Date: Thu, 18 Mar 93 05:22:39 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V16 #331 To: Space Digest Readers Precedence: bulk Space Digest Thu, 18 Mar 93 Volume 16 : Issue 331 Today's Topics: DC-X Just a little tap (was Re: Galileo HGA Retraining at NASA Semi-technical aspects of SSTO SSTO: A Spaceship for the rest of us Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: Wed, 17 Mar 1993 21:43:07 GMT From: "Allen W. Sherzer" Subject: DC-X Newsgroups: sci.space In article <1993Mar15.215111.16934@draper.com> mrf4276@egbsun10.NoSubdomain.NoDomain (Matthew R. Feulner) writes: >I haven't been keeping up to date, so could someone give me a reference >where I can read about DC-X? I'll re-post a couple of papers I have. The first was written by me and is the draft NSS position paper on SSTO. The second was written by Henry Spencer for the Freshmen Orientation project. Allen -- +---------------------------------------------------------------------------+ | Allen W. Sherzer | "A great man is one who does nothing but leaves | | aws@iti.org | nothing undone" | +----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+ ------------------------------ Date: 17 Mar 93 21:01:47 GMT From: "Don M. Gibson" Subject: Just a little tap (was Re: Galileo HGA Newsgroups: sci.space In article 732388252@golem.ucsd.edu, rabjab@golem.ucsd.edu (Jeff Bytof) writes: >This is really off the wall, but would there be any way to calculate >the effect of forces due to induced magnetic fields on the spacecraft >structure and antenna as it passes through the intense Jovian magnetic >and particle fields? Perhaps a way could be found by proper orientation >of the spacecraft to apply differential pressure to some critical area >of the structure. it seems calculatable, but i have no idea how. the S/C orientation is determined by the need for the orbit insertion burn. --DonG ------------------------------ Date: 17 Mar 93 14:19:42 From: Steinn Sigurdsson Subject: Retraining at NASA Newsgroups: sci.space In article szabo@techbook.com (Nick Szabo) writes: Get off this stupid forum and get back to work, you lazy, good-for-nothing exemplar of why socialism sucks. If you Cut it out Nick. | Steinn Sigurdsson |I saw two shooting stars last night | | Lick Observatory |I wished on them but they were only satellites | | steinly@lick.ucsc.edu |Is it wrong to wish on space hardware? | | "standard disclaimer" |I wish, I wish, I wish you'd care - B.B. 1983 | ------------------------------ Date: 17 Mar 93 21:48:19 GMT From: "Allen W. Sherzer" Subject: Semi-technical aspects of SSTO Newsgroups: sci.space [This paper was written for the Freshmen Orientation Project by Henry Spencer] (Semi-)Technical Aspects of SSTO by Henry Spencer This paper will try to give you some idea of why SSTO makes technical sense and is a reasonable idea. We'll concentrate on the overall issues, trying to give you the right general idea without getting bogged down in obscure detail. Be warned that we will oversimplify a bit at times. Why Is SSTO Challenging? Getting a one-stage reusable rocket into orbit doesn't look impossible, but it does look challenging. Here's why. The hard part of getting into orbit is not reaching orbital altitude, but reaching orbital velocity. Orbital velocity is about 18,000mph. To this, you have to add something for reaching orbital altitude and for fighting air resistance along the way, but these complications don't actually add very much. The total fuel requirement is what would be needed to accelerate to 20-21,000mph. So how much is that? (If you don't want to know the math, skip to the next paragraph for the results.) The "rocket equation" is desired_velocity = exhaust_velocity * ln(launch_weight / dry_weight), where "ln" is the natural logarithm. The exhaust velocity is determined by choice of fuels and design of engines, but 7,000mph is about right if you don't use liquid hydrogen, and 10,000mph if you do. The bottom line is that the launch weight has to be about 20 times the dry weight (the weight including everything except fuels) if you don't use liquid hydrogen, and about 8 times the dry weight if you do. This sounds like hydrogen would be the obvious choice of fuel, but in practice, hydrogen has two serious problems. First, it is extremely bulky, meaning that hydrogen tanks have to be very big; the Shuttle External Tank is mostly hydrogen tank, with only the nose containing oxygen. Second, some of the same properties that make hydrogen do well on the weight ratio make it difficult to build hydrogen engines with high thrust, and a rocket *does* need enough thrust to lift off! Both of these problems tend to drive up the dry weight, by requiring bigger and heavier tanks and engines. So how bad is this? Well, it's not good. Even with hydrogen, an SSTO launcher which weighs (say) 800,000lbs at launch has to be 7/8ths fuel. We've got 100,000lbs for tanks to hold 700,000lbs of fuel, engines to lift an 800,000lb vehicle, a heatshield to protect the whole