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Orbital rockets are now easy, page 2: solid-rockets for cube-sats.


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6 hours ago, Exoscientist said:

These were using liquid-fueled rockets though, which are more complicated than simple solid rocket motors. I'm suggesting using essentially "off-the-shelf" high power solid motors such a low cost, small payload rocket can be produced.

 

  Bob Clark

So, something like OTRAG but with model rockets ?

I'd be interested to see Estes becoming a major aerospace company. Bring it on !

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8 hours ago, Steel said:

The complication here is that what you're actually advocating is essentially "gluing" four of these off the shelf motors together to make one larger one. This is not exactly a well known procedure, and I'm not entirely sure how reliable the end product is going to be, after all, for a solid rocket you want a reasonable uniform and continuous burn surface and the seams between these motors would be a big question mark. Just because one motor will work does not automatically mean that four stuck together will.

If you have any performance data from these rockets, it shouldn't be a terribly big deal (although vibration data might be much harder to get).  My kerbal instincts would be to tie them together and simply fire the bottom stack for testing (and this is exactly what NASA did in the early years), but since it is the first stage I'm guessing it would blow your budget.  The next best test would be to find the biggest model rocket engines you can find (the pinned "amature orbital thread" includes a few links to potential large model rocket engines, but there really wouldn't be any need for high Isp for a first stage test - you would just add more ballast to simulate higher stages) and see if fins can keep it stable.

I'd doubt trying to mix spin stabilization and active aero controls will work , but would at least try an exhaustive literature search and more than a little simulation.  Those are likely the easiest tools to stabilize this sort of thing.

I really think that tying a set of "D-type" model rocket engines will tell you a lot more about what will happen than an equal time spend analyzing the final design.  Of course, that isn't claiming that the scaling factors of such tiny things are remotely accurate, just that the full-scale analysis is that hard.  I'd want to have fully controlled 1/10th (or higher if their are off the shelf engines available) scale models before I was confident that this design would work (Ideally I'd launch with full scale and dummy upper stages, but the cost might be prohibitive).

[edit: looks like people have made it here and given up.  Presumably you either need larger carbon-contained SRBs or more reliable manufacturing.  Judging by the "SRBs explode" comments that fill shuttle-bashing threads, I expect that "reliable manufacturing" of SRBs is an unsolved problem that has an absolute ton of money already thrown at it (US ICBM manufacture).]

13 hours ago, DerekL1963 said:

Radio guidance requires a functional and fairly accurate radar - still a complex piece of precision equipment.

Depends on the accuracy.  While RADAR can supply mm and below accuracy, FM radio runs in the meter range.  All you really need is to measure the phase difference between signals producing nothing but carrier signals.  I'm having trouble seeing what type of guidance super strypi had: Wiki claims "SPARK also known as strypi" uses spin stabilization (no guidance) on stage 1, and guidance on stages 2-3, another (not configured) website leaves a search blurb claiming "no complex guidance".

I'd recommend avoiding overthinking the guidance (unless you are strapping multiple rockets together horizontally as the OP claims is "easy", then you have real guidance/stabilization issues).  Another problem with complex guidance is ITAR rules: not only do US regulators take potential missile development seriously, doing so while North Korea is likely shopping around for missile improvements seems especially iffy.

Edited by wumpus
looks like people have tested OPs idea and it doesn't work.
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44 minutes ago, wumpus said:

Depends on the accuracy.  While RADAR can supply mm and below accuracy, FM radio runs in the meter range.  All you really need is to measure the phase difference between signals producing nothing but carrier signals.

Nope.  Because all phase difference (doppler) provides you is instantaneous velocity along line-of-sight.  That's insufficient to determine vehicle velocity or deviation from the (planned) flight path.    

Nor does it provide the vehicle with an attitude reference.(How can it yaw left to return to the desired flight path if it doesn't know where the yaw plane is and which direction is left?)

 

49 minutes ago, wumpus said:

Another problem with complex guidance is ITAR rules


ITAR is only a problem if the design information or the hardware crosses international boundaries.

