Quote from: HMXHMX on 01/27/2009 04:47 pmQuote from: Proponent on 01/27/2009 02:54 pmQuote from: kkattula on 01/27/2009 01:33 pmAirlaunch LLC are developing a 2-stage, air-launched, LOX/Propane rocket called the QuickReach. I'm not sure if it's sub-cooled propane. I suspect not since they use VAPAK, but I could easily be wrong.http://www.airlaunchllc.com/index.htmThanks--that is interesting. But now I am really confused. This is, as you say, a propane-fueled vehicle. It also uses VaPak propellant pressurization. Gary Hudson is deeply involved. But, on Selenian Boondocks Gary Hudson mentions that methane is better than propane for VaPak for operational reasons. Perhaps AirLaunch recently switched from propane to methane and the information on the AirLaunch site is out of date?I'll try to clarify.AirLaunch traded propane and methane (LNG, actually) in 2003. Performance defined as payload deployed was within 1% of each other; as many others have noted there is not much difference between the two propellants. But we chose propane since it was non-cryogenic and we thought that would be beneficial with regard to pressure/temperature control while in the aircraft. We already had to deal with a cryogen (LOX) and didn't want to complicate the issue. Finally, we thought that propane would be easier to obtain and store than LNG for the particular application.After development and testing, however, what we found was LNG would make it much easier to control temp and pressure. This turns out to be a universal truth: if one is using VaPak propellants, the operational temperature of the propellants should be well below ambient. In propane's case, it might be necessary to cool it on a hot day or warm it on a cold day. For a pure cryogen, it is only necessary to vent to control temperature. In hindsight, this is perhaps obvious, but sometimes we can be denser than our propellants...AirLaunch then demonstrated firing the same engine on LNG, and that works fine. If Falcon has gone forward we would have argued for a change to LNG. For purely space launch missions, if VaPak is the pressurization scheme, I would use LNG, especially for external-carriage air-launching. But there are definitely vehicle concepts where propane is desirable in place of LNG; I leave discovery of those as an exercise for the interested.Falcon SLV is cancelled then? I hadn't heard. What a shame. Are you continuing to develop QuickReach? Seeking alternative funding?
Quote from: Proponent on 01/27/2009 02:54 pmQuote from: kkattula on 01/27/2009 01:33 pmAirlaunch LLC are developing a 2-stage, air-launched, LOX/Propane rocket called the QuickReach. I'm not sure if it's sub-cooled propane. I suspect not since they use VAPAK, but I could easily be wrong.http://www.airlaunchllc.com/index.htmThanks--that is interesting. But now I am really confused. This is, as you say, a propane-fueled vehicle. It also uses VaPak propellant pressurization. Gary Hudson is deeply involved. But, on Selenian Boondocks Gary Hudson mentions that methane is better than propane for VaPak for operational reasons. Perhaps AirLaunch recently switched from propane to methane and the information on the AirLaunch site is out of date?I'll try to clarify.AirLaunch traded propane and methane (LNG, actually) in 2003. Performance defined as payload deployed was within 1% of each other; as many others have noted there is not much difference between the two propellants. But we chose propane since it was non-cryogenic and we thought that would be beneficial with regard to pressure/temperature control while in the aircraft. We already had to deal with a cryogen (LOX) and didn't want to complicate the issue. Finally, we thought that propane would be easier to obtain and store than LNG for the particular application.After development and testing, however, what we found was LNG would make it much easier to control temp and pressure. This turns out to be a universal truth: if one is using VaPak propellants, the operational temperature of the propellants should be well below ambient. In propane's case, it might be necessary to cool it on a hot day or warm it on a cold day. For a pure cryogen, it is only necessary to vent to control temperature. In hindsight, this is perhaps obvious, but sometimes we can be denser than our propellants...AirLaunch then demonstrated firing the same engine on LNG, and that works fine. If Falcon has gone forward we would have argued for a change to LNG. For purely space launch missions, if VaPak is the pressurization scheme, I would use LNG, especially for external-carriage air-launching. But there are definitely vehicle concepts where propane is desirable in place of LNG; I leave discovery of those as an exercise for the interested.
Quote from: kkattula on 01/27/2009 01:33 pmAirlaunch LLC are developing a 2-stage, air-launched, LOX/Propane rocket called the QuickReach. I'm not sure if it's sub-cooled propane. I suspect not since they use VAPAK, but I could easily be wrong.http://www.airlaunchllc.com/index.htmThanks--that is interesting. But now I am really confused. This is, as you say, a propane-fueled vehicle. It also uses VaPak propellant pressurization. Gary Hudson is deeply involved. But, on Selenian Boondocks Gary Hudson mentions that methane is better than propane for VaPak for operational reasons. Perhaps AirLaunch recently switched from propane to methane and the information on the AirLaunch site is out of date?
