Author Topic: cheap reusable rockets?  (Read 9226 times)

Offline Jim

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Re: cheap reusable rockets?
« Reply #20 on: 10/03/2011 10:00 PM »

Why isn't "space elevator technology" used in "normal" elevators. Such technology is cheap and energy efficient, no?


no, it is not applicable to normal elevators.

Offline ANTIcarrot

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Re: cheap reusable rockets?
« Reply #21 on: 10/04/2011 11:08 AM »
The fundamental problem is amount of payload and the time it takes to get into orbit. How fast can a train go? And do trains travel faster if going straight up.

Maglev trains can reach 500kph at sea level, and possible higher speeds above the atmosphere. Top speed would be determined by how quickly you could turn the magnets on and off. Such a design would require magnets to be embedded in the stalk/ribbon - so you'd be trading off thousands of tons of cargo capacity for maybe a 90% reduction in journey time. You'd also want a compact nuclear power source to run the train, perhaps in a seperate 'power car' a mile removed from the actual cargo.

But it would still take three days to get to the top. And this is an idealised 'gen VI' design, and probably not something we can build in the next 100 years.

Chemical rockets are going to be the way things work for a long time to come.

Offline pippin

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Re: cheap reusable rockets?
« Reply #22 on: 10/04/2011 11:21 AM »
Errr... Could it be that you haven't understood the principal limitation of space elevators: You have to find a material that is strong enough to be able to support it's own weight (and not a lot more beyond that) when you build a structure 36.000 km tall.
The problem is that we don't know a material light or strong enough to even do THAT (whether carbon nanotubes are strong enough is subject to debates but most people believe they are not). Behind that background it doesn't really help to want to add tons of additional magnet structure to each meter of the elevator.
What you need is something that weights GRAMS per meter, not TONS or the concept is a non-starter.

Offline Robotbeat

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Re: cheap reusable rockets?
« Reply #23 on: 10/04/2011 01:16 PM »
Just a note: Carbon Nanotubes are theoretically strong enough for a space elevator, but practically getting the practical, macroscopic tensile strength high enough is a significant challenge. There are advancements happening in that aspect, though.

And it's not a strict line between working an not working... If a material isn't strong enough, a "taper ratio" can allow a space elevator to still be constructed. If the strength is not high enough, though, the taper ratio is incredibly high and the total mass of the space elevator becomes unrealistic.

But even if a pure space elevator turns out not to be practical, other tether concepts still are feasible (and become more practical with higher tensile strength).
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Offline Epis

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Re: cheap reusable rockets?
« Reply #24 on: 10/05/2011 09:50 AM »
Just had new idea about that Space X Grasshopper, how it could increase payload, and reduce landing fuel/time.
Solution is simple:
 why not takeoff from 7-8km high mountain top ? 
and land on mountain top?
 and it wont cost much money to set up launch port on mountain Top because there would be no need for large infrastructures like road, transport, etc. because reusable rocket stages could fly from factory launch site (empty) to mountain top, by themselves, rocket payload/fuel could be delivered by helicopter or Aerial Tram, so infrastructure would be aerial tramway that will need to be built, and that's all.

today only obstacle form mountain top high altitude sites was heavy rocket delivery that would require extensive ground infrastructure and large workforce for assembly, but if rocket stage is VTVL then first is solved, and second is also solved if rocket is Reusable 100+ times, then some minor checking, inspection could be needed before sticking stages together with payload and fueling it up, that would all reduce needed crew at high altitude mountain top as much as possible.
that would be real game changing if launching from mountain top. :) 

Offline Jim

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Re: cheap reusable rockets?
« Reply #25 on: 10/05/2011 11:43 AM »
Just had new idea about that Space X Grasshopper, how it could increase payload, and reduce landing fuel/time.
Solution is simple:
 why not takeoff from 7-8km high mountain top ? 
and land on mountain top?
 and it wont cost much money to set up launch port on mountain Top because there would be no need for large infrastructures like road, transport, etc. because reusable rocket stages could fly from factory launch site (empty) to mountain top, by themselves, rocket payload/fuel could be delivered by helicopter or Aerial Tram, so infrastructure would be aerial tramway that will need to be built, and that's all.

today only obstacle form mountain top high altitude sites was heavy rocket delivery that would require extensive ground infrastructure and large workforce for assembly, but if rocket stage is VTVL then first is solved, and second is also solved if rocket is Reusable 100+ times, then some minor checking, inspection could be needed before sticking stages together with payload and fueling it up, that would all reduce needed crew at high altitude mountain top as much as possible.
that would be real game changing if launching from mountain top. :) 

Wrong.  It is not game changing.  It still needs extensive ground infrastructure.  "sticking stages together with payload and fueling it up"  is not simple. Still needs the same size ground crew.    Also, the payload cant flight to the mountain top.

