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Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

I did not realize it was as bad as that. On that basis, space panels are not 8 times more effective, but more like 16 times better, so based on what you say, solar power panels cost $1.40/watt and the difference is $18.00/watt.

Where did the 16 times suddenly come from?  Also, The $4 per peak watt figure was a few years old (from 2001).  Apparently, it is now down to $2.50 per peak watt.  That is $12 per average watt.  So now you need launch costs to be $1530/kg to GEO.

Have you any idea how expensive and inefficient—and short-range-- existing surface power transmission is? (So inefficient that beyond about 500 miles it’s so poor (about 10%) it’s not practical.) Have you any notion of how efficient micro-wave power transmission through vacuum can be? (About 90%)

I was assuming that it was free, massless and 100% efficient.  Really though, can microwaves even be produced and absorbed at 90% efficiency, even without the huge distances involved or the atmosphere reducing efficiency?

And even that only applies if you insist on shipping everything from earth. Mine and manufacture on the moon, save a fortune and develop the space infrastructure. A win-win situation.

It will be a very long time before the moon develops the sort of manufacturing capability necessary for this.

Sez who? Surface ones are exposed to more environmental damage-causing factors that are space ones, not least weather.

Surface ones are pretty much immune to the sort of weather that they are likely to experience, and they are easily serviced.  Space solar panels are subject to radiation and micrometeoroids, and they are not easily serviced.

As it has been with your ground-based price, and in 1G, you need more massive support than in 0 G. It may be possible to use the solar wind to hold the panels open like a sail, and use the solar wind for station-keeping into the bargain. The mass of current orbital solar panels has got more to do with the unraveling mechanisms and support structures for panels attached to spacecraft and satellites than the intrinsic needs of the panels themselves.

On the ground, support structures are essentially free (you can use the ground, rooftops, etc).  You also seem to be confused about the nature of the solar wind.  The force from it is negligible, much less even than the light pressure from the sun.  And even a small amount of support structure is more than the free, massless structure that I assumed in my calculations.

The fundamental trouble with coal & gas are the same as oil; they’re going to run out.

Eventually, yes.  However, while we have perhaps 50 years of oil left, we should not run out of coal for hundreds of years.

Biomass and wind are not serious sources of mass power.

Perhaps not, but they are still beating ground based solar right now.  And as we have seen, ground based solar is much cheaper than space based right now.  What does that say about space based solar power?

ANTIcarrot.

Member

From: Herts, UK

Registered: 2004-04-27

Posts: 170

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

The standard 1980s NASA plan for an SSPS fearures a twenty square mile (a rectangle the size of Manhattan) solar array with two 600m diameter transmitters at the top and bottom. A more modern scenario, would be to have (say) a two square mile solar array pointing away from the sun with a flimsy mirror reflecting and concentrating twenty square miles worth on that area. Fit the transmitter wherever convenient.

Yes there are serious problems, but the only one that seems unsolvable is the question of what would that amount of microwaves passing through the atmosphere do to the enviroment?

As near as we can tell, nothing, but we don't know for sure. And until someone builds a small scale prototype (1MW say) we never will.

ANTIcarrot.

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

How much can the light be concentrated before the solar panels overheat?

jpeachman787

InActive

From: Ohio, USA

Registered: 2004-05-30

Posts: 6

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

I don't remember where I read it, but there was an article somewhere about a group developing a new substance which they hoped would one day lead to truely low cost solar power.. It was pretty inefficient, but it could essentially be painted onto any surface, and they spoke of covering every rooftop and road with it.

Now, hypothetically, if the top of every home and skyscraper and factory and every road and parking lot were covered with something like this, why would we need SSPS? (Thats a big if but, at this point, seems a little more likely)

As for cheap access to space, as you've all pointed out to me, its impossible unless theres a huge market.... Zubrin once wrote "More people want to go to Tokyo than to orbit" or something along those lines. So, perhaps it would be best to first produce a large, passenger carrying suborbital rocketplane that could fly many times per day. (Hopefully it wouldn't end up like the concorde) Then, later, such a plane could carry a reusable upper stage which could reach orbit.

