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Thread: british rocketplane by 2020?

  1. #91
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    Bob clark. can you please stop using guesswork about the skylon design? It would please me greatly if you actually checked the facts before making claims about how something is suposed to work.
    The skylon engine does not gimbal. pitch and roll is done with flight controll surfaces. pitch is controlled by forward canards. (those little wing like thingies on the nose of the vehicle you know) and roll is controlled with an all moving tailfin. once out of the atmosphere controll is maintained with the use of fixed forward and aft RCS thrusters.
    The main reason for using hydrogen as fuel in skylon is not ISP. it's the fact that a vehicle of this kind needs an enourmous amount of very cold coolant. Luck has it that hydrogen is excelent as both. Denser fuels cannot act as a coolant in this manner, and is hence limited to an air breathing speed below mach 3,5 barring any revolutions in high temperature alloys.

    The second advantage to using hydrogen is that it fits with a large volume low density vehicle of the kind that get's to have a fairly benign re-entry. This allows the use of much more dammage resistant materials than what the shuttle is allowed to use. This is of critical importanse to the safety and practicality of skylon as a launch vehicle.

    If you actually read the 2004 documents on REL's website you will find the exact trades done when selecting fuel type. ISP was a minor factor. so minor it's hardly even mentioned.
    You are the one doing the asuming here. not REL. You are asuming that RP1 is a superior fuel because it's denser. but that is just one factor in the kind of trades you need to do when selecting fuel types.

    @Danscope. If everyone was thinking like you we would still be living in caves and eating our food raw. I'f you havent actually noticed yet the skylon vehicle is dependant on a critical item of brand new technology. without whitch a vehicle like skylon would not be capable of working at all. Namely preecooled air breathing rocketry. nobody has made that work all that well before. REL is changing that trend as we speak. so how about waiting with the doom and gloom til they have concluded their technology demonstration programme hey? We will know for sure in 2012 or thereabouts.

  2. #92
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    Quote Originally Posted by Antice View Post
    Bob clark. can you please stop using guesswork about the skylon design? It would please me greatly if you actually checked the facts before making claims about how something is supposed to work.
    The skylon engine does not gimbal. pitch and roll is done with flight controll surfaces. pitch is controlled by forward canards. (those little wing like thingies on the nose of the vehicle you know) and roll is controlled with an all moving tailfin. once out of the atmosphere controll is maintained with the use of fixed forward and aft RCS thrusters.
    The main reason for using hydrogen as fuel in skylon is not ISP. it's the fact that a vehicle of this kind needs an enourmous amount of very cold coolant. Luck has it that hydrogen is excelent as both. Denser fuels cannot act as a coolant in this manner, and is hence limited to an air breathing speed below mach 3,5 barring any revolutions in high temperature alloys.
    The second advantage to using hydrogen is that it fits with a large volume low density vehicle of the kind that get's to have a fairly benign re-entry. This allows the use of much more dammage resistant materials than what the shuttle is allowed to use. This is of critical importanse to the safety and practicality of skylon as a launch vehicle.
    If you actually read the 2004 documents on REL's website you will find the exact trades done when selecting fuel type. ISP was a minor factor. so minor it's hardly even mentioned.
    You are the one doing the asuming here. not REL. You are asuming that RP1 is a superior fuel because it's denser. but that is just one factor in the kind of trades you need to do when selecting fuel types.
    By 'gimbal', I did not mean rotating on pylons as I referred to on another thread, I meant the type of gimbaling usually done in rockets where the nozzles on the engines can be angled:

    The SKYLON Spaceplane.
    RICHARD VARVILL AND ALAN BOND
    Reaction Engines Ltd, D5 Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK.
    JBIS, vol. 57, pp. 22-32, 2004
    "Control authority
    whilst in the atmosphere is exerted by
    foreplanes in pitch, ailerons in roll and an aft mounted
    fin in yaw. During the ascent main engine gimballing
    takes over progressively as the dynamic pressure
    reduces until finally handing over to reaction control
    thrusters at main engine cutoff."
    http://www.reactionengines.co.uk/dow..._v57_22-32.pdf

    Kerosene can be used for cooling; its just that hydrogen has a better capacity for it. For instance the kerosene itself is used for the cooling for kerosene-fueled, regeneratively-cooled engines, where the temperatures are even higher than in the Skylon application. For this heat exchanger use though there is a large mass of air that needs to be cooled and hydrogen can do it more effectively. However, there are other hydrocarbon fuels such as methane and propane that have higher energy density than kerosene and better cooling capacity. A trade study would need to be done to see if the lower cooling capacity of using a hydrocarbon fuel would be made up by the greater density of the fuel.
    I read the "Comparison of Propulsion Concepts" article and some of the heat exchanger articles, and I did not see any that made a comparison of using hydrocarbon as the coolant or as the engine propellant in the ones I read. If you've read some that made this comparison, point me to them and I will read them.


