Question regarding flight, atmosphere vs space

I'm not even talking about flying at near light speed. I'm talking about taking off in spacecraft from a space station, flying to another space station, turning around and coming back without having to refuel.

 

Great topic!

The article doesn't actually propose any existing materials that could be used to anchor a line on earth and an object in Earth orbit. The article mentions nanotubes, but we can't make perfect nanotubes anywhere even remotely long enough for an elevator to Earth orbit. A carbon nanotube is ONE molecule and its strength comes from the strength of the carbon to carbon bonds within the molecule. Thus it's said that nanotubes would have to be perfect at the molecular level. Geosynchronous orbit is 22,000 miles above sea level, and the diagram points out that the required length is longer than that. That's one heck of a long molecule considering that the longest nanotube created as of 2013 was 1.5 feet.

As for anchoring something on the MOON and using that to go to/from a point of equal gravity might work with existing materials since lunar gravity is so much weaker - maybe there are materials strong enough for that. But, that can't be then tethered to earth for the same weight reasons and because the rate that the Moon travels around Earth isn't the same as Earth rotation on its axis - 1 day vs. 1 month.

 

All excellent point!

The moon tethering struck me as being absurd because the distance isn't constant either. The variance is about 27,000 miles so that alone would put stresses on the cable let alone the variances in the rotations.

Geosyncronous orbit makes the most sense because we already know how to put satellites in those places and how to keep them there.

That brings us back to the materials that might work. Graphene is a carbon mesh that is one atom deep. We already know that carbon fiber is as strong as steel so perhaps some combination of materials might work. Still needs more research but it has potential and appears to be much more feasible than what is discussed in the OP.

 

Just had another thought that I wanted to bounce off you @WillReadmore.

What about a skyhook?

Yes, I know that has been a joke in the past but what about a geosync satellite with one of these cables attached and the other end was not tethered to the planet but just hung suspended in the atmosphere? We then use atmospheric craft to raise the load to the skyhook and then the satellite it winches the load up into orbit.

Just "floating" that idea out there is see if it might have any merit.

 

A space elevator makes no sense to me at all. It sounds good on the surface but how are you going to anchor it to the earth? And the weight of such a contraption would be astounding. Considering the fact that the further from the earth the less something weighs I wonder if raising a veihical with a balloon may be a viable alternative..... Just spitballing here.

 

Cool idea!

It relieves the need for a line all the way to the surface - certaily good for aircraft, wear/tear, etc.

Unfortunately, geosynchronous orbit is ~22K miles high. So, to make a real difference in the needed strength of the line one would probably have to hook on well above the elevation of aircraft.

 

We can get balloons to ascend into the stratosphere and with lightweight batteries and electric motors they should be able to navigate to the location of the hook. Then the size of the payload would depend on the lifting ability of the balloon.

Given that this is a reusable system that can use renewable energy sources you could probably do multiple small lifts for the price of a single rocket launch.

The only potential issue I can see is navigating a balloon through the jet stream but there are probably sufficient advanced navigation systems that can handle that issue.

 

Another cool idea! Balloons have traveled that high. I don't know how much lift power they retained, but they certainly have gotten as high as geosynchronous orbit. Communications satellites weigh between 2 pounds and 2 tons or more - quite a range.

I don't know why this hasn't been explored more.

We're running out of helium, so maybe hydrogen or methane or something would be used. Surely the balloon would be in geosynchronous motion, so there wouldn't be a huge speed difference between the balloon and the "hook" to overcome.

One issue is that our space station is at about 240 miles up and is traveling at 45 miles per second. So a crane to geosynchronous orbit is only the start of a mission to the space station or any other place outside Earth orbit.

This is just a general limit of the "sky hook" idea, of course.

I think the last rocket to deliver communication satellites to geosynchronous orbits delivered 60 such satellites in one rocket. If one considers the rocket is reusable, that starts to cut down the cost. But, it still seems the "sky hook" idea would have a cost advantage. Any initial investment in a "sky hook" could be paid over time, as there is sure to be a constant stream of such satellites to be delivered.

I don't know why this isn't being done. I hope someone can give a clue!

 

So, here is the most reasonable idea.

1. We will have vehicles for leaving earths atmosphere. ( rockets and shuttles)
2. Vehicle for space travel

3 vehicles for carrying cargo into atmospheres ( disposable shuttles)

4. Vehicles for moving around in atmospheres. ( traditional aircrafts each designed for specific gravity and environmental conditions)

 

Yes, there is a significant difference between a geosync orbit and a low earth orbit. That said once something is in space moving it from one location to another doesn't take a great deal of energy. If a payload needed to be delivered to the ISS it could be lifted to an orbit above 240 miles and released. Then a booster could fire and put the payload into an elliptical orbit so as use the earth's gravity as a slingshot and increase the payload speed until it matched that of the ISS on the same orbit. All of that math is already well understood so it should not be a problem.

The same principle could be applied to putting up satellites.

Now let's try this concept in reverse. Assume we want to try and return astronauts to earth from the ISS. Instead of firing retro rockets they fire a booster to reach a higher orbit which would slow them down relative to the earth. They could time that to reach the sky hook and then transfer to that and be lowered back into the atmosphere. Once back there they could either hitch a ride on the next balloon or use a parachute.

 

Duplicate

 

I doubt that's a great way to look at the problem.

Missions in space are highly varied based on payload, destination characteristics, whether it will return, whether there will be a human onboard, etc., etc. Also, technology is making new choices possible, leaving behind old solutions.

So even within what might seem like a single category we're a long way from stasis.

PS: many destinations (like the many moons, asteroids, small planets, etc.) don't have atmosphere. So, no parachutes, no wings, etc.

 

Not quite useless. You would be correct in saying that a lift-generating wing is incapable on generating lift in no atmosphere...but it's not totally useless.

Imagine from Babylon 5 the Star Fury.



This is the SA-26 Longbow class of Star Fury. The difference between this and the standard SA-23E that you usually see is that the Longbow was designed to fly in atmosphere and not just in space like the SA-23E. While those wings are incapable of generating life...they're not useless as they have as another function of being the pylons that the thruster pods are mounted.

So wings on a space craft needn't be useless in space, but could have multiple functions. Add weapons like the Star Wars T-65 and T-70 X-Wing Star Fighters and those wings really become quite useful in space.

 

That is one of the dumber Star Wars ideas!

Unlike dogfighting in the atmosphere were aerodynamic considerations are paramount out in space having a weapon on a pylon capable of pointing in virtually any direction would be significantly superior for both offensive and defensive purposes. Launching missiles from space at targets flying in the atmosphere below would be more effective than wasting the effort to chase them around.

Unfortunately Star Wars was way more FANTASY than REALISTIC in order to sell tickets.

 

Exactly. Now make those pylons a lifting design so you have a craft that can work in and out of atmo...and the wings are not useless in space.

 

Well, they're still useless in space - you're just suggesting that they would be useful in atmosphere.

I suspect a space fighter would be better off if it didn't have to carry the wing mass required by the rigors of atmosphere.

But, I also strongly doubt it would have a human inside.

SciFi has given us some ideas about space that just don't match up. One is the gigantic overestimation of the requirement for human presence.

 

if it has enough shielding and power for trans-atmospheric travel