A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Peter Stickney on 22 Mar 2010 23:14 On Mon, 22 Mar 2010 11:07:19 -0800, Pat Flannery wrote: > On 3/22/2010 6:54 AM, J. Clarke wrote: >> But your assertion does not convince. You are posting on the Internet. >> Most people posting on the Internet have opinions. Most of those >> opinions are ignorant twaddle. So one must take your opinion as >> ignorant twaddle until you can provide some numbers to go with it. > > Yeah...but you are posting on the internet also, and I'm not seeing any > numbers so far. :-D Pat - don't forget that he's responding to Bbo Hallrb, and therefore is arguing with a twaddle of supreme ignorance. -- Pete Stickney Failure is not an option It comes bundled with the system
From: Jorge R. Frank on 22 Mar 2010 23:35 Peter Stickney wrote: > On Mon, 22 Mar 2010 11:07:19 -0800, Pat Flannery wrote: > >> On 3/22/2010 6:54 AM, J. Clarke wrote: >>> But your assertion does not convince. You are posting on the Internet. >>> Most people posting on the Internet have opinions. Most of those >>> opinions are ignorant twaddle. So one must take your opinion as >>> ignorant twaddle until you can provide some numbers to go with it. >> Yeah...but you are posting on the internet also, and I'm not seeing any >> numbers so far. :-D > > Pat - don't forget that he's responding to Bbo Hallrb, and therefore is arguing > with a twaddle of supreme ignorance. > Ah, yes. The Stimson J. Cat of Usenet himself. <http://sounds.wavcentral.com/televis/renstimp/ignoranc.au>
From: J. Clarke on 22 Mar 2010 23:41 On 3/22/2010 11:11 PM, Peter Stickney wrote: > On Mon, 22 Mar 2010 09:12:41 -0400, J. Clarke wrote: > >> On 3/22/2010 4:07 AM, Pat Flannery wrote: >>> On 3/21/2010 4:53 PM, Marvin the Martian wrote: >>> >>> >>>> It is apparent you're not acquainted with rocket science. Getting >>>> through the "dense lower atmosphere" is no big deal. Von Braun did >>>> that with an single stage alcohol fueled rocket 65 years ago. >>>> >>>> The problem is getting up to orbital velocity. >>> >>> If you can put the LOX aboard the rocket at altitude, where the >>> humidity is very low, you can eliminate the weight and complexity of >>> having to put insulation on the outside of the oxidizer tank section, >>> as ice won't form on it like it would if it were fueled and launched >>> from the surface. Not only does the booster then end up carrying the >>> weight of ice still sticking to it during ascent, but the ice that >>> sheds can damage the booster due to its mass and impact speed. >> >> So how much "weight and complexity" is involved with a little bit of >> spray-on foam? And in practical terms how much difference is this going >> to make? I'm sorry, but you're trying to reduce launch costs by >> tackling an at best second order effect without dealing with the major >> cost drivers. In any case the tankage on the X-33 is does not have >> surfaces exposed to the airflow so this becomes a non-issue. >> >> And if you're talking an X-33 it has to have a thermal protection system >> for reentry anyway. >> >> And the X-33 could not achieve more than half of orbital velocity on >> HYDROGEN so how in the Hell do you expect it to do that with kerosene? >> >> SSTO, if it can be done at all with chemical fuels, is _barely_ doable. > > While LH2 can provide high Isp, its Energy Density (Cubic Ergs, if you will) > 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?
From: J. Clarke on 22 Mar 2010 23:40 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?
From: Peter Stickney on 23 Mar 2010 00:12
On Mon, 22 Mar 2010 23:40:09 -0400, J. Clarke wrote: > 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? At least 80% -- Pete Stickney Failure is not an option It comes bundled with the system |