Science Space Elevator: Gravity on Passengers

[Allan]

First, thanks for allowing me to join in and participate in this community. Second, forgive my ignorace.

As you will no doubt come to know, I write speculative fiction (no, nothing published in this genre yet). I am seeking information which will help to validate and/or refine my projections.

I have read some of the posts related to Space Elevator and Gravity. Although some imply what I need to learn none directly address it (or quite possaibly I could not recognize the answer).

Thanks in advance.

My assumption: People traveling in a space elevator will feel the pull of gravity toward the Earth while the elevator is closer to the Earth. As the elevator moves further away toward its counter balance gravity would shift and they would feel the pull of gravity away from the Earth. In other words they would stand with their heads toward Earth.

If my assumption is correct, a segment of the 22,300 foot tether should offer a transition for the gravity. A place where ther pull of gravity to or from the Earth is negated (zero G?) and where passengers would have to somehow adjust their orientation so as not to drop onto what once was the ceiling.

Is there any truth in what I'm speculating?

 

[N_Molson]

Anyway, I think it would be safe to stay strapped on a seat until the elevator stops

 

[Allan]

TheEyes: But the same force which keeps the tether taut between the Earth bound anchor and its GSO counterpart would be in effect on the elevator as it travelled. If you had a ball on a string an spun around in a fixed position the rope extend its legnth and would stay that way as long as you keep spinning.

I would think the push away from the Earth on the elevator (from the Earths rotation) would eventually offset the pull to the Earth as the elevator gets further away (say 400-600+ miles LGSO)?

---------- Post added at 03:04 PM ---------- Previous post was at 03:02 PM ----------

N_Molson: LOL, true but you don't need escape velocity with a space elevator if you have the time to spare in transit.

 

[martins]

The counter-weight is installed beyond the altitude of a geostationary orbit, while the elevator itself will only go up to GEO. All along its way its tangential velocity will be below the orbital velocity at that altitude, so the centrifugal force will never surpass gravity. The resulting force (in the rotating system), although getting smaller, will always be towards Earth, until reaching freefall conditions at the destination.

 

[Allan]

Thanks! I really needed to understand this point...saved me from writing about 3000 words over again. Your explanation also makes more sense of the counter-weight to me. I truly apprecaite your answer.

TheEyes: Pardon my skeptical nature. Thanks for your gut feeling.

 

[Allan]

follow up

The counter-weight is installed beyond the altitude of a geostationary orbit, while the elevator itself will only go up to GEO. All along its way its tangential velocity will be below the orbital velocity at that altitude, so the centrifugal force will never surpass gravity. The resulting force (in the rotating system), although getting smaller, will always be towards Earth, until reaching freefall conditions at the destination.

A follow up question if you wouldn't mind...if the elevator were to stop its forward motion along its route to the GSO station would Earths gravity be sustantial enough at (400-600 miles, Int. Space Station altitude) to pull the elevator back to Earth, would it hover in place, or would it ascend?

 

[martins]

A follow up question if you wouldn't mind...if the elevator were to stop its forward motion along its route to the GSO station would Earths gravity be sustantial enough at (400-600 miles, Int. Space Station altitude) to pull the elevator back to Earth, would it hover in place, or would it ascend?

That, I think, you should now be able to work out for yourself. If you need to, try an experiment: In orbiter, place a spacecraft at that altitude above the equator with zero radial velocity and 2pi/day prograde tangential velocity, and see what happens.

 

[Allan]

I am not a physicist or a mathematician, I'm just a writer. Though I am intrigued by your suggestion to try an experiment. I am very new here...what do you mean by "In orbiter, place a spacecraft"...are there progams attached to this site which allow for this type of experimentation?

 

[Izack]

what do you mean by "In orbiter, place a spacecraft"...are there progams attached to this site which allow for this type of experimentation?

Are you serious?? :rofl:

Okay, sorry. Orbiter is the spaceflight simulator that this forum is dedicated to. The person you've been speaking to (martins) is the one who made it. See here.

If you're a writer of speculative fiction (which I myself am as well :tiphat, I absolutely cannot let this topic slip by without posting a link to Atomic Rockets. It is an enormous compendium of unbelievably useful information for science-fiction writers. I almost always have a tab opened to it.

By the way, to Orbiter-Forum!

 

[martins]

I am not a physicist or a mathematician, I'm just a writer.

Don't put yourself down - and don't worry, these questions can be answered by anyone with basic school knowlege. Since you are writing about it, it's probably a good idea to get to grips with the concepts.