What other way can cheap access to space be achieved? There has to be some way to do it. I've read "The Space Elevator" by Bradley Edwards and he made a good argument that a space elevator could be viable, but unless theres a huge market such a project is doomed to financial failure. So, how do you people think we could pull this off?

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

You are thinking about the polymeric solar cells, that is, ones made from plastic, not silicon. Right now they are a little bit too inefficent (3-5%) but when they can reach 8-10% then the low cost versus silicon will make them practical for very large batch production. This level of efficency seems attainable with a little polymer science and a dash of nanotechnology...

I agree with you that no rocket has the efficency to get people into orbit en-mass, but i'm not sure what kind of market there would be for a supersonic very-high-altitude airliner that would trade efficency for a berth for an upper stage. A spaceplane is ultimatly the answer, there isn't going to be a Pan Am space capsule, but I think that it would have to be built with space launch as its primary function from day one.

Also, since Big Dumb Booster production isn't scaleable, I imagine that such a vehicle able to carry people with a high degree of reliability would have enough mass margin for a cargo-only medium lift upper stage. Flying that every week or two could deliver substantial masses to orbit inexpensively and take advantage of economies of scale.

---

[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

ANTIcarrot.

Member

From: Herts, UK

Registered: 2004-04-27

Posts: 170

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

It is my understanding that Pan Am no longer exists as a comercial venture. It imploded shortly after one of it's aircraft exploded over the town of Lockerby. Therefore whatever aerospace craft it will or will not be flying is largely irrelevent.

A few practical issues to consider:

By far the most difficult part of space flight is reentry. For any spacecraft to be reusable it's heatshield must be able to easily withstand entry hundreds of times with minimal maintinance, or it must have a heat-shield that can be replaced between flights at very low costs. On that basis we should try and solve this problem first.

You can do so in two ways; solving it for the crew and solving it for the ship. The first means reducing G loadings. The second means getting reentry over with as quickly as possible. Unfortunately these are mutually exclusive.

Imagine a bullet and a balloon reentering earth's atmosphere. We'll ignore heating effects for the moment and concetrate on heat itself. Which will be subjected to the greater heating? The bullet. It's high density and efficient aerodynamics means it will slow down slowly, will be passing through high energy plasma for longer, and will absorb more heat. The balloon has lousy aerodynamics, and low density and will slow down much faster, even if it's of equal weight to the bullet.

Though the balloon needs a larger heat-shield, it needs it for a very short period of time. Shorten that period of time enough and you can use ordinary metal without any of this high tempreature ceramics or 3D metal fabric nonsense. At least that's the theory. A lot of designs for space planes were MASSIVE not only to contain the required fuel but to behave like a balloon during reentry.

Unfortunately there are significant engineering problems associated with building an aircraft or glider with a wingspan three times that of a 747 (not least of which was the landing gear) and so it was never done.

The core theory still stands. If you want to reduce g loadings, you give up on light weight heat shields, and shoot yourself in the foot over launch costs. If you want to reduce heat loadings, you give up on gentle reentries.

Space planes, especially shuttle size or smaller though, won't do that. And 747 size and larger means their use will be restricted to those who can afford to build their own private airports. Because no ATC will willingly let a 1kt bomb near their priceless runways.

ANTIcarrot.
NB: Not given up on the DH-1 yet. Just gone back to my calculator.

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

As for cheap access to space, as you've all pointed out to me, its impossible unless theres a huge market.... Zubrin once wrote "More people want to go to Tokyo than to orbit" or something along those lines. So, perhaps it would be best to first produce a large, passenger carrying suborbital rocketplane that could fly many times per day. (Hopefully it wouldn't end up like the concorde)

Sorry, that's a classic repeat of what i've called the 'Concorde Syndrome'. Or if you prefer, the Shuttle Syndrome. Or (Heaven forfend) one day may be the DH-1 Syndrome: "Build It And They Will Come. And Lo! They Did Not Come."

