The single-stage-to-orbit vehicle problems

nec208 · Apr 8, 2008

A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body without throw away hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles.No Earth-launched SSTO launch vehicles have ever been constructed. Current orbital launches are either performed by multi-stage fully expendable rockets, or by the Space Shuttle which is multi-stage and partially reusable. Several research spacecraft have been designed and partially or completely constructed, including the DC-X, the X-33, and the Roton SSTO. However, none of them has come close to achieving orbit.Single-stage-to-orbit has been achieved from the moon by the Apollo program's Lunar Module; the lower lunar gravity and absence of any significant atmosphere makes this much easier than from Earth.For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight.An SSTO vehicle has one major problem: it needs to lift its entire structure into orbit. To reach orbit with a useful payload, the rocket requires careful and extensive engineering to save weight. This is much harder to design and engineer. A staged rocket greatly reduces the total mass that flies all the way into space; the rocket is continually shedding fuel tanks and engines that are now dead weight. <div class="Discussion_UserSignature"> </div>

nec208 · Apr 8, 2008

For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight.---------------------------------------------------------------------------------------I guess they are saying here , the vehicle mass is having a hard time holding the sufficient propellant .Because of the problem you need more propellant  than the vehicle.This plays well into the  ...400+ punds of fuel for every 1 pund to go into space.The fuel is more weight than the object.  <div class="Discussion_UserSignature"> </div>

qso1 · Apr 8, 2008

I guess they are saying here , the vehicle mass is having a hard time holding the sufficient propellant .Because of the problem you need more propellant  than the vehicle.This plays well into the  ...400+ punds of fuel for every 1 pund to go into space.The fuel is more weight than the object. Posted by nec208Exactly...the propellant to weight ratio is something like 10 to 1 or maybe much greater. The only way an SSTO design might achieve such a ratio is through development of lighter materials that would reduce the weight of the vehicle. The problem you run into there is that the materials also have to be strong enough to withstand its operational environment.  <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 · Apr 8, 2008

Or use a different propulsion or better and more powerful engines.May be better fuel saving.When one looks at cars in the old day , the cars would use more fuel  just to go one mile than the cars today.May be they can do this with rockets. <div class="Discussion_UserSignature"> </div>

qso1 · Apr 8, 2008

Thats possible, although it appears they have squeezed about as much out of chemical propulsion as they can. That was one reason they looked at lightweight, even composite materials. Also like cars, chemical rockets have matured to the point that they get refined rather than make quantum technical leaps.The other obstacle is that SSTOs are mainly an application for human space flight, tho not limited to that, the cost barrier as I call it. NASA was unable to put any kind of SSTO into practical operation because of the development cost and NASAs inability to gain enough support for the budgets they thought they needed to develop SSTOs.This is why its now up to private industry to tackle the problem. NASA being government, has some inherant inefficiencies that may be part of the reason they require the budgets they ask for. Private industry will be seeking practical operation at profitable cost.Now the only question will be, can private industry actually demonstrate practical, safe operations at economical prices?  <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 · Apr 8, 2008

Thats possible, although it appears they have squeezed about as much out of chemical propulsion as they can. That was one reason they looked at lightweight, even composite materials. Also like cars, chemical rockets have matured to the point that they get refined rather than make quantum technical leaps.--------------------------------------------------------------------------------------------------That may be true , but in 15 or 20 years from now , they may find ways for rockets and even cars to save on fuel.You say rockets like cars have reached a point they are not going to save too much at this point on fuels. And get less fuel and more mileage.I still think much research and money is needed here.The problem is we don't know what more is to learn or do with chemical propulsion .We may be at the point we cannot do any thing or may be not.This is why I look down on the space elevator or just do away of human space flight.They have bean going to space for 50 years and want to back it in with chemical propulsion !!! <div class="Discussion_UserSignature"> </div>

qso1 · Apr 8, 2008

When you get right down to it, technical problems are not really the reason we haven't advanced much in human space flight. Its cost. Any new idea is shunned due to the cost of developing it. This because NASA is taxpayer funded and most taxpayers see NASA manned spaceflight as a waste. And it didn't help matters when ISS originally was proposed in 1984 as an $8 billion dollar station designed for initial operation in 1992.Then like shuttle, we see huge cost overuns and delays due to constant major redesigns of the station. Solutions like space elevators are beyond NASAs reach IMO because they would end up making it too costly. Thats why I see private enterprise as the solution provided they can pull it off.We have been screwing around ever since Apollo ended in part due to the budget cuts that followed, and in part due to severely miscalculating what it would actually take to operate a reusable chemically propelled rocket system, the shuttle cost wise.We are perilously close to doing away with government funded human spaceflight right now. All it will take is a new Presidential Admin to decide its no longer worth pursuing and NASAs done with human spaceflight. This is fine as long as private industry successfully fills the void.Then we may one day see stuff like routine SSTO operations, or maybe 2STOs until they really nail SSTO technology.  <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 · Apr 8, 2008