Though I am intrigued by your suggestion to try an experiment. I am very new here...what do you mean by "In orbiter, place a spacecraft"...are there progams attached to this site which allow for this type of experimentation?

http://orbit.medphys.ucl.ac.uk/home.php

 

[Allan]

I found this site by chance...I hide in coffee shops ridiculously early Saturday and Sunday mornings to write while my family sleeps. After having written 3 chapters I doubted my intial ideas (yes, Martins validated what I wrote (thankfully)) and google searched on Space Elavator and gravity. I had no knowledge of this site at all before about two hours ago.

I owe Martins a beer (or coffee) for all the work he's saved me already. If he's ever in Arizona or I ever return to Jamaca I owe him one ( or more). BTW I found the orbiter download...I appreciate the info.

---------- Post added at 04:00 PM ---------- Previous post was at 03:56 PM ----------

Martins, Thats exactly what I'm doing...believe me you are a lifesaver. There's a ton of conflicting information on the web. Good fortune brought me here. I'm amazed in all my searches over the months i've never come across this site before.

 

[Izack]

Okay, I can see how searching for space-related topics can lead to this forum. There are, after all, a lot of space-related topics here. :lol:

There was a somewhat similar thread a while back that's probably worth reading: Space Elevator Gravity. It describes what happens below and above geostationary orbit.

 

[Allan]

Yep, thats the link google found that brought me here to begin with. Thanks for looking for me!

 

[Skookum]

...what do you mean by "In orbiter, place a spacecraft"...are there progams attached to this site which allow for this type of experimentation?

Yes. There is a very powerful and addictive program on which the members here (myself included) have been hopelessly hooked for some time. Good God! Please help us, we can't stop!
"Must...get...to ISS. Must...deliver...cargo...modules.
Yes Honey, I'll be to bed soon! Yes, I know it's 2 AM!"

Forum search "hail probe" to find out how bad it can get.

Investigate and experiment with Orbiter at your peril. Quitting smoking is easier than quitting Orbiter.

Cheers

:hail:

 

[Allan]

HAHA! I already downloaded it to my laptop and will to my desktop shortly. I'm going to have to read up on how to use it, but I think this is going to prove very useful once I figure it out.

 

[Izack]

Yes, it probably will if my experience is any indication.
When I found Orbiter it completely changed my view on space travel, as well as giving me a new insight into the scale of celestial distances and bodies.
A common flaw with sci-fi writers is that they have absolutely no sense of scale. That wouldn't be such a problem if more people played Orbiter.
This isn't even mentioning my previous ignorance of the workings of astrodynamics. Hopefully Orbiter (and the Atomic Rockets site I linked earlier) will be of assistance to you.

May I ask what it is you're writing about generally? No spoilers or the like, of course.

 

[Allan]

You may not like it. I'm writing speculative fiction along the lines of Alduos Huxley, George Orwell and with undertone of (less so) Ayn Rand. Thats should be crypic enough Thanks for asking.

 

[Linguofreak]

The counter-weight is installed beyond the altitude of a geostationary orbit, while the elevator itself will only go up to GEO. All along its way its tangential velocity will be below the orbital velocity at that altitude, so the centrifugal force will never surpass gravity. The resulting force (in the rotating system), although getting smaller, will always be towards Earth, until reaching freefall conditions at the destination.

Well, that depends alot on space elevator design.

Your "counterweight" could just be a length of cable going out aways. If you go to the end and jump off, you could find yourself on an escape trajectory. By waiting for the correct time of day to jump off, you could send yourself in the direction of anything roughly along the ecliptic (though because of Earth's axial tilt you'd need to spend some DV on a plane change). By taking a "running start" (using whatever mechanism you use to climb the elevator (probably something akin to maglev if you want to be able to get up there at all quickly) to give yourself a speed boost along the elevator), and also letting centrifugal force help you accelerate along the elevator cable, you could get a ton of easy delta V towards an interplanetary trip. (If you're really daring, you could do the reverse of this too: Come in with a huge velocity from interplanetary space, and "land" on the cable and use it to slow yourself down).

In that case, you would be going beyond geosynchronous orbit, but the forces you'd feel would depend entirely on your acceleration profile.

 

[Allan]

Interesting...the only thing you'd need fuel for after being "thrown" from the cable would be to adjust your course heading. But this only applies to the point past the platform at GSO, correct?

 

[ar81]

The intro of Independence War has a space elevator.

This may give you an idea of how things may look like from a close to real (as close as it may seem in 1999) point of view. At the time it was the most "close to real" commercial combat sim available for gamers.

Here you have a [ame="http://orbithangar.com/searchid.php?ID=1891"]Space Elevator addon[/ame] that you can use with Orbiter.