Concorde at least had the advantage of flying between large population centers with many rich inhabitants in a hurry to get from one to the other: London and New York, for example. And lo and behold, not nearly enough rich inhabitants in a hurry came. It was not a viable proposition.

Shuttle... well, Shuttle was a vastly more expensive Concorde (in a sense) without any serious destination, so far as people wanting to get there (at any speed) was concerned. Virtually nobody came.

(Has it occurred to anyone in NASA or elsewhere that if there really are lots of multimillionaires out there prepared to pay say $10m for a ticket to orbit, it would not be so hard to fix up a module to go in the Shuttle Payload Bay that could take maybe 50 to 70 of these rich but frustrated astronauts on a few days trip to orbit and so run the Shuttle at a per-trip profit, based on NASAs own Shuttle per-flight cost figures, even if no-one elses? Just a passing thought....)

As for DH-1. I think it would be kindest just to draw a veil over DH-1.

So, based on the experience of Concorde (which is the most relevant comparison for your proposed New York(say?) to Tokyo suborbital rocket, forget it. Looking at the track record, no financier (ie. banker, etc.) is going to bet a red cent on the concept. Apart from the cost of the vehicle itself, including the technological developments and breakthroughs needed, just think about the air (space?) traffic control issues... these things can't just stack until there's a runway free to land. And can you imagine the environmentalist objections (not to mention the military objections) to a rocket, on what would seem to most people to be tantamount to a ballistic trajectory, taking off and/or landing near population centers? I'm not saying these problams can never be overcome, but don't expect resolution to be cheap or quick. Think tens and tens of $billions and several decades.

And then ask yourself, are there really that many rich people in a hurry to get from New York to Tokyo at the sort of astronomical price per seat that would be essential for this project to be profitable?

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Imagine a bullet and a balloon reentering earth's atmosphere. We'll ignore heating effects for the moment and concetrate on heat itself. Which will be subjected to the greater heating? The bullet. It's high density and efficient aerodynamics means it will slow down slowly, will be passing through high energy plasma for longer, and will absorb more heat. The balloon has lousy aerodynamics, and low density and will slow down much faster, even if it's of equal weight to the bullet.

I think your physics is wrong.

If the bullet and balloon both have the same mass but the balloon has much the largest cross-sectional area, then the balloon will as you rightly say, slow down more quickly. But this does not mean it will absorb less heat. Bullet and balloon will both absorb the same. However, the balloon will experience the higher peak temperature during the decelleration phase because it will happen more rapidly than for the bullet.

Aerodynamic heating is a direct product of the resistance of the atmosphere to the object traveling though it. Technically, it is the transformation of kinetic energy K(e) to heat. It does not matter if this energy-change happens quickly or slowly, the final result will be the same.

(This in a idealised world where balloons do not burst, and bullets and balloons have the same specific heat, mass and shape-- say, a sphere.)

Bill White

Member

Registered: 2001-09-09

Posts: 2,114

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

As for cheap access to space, as you've all pointed out to me, its impossible unless theres a huge market.... Zubrin once wrote "More people want to go to Tokyo than to orbit" or something along those lines. So, perhaps it would be best to first produce a large, passenger carrying suborbital rocketplane that could fly many times per day. (Hopefully it wouldn't end up like the concorde)

Sorry, that's a classic repeat of what i've called the 'Concorde Syndrome'. Or if you prefer, the Shuttle Syndrome. Or (Heaven forfend) one day may be the DH-1 Syndrome: "Build It And They Will Come. And Lo! They Did Not Come."

I have started thinking about DH-1 and related alt-space efforts as being a "supply side" solution to humnaity getting out into space. Invent low cost Earth to LEO access (provide supply) and people will find things to do with that supply.

The other way round is to look at the "demand side" and think about whether we can locate a potential demand for space access that might be more price inelastic, or which can be funding by supplemental means besides taxpayer revenue.