thing on return, structure to hold it all together at high acceleration... and quite incidentally, for some payload to make it all worthwhile. Most of the dry weight has to go for the vehicle itself; only a small part of it can be payload. (That is, the "payload fraction" is quite small.) To get any payload at all, we need to work hard at making the vehicle very lightweight. The big problem here is: what happens if the vehicle isn't quite as light as the designer thought it would be? All rockets, and most aircraft for that matter, gain weight during development, as optimistic estimates are replaced by real numbers. An SSTO vehicle doesn't have much room for such weight growth, because every extra pound of vehicle means one less pound for that small payload fraction. Particularly if we're trying to build an SSTO vehicle for the first time, there's a high risk that the actual payload will be smaller than planned. That is the ultimate reason why nobody has yet built an SSTO space launcher: its performance is hard to predict. Megaprojects like the Shuttle can't afford unpredictability -- they are so expensive that they must succeed. SSTO is better suited to an experimental vehicle, like the historic "X-planes", to establish that the concept works and get a good look at how well it performs... but there is no X-launcher program. Why Does SSTO Look Feasible Now? The closest thing to SSTO so far is the Atlas expendable launcher. The Atlas, without the Centaur upper stage that is now a standard part of it, has "1.5" stages: it drops two of its three engines (but nothing else) midway up. Without an upper stage, Atlas can put modest payloads into orbit: John Glenn rode into orbit on an Atlas. The first Atlas orbital mission was flown late in 1958. But the step from 1.5 stages to 1 stage has eluded us since. Actually, people have been proposing SSTO launchers for many years. The idea has always looked like it *just might* work. For example, the Shuttle program looked at SSTO designs briefly. Mostly, nobody has tried an SSTO launcher because everybody was waiting for somebody else to try it first. There are a few things that are crucial to success of an SSTO launcher. It needs very lightweight structural materials. It needs very efficient engines. It needs a very light heatshield. And it needs a way of landing gently that doesn't add much weight. Materials for structure and heatshield have been improving steadily over the years. The NASP program in particular has helped with this. It now looks fairly certain that an SSTO can be light enough. Existing engines do look efficient enough for SSTO, provided they can somehow adapt automatically to the outside air pressure. The nozzle of a rocket engine designed to be fired in sea-level air is subtly different from that of an engine designed for use in space, and an SSTO engine has to work well in both conditions. (The technical buzzword for what's wanted is an "altitude-compensating" nozzle.) Solutions to this problem actually are not lacking, but nobody has yet flown one of them. Probably the simplest one, which has been tentatively selected for DC-Y, is just a nozzle which telescopes, so its length can be varied to match outside conditions. Making nozzles that telescope is not hard -- many existing rocket nozzles, like those of the Trident missile, telescope for compact storage -- but nobody has yet flown one that changes length *while firing*. However, it doesn't look difficult, and there are other approaches if this one turns out to have problems. We'll talk about landing methods in more detail later, but this is one issue that will be resolved pretty soon. The primary goal of the DC-X experimental craft is to fly DC-Y's landing maneuvers and prove that they will work. So... with materials under control, engines looking feasible, and landing about to be test-flown, we should be able to build an SSTO prototype: DC-Y. The prototype's performance may not quite match predictions, but if it works *at all*, it will make all other launchers obsolete. Why A Rocket? As witness the NASP (X-30) program, air-breathing engines do look like an attractive alternative to rockets. Much of the weight of fuel in a rocket is oxygen, and an air-breathing engine gets its oxygen from the air rather than having to carry it along. However, on a closer look, the choice is not so clear-cut. The biggest problem of using air-breathing engines for spaceflight is that they simply don't work very well at really high speeds. An air-breathing engine tries to accelerate air by heating it. This works well at low speed. Unfortunately, accelerating air that is already moving at hypersonic speed is difficult, all the more so when it has to be done by heating air that is already extremely hot. The problem only gets worse if the engine has to work over an enormous range of speeds: NASP's scramjet engines would start to function at perhaps Mach 4, but orbital speeds are roughly Mach 25. Nobody has ever built an