The extra altitude is not that much of an advantage.
 
"in the end advantage if is, is so small, then whats a point ? "

Just give it up with the mountain top or tunnels.  They don't help.
« Last Edit: 10/05/2011 11:47 AM by Jim »

Offline Epis

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Re: cheap reusable rockets?
« Reply #26 on: 10/05/2011 02:07 PM »
Wrong.  It is not game changing.  It still needs extensive ground infrastructure.  "sticking stages together with payload and fueling it up"  is not simple. Still needs the same size ground crew.    Also, the payload cant flight to the mountain top.

The extra altitude is not that much of an advantage.
 
"in the end advantage if is, is so small, then whats a point ? "

Just give it up with the mountain top or tunnels.  They don't help.

Extra advantage will be high launching from high altitude, just make quick read on http://www.g2mil.com/high.htm  advantages are:
- higher rocket engine Thrust thanks to lower atmospheric pressure.
- No Max-Q so full engine throttle all the time = less gravity losses.
- less air drag losses.
- at least 50% payload to LEO improvement if launched from >5km mountain top at near equatorial location, or close to it.

basically that extra payload boost could be used to add mass to rocket, to make it not just more rugged, for re usability, but also to add extra hardware for easier stage assembly and even make it automated with external crane help. so goal is human free mountain top rocket stage assembly. also launch pad must be as simple as possible that would mean heavier grasshopper launch pads to hold full rocket weight on launch. all extra hardware weight to reduce launch assemble and pad complexity will eat mountain top payload surplus advantage, but cost from re usability will make it >20-30x cheaper than current launches.
rocket payload or 3 rocket stage could be assembled on sea level in some existing facility, then by helicopter transported to mountain top, at least it is in current helicopter payload capability range ( largest machine Mil V-12 has max 44,205 kg payload lift capability so entire 3 rocket stage could be delivered to launch site for Falcon 9 rocket with 10ton payload), for falcon heavy in future  more powerful helicopter could be  developed. or if large cargo capacity areal Tram be built then it could be used, but first business model can be started with smaller rockets (F9) using helicopter cargo transport services only, it succeeds then high infrastructural investments in heavy cargo lifting system could be more economical.

 in north America continent there is >5Km volcano mountain tops in Mexico for example Iztaccihuatl mountain http://en.wikipedia.org/wiki/Iztacc%C3%ADhuatl
height 5230m it has snow, glaciers from where to get Water for Oxygen/hydrogen fuel.

there is some rumor on net about spaceX f9 latest reusable launch video animation that some parts are not shown, maybe they don't show that rocket launches/lands on higher altitude launch pads, maybe not mountain top as high as 5-7-8km but 3.4-4km altitude pads could be that secret that is missing ??

I am definitely seeing this trend where reusable rockets will go to high altitude launch sites to squeeze missing performance boost to be able to cover for added re usability rocket weight penalty.

one more thing is that rocket must use Lox/Lh2 fuel in order to not pollute snow that is future water source and no one will allow tech that could pollute snow water. so electrical power line will be needed and snow water separator for rocket fuel. I quickly checked how high are temperatures at highest earth mountain (mount Everest) and in winter they have average -30 degrees (lowest record -60) i guess for cryogenic fuels like LOX and Lh2 it is much better than +20-30C on hot equatorial launch pad, so less thermal protection will be needed that means lighter stronger fuel tanks could be made. 
« Last Edit: 10/05/2011 02:38 PM by Epis »

Offline Jim

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Re: cheap reusable rockets?
« Reply #27 on: 10/05/2011 04:29 PM »
Wrong.  It is not game changing.  It still needs extensive ground infrastructure.  "sticking stages together with payload and fueling it up"  is not simple. Still needs the same size ground crew.    Also, the payload cant flight to the mountain top.

The extra altitude is not that much of an advantage.
 
"in the end advantage if is, is so small, then whats a point ? "

Just give it up with the mountain top or tunnels.  They don't help.

Extra advantage will be high launching from high altitude, just make quick read on http://www.g2mil.com/high.htm  advantages are:
 
- at least 50% payload to LEO improvement if launched from >5km mountain top at near equatorial location, or close to it.

