space challenge

nec208 · Mar 5, 2008

I'm starting a new topic, because I can't find my old one .The challenge going up into space is the energy problem and not the engine or craft.Just look at the space shuttle,the size of the boosters are just so big to launch the space shuttle and this seems to be the problem . Thats use a metaphor its like it needs a river of energy just to burn to get off the ground.What other energy are they working on to fix this problem?Would fission or fusion fix this problem? Or would it still be the same energy or what about plasma?Burning oil, gas or coal, I don't think would work?What about making better engine that use less power?What energy has more power than other energy when burn?What about better boosters?I would like to say if some one has some web sites at a elementary school level on this can you post it Howstuffworks and wikipedia is not a good layout and not simplified enough..  <div class="Discussion_UserSignature"> </div>

nec208 · Mar 9, 2008

I know my english is bad, but where is everyone? Any ideas?  <div class="Discussion_UserSignature"> </div>

spacelifejunkie · Mar 10, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I know my english is bad, but where is everyone? Any ideas?  Posted by nec208</DIV> Nec, I don't think your English is that bad.  Like many others, I'm still recovering from the "new discussion board hangover" and not quite back in the groove. I believe that we still have some cost and safety improvements to make still with chemical rockets.  SpaceX, Bigelow Aerospace and others are making great strides in maximizing traditional space technologies.  Combined with nanotechnologies and improving artificial intelligence monitoring increasingly complicated systems (like air traffic control computers) space travel cost and access can be greatly improved.I believe the next generation will be nuclear.  A nuclear fission upper stage rocket or earth departure stage  would maybe double payloads to the moon or mars. Don't count out nuclear fusion.  We're currently holding our breath on an experiment at Los Alamos National Labs with results being publicly released any time now.  The late Dr. Robert Bussard has been in the lead for the last 20 years or so quietly doing experiments funded by the Navy to build compact, radiation free nuclear fusion.  Links below.  If all goes to plan, we could see fusion powered spacecraft by the year 2020 - 2025.  Keep your fingers crossed.http://www.emc2fusion.org/http://www.talk-polywell.org/bb/index.phphttp://forum.nasaspaceflight.com/forums/thread-view.asp?tid=5367&posts=2029&start=1A lot of info and a little technical but a good start. SLJ

hal9891 · Mar 10, 2008

I'm also holding my fingers crossed for polywell fusion, if it works out this can possibly replace all fossil fuel plants down here on earth and open the solar system for humanity (finally!) Also don't count out advanced chemical propulsion - cyclic ozone, tetraoxygen, metallic hydrogen,  hydrogen free radicals,  metastable hellium.Moreover thrust augmentation nozles could improve performance of existing boosters without any exotic  (and possibly dangerous) propellants. <div class="Discussion_UserSignature"> <div style="text-align:center">"I predict that within 100 years computers will be twice as powerful, 10000 times larger, and so expensive that only the five richest kings of Europe will own them" </div> </div>

qso1 · Mar 11, 2008

Your absolutely right about the problem of getting vehicles into space. Its been said the costliest part of any space mission is the initial climb to orbit.The shuttles liftoff mass is about 4.5 million lbs. Of this, an average of 48,000 lbs of payload is placed into Low Earth Orbit (LEO). Thats just a tad over 1% of the shuttles liftoff weight.The shuttle "C" or other SDV concepts improves this figure but not by much. The shuttle, Saturn-V, and Former Soviet Energia and N-1 rockets are the four most powerful ever built. All are chemical rockets and all but one (N-1) utilize cryogenic propellants in the upper stages yeilding average ISPs of 450. And all are capable of only 1-2% payload mass vs liftoff mass.Nuclear powered vehicles have been researched on and off for decades. Nuclear thermal yeilds ISPs of 800 and a little higher and NTRs are mainly attractive for deep space applications.Then theres VASIMR (VAriable Specific Impulse Magnetoplasma Rocket) based propulsion, nuclear electric system which provides thrust continuously and as the name implies, the ISP varies.Interstellar craft would probably require propulsion systems beyond even VASIMRs capabilities. Antimatter being one example, or solar sails though solar sails theoretically gain their energy from the sun rather than onboard propulsion. I tend to think by the time we reach interstellar travel capability, we will be on the verge of developing propulsion systems not yet even concieved today.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