air-breathing engine that can do this... but rockets do it every week. Air-breathing engines have other problems too. For one thing, to use them, one obviously has to fly within the atmosphere. At truly high speeds, this means major heating problems due to air friction. It also means a lot of drag due to air resistance, adding to the burden that an air-breathing engine has to overcome. Rocket-based launchers, including SSTO, do most of their accelerating in vacuum, away from these problems. Perhaps the biggest problem of air-breathing engines for spaceflight is that they are *heavy*. The best military jet engines have thrust:weight ratios of about 8:1. (This is at low speed; hypersonic scramjets are not nearly that good.) The Space Shuttle Main Engine's thrust:weight ratio, by comparison, is 70:1 (at any speed). The oxygen in a rocket's tanks is burned off on the way to orbit, but the engines have to be carried all the way, and air-breathing engines weigh a lot more. And what's the payoff? The X-30, if it is built, and if it works perfectly, will just be able to get into orbit with a small payload. This is about the same as SSTO, at ten times the cost. Where is the gain from air-breathing engines? The fact is, rockets are perfectly good engines for a space launcher. Rockets are light, powerful, well understood, and work fine at any speed without needing air. Oxygen may be heavy, but it is cheap (about five cents a pound) and compact. Finally, rocket engines are available off the shelf, while hypersonic air-breathing engines are still research projects. Practical space launchers should use rockets, so SSTO does. Why No Wings? With light, powerful engines like rockets, there is no need to land or take off horizontally on a runway, and no particular reason to. Runway takeoffs and landing are touchy procedures with little room for error, which is why a student pilot spends much of his time on them. Given adequate power, vertical takeoffs and landings are easier. In particular, a vertical landing is much more tolerant of error than a horizontal one, because the pilot can always stop, straighten out a mistake, and then continue. Harrier pilots confirm this: their comment is "it's easier to stop and then land, than to land and then try to stop". What if you don't have adequate power? Then you are in deep trouble even if your craft takes off and lands horizontally. As witness the El Al crash in Amsterdam recently, even airliners often don't survive major loss of power at low altitude. To make a safe horizontal landing, especially in less-than-ideal weather conditions, you *must* have enough power to abandon a bad landing approach and try again. Shuttle-style gliding landings are dangerous, and airline crews go to great lengths to avoid them; the Shuttle program, with the nation's best test pilots doing the flying and no effort spared to help them, has already had one near-crash in its first fifty flights. Routine access to space requires powered landings. If we are going to rely on powered landings, we must make sure that power will be available. Airliners do this by having more than one engine, and being able to fly with one engine out. SSTO is designed to survive a single engine failure at the moment of liftoff, and a second failure later. Since (at least) 7/8ths of the takeoff weight of SSTO is fuel, it will be much lighter at landing than at takeoff. Given good design, it will have enough power for landing even if several engines fail. If SSTO has an engine failure soon after liftoff, it will follow much the same procedure as an airliner: it will hover to burn off most of its fuel (this is about as quick as an airliner's fuel dumping), and then land, with tanks nearly empty to minimize weight and fire hazard. Note that in an emergency, vertical landing has one major advantage over horizontal landing: horizontal landing requires a runway, preferably a long one with a favorable wind, while a vertical landing just requires a small flat spot with no combustible materials nearby. A few years ago, a Royal Navy Harrier pilot had a major electronics failure and was unable to return to his carrier. He made an emergency landing on the deck of a Spanish container ship. The Harrier suffered minor damage; any other aircraft would have been lost, and the pilot would have had to risk ejection and recovery from the sea. Given vertical landing and takeoff, is there any other use for wings? One: crossrange capability, the ability to steer to one side during reentry, so as to land at a point that is not below the orbit track. The Shuttle has quite a large crossrange capability, 1500 miles. However, if we examine the history of the Shuttle, we find that this was a requirement imposed by the military, to make the Shuttle capable of flying some demanding USAF missions. A civilian space launcher needs a crossrange capability of, at most, a few hundred miles, to let it make precision landings at convenient times. This is easily achieved with