There is nothing that shows 50% improvement in that website. 

And you don't know what you are talking about.

Better performance does not mean cheaper launch

Offline Jim

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Re: cheap reusable rockets?
« Reply #28 on: 10/05/2011 04:31 PM »
then by helicopter transported to mountain top, at least it is in current helicopter payload capability range ( largest machine Mil V-12 has max 44,205 kg payload lift capability so entire 3 rocket stage could be delivered to launch site for Falcon 9 rocket with 10ton payload),

No, a helicopter can not lift heavy loads at high altitudes.  The Mil V-12 could only lift that to less than 2250 meters. The Mil V-12 could only fly to 3,500 m empty.

See you don't know what you are talking about.  Your ideas are not viable or cheaper.  When will you learn that!!!

« Last Edit: 10/05/2011 04:35 PM by Jim »

Offline Jim

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Re: cheap reusable rockets?
« Reply #29 on: 10/05/2011 04:36 PM »

I am definitely seeing this trend where reusable rockets will go to high altitude launch sites to squeeze missing performance boost to be able to cover for added re usability rocket weight penalty.

Huh?  You are seeing things that are not there.

No, the cost of logistics out weighs the performance gains.
« Last Edit: 10/05/2011 04:36 PM by Jim »

Offline Robotbeat

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Re: cheap reusable rockets?
« Reply #30 on: 10/05/2011 04:41 PM »
If you have to deliver stuff via helicopter, no way it's going to be cheap.

It's logistics, you guys... Remember, SpaceX recently essentially abandoned Kwaj, partly because of logistics reasons (partly because it is too small for anything much more than Falcon 1, for which there is only a small market).
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Offline ANTIcarrot

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Re: cheap reusable rockets?
« Reply #31 on: 10/06/2011 01:26 AM »
Errr... Could it be that you haven't understood the principal limitation of space elevators:
Could it be you've overlooked basic concepts of material science? Or maybe you skipped over parts of my post, and missed certain caveats? ::)

There is no scientific reason why we can't build a space elvator, and material limitations are usually temporary in the long term (sometimes very long term) so assuming that building a space elevator is possible at all...

Current semi-serious designs for space elevators envisage a very thin ribbon cable, which can only support a ton at most. Until additional climbers are sent up to thicken it, at which point it can support more weight. Taken to it's logical conclusion, a very thick cable with a CSA in the dozens of square meters (or more) could support hundreds or thousands of tons of cargo. Keep increasing the thickness and eventually you'll have a cable that can support a small fast car AND the weight of the magnets it needs to speed to orbit. This is why it's a trade off; and a pretty bad one at that.

Someone asked about maximum elevator speeds. Less than 200mph is true for wheel/friction near-term based designs. But it is not an absolute limit, as I explained. Rapid field switching is the next problem. Solve that litle nugget and you can use a slightly lighter car and get to GSO in ten hours or less at 0.1G all the way.

In summery: We can't build one today. We probably will be able to build one some day in the far future. Even though the early ones will be slow, we'll eventually be able to build a concorde equivolent if for some daft reason we wanted to. But baring a material breakthrough, for the next few decades, rockets will be the best way of getting into space.

Offline Epis

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Re: cheap reusable rockets?
« Reply #32 on: 10/06/2011 09:47 AM »
There is nothing that shows 50% improvement in that website. 
And you don't know what you are talking about.
Better performance does not mean cheaper launch
its not in that site, there could be find figures as high as <30% payload increase for concepts that are described there, but for Max TOp theoretical performance boost that could be possible at highest earth mountain top (like Everest 8820m ) 50% payload increase could be real, for proof lets take rocket equation where if we have LOX/RP-1 engine with 338s isp (3312.4m/s) and orbital LEO for 0m sea level will need 9756m/s then payload+rocket empty mass for SSTO would be 5.26%.
I predicted that 50% increas in payload could be possible so lets add 50% payload to 5.26% we get 7.89% and make backward calculation to get orbital speed that SSTO rocket could reach with previous engine and we get 8412.48m/s so if orbital speed is 7800m/s we have surplus of 612m/s for Gravity losses and Atmospheric drag. I think it will be enough because at such altitude there is 1/3 air pressure and it sharply drops (at 15km it is ~1/10) so air drag/pressure will be no problem, so high power engines could be used to fly with 3-4G acceleration that would mean large reduction in gravity losses .
1527m/s could be saved. of course that would be MAX available performance.
No, the cost of logistics out weighs the performance gains.
at current launch rates I agree there is no need for that, but if launch rates and demand increase to 1-2 launch per week then it will pay back fast, similar like airplanes fly each day and ticket prices are low, and plane/infrastructure cost is long term investments and more frequently it is used less it will cost.
I am not saying that now spaceX must go to >8km mountaintop  !, I say they would need to consider starting with 3.5-4km mountain tops or high altitude places preferably with all infrastructure already available like railway, roads,power lines.  and try to lower cost to 500$/kg to make at least 2 launches per month, with target 1 per week. and when market will develop they could plan for higher performance launch sites with more frequent launches as high as 1 per day.  that would be incremental development path and could take 10 years till next step.