webtaz99 · Mar 11, 2008

If we can just convince the great unwashed that "nuclear" is not a dirty word, orbit will be easy. <div class="Discussion_UserSignature"> </div>

qso1 · Mar 12, 2008

If we can just convince the great unwashed that "nuclear" is not a dirty word, orbit will be easy. Posted by webtaz99For orbit, I think its hard for nuclear to compete with chemical on a cost basis. But for deep space, nuclear offers more advantage. The type of system would increase that advantage as well but would probably increase cost too.These days, cost of human spaceflight is as much a detterent as using nuclear propulsion to go deep space.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

j05h · Mar 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I'm starting a new topic, because I can't find my old one .The challenge going up into space is the energy problem and not the engine or craft.Just look at the space shuttle,the size of the boosters are just so big to launch the space shuttle and this seems to be the problem . Thats use a metaphor its like it needs a river of energy just to burn to get off the ground.What other energy are they working on to fix this problem?Would fission or fusion fix this problem? Or would it still be the same energy or what about plasma?Burning oil, gas or coal, I don't think would work?What about making better engine that use less power?What energy has more power than other energy when burn?What about better boosters?I would like to say if some one has some web sites at a elementary school level on this can you post it Howstuffworks and wikipedia is not a good layout and not simplified enough..  Posted by nec208</DIV> The real challenge with getting to space is the economics, not the amount of energy or technology used. The best answer is flight frequency, just like with the creation of aircraft and powered ship markets. Specific technology that can increase flight frequency include assembly lines (such as Soyuz and Delta use), extreme reusability and possibly commodity fuels like propane/CNG combined with ocean/harbor operations (spaceflight integrated into modern cargo shipping). The single largest leverage in price-to-orbit is flying a standardized rocket core as much as possible. People have suggested nuclear space launchers such as Orion, Nerva/Timberwind or recently the Liberty Ship. These could work theoretically but are unlikely to fly politically, even with zero radioactive emmisions. Better routes of investigation, as QSO suggests, include nuclear upper stages and more advanced Earth-to-orbit tech such as laser launch or space elevators/rotovators. Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

qso1 · Mar 14, 2008

Yep...no bucks, no Buck Rogers. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

azorean5000 · Mar 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The real challenge with getting to space is the economics, not the amount of energy or technology used. The best answer is flight frequency, just like with the creation of aircraft and powered ship markets. Posted by j05h</DIV>In order for that flight frequency to exist there must be an economic need/reason. It has to be there for people to  go to space in large scale. Without demand there is no offer. That applys to all economic activities. <div class="Discussion_UserSignature"> </div>

nec208 · Mar 17, 2008

So if they use nuclear will the booster be smaller?I think the problem is the boosters have to be so big, and it takes lots of energy to go up in space.If they found that magic energy you could have boosters no bigger than your car!!!!Has for the coast it may take 50 or 100 years to bring the coast down.That say there is new space shuttle every 15 years!! It may take 15 new space shuttle to they find a way to bring the coast done. The space shuttle they have now is nothing more to prove that a space shuttle is possible and not sci-fi.The American people better learn they can't built a space shuttle and be safe and coast like a airplane. If people use the same behavior with the space shuttle  they did with the Wright Brothers there would be no airplanes.They would want the Wright Brothers to be 100% safe and coast very little.It may take 50 or 100 years from now to they bring the coast down.Or it may always coast lots because the space shuttle is just very complex!!I believe the space shuttle and the Lockheed SR-71 is the most complex thing ever built!! <div class="Discussion_UserSignature"> </div>

