Jet Engines as 1st Stage cluster

[rocketwatcher2001]

I'm all for killing that darn chicken, too, but what good is it to launch a really small payload even if it is cheap? That technology isn't going to carry over into larger payloads. It's the big payloads that I want to launch cheaply. <div class="Discussion_UserSignature"> </div>

 

[dobbins]

If you can launch the little ones cheaper then you create the customers that are needed to achieve the higher launch rates. That will attract the R&D dollars for a medium payload system creating more customers in turn. Then it will be time for the big payload system.<br />

 

[rocketwatcher2001]

That sounds good to me. How big of an improvement over the Pegasus do you think is possible using existing technology? <div class="Discussion_UserSignature"> </div>

 

[dobbins]

To 5,000 Kg. That is a ten fold increase in payload capicity.<br />

 

[tap_sa]

<font color="yellow">"what good is it to launch a really small payload even if it is cheap? "</font><br /><br />First, for example an <i>unfueled</i> GEO comsat isn't small payload. It's quite big actually. Large portion of comsat's weight is the apogee kick motor plus station keeping fuel... err.. propellant (S_G <img src="/images/icons/wink.gif" />)<br /><br />This leads to the second; Make orbital assembly and refueling a routine job. This will need combined 'garage' + propellant depot in LEO. Lift the empty 5t comsat there, fill it up with f..propellant that's already waiting there because there is regular supply line servicing the station. Eventually this leads to a new way to build comsats. Instead of lifting the thing in one piece you transport frames, solarpanels, electronics etc and put it together in orbit. Why? Because the ride from Earth to orbit is rough, forcing you to overengineer the satellite just for the first 10 minutes of it's maybe ten year lifetime. Better take the individual parts up, assemble them in shirtsleeve zerogee environment, test that everything works and then send it on it's way, using some gentle LEO-GEO tug.

 

[rocketwatcher2001]

You think 10,000 lbs into orbit is possible from a Pegasus type vehicle? How much is it going to weigh at release? <div class="Discussion_UserSignature"> </div>

 

[rocketwatcher2001]

Tap-<br />I'm all for building an orbital "Dry Dock" with a 5 psi shirtsleeve environment. <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

You could even have the familiar 14.7 psi. No need to drop the pressure because you aren't wearing a suit that would turn into rigid michelin man <img src="/images/icons/wink.gif" />

 

[dobbins]

Assuming a 10 to 1 rocket to pay load ratio about 100,000 lbs, about the weight of those shuttles NASA carrys on 747s.<br /><br />Pegasus is optimized for a quick launch, like when the DoD needs some small satellite up in a hurry because of some emergancy. We need a different optimization, one for payload.<br />

 

[dobbins]

I can think of another market for small payloads, schools. Right now if the research department at Whatever State wants to do some microgravity research it has to go hat in hand to NASA and try to convince them that their research is more important than the other two dozen scientists who are also begging for a spot on the ISS.<br /><br />If Acme Launch can offer a small satellite launch for a hundred thousand dollars, then the research department can bypass NASA and pay Acme to launch it out of their research funds. They wouldn't have any problem raising money, Alumni would kick in that kind of money just for the bragging rights to a M.I.T or whatever satellite.<br />

 

[rocketwatcher2001]

<font color="yellow">Pegasus is optimized for a quick launch, like when the DoD needs some small satellite up in a hurry because of some emergancy. We need a different optimization, one for payload.</font><br /><br />I'm not all that smart, so you are going to have to type really slowly. What does that mean? I understand that the Pegasus and the Monitor (I think that's it, it's the one with the MX missile booster) are designs based on DOD programs for really quick access to space, like within 48 hours. <br /><br />If there is a better way of launching 10x the payload of the Pegasus, why isn't Orbiital Science drumming up investment capital? <div class="Discussion_UserSignature"> </div>

 

[dobbins]

OS doesn't own the engines, the DoD does and they won't let then use the engines for other people's launches.<br /><br />Here are some Air Launch Concepts.<br />http://mae.ucdavis.edu/faculty/sarigul/aiaa2001-4619.pdf<br />

 

[cuddlyrocket]