Almost forgot, we need to limit the duplication of posts. You have at least two posts here addressing the same basic issue. Your posting threads are excellent and I'd like to see you continue that but just try to do it more efficiently. <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>

KosmicHero · Apr 13, 2008

Chemical propulsion is the real work horse of space operations (especially space access).  With the exception of exotic alternatives such as NTR launch vehicles (hampered by safety and therefore political constraints) and the space elevator/skyhook concepts (hampered by a host of constraints) chemical is the ONLY method to access space from Earth.   Air-breathing options like SSTO designs offer some interesting options.  They aren't nearly as robust as your standard stacked LV but with some investment I think they could compete.  I do NOT however think that we're going to get much more out of chemical propulsion.  We're already pushing the limits there.  Scramjets allow a lot of savings but if you look at most flight profiles you spend about 15% of the launch in this mode.  The rest of the time you're in turbine (for turbine-combined-cycle) and rocket (for space propulsion and rocket-combined-cycle engines) and ramjet.   This seems like a lot of investment for such a short payoff.  However, where I think there might be some hope is more in the field of 'systems engineering' rather than 'propulsion'.  One configuration that I've worked on is a TBCC that launches with no oxidizer for the space-propulsion phase (the rocket) and cruises for a period of time on low-throttle ramjet mode while using the inlet ramp and some additional hardware to collect liquid oxygen from the air.  This takes advantage of the high-efficiency ramjet to collect an otherwise expensive (to launch) oxidizer.   <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 13, 2008

I was thinking in physics does it not state that only large matter can push other smaller matter than it size?If so that may be the reason the boosters and fuel are so much bigger than the object.Only large objects can move smaller objects.And small ojbjects cannot move big objects.Other thing ,  may be Newton got it wrong and every action there is no equal reaction? Or every action there is no opposite reaction that is equal.What does it state about energy or force?Can you have a smaller energy input and getter bigger out-put or does it have to be equal?May be they don't really know how rockets work ,  but can only explain what rockets do by looking at it and observing it.  <div class="Discussion_UserSignature"> </div>

KosmicHero · Apr 14, 2008

No.  It does not state that only large objects can move smaller objects.  Rockets are very well known.  Rockets are governed by a conservation of momentum.  When a rocket (or any body) ejects some of its mass at some velocity momentum is exchanged.  This causes both bodies to accelerate.  This is why when the ejected propellant goes one way, the rocket goes the other way.   No, you cannot have more energy out of a system then energy inputted.  In fact, you must get equal-to, but most likely less-than you put in.  This is called the Second Law of Thermodynamics. <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 15, 2008

Rockets are very well known.  Rockets are governed by a conservation of momentum.  When a rocket (or any body) ejects some of its mass at some velocity momentum is exchanged.  This causes both bodies to accelerate.  This is why when the ejected propellant goes one way, the rocket goes the other way.  -----------------------------------------------------------------------------------------------------Sorry can you explain more what is conservation of momentum.They know that when Rockets burn fuel the Rockets move and gas comes out.But may be they should tap into that gas coming out and feed it back and burn it again.They don't know what is going on and can only observe the effects like the apple coming from a tree we call gravity.The more mass the more gravity.But what really is gravity or can we manipulate gravity they do not know. <div class="Discussion_UserSignature"> </div>

