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<font color="yellow"><br />Second, the STS was designed from the beginning to be a man-rated HLLV (if you count the orbiter as part of the payload). </font><br /><br />Not to nitpick or anything, but to be "man-rated" you'd want some sort of powered abort capability in your system, which the orbiter didn't exactly have for the majority of its flight envelope.
<font color="yellow">That is highly desirable but has nothing to do with man rating the booster since the powered abort is a spacecraft responsibility.</font><br /><br />Ok, if having a working abort system has nothing to do with "man-rating", then in a modern launch system what exactly does this so called "man-rating" involve?
Ok, so what you're saying is that man-rating involves making sure the rocket doesn't explode on the pad at launch, and maintaining a inventory of the components used to construct the vehicle?<br /><br />I'm fairly certain that every commercial booster designed from the 70's onwards had these two goals in mind.
Man-rating a booster also has certain g-loading and vibration limits each stage must meet or exceed. (Satellites are more tolerant than humans for those.)<br />Boosters have to either be designed to those spec's from the beginning, or fully instrumented test flights would be required with a boilerplate vehicle and any appropriate alterations (or redesigns) made to meet them. <br /><br />That's why it was mentioned that man-rating the Delta IV or Atlas V heavy model boosters for a CEV could very well turn out to be quite expensive, considering all the additional testing and development involved.<br />
There is didly squat extra development involved in "man-rating" EELV's. They have a 98% design reliability already, strapping on a few extra sensors shouldn't take half a dozen engineers more than a few months.<br /><br /><font color="yellow">Man-rating a booster also has certain g-loading and vibration limits each stage must meet or exceed.</font><br /><br />Wait, let me get this straight... You're peddling vibration and g-loads as advantages of using solids?
I think one of the most positive aspects of the new SDLVs is the flexibility. The STS could only carry the orbiter or a Shuttle C, which is really not much more than an orbiter without the wings. But the new LVs can potentially carry a wide variety of crew and cargo modules. Yes, Project Constellation takes a step back in some ways by using an updated version of the Apollo capsule, but that is all that is needed right now. Why build a tractor trailer when an SUV will do the job? There is nothing to stop NASA from down the road developing all manner of lifting bodies, space planes, Skylab-sized space stations, etc. should these thing become needed for the US's space goals.<br /><br />The most important thing right now for manned space exploration is to have a robust, flexible, safe, and most importantly cost effective launch system. The original STS tried to do this, but for a variety of reasons (too little development money, too much emphasis on down payloads--a market that never really materialized, too much cutting edge technology) the system was far too inflexible to be cost effective.
Not a reply to anyone in particular, but just an observation: many of the criticisms of the CEV contain the implication that the capsule approach is a step backwards from wings and lifting bodies. Even a lot of supporters are a bit apologetic about it, like an embarrassing relative. The more I look at it, the more I've come to the opposite conclusion (as the Mercury team probably did). Airplanes are a more primitive from of transportation, and before you go lugging wings other areodynamic surfaces into space, you'd better be sure you really have justified it. You very well may have a good reason, just don't assume it's a more advanced spacecraft!
The large, heavy wing was there to let a shuttle fly a polar orbit from Vandenberg and have enough cross range to land back at Vandenberg after doing whatever shady stuff the spooks wanted to do over the USSR. That is the ONLY reason the shuttle ended up with a large delta wing. <br /><br />There were (and will be I hope) much better space planes designs where the wings added only a little more weight, but a lot more convenience over a parachute system. The "DC-3 Shuttle" design is one of my favorites. In fact the current X-34 looks a lot like that design. It had small, straight wings used only for landing. During reentry it acted just like a blunt body capsule--with all of the advantages of a capsule. It did not try to fly until it had decelerated to well below the speed of sound. Contrast that to the present shuttle that has to fly from hypersonic speeds all the way to landing. We need to be careful not to judge the entire concept of a space vehicle that can make pinpoint runway landings based on how the shuttle turned out. <br /><br /> I only used the term "step back" because the designers are intentionally going back to data from the Apollo program to design the CEV.
<i>"Not a reply to anyone in particular, but just an observation: many of the criticisms of the CEV contain the implication that the capsule approach is a step backwards from wings and lifting bodies."</i><br /><br />I will admit, I just have a strong dislike for ballistic entry capsules and parachute landings! I'm not sure why...I guess landing on a runway just seems less primitive. Landing in a capsule is for beginners, not for those who do spaceflight in style! <img src="/images/icons/wink.gif" /> Also, I question the safety and reliability of parachutes. I suppose 40(?) years of Soyuz flights have proven them to be reliable, but what happens if a parachute fails to deploy or gets tangled? Will the crew be able to bail out? I doubt it, based on the Apollo CM-like design of the proposed "CEV". Parachutes are what you use when you have to bail out of a crippled vehicle, not what you use to land a healthy vehicle! <img src="/images/icons/wink.gif" /><br /><br />Honestly, I probably would be more enthusiastic about the "CEV" if it were an X-37-like "space plane" that would perform a runway landing. Perhaps I'm letting emotion dictate over logic, something I guess I shouldn't do as an engineer, but a controlled runway landing just ups the "coolness factor" tremendously over 1960's style capsules that parachute down like a $10 Estes model rocket!
Or, here is one for a slightly radical vehicle.<br /><br />Start with the Heavy Lift Launch vehicle (cargo version)<br /><br />Store the heat shield above the engines , but below the fuel tank during ascent. After jettison of the fuel tank, you've got a heat shield on the engines.<br /><br />Maybe, the ends of the exhaust chambers can be disposable, I don't know expensive they are.<br /><br />To avoid poking holes through the heat shield. Run the fuel lines externally around it.<br /><br />The external fuel hoses would of course be disposable.
Well, along with those wings and lifting body comes a large massive TPS which is delicate and prone to being damaged. Sadly, look at Columbia.<br /><br />I don't think we lost a single astronaut to a parachute system, and I only know of one case where the Russians lost a cosmanaut to parachute failure.
Didn't I just post that a rational (i.e. not meant for military purposes) space plane doesn't need a wing as big and heavy as the shuttle's? There is no reason that a winged reentry vehicle can't have a TPS every bit as sturdy as a capsule's. A large fragile TPS is only necessary for a craft that tries to generate significant lift at hypersonic speeds adn thus extends the time it is exposed ti reentry heating.
tomnackid,<br /><br />I was unaware of that. I assumed that if it wasn't a capsule that the TPS would be large and delicate.<br /><br />Conversly, if you had wings enough to land on, than you had a large and delicate TPS.<br /><br />What is the runway speed for your vehicle?<br /><br />Does that limit the number of landing sites?
Sorry, I didn't mean to be huffy! <img src="/images/icons/smile.gif" /><br /><br />A straight wing oribiter, promotede by Max Faget, would have been smaller than the current shuttle (the payload bay size was requirecd by the Air Force) and it would have landed at a slower speed. Also it would have had turbojets mounted above the wings for a controlled landing. TPS system would have been the same ablative material as used on Mercury, Gemini and Apollo. On the current shuttle using an ablative TPS would prohibitive in terms of weight and expense because it would have to cover such a large area, both because the shuttle is large and because it flies durring reentry, exposing more of its surface to reentry heat. The straight wing shuttle "belly flops" during reentry so that only its underside experiences the brunt of reentry. Also, like a capsule it gets reentry over with quicker so that vehicle is exposed to high heat loads for a shorter period of time. 5 minutes as opposed to something like 15 minutes for the shuttle.<br /><br />I'm not advocating a spaceplane for the CEV, nor am I saying they are better than capsules. I'm jsut saying that having a flexible launch system will let us have spaceplanes in the future if we need them. Also that we shouldn't judge the whole winged reentry vehicle concept from the shuttles flawed implementation of it.<br /><br />
"The most important thing right now for manned space exploration is to have a robust, flexible, safe, and most importantly cost effective launch system."<br /><br />I would say: "The most important thing right now for US manned space exploration is for the US to have a robust, cost effective, and most importantly, safe launch system that is capable of carrying out the missions that NASA is tasked with, but with flexibility to carry out other missions should they be later mandated".
I didn't take your post to be huffy at all.<br /><br />I simply don't have a very good understanding of all of the engineering issues for the flight systems and re-entry systems of the shuttle.<br /><br />I also am not aware of all of the design comprismises that NASA had to make to get backing to get the shuttle built in the first place.<br /><br />Now that you mention it. That payload bay area is really large. I seem to remember, but I'm sketchy on this, that some payloads completely filled up that bay.<br /><br />Is that correct? And/or is it that people just filled up the available space since it was there?<br /><br />Somebody else pointed out that the shuttle has one major advantage over anything else we've got. It can land more cargo from orbit than anything else we've got.
I will also admit that I don't have a good understanding of all of the engineering details and merits of TPS systems.<br /><br />I understand that ablative systems are one shot and tiles can be re-used.<br /><br />I was under the belief that tile systems are more fragile than ablative systems. Is that correct?<br /><br />I was under the assumption that tile systems were heavier than ablative systems. Of course I never had facts to back up that assumption. But your saying that the reverse is true. <br /><br />I would think that the reason for my assumption was that the few cases I know of where a tile based system is used, Space Shuttle. The TPS has a huge area to protect. If tiles are lighter, than in retrospect it now makes sense why they would have used tiles on the shuttle. They had no choice.
A successful plan will be the best possible compromise between proven technology and advanced technology which may have unpleasent surprises. Each launch involves a million or so possible failures which can turn the launch into a failure, therefore we can do very few things with a 50 -50 chance of success, or launch success will be very rare. We need mostly successful launches to get funding increases. Neil
<i> There is nothing to stop NASA from down the road developing all manner of lifting bodies, space planes, Skylab-sized space stations, etc. should these thing become needed for the US's space goals. </i><br /><br />It'd certainly suck to have Russia, France, China or somebody else go and develop some of the things we *ought* to be developing while we're busy taking pictures on the moon again. Perhaps our trouble is that we become fixated on using NASA's manned spaceflight program toward only one purpose. Under Apollo some of the great scientific experiments started under Gemini atrophied, then the Shuttle's promise caused our expendibles program to wither to the point where the ESA was able to swoop in and grab a lot of our customers, and now we're again pointing toward the moon while some advocate dropping some really good research which is just starting to show promise. I'm beginning to think US Manned spaceflight is never going to get anywhere useful, we're stuck into a cycle wherein we go full-steam into some project, do it, then get bored and move on before we've improved anything. <br /><br />By all rights the experience of the Shuttle and the ISS *should* provide a basis for designing the next spaceplane and for assembling a Moon or mars spacecraft in earth orbit. By the same token at the end of the apollo program that project should have formed the basis for either a more economical, more permanent moon program, or at least a backup capsule to the Shuttle. And of course during apollo it's possible that the Gemini LEO program should have been maintained, as it possibly could have been of more use for what we did post-Apollo than Apollo turned out to be. Now we're falling into the same trap, throwing away our current technology because we're "bored with going around in circles" (just as aside, since when is going around in an ellipse any better?) while reverting to capsules. I fear that since the SDLV and CEV do not really break any new ground we may fin
"An interesting POV considering your namesake was a great proponent of spaceplanes, space stations and other incremental infrastructure to reaching the moon before he became part of the Marshall Spaceflight Center and Apollo/Saturn. It's likely that if we'd followed Von Braun's original plan we'd have a permanent moonbase and Mars missions by now, all launched from a LEO space station operational in the 1960s."<br /><br />The US could not have landed men on the moon before 1970 using that approach. And it doesn't really matter what might have been. What matters is the present and the future. I say it again: Griffin's plan is the best we'll get. Anything else would be too expensive/technically challenging/politically unfeasible. <br /><br />Regarding spaceplanes: NASA tried that and failed miserably. Let the private sector develop CATS while NASA takes us back to the Moon and on to Mars.