A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: kT on 1 Nov 2009 22:27 Sam Wormley wrote: > Fred J. McCall wrote: >> Sam Wormley <swormley1(a)mchsi.com> wrote: >> >> :Fred J. McCall wrote: >> :> Sam Wormley <swormley1(a)mchsi.com> wrote: >> :> :> :Fred J. McCall wrote: >> :> :> Sam Wormley <swormley1(a)mchsi.com> wrote: >> :> :> :> :> :Sylvia Else wrote: >> :> :> :> :> :> :> Depends which market you're in. Space tourism, for >> example, needs low :> :> :> cost per kg, but not particularly large >> payloads. >> :> :> :> :> :> : >> :> :> : I would think that space tourism, would require some >> margin--some extra >> :> :> : safety. >> :> :> : >> :> :> :> :> Why? You need what you need. Why would tourists require >> 'extra'? >> :> :> :> : >> :> : You lose a human in a rocket, people will want their money back. >> :> : >> :> :> You lose a billion dollar satellite in a rocket and they're >> going to >> :> want their money back, too. That's what insurance and liability >> :> waivers are for. >> :> : >> : Agreed--And they will probably use more reliable rockets too. >> : >> >> So we're to "all rockets will be reliable". So why do you think >> "space tourism, would require some margin--some extra safety", again? >> > > Let me clarify. > > 1. SSTO launch vehicles have never been used to put things in orbit. > 2. SSTOs are hard to design. > 3. I'm guessing the are not the best candidate for space tourism. Sam, you misunderstand the modern definition of SSTO. What most people mean is a single core whose engine is started on the ground and flies entirely to orbit in a single burn (either direct or with an OMS burn). In other words there is no vertical staging event on that core, the boosters are ... heaven forbid ... side mounted. Ideally those boosters would be flyback hydrocarbon powered boosters, flying paying tourists.
From: Sam Wormley on 1 Nov 2009 23:59 Fred J. McCall wrote: > Sam Wormley <swormley1(a)mchsi.com> wrote: > > :Fred J. McCall wrote: > :> Sam Wormley <swormley1(a)mchsi.com> wrote: > :> > :> :Fred J. McCall wrote: > :> :> Sam Wormley <swormley1(a)mchsi.com> wrote: > :> :> > :> :> :Fred J. McCall wrote: > :> :> :> Sam Wormley <swormley1(a)mchsi.com> wrote: > :> :> :> > :> :> :> :Sylvia Else wrote: > :> :> :> :> > :> :> :> :> Depends which market you're in. Space tourism, for example, needs low > :> :> :> :> cost per kg, but not particularly large payloads. > :> :> :> :> > :> :> :> : > :> :> :> : I would think that space tourism, would require some margin--some extra > :> :> :> : safety. > :> :> :> : > :> :> :> > :> :> :> Why? You need what you need. Why would tourists require 'extra'? > :> :> :> > :> :> : > :> :> : You lose a human in a rocket, people will want their money back. > :> :> : > :> :> > :> :> You lose a billion dollar satellite in a rocket and they're going to > :> :> want their money back, too. That's what insurance and liability > :> :> waivers are for. > :> :> > :> : > :> : Agreed--And they will probably use more reliable rockets too. > :> : > :> > :> So we're to "all rockets will be reliable". So why do you think > :> "space tourism, would require some margin--some extra safety", again? > :> > : > : Let me clarify. > : > : 1. SSTO launch vehicles have never been used to put things in orbit. > : 2. SSTOs are hard to design. > : 3. I'm guessing the are not the best candidate for space tourism. > : > > You mean "let me move the goal posts", don't you? So it has nothing > to with "extra safety" at all. > > Now that that's out of the way, let's look at the mission requirements > for a vehicle intended for 'space tourism': > > 1) No more likely to blow up than any other vehicle. > > 2) Fast cycle times (space tourism needs to fly frequently to get > costs down to the point where it's practical). > > 3) Low support costs (we're looking at an airliner model of costs > here, not what is currently happening with present launch vehicles). > > 4) Cargo fraction can be low, since the bulk of your 'cargo' is meat > and seats. You're not staying up long enough to need to worry too > much about consumable supplies other than air and a minimum of fluids. > > So what does that lead us to? > > 1) Liquid fuel. Failure rates are similar to solids, but > instantaneous catastrophic failures are much rarer. Plus the > vibration environment is much better. > > 2) Reusable. If you have to buy new hardware for every shot, there's > a very real limit to how low you can drive costs and you'll never get > anywhere near airline cost models. > > 3) SSTO or air launched. 'Winged flyback booster' falls in this > category, although the technology there is more difficult than > launching from a manned aircraft. If we want fast cycle times, we > can't just be dropping pieces randomly. Plus having to retrieve them > rather than having them come home on their own increases cycle costs. > > 4) Don't push the technology too hard. Doing that gets you better > performance, but it also leads to higher refurbishment costs between > flights as pushing limits harder means closer tolerances and running > things closer to failure points. > > Conclusion: What we're looking for for space tourism (or a personnel > transport vehicle) is a reusable liquid fueled SSTO (or air-launched > vehicle) that can fly back to the launch facility and land, then take > off for another flight with minimal processing. > > Seems obvious to me. Also to pretty much everyone else talking about > doing space tourism. If you think you know better, perhaps you should > get some backers and start a company? > Go for it!