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Imagine a bullet and a balloon reentering earth's atmosphere. We'll ignore heating effects for the moment and concetrate on heat itself. Which will be subjected to the greater heating? The bullet. It's high density and efficient aerodynamics means it will slow down slowly, will be passing through high energy plasma for longer, and will absorb more heat. The balloon has lousy aerodynamics, and low density and will slow down much faster, even if it's of equal weight to the bullet.

I think your physics is wrong.

If the bullet and balloon both have the same mass but the balloon has much the largest cross-sectional area, then the balloon will as you rightly say, slow down more quickly. But this does not mean it will absorb less heat. Bullet and balloon will both absorb the same. However, the balloon will experience the higher peak temperature during the decelleration phase because it will happen more rapidly than for the bullet.

No, he was right.  The ballon does not get as hot because the energy is spread out over more surface area.  Actually, the deceleration phase does not happen that much faster for the ballon, it mainly just happens higher up in the atmosphere where the air is thinner.

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

No, he was right.  The ballon does not get as hot because the energy is spread out over more surface area.  Actually, the deceleration phase does not happen that much faster for the ballon, it mainly just happens higher up in the atmosphere where the air is thinner.

No, you are both wrong.

The amount of heat to be absorbed is equal to the kinetic energy of the object, be it bullet or balloon. Kinetic energy is a function of velocity and mass. (Our old friend Sir Isaac Newton again.)

E(k) = 1/2M * V^2

where E(k) is kinetic energy
M is mass
V is velocity

We have already specified that the mass is identical in both balloon and bullet. As both are re-entering at identical velocities, it follows that...

E(k) Bullet = E(k) Balloon

End of argument.

In a dispute between instinct and physics, physics wins every time.

You are wrong.

----
The race is not always to the swift nor the battle to the strong, but that's the way to bet.

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

I have started thinking about DH-1 and related alt-space efforts as being a "supply side" solution to humnaity getting out into space. Invent low cost Earth to LEO access (provide supply) and people will find things to do with that supply.

Wanna bet? (see below)

The other way round is to look at the "demand side" and think about whether we can locate a potential demand for space access that might be more price inelastic, or which can be funding by supplemental means besides taxpayer revenue.

Bingo!

Demand side is what I've been preaching for years.

That's why I believe SPSs are the way to create a huge demand-- indeed, a case for a huge manned presence in space that is logical and stands up to examination even by people like politicians, bankers and corporations that have no intrinsic interest in space per se.

That's also why I favor BDB as a way to lift huge payloads to orbit cheaply, but only when needed. It does not have to keep to a flight schedule or fly so many times a year to justify itself, like Shuttle was supposed to and spaceplanes, DH-1 and all the rest are supposed to too (but won't).

----------------
Demand-pull not supply-push, in other words.

To see the difference, take any small object, tie some string around it so about a foot or so is left free for you to hold, place it on a smooth surface and try to ...

(a) Push it away using only the string. (That's supply-push)
(b) Pull it towards you with the string. (That's demand-pull.)

Honestly now, which works better?

ANTIcarrot.

Member

From: Herts, UK

Registered: 2004-04-27

Posts: 170

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

JimM, tempreature during re-entry is a function of speed and altitude. If all things are equal, and both the bullet and balloon begin reentry at the same speed and theoretical height, then how can one be subjected to higher tempreature plasma than the other?

Tecnically though my language was flawed. You were right to point out the same amount of thermal energy gets transfered to both shapes. However english is (almost by design) an imprecise language, and that many meanings can be attached to one word. You took heat to mean energy apparently without considdering that it might have meant tempreature.

Dismissing a concept based purely on wether you do or do not think the other person is using correct english (without reguard to the physics or maths) is a poor habit shared by politicians, preachers and GCNR.

And now we return you to your regularly schedualed DH-1 debate:

At sea level orbital velocity (if there was no atmosphere) would be 7908mps. As you go higher it gets less and less. At 100km and 300km respectively it's 7846mps and 7728mps respectively. Last being ISS orbit.

