold only to companies or government institutions that have the ability to properly handle and utilize the material.

Maybe I missed in the discussion HOW you plan to retrieve, store and handle fuels and oxidizers, but anything good enough to fuel an hybrid rocket is equally good enough to make a bomb.

This is something else which absolutely must be incorporated into our whitepaper or whatever it is we publish. Ideally, we need to be able to project a reasonably accurate budget for launching an amateur orbital rocket. There are two options for getting HTP: purchasing medical-grade peroxide and concentrating it ourselves with a fairly simple distillation lab setup, or purchasing it at a premium. In either case, there will be some degree of paperwork and permitting, both for handling and the actual launch.

Fortunately, HTP isn't actually good for making real bombs, so that's a bit less of a problem. And while napalm is obviously very nasty stuff, precursors are all available without any special permitting (though, again, we'll want to figure out the necessary steps to avoid visits from the BATF).

1 hour ago, wumpus said:

I'm curious to know if enough would be available to use as an igniter.  The whole engine appears to be designed in such a way as you could replace the N₂ with NO₂ and simply remove the HTP.  You would still need an igniter, where HTP would work.  This becomes even more important in the second stage where air ignition would likely be a big deal.

Are "launch clamps" viable in amatuer rocketry?  I'd expect them to be built around explosive bolts holding the thing down, but it would reduce most of the ignition issues of the first stage.

N₂O's specific impulse is far, far too poor. 

Launch clamps shouldn't be a problem.

 

46 minutes ago, zeta function said:

1 hour ago, DerekL1963 said:

I'm on a private [very serious] amatuer rocketry mailing list (I.E. actual builders and operators) and the difficulty of obtaining HTP is a frequent topic of discussion, to the point where no design that uses it is regarded as viable.

Hydrogen peroxide is synthesis-able using the anthraquinone process. It might be doable at home. Or one could heat hydrogen peroxide (low concentration, from medicine stuff) to 105 degrees Celsius to let the water boil off.

This is something we can discuss at length in our whitepaper. One possible route would be to synthesize or distill peroxide "by hand", to a high enough concentration for single-stage flight testing, and then use the positive press from that to help with some of the hurdles in getting large quantities of the high-purity stuff.

[Hesp]

2 hours ago, sevenperforce said:

This is something else which absolutely must be incorporated into our whitepaper or whatever it is we publish. Ideally, we need to be able to project a reasonably accurate budget for launching an amateur orbital rocket. There are two options for getting HTP: purchasing medical-grade peroxide and concentrating it ourselves with a fairly simple distillation lab setup, or purchasing it at a premium. In either case, there will be some degree of paperwork and permitting, both for handling and the actual launch.

Right now the highest grade peroxide I can order online is a 35% solution, at about 10€/liter. You make things too easy, hot peroxide vapours are explosive and that distillation lab setup, although feasible, is very far from the "amateur" concept. Especially for the quantities needed.

Quote

Fortunately, HTP isn't actually good for making real bombs, so that's a bit less of a problem. And while napalm is obviously very nasty stuff, precursors are all available without any special permitting (though, again, we'll want to figure out the necessary steps to avoid visits from the BATF).

TATP , quite popular these days. And it's doable with hair bleach grade peroxide.

I bet you'll raise more than an eyebrow buying truckloads of H2O2 (any useful grade)

[TheEpicSquared]

About the HTP issue. Whoever ends up doing this (if anyone) obviously have to get permission from the government, and clearly state their intentions: building and launching a PEACEFUL (i.e. not intentionally hostile to anyone) rocket into orbit. I'd say that they would have a little bit of wiggle room if an entity as large as a national government allowed them to push forward with this project. And I wouldn't be surprised if they got regular visits from organizations like the FBI and equivalents to make sure everything was going according to plan. Hell, the FBI checks in when farmers order large amounts of fertilizer to make sure they're not up to something, so I'd say that whoever does this (if anyone) should expect visits from the authorities frequently. 

With the correct licensing (which will be a pain in the backside to get), it should be doable.

[sevenperforce]

@Hesp

Yeah, like @TheEpicSquared said, this is an entirely aboveboard operation. There's no intention of not raising eyebrows. All the intricacies of licensing and permitting would need to be included in our whitepaper.

Thankfully I have a legal background (and career) in addition to my physics degree, so I can probably take care of all that research.

[DerekL1963]

11 hours ago, zeta function said:

Hydrogen peroxide is synthesis-able using the anthraquinone process. It might be doable at home. Or one could heat hydrogen peroxide (low concentration, from medicine stuff) to 105 degrees Celsius to let the water boil off.

Both are very good ways of blowing yourself up.  While HTP isn't good for building actual bombs, it's still dangerous stuff and not very tolerant of mishandling.  There's a reason why it's not sold in quantity except to "companies or government institutions that have the ability to properly handle and utilize the material".  "Not good for building bombs" != "safe to handle".
 

10 hours ago, sevenperforce said:

And while napalm is obviously very nasty stuff, precursors are all available without any special permitting (though, again, we'll want to figure out the necessary steps to avoid visits from the BATF).

Not just the BATF, but state, county, and possibly municipal authorities will take an interest as well.

[magnemoe]

16 hours ago, DerekL1963 said:

Both are very good ways of blowing yourself up.  While HTP isn't good for building actual bombs, it's still dangerous stuff and not very tolerant of mishandling.  There's a reason why it's not sold in quantity except to "companies or government institutions that have the ability to properly handle and utilize the material".  "Not good for building bombs" != "safe to handle".
 

Not just the BATF, but state, county, and possibly municipal authorities will take an interest as well.

You can make napalm out of gasoline and detergent, its not quite as good as the real stuff but should work well enough. This has been in infantry handbooks for generations.
LOX is pretty common and also very dangerous. 
 

[TheEpicSquared]

58 minutes ago, magnemoe said:

LOX is pretty common and also very dangerous. 
 

Which is why it was ruled out in favor of HTP.  

[qzgy]

2 hours ago, TheEpicSquared said:

Which is why it was ruled out in favor of HTP.  

Which itself is quite dangerous. But less so than LOX. Also less annoying to work with.

[sevenperforce]

3 hours ago, qzgy said:

Which itself is quite dangerous. But less so than LOX. Also less annoying to work with.

I suppose it's a tossup as to which is more dangerous, LOX or HTP. But HTP is much easier to work with, as far as equipment and handling expenses are concerned.

[sevenperforce]

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