"I think it's going to take a revolutionary step, rather than many evolutionary steps. Much like the 707 was a step over the Stratocruiser. If we are going to do airlaunch, hypersonic is the way to go."<br /><br />Most revolutions end in disaster. The Shuttle was supposed to revolutionise travel to LEO, but as Griffin has recently admitted, they didn't know enough to make it work as intended (and they still don't). We don't know how to make a hypersonic aeroplane, let alone launch another vehicle from one. We don't know how to make scramjets work on a sustained basis. We don't even know if it's <i>possible</i> or, more importantly, how much it will cost (we do know how to make supersonic passenger aircraft, but you don't see any flying around.) We do know how to make large, efficient, subsonic aircraft.<br /><br />Dobbins' idea of continual, small, incremental improvement (known as <i>kaizan</i> - a lesson the Japanese taught manufacturers worldwide) is propabably the way to go - at least at the present time. This doesn't mean that revolutionary developments cannot be incorporated once demonstrated to work - like the jet engine for passenger aircraft. (Although, incremental improvements can be both in reduction of cost and in performance - preferably simultaneously.)

 

[stex6109]

<blockquote><font class="small">In reply to:</font><hr /><p>rocketwatcher2001 wrote: can't imagine a turbofan powered lifting launch platform being practical in any way. If you want to use turbofans to get you to 40,000 ft, the Orbital Science's L1011 launched Pegasus looks like the way to go. <p><hr /></p></p></blockquote> <br /><br />A problem with Orbital Science's L1011 aircraft is that it was not designed for the purpose that it is used for. Having unneeded wings, a massive fuselage, a cockpit with life support systems, and unnecessary control surfaces to name a few. All of which are not needed and add large amounts of weight to the total package. Which in return limits the carrying capacity for the Pegasus rocket. <blockquote><font class="small">In reply to:</font><hr /><p> The problem with that is it can't put anything bigger than a breadbox in orbit. <p><hr /></p></p></blockquote><br /><br />Well, I didn't refer to the Pegasus as I don't consider it a very safe and economic design. For starters in uses a solid fuel design. Which lowers its payload to LEO capacity as compared to a liquid-fueled design such as the Falcon family. <br /><blockquote><font class="small">In reply to:</font><hr /><p> The link you provided was cool, thanks. I'm very excited about the mach 4 engines that are under development, but they are nothing like the big turbofans on today's modern airliners. The GE90-115B turbofan you mentioned has a fan diameter of 115 inches, that's what the 115 means.<p><hr /></p></p></blockquote><br /><br />The design I was referring to in my orginal post was not intended to use the developmental Mach 4 engines. Yes, the more powerful Turbofans are large diametered, but as I stated the first time. This is not a concern as the 1st stage in not intended to travel very fast. (subsonic) <br /><blockquote><font class="small">In reply to:</font><hr /><p> That's about 20 feet in diameter by the time it's cowled up, and that just gives you about 10% of the amount power that a SRB of the same diameter gives y</p></blockquote>

 

[stex6109]

Here's two research articles done by Dani Eder (ederd@bcstec.ca.boeing.com) whose research team from Boeing, studied the practical use of jet-powered first stages. They opted to use turbojets over turbofans in light or greater acceleration. Though I believe each design is both safe and practical.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><br /><br />A jet-boosted launcher keeps only the minimum necessary jet propulsion -<br />the engines - and dispenses with wings and landing gear in favor of<br />parachute recovery.<br /><br />The concept we did a study of used ten Pratt & Whitney F100-229 jet<br />engines (used on the F-15 fighter). They have a sea-level static<br />thrust of 29,100 lb on afterburner each, or a combined liftoff <br />thrust of 291,000 lb. Each bare engine weighs 3700 lb. When a<br />parachute system, landing legs, fuel tank, and fuel are added, you<br />get a 6000 lb unit at takeoff. The rocket core weighed 85,000 lb<br />and had 3 pieces. Each piece had the same diameter tanks (about<br />2 meters) and 2 RL10A-3 rocket engines (except for nozzle size,<br />identical to those used on the DC-X, and identical to those on the<br />Centaur upper stage). The middle piece had a longer fuel tank,<br />and goes all the way to orbit. The other two had shorter tanks<br />and were staged off when they got empty.<br /><br />The entire launcher thus had a weight of 145,000 lb, and under<br />jet power only took off at 2 g's. As opposed to rockets which<br />avoid high dynamic pressure because it makes more drag, if you<br />are flying on jet power you get more thrust, so you want to<br />take off fast and accelerate fast to get the maximum acceleration<br />before you run out of air.<br /><br />We used a sophisicated trajectory analysis program to find out what<br />the best ascent trajectory was, considering maximum allowable<br />dynamic pressure, variation of jet thrust with altitude and speed,<br />and drag and lift as a function of vehicle speed a</p></blockquote>

