Rocket engines - from speculations to successful flights

[barbos]

I worry that any and all and all analyses of future beanstalk developments will have to answer the question, "What will happen if someone flies an airplane into it?"

That one is easy, you will have giant nanotube cable orbiting earth violently.

 

[bilby]

I worry that any and all and all analyses of future beanstalk developments will have to answer the question, "What will happen if someone flies an airplane into it?"

Given that a snapped beanstalk would eventually collapse by wrapping around the entire planet, the potential devastation will forever make it a non-starter.

Given the required strength of the cable, I suspect that the plane would be simply cut in half, with little damage to the space elevator. Barrage balloons with simple steel cables have been used since the early 20th century as a passive anti-aircraft defence, and cable failure doesn't seem to be a problem.

When a plane hits a mountain, the mountain isn't demolished.

And the art of not flying aircraft into fixed obstructions is well understood. We don't refuse to build skyscrapers because of the small risk that they might be hit by aircraft.

 

[James Brown]

I worry that any and all and all analyses of future beanstalk developments will have to answer the question, "What will happen if someone flies an airplane into it?"

Given that a snapped beanstalk would eventually collapse by wrapping around the entire planet, the potential devastation will forever make it a non-starter.

Given the required strength of the cable, I suspect that the plane would be simply cut in half, with little damage to the space elevator. Barrage balloons with simple steel cables have been used since the early 20th century as a passive anti-aircraft defence, and cable failure doesn't seem to be a problem.

Fair point. Would need more testing.

And the art of not flying aircraft into fixed obstructions is well understood. We don't refuse to build skyscrapers because of the small risk that they might be hit by aircraft.

True. But the destructive path of a collapsed skyscraper is contained. The length of a proposed space elevator ranges from 100,000 km to 144,000 km, half the distance to the moon, the end of which is travelling at 11 km/sec.

Don't get me wrong; I'd love to see us implement a pincushion of beanstalks to get to LEO and beyond. I just think that the technical challenges are quite high, over and above the engineering problems.

 

[bilby]

Fair point. Would need more testing.

And the art of not flying aircraft into fixed obstructions is well understood. We don't refuse to build skyscrapers because of the small risk that they might be hit by aircraft.

True. But the destructive path of a collapsed skyscraper is contained. The length of a proposed space elevator ranges from 100,000 km to 144,000 km, half the distance to the moon, the end of which is travelling at 11 km/sec.

Don't get me wrong; I'd love to see us implement a pincushion of beanstalks to get to LEO and beyond. I just think that the technical challenges are quite high, over and above the engineering problems.

The destructive path of a failed space elevator is going to be constrained to within a small band of latitude centred on the equator. It's likely got a total population within an order of magnitude of that of a metropolitan district with skyscrapers.

And a failure probability that's far lower, both due to higher structural strength, and lower number of units - I don't envisage a world where space elevators ever come close to outnumbering skyscrapers.

 

[lpetrich]

About seaports, I've found World Port Source - Home Page -- both seaports and freshwater ports.

Kenya's best one is Mombasa, the nation's second-largest city with 1.2 million people and a port that WPS calls medium-sized. Also, China recently built a Mombasa - Nairobi railroad line (Kenya Railways official site,  Kenya Railways Corporation), one that may be extended further inland to Kampala. Mombasa - Nairobi is about 480 km by road, and Nairobi - equator is a further 130 km. Nakuru, a city with about 300 thousand people and Kenya's 4th largest, is some 160 km away form Nairobi by road, and 33 km south of the equator.

Gabon's best one is Port-Gentil, the nation's second largest city with 140 thousand people. Its capital, Libreville, with 700 thousand people, has a smaller port. But Libreville is only 43 km north of the equator.

Turning to Sao Tome and Principe, the best port is that island nation's largest city and capital, Sao Tome City, on Sao Tome Island. It has about 72,000 people. The equator passes through Ilhéu das Rolas, a small island south of Sao Tome Island about 44 km south of Sao Tome City. IdR is about 1.4 km across.


Brazil has a city very close to the equator, Macapá, only 4 km north of it. Macapá has 400 thousand people, and what WPA calls a small seaport.

In Ecuador, Guayaquil is the best port and the nation's largest city at 5 million people. It is connected by a railroad line to Quito, the nation's capital, with 4.7 million people. Quito is 440 km by road from Guayaquil, and it is only 26 km south of the equator.

In the Galapagos Islands, the northern end of Isabela Island crosses the equator. The islands do not have any seaport that WPS lists, so its ports are likely very small. Its capital is Puerto Baquerizo Moreno, on San Cristóbal island, with population 7 thousand people.

So it's
Kenya / Brazil
Ecuador
Gabon

 

[lpetrich]

Singapore is about 140 km north of the equator, and it does not extend far enough south to reach the equator.