Airlaunch LLC are developing a 2-stage, air-launched, LOX/Propane rocket called the QuickReach. I'm not sure if it's sub-cooled propane. I suspect not since they use VAPAK, but I could easily be wrong.http://www.airlaunchllc.com/index.htm
Quote from: jongoff on 02/06/2009 07:18 amTo be fair, a cryogenic fuel is a much bigger pain in the backside than a cryogenic oxidizer (and both John and some of my friends at XCOR agree). GOX vapors can't burn in air--methane or propane vapors can. While dealing with those issues isn't a show-stopper, it is a lot more of a hassle than dealing with LOX leaks.This is all very interesting, and I think I've learned more from your posts and from HMXHMX's posts in this thread than just about any others I've ever read.If I could ask a couple of other questions about sub-cooled propellants....In practice how would one keep the propellant cool in a largish vehicle launched from the earth's surface? From HMXHMX's posts about the AirLaunch Falcon, it sounds like insulation alone would probably not be sufficient If cooling is needed, would it be done by circulating propellant or by building a refrigerator around the vehicle? Or something else entirely...?Secondly, is the large thermal expansion as a densified propellant warms up to the boiling point a major engineering issue? I mean, if you're using a cryogen at its boiling point, then as long as your vents don't freeze shut, I would imagine that the worst that's likely to happen is that the tank boils dry. But if I've got a tank of sub-cooled propane and cooling fails and I can't detank for some reason, do I have a time bomb on my hands? Picture a tank of propane that's warming up and spurting liquid propane through its vents and may still burst.EDIT: Corrected attribution of quote
To be fair, a cryogenic fuel is a much bigger pain in the backside than a cryogenic oxidizer (and both John and some of my friends at XCOR agree). GOX vapors can't burn in air--methane or propane vapors can. While dealing with those issues isn't a show-stopper, it is a lot more of a hassle than dealing with LOX leaks.
Great posts guys! I had a few ideas myself and just wanted to know what you think. As previously mentioned the key technologies necessary for SSTO are:- lightweight structures- hypersonic flight capability for airbreathing mode- high specific impulse for rocket modeI did some calculations and propose the following for an SSTO vehicle (possibly winged aircraft)-Hybrid Engine with an airbreathing and a rocket mode. The airbreathing mode is capable of sustaining speed of Mach 4 and has a specific impulse of 2000sec. The rocket mode is based on tri-propellant combustion of flourine, berillium, and hydrogen and has a specific impulse of 700sec.-Composite structure with a mass ratio of 2.5:1
Quote from: space_man on 04/09/2009 03:08 pmGreat posts guys! I had a few ideas myself and just wanted to know what you think. As previously mentioned the key technologies necessary for SSTO are:- lightweight structures- hypersonic flight capability for airbreathing mode- high specific impulse for rocket modeI did some calculations and propose the following for an SSTO vehicle (possibly winged aircraft)-Hybrid Engine with an airbreathing and a rocket mode. The airbreathing mode is capable of sustaining speed of Mach 4 and has a specific impulse of 2000sec. The rocket mode is based on tri-propellant combustion of flourine, berillium, and hydrogen and has a specific impulse of 700sec.-Composite structure with a mass ratio of 2.5:1And who were you going to get to handle the Fluorine? You'd need more than just one mother-in-law. . .
Yes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?
A better idea, once the nation finally gets over its mamby pamby fears, is to go nuclear. The exhaust is not radioactive. It’s practically impossible to make hydrogen radioactive, just very, very hot with lots of thrust and high isp.
But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?
Quote from: space_man on 04/09/2009 06:23 pmYes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?Well you can get more bang for your buck using these odd options but, you need to understand the practical reasons folks don't normally mess with Fluorine. It's just a nightmare to deal with and that is never going to lead to a cost effective transport system. We need to reduce support infrastructure in order to bring costs down, not create more infrastructure needs. This is one of the reasons QR is such a good idea, the entire first stage is nothing like "rocket science." It has the same safe, quick, convenient and economical advantages as all modern air transport. Gary had basically a two stage rocket with the hassles of only a one stage rocket. That was a VERY good idea. I'm surprised that no one else wants to pick up that ball and run with it. No one in Europe? India? Just out of curiosity, if HMX is still around; I'd love to know why solids were passed over for QR. That would have added a huge convenience to the entire concept. Did solids just not have the get-up-and-go power you needed? I'm also curious whether anyone ever considered the crazy option of carrying the rocket externally, pulling the plane up and releasing, then winging over the aircraft to get it away from the rocket quickly. I know this sounds like a crazy stunt but in fact, B-47 pilots used to practice this maneuver to literally "throw" their payload at the target and get as far away as possible before the boom. For anyone who has an interest, there's a DVD out there that describes this. I had occasion to view it myself since I picked it up for my father who crewed an RB-47 during the Korean conflict. Very fun video and a little suprising to consider a bomber acting like a fighter.
Hmmm, if ethane isn't too hard to produce from methane, then that's another Martian fuel choice. It has somewhat better handling properties and density for a touch less isp. And of course, from ethane you can make ethylene, base stock for the plastics industry.
Scenario MR Payload (mean) (kg)Max Isp 5.281 7389Dunn 6.000 9333Opt Fixed 7.622 11488Variable 7.719 11873Stoich 7.937 11270Max Impulse 17.192 -12427
Having a little spare time during the summer lull, I've had a quick look at the effect of variable mixture ratios on lox-hydrogen SSTO.
Frankly I'm disappointed that the variable MR appears to boost the payload by just a few percent over the optimal fixed-MR case. I do suspect, though, that the benefit of variable-MR is understated, because the oxygen-rich mixture burned at lift-off would produce high thrust, thus reducing gravity losses. (On the other hand, there's the complexity of building an engine which can handle a large range of MRs -- that's well beyond the scope of this simple calculation).
It must be the case in principle that right at lift-off, the optimal MR is that which maximizes the density impulse (density times Isp). The reason is that the initial infinitesimal volume of propellant does not need to be accelerated of lifted off the pad, so the volume it occupies in the tanks might as well be packed as full of impulse as possible*. I presume the fact that the present calculation does not show the MR rising that high at lift-off is that the optimal MR falls very quickly to lower values.
Short article on Escape Dynamics announcement in popular press. Includes embedded video.http://www.engadget.com/2015/07/20/escape-dynamics-microwave-spacecraft/