speaking about helicopters then there are 9km altitude capable machines specially designed for Himalaya rescue   
here is pic
http://www.gizmag.com/go/6793/
that is not high payload capable but it shows that technology exist and it needs scaling up, and after 10-15+ years when there will be such need for extreme altitude mountain top Rocket launch such machines will already be developed.

See you don't know what you are talking about.  Your ideas are not viable or cheaper.  When will you learn that!!!
I think problem is time, these Ideas are >15-30 years in future, with clear development path which I try to show how rocket industry will get from now to future.
currently development path looks like this:
1. current rocket level. cost of launch 1000-3000$/kg
2. Reusable VTVL 2 stage rocket launched from 3.5-4km altitude. cost of launch 300-600$/kg  (LOX/RP-1) fuel
3. reusable  VTVL 1 or 2 stage rocket launched from 7-8km altitude cost of launch could be 100-250$/kg ( LOX/LH2 fuel )
4. Reusable SSTO rocket launched from Maglev- electric/chemical propulsion 5-6km long mountain (7-8km high) Slope  track at speeds Mach 2-3. launch cost 20-50$/kg.
5. Full Electrical Maglev Mach 8 vacuum tube track  15-20 km long on highest mountain TOp that is out there (>8Km exit altitude )  this in year 2150-2200  with launch rates as high as 2 in hour, for orbital civilization, and moon base+ mars base human transport cost to LEO is extremely low 7-10$/kg
at that final stage of development humans could start to think about building 100 year starship to make first mission to closest habitable exoplanet.
orbital elevator could be built starting at 4th stage, and it could decrease cost of 4 and 5th stage.

you can call this pure since fiction, speculation.

this list doesn't contain any plane style orbital vehicles, because they are not energy efficient, I think movies has created this type of imagination that future we will have orbital planes, or such style vehicles because they look cooler, has more style like virgin galactic SS2/WK2 but lows of physics say different thing, and path is going to mountain slope track style high energy efficient accelerators.
« Last Edit: 10/06/2011 09:48 AM by Epis »

Offline Kaputnik

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Re: cheap reusable rockets?
« Reply #33 on: 10/06/2011 10:40 AM »
On the subject of space elevators...

has any serious work gone into a *partial* elevator? i.e. one that does not go all the way to the ground. I'd envisage a landing/docking platform suspended from its tether just above the atmosphere; the speed over the ground would depend on how long you made the whole system and where its centre of mass was located. In operation, relatively low-tech single-stage RLVs would be able to boost up and rendezvous with the platform as it flew overhead. Payloads would be sent up the tether section and released into a higher orbit, having gained orbital velocity along the way.

Would such a thing be feasible with current technology?
Waiting for joy and raptor

Offline Jim

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Re: cheap reusable rockets?
« Reply #34 on: 10/06/2011 12:14 PM »

that is not high payload capable but it shows that technology exist and it needs scaling up,


Wrong.  Learn something instead of posting unrelated references from the internet.  Scaling up doesn't work for helicopters.   There is a limit on rotor tip speed and increasing rotor length "scaling up", quickly exceeds the limit.