    Bob Clark
    Last edited by RGClark; 2010-Aug-25 at 12:09 PM. Reason: clarity

  3. #93
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    People have pointed you towards facts, data, evidence and proffesio al opinion in many other threads many other times, and it has achieved nothing. Not a damn thing. PLEASE take your pseudo-engineering elsewhere.

  4. #94
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    Quote Originally Posted by RGClark View Post
    By 'gimbal', I did not mean rotating on pylons as I referred to on another thread, I meant the type of gimbaling usually done in rockets where the nozzles on the engines can be angled:

    The SKYLON Spaceplane.
    RICHARD VARVILL AND ALAN BOND
    Reaction Engines Ltd, D5 Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK.
    JBIS, vol. 57, pp. 22-32, 2004
    "Control authority
    whilst in the atmosphere is exerted by
    foreplanes in pitch, ailerons in roll and an aft mounted
    fin in yaw. During the ascent main engine gimballing
    takes over progressively as the dynamic pressure
    reduces until finally handing over to reaction control
    thrusters at main engine cutoff."
    http://www.reactionengines.co.uk/dow..._v57_22-32.pdf

    Kerosene can be used for cooling; its just that hydrogen has a better capacity for it. For instance the kerosene itself is used for the cooling for kerosene-fueled, regeneratively-cooled engines, where the temperatures are even higher than in the Skylon application. For this heat exchanger use though there is a large mass of air that needs to be cooled and hydrogen can do it more effectively. However, there are other hydrocarbon fuels such as methane and propane that have higher energy density than kerosene and better cooling capacity. A trade study would need to be done to see if the lower cooling capacity of using a hydrocarbon fuel would be made up by the greater density of the fuel.
    I read the "Comparison of Propulsion Concepts" article and some of the heat exchanger articles, and I did not see any that made a comparison of using hydrocarbon as the coolant or as the engine propellant in the ones I read. If you've read some that made this comparison, point me to them and I will read them.


    Bob Clark
    Hmmm... I have this feeling something doesn't work out, but I am not sure exactly what...

    This will probably be a rather rambling series of thoughts, but perhaps something will be understandable and somewhat correct...


    Lets see, Our hydrocarbon fueled craft can carry 10 times the reaction mass in the same volume, however, this fuel has less heat capacity, was that the idea? Hmmm. So you have to use what... 7 times?(I seem to remember HC fuels being around 2 and hydrogen around 14 on some list or other for heat capacity) the fuel mass to cool the same amount of air(is it even practical to use HC as a sink for cooling air from around 1000C to cryogenic temperatures?). Then, as you carry 10 times the fuel, the engines will have to larger, so you need even larger precoolers. and the structure of the craft is would have to be reinforced to carry the extra load, I should think. Still, wouldn't you have a lot more HC fuel in mass relative to a LH system that can not be used for the rockets, what would we do with this? more ram burners? or just dump it? That last does not seem practical, as there is no point in carrying the weight just to dump it... and I would think there was a limit to how practical the rams would be in larger numbers or sizes... Are you sure we get any significant improvement from using HC?

    Hmmm.. Wait a minute... Doesn't the Skylon design use the remaining liquid hydrogen for the reentry thermal rejection screens, and basically keeping its insides cool by allowing the fuel to evaporate? I have a feeling that the LH would have a lot more capacity than HC for evaporative cooling... Is it feasible, or are we going to loose the ship on reentry(if we do get it into space) as everything inside gets cooked? Do we need to carry some additional coolant for this use?

    Hmmm... seems to me that one of the integral parts of the skylon design is the relatively low mass it has in relation to the size, I can't really see how it would be practical to add all the reenforcement stuff needed for carrying 10 times the fuel mass...