a wingless craft: the Apollo spacecraft could do it. Finally, wings are a liability in several important ways. They are heavy. They are difficult to protect against reentry heat. And they make the vehicle much more susceptible to wind gusts during landing and takeoff (this is a significant limitation on shuttle launches). SSTO does not need wings, would suffer by carrying them, and hence does not have them. Why Will It Be Cheap And Reliable? This is a good question. The Shuttle was supposed to be cheap and reliable, and is neither. However, there is reason for hope for SSTO. The Shuttle's costs come mainly from the tremendous army of people needed to inspect and refurbish it after each flight. SSTO should get by with many fewer. The basic SSTO concept opens major possibilities for simple, quick refurbishment. With no discarded parts, nothing needs to be replaced. With no separating parts, there is no need to re-assemble anything. In principle, an SSTO vehicle should be able to "turn around" like an airliner, with little more than refuelling. Of course, this is easier said than done. But there is no real reason why SSTO should need much more. Its electronics experience stresses not much worse than those of an airliner -- certainly no worse than those of a jet fighter. Its structure and heatshield, designed to fly many times, will have sufficient margins that they will not need inspection and repair after every flight. Most space-vehicle components don't inherently need any more attention than airliner components. The one obvious exception is the engines, which do indeed run at much higher power levels than airliner engines. But even here, airliner principles can be applied: the way to make engines last a long time is to run them at less than 100% power. SSTO engines have it easy in one respect: they only have to run for about ten minutes at the start of the flight and two or three minutes at the end. Still, the Shuttle engines certainly are not a shining example of low maintenance and durability. However, it's important to realize that the Shuttle engines are not the only reusable rocket engines. Most liquid-fuel engines could be re-used, were it not that the launchers carrying them are thrown away after every flight. And the durability record of these other engines -- although limited to test stands -- is *much* better. The RL-10 engine, which will be used in DC-X, is rated to fire for over an hour, in one continuous burn or with up to ten restarts, with *no* maintenance. Several other engines have comparable records. Conservatively-designed engines are nowhere near as flakey and troublesome as the Shuttle engines. Here again, DC-X should soon supply some solid evidence. Although its engines and other systems are not the same ones that DC-Y would use, they should be representative enough to demonstrate rapid, low-effort refurbishment, and the DC-X program will try to do so. Airliners typically operate at about three times fuel costs. The fuel cost for an SSTO vehicle would be a few dollars per pound of payload. It may be a bit optimistic to try to apply airline experience to the first version of a radically new vehicle. However, even advanced aircraft typically cost no more than ten times fuel cost. Even if SSTO comes nowhere near these predictions, it should still have no trouble beating existing launchers, which cost several thousand dollars per pound of payload. We can look at this another way: head counts. Airlines typically have about 150 people per aircraft, and most of those sell tickets or look after passengers' needs. Perhaps a better example is the SR-71, which is like SSTO in that it was an advanced craft, pushing the frontiers of technology, operated in quite small numbers. Although it is hard to get exact numbers because of secrecy, it appears that USAF SR-71 operations averaged perhaps one flight per day, using perhaps eight flight-ready aircraft, with a total staff of about 400 people. That's 50 per aircraft. If SSTO can operate at such levels -- and there is every reason to think it can -- it should have no trouble beating existing launchers, which typically have several thousand people involved in preparations for each and every launch. (NASA's Shuttle ground crew is variously estimated at 6,000-10,000 for a fleet of four orbiters flying about eight flights a year.) As for reliability, the crucial reason for thinking that SSTO will do a lot better than existing launchers is simple: testing. It should be feasible and affordable to test an SSTO launcher as thoroughly as an aircraft. This is *vastly* more thorough than any launcher. The F-15 fighter flew over 1,500 test flights before it was released for military service. No space launcher on Earth has flown that many times, and the only one that even comes close is an old Soviet design. It is no wonder that the Shuttle is somewhat unreliable, when it was declared "operational" after a grand total of four test flights. By aircraft standards, the