KosmicHero · Apr 16, 2008

First I would like to point out that the study of 'Mechanics' which this problem squarely falls under is probably the most thoroughly verified scientific field.  Science is about theory and verification, and rocket science, insofar as what I'm explaining here, is verified.I will not go into the entire derivation, but you could probably google 'Rocket Equation' and find many derivations.  Fundamentally, rocket thrust is generated by momentum exchange.  Momentum is mass * velocity.  Imagine you're floating in space and you're holding a beer cooler.  If you push the cooler toward you're buddy on the other end of the module you're in it (some mass) will move (velocity) toward them.  Because momentum is conserved in this example, just as it is in rocketry, you will also move in the opposite direction proportional to the momentum of the cooler.  Rockets do this by expelling, at very high speeds, propellant gases.  The faster the gases are expelled the more effective the thrusting is (actually the exit velocity of the fuel is directly proportional to the specific impulse which is common measure for the efficiency of a rocket engine).  This is why the fuel could not be pumped back into the tanks for reuse.  This problem actually occurs on many electric thrusters.  Instead of using combusted gases, electric thrusters (depending on the type) acclerate charged particles over a voltage difference.  The problem that they run into sometimes is the charged particles that are expelled from the thruster can be drawn to the frame of the spacecraft (due to its electrical charge).  Even though this propellant was discharged (to create the thrust) it won't if the particle clings back to the spacecraft. Like I said, this phenomena is well known and you could likely find a better explaination and more detailed online.  There are some great books out there too.  Space Propulsion Analysis and Design by Ronald Humble is a treasure of material if you plan on working on rocket systems.  For a more introductory book, I would recommend Fundamentals of Flight by Richard Shevell (it covers aircraft and spacecraft flight). <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 17, 2008

You say momentum is when a body ejects some thing , momentum is exchanged..A fire hose ejects water and the momentum pushes the fire guys back and need 2 or 3 fire guys to hold the fire hose downA car that is speeding very fast and hits a parked car the momentum pushes the car back and the car park is ejects the other way.If 2 football players are running and run into each other the momentum pushes them back . The rocket moves before the flames shoot out or the air molecules will cause friction.And because the rocket has bigger mass the smaller ejects of the rocket will need more energy than the rocket it size + fuel and boosters will be too much weight for take off. If the is the case no rocket will work.A aire plane takes in oxygen and burns it with jet fuel and ejects it , and the momentum moves plane forward  and the ejects backwards.I think there is some thing more to it than momentum that seems to be a problem they are having going up into space. <div class="Discussion_UserSignature"> </div>

KosmicHero · Apr 17, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>You say momentum is when a body ejects some thing , momentum is exchanged..A fire hose ejects water and the momentum pushes the fire guys back and need 2 or 3 fire guys to hold the fire hose downA car that is speeding very fast and hits a parked car the momentum pushes the car back and the car park is ejects the other way.If 2 football players are running and run into each other the momentum pushes them back . The rocket moves before the flames shoot out or the air molecules will cause friction.And because the rocket has bigger mass the smaller ejects of the rocket will need more energy than the rocket it size + fuel and boosters will be too much weight for take off. If the is the case no rocket will work.A aire plane takes in oxygen and burns it with jet fuel and ejects it , and the momentum moves plane forward  and the ejects backwards.I think there is some thing more to it than momentum that seems to be a problem they are having going up into space. Posted by nec208</DIV>Actually there is a lot more.  You have gravity, you have aerodynamic lift and drag, you have system vibration, thermal issues (both launch and reentry), changing center of mass, changing center of pressure, control surfaces, nozzle augmentation, nozzle cooling, etc.  However, the *primary* function that causes a rocket (or an SSTO, etc.) to propel is a change in momentum.  I have told you how a rocket works in this manner.  A heavy rocket expels relatively lighter propellant and very high speeds to move at relatively very low speeds.  As the mass of the rocket becomes less, the so-called lift-to-mass ratio (must be greater than 1 for a launch vehicle... they are usually around 10) increases which causes the acceleration of the rocket to increase.  Thrust as I have mentioned is the lifting force.  In order to take off, a rocket must produce more thrust than it weighs (T/W > 1).  And actually the higher your T/W the less time is spent thrusting against gravity (which causes greater losses).  Once in orbit, you don't thrust agaist gravity, you thrust against the dirction of travel which is perpendicular to gravity.  (For reference Thrust = Ue * mdot; Ue is the exhaust velocity of the propellant, and mdot is the first time derivative of mass (aka the mass flow rate)).The rocket does not move before the 'flames shoot out'.  The rocket's motion is a reaction to the expulsion of propellant.  One final note for easy comparison.  Look at the thrust of a particular rocket and the specific impulse.  From the specific impulse you can determine how fast the flow of the propellant is by this equation: Ue = Isp/g (Isp is specific impulse, g is 9.8 m/s^2; gravitational constant).Then you can find the mass flow rate from: mdot = Thrust/Ue <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 21, 2008