    I expect that if the Skylon or some derivative gets of the ground, we will see some research into improvements, but for now getting there is the important thing, not trying to improve the wheel before it has been created, that sort of thing can kill a project. It may forever be just trying to keep up with the changing requirements, especially for projects where a lot of new technologies are involved, you may find that just to facilitate the new requirements you actually end up with an abomination worse than the original design or any derivative it might have had once the technologies and real world challenges was better known.

  5. #95
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    Quote Originally Posted by RGClark View Post

    Kerosene can be used for cooling; its just that hydrogen has a better capacity for it. For instance the kerosene itself is used for the cooling for kerosene-fueled, regeneratively-cooled engines, where the temperatures are even higher than in the Skylon application. For this heat exchanger use though there is a large mass of air that needs to be cooled and hydrogen can do it more effectively. However, there are other hydrocarbon fuels such as methane and propane that have higher energy density than kerosene and better cooling capacity. A trade study would need to be done to see if the lower cooling capacity of using a hydrocarbon fuel would be made up by the greater density of the fuel.

    Bob Clark
    And you have an example of your 'for instance' that's actually under development? You know something with actual engineering rather than a Kerosene fetish? Not to mention you seem to have ignored Antice's point about the alloy's necessary for higher temperature operation. You simply cannot accept that there are applications where LOX/LH2 is the better choice. Kerosene has it's applications as rocket fuel, air breathing SSTO's do not appear to be one of them.

  6. #96
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    Quote Originally Posted by TrAI View Post
    I expect that if the Skylon or some derivative gets of the ground, we will see some research into improvements, but for now getting there is the important thing, not trying to improve the wheel before it has been created, that sort of thing can kill a project. It may forever be just trying to keep up with the changing requirements, especially for projects where a lot of new technologies are involved, you may find that just to facilitate the new requirements you actually end up with an abomination worse than the original design or any derivative it might have had once the technologies and real world challenges was better known.
    TrAI I think you just summed up what happened to the X-33...

  7. #97
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    About the gimbaling on the engines. my bad.
    I forgot about the intermediate step between the area of the flight were air control surfaces are effective and the short period until RCS becomes truly effective. Gimbaling can not be used early in the flight because a fair amount of the thrust coming from the engine is trough the bypass system and not trough the gimbaled nozzles. A pretty unique issue for turbo-rockets. Thrust vectoring would require a separate system mounted outside the nozzles of the rocket part. this is a mass trade-off where it might be lower mass to use thrust vectoring instead of canards. but thrust vectoring is a higher risk technology than canards so going with canards for a first gen vehicle makes a lot of sense.

    Kerosene is useless as a heat sink for the helium loop because at the temperatures that is required in that regard is below the freezing point of not only kerosene, but more or less all reasonable fuels we know of, except hydrogen. The hydrogen is sub cooled even. to increase it's heat capacity.
    Thrust has been traded away on skylon. so much so that the vehicle has a TW at takeoff of only around 0.5

    LH2 is giving us these benefits:
    Fluffy vehicle with a low mass to volume ratio allowing a benign re-entry profile.
    High heat capacity as well as deep cryogenic temp cold side for the heat engine cycle.
    High caloric energy content per unit mass, translates into a high ISP upper stage burn mode for the final ascent to orbit.
    That last point translates into a benign ascent environment with low G loading on the cargo. especially important if the cargo is going to be passengers, but also for some science experiments and satellites.

    LH2 usually have some drawbacks, but they do not apply for skylon because skylon is designed so that it turns them into strengths instead. Which I think is a very nifty way of doing things. Trying to change the fuel type to anything but hydrogen simply breaks the design entirely. it no longer works at all.