Shuttle is still in early testing. Some expendable launchers have been declared operational after *two* tests. Each and every SSTO vehicle can be tested many times before it carries real payloads. Moreover, since SSTO can survive most single failures, it can be tested under extremes of flight conditions, like an aircraft. For example, unlike Challenger, an SSTO vehicle would launch with passengers and cargo in freezing temperatures only after multiple test flights in such conditions. There will always be surprises when a new craft is flown in new conditions, but SSTO should encounter -- and survive -- most of them in test flights. Conclusion Although there is reason for some uncertainty about the exact performance of the first SSTO spacecraft, the basic approach being taken is sensible and reasonable. It should work. The imminent test flights of the DC-X test craft should resolve most remaining technical concerns. Nobody can be sure about costs and reliability until DC-Y is flying, but there is reason to believe that SSTO should be much better than current launchers. If the program is carried through to a flying DC-Y prototype in a timely way, it really could revolutionize spaceflight. From k.c.sheppardson@LaRC.NASA.GOV Thu Jan 28 08:55:06 1993 Received: from express.larc.nasa.gov by iti.org with SMTP (5.65b/IDA-1.2.8) id AA18457; Thu, 28 Jan 93 08:55:03 -0500 Received: from sheppardson.larc.nasa.gov by express.larc.nasa.gov with SMTP id BA01875 (SMTP/Lite-1.15) for ; Thu, 28 Jan 93 08:51:52 -0500 Message-Id: <728229112.BA01875@express.larc.nasa.gov> Date: Thu, 28 Jan 93 08:51:52 -0500 From: Ken Sheppardson To: aws@hela.iti.org Subject: Resume (text) Status: R Kenneth C. Sheppardson 125 Signature Way #216 Hampton, VA 23666 (804) 827-4924 OBJECTIVE To use my expertise in system modeling and analysis to support the design, development, operation and management of complex dynamic systems. EDUCATION * Stanford University, Stanford, California M.S. Engineering-Economic Systems June 1992 - Courses included Decision Analysis, Economic Analysis, Optimization, Probabilistic Analysis, Strategy and Planning Models, Accounting, and Investment Science - Projects included the application of decision analysis and optimization methods to develop a facility operations and maintenance plan for a division of Sandia National Laboratories * The University of Michigan, Ann Arbor, Michigan M.S.E. Aerospace Engineering April 1990 B.S.E. Aerospace Engineering August 1988 - Courses included Dynamics, Simulation, System Theory and Computer Aided Design - President of the Epeians Engineering Leadership Honor Society, Engineering Council Executive Secretary, College of Engineering Curriculum Committee Rep., University Research Policy Committee Rep., and a member of Tau Beta Pi and Sigma Gamma Tau EMPLOYMENT * NASA / Langley Research Center Space Station Freedom Advanced Programs Office Aerospace Engineer since 1990 Graduate Student Researchers Program Participant 1989 - 1990 Langley Aerospace Research Summer Scholar Summer 1989 - Managed and took part in space station systems engineering and analysis studies - Developed software to perform static and dynamic analysis of spacecraft and to facilitate the exchange of data between analysis packages * The University of Michigan Computer Aided Engineering Network RA - Control System Software Support Coordinator 1989 - 1990 RA - Instructional Innovation Program 1988 - 1989 Counselor / Lab Monitor 1988 - 1989 - Developed instructional material and provided group and individual instruction on the use of system modeling and analysis software * McDonnell Douglas Helicopter Company Engineering and Training Simulation Engin. Assoc.- Flight Dynamics Group Summer 1987 Engin. Assoc.- Visual Database Development Group Fall 1986 - Developed computational models of helicopters and missiles for flight simulation - Developed software to expedite the generation of flight simulator terrain databases and to allow real-time communication between simulation system workstations and mainframes * Houk and Soles, Inc. - Food Service Computing Consultants 1984 - Worked with food service industry clients to design and develop planning, inventory control, and purchasing systems for restaurants and institutions COMPUTER - Developed software in Ada, BASIC, C, FORTRAN, Pascal, and SKILLS assembly languages - Developed and supported software on platforms including UNIX workstations, Apple Macintosh systems, DEC VMS systems, Gould TSM systems, and IBM PCs - Extensive use and support of software including I-DEAS, MatrixX, ADAMS, MatLab, Easy5, MSC/NASTRAN, word processors, graphics packages, and spreadsheets -- +---------------------------------------------------------------------------+ | Allen W. Sherzer | "A great man is one who does nothing but leaves | | aws@iti.org | nothing undone" | +----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+ ------------------------------ Date: Wed, 17 Mar 1993 21:45:22 GMT From: "Allen