With an ISP of 465 (curtesy of the RL-60, Pratt & Whitney, and twenty years of aerospace advances since the SSMEs were designed) and a mass ratio of 5.8 the upper stage is capable of 8018mps without any kick from the equator. At sea level, 100km and 300km the orbital stage would have a deltaV of 109mps, 170mps, and 289mps.

From the How Things Work website:
http://travel.howstuffworks.com/space-s … uttle2.htm
"The OMS engines together can ... change the shuttle's velocity by as much as 1,000 ft/s (305 m/s). To place into orbit or to de-orbit takes about 100-500 ft/s (31-153 m/s) change in velocity."

Which means that for orbits within the shuttles range you need an orbital deltaV in the 60mps-300mps range. The DH1OS would seem to have this. Now personally I don't know the maths to work it out for precise orbits, but based on the velocity it seems workable.

I imagine the next thing you're going to argue is whether it can get to such heights at all! And that I'm currently working on. A recent computer crash trashed my DH-1 Space flight Simulator spread sheet and I'm having to rebuild it.

Merry nitpicking!  :;):

ANTIcarrot.
PS: And thank you Euler for the Happy Barthday! I would have said so at the time but my acess has been a little glitchy of late. Cheers!

ANTIcarrot.

Member

From: Herts, UK

Registered: 2004-04-27

Posts: 170

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

The main (only?) commercial interest in space at the moment is telecommunications satellites. To their owners these satellites are valued based upon the amount of data thoughput they posess, whether that's measured in tv channels, telephone calls or MBps.

To have high throughputs you need either a lot of small satellites or a few big ones. Most companies would prefer the second because it offers them much greater redundancy, but because there is a limit to the numbers of sattilites you can place in GSO they're lumbured with a few big ones.

This trend continued until the advent of trans-continental fibre-optic links, which have proved over the past decade to be cheeper than satellites for many applications. Of course the current generation of GSO satellites near approach the limit of what GTO stages can accomadate. Maybe if they could be bigger, such a trend would reverse...

Hmm.

Oh - but wait! That's an example of supply pushing demand! Yes, multi GBps fibre-optics were laid long before there was a use for such things and thier full bandwidth was wasted for quite a number of years before the market needed; thanks mostly to the internet.

Another example of push string which we should all be familiar with is the way the number of cars on the road increases with the road space governments fill. Build a new road to speed up traffic? People buy more cars. This is of course driven by an interest in personal freedom (not waiting for public transport) personal choice (there isn't public transport) and keeping up with the Jones' Next Door. (They're destroying the enviroment 50% more than we are! We can't let them snub us like that!)

Neither the Jones' nor their foolish neighbours have any interest in space travel, but many nations do. America, Russia, and now China are all players in manned space flight. French led europe, India, Japan and the above can and do launch satellites, with the last two also making non-comital noises about manned spaceflight. In many cases these programmes are a way of proving they really can build big rockets that can carry cargos great distances.

However one country is doing it to prove it can build the biggest and best rockets around, and another is doing it to prove it's not quite as backward as people seem to think it is. And the second goal of many is to attact investment in thier countries by proving the existance of a sophisticated and wide ranging industrial infrastructure.

And that does require that they keep up with the Jones'. If and when a cheap RTV is built, countries, space programmes and militaries will want to buy it. Merely so they can keep up with everyone else.

ANTIcarrot.

Bill White

Member

Registered: 2001-09-09

Posts: 2,114

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

I have started thinking about DH-1 and related alt-space efforts as being a "supply side" solution to humnaity getting out into space. Invent low cost Earth to LEO access (provide supply) and people will find things to do with that supply.

Wanna bet? (see below)

The other way round is to look at the "demand side" and think about whether we can locate a potential demand for space access that might be more price inelastic, or which can be funding by supplemental means besides taxpayer revenue.

Bingo!

Demand side is what I've been preaching for years.

That's why I believe SPSs are the way to create a huge demand-- indeed, a case for a huge manned presence in space that is logical and stands up to examination even by people like politicians, bankers and corporations that have no intrinsic interest in space per se.