 

[rocketwatcher2001]

So you want to use 10 engines, at full AB, and you think this is going to be reliable? Please don't try to fly this thing near my house. This thing sounds like the Soviet N1 moon rocket. Isn't it simpler to just use 1 engine? If you guys are Hellbent on launching in the stratosphere it seams like a tethered balloon is the way to go, it's dirt simple, and dirt cheap. <br /><br />10 engines? That's a dumb idea. Here's why. There are 10 fuel pumps, 10 fuel controls, 10 AB fuel controls, 10 lube pumps, 20 stater vane actuators, 30 exhaust nozzle actuators, plus 10 engine cores that are going to be ingesting anything that falls off of the rocket, like ice, and failure of any one of those components is going to hurt or kill the mission. A single rocket engine can get rid of all of that extra complexity, plus you need that rocket anyway, why not use it? <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

Because ordinary jet engines clock thousands of hours lifetime and their combined lifetime is measured in, uh, tens or hundreds of millions hours. IOW unlike with rocket engines there's <i>a lot</i> of experience in making them reliable. <br /><br />edit: And show me a balloon that can take, say, 100,000lbs to stratosphere and I'll show you a picture Elvis riding EZ-rocket. No, DaVinci isn't a good example, it is a joke.

 

[rocketwatcher2001]

<font color="yellow">there's a lot of experience in making them reliable.</font><br /><br />I've got a plenty of skinned knuckles working on jet engines with afterburners. I've worked on a test cell for 2 years primarily working on fighter engines. I wouldn't go with 10 of them in a situation where failure of any one of them is going to hurt/kill the mission. In 2 years I can't count the number of engine failures I saw even with my shoes off. I personally had an engine failure on a JT-8D in August, and the JT-8D is a lot more reliable than the F100.<br /><br />As far as a ballon up to the Stratusphere, off of the top of my head, it would take about two and a half million cubic feet of Helium, or about 1/3 the size of Hindenberg. It would sure be cheaper and easier than that 10 engine smoking hole you guys are talking about. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

Well you were working on a <i>test</i> cell, sounds like you were deliberately pushing the engines to their limits, yes? Accidents are inevitable in such business. <br /><br />How many accidents were 'explosive'? Loose blade(s) shooting of the engine? And how many were bening failures, meaning the engine just had to be shut down, but in an orderly fashion? With ten engines cluster one bening failure doesn't necessary even scrub the mission. Like someone already said, put a KORD into that system <img src="/images/icons/wink.gif" /><br /><br />And with your jet engine experience, what's your opinion on raising the T/W of them via tweaks? How high it could realistically go? AFAIK fighter jet go a little over 10 but more would be merrier for a jet stage. Could methane as fuel help the case, with it's cryogenic cooling power?<br /><br />Sorry about the flood of questions, but I get questiontriggerhappy when bump into unexpected reserve of interesting knowledge <img src="/images/icons/laugh.gif" /> <br /><br />PS the jet stage doesnt necessarily have ABs, for instance the GE90-115 might be fine (or GEnx). Initially even just the altitude and high subsubsonic speed would do wonders for the rocket part.

