A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Jeff Findley on 23 Mar 2010 09:51 "J. Clarke" <jclarke.usenet(a)cox.net> wrote in message news:ho9ek102dm8(a)news3.newsguy.com... > On 3/22/2010 11:07 PM, Peter Stickney wrote: >> On Mon, 22 Mar 2010 14:34:15 -0400, J. Clarke wrote: >> >>> On 3/22/2010 1:56 PM, Jeff Findley wrote: >>>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>>> news:ho7rdm02ink(a)news7.newsguy.com... >>>>> On 3/22/2010 8:32 AM, Jeff Findley wrote: >>>>>> "Greg D. Moore (Strider)"<mooregr_delet3th1s(a)greenms.com> wrote in >>>>>> message >>>>>> news:X6-dnTN9SfCfDzvWnZ2dnUVZ_rWdnZ2d(a)earthlink.com... >>>>>>> J. Clarke wrote: >>>>>>>> Why do people think that launching from 50,000 feet will help >>>>>>>> somehow? Going into orbit is not a matter of going high, it's a >>>>>>>> matter of going _fast_. Launching from 50,000 feet or from sea >>>>>>>> level you still need to impart 18,000 miles an hour of delta-v. >>>>>>>> That's the hard part. >>>>>>> >>>>>>> Because 50,000 feet gets you above the bulk of the atmosphere which >>>>>>> provides a decent bonus. >>>>>> >>>>>> Specifically, you can optimize your engines for the much lower >>>>>> pressure of >>>>>> 50,000 feet (to vacuum), as opposed to the compromises necessary to >>>>>> make them run at sea level. >>>>> >>>>> So how much do you think this gains you? >>>> >>>> For a conventional bell engine design, quite a bit of ISP as you can >>>> optimize the engine bell shape for vacuum. >>> >>> How much Isp? And how much of the time during boost is it running in >>> vacuum? >> >> It depends on the chamber pressure of the engine - but a fair bit - >> the J2 engine optimized for Sea Level has a vacuum Isp of 390, and >> the vacuum optimized J2 has an Isp of 421. = a gain of 8% over Sea Level. >> >> A launch vehicle engine spends most of its time in vacuum. The initial >> trajectory is as much vertical as possible to get it out of the thick >> air. >> When a reasonably high altitude is reached, you pitch over to accelerate. > > So what percentage of the time in a typical launch is spent in vacuum? For someone who was asking others to "do the math", you seem incapable of that task yourself. Furthermore, you seem incapable of using Google to look for information from others who have done the math. What's up with that? Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: Jeff Findley on 23 Mar 2010 09:55 "Pat Flannery" <flanner(a)daktel.com> wrote in message news:5audncWlgt8o2DXWnZ2dnUVZ_g2dnZ2d(a)posted.northdakotatelephone... > On 3/22/2010 9:55 AM, Jeff Findley wrote: >> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >> news:ho7rdn12inj(a)news7.newsguy.com... >>> SSTO, if it can be done at all with chemical fuels, is _barely_ doable. >> >> There are several expendable stages which could theoretically do SSTO, >> with >> a usable payload, if launched by themselves. > > I've never heard of one that could do that without dropping something on > the way up like Atlas did. > Someone here* suggested that Thor might be able to do it, but that proved > not to be the case. > > * Someone who owns a lot of cats and a machine gun, IIRC. :-) Henry Spencer did the math for several existing rocket stages. What most needed to make this happen would be a deeply throttlable engine. Atlas was an example. From memory, one of the Titan II stages and I think one of the Saturn V stages also had the appropriate mass fraction. If you do the math an expendable SSTO isn't really that hard. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: Pat Flannery on 23 Mar 2010 13:23 On 3/22/2010 7:41 PM, J. Clarke wrote: >> is quite poor. Since an SSTO is fairly limited in volume, you need a high >> energy density fuel. >> Kerosene has about 6 times the energy density of LH2. >> The drawback is it weighs more, and thus incurs structural weight >> penalties. > > So you're saying that the Lockheed Skunk Works didn't know what they > were doing when they chose to use hydrogen? VentureStar relied on its large size when its propellants were exhausted to reduce reentry heating to the point where fragile Shuttle-type tiles weren't going to be needed and more robust metallic tiles could be substituted for them. That having been said, LH2 had once before led Lockheed astray: http://en.wikipedia.org/wiki/Lockheed_CL-400_Suntan In retrospect, the metallic tile concept for VentureStar may have been a flop if employed, as they were supposed to be based on titanium, and as was discovered after Columbia broke up on reentry, titanium burns at a lower temperature than aluminum when in a atomic oxygen-rich environment; so the first orbital flight of the VentureStar prototype would have probably been its last. Assuming they could have fixed that somehow, VentureStar was only missing its performance goals marginally, due to the need to replace the composite LH2 tank with a aluminum-lithium one, and the added weight and drag of the twin vertical fins that were found to be necessary to assure the vehicle's stability during atmospheric flight to and from orbit. It would have taken a monster aircraft to carry it, but air-launching the VentureStar at high altitude might have given it enough added "umph" to have made it work as designed. Pat
