Why can't amateur rockets reach space on an O motor?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

ali8bongo

Active Member
Joined
Dec 21, 2014
Messages
28
Reaction score
0
Hi
I have been doing research on sounding rockets used in the 60s and I found three of specific interest: Skua2, Petrel 1 and the INTA 100. All of them reached an apogee of 100Km using AP based propellants that provided less than 25KN of thrust. They used old technology, steel construction, have similar empty weights to what can be achieved today while using AP fuel which is readily available in O motor form. As O motors can provide anywhere between 20 and 40KN then surely a 40KN motor rocket if well designed could easily reach 100KM, yet I see very few O motor flights achieving an apogee of over 90,000ft. Why is this? Thanks :)
 
I am not an expert but I can point out that our recovery mechanisms add significant weight, which are likely unnecessary on those flights, and that there is much much more to thrust curves than total impulse.
 
Our motors are designed to existing standards; they are designed to be reusable; they are designed to be flown with different propellants; and they are designed to be especially safe. Our rockets are designed to use these standard motors and to be recovered and reusable.

Professional rockets, on the other hand, are usually designed for a specific purpose. The motor and the rest of the rocket are designed together and optimized as a single system for a specific purpose. The motors and rocket are not overly-designed for safety as ours are.

-- Roger
 
nasa:
_38804205_flagap300.jpg


us:
Ape-man-with-bone-from-Stanley-Kubricks-2001-A-Space-Odyssey.jpg
 
I considered these factors however they do not solve the conundrum. The reasons being that the empty weights that the sounding rockets had can be achieved using modern processes which eliminates the argument that the recovery system make the total empty weight higher than on the sounding rockets. Also surely if you are delivering the same amount of thrust over the same time frame with the result being an empty rocket of a comparable weight and aerodynamics; results achieved by these sounding rockets would be achievable? Thanks for the quick replies btw :)
 
The overall impulse may be the same, but the burn times typically are not. The Arcas, for example, was an endburning motor. Lots of heat, and expensive (and in some places asbestos) materials to deal with that heat. I've yet to find much info on the actual propellant, but I've heard there were other magic tricks in there, not just a simple endburning AP casting.

Almost all hobby motors have a relatively fast burn time.
 
The rockets I mentioned were dart sounding rockets so the idea was to get as much speed as quickly as possible with some of them reaching mach before they left the launch tower. For instance the SUPER LOKI had a burn time of 2.1 seconds and reached apogee (75km) in 120 seconds.
 
Ah....I was thinking of the longer 30 second burning ones. I revert to my ape (me) theory.
 
The overall impulse may be the same, but the burn times typically are not. The Arcas, for example, was an endburning motor. Lots of heat, and expensive (and in some places asbestos) materials to deal with that heat.

That reminds me of things I didn't mention. Costs are higher and technology is more advanced in the "real" rockets.

-- Roger
 
I understand that they might have better technology and slightly different propellants but surely as the fundamentals of what can be achieved today with an O class rocket and what was achieved with the sounding rockets should be the same.
If the same drag coefficient can be achieved, the same thrust can be achieved, the same burn time and rate can be achieved, the same full weight and empty weight can be achieved then surely the same apogee can be achieved?
 
Hi
I have been doing research on sounding rockets used in the 60s and I found three of specific interest: Skua2, Petrel 1 and the INTA 100. All of them reached an apogee of 100Km using AP based propellants that provided less than 25KN of thrust. They used old technology, steel construction, have similar empty weights to what can be achieved today while using AP fuel which is readily available in O motor form. As O motors can provide anywhere between 20 and 40KN then surely a 40KN motor rocket if well designed could easily reach 100KM, yet I see very few O motor flights achieving an apogee of over 90,000ft. Why is this? Thanks :)

It's not a question of thrust but more a question of impulse. What are the relative impulse ratings of the sounding rocket motors?


Sent from my iPhone using Rocketry Forum
 
I understand that they might have better technology and slightly different propellants but surely as the fundamentals of what can be achieved today with an O class rocket and what was achieved with the sounding rockets should be the same.
If the same drag coefficient can be achieved, the same thrust can be achieved, the same burn time and rate can be achieved, the same full weight and empty weight can be achieved then surely the same apogee can be achieved?

Same drag coefficient: It's hard without using steel components (fins).

Same thrust/burntimes: It's hard without using steel components (casings) and ridiculously expensive processing (wires in the propellant for endburners).

Same full weight and empty weight: We have parachutes. They have White Sands Missile Range and other deserted areas (ocean, for example) and don't need parachutes.


We're not allowed to use steel, and we have to use parachutes. "Old technology" it may be, but steel is less safe in case of a failure, so we're not allowed to use it.
 
If you want to make a Loki type rocket it would be single use but then nearly all high flying ones are.
The flight hardware would not be too bad as there are no casting or liner tubes, just short insulators at the ends.
The big cost would be the great long mandrill but it would be reused if the configuration stays the same.

As said above recovery weight is the performance killer. In the dart it no issue but a chute on the booster is wasted energy in getting to space. Since the goal is just to get there and not have a real payload like the Loki carried a smaller, meaning lighter, dart can be used. The 1 3/8 dart is ballpark 11 pounds, if a 7/8" dart could hold the required electronics there is 5 pounds that can be budgeted to booster recovery. So if a full O is used it may make it.