qso1 · Mar 18, 2008

Nuclear boosters operated endoatmospherically probably will not offer that much of an advantage. At least not enough to offset potential environmental risks. They would be a little smaller but as far as size. Most booster rockets are not that large. The Delta rockets (Not counting heavy lift versions) are pretty easy to manage relatively speaking. Certainly easier than processing shuttles.Nuclear rockets operated outside earths atmosphere would be more cost effective and offer more advantage payload wise. Chemicle boosters are fine as they are now. Nuclear upper stages are probably worth developing, especially for deep space apps. Your right about energy to go into space. The hardest part of getting into space is overcoming the first 100 miles. Earths gravity and atmosphere.The cost of spaceflight will probably come way down within the next decade provided private industry is able to take over the low earth orbit sector. Part of the cost problem is that government is currently our only means of regular access to space and government run programs are not very effificent. Although NASA is one of those programs where we get the most bang possible for the government buck. Most folks, including myself, think that the private sector would do better costwise.NASA will never be able to build 15 new shuttles. In fact, NASA had planned to build a shuttle replacement and studied several concepts before throwing in the towel and going back to capsule spaceflight. They did this because they just can't get the funding for replacing the shuttle. They couldn't even get sufficient funds for developing a small shuttle type vehicle mounted on top of a rocket.This is where private industry comes in.The shuttle is actually as safe as its possible for such a complex vehicle to be. Considering both accidents were directly traceable to poor management decisions. The shuttles actual flight record puts it at close to a 99% safety performance figure. But as you mentioned, the public has to realize chemical rockets and human spaceflight are potentially dangerous. They will likely never be as safe as operating 747s etc.It would have been interesting to see how todays attitudes would have been in 1903 when the Wright Brothers made their first flight. But there again, the Wright Brothers were private citizens and financing their venture was within reach.Burt Rutan could be seen as a modern day Wright Brother type but even he has yet to establish regular space flight, much less regular orbital flights.With shuttle about to retire, one can look at what we got from it and in the long run...the legacy of shuttle was demonstrating on a regular basis, that reusability was possible. Now we just have to establish that reusability can be economical enough to compete with, and even phase out throwaway boosters.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

nec208 · Mar 18, 2008

Nuclear boosters operated endoatmospherically probably will not offer that much of an advantage. At least not enough to offset potential environmental risks. They would be a little smaller but as far as size. Most booster rockets are not that large. The Delta rockets (Not counting heavy lift versions) are pretty easy to manage relatively speaking. Certainly easier than processing shuttles.=============================================The problem with the boosters is the size of it and it is so much bigger than the object to be launched in space.To they find out a way to make the booster smaller than the object there will always be problems.Just think a size of a 5 story apartment, it would take a apartment 25 times bigger to launch it!! =============================================With shuttle about to retire, one can look at what we got from it and in the long run...the legacy of shuttle was demonstrating on a regular basis, that reusability was possible. Now we just have to establish that reusability can be economical enough to compete with, and even phase out throwaway boosters. =============================================The public has to learn going up into space is complex and coast so much .And it may take 50 or 100 years from now, to they bring the coast down.And remember you get what you pay for!!There is 3 solutions.1 find other propulsion system2 launch the craft from 747 plane.3 take of like a plane using jet engine than the rocket starts up when your are at altitude xx.4 launch  from a mountain top. <div class="Discussion_UserSignature"> </div>

qso1 · Mar 21, 2008

The problem with the boosters is the size of it and it is so much bigger than the object to be launched in space.To they find out a way to make the booster smaller than the object there will always be problems.Just think a size of a 5 story apartment, it would take a apartment 25 times bigger to launch it!! Posted by nec208True the booster size is a problem, an obstacle to regular access to low orbit. Coupled with the power a booster must produce. The shuttle weighs about 4.5 million pounds at liftoff and delivers roughly 50,000 lbs to low orbit.The Saturn weighed 6 million lbs or 3,000 tons at liftoff and could deliver about 125 tons to low orbit and 45 tons or so to lunar orbit. This all contributes to the cost of getting into low orbit or anywhere else in space. The public has to learn going up into space is complex and coast so much .And it may take 50 or 100 years from now, to they bring the coast down.And remember you get what you pay for!!There is 3 solutions.1 find other propulsion system2 launch the craft from 747 plane.3 take of like a plane using jet engine than the rocket starts up when your are at altitude xx.4 launch  from a mountain top. Posted by nec208Your solutions are for the most part, right on target. Some of them are also solutions private industry startups are looking at or actively working on. Jeff Bezos of Amazon fame is working on a craft called Blue Origins which is based on the old Delta Clipper technology demonstrator. Elon Musk of Paypal fame is working on a more traditionally launched Dragon space capsule. Hotel magnate Bigelow is working on hotels in space rather than access to space which he's leaving up to Bezos, Rutan etc.Astrium, a company not well known has plans to go more along the lines of what your talking about. A sub orbital biz jet with rocket engines. Then theirs Burt Rutan with his suborbital Spaceship two vehicle which is a larger version of Spaceship one. Spaceship one being the only privately financed human spaceflight vehicle flown so far. Bigelow has sent hardware to orbit but its unmanned for now. If they succeed, we may see space open up much sooner than 50-100 years. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