Going south of Singapore, one reaches Indonesia, and one has a lot of choice there.

Pontianak, on Borneo, has 570 thousand people, a big seaport, and is at the equator.

Padang, on Sumatra, has 1 million people, a big seaport, and is 110 km south of the equator. Going north, one gets to Bukittinggi, with 120 thousand people, and only 33 km south of the equator.

Balikpapan, on Borneo, has 740 thousand people, a big seaport, and is 140 km south of the equator. Going north, one gets to Samarinda, with 840 thousand people, and only 46 km south of the equator.

There are some other cities that I could consider, like Palu and Gorontalo, but they have smaller seaports.


These nations all have land area at the equator: Indonesia, Somalia, Kenya, Uganda, DR Congo, R Congo, Gabon, STP, Brazil, Colombia, and Ecuador.

Of these, I think that these are the best hosts for a space elevator: Indonesia, Kenya, Uganda, Gabon, Brazil, and Ecuador.

 

[bilby]

Singapore is about 140 km north of the equator, and it does not extend far enough south to reach the equator.

Going south of Singapore, one reaches Indonesia, and one has a lot of choice there.

Pontianak, on Borneo, has 570 thousand people, a big seaport, and is at the equator.

Padang, on Sumatra, has 1 million people, a big seaport, and is 110 km south of the equator. Going north, one gets to Bukittinggi, with 120 thousand people, and only 33 km south of the equator.

Balikpapan, on Borneo, has 740 thousand people, a big seaport, and is 140 km south of the equator. Going north, one gets to Samarinda, with 840 thousand people, and only 46 km south of the equator.

There are some other cities that I could consider, like Palu and Gorontalo, but they have smaller seaports.


These nations all have land area at the equator: Indonesia, Somalia, Kenya, Uganda, DR Congo, R Congo, Gabon, STP, Brazil, Colombia, and Ecuador.

Of these, I think that these are the best hosts for a space elevator: Indonesia, Kenya, Uganda, Gabon, Brazil, and Ecuador.

Somalia, Uganda, and the two Congolese republics are all politically and economically unsuitable right now. Of course, politics and economics may well have changed by the time we have the materials to do this (if we ever do).

 

[Loren Pechtel]

You are allowed to have a childish fascination with missile technology.

But don't think these are great advancements and a great help.

They are probably going to kill all humans in some form.

Faith-based typing detected.

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What do you not understand about this having zero relationship to the topic of the thread? None of the rocket engines under discussion are in any way suitable for ICBM use; You could as well interrupt a discussion on soldering techniques, with a diatribe about how deadly swords are, on the basis that metallurgy can lead to the making of edged weapons.

Item #1 is chemical--what currently propels ICBMs.

 

[Loren Pechtel]

Missile technology has endangered all of humanity.

That's rather off-topic.

Let's get back to discussing the feasibility of different sorts of rocket engines and alternatives like space elevators.

Space elevators will be a game changer; but finding materials with high enough tensile strength per unit mass, at a low enough price and high enough volume will be a big ask.

As for suitable sites for the base station, given that it must be on the equator, Singapore seems like the obvious choice, as it's already a major transportation hub. Having said that, the distance of Singapore from the wealthy customers in the USA could make somewhere like Soure, on the Brazilian Atlantic coast a better choice.

I'm very skeptical of whether an Earth-based elevator is possible--while it's at the edge of what might be possible in a physical sense but how can we protect it from debris?

 

[Loren Pechtel]

For our planet, space elevators need superstrong cables, stronger than anything that we have been able to make.

Here is a rather hand-waving estimate of how much strength a space-elevator cable will need. It is

P/ρ = v²

where P is the cable's tensile strength, ρ = its density, and v is the surface-satellite orbit velocity of the celestial body where we wish to construct this elevator. It is (escape velocity) / sqrt(2).

For the Earth and the density of water, this means a tensile strength of 63 gigapascals. I checked on some engineering-data sites, and I found that most materials are hopelessly wimpy -- their yield strengths are usually less than 1 GPa, and sometimes much less.

Here are some more numbers. Mars: 13 GPa, the Moon: 2.8 GPa, Ceres: 130 MPa.

If one wishes to use diamond, one must multiply these numbers by 3, for titanium, 4.5, and for steel, 7.8.

Modulus of Elasticity Young's Modulus Strength for Metals - Iron and Steel | Engineers Edge | www.engineersedge.com, Modulus of Elasticity or Young's Modulus - and Tensile Modulus for common Materials -- those two sites also contain oodles of other data.

So space elevators may only be practical for the smaller Solar-System bodies.

This does not consider taper. A 1GPa material could be used for a lunar cable if your numbers are right.

 

[beero1000]

I find it amazing that one of the few things that brings the diverse members of this board together is pointing out untermensche's batshit opinions.