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15 hours ago, Kryten said:

Project pilot attempted to produce an orbital vehicle by attaching OTS motors together like this; it did not go well. Most either exploded or suffered catastrophic structural failure.

 I hadn't heard of that one before. Do you have a reference?

 

16 hours ago, YNM said:

So, something like OTRAG but with model rockets ?

I'd be interested to see Estes becoming a major aerospace company. Bring it on !

 

 These ain't your "Estes size" solid motors bud:

sDSC_0831-2.jpg

http://www.nar.org/high-power-rocketry-info/

 

  Bob Clark

Edited by Exoscientist
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57 minutes ago, Exoscientist said:

These ain't your "Estes size" solid motors bud:

 

http://www.nar.org/high-power-rocketry-info/

 

  Bob Clark

Well, the higher you move up the power rating, the less available they are. Which means, again, it's either OTRAG-like and still isn't exactly off-the-shelf, or completely off-the-shelf but impractical, or you'll be a professional at that point.

Edited by YNM
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21 hours ago, Steel said:

The ones listed on the blog are 8kN of thrust each motor, so they're pretty much as big as you'd ever need. http://www.pro38.com/products/pro150/pro150.php

Ah.  Now I understand what the OP was saying, and it is an interesting possibility.  The data I saw didn't go into vibrations, variations, nor anything you might need to even stabilize a single engine.  Their stabilization solution was "launch at 5g or more", something that in KSP will quickly lock the rocket in position and remove all instability (including all player control).  I have if KSP is being remotely accurate, but I assume this works for their models.

If you wanted a cluster of lower stages, I'd recommend welding a bunch of steel-tubed lower engines together along with some means of dampening any vibration harmonics thus created (unless you really wanted aluminum and were willing to deal with the welding requirements).  I don't think anyone has mentioned the necessity of launch clamps (that can take >6g thrust, natch), something I've never heard of on amature rocket design.  Not to mention launchpad issues with >6g thrust pouring out until you release the clamps.

Using carbon pressure containers and single engines outside the atmosphere appear to reduce the problem as much as possible (although guidance is still an issue.  Possibly as much an ITAR/legal one as a physical/technical one).  I'd assume at least a third stage (mostly a scaled down second stage, or more likely vice versa) especially with the heavy subsystem a cluster might require.

I'd expect that a cluster of SRBs shouldn't have the same issues of liquid clusters: they aren't high precision equipment and as long as their steel pressure containers don't shake apart should continue functioning fine.  Of course, stabilization is much more of an issue (any guesses how well spin stabilization works against having different thrusts offset from your center of mass?).  Even if the "launch over 5g" does wonders for the stabilization, that really sounds like a solution for sounding rockets.  Getting a rocket to follow a proper pitchover ("gravity turn" to KSP players) at 5g (presumably the thrust decreases as mass decreases, I didn't see any options mentioned or such things on the faq) is likely impossible (that's the whole point of the acceleration: to keep the thing in a straight line).  The second stage may require a wildly more complicated guidance system to pull off a "KSP pre-release souposphere" move to fly horizontally as it flies out of the atmosphere.

- Note: I'm not a mechanical or aeronautical engineer and my gut feeling is not only likely wrong in the above, it sounds like there is plenty of experimental data to conclude that SRB clusters are a bad idea.  Unfortunately since such things are pretty much all "null data", I'm not sure how much of them are published (I'd expect to see them in abandoned 'in progress' rocket blogs if anywhere).

While the whole cluster idea appears highly controversial, I suspect the replacement SRB core in a 'lightweight [carbon] pressure container' idea might be a great one.  In the "amature thread to orbit", the final stage is a "SRB kicker", which seems to be an afterthought.  Multiple (single engine per stage) stages made this way could replace the "kicker" and greatly reduce the rest of the delta-v needed.  Although adding high thrust SRBs at the first stage to increase thrust (while using pressure fed liquid rockets for guidance) might be appealing, it also looks like burnout and release give far too many ways to destroy such a rocket.

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On 8/29/2017 at 1:55 PM, MaverickSawyer said:

Regarding Super Strypi, the failure was due to an improperly manufactured motor casing that burned through, not any flaw in the concept.