nec208 · Mar 25, 2008

What is the UK,China or India working on? I think why the boosters are so big is because what they burn now has very little power. <div class="Discussion_UserSignature"> </div>

wick07 · Mar 26, 2008

I think Nuclear Rocket engines are the future.  We have pretty much reached our limit with chemical engines.  Yeah, we can squeeze a bit more juice out of them, but if we really want to explore space we need to improve our engine by orders of magnitude.  I wish I could find it, but I had seen some calculations that demonstraited the payload increase by switching to nuclear engines, it was significant.  The downside is that nuclear is not politically palatable, so even though it is within our grasp now we won't go to it.http://www.nuclearspace.com/A_PWrussview_FINX.htm <div class="Discussion_UserSignature"> _______________________________ "If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum. If you feel like trying to make a difference, you have to BE different. How can you do that without interacting with those who are different from yourself?"- a_lost_packet_ </div>

bearack · Mar 26, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I think Nuclear Rocket engines are the future.  We have pretty much reached our limit with chemical engines.  Yeah, we can squeeze a bit more juice out of them, but if we really want to explore space we need to improve our engine by orders of magnitude.  I wish I could find it, but I had seen some calculations that demonstraited the payload increase by switching to nuclear engines, it was significant.  The downside is that nuclear is not politically palatable, so even though it is within our grasp now we won't go to it.http://www.nuclearspace.com/A_PWrussview_FINX.htm Posted by wick07</DIV> Could keep chemical launches to land based while having nuclear at the ISS for lauches to palces such as Mar?  That would at least calm some of the impact scares? <div class="Discussion_UserSignature"> <img id="06322a8d-f18d-4ab1-8ea7-150275a4cb53" src="http://sitelife.space.com/ver1.0/Content/images/store/6/14/06322a8d-f18d-4ab1-8ea7-150275a4cb53.Large.jpg" alt="blog post photo" /> </div>

qso1 · Mar 26, 2008

The UK has the Ariane V as its most powerful chemical launcher but no man in space program as of yet. China has the chemical rocket Long March 2F/Shenzou manned spacecraft combo and India has the GSLV rocket which is its most powerful chemroc. India is reportedly planning human spaceflight eventually but has yet to actually send humans up.None of the above nations are known to be activelly working on nuclear propulsion.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

qso1 · Mar 26, 2008

Could keep chemical launches to land based while having nuclear at the ISS for lauches to palces such as Mar?  That would at least calm some of the impact scares? Posted by bearackTrue, nuclear vehicles limited to orbit and beyond is the most likely scenario. In nuclear thermal rockets, I don't really see any advantage to a nuclear endoatmospheric stage considering the ISP is only about double the highest ISPs for chemrocs. The weight increases substantially as does the cost. Endoatmospheric nuclear  thermal stages will probably never be cost competitive with equivalent chemical stages.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

nec208 · Mar 26, 2008

I think Nuclear Rocket engines are the future.  We have pretty much reached our limit with chemical engines.  Yeah, we can squeeze a bit more juice out of them, but if we really want to explore space we need to improve our engine by orders of magnitude------------------------------------------------------------------------------------------ Read the post above!! The boosters are not that much smaller using nuclear .And really is no good for doing earth orbits.Going to the moon or mars is where the nuclear rocket comes in!! But its does not seem to be that powerful. Replying to: <DIV CLASS='Discussion_PostQuote'>The UK has the Ariane V as its most powerful chemical launcher but no man in space program as of yet. China has the chemical rocket Long March 2F/Shenzou manned spacecraft combo and India has the GSLV rocket which is its most powerful chemroc. India is reportedly planning human spaceflight eventually but has yet to actually send humans up.None of the above nations are known to be activelly working on nuclear propulsion.  Posted by qso1</DIV> Wow the Ariane V sure looks cool!! They seem to have a potential in the UK for man space in the UK , using the Ariane V.But problem seems to be the government not interested. <div class="Discussion_UserSignature"> </div>

