A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: J. Clarke on 23 Mar 2010 10:52 On 3/23/2010 9:55 AM, Jeff Findley wrote: > "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. So why are they not in common use?
From: J. Clarke on 23 Mar 2010 10:55 On 3/23/2010 1:23 PM, Pat Flannery wrote: > 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. The X-33 is not VentureStar, VentureStar is not the X-33, the X-33 was a subscale prototype never intended to achieve orbit. So why are you bringing VentureStar into the discussion?
From: J. Clarke on 23 Mar 2010 10:51 On 3/23/2010 9:44 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:ho8ggg0125v(a)news5.newsguy.com... >> On 3/22/2010 2:37 PM, Jeff Findley wrote: >>> "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message >>> news:ho8cvh2rfj(a)news6.newsguy.com... >>>> While I'm not going to give a cite for it, it is generally accepted that >>>> all else being equal a kerosene rocket will have lower specific impulse >>>> than a hydrogen rocket, so whatever performance the X-33 achieves with a >>>> kerosene rocket will be less than for a hydrogen rocket. >>> >>> ISP is one measure of engine performance. Vehicle performance is much >>> more >>> complicated and depends on many more variables besides engine ISP. In >>> particular, LH2 isn't very dense. Kerosene is far more dense than LH2 >>> plus >>> it doesn't need cryogenic storage. In a vehicle design, kerosene has >>> some >>> distinct advantages which may make up for its lower ISP. >> >> And those are going to put an X-33 in orbit? > > I never claimed they would, Then why are you introducing them to this thread? <Remainder, with no relevance to the kerosene-fueled X-33 concept snipped>
From: J. Clarke on 23 Mar 2010 10:49 On 3/23/2010 9:51 AM, Jeff Findley wrote: > "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? What's up with that is that if you make the assertion it's up to you to defend it. If you think that a kerosene fueled X-33 dropped off an airliner is a good idea then say why. If you think it isn't, say why. If you have no opinion on it and want to discuss some unrelated system, please start a new thread.
From: J. Clarke on 23 Mar 2010 10:53
On 3/23/2010 9:50 AM, Jeff Findley wrote: > "J. Clarke"<jclarke.usenet(a)cox.net> wrote in message > news:ho9ejv02dm9(a)news3.newsguy.com... >> 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? > > Perhaps they knew their customer has much experience with LH2 and believes > that LH2 is the "best" fuel to use. Think about it. Lockheed got paid > regardless of the project success. Their goal was to win the contract, > which means give the customer what the customer thinks they want, not what > will actually succeed. > > In the end, the X-33 failed, but Lockheed got paid and their existing EELV > related contracts continued. So from their point of view (i.e. upper > management), did they really fail from a business point of view? I see, so the Lockheed Skunk Works is in the business of designing flying machines that can't fly? |