That's also why I favor BDB as a way to lift huge payloads to orbit cheaply, but only when needed. It does not have to keep to a flight schedule or fly so many times a year to justify itself, like Shuttle was supposed to and spaceplanes, DH-1 and all the rest are supposed to too (but won't).

----------------
Demand-pull not supply-push, in other words.

To see the difference, take any small object, tie some string around it so about a foot or so is left free for you to hold, place it on a smooth surface and try to ...

(a) Push it away using only the string. (That's supply-push)
(b) Pull it towards you with the string. (That's demand-pull.)

Honestly now, which works better?

As for alt-space efforts, I say "hope for the best but plan for the worst" in other words, don't count on $100 per pound Earth to LEO, ever.

Next, I regret to say that I am not persuaded by the solar power satellite scenario. I hope the economics work out of SPSS and if the economics do allow a profitable business model, well someone will surely do it eventually.

But if the economics don't work for SPSS, or helium-3, then what?

= = =

I see a possible source of inelastic demand being the attraction of more people. China, for example has a one baby policy.

Once space-faring is mastered and the ability to fabricate CELSS from space harvested resources is mastered then growing populations in space are inevitable. Seed space with well trained, highly motivated, tech-savvy people who have already developed robust CELSS and I predict a human population explosion.

No more one child policies for Chinese settlers in the asteroid belt.

= = =

Whichever Terran civilization best seeds space will reap a future powerful ally. The loyalty between America and England is an historical example.

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

JimM, tempreature during re-entry is a function of speed and altitude. If all things are equal, and both the bullet and balloon begin reentry at the same speed and theoretical height, then how can one be subjected to higher tempreature plasma than the other?

Look, you started this by saying--

Which will be subjected to the greater heating? The bullet. It's high density and efficient aerodynamics means it will slow down slowly, will be passing through high energy plasma for longer, and will absorb more heat.

But neither bullet or balloon 'absorb' heat from their surroundings. They become heated by trading energy of velocity (kinetic energy) for heat energy. As the Second Law of Thermodynamics makes clear, all energy eventually deteriorate into its most chaotic form, which is to say heat. The shortest way to state that is, "entrophy maximises". But outside nuclear reactions which we are not discussing here (where still, mass-energy cannot be created or destroyed) energy can neither be created or destroyed. All it can do is change its form.

Thus I did NOT "point out the same amount of thermal energy gets transfered to both shapes." NO thermal energy gets transferred TO them. The thermal energy (more popularly called "heat") is "created" within them from kinetic energy as the object decellerates.

However english is (almost by design) an imprecise language, and that many meanings can be attached to one word. You took heat to mean energy apparently without considdering that it might have meant tempreature.

English can be as precise as you want it to be.The whole business of lawyers is built around that very fact.

And I did not for a moment confuse heat, energy and temperature. But you have and I fear still do.

Dismissing a concept based purely on wether you do or do not think the other person is using correct english (without reguard to the physics or maths) is a poor habit shared by politicians, preachers and GCNR.

I did not do this; I just took you at your word.
The trouble about using incorrect english is that it's a good way to lose an argument, perhaps especially in physics where the correct language to use is really mathematics, exactly because it is a highly precise subject. Serious discussions on physics topics all 'happen' in mathematics; all non-math discussions on physics are really just attemps to enlighten the non-mathematical.

Bill White

Member

Registered: 2001-09-09

Posts: 2,114

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Oh - but wait! That's an example of supply pushing demand! Yes, multi GBps fibre-optics were laid long before there was a use for such things and thier full bandwidth was wasted for quite a number of years before the market needed; thanks mostly to the internet.

Yes, and how many bankruptcies happened first?

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Time to chip in... Mmmmm i'm pretty sure that having a larger surface area would give you more material to spread the heating out across, lowering the heating experienced by any one spot on the vehicle's heat shield. The Venturestar, the son of the X-33 technical demonstrator, was to use a steel heat shield. I also believe that our materials science has come far enough now to make an entirely reuseable heat shield out of W/Ti+Al foam or ceramics (Sandia has some that do ~4000K and maybe take 5000K) on a vehicle with not much less heating than Shuttle. I consider the problem solved for a spaceplane where cross-range isn't a big factor (smaller wings, lift body), where it is for Shuttle because the USAF demanded it (big delta wings, narrow body). The shallower trajectory does lengthen the heating time, but the temperatures practical to attain are lower.

