A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Robert Clark on 23 Mar 2010 08:06 On Mar 14, 9:24 pm, Robert Clark <rgregorycl...(a)yahoo.com> wrote: > ... > Even though the mathematics says it should be possible, and has been > for decades, it is still commonly believed that SSTO performance with > chemical propulsion is not possible even among experts in the space > industry ... > > Then it is important that such a SSTO vehicle be produced even if > first expendable to remove the psychological barrier that it can not > be done. Once it is seen that it can be done, and in fact how easily > and cheaply it can be done, then there it will be seen that in fact > the production of SSTO vehicles are really no more difficult than > those of multistage vehicles. > Then will be opened the floodgates to reusable SSTO vehicles, and *low > cost passenger space access as commonplace as trans-oceanic air > travel*. > This last may seem a bit extreme. However, Burt Rutan in this recent video interview about 8 minutes in noted that if rockets were operated with the efficiencies of airliners, the price for a passenger to orbit would be in the $12,000 range: Big Think Interview With Burt Rutan. A conversation with the aerospace engineer and founder of Scaled Composites. March 3, 2010 http://bigthink.com/ideas/18881 Robert Zubrin in his book, "Entering Space: Creating a Spacefaring Civilization" comes to a similar conclusion: "Current -day rockets, such as the kerosene/oxygen-fueled Atlas can deliver about 1 percent of their takeoff mass to orbit - most (about 90 percent) of the remaining mass is propellant. The cost of a kerosene/oxygen propellant mxture (at 3:1 oxygen/kerosene mixture ratio) is about $0.20/kg. Since the propellant consumed during launch has 90 times the mass of the payload delivered, the propellant cost of sending a mass to orbit is about $18/kg. Assuming a total system operating cost of six times the propellant cost (about double the total cost/fuel ratio of airlines), the resulting price of a rocket ride to orbit would be in the neighborhood of $100/kg, or $10,000 for a 100-kg passenger. There is no fundamental reason why space-launch prices in this range cannot be achieved." "Entering Space", by Robert Zubrin, p.22-23. Then it is notable that trans-Pacific flights are in this cost range. For instance I earlier did a search on the Japan Airlines site for round trip business class tickets from my town of Philadelphia to Tokyo. It ranged from $6,600 to $21,000: ========================================= Quote: Select Your Flights Philadelphia to Tokyo Thursday, April 9, 2009 Tokyo to Philadelphia Tuesday, April 14, 2009 Travelers: 1 Travel class: Business and First Select your fare: Price differences within a fare type may be due to flight connections or availability. Prices are per adult passenger and include Taxes and Surcharges. Fare type Fare description Lowest price Business Saver Special Restricted. Bed-style seating on most long-haul routes - Executive Class. more details $6,672.48 Business Saver Restricted. Bed-style seating on most long-haul routes - Executive Class. more details $7,611.48 Business Normal Flexible. Bed-style seating on most long-haul routes - Executive Class. more details $12,330.48 First Normal Flexible. World-renowned service and comfort - First Class. more details $21,589.48 ========================================= And first class tickets even one-way on Qantas from Los Angeles to Australia are in this price range: ========================================= Your Search From: Los Angeles To: Sydney Depart: Adults: Children: Infants: Search Options: Must travel on these dates Flexible with dates From: Los Angeles To: Sydney Depart Arrive Morning Afternoon Evening Stops: Non-stop All flights Step 2 - Select your flight Price displayed is for 1 adult and includes surcharges, fees and taxes. > View lowest fare around this date Flights Out: Los Angeles to Sydney - Wed 24 Mar 10 From To Flight Business First 23:50 Los Angeles 08:25 (Fri) Sydney QF108 $7926 $15881 Duration: 14h 35m 22:30 Los Angeles 07:25 (Fri) Sydney QF12 $7926 $15881 Duration: 14h 55m ========================================= Then recall for the full-sized VentureStar RLV by switching to kerosene we could get in the range of $166/kg launch costs or $16,600 for a 100 kg passenger. Bob Clark
From: Jeff Findley on 23 Mar 2010 09:28 "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! Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon 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 09:33 "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. 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 09:44 "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, I claim that LH2 isn't necessarily the best choice for a rocket fuel because all else is NOT equal when you change the fuel in a vehicle design. You can't look at a rocket engine's specs and immediately conclude that LH2 is superior to kerosene. The devil is in the details, particularly the details of the *vehicle* design. As an example, compare the Saturn V first stage design to the second stage design. Note the relative difference in size of the kerosene/LOX tanks on the first stage to the LH2/LOX tanks on the second stage. The difference is quite striking. Then as a thought experiment, try to figure out how big the Saturn V first stage would need to have been if the fuel was LH2 instead of kerosene. 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 09:50
"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? Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon |