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Back To The Future? I've not written much about NASA's planned "Orbital Space Plane" (OSP) program because, for various reasons, I've thought it beside the point. I'll explain why shortly. It's just the next stage in a continuing progression of abortive plans to either replace or complement the space shuttle that have been put forth for over a decade and a half. Of course, with the loss of a quarter of the essentially irreplaceable shuttle fleet three months ago with the Columbia disaster, the matter has taken on a seeming new urgency. The OSP is viewed as an admission that (at least for our government space agency) the more grandiose plans for "Shuttle II" were unrealistic, with the failures of (among other things) the National Aerospace Plane, and the X-33 fiasco. Instead, because the government (mistakenly) perceived that, as a result of these program failures, fully-reusable space transports were not achievable, they decided to back off to nascent plans of forty years ago--to place a reusable entry vehicle on top of an expendable launch system. The original concept for this was called Dynasoar--a winged vehicle that would provide access to space on a rocket, and then return to earth to land on a runway. In fact, it was the first concept for manned space, predating Mercury, but it was cancelled in 1963. But the dream never died. NASA's OSP program is just the latest reincarnation of this ancient desire for a small, flexible winged passenger transport system. Wings were desired because they provide much more accurate and precise control over landing locations, and a much more gentle touchdown (an important factor if the vehicle is to serve as an ambulance for ill or injured crew). Winged entry vehicles have disadvantages as well, however. The guidance and navigation requirements are more exacting, because the vehicle must enter at precisely the right angle, with little margin for error, to avoid the kind of overheating and stresses that apparently destroyed Columbia in February. Moreover, the heat loads on wing leading edges are much higher than a more distributed load over a broad surface (such as a ballistic capsule) would be, so the thermal protection requirement is much more stringent. As we saw with Columbia, the thermal protection system was the ultimate "Achilles heel" for winged entry vehicles, and at this point, given that recent experience, it's almost certainly one of the highest areas of technical risk, with extreme implications for safety. Due to these and other factors (some of which are inherent to NASA's way of doing business), resulting in absurdly high estimates (perhaps in excess of ten billion dollars) for cost and schedule to develop such a system, the agency has now been led to look at something simpler and less costly, albeit less capable and flexible as well. The latest news is that NASA is looking back to Apollo as a concept for near-term crew access to and from space. The idea is to use a ballistic entry vehicle, that we know works well, based on the Apollo command module concept. Just how much of that original design would be used is still to be determined, as the article in the link shows, but at a minimum, the vehicle would employ the same outer mold line, or body shape, as the original capsules that returned our astronauts safely from the Moon several times in the late sixties and early seventies, with a great deal of margin in the thermal protection system. There are many trade studies to be done, including whether or not to attempt to come up with a way of bringing it down on land rather than (as was done in Apollo) in the ocean, and how reusable to make the system, in which the type of thermal protection system will be the largest factor. Apollo used an ablative system, in which the insulation actually charred and came off in thin layers, carrying the heat away with it. This approach may make sense for the new vehicle as well, if such a shield can be made cheaply and easily changed each mission, but fully reusable shields employing more modern materials will be considered as well. Such a system, with its greater forgiveness of guidance failures (demonstrated by the mishap on the Soyuz entry vehicle last week, in which the landing was hundreds of miles off target, and much harder than planned, due to a computer malfunction) might well be more robust than a more sophisticated space plane, in which a similar failure might have resulted in loss of vehicle and crew. But as I said at the beginning of this column, I consider the whole issue personally moot, even if (in defiance of the long history of such programs) it turns out to be technically successful, because it is all based on a flawed premise--that we as a nation know what we want to accomplish in space, and that is to continue to send a few government employees up to a space station each year, and that we don't mind spending billions of dollars per year to do so. No one should be deluded that OSP in any form will reduce the costs of access to space, though it may make it moderately safer than the shuttle. No system that costs billions of dollars to develop and is used only a few times a year will ever even pay for itself, as we've seen with shuttle itself. And if we phase out shuttle, we will be back to a single, fragile infrastructure for getting people to and from space. As long as the space agency's and Congress' focus remains on their own institutional and political needs, rather than on those of the nation, and they continue to ignore the yearning of millions of people for space activities of their own, we will continue to squander billions on a mission to nowhere. And sadly, that too would be "back to the future." Posted by Rand Simberg at May 07, 2003 09:07 PMTrackBack URL for this entry:
http://www.transterrestrial.com/mt-diagnostics.cgi/1225 Listed below are links to weblogs that reference this post from Transterrestrial Musings.
Apollo Redux? Not Likely
Excerpt: Transterrestrial Musings talks about NASA's plans for the Orbital Space Plane, which is "intended to provide crew and limited cargo access to and from the International Space Station." Apparently, NASA is considering an Apollo CM-inspired design, becau... Weblog: Caerdroia Tracked: May 8, 2003 10:31 AM
Apollo Redux? Not Likely
Excerpt: Transterrestrial Musings talks about NASA's plans for the Orbital Space Plane, which is "intended to provide crew and limited cargo access to and from the International Space Station." Apparently, NASA is considering an Apollo CM-inspired design, becau... Weblog: Caerdroia Tracked: May 8, 2003 10:32 AM
Comments
Wasn't there the problem of the lifting body inducing huge bending moments into the stack with the dynasoar? I recall chatting to an ESA engineer a few years ago at a convention and he was saying that it was one of the more annoying problems with the Hermes design. Posted by Dave at May 8, 2003 09:16 AMYes, that's another issue, but this is today's Fox column, that has to live with a thousand words. I might update this post to reflect that, though. Posted by Rand Simberg at May 8, 2003 10:00 AMRe-usable launch rockets and manned spacecraft that can not only return the crew capsule for re-use, but the 'expensive service module' as well, are the only affordable way to consistently access space. The Space Shuttle’s inability to satisfactorily demonstrate this should not mean reverting back to single-use launchers and, at best, only a reusable capsule. Overcoming the shuttle’s shortcomings with a completely new ‘fly-back booster/Shuttle system,’ and addressing the tremendously beneficial use of recoverable nuclear rocket engines for use within the atmosphere could recover lost time wasted on the failings of the shuttle: a vehicle I don’t believe Wernher Von Braun ever supported! The Shuttle was a compromise. They new the system would be more expensive and complex to operate, but chose it because it was less expensive to develop to get it past congress. NASA’s problem is that it is too willing to beg for dims, when it really need to save up its dollars. They need a level of expert resolve that can say back to the government – “this is the sound way to do it. If you are not willing to fund it – lets shelve it until we can.” Sending people into space is an almost senseless notion unless you have a BIG re-usable shuttle-like system to give them the ability and resources they need to actually do something of value. A small taxi (like OSP) only exacerbates the cost and limited use of Alfa: whose critical parts (only intended to operate 10 years) will be old by the time OSP flies. At this defining moment, let’s scrap the station instead (and thus the need for OSP), and develop a new and more powerful Shuttle (of some kind – a Multi-use flyback Energia or something). "The tremendously beneficial use of recoverable nuclear rocket engines within the atmosphere"? I'm with you most of the way, but what kind of rockets are you talking about? If it's NERVA-type nuclear thermal, isn't the exhaust from those more than a bit radioactive? Are you sure you want to light that in the atmosphere? Posted by Jeff Dougherty at May 8, 2003 02:29 PMI think our priorities should be set on building a space elevator. Once we can get hardware on the ground into space for pennies a pound then we will be able to really start exploring the universe. We will be able to start building spacecraft on the scale needed to travel to neighboring planets and eventually to the stars. Also I was reading about how Nixon and NASA had made the decision back in the 70's to go strictly LEO instead of continuing to go to the moon or trying on Mars. I just think that was such a bad decision for NASA to even consider LEO as a project goal. From the get go, LEO should have been left to the private enthusiast and NASA should have stayed focused on getting a Moon base built with a fully capable rocket launch facility. After all NASA seems to have a hard time launching vehicles from a heavy Earth with a thick atmosphere so they might have better luck on the Moon. I agree with Hefty all the way. The only technology we lack to build a space elevator is the ability to create and manufacture carbon nanotubes in the needed strengths and quantities. CNTs seem to be getting better everyday and I have little doubt that space elevators will be built within my lifetime. Posted by Starlight Express at May 8, 2003 06:59 PMTwo words: retractable wings. Posted by John S Allison at May 9, 2003 06:47 AMRetractable Wings? I'm not sure this could feasible within any sensible weight constraint. Not to mention if all you are going to use them for is a final glide in once you've killed your velocity with a ballastic re-entry then you may as well use a parachute. I can't see the benefit other than that. Posted by Dave at May 9, 2003 06:51 AMNot to mention how bad a day it is when they don't, for some reason, unretract... Posted by Rand Simberg at May 9, 2003 07:33 AMJeff, I'll be sure to get the exact figures but I did a study on the Radioactivity of a large air-burst nuclear weapon (over 100KT) and was shocked to find that it only imparted 7 RADS on an unexposed person 2.5 miles away: barely enough to make a person sick and all would recover in seven days. You'd think a nuclear explosion of that size would make everyone glow within a 100 miles but they are not made mostly of Uranium anymore like the WWII bombs were. Mr. Eldridge might want to check out Nuclearspace.com to start his nuke engine research. Simply put, though a nuclear reactor produces a great deal of heat energy and, adequately shielded, need not irradiate any working fluid used to transfer that heat energy from its source to the environment. (In the case of a power reactor, this working fluid is water/steam and the movement of that fluid from the reactor to the environment, by way of a steam turbine, is what produces electricity.) The primary problem with nuclear engines used for transportation in the atmosphere or in space is that "adequately shielded" part. Shielding is bulky, heavy, or both and this goes directly against aerospace design criteria for 'good materials'. For the record, (and before the readership, or worse, Rand, pounces on me) included in my use of the term 'shielding' with regard to nuclear engines are such minor concepts as separation of the coolant from the working fluid (ie. closed coolant cycles) as well as absorbers for ionizing radiation and stray neutrons. Posted by Mike Sargent at May 9, 2003 09:39 AM(1) A winged space plane needs to be either side mounted on a booster, similar to the Shuttle, or have folding wings similar to those on a Navy carrier aircraft which would be unfolded while in orbit. An old study indicated that putting a fixed wing spaceplane atop its booster would need an intestage interface wighing about 1/4 as much as the space plane itself. No good! (2) Nuclear thermal boosters will never fly within the atmosphere for public relations and poltical reasons. I'd suggest sending nuclear thermal propulsion devices into orbit as a payload, and testing and using them only outside Earth's atmosphere. (3) Space elevators are bonkers. Save that stuff for press packages to be sent to Popular Mechanics magazine. (3) Parafoil n.g. for a re-usable craft. -- David Davenport Posted by David Davenport at May 9, 2003 10:55 AMSpelling corrections: "political" and "interstage." Re Rogallo wings: NASA tested one in the 1990's for the X-38 Assured Crew Return Vehicle full-sized prototype. Reportedly, it worked OK after early difficulties with flutter of the semirigid airfoil were overcome. Again, if an Orbital Space Plane/mini-Shuttle is to be built, the correct configuration is to have it mounted in parallel with its booster, with the main engines on the booster. Such a parallel arrangement is structurally stronger than a stacked or series configuration. These was realized circa 1972 when the present Shuttle desing was finalzied. NASA is putting out press releases showing the new OSP stacked atop a two stage missile because NASA wants to use Delta or Atlas missiles whose upper stage are designed for a "stakced" terminal stage. I think that wanting to use current the EELV Atlas or Delta system to launch the OSP/ mini-Shuttle is a pseudo-expedient shortcut that will turn out not to be a shortcut at all. Whether a single stage or two booster stages will be needed to launch the mini-shuttle is TBD. Since the the mini-Shuttle has no main engines to fire, it can be mounted further up, with its nose approximately level with the nose of its booster, thereby minimizing the danger of being struck by debris from the booster. The new booster won't have spray-on external insulation, in any event. The mini-Shuttle will be designed to be able to separate from the booster at any ascent speed, including zero m.p.h. while still on the launch pad. Yep, this can be done with a side mounted, a.k.a. parallel, configuration. The OSP/mini-Shuttle will have sufficient propulsive power of its own to ascend from zero altitude to parachute opening altitude. The mini-Shuttle will be designed to float and to survive an emergency water landing. Whether the mini-Shittle would try to land on the runway or in the lagoon after a zero-altitude ejection event at the Cape is TBD. The mini-Shuttle will also be provided with ejction seats or pods for the 4-6 humans aboard. Soory, it's probably not possible to design a escape pod that could BE deployed during the hottest part of re-entry. -- David Davenport Posted by David Davenport at May 9, 2003 11:20 AMSpelling corrections: "political" and "interstage." Re Rogallo wings: NASA tested one in the 1990's for the X-38 Assured Crew Return Vehicle full-sized prototype. Reportedly, it worked OK after early difficulties with flutter of the semirigid airfoil were overcome. Again, if an Orbital Space Plane/mini-Shuttle is to be built, the correct configuration is to have it mounted in parallel with its booster, with the main engines on the booster. Such a parallel arrangement is structurally stronger than a stacked or series configuration. These was realized circa 1972 when the present Shuttle desing was finalzied. NASA is putting out press releases showing the new OSP stacked atop a two stage missile because NASA wants to use Delta or Atlas missiles whose upper stage are designed for a "stakced" terminal stage. I think that wanting to use current the EELV Atlas or Delta system to launch the OSP/ mini-Shuttle is a pseudo-expedient shortcut that will turn out not to be a shortcut at all. Whether a single stage or two booster stages will be needed to launch the mini-shuttle is TBD. Since the the mini-Shuttle has no main engines to fire, it can be mounted further up, with its nose approximately level with the nose of its booster, thereby minimizing the danger of being struck by debris from the booster. The new booster won't have spray-on external insulation, in any event. The mini-Shuttle will be designed to be able to separate from the booster at any ascent speed, including zero m.p.h. while still on the launch pad. Yep, this can be done with a side mounted, a.k.a. parallel, configuration. The OSP/mini-Shuttle will have sufficient propulsive power of its own to ascend from zero altitude to parachute opening altitude. The mini-Shuttle will be designed to float and to survive an emergency water landing. Whether the mini-Shittle would try to land on the runway or in the lagoon after a zero-altitude ejection event at the Cape is TBD. The mini-Shuttle will also be provided with ejction seats or pods for the 4-6 humans aboard. Soory, it's probably not possible to design a escape pod that could BE deployed during the hottest part of re-entry. -- David Davenport Posted by David Davenport at May 9, 2003 11:20 AMRe folding or retractable wings: think of the wings on carrier aircraft which fold upwards -- and no, they don't do that while in flight. A mini-Shuttle with folding wings would unfold 'em while in orbit, with no air pressure on the wings and with opportunity to verify that the wings were proper position before re-entry. Why bother with folding wings on a side mounted mini-Shuttle? It would be nice if the new space plane had a slower touchdown speed than the current Shuttle. -- David Davenport Posted by David Davenport at May 9, 2003 11:26 AMI forgot to complete the thought: folding wings might be used to afford a wider wingspan/weight ratio ( i.e. lower induced drag ) and more lifting area/weight than the current Shuttle, thereby allowing a slower touchdown speed as well as more cross range gliding capability. ... Perhaps enough gliding range to traverse the Eurasian land mass while decending inside the atmosphere on missions of military interest. The idea here is to address as many safety issues as possible when designing our shiny new fully re-useable mini-Shuttle system. The question I'd like to debate is whether to settle for a vertically launched, horizontal landing system, or to swing for the home run, which be the Saenger II configuration -- two stage horizontal takeoff, with an airbreathing first stage.
No one thinks we should ‘can’ the space station? I don’t think it is very useful. At least it has set a low benchmark that will make the next proposal sound like the bargain of a lifetime! Hey, if it had a nuclear generator, think how much less shuttle construction trips would have been needed. In regard to the use of such propulsion in atmosphere, I’ve been looking and found at least this quote (repeated at several sites): “Interestingly enough, one of the major justifications for selecting a nuclear rocket for the reference design was to reduce the total radiation dose received by the astronauts participating in the mission.” “Natural radiation levels in space are much higher than on earth, since there is no atmospheric shielding, and the higher speed of travel made possible by the use of nuclear power reduced the time of exposure to high background radiation enough to make up for the increased exposure to the on-board source” I also found that nuclear propulsion was proposed for future launch vehicles as well. RAD’s are still a question, and thus I have written the University of Florida for their take on it. Dave, With due respect to Mr. Davenport's opinions, I offer the following, enumerated responses: 1) "An old study" is, by definition, not the current state of the engineering art. Again, I refer to Dr. Forward's research as a starting point for consideration of 'active materials' and alternative engineering approaches to the, admittedly difficult, requirements of a space vehicle. 2) While I agree that nuclear-thermal rocketry within the atmosphere could be a hard sell, it might in fact literally be 'sold' with a sufficiently creative (which is NOT to say 'false') advertising campaign. Starting with renaming the technology 'geothermal propulsion', which is a technically accurate characterization, would avoid using the 'N-word'. 3) [space elevators] "When an eminent scientist tells you something is possible, he should be believed. When he tells you something is impossible, he shouldn't be." Note: I'm paraphrasing. Again, I refer you to Dr. Forward who's personal investment in space tethers indicates that he believed that the 'space elevator' or 'beanstalk' concept was, at least in some part, valid and acheivable. Please at least read the available scientific literature on this one before dismissing an elegant and inspiring possibility. 3) [sic] [parafoil] While a parafoil may not, itself, be reusable, that would not invalidate its use on an otherwise wholly reusable spacecraft. Additionally, a parafoil pack that added lifting area to a lifting-body spacecraft could add the benefits of increased wing area on landing, reduced wing area on takeoff, and be engineered to separate at some arbitrary speed and altitude for later recovery and reuse. And I'd bet that all of these could be done within the mass and money budget that would go into fixed or swing wings. Mr. Eldridge- thanks for your comments. While theoretically a nuclear thermal rocket only has heat imparted by the reactor to your working fluid, in practice most of the designs I have seen use one fluid as both coolant and working fluid- i.e. the cryogenic fuel is used as a temperature moderator, and then injected into the core for use as working fluid. I believe that the alternative, having separate fuel and coolant, was rejected as weight prohibitive. Also, due to weight constraints, the designs for aerospace reactors tend to be less well shielded, leading to some radioactivity in the working fluid even if it is separate. Now, leakage might not be a problem, but if your exhaust itself is being used as reactor coolant it's probably going to be pretty heavily irridiated. And if you're firing this thing in the upper atmosphere, you have the potential to spread that radiation over a pretty large area, similar to the upper-atmosphere bombs tests of the 1950s. In my opinion, nuke engines are a great idea once you're out of the atmosphere- as you said, they reduce the total travel time, which is all kinds of good. Once you're out in space, who cares if your exhaust is radioactive? If you're in the atmosphere, on the other hand, plenty of people might care. Posted by Jeff Dougherty at May 9, 2003 01:29 PMI've just taken the time to review the commentary to date and would like to point out the sheer beauty of 'back of the envelope' engineering sessions like this. In less than 36 hours there have been at least five possible design approaches forwarded against the concept 'manned space vehicle'. A month or so of tinkering by a talented class of aeronautics undergrads could conceivably result in as many, technically workable, prototypes. What happens after that, though, is the telling part. In the first scenario, these prototypes and the operations plans associated with them are handed over to a vast bureaucracy (public, ie NASA, or private, e.g. Lockheed, Boeing, or others) and they are either studied to death, engineered within an inch of their lives, or are divvied up among a number of established power-bases to curry favor (congressional districts, space centers, or corporate divisions) and wither on the vine. (Sometimes, rarely, one concept might make it to a testing stage, but the last truely new spacecraft, manned or otherwise, to come from these sources was the current Shuttle and it launched when I was in grade school.) In the other scenario, the undergrads turn it over to the business and finance undergrads who, after another month, develop business plans around them and market them for venture capital and offer them for true competition on the international market for launch services. I'm not saying that this scenario leads to all or any of the concepts performing a single orbit, but it does seem the more likely way for at least one to see the pad. Posted by Mike Sargent at May 9, 2003 01:47 PMDave, With respect to the Saenger II concept, how well understood are the aerodynamics of separtaing one aircraft from another at high speeds? IIRC the concept calls for a Mach 3+ separation, which gives you some pretty wicked slipstreams. The only time I can remember that being done in real life is with the A-12/D-21 drone program, which ended up being cancelled after a couple of in-flight disasters involving the just-launched drone colliding with the carrier aircraft. Could be some bad juju if you're depending on a supersonic separation of your launch vehicle from an air-breathing first stage. Also to weigh in on the "spaceplane on a stick" concept: unless we want to use active materials, IIRC the bending stress caused by having part of your stack generate lift and part of it not doing so is really more than you want to deal with. Now, if your heart is set on a lifting body or winged configuration, you can always use a shroud on launch, but that's one more thing that isn't coming back. Could complicate launch escape scenarios, too. Posted by Jeff Dougherty at May 9, 2003 03:51 PMMy money is riding on the MMO - Neat! It sounded like they were planning on using this as more of an in-space propulsion system, since Orion is probably a no-go in atmosphere for a whole bunch of reasons, but this could be really great for interplanetary applications. It also seems a lot more sound to my (admittedly non-engineering) mind than the original Orion concept- sounds like it would be practical for much smaller vehicle masses, for one thing. Very cool stuff. Posted by Jeff Dougherty at May 9, 2003 07:46 PMRe Rogallo wings: NASA tested one in the 1990's for the X-38 Assured Crew Return Vehicle full-sized prototype. Reportedly, it worked OK after early difficulties with flutter of the semirigid airfoil were overcome.This turns out not to be true. NASA tested a series of large parafoils on X-38, but parafoils are definitely not Rogallo wings (Rogallos were tested on the Gemini land-landing system, however). Parafoils are what skydivers presently use for parachutes, deployable ram-air inflated wings; Rogallos are batten-stiffened, single-surface, lower-performance devices. The problems experienced on the X-38 project (and on earlier large-parafoil developmental programs) weren't "flutter"; they were several other things, however, only some of which have been successfully addressed. Despite the success of smaller parafoils as personnel parachutes, I think it would be fair to say that large parafoils (payload capacities of 5000-25,000 pounds) are still very much in the developmental stage, especially toward the higher end of the range. Please forgive me for not going into more detail about the large-parafoil problems, and for including no name nor email. I really want to keep my job. Posted by at May 9, 2003 09:35 PMTo the anonymous poster: My sympathies. To paraphrase Jefferson; "When the press is free (ie when all may write without fear of censure) and all may read, only then is a nation truly free." Whether the censor is the government or one's employer, censorship seldom contributes to open consideration of ideas. [Steps down from soapbox.] Now, could you give us some open source reference(s) to large capacity parafoils and their performance problems? Much of what I've read is long on optimism but short on test-derived meat. Proposals for GPS-guided steerable chutes, making possible long standoff delivery of logistics support to the battlefield or of stable launch platforms for cruise missiles from cargo aircraft seem to indicate that the engineering issues are surmountable but give little in the way of specifics. Posted by Mike Sargent at May 10, 2003 07:54 AMI stand corrected, or partially corrected. Rogallo did not invent the ram-air parafoil, although he is credited with a non-rigis, single membrane antecedent to the ram-air parafoil: http://www.parachutehistory.com/eng/drs.html " ... During the early space projects, Rogallo developed a single membrane flexible wing, known as the parawing. The large parawings designed for recovery of reentry vehicles did not have reliable opening characteristics at high speeds and were not used in the actual manned flights. There are several review articles describing the subsonic deployment and control of parawings. The parawing parachute, designed for maximum lift as opposed to maximum drag, was primarily used in sport parachuting during the 1970's.