I agree that "build it and they will come" is a shakey business case, nor can SSPS compete with Earth-bound sources of energy... the only reason I am sticking up for a spaceplane is that someday I think there will be such demand (colonization, flights to and from) and that day will be sooner with the technology available for easy orbital access. Neither dinky rockets like DH-1 or now-and-then megaultrasuperboosters are suited... I used the Pan Am space example because that was one of the companies flying passengers into orbit on 2001 Space Odessy.

---

[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Another example of push string which we should all be familiar with is the way the number of cars on the road increases with the road space governments fill. Build a new road to speed up traffic? People buy more cars. This is of course driven by an interest in personal freedom (not waiting for public transport) personal choice (there isn't public transport) and keeping up with the Jones' Next Door. (They're destroying the enviroment 50% more than we are! We can't let them snub us like that!)

Nope. The philosophy behind building new roads is called "predict and supply". The engineers who decide where new roads go look at the existing and forecast traffic demand, and build roads to meet that demand. It is a crystal-clear example of demand-pull.

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

I agree that "build it and they will come" is a shakey business case, nor can SSPS compete with Earth-bound sources of energy... the only reason I am sticking up for a spaceplane is that someday I think there will be such demand (colonization, flights to and from) and that day will be sooner with the technology available for easy orbital access. Neither dinky rockets like DH-1 or now-and-then megaultrasuperboosters are suited... I used the Pan Am space example because that was one of the companies flying passengers into orbit on 2001 Space Odessy.

(I'll get back to SSPS and why you are wrong there later.)

Meanwhile your reason for sticking with the spaceplane now does not compute.

If we are agreed that (1) the demand does not exist yet, and (2) it will be cheaper and easier to do the job later as our technology in general gets better, and (3) it will only be possible to fund once the demand is perceptable even to boring people like bankers, etc., then trying to build a spaceplane now is basically daft, like trying to push things around a tabletop with a length of string-- or maybe trying to build a jumbo jet back in 1904.

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For everything there is a season...

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

We will need it eventually, and I have said many times that we don't at the moment, but I don't think the basic technology is signifigantly beyond us at all. When that day does near, it will take time and loads of money to engineer such a vehicle, such that it might delay that day that we look forward to... it won't come at all without easy access to orbit.

So, as Nasa has been slowly and half-heartedly tinkering with for decades is to get more of the basic development done so such a vehicle is not so hard to make... high-temp heat shield materials, dual-mode jet engines, slushed LH2, composit fuel tanks, Scramjet engines, composit airframes... these things are not beyond us technologicly to any substantial degree, but they aren't easy technologies to use.

Should we invest the few tens of billions needed to make a spaceplane for real for keeps, unlike the silly rocket/space/shuttle/thing, right now? No, but I think it is prudent to keep such a vehicle in the backs of Nasa's minds, - concept and componets not blueprints - working on the hard pieces, so it can be made ready with less effort down the road since we know for fact that regular rockets won't do and that a spaceplane will probably work.

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[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Should we invest the few tens of billions needed to make a spaceplane for real for keeps, unlike the silly rocket/space/shuttle/thing, right now? No, but I think it is prudent to keep such a vehicle in the backs of Nasa's minds, - concept and componets not blueprints - working on the hard pieces, so it can be made ready with less effort down the road since we know for fact that regular rockets won't do and that a spaceplane will probably work.

Apart from the highly dubious proposition that the back of NASA's mind is a good place for anything that you want to work and be effective one day, I might just about go along with you here.

I admit it, I suspect the single most effective step forward for manned spaceflight would be to abolish NASA...

ANTIcarrot.

