I recenly heard that NASA engineers said that a spacecraft with one stage to orbit is impossible. I want to prove this otherwise. What thrust-to-weight ratio would be needed, what fuel to use (how much), what material, and what shape would be needed to make this kind of spacecraft? Just think of how much cheaper space flight would be!
Single Stage to Orbit
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Not "impossible" but no sane person would try it (from Earth) as multi-stage rockets where early stage weight can be discarded once their fuel is gone are much more efficient and therefore, MUCH MUCH CHEAPER.
An alternate to rockets for the first two stages of a 3 stage system may be possible. It uses atmospheric oxygen for these first two stages. See:
http://www.sciforums.com/showpost.php?p=1652758&postcount=36
Also a few post earlier in that thread ael65 gives some good links that tell exactly how to calculate the ratio of the intital weight to " fuel exhausted" or "burn out" weight of a rocket or each stage of a multi- stage rocket and several different fuels. If seriously interested you could calculate how many times more tons of fuel would be required to launch the shuttle with only one stage.
There are better fuels than H2 and O2 in terms of what is most important (the "specific impulse") for keeping the lift off to burn out ratio as small as possible but they are more expensive and often would put hundreds of tons of toxic gas into the air near the lauch pad. The governor of Florida would not like you killing roughly 100,000 tax payers. Note that oxygen is 16 times heavier than hydrogen and burns to H2O, very non toxic, but the lift off weight of the shuttle rocket is 63% liquid oxygen! (I think this is only after the two solid fuel booster have fallen off, but they contain oxygen in chemical compound so perhaps the 63% is "at launch." These boosters get a lot of their energy from the aluminum dust they contain, which is in a rubber like solid also contining an oxygen rich chemical. I.e. Al2O3 is formed with great heat released. Al2O3 is non toxic also, Unless buried under huge pile of it.
) The shape of a single stage rocket would be essentially the same as current rockets - just a lot bigger and more expensive (at least 10 times more, I would guess.)
As far as the thrust to weight ratio required (and desired) just a little greater than unity at lift off is usually ok as the thrust remains nearly constant but the weigh is decreasing as the fuel makes exhaust gasses.
There are special time-of-flight critical cases where one needs much greater than unity for this ratio. For example, if you want to use a rocket to deliver an exploding war head near an incoming "sea skimmer" missle, which just "popped up" over the horizon and will sink your ship in about 5 seconds, you can not afford to accelerate your ship-defense counter missle at a tiny fraction of G. It had beter come off the rail (or out of the vertical launch tubes of modern Aegis ships) with an acceleration of many Gs or you are dead. Same is true, if you are trying to shoot down an incoming ICBM.
PS why is this posted here? Are you an architect? I thought "commies" were only interested in big blocks of concrete as cheap buildings, not more interesting shapes.
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it is possible all right to have single stage to orbit vehicle. They key is to achieve hypersonic speed and X-43a is up to the job.
Also if anyone is interested in some technical AIAA files on latest SSTO vehicles...ask me, I can get them from online for free.
The SSTO vehicle that grasped my attention is called Hyperion
but to tell you the truth...it doesnt look practical
http://machinedesign.com/ContentItem/70398/LoweringTheTollOnTheHighwayToSpace.aspx
Hyperion technical files: http://www.uploading.com/files/0WWVNRFG/Hyperion.pdf.html
Also if anyone is interested in some technical AIAA files on latest SSTO vehicles...ask me, I can get them from online for free.
The SSTO vehicle that grasped my attention is called Hyperion
but to tell you the truth...it doesnt look practical
http://machinedesign.com/ContentItem/70398/LoweringTheTollOnTheHighwayToSpace.aspx
Hyperion technical files: http://www.uploading.com/files/0WWVNRFG/Hyperion.pdf.html
ATK microcraft company was selected for the X-43 design. check out their site: http://www.atk.com/
What I am trying to say is a single stage that is about the size of a normal aircraft that could carry the same load a rocket could carry, using a lot less fuel and requiring a lot less material. Discarded stages require tons of fuel and the amount of thrust required to lift them off the ground is in the millions. The kind of SSTO that I am thinking of should, in theory, should be a lot cheaper and could potentially popularize space travel a lot more.
What I mean by SSTO is an air/spacecraft that can take off a normal runway with its payload, once it has reached a maximum altitude for its conventional jet engines, it would simply use rockets to reach orbit. Since it is not going vertical, it would not need a high thrust-to-weight ratio (saves fuel). Similar to the space shuttle, it would return to earth with no discarded stages and could be refueled and reused again and again. They could be manned or unmanned.