M
 
I understand that they might have better technology and slightly different propellants but surely as the fundamentals of what can be achieved today with an O class rocket and what was achieved with the sounding rockets should be the same.
If the same drag coefficient can be achieved, the same thrust can be achieved, the same burn time and rate can be achieved, the same full weight and empty weight can be achieved then surely the same apogee can be achieved?

It can be done. Emulating the performance of these devices isn't necessarily impossible but it involves designing to lower margins and doing lots of homework and testing. Most people want to go out and get flights in and don't necessarily care how high a rocket goes.

It also becomes painfully obvious that tracking and recovery - aspects that aren't really part of rocket design - become part of the flyer's responsibility and grow the scope of these projects to be quite large. Again, not impossible, but for most it doesn't have the "wow" factor of a Q motor flying a mini keg.
 
Hi
I have been doing research on sounding rockets used in the 60s and I found three of specific interest: Skua2, Petrel 1 and the INTA 100. All of them reached an apogee of 100Km using AP based propellants that provided less than 25KN of thrust. They used old technology, steel construction, have similar empty weights to what can be achieved today while using AP fuel which is readily available in O motor form. As O motors can provide anywhere between 20 and 40KN then surely a 40KN motor rocket if well designed could easily reach 100KM, yet I see very few O motor flights achieving an apogee of over 90,000ft. Why is this? Thanks :)

It's not a question of thrust but more a question of impulse. What are the relative impulse ratings of the sounding rocket motors?

Here you have, at least part of the answer. None of these rockets were using O motors. They might have a lift-off thrust between 20kN and 40kN, but the don't have a total impulse between 20.48kNs and 40.96kNs, which defines the O range (note the 's' in the unit). The INTA 100 and the Skua 2 have both nearly the same weight, 63kg and 64kg, excluding the payload. Making some semi random guess (70% mass fraction, 220s Isp) results in an estimated total impulse of about 95kNs, which would make it an small Q. Maybe their motors are a bit smaller, but even then they will at least fall in the upper end of the P range. The Petrel weighs about twice as much, so it might even have an R motor. The smaller ARCAS and Super Loki are still using P motors (just barely, in the case of the latter at 44.2kNs) and they both stay below 100km, despite their already mentioned "tricks". In other words, even the professionals don't reach space on O motors, but they are close enough to make one think it is possible.

Reinhard
 
As P motors require a heck of a lot of paperwork, I am guessing that this is why they are not used ... Does anybody know the total impulse of the 2004 Go Fast rocket as I can't seem to find it anywhere?
 
If I recall correctly it was an S motor. 700+ lbs of AP
 
You need to understand that going to space is easy. A O rocket could achieve the altitude if optimized and configured properly (and especially absent a recovery system). HOWEVER going to space is easy, staying there is not.

Read this for some clarification (at least something the average person can read): https://what-if.xkcd.com/58/

Basically in order to STAY in low earth orbit, your rocket needs to reach speeds of about 8000 meters per second. By the way mach 1 is about 4-500 meters per second, and a .308 caliber bullet has a muzzle velocity of about 800 meters per second. So in order to reach that speed, you need lots of fuel. However the fuel adds weight, so you need more fuel at lift off to get it up there. Additionally the rocket needs thrust vectoring capability to stay on course and steer into orbital path, since there is no air up there fins won't do a whole lot of good (which is why you will notice those big rockets only have fins on the FIRST stage). Gravity is about 9/10 of the surface level at low earth orbit altitude by the way, so without the speed to keep it going around the earth, it will just fall back down. Astronauts are weightless in space NOT because of the absence of gravity, but because they are basically in free fall the whole time!

Now if you can make an altitude of around 45,000km, you will have reached geostationary orbit, and you won't really need to be moving 10 times faster than a bullet. However in order to get up there, you need to reach escape velocity (11,000 meters per second) which again, requires a huge rocket. It's why it costs over 10,000 dollars a pound to send something up there...

Now if someone invents a propellant with about 100,000 isp....
 
Mass fraction. Most rockets that reach space, have a much higher mass fraction that our rockets.

Also, I think the steel construction might allow for higher motor pressures. Also, they are not limited by what they can put into their fuel.


Mark Koelsch
Sent from my iPhone using Rocketry Forum
 
How about the altitude waiver? I don't think our or anyone elses government just hand out waivers to go into space like candy.

Andrew
 
As P motors require a heck of a lot of paperwork, I am guessing that this is why they are not used ... Does anybody know the total impulse of the 2004 Go Fast rocket as I can't seem to find it anywhere?

From Derek Deville's 2012 article:

S50,150 with 411,309 Ns. 71.6 % motor mass fraction
 
Well, there are also a huge amount of junk in space that makes future space mission more complicated, so I can understand governments not giving everyone permission to shoot stuff into space.
 
How about the altitude waiver? I don't think our or anyone elses government just hand out waivers to go into space like candy.

Andrew

At BALLS we can get windows to 150 km.
The paperwork for P and above is not bad with the TRA committee.
I would suggest making and launching, and recovering successful smaller motors of similar design before going for space.

M
 
Well, there are also a huge amount of junk in space that makes future space mission more complicated, so I can understand governments not giving everyone permission to shoot stuff into space.

It tends to come right back down without very significant horizontal speed.
 
Two letters: delta v. As Reinhard and Mark K indicated, Isp and mass fractions play a pretty big role in that. Rockets need a certain amount of delta v just to get off the surface and up to 100km. The small mass fractions (ie - mostly not propellant) and the poor Isp of solids makes achieving those high delta v's difficult.
 
Back
Top