I suspect that rocket technology has helped save more lives than it's taken. Satellites are used for weather prediction, search and rescue, GPS, emergency communication, etc.

Since the program’s inception in 1982, COSPAS-SARSAT has been credited with supporting more than 41,000 rescues worldwide, including more than 8,000 in the United States and its surrounding waters.

 

[Loren Pechtel]

I worry that any and all and all analyses of future beanstalk developments will have to answer the question, "What will happen if someone flies an airplane into it?"

Given that a snapped beanstalk would eventually collapse by wrapping around the entire planet, the potential devastation will forever make it a non-starter.

Reality check:

The highest flying planes around don't even make it 20 miles up. Should a kamikaze snap the cable they will do it within 20 miles of it's ground tether. The cable is under tension, everything above that point goes up, not down. The only part that falls on the Earth is the part below the tether. It's not moving, it's going to fall down. Assuming it was snapped 20 miles up the end is moving 5 miles/hour faster than the tether, the fall time is 81 seconds. Neglecting drag it hits a couple hundred yards from the tether.

Even if it was snapped in space drag is going to limit how fast it comes down.

 

[steve_bank]

I used to have a copy of the original analysis for the space elevator. I forget the guys name, I'd have to look it up. In the 90s I went to a Mars Society meeting on it.

He got a phase 1 grant for a feasibility study. The last I heard of it the company got taken away from him in phase 2 proof of concept.

I read that all NASA was really interested in was the nano tube development. I believe there have been applications.

 

[lpetrich]

(my detailed calculations snipped for brevity)
So space elevators may only be practical for the smaller Solar-System bodies.

This does not consider taper. A 1GPa material could be used for a lunar cable if your numbers are right.

Seems like it would need a LOT of taper. How much do you think is needed?

 

[Treedbear]

Saw astronaut Mae Jemison on StarTalk yesterday. She has a project promoting research into interstellar travel.

The 100 Year Starship (100YSS) is a joint U.S. Defense Advanced Research Projects Agency (DARPA) and National Aeronautics and Space Administration (NASA) grant project to a private entity. The goal of the study is not to have the government fund the actual building of spacecraft, but rather to create a business plan that can last 100 years in order to help foster the research needed for interstellar travel.

 

[Treedbear]

The cheapest way to travel into interstellar space might be to hitch a ride on one of them interstellar asteroids. Actually there is recent evidence that Oumuamua contained water ice like a comet. That means rocket fuel might be produced. Also it could provide shielding from cosmic rays if it can be burrowed into. Of course you still need to catch up to one. (ETA: That is, if you have enough velocity to catch one of these things then you have enough velocity to go interstellar on your own. But the asteroid/comet provides some resources you don't need to bring from Earth.)

 

[lpetrich]

Except that to land on an interstellar asteroid requires matching velocities, and doing so without crashing into it requires the same expenditure of rocket fuel as would be necessary without that asteroid. So that method does not get us anything.

There is also the difficulty of finding a suitable asteroid, because once it starts departing, it will not return. Traveling to such an asteroid is also a problem, since one has to reach it before it gets too far away, and one decides to chase it into interstellar space, one has to do what one would do if it was never present.

 

[Loren Pechtel]

I used to have a copy of the original analysis for the space elevator. I forget the guys name, I'd have to look it up. In the 90s I went to a Mars Society meeting on it.

He got a phase 1 grant for a feasibility study. The last I heard of it the company got taken away from him in phase 2 proof of concept.

I read that all NASA was really interested in was the nano tube development. I believe there have been applications.

Yeah, the theoretical strength of nanotube cables is enough for an Earth-based elevator.

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Except that to land on an interstellar asteroid requires matching velocities, and doing so without crashing into it requires the same expenditure of rocket fuel as would be necessary without that asteroid. So that method does not get us anything.

Actually, it does get you something--a whole bunch of material already at velocity. That means you can send a factory rather than the whole craft. That is not a mass savings yet, but someday it probably will be.

 

[bilby]

Except that to land on an interstellar asteroid requires matching velocities, and doing so without crashing into it requires the same expenditure of rocket fuel as would be necessary without that asteroid. So that method does not get us anything.

There is also the difficulty of finding a suitable asteroid, because once it starts departing, it will not return. Traveling to such an asteroid is also a problem, since one has to reach it before it gets too far away, and one decides to chase it into interstellar space, one has to do what one would do if it was never present.

If such an asteroid was detected sufficiently early, then lassoing it could provide useful acceleration. You might need to use something stretchy, like a bungee-cord, to keep the payload acceleration down to survivable levels; And of course the cord will need to be super strong - perhaps a byproduct of the space elevator research will be a material that is suitable. But predicting its path around the sun, and waiting for it on the other side, shouldn't be too big a task, as long as you detect it (and are able to establish its exact velocity) early enough.

 

[fromderinside]

Bungy space orbital tennis anyone?