KosmicHero you post are getting too much at a engineering level.I'm trying to understand change in momentum. Rockets are governed by a conservation of momentum.  When a rocket (or any body) ejects some of its mass at some velocity momentum is exchanged.  This causes both bodies to accelerate I think what you saying is any body that ejects some thing that causes both body to move away from each other.The rocket the gas goes out and the rocket moves up .You do not see the rocket and gas move up or both down.They move apart.I'm also tying to understand how this relates to the other stuff I posted above. I think I understand exchanged of momentum it is just hazy. I will get to the other stuff in your post but first what to understand this. <div class="Discussion_UserSignature"> </div>

KosmicHero · Apr 21, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I was thinking in physics does it not state that only large matter can push other smaller matter than it size?No.  Physics states that when a large object expels smaller objects (gases from rockets) at high speeds the two move opposite each other (Newton's Third Law). This is called conservation of momentum.Posted by nec208</DIV> <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 21, 2008

No.  Physics states that when a large object expels smaller objects (gases from rockets) at high speeds the two move opposite each other (Newton's Third Law). This is called conservation of momentum. Okay I can understand this 100% but how does this relate to airplanes,car speeding ,the fire hose.football player ,guy in space, the gun so on.That is what I'm having a hard time grasping..  <div class="Discussion_UserSignature"> </div>

KosmicHero · Apr 21, 2008

I guess I'm not sure what you're question is.  Jet engines, fire hose and gun recoil, all involve momentum too.  <div class="Discussion_UserSignature"> kosmichero.wordpress.com </div>

nec208 · Apr 28, 2008

No.  Physics states that when a large object expels smaller objects (gases from rockets) at high speeds the two move opposite each other (Newton's Third Law). This is called conservation of momentum -------------------------------------------------------------------------------------------------------------------------------I understand this and how this relates to rockets.When the rockets expels matter at high speeds it cause both to move in opposite each other.The rocket one way and expels the other way.When a fire hose expels water at high speeds the two move opposite to each  other , same for jet  engines and gun recoil.Take a machine gun, the fast expels at high speeds the two move opposite each other .The bullets move one way and the gun the other way.When a rockets expels smaller objects at high speeds the two move opposite each other and called conservation of momentum.If the rocket does not expels any thing the rocket will not move and same with jet engines .The rocket or jet engines move before the flames shoot out.What I was saying was using those flames or expels smaller objects again over and over has fuel. <div class="Discussion_UserSignature"> </div>

qso1 · Apr 30, 2008

What I was saying was using those flames or expels smaller objects again over and over has fuel. Posted by nec208The problem here is getting back expelled material to reshoot as it were. Especially chemical agents which by their nature, are unusable once burnt. Using objects involves recovery of those objects for their reuse as "Expellant" which is not practical with todays technology.  <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>

scottb50 · May 1, 2008

Pretty much this whole discussion points out that SSTO is not attainable with known technology. Nice idea, but not currently possible. TSTO is another situation, it can be done with current technology and could be done far cheaper then currently available expendable launchers. The problem is the first stage that has to bear the brunt of the launch. To take it to LEO and return it intact is just not currently possible. Not that it might not be in the future, but right now it isn't.With a TSTO system you have a brute force first stage and a very flexible second stage tha can have multiple re-light capabilites, not only to reach a LEO staging area, but to continue on to other locations in or out of LEO.Even the Delta and Atlas engines are run in testing befor they are used, the SSME's was designed for multiple uses and the Delta engine is a beffier version of the same engine. The RL-10 is also capable of multiple relights and does so on a regular bases and has been tested for a whole lot more relights. It could be a workhorse as an Second Stage and in orbit Tug.The key, as I see it is a simple structure, which would be primarlily tanks, which I have already, described, combined with these existing engines. As an example a Delta IV, could have an aerodynamic fairing and turrbojet engines to allow return strapped to the Cores. Come back, refuel the cores and add another upper stage ond launch it again.The onl problem even with the three core Delta it needs more power, a couple of SRB's would do the job and as long as the tubojet engines carried their own weight at takeoff, they would complete the package.   <div class="Discussion_UserSignature"> </div>