Cpmapare the pix of the two lifting devices at the afore mentioned website. Re directional stability difficulties due to flexing of the ram-air parafoil lifting surface, i.e. flutter, consider this: "http://www.space.com/businesstechnology/technology/x43a_destroyed_010602.html "... One of the toughest challenges faced by X-38 engineers has been use of a large parafoil. Roughly one-and-a-half times the wing area of a 747 jumbo aircraft, the giant-sized parachute has proven troublesome during deployment. Transitioning from a falling lifting body to a craft hanging blissfully underneath the parafoil "was not a trivial deal," Nagy said. "There's a lot of technology with parafoils used in the skydiving community. But nobody had data on a parafoil this big," he told SPACE.com. Last month's drop test checked advances in the two-stage repositioning deployment of a drogue parachute that initially cuts the vehicle's speed, setting the stage for the step-by-step blossoming of the 7,500-square-foot-parafoil wing. While largely successful, Nagy said, "fine tuning" of the parafoil's unfurling is needed in subsequent tests. "But we've gone from a point in 1997 where a lot of people were saying if the parafoil gets out and deployed. Now we're working on how smooth it comes out…and making it a good ride for the people on board," Nagy said. ..." My point is this: the X-38 prpgram did perform a successful landing using a large p[arafoil. However a parafoil is not optimal for a true aerspace plane that would return to Earth many times a year -- as opposed to emergency returns. Why? Because nonrigid or semirigid airfoils, particularlly very large ones, inherently have more stability and control difficulties than do rigid lifting surfaces. -- David Davenport Posted by David Davenport at May 10, 2003 08:50 AMOnce again, plaeas pardon my spelling errors in the previous post. I'm a hasty typist. More X-38 background: http://www.astronautix.com/craft/x38.htm X-38 Code Name: Spacewedge. Class: Manned. Type: Rescue. Nation: USA. Agency: NASA. Manufacturer: Orbital Sciences. Parafoil tests began in 1996, roll out of first of two slightly subscale 7.31 m long atmospheric test vehicles was in November 1996. After captive-carry flights from NB-52 in February 1997, first drop test is to occur in May 1997. First test of space vehicle planned for 1999. All test flights to be unmanned. NASA hopes to break all precedents and develop this manned vehicle for under $ 500 million. ( Forlorn hope, that. )Later spaceframe could be stuffed with more elaborate life support, attitude control, and avionics systems to provide manned spacecraft for launch from Ariane 5, Titan 4, Atlas 2, Delta 3, H-2, Proton, or Zenit (thereby finally achieving objective of cancelled Hermes, X-24C, HOPE, and Urgagan projects). ... Posted by David Davenport at May 10, 2003 09:06 AMThere are more pix of X-38 parafoil testing here: http://www.engr.uconn.edu/~adstc/imagepage.html. Also note the photo of the "Experimnetal Semi Rigid Wing Rest Flight." That's a strict sense Rogallo wing, I suppose. Posted by David Davenport at May 10, 2003 09:28 AMLooking at those pictures of the X-38 seems you could probably design the wings to fold back for launching on top an EELV. Only question would be would folding the wings back be enough to spoil the lifting properties of the rest of the vehicle? Posted by Shawn at May 10, 2003 12:34 PMSeems I saw a recent space-elevator analysis that said nanotubes are currently lacking in strength but theoretically they are more than sufficient. I'm not sure if the problem is impurities or getting the nanotubes to grow uniformly. I'm not sure why low-angle reentry is so undesirable; is the "skipping-off" effect so random as to preclude any ability to land where you wish to? I'd think it'd be a huge plus to skip a few times before reentry, to get the velocity down. Having no idea what I'm talking about in this area helps a lot, let me tell you. Posted by David Perron at May 10, 2003 02:00 PMI'm still not sure why the wings and steering are necessary. If you're using ablative shielding, you only need to be able to dodge an obstacle right before you land. The Soviets have obviously chosen the cheapest landing system for maneuvering, called a truck. During the Shuttle design the thermal limits of the wings gave it a smaller cross-range capability than the Apollo. Considering that our ballistic missiles can hit with extreme precision, I would think it odd if we couldn't accurately hit the Mojave desert. The Apollo was never even designed to have its electronics taken apart, much less re-used. If the craft were designed to be a replaceable shell wrapped around some seats, electronics, and thruster assemblies, even replacing the entire hull should be cheaper than refurbishing just one SSME. It may not be the way to go, but many of the dyna-soar derivatives just look like a much heavier, clunkier, riskier, and more expensive way to avoid a 10 mile road trip. Posted by George Turner at May 11, 2003 02:36 PMGeorge is right, which is obvious when you focus on the goal which is to get people back to dirt with safety and a reasonable cost. Wings and parafoils are of negative value. I believe this has been successfully argued by the comments so far. A reusable capsule with a disposable heat shield could land on land or sea. The capsule could easily be designed to float, whereas airbags could soften a parachute landing on soil. Another plus, land close enough to Las Vegas (which has a lot of the required desolation nearby) and we could provide poker chips and show tickets for relaxation from the stresses of the mission! Sign me up! If I understand the problem of mounting a lifting body to the top of a booster right, I agree with Jeff who said to use a shoud I think. Much as the slight buildup of ice on a wing's leading edge disrupts lift, so too we could add discarding plastic sabots to the surface of an OSP. Such light plastic add-ons could cocoon and, thus, negate and nullify the lifting shape of the OSP inside a cylinder if needed, but only minor alterations to air flow are probably necessary. Post a comment |