W. Sherzer" Subject: SSTO: A Spaceship for the rest of us Newsgroups: sci.space [First of two papers on SSTO. This is also the draft NSS position paper on SSTO] SSTO A Spaceship for the Rest of US Introduction Space is an important and growing segment of the U.S. economy. The U.S. space market is currently over $5 billion per year, and growing. U.S. satellites, and to a lesser degree U.S. launch services, are used throughout the world and are one of the bright stars in the U.S. balance of trade. The future is even brighter. The space environment promises new developments in materials, drugs, energy, and resources, which will open up whole new industries for the United States. This will translate into new jobs and higher standards of living not only for Americans but for the rest of the world's people. Standing between us and these new industries is the obstacle presented by the high cost of putting people and payloads into space. This paper addresses the reasons why access to space is so expensive and how those costs might be reduced by looking at the problem in a different way. Finally, this paper will describe a radical new spacecraft currently under development. Called Single Stage to Orbit (SSTO), it promises to greatly reduce costs and increase flexibility. Access to Space: Expensive and Dangerous Access to space today is very expensive, complex, and dangerous With U.S. expendable launchers like Atlas, Delta, and Titan, it generally costs about $3,000 to $8,000 to put a pound of payload into low Earth orbit (LEO). In addition, U.S. expendables require extensive ground infrastructure to do final assembly and payload integration and complex launch facilities to actually launch the rocket. Finally, despite all the extra care and effort, they don't work very well and even the best launchers fail about 3% of the time (would you go to work tomorrow if there was a 3% chance of your car exploding?). Even the U.S. Space Shuttle, which was supposed to give the U.S. routine low cost access to space, has failed. A Shuttle flight costs about $500 million (roughly $10,000 per pound to LEO). Even going full out, NASA can only launch each Shuttle about twice a year (for a total of eight flights). The effects of these high costs go deeper than the price tag for the launches themselves. Space equipment is much more expensive than comparable equipment meant for use on Earth, even when tasks are similar and the Earthly environments are harsh. The difference is that space equipment must be as lightweight as humanly possible and must be as close as humanly possible to 100% reliability. Both of these extra requirements are ultimately problems of access to space: if every extra pound costs thousands of dollars, and replacing or repairing a failed satellite is impossibly expensive, then efforts to reduce weight and improve reliability make sense. Unfortunately, they also greatly increase price. With equipment so expensive, obviously building extra copies is costly, and launching them is even worse. This encourages space projects to try to get by with as few satellites as possible. Alas, this can backfire: when something does go wrong, there isn't any safety margin...as witness the U.S.'s shortage of weather satellites at this time. Expensive access to space not only produces costly projects, it produces fragile projects that assume no failures, because safety margins are too expensive. Lamentably, failures do happen. Finally, although research in space holds great promise for new scientific discoveries and new industries, it is progressing at a snail's pace, and companies and researchers often lose interest early. Why? Because effective research requires better access to space. Scientific discoveries seldom come as the result of single experiments: even when a single experiment is crucial, typically there is a long series of experiments leading up to it and following through on it. And getting the "bugs" out of a new industrial process almost always requires a lot of testing. But how can such work be done if you only get to fly one experiment every five years? Good researchers and innovative companies often decide that it's better to avoid space research, because it costs too much and takes too long. The ones who haven't abandoned space research are looking hard at buying flights on Russian or Chinese spacecraft: despite technical and political obstacles, they can fly their experiments more often that way. People excuse this because it has always been this way and so probably always will be (after all, this is rocket science). But there are a lot of reasons to think that it needn't be so complex and expensive. Spacecraft are complex, expensive, and built to aerospace tolerances but they are not the only products of that nature we use. A typical airliner costs about the same as a typical launcher. It has a similar number of parts and is built to similar tolerances. The amount of fuel a launcher burns to reach orbit is about the