Offline Jim

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Re: cheap reusable rockets?
« Reply #35 on: 10/06/2011 12:22 PM »

I think problem is time, these Ideas are >15-30 years in future, with clear development path which I try to show how rocket industry will get from now to future.
currently development path looks like this:
1. current rocket level. cost of launch 1000-3000$/kg
2. Reusable VTVL 2 stage rocket launched from 3.5-4km altitude. cost of launch 300-600$/kg  (LOX/RP-1) fuel
3. reusable  VTVL 1 or 2 stage rocket launched from 7-8km altitude cost of launch could be 100-250$/kg ( LOX/LH2 fuel )
4. Reusable SSTO rocket launched from Maglev- electric/chemical propulsion 5-6km long mountain (7-8km high) Slope  track at speeds Mach 2-3. launch cost 20-50$/kg.
5. Full Electrical Maglev Mach 8 vacuum tube track  15-20 km long on highest mountain TOp that is out there (>8Km exit altitude )  this in year 2150-2200  with launch rates as high as 2 in hour, for orbital civilization, and moon base+ mars base human transport cost to LEO is extremely low 7-10$/kg
at that final stage of development humans could start to think about building 100 year starship to make first mission to closest habitable exoplanet.
orbital elevator could be built starting at 4th stage, and it could decrease cost of 4 and 5th stage.


No, the problem is not time, these ideas not going to happen.  Your "path' will not be followed.  Each step is not viable nor worth the effort.  There won't be flight rates to support them. You have this crazy idea and wont let it go


Offline aquanaut99

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Re: cheap reusable rockets?
« Reply #36 on: 10/06/2011 12:28 PM »
Errr... Could it be that you haven't understood the principal limitation of space elevators: You have to find a material that is strong enough to be able to support it's own weight (and not a lot more beyond that) when you build a structure 36.000 km tall.

No. The principle limitation of a space elevator is that it won't survive. Even if some miracle material is found that could actually stand the tensile strength of being a 72'000 km long structure (not 36'000, since you have to build it twice as long so that the structure's center of gravity is in GSO), the cable will sooner or later be cut by the swirling cloud of debris (natual and man-made) circling Earth, especially in LEO. Also, after being severed, the falling half of that space elevator has the potential to cause immense (read: asteroid-strike-level) damage on Earth.

The space elevator concept will always remain science fiction.
« Last Edit: 10/06/2011 12:30 PM by aquanaut99 »

Offline pippin

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Re: cheap reusable rockets?
« Reply #37 on: 10/06/2011 01:17 PM »
No. The principle limitation of a space elevator is that it won't survive. Even if some miracle material is found that could actually stand the tensile strength of being a 72'000 km long structure (not 36'000, since you have to build it twice as long so that the structure's center of gravity is in GSO)
Well, no. You just need a sufficiently large counterweight just above GSO.

Of course, your point then still holds true, the elevator would still have to take that force and it's the same as for a 72'000 km structure.

That said, you can't build it straight up because of the different directions of the centripetal forces so you'll end up with something that is way longer than  72'000km AND has to have the counterweight.
And it has to be flexible because it will have to be able to move, quite a bit of wind, solar winds and magnetic forces out there. Which brings back my point about the excess weight you don't want to have.
Quote
The space elevator concept will always remain science fiction.
probably.

Offline RobLynn

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Re: cheap reusable rockets?
« Reply #38 on: 10/06/2011 01:20 PM »
I like high altitude (land based) launch, though most estimates I've seen put the payload gain at only about 10-15%.  The gains might be better for RLV vehicles with low payload fractions (like where SpaceX seems to be going).

There is no problem living and working at 4-5km altitude for people who are aclimatised (for most people takes a few days), and for short visits of a few hours it is not too much of a problem even if you are not aclimatised.  Close to the equator the temperature is not a problem either.

SpaceX Falcon9 charges about $50million for 10tonnes to LEO = $5000/kg.  Increasing that by 10% would be worth about $5million, which is probably far more than the marginal costs would be for mountain top launches.

Big problem is lack of suitable 4km+ mountains. Pikes Peak is too far north, Hawaii swarming with rich NIMBY environmentalists, Ecuador, Mexico, Chile and Kenya too unstable/unreliable and lacking infrastructure. 4.2km Mt Kinabalu on the equator in Malaysia close to major city could be good and I expect that China will eventually set up sites on the Tibetan Plateau.

Might be made easier using heavy duty radio mast - they apparently only cost about $500k per 100m (630m KVLY mast cost $500k in 1963), and might only cost a 1-200 million doallrs for a few km tall capable of supporting a large rocket.
I'm a "glass is twice as big as it needs to be" kinda guy

Offline aquanaut99

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Re: cheap reusable rockets?
« Reply #39 on: 10/06/2011 01:25 PM »
And it has to be flexible because it will have to be able to move, quite a bit of wind, solar winds and magnetic forces out there. Which brings back my point about the excess weight you don't want to have.

And it will still be cut by space debris, sooner or later...
« Last Edit: 10/06/2011 01:25 PM by aquanaut99 »

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