A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Pat Flannery on 25 Mar 2010 04:29 On 3/24/2010 6:48 PM, Marvin the Martian wrote: >> 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. >> >> Jeff > > The paper I read on kerosene rockets argued that the rocket mass was > increased so much because of the size of the liquid hydrogen tank and > compressors to keep it liquid No refrigeration compressors are used on LH2 fueled boosters. The LH2 is put aboard and topped up to make up for boil-off till just shortly before launch. Pat
From: Jeff Findley on 25 Mar 2010 08:27 "Pat Flannery" <flanner(a)daktel.com> wrote in message news:ebWdnTfl_slWaTfWnZ2dnUVZ_oudnZ2d(a)posted.northdakotatelephone... > On 3/24/2010 6:48 PM, Marvin the Martian wrote: >> The paper I read on kerosene rockets argued that the rocket mass was >> increased so much because of the size of the liquid hydrogen tank and >> compressors to keep it liquid > > No refrigeration compressors are used on LH2 fueled boosters. > The LH2 is put aboard and topped up to make up for boil-off till just > shortly before launch. True. That's why it's called a cryogenic fuel. It's liquid mostly because it's been chilled to cryogenic temperatures, not because it has been compressed to very high pressure. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
From: Pat Flannery on 25 Mar 2010 11:29 On 3/25/2010 2:24 AM, J. Clarke wrote: > You haven't shown that insulation of the tank is the major obstacle to > SSTO. As has been pointed out, it didn't stop Atlas from coming very > close to achieving that objective with '50s material technology. It certainly would be possible to make a expendable SSTO with today's technology...they almost got VentureStar to work, and that had to return to Earth after placing its payload in orbit. The problem is an economic one as far as expendable SSTO payload fraction versus overall launch cost. As I pointed out earlier, a rocket possessing a second stage can more than double the payload placed in orbit without doubling the launch cost, which is why no one was really interested in building a SSTO expendable system. Discussion has been made here about sticking deep throttling engines on the Atlas to give it true SSTO ability without having to drop the booster engines during ascent. While that may have been possible to do, does it give any real advantage over the way it was actually done? You still lose the whole vehicle and its three engines on every mission, and the deep throttling engines probably cost more than the ones it actually used. So other than proving a philosophical point, the SSTO version doesn't give you any real advantage. The SSTO Titan II is an interesting concept (assuming it really could do that - that 25/1 mass fraction seems off), but one has to ask oneself if you could use a smaller two-stage rocket of lower cost to orbit the same usable payload weight as the Titan II's first stage? Note that the descriptions of the SSTO Titan II don't even talk about it carrying a payload, just putting itself into orbit. The Saturn V first stage with the droppable outboard engines might have made some sense if you could have figured out some way to recover the four outboard F-1s for re-use, or maybe just as it was designed, as a expendable super-Atlas concept. We'll never know on that one, as all the advanced Saturn V concepts were killed by the Shuttle program, if for no other reason than to allow the Saturn V launch pads to be converted for Shuttle use. If the Shuttle had met the rosy economic predictions that were originally claimed for it - with all the SRB segments being re-used and the orbiter being very easy to refurbish for relaunch - it might have been even cheaper to fly than the expendable Saturn V first stage vehicle. Pat
From: Marvin the Martian on 25 Mar 2010 10:41 On Thu, 25 Mar 2010 00:17:08 -0800, Pat Flannery wrote: > On 3/24/2010 6:33 PM, Marvin the Martian wrote: >> >> To get to orbit, your minimum speed is 7 km/sec. The fastest airplanes >> can travel about .9 km/sec, and those are fighter jets, not tankers. >> >> You're talking about an energy difference of 7^-0.9^2 = 49 - 0.8, or >> 0.8/49 =~ 2%. And for that piddly advantage, you have to including >> docking, refueling hardware, and screw around with transferring >> CRYOGENIC liquid oxygen at super sonic speeds. >> >> That's just stupid on the face of it. > > If it's a subsonic aircraft, you only get the advantage of lower ascent > air drag by launching in the thin air at altitude (which is why the > sub-orbital SpaceShip 2 will get launched at altitude from its carrier > aircraft rather than being verticaly launched from the ground.) "Space ship 2" is a damned sounding rocket that amazes the simple minded. IT doesn't get anywhere NEAR orbital velocity, so yeah, carrying it aloft makes sense. That's a big apples and oranges comparison. < snip blather > What the hell was that about? I just explained why it wouldn't work. Don't be obtuse.
From: Marvin the Martian on 26 Mar 2010 13:22
On Sun, 21 Mar 2010 17:40:19 -0400, Greg D. Moore \(Strider\) wrote: > J. Clarke wrote: >> On 3/21/2010 10:42 AM, hallerb(a)aol.com wrote: >>> Why take along EVERYTHING for a SSTO when the vehicle could use a >>> airplane to get the in orbit portion to at least 50,000 feet above >>> most of the atmosphere, not tied to a single launch location, fly the >>> airplane to a convenient launch location, fuel to get to 50,000 feet >>> can be from tanker refueling along the way.......... >>> >>> granted for a really large payload a BIG HUGGER AIRLINER might need to >>> be a custom build, but the upsides are huge. >>> >>> no risky loaded bomb launch being the first. >>> >>> SSTO is just a distraction from the more important...... >>> >>> LOW COST TO ORBIT!! >> >> 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. Its trivial. If you knew anything about the subject, you wouldn't have said that. All these people who think that they're so damned smart with all their cockeyed ideas, as if they've never been looked at before. |