  8. #98
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    Quote Originally Posted by TrAI View Post
    Hmmm... I have this feeling something doesn't work out, but I am not sure exactly what...
    This will probably be a rather rambling series of thoughts, but perhaps something will be understandable and somewhat correct...
    Lets see, Our hydrocarbon fueled craft can carry 10 times the reaction mass in the same volume, however, this fuel has less heat capacity, was that the idea? Hmmm. So you have to use what... 7 times?(I seem to remember HC fuels being around 2 and hydrogen around 14 on some list or other for heat capacity) the fuel mass to cool the same amount of air(is it even practical to use HC as a sink for cooling air from around 1000C to cryogenic temperatures?). Then, as you carry 10 times the fuel, the engines will have to larger, so you need even larger precoolers. and the structure of the craft is would have to be reinforced to carry the extra load, I should think. Still, wouldn't you have a lot more HC fuel in mass relative to a LH system that can not be used for the rockets, what would we do with this? more ram burners? or just dump it? That last does not seem practical, as there is no point in carrying the weight just to dump it... and I would think there was a limit to how practical the rams would be in larger numbers or sizes... Are you sure we get any significant improvement from using HC?
    Hmmm.. Wait a minute... Doesn't the Skylon design use the remaining liquid hydrogen for the reentry thermal rejection screens, and basically keeping its insides cool by allowing the fuel to evaporate? I have a feeling that the LH would have a lot more capacity than HC for evaporative cooling... Is it feasible, or are we going to loose the ship on reentry(if we do get it into space) as everything inside gets cooked? Do we need to carry some additional coolant for this use?
    Hmmm... seems to me that one of the integral parts of the skylon design is the relatively low mass it has in relation to the size, I can't really see how it would be practical to add all the reenforcement stuff needed for carrying 10 times the fuel mass...
    I expect that if the Skylon or some derivative gets of the ground, we will see some research into improvements, but for now getting there is the important thing, not trying to improve the wheel before it has been created, that sort of thing can kill a project. It may forever be just trying to keep up with the changing requirements, especially for projects where a lot of new technologies are involved, you may find that just to facilitate the new requirements you actually end up with an abomination worse than the original design or any derivative it might have had once the technologies and real world challenges was better known.
    Thanks for that insightful analysis. I think the Skylon is a great design, and I definitely think it will work. Because these speculations of mine might be interpreted as criticisms of its feasibility I'll just leave it at that.

    Bob Clark

  9. #99
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    Newsflash. August news report just in. No news to report except that they claim to have a treat for us in store for the next update, and that the first tube manufacturing unit is online at the heat exchanger factory. (now that was a bit of a downplay for what i would consider worthy of a better write up. but that's just me I guess)

    /wild speculation

    I am hoping that next month will feature the much anticipated D1 revision of the skylon. If it does it will definitely tickle my cerebral pleasure centers greatly. But It may not, so don't get our collective hopes up to much now ya hear

    /end speculation

  10. #100
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    Skylon is getting some more press. A pretty nice article overall.
    Nothing we havent heard before, but it is worth repeating imho.

  11. #101
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    Quote Originally Posted by Antice View Post
    Skylon is getting some more press. A pretty nice article overall.
    Nothing we havent heard before, but it is worth repeating imho.
    Point in the article that's worth picking out is that the science minister in the new Westminister government has said he isn't going to abandon good policies just because they were put in place by the previous administration. That's almost more radical than the Skylon.

  12. #102
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    Even more skylon in the news. The project is really gaining momentum now.
    Cant wait to see the results from the skylon systems requirements review hosted by UKSA.

    I'd say this rates a and a

  13. #103
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    The latest news update is in.
    there isn't much controversy in it. It's mostly about the skylon systems requirements review. The results of which we may get to see in the next update in a month or so. They are also starting the first financing round for obtaining the funds to push forward and start bending metal for the rest of skylon.

    All in all it's good news I'd say. but not exactly what I was wishing for. (I really wanted to see the D1 updated configuration)

  14. #104
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    Quote Originally Posted by Antice View Post
    The latest news update is in.
    there isn't much controversy in it. It's mostly about the skylon systems requirements review. The results of which we may get to see in the next update in a month or so. They are also starting the first financing round for obtaining the funds to push forward and start bending metal for the rest of skylon.

    All in all it's good news I'd say. but not exactly what I was wishing for. (I really wanted to see the D1 updated configuration)
    I think they are saving that up for your Xmas present...

  15. #105
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    I do like Skylon, enough in fact to be quite wary that it seems too good to be true. Always bear in mind that when Reaction Engines talk about 2 week turn arounds, that is precisely what they were saying about the Space Shuttle in the 1970s. Many launcher projects have promised to give us airline-like access to space, and they've all running into crippling technical difficulties.

    Also, unless it delivers prices that completely decimate the rest of the launch market and everyone and their dog puts their satellite in a Skylon, it runs the risk of being a remarkable piece of engineering with nothing to do. A recent video they did showed Skylon visiting the ISS - is it worth going to this much trouble to develop something that would only be used as a Soyuz replacement?