First of all "Architecture and Engineering." Secondly, I am suppose I am more of a socialist than a pure communist. I am really fascinated with space travel and just getting off this planet.
By the way, welcome back Draqon!
The links given in this thread to various efforts on SSTO are interesting, but I think never will be as succesful as my suggested alternative to the multi-stage rocket. (That is not any claim that my alternative is more economical than what is now done with multi-stage rockets. It is only a claim that it is a better approach than the SSTOs that are being considered.)
I say this because by definition, SSTO machines take all the non-fuel mass to orbit, whereas my system, like the conventional multi-stage rocket takes only a small fraction of the launch mass to orbit.
Also as most of the SSTO machines do operate with different lift means at different altitudes, it means that none of these are optimium designs for those different regions. I.e. the SSTO is a "comprmissed design," not an "optimised one."
My alternate to rockets for the first two stages of a 3 stage system has each of the three stages optimized for its task. It, like the SSTO, uses atmospheric oxygen for these first two stages. See:
http://www.sciforums.com/showpost.php?p=1652758&postcount=36
I say this because by definition, SSTO machines take all the non-fuel mass to orbit, whereas my system, like the conventional multi-stage rocket takes only a small fraction of the launch mass to orbit.
Also as most of the SSTO machines do operate with different lift means at different altitudes, it means that none of these are optimium designs for those different regions. I.e. the SSTO is a "comprmissed design," not an "optimised one."
My alternate to rockets for the first two stages of a 3 stage system has each of the three stages optimized for its task. It, like the SSTO, uses atmospheric oxygen for these first two stages. See:
http://www.sciforums.com/showpost.php?p=1652758&postcount=36
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The problem with this idea is that the speeds that can be reached with current jet engine technology are nothing compared to the speeds needed to reach orbit. Even the fastest jets like the SR-71 can “only” go around Mach 3, about 1000 m/sec. To achieve orbit you have to reach speeds of around 8000 m/sec, so you would still need to make up the remaining 7000 m/s under rocket power. So having the jet engines really doesn’t accomplish very much; you’re only reducing the work that you have to do with your rocket engine by 1/8. Except now in addition to boosting just your rocket, you also have to boost the weight of the jet engines and all the other extra parts that were allowing your plane to fly as a jet. It’s easier to have a vehicle that does 8000 m/sec under rocket power than to have a vehicle that does 1000 m/sec under jet power then 7000 m/sec under rocket power, especially since the extra mass of fuel needed to get the first 1000 m/sec will be expended in the first part of the flight, after which time you no longer need to lift it. If you get the first 1000 m/sec from jet engines, you’re stuck lifitng the mass of the engines all the way up.
Of course, it’s possible that in the future some fantastic new jet engine technology will be developed that would allow planes to fly at Mach 20+ under jet power, which would certainly change things…but for the moment it’s probably impossible.
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Flying mach 20+ under jet power isn't actually that far away, scramjets or ramjets would be able to make it happen, in addition to that, the most powerful jet engine ever made is currently capable of a 100,000 lb thrust output. It's very likly that the SSTO will not be powered by a heavy axial-jet engine.
A simple design such as this would be able to work in extremly high altitudes and be able to accelerate extremely quick.
Pretty picture, but subersonic combustion is not easy to achieve. There are reaction rate limations among other problems. Why not read a little about the several decades of work in this area and the dismal record achieved, thus far. Even a quick wiki review of scram jets would be informative for you I think. Many, very experienced with and knowledgable about scram jets are not very optimisitc they can ever work. Some call them "scam jets" as they do get research funding still from the taxpayers via military interest.
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In the future, when technology and fuel resouces have changed, then the scram-jet, and the SSTO will look a lot more possible. One of the key factors is simply what fuel is being used. Oxidized ethanol is the most popular on right now, but what could burn more efficiently?
That's easy to say, but aerospace engineers have been trying to do it for 30+ years without any success. There was a National Aerospace Plane project in the U.S. that ran for over a decade and burnt through over 20 billion dollars before they gave up.
It’s certainly possible that very fast jet engines will be developed in the future, but I agree with the NASA people that it’s probably impossible with current technology.
Yes, and what if pigs could fly? At APL/JHU where I worked we had one (if not the) world's leading experts on combustion.
APL/JHU has since WWII been the US Navy's lead agency in ship self defense, which means rockets that go super sonic very quickly and had for more than decade SCRAM jet project when I retired. - Was trying to solve some of the many problems. It may still be on going. - That would give it more than three decades of research on scram jets.
