Author Topic: cheap reusable rockets?  (Read 10016 times)

Online pippin

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Re: cheap reusable rockets?
« Reply #40 on: 10/06/2011 01:40 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...
Well, if you can build a maglev around it the little excess weight for the strong laser cannons for the defense system can't be that much of an issue.  ;D

I wonder whether the power you can generate by moving the whole structure through the magnetosphere (relative to the sun) can contribute significantly to it's operation, otherwise it would be just too annoying to get rid of all the excess voltage...

Online Robotbeat

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Re: cheap reusable rockets?
« Reply #41 on: 10/06/2011 03:33 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...
And if it does, it'll float down relatively gently or burn up. It's a lightweight ribbon, after all.

You're ignoring several things. First of all, the timescale until being struck by debris matters quite a bit. If it's after 1 year (not at all likely), then the concept isn't viable. If it's 100 or 1000 years, then it is. Also, you can make the ribbon wide enough to survive strikes by small pieces of debris and able to dodge larger pieces. This may not be achieved in our lifetimes, but it's not as impossible as you make it seem.

That said, I don't think in the near-term it can be cheaper than RLVs can be near-term. Material science is not at the point where it's feasible (though I think that part will get there eventually... it's at least physically possible). Tethers make sense in other concepts. Mars, for instance, rotates just as fast as Earth but has much less gravity (making the material science case easier) and has big difficulties with EDL (which can also be solved by a tether). The concept has merit, even if not at Earth for 300 years (say).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online pippin

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Re: cheap reusable rockets?
« Reply #42 on: 10/06/2011 03:47 PM »
And if it does, it'll float down relatively gently or burn up. It's a lightweight ribbon, after all.
Well, not with ANTIcarrot's few tons of maglev structure per meter of "ribbon"

Online Robotbeat

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Re: cheap reusable rockets?
« Reply #43 on: 10/06/2011 03:53 PM »
And if it does, it'll float down relatively gently or burn up. It's a lightweight ribbon, after all.
Well, not with ANTIcarrot's few tons of maglev structure per meter of "ribbon"
Okay, that's probably true.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online douglas100

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Re: cheap reusable rockets?
« Reply #44 on: 10/06/2011 04:03 PM »
Just to add: if you're thousands of miles up the ribbon and it gets severed above you, your vehicle is certainly not going to float down. Hope you've got a heat shield, or you're toast. Above a certain height (16000 miles comes to mind, but probably wrong) you would end up in an elliptical orbit with a perigee above the atmosphere: not so bad, but not to be desired.

As far as magnetic fields are concerned, if the ribbon is a good conductor, you would have to take special care to ground it. Large currents could be induced in it by magnetic storms.

Like some other posters I don't see a system like this being developed near term. In principle it would work, given the right material, but in practice the investment would be very large for an uplift capacity that will not be needed for a long time.
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Offline aquanaut99

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Re: cheap reusable rockets?
« Reply #45 on: 10/06/2011 04:08 PM »
Just to be clear: With "space debris", I also mean every commercial, military and other satellite ever launched into LEO, active or not. Their paths will all eventually cross the elevator and crash into it, and in LEO they have the highest relative velocity to the elevator and therefore cause the most damage.

A space elevator should have been built pre-1957 if at all. Nowadays, it's impossible and it would also be a mortal threat to every commercial and military satellite up there.

Yet another reason why it will never be built even if the technical issues were solvable.

Online Robotbeat

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Re: cheap reusable rockets?
« Reply #46 on: 10/06/2011 04:41 PM »
Just to be clear: With "space debris", I also mean every commercial, military and other satellite ever launched into LEO, active or not. Their paths will all eventually cross the elevator and crash into it, and in LEO they have the highest relative velocity to the elevator and therefore cause the most damage.

A space elevator should have been built pre-1957 if at all. Nowadays, it's impossible and it would also be a mortal threat to every commercial and military satellite up there.

Yet another reason why it will never be built even if the technical issues were solvable.
That threat also applies to existing satellites running into each other.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline kch

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Re: cheap reusable rockets?
« Reply #47 on: 10/06/2011 04:44 PM »

Yet another reason why it will never be built even if the technical issues were solvable.