 

 This indicates even with "small" launchers the development costs are so high that even with an easily correctable defect, there is no scheduled retest of the concept.

   Bob Clark

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 It's remarkable what some amateurs groups have done in high powered rocketry. For instance, In this video at about the 7:15 point is discussed a rocket built by high school students under the supervision of professional rocket engineers consisting of two stages and a clustered first stage:


Amateur Rocketeers Reach For The Stars - KQED QUEST.


 Their rocket reached Mach 2.8 and 100,000 feet altitude.

 And this amateur group built a rocket that crossed the Karman line of space of 100 km altitude:

DIY Rocket Fly Into Space - Amateur High Power Solid Model Rocket Launch to Space.

 

  Bob Clark

Edited by Exoscientist
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8 hours ago, DerekL1963 said:

Which means it had, what, 1/16th of the energy needed to get a couple of grams to orbit?  Impressive but irrelevant.

Only 30 more stages and 256 times the size needed (for the new first stage).  Scale her right up!

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6 hours ago, DerekL1963 said:

Which means it had, what, 1/16th of the energy needed to get a couple of grams to orbit?  Impressive but irrelevant.

 As an educator I loved that segment in the "Amateur Rocketeers Reach For The Stars - KQED QUEST" video dealing with the high school students building their own rocket. The professional engineers who founded this program instructing high school students in rocketry deserve great kudos for inspiring interest in STEM fields in young people.

 I'm suggesting that the rockets that can be possible for young people under professional supervision to build extends to orbital rockets. But then Robert Heinlein has said, once you reach orbit you're halfway to anywhere. So it would also be possible for them to build cubesat-based planetary missions. Imagine the enthusiasm for science generated among young people who built their own planetary orbiters and landers.

  But beyond that there are technical reasons why it is important that such high altitude rockets can be built by amateurs. Elon Musk has said the cost of the first stage is 3/4ths the cost of the Falcon 9. And this is the case in general that the first, booster stage makes up the largest bulk of the cost. So finding the cost that amateurs spent in constructing these high altitude rockets gives a good way of estimating the full cost of the launch system.

 Also, one of the questions raised about this solid rocket proposal for an orbital rocket is the fact that the solids used have a quite high thrust/weight ratio, in the range of 25 to 1, while orbital rockets typically have a T/W ratio in the range only about 1.2 or so. The high T/W ratio for the solid would mean it would reach high speed while still in the dense, lower part of the atmosphere. On top of that also smaller rockets generate more drag than larger rockets. These two facts mean this rocket would generate significantly more air drag than standard orbital rockets. The solid rocket though would have the advantage that the gravity drag would be reduced. Accurate trajectory simulations need to be done to see how these two competing effects would effect the final delta-v of the rocket.

 Therefore the fact the amateur built rockets even with the high T/W solids can reach high altitude of 100,000+ feet suggests that the remaining stages, at greatly reduced air density of 1% or less of sea level, could attain the required delta-v for orbit.

   Bob Clark

 

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3 hours ago, Exoscientist said:

So finding the cost that amateurs spent in constructing these high altitude rockets gives a good way of estimating the full cost of the launch system.

In the same way that finding the cost of a soap box derby racer is useful estimating the full cost of an F1 racer.  I.E. there are no words in the English language to describe how ludicrous it is to suggest such a thing.  Apples and the thing least like apples you can imagine doesn't even begin to describe the gap.
 

3 hours ago, Exoscientist said:

 Therefore the fact the amateur built rockets even with the high T/W solids can reach high altitude of 100,000+ feet suggests that the remaining stages, at greatly reduced air density of 1% or less of sea level, could attain the required delta-v for orbit.


Other than the fact that amateur built rockets of that class don't have even a fraction of percent of the performance required.  Again, you're extrapolating to a ludicrous degree.

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2 hours ago, DerekL1963 said:

In the same way that finding the cost of a soap box derby racer is useful estimating the full cost of an F1 racer.  I.E. there are no words in the English language to describe how ludicrous it is to suggest such a thing.  Apples and the thing least like apples you can imagine doesn't even begin to describe the gap.

