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Orbital and suborbital in tandem

Posted by: jasohill - Fri Oct 01, 2004 12:36 am
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Orbital and suborbital in tandem 
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Post Orbital and suborbital in tandem   Posted on: Fri Oct 01, 2004 12:36 am
I just had an idea for a space shot that might be cheaper and easier then an orbital trajectory. Why not have a landing pad at geo stationary orbit, and then have a ship make a suborbital trajectory towards it(since it is geo stationary, it should be rather easy to find and not move away at mach 25.) Once the ship hits the peak of it's parabolic trajectory, then it can use maneuvering thrusters to land on the platform. Therefore, all that is required is a suborbital trajectory to that height. I know it would be quite hight at geo stat. but I think it still might be a cheaper alternative. Would this be feasible? It's just something that came into my head when I was trying to solve this gravity well issue.


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Post    Posted on: Fri Oct 01, 2004 5:56 am
We allready thought about it some time ago. The idea is good, but you really need a 300 km cable just to pull a suborbital plane in. And we dont have anything which can do that for reasonable prices.

I think it would be nice to see where SS1 could end up if it would be brought up to 100 km first and then ignites his engines.


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Post    Posted on: Fri Oct 01, 2004 7:03 am
Hello, jasohill,

the first problem is that the platform has to be launched to geostationary orbit. But if this could be done privately orbital launches automatically are solved too - then your idea in principle isn't required anymore.

The real advantage of your proposal is that it causes a reduction of costs and provides the possibility to carry suborbital spacecrafts to an orbit.

The platform could be of use at altitudes below geostationary altitudes too.



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Post    Posted on: Fri Oct 01, 2004 10:42 am
Hmm. A cable is a good idea. And at those altitudes it wouldn't have to be a carbon nanotube cable either. At the end of it, you could have web like device that makes the craft "stick" to it. I know it sounds nuts, but I think it could work.

And yes, you nail it right on the head. The platform could be like the ISS. Once it's set up then all you need are suborbital flight to get up in that range. It's like a mix between an elevator and a jet booster.


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Post    Posted on: Fri Oct 01, 2004 10:56 am
Your point concerning the cable I tried to discus under other topics too.

To catch a suborbital spacecraft is a similar idea to that published by the NIAC study considering an orbital spacecraft diving into the atmosphere to catch a payload from an airplane. This spacecraft uses a cable or tether too.

The cable should be rotating and because of the difference of the velocities it has to able to roll down and later to roll on again.

But in such concept is hidden very much more...



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Post    Posted on: Fri Oct 01, 2004 12:19 pm
You know, I'm thinking that tandem wasn't the best word to use. Then again, maybe it was. I think throwing interesting ideas out there is a great way to drive creativity. Who knows what crazy thought could be tomorrows interstellar spaceship? :wink:


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Post    Posted on: Fri Oct 01, 2004 12:26 pm
A Geo-synchronous satellite is everything but stationary. The orbital velocity at Geo is around 3.1 kms (Orbit radius 42230 km, one orbit every 24 hours), while the equatorial speed is only about 0.5 km/s. A suborbital vehicle launched at equator will have only that 0,5 km/s of orbital velocity, give or take some. The speed difference at that point is about 2.6 km/s, or 8530 fps. A regular hunting rifle bullet has a velocity of a bit over about 1/3rd of that.

It's like catching a bullet while riding a cannonball going the other way.


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Post    Posted on: Fri Oct 01, 2004 12:43 pm
This moment I remember not long ago at this message board having read a post refering to www.xprize.cz which is describing a concept similar to your's too, jasohill.

This concept proposes to lift an object like a helicopter does. But the rotator is driven electrically by a cable going down to earth. Maximum altitude proposed is 30 km. For this reason special equipment in space is proposed - a cable that can come down (may be GEO is proposed) and link to the object already lifted to 30 km. This cable now will lift the object to space.

The concept was referred to in one of the discussions considering space elevators.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

PS: Besides a tandem to me would be a "suborbital" spacecraft carrying another spacecraft that is an orbital vehicle.


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Post    Posted on: Fri Oct 01, 2004 3:27 pm
Vendigo got to the real problem behind this - your idea is based upon a dubious understanding of the physics involved.

Geostationary orbits to stay consitently above one point on the planet, yes. But that does not mean you only need to achieve "suborbital velocities".

It's quite hard to describe, but due to the fact that the Earth is a rotating object, not a flat plane, if you just head straight up from Earth you will not end up directly above the same place as you left off. While you do stay pretty much in the same place while in the atmosphere (largely because of both the atmosphere, and the fact that you really haven't gone very far), things will change quite a lot by the time you get sufficient altitude to be in geostationary orbit.