same as an airliner burns to go from North America to Ausralia. Looked at this way, it would seem that the cost of getting into orbit should be much closer to the $1500 it takes to get to Australia than to the $500 million dollars plus it takes to put an astronaut up. Why the differences in cost? Largely they are due to different solutions to the same problems. Some of these differences are: 1. Throw away hardware. A typical expendable launch vehicle costs anywhere from $50 to $200 million to build (about the cost of a typical airliner) yet it is used one time and then thrown away. Even the 'reusable' Space Shuttle throws away most of its weight in the form of an expendable external tank and salvageable solid rocket motors. This is the single biggest factor in making access to space expensive. Airlines use reusable hardware and fly their aircraft several times every day. This allows them to amortize the cost of the aircraft over literally thousands of passenger flights. The entire Shuttle fleet flies only eight times a year, while many airliners fly more than eight times per day. 2. Redundant Hardware and Checks. Since expendable launchers are used one time and then thrown away, they cannot be test-flown; huge amounts of effort therefore go into making sure they will work correctly. Since the payloads they launch are typically far more expensive than the launcher (a typical communication satellite can cost three times the cost of the launcher) millions can be and are spent on every launch to obtain very small increases in reliability. This is well beyond the point of diminishing returns and sometimes results in greater harm. For example, a couple of years ago a Shuttle Orbiter was almost damaged when it was rotated from horizontal to vertical with a loose work-platform support still in its engine compartment. The support should have been removed beforehand...and three signatures said it had been. Airliners, since they are reusable and can also be tested before use, thus are able to be built to more relaxed standards without sacrificing safety. The exact same aircraft flew to get to your airport and it is likely that any failure would already have been noticed. In addition, aircraft are built with redundancy so they can survive malfunctions; launchers usually are not. Most in-flight failures of airliners result, at most, in delays and inconvenience for the passengers; most in-flight failures of launchers result in complete loss of launcher and payload. 3. Pushing the Envelope on Hardware. Current launchers tend to use hardware that is run all the time at the outside limit of its capability. This may be fine for expendable launchers which are used one time and don't need to be repaired for reuse. But this has also tended to carry over to the Shuttle which, for example, operates its main engines at around 100% of its rated thrust (this is like driving your car 55 MPH in first gear all the time). Because the hardware is used to its limit every time, it needs extensive checkout after every flight and frequent repair. Airliners tend to be much more conservative in their use of hardware. Engines are used at far less than their full rated thrust and airframes are stressed for greater loads then they ever see. This results in less wear and tear which means they work with greater reliability and fewer repairs. 4. Labor Requirements. For all of the reasons given above, existing launchers require vast amounts of human labor to fly. The efforts of about 6,000 people are needed to keep the Shuttle flying. This represents a huge expense and is amortized only over eight or so Shuttle flights every year. Airliners are far more streamlined and, for the reasons given above, don't need nearly as many people. A typical airliner only has 150 people supporting it, including baggage handlers, flight crews, ticketing people, and administration. Since the cost of those 150 people are amortized over thousands of flights per year, the cost per flight is very low. Our current launchers are expensive and complex vehicles. Yet the fact that we routinely use vehicles with similar cost and complexity for far less cost indicate that the causes of high launch costs lie elsewhere. If we looked at the problem in a different way, we could try to build launchers the same way Boeing builds airliners. The next section will describe just such a launcher and how it is being built. A Spaceship that Runs Like an Airliner: SSTO For a long time, some launcher designers have realized that designing launchers the way airliners are designed would result in lower costs. Several designs have been proposed over the years and they are generally referred to as Single Stage to Orbit (SSTO) launchers. 1. Single Stage to Orbit (SSTO). Unlike an existing launcher which has multiple stages, a SSTO launcher has only one stage. This results in far lower operational costs and are key to reusability. Conventional launchers need expensive assembly buildings to stack the stages together before going to the launch pad. An SSTO only has one stage, so these facilities are not needed. This means that the only infrastructure needed to launch a SSTO is a concrete pad and a fuel truck. 