Member

From: Herts, UK

Registered: 2004-04-27

Posts: 170

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

A ship during re-entry heats up because of interaction with the atmosphere, not because of any internal energy conversion.

The shuttle hits the air. The air heats up and turns to plasma. The shuttle absorbs heat from the initial impact and the plasma. Soon the shuttle is surrounded by a bow-wave of plasma and that's what breaks up the air. From this point on the shuttle is slowed and absorbs heat almost exclusively from the plasma.

It is an external process not an internal one. Why do you think all the old space capsules are chared on the inside if it's part of some interal conversion?

But you want it in physics: Fine. Tempreature rise is proportional to energy absorbed per unit mass. In a heatshield of uniform thickness this means it's indirectly proportional to area.

Therefore in two theoretical reentry shields, one having 1m2 area and the other 100m2 area, the second will absorb 1% of the energy per square meter, and will not get as hot as the first. In fact, if they form part of equal weight space-craft, the second ship's heatshield will experience roughly 1% of the tempreature rise of the first.

Get the heat rise low enough and you can use the same metals used in aircraft engines, which last for thousands of hours between serious inspection/maintinance.

ANTIcarrot.
PS: And do you seriously deny that traffic expands to meet supply when new roads are built??

JimM

Member

From: England

Registered: 2004-04-11

Posts: 247

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

A ship during re-entry heats up because of interaction with the atmosphere, not because of any internal energy conversion., etc., etc., (more rubbish)

No. Stick to things you know about.

The atmosphere heats up because the kinetic energy of the projectile turns into heat, and as it does some of that heat radiates or is conducted to the atmosphere. Your description of what you apparently imagine to be the physics of the Shuttle's reentry is so wrong it's either comic or pathetic.

Therefore in two theoretical reentry shields, one having 1m2 area and the other 100m2 area, the second will absorb 1% of the energy per square meter, and will not get as hot as the first. In fact, if they form part of equal weight space-craft, the second ship's heatshield will experience roughly 1% of the tempreature rise of the first.

No. If everything else is equal as we previously discussed (the mass and specific heat of the two are identical) then it should be obvious that --

-- the LARGER shield (the second) will decellerate much more rapidly and therefore will momentarily be much hotter than the smaller one. (This is the exact opposite of what you would have us believe.)

-- therefore, the larger the heat shield (everything else being equal) the higher the peak gee experienced during reentry, NOT the lower.

-- however, over the entire reentry process, both will emit IDENTICAL amounts of heat. They MUST do this, because ALL the heat comes from convertion of exactly the same quantity of kinetic energy.

-- the true function of a heat shield, in terms of the physics, it to act as a heat sink for the dissipating kinetic energy of the whole vehicle as it slows.

Newton is still right and you are digging yourself into a deeper and deeper hole. The first thing to do when you find yourself in a hole is-- stop digging.
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PS: And do you seriously deny that traffic expands to meet supply when new roads are built??

That is not the normal purpose that a road is built for. I cannot say that political pressure never causes roads to be built for wrong reasons, or NOT built for wrong reasons. And I can't deny that somethimes there is SOME traffic growth due to the arrival of a new road. But that is 'spin-off' as it were. It would never be enough to justify the construction of the road on its own-- just as SOME people used Concorde to cross the Atlantic, but not enough to justify the project. (You're clutching at straws.)

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Low-cost-reusable vehicle design-FICTION *2* - last topic got borked

Hey Jim, I know i'm guilty of getting in a huff with you about spaceplanes, but "comic or pathetic" and "grasping at straws" is extremely... poor form. State that he is incorrect and list reasons, fine, but Anti deserves a more... civil response.

It would be enough to say your entire previous post in two quick bullet points...

1: The amount of kinetic energy that all deorbiting vehicles must get rid of is the same per unit mass and this energy has to go some place, generally arising as heat against the heat shield.

2: The amount of peak heating at any point on the shield does not drop proportionatly with surface area of the heat shield because the larger shield causes more rapid deceleration and faster generation of heat. "Its more complicated then that" would suffice.

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[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]