Geostationary orbit is just like a normal orbit, the only unusual thing is that you happen to be travelling around the Earth at the same speed as the ground below you. Keep in mind, that the Earth rotates far more slowly than would be required for an orbit at it's altitude. If the Earth did try to rotate that fast, it would almost certainly fly apart under the acceleration.

(Remember when calculating orbits, the center point you are measuring to is the center of the Earth, not the ground. There's 16000 miles difference between the two).

It's kinda hard to describe without getting to mathematical, but suffice to say that you won't gain anything out of this, except possibly not having to figure out where the station is every time you launch.

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Post    Posted on: Fri Oct 01, 2004 10:59 pm
No, it's okay, I think I've got it now. I do understand the physics involved, and when you pointed it out to me then I understood that this might not be such a great idea. It's kind of how the speed of a record is different at the edge when it's spinning then it is towards the center. Now that I've remembered all my college physics classes, it does seems like a rather lame idea.


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Post    Posted on: Sat Oct 02, 2004 8:01 am
jasohill,



please consider your idea only required to be modified a little bit.

The arguments "against" your idea in its original version are right - suborbital velocity at geostationary altitude doesn't mean to reach geostationarx orbit.

But at the geostationary platform equipment could be provided perhaps that can accelerate the suborbital spacecraft by docking to ist.

This I had in mind when I mentioned the cable that could catch the suborbital spacecraft.

PERHAPS this might be a solution - it has to be calculeted concerning differneces in velocity, tense of cable, lnght of cable, effects on the suborbital spacecraft, effects on the platform..

Another possibility is to launch a small spaccraft from the platform that docks to the suborbital spacecraft and accelerates it - this would be a kind of space-based third stage or additional stage. It's similar to the catching spacecraft studied by a document at the NIAC site.

But without such additinaly accelerations a suborbital spacecraft hardly could land on a geostationary platform I think.



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Post    Posted on: Sat Oct 02, 2004 9:48 am
The platform would need to be absolutely enormous compared to the cargo to minimize the orbit decay and tumble during the cargo hookup. The platform could be powered with solar cells and thrusted by ion engines; it's orbit would need to be restored after cargo haul, and the cargo satellite would need to carry the required propellant with it. The logistical and technical problems seem overwhelming compared to the benefits (use of high-impulse engine for GEO orbit).

(Edit: typofix)


Last edited by Vendigo on Sat Oct 02, 2004 1:54 pm, edited 1 time in total.



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Post    Posted on: Sat Oct 02, 2004 1:04 pm
All problems and costs might be rediced by studying all in detail. And it might help to use the NIAC study as part of the basis.

Don't forget - the study say that it would work to have a spaccraft in the orbit that dives into the atmosphere and catches a payload from an airplane while rushing in. Then it accelerates to leave for the orbit again.

This orbital spacecraft actively leaves the orbit which means that it destabilizes its orbit itself and later works explixitly to rech the orbit and stabilize it again.

That could be done by the platform too despite it doesn't stabilize and leave its orbit actively but by an effect that perhaps cannot be prevented (there might be technologies and techniques to be found that could prevent it).

So at the platform-side there is only a very small difference to the subject of the study - and the spacecraft considered by the study has to handle the effects and the forces of the atmosphere too but the platform has not.

Additionaly the payload to be catched from the airplane will have a velocity significantly less than the suborbital spacecraft to be catched by equipment of the platform but the catching spaccraft will be significantly faster than the platform. So the difference of velocities between the payload and the spacecraft may be greater than the velocity differendec between the platform and the suborbital spaccraft - note that a suborbital spacecraft reaching geostationary altitude must have a signifacnt greater velocity than another suborbital spaccrfat reacdhing an apogee of afew hundred km only. And the apogee could be chosen above geostationary orbit to provide a velocity closer to the velocity of the platform.

Additionaly it will be adifference if the suborbital spacecraft will be catched BEFORE the platform has passed the course of the spaccraft or AFTER it has passed that course...



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Post    Posted on: Sun Oct 03, 2004 11:40 am
Okay, here is the question: if the aerograb tether launch is a viable and cost-effective alternative for rocket launch, then why bother battling it out at 36000km?


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Post    Posted on: Sun Oct 03, 2004 1:30 pm
Not to mention many of the technologies required for a proper rotating space tether would also mean that a space elevator would probably only be just around the corner.

Aside from...logistical problems, the main technology holding such a thing back is the lack of a strong enough tether - the same problem that exists for elevators. And yes, while nanotube research is coming along quite nicely, there is still a long way to go.

Personally, I don't see either of them becoming very likely methods for getting into orbit - or at least not from Earth. Just having a big ass rocket isn't all that hard, or even expensive once the economics of scale come into play.

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