From: J. Clarke on 23 Mar 2010 10:45 On 3/23/2010 9:28 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:ho8eok2vun(a)news5.newsguy.com... >> On 3/22/2010 1:55 PM, Jeff Findley wrote: >>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>> news:ho7rdn12inj(a)news7.newsguy.com... >>>> SSTO, if it can be done at all with chemical fuels, is _barely_ doable. >>> >>> There are several expendable stages which could theoretically do SSTO, >>> with >>> a usable payload, if launched by themselves. >> >> Which would those be? > > Google is your friend. Try Googling for something like "expendable ssto > henry spencer". It's been discussed here several times, when this group had > a far better signal to noise ratio. Unfortunately, Henry Spencer no longer > posts here. Sigh... > >>> Note that Atlas was able to >>> put Mercury into orbit, but it did cheat a bit by dropping the two outer >>> engines on the way up, partly to reduce thrust and partly to reduce the >>> dry >>> mass of the booster. >> >> Yep, it's called a half-stage". > > But as Henry Spencer said of Atlas in one of his posts: > > More precisely, its first stage could have taken 1-2klb of payload into > orbit all by itself, assuming suitable engines with the same Isp and > engine mass as the standard ones. > > In other words, the stage as flown couldn't be considered an SSTO, but a bit > of development to produce a deep throttling sustainer engine could have made > it an SSTO. Atlas easily had the mass fraction and engine performance > necessary, but it lacked the deep throttling necessary to make it happen. > >>> That said, a resuable SSTO is a matter of debate. Some say it's >>> possible, >>> others say it's too hard or impossible. >> >> In any case, do you think that it's going to be achieved by replacing the >> hydrogen aerospike engines in the X-33 with something burning kerosene and >> sticking it on top of an airliner? > > I'm not going to argue that point. But you might want to Google Black > Horse. It's a very interesting concept on which there was extensive number > crunching done. Oh heck, it's interesting enough I'll GIVE you a link: > > http://www.ai.mit.edu/projects/im/magnus/bh/analog.html > > This is the sort of "outside the box" thinking for a (near) SSTO that > doesn't violate physics and relies on the proven technology of in flight > refueling, which is done routinely by the military. Heck, even Air Force > One is equipped to receive fuel via this method. If it's safe enough and > reliable enough for the President of the United State's aircraft, it ought > to be good enough for a launch system! Black Horse is an interesting concept but much different from the notion of sticking some kerosene fueled engines in the X-33 design and dropping it off a commercial airliner. > > Jeff
From: J. Clarke on 23 Mar 2010 10:50
On 3/23/2010 9:33 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:ho8eoi0vuo(a)news5.newsguy.com... >> On 3/22/2010 1:56 PM, Jeff Findley wrote: >>> For a conventional bell engine design, quite a bit of ISP as you can >>> optimize the engine bell shape for vacuum. >> >> How much Isp? And how much of the time during boost is it running in >> vacuum? > > You're the one claiming the virtues of a high ISP fuel like LH2/LOX, so I > assumed you were one of those "performance uber alles" types who would know > these things. Some engines have sea level and vacuum versions. Do a little > research and find the data for yourself. Either that or do the math (i.e. > college level aerospace engineering stuff). > > To partially get around this very issue, the SSME's run at a relatively high > chamber pressure compared to other engines. These high chamber pressures > create issues of their own. The SSME has literally taken decades to > perfect. So you're saying that the space shuttle program ran its entire course from development to retirement without a "perfected" engine? And what does this have to do with a kerosene fueled X-33? |