qso1 · May 1, 2008

Pretty much this whole discussion points out that SSTO is not attainable with known technology. Nice idea, but not currently possible. TSTO is another situation, it can be done with current technology and could be done far cheaper then currently available expendable launchers. The problem is the first stage that has to bear the brunt of the launch. To take it to LEO and return it intact is just not currently possible. Not that it might not be in the future, but right now it isn't.With a TSTO system you have a brute force first stage and a very flexible second stage tha can have multiple re-light capabilites, not only to reach a LEO staging area, but to continue on to other locations in or out of LEO.Even the Delta and Atlas engines are run in testing befor they are used, the SSME's was designed for multiple uses and the Delta engine is a beffier version of the same engine. The RL-10 is also capable of multiple relights and does so on a regular bases and has been tested for a whole lot more relights. It could be a workhorse as an Second Stage and in orbit Tug.The key, as I see it is a simple structure, which would be primarlily tanks, which I have already, described, combined with these existing engines. As an example a Delta IV, could have an aerodynamic fairing and turrbojet engines to allow return strapped to the Cores. Come back, refuel the cores and add another upper stage ond launch it again.The onl problem even with the three core Delta it needs more power, a couple of SRB's would do the job and as long as the tubojet engines carried their own weight at takeoff, they would complete the package.   Posted by scottb50IMO, the real problem lies with the willingness to fund efforts such as SSTO/TSTOs. NASA could not get the X-33 program off the ground once techical problems became evident. Problems that would have been solved most likely had the funding environment been friendlier.This is in part, what has led to private enterprise/industry efforts to come up with an economic low orbit access solution on their own which in a couple of cases, include SSTOs. During the X-33 (Venture Star) days, the U.S. economy was enjoying budget surplusses thought not to be possible in the early 1990s, 80s and 70s. Yet no plans emerged to use a small bit of that surplus to help NASA achieve its so called cats (Cheap Access To Space) plans.  <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>

scottb50 · May 1, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> During the X-33 (Venture Star) days, the U.S. economy was enjoying budget surplusses thought not to be possible in the early 1990s, 80s and 70s. Yet no plans emerged to use a small bit of that surplus to help NASA achieve its so called cats (Cheap Access To Space) plans.  Posted by qso1</DIV>While a great idea on paper the X-33 had a lot more problems then building complicated shaped tanks. That it would have worked at all is questionable, even as a small scale demonstrator.Just like machines, people, animals and plants the key is evolution. What works best dominates and spawns chnages that improve on the initial product. The Shuttle not spawning an offspring makes it an evolutionary dead end. The dinosaurs survive, Delta, Atlas, Soyus, Aerianna are all improved and updated versions of the earliest designs.Shuttle pushed the technology too far too fast. Saturn could have been used to build the ISS and with refinements would probably be launching a runway landing vehicle today.One thing the well over 100 Shuttle flights has done is prove the basic hardware, it seems a shame not to evolve to the next stage and continue the reign of the donosaurs. While Shuttle was designed well beyond it's needs it has proven the core concepts works, the next stage should be looking at the failings in the design and making changes the make it work better, not put it in museums and return to the beginning. I look at current Soyus, Delta and Atlas as 3.0 versions while Shuttle started as 5.0 and is 5.5 now. I would rather see Shuttle 6.0 then 2.5. <div class="Discussion_UserSignature"> </div>

nec208 · May 2, 2008

Pretty much this whole discussion points out that SSTO is not attainable with known technology. Nice idea, but not currently possible. TSTO is another situation, it can be done with current technology and could be done far cheaper then currently available expendable launchers. The problem is the first stage that has to bear the brunt of the launch. To take it to LEO and return it intact is just not currently possible. Not that it might not be in the future, but right now it isn't.-------------------------------------------------------------------------------------------- No one knows if SSTO is attainable or not with the technology we have.It has not got the funding that the army gets and the time doing resarch .Well weight and size is a big problem do to coast and enormous power to get it in space.And SSTO is a a very big challenge and if they do fix it ,DO NOT  count on any thing big.If you want rocket evolution get DARPA running it and do away of NASA .Or have NASA do it and we can use rafts , because of the lack of  funding and research.It is too costly to progress over a capsule , even a bigger capsule.Every inch and pound is paradise to do coast.They must keep weight and size down to do coast and the enormous power to get it in space.My guess is in 5 or 10 years SSTO will be fixed but it will be too costly and be like the space shuttle and any SSTO will be small do to the enormous power to take it in space.Any way you look at it <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-frown.gif" border="0" alt="Frown" title="Frown" />the rocket evolution is complex and very costly and needs trillions  and trillions  of money for research and will take years and years .And be much slower than the 100+ years of airline evolution.In the end it may have to be the world building it than the US.Do to the resources and money needed and will power of every place on earth doing it. <div class="Discussion_UserSignature"> </div>

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