From: Sylvia Else on 2 Nov 2009 00:27 Fred J. McCall wrote: > 3) SSTO or air launched. 'Winged flyback booster' falls in this > category, although the technology there is more difficult than > launching from a manned aircraft. If we want fast cycle times, we > can't just be dropping pieces randomly. Plus having to retrieve them > rather than having them come home on their own increases cycle costs. Also, not dropping bits off gives you much more flexibility about where you launch from, particularly if you get the chance of raining burning debris over inhabited areas down to somewhere around airliner numbers (whether or not the rest of the mission is that safe). Sylvia.
From: Robert Clark on 2 Nov 2009 08:00 On Nov 1, 5:46 pm, Pat Flannery <flan...(a)daktel.com> wrote: > Robert Clark wrote: > > Most concepts for such a vehicle centered on hydrogen, since a hydrogen/LOX combination > > provides a higher Isp. However, some have argued that dense fuels > > should be used since they take up less volume (equivalently more fuel > > mass can be carried in the same sized tank) so they incur less air > > drag and also since the largest hydrocarbon engines produce greater > > thrust they can get to the desired altitude more quickly so they also > > incur lower gravity drag loss. > > Another key fact is that for dense fuels the ratio of propellant mass > > to tank mass is higher, i.e., you need less tank mass for the same > > mass of propellant. > > You are missing a key point here; Lockheed chose LOX/LH2 for two reasons: > > 1.) Its superior isp. > 2.) The large size of the propellant tankage for it. > > VentureStar was to rely on the large volume of the empty propellant > tankage to make the vehicle very light for its size on reentry to > decelerate the spacecraft quickly and reduce the heat loads on the TPS. > Shift to kerosene/LOX and you are going to need a far heavier TPS, and > combined with the lower isp, that is going to make SSTO very difficult > to do, especially with a worthwhile payload. > > Pat The very key aspect of this proposal is that the tanks remain the *same* size, but at a *lighter* weight. In fact the intent was to keep the same shape of the X-33 and just switch out the propellant tanks and engines. So in fact the vehicle becomes lighter for its volume with hydrocarbon fuels. When you consider the other benefits of hydrocarbon fuels over hydrogen, the higher Isp of hydrogen/LOX propellant becomes less of an advantage. In fact, kerosene is not necessarily the best hydrocarbon to use, which I'll discuss in a following post. Bob Clark
From: Robert Clark on 2 Nov 2009 08:11
On Nov 1, 7:46 pm, Sam Wormley <sworml...(a)mchsi.com> wrote: > Sylvia Else wrote: > > Sam Wormley wrote: > >> Single Stage to Orbit really limits payload "weight". > > > Why does that matter? The point of an SSTO is to get down the cost to > > orbit per payload kg. An SSTO is likely to mass more than a disposable > > multi-stage for a given payload, but that is not in itself a source of > > concern. > > > Sylvia. > > http://en.wikipedia.org/wiki/Single-stage-to-orbit#SSTO_Cons Thanks for that link. It also neatly discuses the reasons why a dense hydrocarbon fuel can be superior to hydrogen for a SSTO, particularly for the savings in tank weight and gravity losses: Dense versus hydrogen fuels. http://en.wikipedia.org/wiki/Single-stage-to-orbit#Dense_versus_hydrogen_fuels In regards to the payload to orbit, in my suggested reconfigured kerosene-fueled VentureStar it would exceed the payload of the Saturn V, and nearly match that of the Ares V. And with even more efficient hydrocarbon fuels than kerosene it would exceed even that of the Ares V. Bob Clark |