2. Built for Ease of Use. SSTO vehicles are built to be operated like airliners. They can fly multiple times with no other maintenance needed other than refueling. If a problem is discovered, all components can be accessed with ease (by design). The defective Line Replaceable Unit (LRU) is replaced and launch can occur with only a short delay. If the problem is more complex or other maintenance is needed, the SSTO is towed to a hanger where the easy accessibility of parts insures rapid turnaround. 3. Standard Payload Interface. Payloads need access to services like power, cooling, life support, etc., while waiting for launch. The interfaces which provide these services are not standardized, adding cost and complexity to existing launchers. In effect, part of the launcher must be redesigned for each and every launch. SSTOs, however, would be designed with standard payload interfaces. This allows payload integration to occur hours before launch instead of weeks before launch. (Although in all fairness, the makers of expendable launchers are also slowly moving in this direction). 4. Built to be tested. Unlike expendables, SSTO vehicles do not have to be perfect the first time. Like airliners, they can survive most failures. Like airliners, they can be tested again and again to find and fix problems before real payloads and passengers are entrusted to them. Even when a failure does occur with a real payload aboard, usually neither the vehicle nor the payload will be lost. The reliability of SSTO vehicles should be close to that of airliners -- a loss rate of essentially zero -- and far better than the 3% loss rate of existing launchers. SDIO Single Stage Rocket Technology Program Recent advances in engine technology and materials have made most critics believe that the technology is now available to build a SSTO. In 1989, SDIO recognized the potential of this approach and commissioned a study to assess its risk. The study concluded that a SSTO vehicle is possible today. As a result of this study, SDIO initiated the Single Stage Rocket Technology Program (SSRT). The goal of the three phase SSRT program is to build a SSTO, thus providing routine cheap access to space. Phase I consisted of four study contracts to develop a baseline design for a SSTO. General Dynamics and McDonnell Douglas proposed vehicles which both take off and land vertically (like a helicopter). Rockwell proposed a vehicle which takes off vertically but lands horizontally (like the Space Shuttle does today). Finally, Boeing proposed a vehicle which both takes off and lands horizontally (like a conventional aircraft). In August 1991, SDIO selected the McDonnell Douglas vehicle (dubbed Delta Clipper) for Phase II development, and contracted for the construction of a 1/3 scale prototype vehicle called DC-X. This prototype is currently under development and should begin flying in April, 1993. DC-X will provide little science data but a wealth of engineering data. It will validate the basic concepts of SSTO vehicles and demonstrate the ground and maintenance procedures critical to any successful orbital vehicle. Phase III of the program will develop a full scale prototype vehicle called DC-Y. DC-Y will reach orbit with a substantial payload, hoped to be close to 20,000 lbs, and demonstrate total reusability. In addition, McDonnell Douglas will begin working with the government to develop procedures to certify Delta Clipper like an airliner so it can be operated in a similar manner. Phase III was scheduled to begin in September of 1993 but SDIO will not be able to fund the Phase III vehicle. There is some interest in parts of the Air Force and it is hoped that they will fund DC-Y development. It will be a great loss for America if they do not. After Phase III, it will be time to develop an operational Delta Clipper launcher based on the DC-Y. At this point government funding shouldn't be needed any longer and the free market can be expected to fund final development. Conclusion If a functional Delta Clipper is ever produced it will have a profound impact on all activities conducted in space. It will render all other launch vehicles in the world obsolete and regain for the United States 100% of the western launch market (half of which has been lost to competition from Europe and China). It will allow the United States to open up a new era for mankind, and regain our once commanding lead in space technology. -- +---------------------------------------------------------------------------+ | Allen W. Sherzer | "A great man is one who does nothing but leaves | | aws@iti.org | nothing undone" | +----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+ ------------------------------ End of Space Digest Volume 16 : Issue 331 ------------------------------