Other than the fact that amateur built rockets of that class don't have even a fraction of percent of the performance required.  Again, you're extrapolating to a ludicrous degree.

 

 It's the same type of construction of the lower stages and the upper stages. It's a general principle that the first stage makes up the bulk of the size and cost of a launcher that's true across very different kinds of launchers.

 

7 hours ago, wumpus said:

Only 30 more stages and 256 times the size needed (for the new first stage).  Scale her right up!

 With staging for orbital rockets, the upper stages are a fraction of the size of the first stage, so you wouldn't multiply the size of the first stage to get the size of the full rocket.

  Bob Clark

Edited by Exoscientist
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18 hours ago, Exoscientist said:

 With staging for orbital rockets, the upper stages are a fraction of the size of the first stage, so you wouldn't multiply the size of the first stage to get the size of the full rocket.

  Bob Clark

While the upper stages are a fraction of the size, they can thus only deliver a fraction of the payload.  So twice the size, 1/256 the payload.  I'm guessing you want a raspberry pi and enough radio circuits to manage a sputnik-style "beep" from space.  When it doubt, cut down the computer.

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On 8/29/2017 at 1:55 PM, MaverickSawyer said:

Regarding Super Strypi, the failure was due to an improperly manufactured motor casing that burned through, not any flaw in the concept.

I keep seeing the words “easy” and “simple.”

This exemplifies exactly why it’s hard. Engineering is hard, especially when it's on the cutting edge of what is possible, like rocket engineering.

Sure. The concept is easy. So is running the marathon under two hours: just keep putting one foot in front of the other, at a sufficient pace. Easy peasy lemon squeezy!

If you're ever wondering if something is truly easy, here's the litmus test for “easy:” is everyone doing it already?

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2 hours ago, Kerbart said:

I keep seeing the words “easy” and “simple.”

This exemplifies exactly why it’s hard. Engineering is hard, especially when it's on the cutting edge of what is possible, like rocket engineering.

Sure. The concept is easy. So is running the marathon under two hours: just keep putting one foot in front of the other, at a sufficient pace. Easy peasy lemon squeezy!

If you're ever wondering if something is truly easy, here's the litmus test for “easy:” is everyone doing it already?

^THIS^

There is absolutely nothing difficult about the rocket science behind making an orbital rocket from off the shelf components for $100,000. What is difficult is the engineering. That's why rocketry costs so much, because the hard bit is working out why the real world doesn't match what your calculations are telling you.

 

In the same way there is nothing fundamentally difficult about the rocket science behind making a cross-feed Falcon 9 Heavy. The engineering, on the other hand, is near impossible. See Elon on the matter:

Quote

And it ended up being way harder to do Falcon Heavy than we thought. Because at first it sounds really easy to just stick to first stages on as strap-on side boosters. But then everything changes. The loads change, the air dynamics totally change. You triple the vibration and acoustics. So you break the qualification levels and so much of the hardware. The amount of load you’re putting through that center core is crazy because you have two super powerful boosters also shoving that center core. So we had to redesign the whole center-core airframe on the Falcon 9 because it’s going to take so much load. And then you’ve got the separation systems... and, yeah, it just ended up being way way more difficult than we originally thought. We were pretty naive about that.

 

Edited by Steel
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2 hours ago, Steel said:

^THIS^

There is absolutely nothing difficult about the rocket science behind making an orbital rocket from off the shelf components for $100,000. What is difficult is the engineering. That's why rocketry costs so much, because the hard bit is working out why the real world doesn't match what your calculations are telling you.

In the same way there is nothing fundamentally difficult about the rocket science behind making a cross-feed Falcon 9 Heavy. The engineering, on the other hand, is near impossible. See Elon on the matter:

Minor nitpick that (hopefully) makes your point even more forcefully. That was Elon talking about the current iteration of Falcon Heavy without crossfeed. Adding crossfeed to the mix... well I'm guessing there's a reason (or more likely, many reasons) why they shelved that plan.

To paraphrase Tom Mueller:  "When you light those engines, about a thousand things could happen. One of those things is a successful launch."

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