qso1 · Mar 26, 2008

I like the Arianne V myself, Europes homegrown heavy lifter. Human spaceflight is viewed as so expensive and in competition with so many other more directly down to earth government services that they usually shy away from it.The European Space Agency (ESA) has for the past two decades, studied the possibility of their own human spaceflight systems...Hotol being one and Sanger being another proposal that died in the concept stage due largely to cost. Here in the U.S. the cost barrier as I call it, keeps NASA pinned nearly to the ground. NASA proposed sending humans to mars as far back as 1969 and were not there yet, due mainly to cost.This is why private industry may now be the only way we will ever see human space flight expand beyond low orbit IMO.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

qso1 · Mar 26, 2008

Read the post above!! The boosters are not that much smaller using nuclear .And really is no good for doing earth orbits.Going to the moon or mars is where the nuclear rocket comes in!! But its does not seem to be that powerful. Nec208.Go easy on the guy (Wick07) who said nuclear would eventually replace chemical. What I said is essentially based on the grounds of expense. And based on the use of a nuclear thermal rocket as opposed to nuclear concepts still on the drawing boards.I do think operational expense will keep nuclear stages from being utilized endoatmospherically simply because the disadvantages outweigh any small gain over chemical rockets. Imagine throwing away a nuclear stage after two minutes use as a booster or five to ten minutes as an upper stage.Radioactive material plunging into the ocean, the cost in terms of time and expertise to build the stage. Throwing all that away when its cheaper just to use a chemical stage. Outside Earths atmosphere and particularly for deep space apps, this is where nuclear propulsion of any type outshines chemical propulsion, and even then thats still largely theoretical since we have yet to operate a nuclear propulsion system on a regular basis.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

nec208 · Mar 26, 2008

Go easy on the guy (Wick07) who said nuclear would eventually replace chemical. What I said is essentially based on the grounds of expense. And based on the use of a nuclear thermal rocket as opposed to nuclear concepts still on the drawing boards. So you are saying there is no nuclear rocket and it is too expensive .magine throwing away a nuclear stage after two minutes use as a booster or five to ten minutes as an upper stage.So it is more powerful than the chemical rockets and gets of the ground faster.But the boosters are still little smaller than chemical boosters. Radioactive material plunging into the ocean, the cost in terms of time and expertise to build the stage.That seem to be the problem the radioactive and may be in 15 years or so they fix that problem.Outside Earths atmosphere and particularly for deep space apps, this is where nuclear propulsion of any type outshines chemical propulsion, and even then thats still largely theoretical since we have yet to operate a nuclear propulsion system on a regular basis.So going to mars how long will it take using chemical rockets and how long will it take using nuclear rockets?But if you really want the boosters to be smaller than there has to be other propulsion system .The boosters are a little smaller using nuclear rocket than a chemical rocket <div class="Discussion_UserSignature"> </div>