Getting something to burn, and not just be convected away by the super sonic flow, is an accomplishment in itsself. How do you establish a "flame front" in super-sonic flow, how do you overcome fundamental chemical reaction rate limitations, etc.? If you can deliver it in quanity super sonically you can put almost any fire out with a stream of gasoline!
In some military applications, they do not worry about efficiency - they are happy if it will even work. Personally, my money is on the genetic engeneering people making pigs fly, before anyone makes a practical (economically competitive) CSRAM jet that is useful for placing anything (other than the US budget) into even low Earth orbit.
I know that even 30 years ago, one could find pretty illustration of how the "work" in print. None have ever flown or even come close to that as far as I know. Getting thrust greater than drag even very biefly* in the lab's supersonic wind tunnel is a cause for opening champaign bottles. - I think that has been achieved, if there was no instrumentation error, but am not even sure even that has been achieved. (I have had no contact with people working on the problem for more than 15 years and they would not have told me, with no need to know, if they had gotten net thrust, but I never saw them suddenly very happy.)
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*In these second(s) duration test, you do not need to be concerned with the terrible thermal problems - so that helps in the lab.
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Scramjets have come a (little) ways in the past 10 or so years. America has flown successful (although not terribly impressive) test flights, and there's a joint Australia/UK demonstrator project as well:
http://en.wikipedia.org/wiki/Boeing_X-43
The other thing about the "simple" scramjet design is that you have to already be going faster than the speed of sound for it to work at all. To achieve this, they attach a primary stage to the craft which consists of a rocket engine. Then they attach this whole thing to a plane, fly it to high altitude, and launch it from there. So even if the scramjet worked well, it would still add up to three stages to orbit.
Similar considerations applied to the ramjet, which is fairly simple on its own, but must be modified in very complex ways to operate at subsonic speeds (in order to obviate the need for a booster stage). It's dubious that this will be achievable at all with scramjets.
To Quad:
Thanks for the up date. If you have time and inclination take a look at my potential alternative:
My alternate to rockets for the first two stages of a 3 stage system has each of the three stages optimized for its task. It, like the SSTO, uses atmospheric oxygen for these first two stages. See:
http://www.sciforums.com/showpost.php?p=1652758&postcount=36
You know I value your comments, knowledge of facts.
Thanks for the up date. If you have time and inclination take a look at my potential alternative:
My alternate to rockets for the first two stages of a 3 stage system has each of the three stages optimized for its task. It, like the SSTO, uses atmospheric oxygen for these first two stages. See:
http://www.sciforums.com/showpost.php?p=1652758&postcount=36
You know I value your comments, knowledge of facts.
I only know the basics about propulsion. It sounds like your idea is a ramjet (with the usual modifications for subsonic flight) that cruises you up to the upper atmosphere, and then you switch to a rocket engine? Seems fairly reasonable to me, although I suspect there's some problem with it, or someone would already be using that approach... Maybe it's not economical to have both the liquid jet fuel and the solid rocket fuel?
I do not know much about this either. Idea just evolved in exchanges with aep65. I think the fuel would be liquid for both stages 2 & 3, but that need not be if solid is better for 3.
Really the only novality in my idea is the sub sonic climb to around 40K feet of a "lift airplane" which is strong enought to pull about 5Gs, at least 4Gs, following a power dive straight down which gets it up to about M = 3 while still above about 35K feet where it pulls those Gs to get the still joined 2&3 stages, still "piggy backed on top," and itself headed upwards at about 45 degrees when the ram jet begins to operate and fly off the top with stage 3 rocket still attached. I.e. the ram jet starts at at least M= 2.5 above 33K feet and is designed for swallowing a lot of volume each ms. Initially it climbs slowly as drag in the air of ~35 K feet will be larger than normal with that "big mouth" but it should be steadily gaining speed and increasingly turning upward as the air gets thinner. Perhaps it can function to almost 100K feet and be going at M= 7+ when the rocket 3d stage takes over.
Advantage of my approach is that more than half of the weight of the shuttle at launch (oxygen is 63% of the total) is avoided by oxygen taken from the air and that oxygen in not lifted even a meter. -I.e. cheaper and more efficient, with both first and second stages reused for many more launches.
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kmguru
Staff member
Many years ago [the time of Challengers accident] NASA wanted to build an Advanced Solid Rocket Motor (ASRM) facility at Yellowcreek, Mississippi that would have next generation technologies. Unfortunately due to the Challenger accident, that project was selved. I was the automation and systems engineer for that project. From what I understand, the new motor would have had much larger thrust and use new chemicals along with the micronized aluminium and perchlorates.
If we can come up with a high density energy source...perhaps single stage is possible.
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