  16. #106
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    Quote Originally Posted by Damburger View Post
    I do like Skylon, enough in fact to be quite wary that it seems too good to be true. Always bear in mind that when Reaction Engines talk about 2 week turn arounds, that is precisely what they were saying about the Space Shuttle in the 1970s. Many launcher projects have promised to give us airline-like access to space, and they've all running into crippling technical difficulties.
    Well actually I would say that in many, if not most, cases the porblems were political not technical. The shuttle is a good example of this. It's worth looking up the original design ideas for the shuttle and comparing them to what was actually built; the differences are startling and mostly the product of budget cuts and politicians adding ever more requirements onto the STS. Skylon has avoided the grasp of the politicians to date, which is a big plus.

    Also, unless it delivers prices that completely decimate the rest of the launch market and everyone and their dog puts their satellite in a Skylon, it runs the risk of being a remarkable piece of engineering with nothing to do. A recent video they did showed Skylon visiting the ISS - is it worth going to this much trouble to develop something that would only be used as a Soyuz replacement?
    Well that's pretty much the point of the project, to drastically reduce the costs of space access. The video just shows one role that is envisioned for the Skylon, it's primary objective is the satellite launching market. Of course if it can open the way for people like Bigelow to get their plans off the ground then people moving could be big business. REL also has plans for an orbital tug that would transfer Satellites to higher orbits than the Skylon can reach directly.

  17. #107
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    Quote Originally Posted by Garrison View Post
    ... in many, if not most...
    While agreeing with that statement...
    I think another issue was they never decided to use the shuttle to it's full capacity either.

    Quote Originally Posted by Damburger View Post
    A recent video they did showed Skylon visiting the ISS - is it worth going to this much trouble to develop something that would only be used as a Soyuz replacement?
    Why would you think a video like that would indicate that kind of restriction? I'm not familiar with the video, but my suspicion is that it is meant for PR purposes. What better PR than to show something people can be impressed with? Satellites are boring, and other potential applications are out of their control.

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    Quote Originally Posted by NEOWatcher View Post
    Why would you think a video like that would indicate that kind of restriction? I'm not familiar with the video, but my suspicion is that it is meant for PR purposes. What better PR than to show something people can be impressed with? Satellites are boring, and other potential applications are out of their control.
    It's the video for the Passenger & Logistics Module (video at YouTube). They got BRIAN BLESSED! to narrate it.

    I thinks it's more of an example destination. It may be also subtle advertising: "We can build the Skylon before they de-orbit the Station." Or, "It can do the same stuff the Shuttle did, only safer/cheaper, so please fund the development of the module."
    (English is not my first language, so please excuse any mistakes and unintended ambiguities.)

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    Quote Originally Posted by NEOWatcher View Post
    While agreeing with that statement...
    I think another issue was they never decided to use the shuttle to it's full capacity either.
    True, the irony of insisting on building a vehicle designed to do everything, and then deciding they didn't want it to do those things after all. Fortunately the bulk of REL's funding still comes from the private sector, with a little help from governmental agencies like the ESA, so fingers crossed.

  20. #110
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    Quote Originally Posted by NEOWatcher View Post
    Why would you think a video like that would indicate that kind of restriction? I'm not familiar with the video, but my suspicion is that it is meant for PR purposes. What better PR than to show something people can be impressed with? Satellites are boring, and other potential applications are out of their control.
    Because I assume they wish to promote their spacecraft, and if that is the best mission they envision for it then it indicates a worrying lack of purpose. Personally, I wouldn't build a Skylon to visit the ISS, I would build a Skylon to visit Space Station V.

  21. #111
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    Quote Originally Posted by Damburger View Post
    Because I assume they wish to promote their spacecraft, and if that is the best mission they envision for it then it indicates a worrying lack of purpose. Personally, I wouldn't build a Skylon to visit the ISS, I would build a Skylon to visit Space Station V.
    This is just one of several promotional videos of skylon. why get so hung up on the ISS being used in this one? The other vids don't even use it. the skylon mission animation show a satelite deployment and a trip to the envisioned Orbital Base Station used in the Troy mission study.