qso1 · Mar 26, 2008

So you are saying there is no nuclear rocket and it is too expensive .There are no operational nuclear rockets at this time. The closest we have ever come to having one was a project called Nuclear Engine for Rocket Vehicle Applications (NERVA) in which nuclear engines were tested at a place called Jackass flats Nevada in the late 1960s. That program was terminated in the early 1970s.So it is more powerful than the chemical rockets and gets of the ground faster.But the boosters are still little smaller than chemical boosters.Here think ISP or Initial Specific Impulse. A measure of a rockets propellant efficiency combined with engine design. Typical ISPs are roughly 250 or so for solid rockets. Around 450 for liquid hydrogen oxygen powered rocket engines such as the shuttle SSMEs.NERVA engines were above 800 IIRC.The biggest hurdle the rocket has to overcome is the weight of a nuclear system which is largely sheilding which would be required on a deep space vehicle to protect the crew. But the deep space vehicle is already out of earths gravity well which is why nuclear is good for deep space operations.Closer to the ground, there may have to be some type of shield or system to protect those closest to the launch from possible fallout. This would add weight to the stage but the ISP would still be enough to allow some advantage. But I don't think the advantage of a nuclear stage operated endoatmospherically can be outweighed by chemical stages, especially if we should finally be able to develop SSTOs.That seem to be the problem the radioactive and may be in 15 years or so they fix that problem.There is a promising program underway called Variable Specific Impulse Magneto plasmadynamic Rocket (VASIMR) which would be more of a nuclear electric rather than thermal design. NERVA was nuclear thermal which essentially uses a nuclear core similar to a conventional nuclear powerplant core in which liquid hydrogen passes through the rods before being exhausted out as high energy reaction mass. A little about NERVA can be seen at the link below:http://en.wikipedia.org/wiki/NERVAVASIMR uses radiowaves in a manner similar to a microwave oven to ionize a propellant such as hydrogen and then magnetically contains the resultant reaction mass as it is expelled. as the VASIMR acronym implies, the ISP is variable and could be as high as 30,000 seconds as opposed to the shuttles 450 and NERVAs 800 to 1,000.  http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocketSo going to mars how long will it take using chemical rockets and how long will it take using nuclear rockets?Chemical rockets entail reliance on planetary alignments that occur roughly every 26 months. This results in an outbound leg typically lasting 6 to 9 months depending on the particulars of the trajectory and time of EOD (Earth Orbit Departure). A nuclear thermal system might cut this down a little but a VASIMR type system is supposed to be able to cut the in and outbound legs to as little as three months.In some cases, the planet Venus could be used as a gravitational assist provided all three planets are in proper alignment at the time of the Venus flyby whether in or outbound.But if you really want the boosters to be smaller than there has to be other propulsion system .The boosters are a little smaller using nuclear rocket than a chemical rocketWithout knowing for certain, I would say a nuclear thermal booster would be smaller simply due to the elimination of the oxidizer. Oxidizer in the shuttle for example is liquid oxygen which is much heavier than hydrogen. So you are almost trading off the added weight of nuclear system shielding for chemical oxidizer not required in the nuclear system. Bottom line, chemicl rockets require fuel and oxidizer while nuclear thermal requires fuel and a reactor.A VASIMR based booster operating endoatmospherically would be not only expensive but oddly enough, part of the VASIMR design makes it impossible to operate within the atmosphere and earths gravity due to low thrust operation of a VASIMR type system for much longer times.  <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

mako71 · Mar 27, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>...Chemical rockets entail reliance on planetary alignments that occur roughly every 26 months.</DIV>For Earth-Mars -system, right? Replying to: <DIV CLASS='Discussion_PostQuote'> ...Without knowing for certain, I would say a nuclear thermal booster would be smaller simply due to the elimination of the oxidizer. Oxidizer in the shuttle for example is liquid oxygen which is much heavier than hydrogen.</DIV>Really? I thought, that oxidier together with hydrogen form propellant, and that it is the exhaust velocity of _propellant_ combined with amount of it that which tells the end velocity of the payload (v = ln(m[full]/m[empty])*v[exhaust]). Chemical rockets use binary propellant, because the chemical reaction between propellant components is the source of energy for throwing that propellant...Tsiolkovsky rocket equation So, AFAIK, the larger ISP is the only reason for decreasing the amount of propellant needed for nuclear rockets.About the subject itself; surely accessing LEO is the most expensive phase in space travelling. I think that nothing can change it, meaning that also in long run we need to think what to launch to LEO - that is, although it may became cheaper with advanced technology, it is still going to be relatively expensive, meaning that we probably want to exploit space materials in space rather than launch everything from the surface(*).EDIT: (*) That is, in case we need heavy structures in space; at the other side, we're making the needed structures lighter with advances in material technologies. I think that in long run, the driving force for surface launchers is to put humans to orbit (i.e. manned flights). Technological improvements probably make our satellites smaller and smaller, and improved robotics make the deep space probes smaller.What I think, is that the "optimal" launch vehicle may be reusable 3STO; the first stage uses turbine engines, the second one SCRAM-jet and the last stage uses chamical rockets. The last stage may be disposable, and only the crew cabin is shielded to re-enter to atmosphere. The reason for this is that in this way the atmosphere oxygen can be used as a part of propellant, saving some mass. I know that these designs are currently not the most interested, since there is a shift to simple disposable rockets due to several rational reasons, e.g. flight frequencies. So, all in all, I think that the expensiveness of space flights is not entirely solved with any technological solutions, but it is more a question of economics and advances in other technology than launch vehicles (e.g. robotics). We may make accessing the LEO cheaper of a magnitude with some ways; (1) using inexpensive, easily storable propellants, (2) decreasing the labor costs (in building a spaceship, as well as when preparing it to be relauched), (3) reusing all that can be reused, and so on. But still, LEO access will be expensive. You are free to disagree, since I haven't thought these issues very deeply; I'm open for any comments.  <div class="Discussion_UserSignature"> ________________ reaaliaika.net </div>

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