"Never" is a long time -- could be as much as 100 trillion years, last I heard.  ;)

Offline Hop_David

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Re: cheap reusable rockets?
« Reply #48 on: 10/06/2011 05:00 PM »
Just to be clear: With "space debris", I also mean every commercial, military and other satellite ever launched into LEO, active or not. Their paths will all eventually cross the elevator and crash into it, and in LEO they have the highest relative velocity to the elevator and therefore cause the most damage.

A space elevator should have been built pre-1957 if at all. Nowadays, it's impossible and it would also be a mortal threat to every commercial and military satellite up there.

Yet another reason why it will never be built even if the technical issues were solvable.
That threat also applies to existing satellites running into each other.

Satellites have a much smaller cross sectional area than an elevator.

Also most of the debris in a satellite's orbit would be in roughly the same orbit, therefore the debris flux through the cross sectional area would be less. But with an elevator, relative velocity of debris will climb as the stalk becomes more distant from geosynch altitude.
« Last Edit: 10/06/2011 05:01 PM by Hop_David »

Offline Epis

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Re: cheap reusable rockets?
« Reply #49 on: 10/06/2011 08:02 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.

there are 2 high altitude railway roads  that run at more than 4.5km altitudes and they are:
Quote
# Beijing-Lhasa Express, China, running at an altitude of 16,640 feet (5,072 meters) above sea level.
# Lima to Huancayo, through the Central Andes of Peru. It took nearly forty years to be completed, from 1870 to 1908.
The track's highest point is at La Galera, some 15,685 feet (4,781 meters) above sea level.
main argument was that extra payload boost by high altitude launch pad  close as possible to equator could compensate for extra weight penalty for each rocket stage re-usability fly back feature, that will need landing pads, extra return fuel, thermal protection, and etc.. that currently will cut payload weight making it less cost efficient and more hard to make such reusable fly back rocket stages.
Question is simple why complicate things?
here is Quote of recent Space X Elon Musk anouncment about reusable rocket.
Quote
"We have a design that on paper doing the calculations, doing the simulations it does work," Musk said. "Now we need to make sure those simulations and reality agree because generally, when they don't, reality wins."
so they don't know if it will work in reality, and why risk ?
if problem could be solved simply by going to high altitude launch site that will give missing performance, and they could build rocket with more rugged hardware instead of making it on the edge with low payload fraction.

and there is already example when rocket launch is taken to country far away like ESA went to French Guiana.

if high altitude close to equator launch pad could enable true 100+ times reusable/ fly back rocket design, then some one must do that, and in future someone will try that.

Offline Jim

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Re: cheap reusable rockets?
« Reply #50 on: 10/06/2011 08:36 PM »
1.  so they don't know if it will work in reality, and why risk ?

2.  if problem could be solved simply by going to high altitude launch site that will give missing performance, and they could build rocket with more rugged hardware instead of making it on the edge with low payload fraction.

3.  if high altitude close to equator launch pad could enable true 100+ times reusable/ fly back rocket design, then some one must do that, and in future someone will try that.

1.  Because the pay off is greater and rocket can be used in many more places.  That what will reduce costs.  Launching from a few isolated places for a little performance enhancement is not going to reduce costs.

2.  Because it isn't 'solved' and it isn't simple, you are trading one risk for another.  The high altitude has more risks and issues and cost.  The increase in performance is not offset buy the increase in logistics and infrastructure.

3. If, if, if, ends up being won't, won't, won't.  It won't enable and someone is not going to try it.  It will be the last place to enable an RLV.
The places that will enable RLV's are existing ones or ones that are easier to get to. 

Why do you keep this illogical line of thinking? 

Have you ever seen the process of preparing a launch vehicle or spacecraft for flight?  When you have done this then you can have some assertions about launch ops.
« Last Edit: 10/06/2011 08:39 PM by Jim »

Offline Jim

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Re: cheap reusable rockets?
« Reply #51 on: 10/06/2011 08:38 PM »

and there is already example when rocket launch is taken to country far away like ESA went to French Guiana.


It is not applicable to your argument.  It is on a sea coast and it is easily accessible.  And it has a large runway.  Hence, it is not far away

Online Chris Bergin

Re: cheap reusable rockets?
« Reply #52 on: 10/06/2011 11:58 PM »
Strange thread. Seems to have nothing to do with the thread title for the most part. Locking.

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