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    Quote Originally Posted by Damburger View Post
    Because I assume they wish to promote their spacecraft, and if that is the best mission they envision for it then it indicates a worrying lack of purpose. Personally, I wouldn't build a Skylon to visit the ISS, I would build a Skylon to visit Space Station V.
    Hmmm... On what basis do you conclude this video shows the definitive best mission? The Skylon mission animation shows the Skylon placing a satelite into orbit, and delivering a passenger module to the Orbital Base Station, in the Troy Mars Mission video it is described how the Skylon would transport the Troy modules to the Orbital Base Station for assembly, and how the PLM would be used for ferrying crew to the Troy space craft. Why are these, to your mind, not showing any alternative purpose for the Skylon than to visit the ISS?

    Actually, it is probably a good idea to show that you can use the Skylon to support existing infrastructure. The ISS may be considered something of a money sink without a future by many people that are interested in space topics, but in most people's minds I suspect it is The Space Station, the only real destination for people in space that isn't some science fiction thing, it may be easy to dismiss this as just another of a long line of fictional space ships with even more fictional destinations, showing some uses that is a bit more tangible, like launching satellites or going to the ISS may help get a bit more support. After all REL is not like a space agency, they will have to convince a wider segment of the population to get support.

  23. #113
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    Your link to " The Space Station " does not function. Hmmm......

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    Well, I must say this is a very ambitious undertaking and I wish it all the best.

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    Quote Originally Posted by danscope View Post
    Your link to " The Space Station " does not function. Hmmm......
    Probably because it isn't a link at all, it is underlined text

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    I picked the ISS mission because, unlike the Troy Mars Mission (which seems a bit BSG to me, but thats another story) its a real mission that Skylon would have right from the start. As for satellite launch - the low price they promise looks to be based on a fast turnaround which itself is only useful if you've got a substantial increase in the demand for satellites - so again, the need is for a mission worthy of the design.

    As I said above, I am excited by the Skylon idea, but I also have in my possession a book written in the late 1970s promising basically the same stuff from the Space Shuttle. I'm just trying to moderate excitement with a little realism (pessimism?)

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    Did you have a particular concept in mind for "The Space Station " ?

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    Quote Originally Posted by Damburger View Post
    I picked the ISS mission because, unlike the Troy Mars Mission (which seems a bit BSG to me, but thats another story) its a real mission that Skylon would have right from the start. As for satellite launch - the low price they promise looks to be based on a fast turnaround which itself is only useful if you've got a substantial increase in the demand for satellites - so again, the need is for a mission worthy of the design.

    As I said above, I am excited by the Skylon idea, but I also have in my possession a book written in the late 1970s promising basically the same stuff from the Space Shuttle. I'm just trying to moderate excitement with a little realism (pessimism?)
    Your idea that skylon needs a higher launch rate to make launches cheaper is false.
    The worst case estimate presented for launch prising by REL is based on the assumption that the market is totally unchanged.
    The price per launch in this scenario is 40 mill. so still cheaper than anything else out there on a per kg cost basis.

    Then there is the added value of having on orbit checkout capability as well as earth return capability in case the satelite does not pass all it's comissioning tests on orbit. In fact 40 mill is almost cheap enough to make it viable to go fetch a satelite that has failed on orbit and return it home for repairs and relaunch. a big telecom sat can easily cost a bill$ or more depending on the capabilities of the satelite in question. No other vehicle sans the shuttle has ever been able to offer such a service. and the shuttle no longer offers it due to safety issues unique to the shuttle.
    The skylon vehicle has a market able to sustain it. the biggest unknowns at this time is if it can be delivered on schedule and on target cost wise.

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    We know little about the skylon motors peformance and especially durability and in particular it's material condition after re-entry . And when you talk about a mars mission(?) what about the motor's ability to re-start for Earth return? None of these questions have solid answers.
    Good wishes, yes.

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    Quote Originally Posted by danscope View Post
    We know little about the skylon motors peformance and especially durability and in particular it's material condition after re-entry . And when you talk about a mars mission(?) what about the motor's ability to re-start for Earth return? None of these questions have solid answers.
    Good wishes, yes.
    The Skylon wouldn't actually be part of the Mars mission per se, it would simply launch the components of the mission vehicles. More details here:

    Troy

    And again it's more of an illustration of what the Skylon might make possible at this point, which is important for generating interest and funding.

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