 

[rocketwatcher2001]

Most of the engine failures on the test cell itself was due to bad parts put on during maintenance/overhaul. Most of the engine failures that I have seen outside of the test cell have been for any number of reasons, stuck actuators, inop pumps, FOD, stuck valves, you name it. I have seen an Afterburner module that was <i>melted</i> on the inside because of a broken fuel nozzle. Most of the failures were caught before launch, luckily.<br /><br />One of the things that bugs me about this is that these engines have not been designed for this, so there is a lot of stuff on the engines that is meant to be run right side up, like the combustion chambers, drains, lube sump and scavage, the bearings. It seems to me that a better engine could be design specically for this, and they would be better suited for it. But rockets are still better. <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Keep in mind that a lot of the airframe necessary for high speed travel through the lower atmosphere is on the upper stage. Every pound shed on the upper stage is worth several pounds on the lower stages.

 

[barrykirk]

I wouldn't want any launch of any rocket too close to my house. Just within driving range so that I can watch.

 

[barrykirk]

The jet engine(s) can also be mounted on top of the stack. That keeps things from falling in. But once you start thinking along those lines. HTOL for the jet engine stage starts to look like a possibility and you need a lot less raw jet engine thrust if you've got wings developing some of your lift.

 

[scottb50]

The only way turbine engines could be used effectively is as a suplimentary launch power source and as a flyback approach and landing aid. The problem using it solely as a first stage is the limited capability. A very high powered turbofan will only work sub-sonic, more or less an engine capable of mach 3-5 would have to be completely different and would not produce enough thrust to be useful at lower speeds. Beyond mach5 you need a totally different air breathing type engine that would be usable for a very short time when rocket motors, or engines would have to be used for the rest of the trip.<br /><br />With inlet tricks you can take a turbofan to about mach 2, but the only ones that can do that are in the 20-30,000 pound class and that's why the study recently cited talks about up to 10 engines. Beyond that you need another engine, mach 2 is not fastr enough to light a scram-jet, so you would need another intermediate engine.<br /><br />The idea of an airbreathing first stage that can get a substantial upper stage to mach 5+ is beyond known technology. I've pointed out before a T-38 can go from Denver to any point in the U.S. at M.9, push it to M-1.2 and it can fly less than 10 minutes. The bigger your payload gets, the bigger the first stage gets and the bigger they get the more drag they have in the atmosphere. <br /><br />While it might sound nice to takeoff like an airplane and get to orbit it just can't be done with a substantial payload. It takes an L-1011 to put 1,000 pounds into orbit.<br /><br />That's why a hybrid system makes much more sense. Vertical launch with rocket engines supplimented by turbines for the first minutes, carrying a second stage that uses rockets. Once the second stage is released the turbine engines are used to flyback the first stage. <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Well, I'm just thinking about subsonic.... Remember that Burt Rutan's White Knight was subsonic.<br /><br />So, going to a falcon 1. How much would the payload increase if the launch pad was located at 40,000 feet instead of sea level? How about 60,000 feet?<br /><br />If the payload is doubled, then this idea has a lot of merit. If the payload goes up by 1% then I would say this idea needs to be abandoned.<br /><br />Remember that if your launch pad is at those high altitudes you can totally redesign your rocket. You can use vacuum optimized rocket engines.<br /><br />As an example, let's say that launch altitude is 60,000 feet and zero velocity. I'm guessing from the falcon specs that acceleration is about 20 ft /sec / sec.... Actually at the launch it's a little lower.<br /><br />Starting at 60,000 feet, the falcon would be over 80,000 feet altitude before going supersonic. SpaceX is calling for fairing seperation at T=194 seconds. Eighteen seconds after stage 2 ignition. Well, given that the point of Max Q is now occuring much higher in the atmosphere. How much lighter and thinner can it be?<br /><br />According to the payload users guide they added a 1-2 inches of foam to the fairing for protection against aerodynamic noise to the payload. Well starting at higher altitude may eliminate most of the need for that.<br /><br />Question at what launch altitude can a rocket be launched without the fairing at all? Probably too high to be practical.<br /><br /><br />Also from the falcon one payload users guide.<br /><br />http://www.spacex.com/payloaduserguide.pdf<br /><br /><br />Flight Environment<br />Most of a satellite’s design and a great deal of the weight are driven by the launch loads<br />experienced in the first ten minutes of its life. After separation, the satellite spends the rest of its<br />time in microgravity and does not experience such loads again during its useful life.<br />We have worked ha