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Object hopping...

Posted by: Ekkehard Augustin - Sat Aug 13, 2005 8:20 am
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Object hopping... 
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Post Object hopping...   Posted on: Sat Aug 13, 2005 8:20 am
In the thread about spaceships I posted the thought of planet-hopping - hopping from planet to planet out of the solar system into the system of Alpha Centauri if that system contains any objects or planets at all or into another nearby system around a dwarf starif there is one not detected yet.

I currently don't wnat to work that out in this thread - form time to time I am thinking about planet hopping merely to move to the outer planets and the outer regions of the solar system. I am just playing around only

What I have in mind is to send a vehicle along a course where an object going along an ellipse with significant excentricity would approach it from behind which would result in a landing of the vehicle on that object.

A safe landing on an asteroid is possible if the vehicle is made spiraling around the asteroid downwards to its surface which has been done when NEAr landed on EROS. This could be applied to planet-hopping too but I personally could imagine that it might be possible to let a vehicle move ahead of an object to the same direction by a velocity slightly less than the object's velocity. The problem I recognize is the rotation of the object - could the course of the vehcile be adjusted so that it doesn't need to spiral that much but simply touches down because of the object's surface moving onto it by its rotation?

The vehicle could have quipped by a tank containing sufficient propellant for several take-offs.

The object would carry the vehicle farther outwards where the vehicle takes off again and follows a course to another obejct going out farther. The whole procedure could be repeated - and it could be used to retrun the vehicle to Earth too.

The first touch down to such an object could occur at or inside Earth's orbit.

Asteroids could be used but to me it seems to be interesting to land the vehicle on the night side of a conmet too - I will have to look for the information but I seem to remeber that there will be a first ladning on a comet in the nearby future. Isn't Rosetta or another ESA-probe intended to land on a comet?

What landing-technologies could be used and which innovations or improvements are required? What about installing artificial objects for this way?



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

EDIT: I looked for informations about Rosetta at ESA's homepage: I remembered correct - there is a lander to touch down on the comet's surface. It will "anchor" there but this may be a metaphor.


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Post    Posted on: Thu Sep 08, 2005 12:45 pm
Another reason to do object hoping may be propellant that is available at asteroids. At the largest asteroid Ceres there could be a large reservoir of water - larger than the earthian oceans according to the article "Largest Asteroid Might Contain More Fresh Water than Earth" ( www.space.com/scienceastronomy/050907_ceres_planet.html ).

The flight of a vehcile could start to achieve a small asteroid to be taken by it farther out.

From that small asteroid the flight could go to Ceres to refuel and then to another small asteroid (or comet) going even farther out.

Perhaps propellant depots somewhere in the outer solar system could be formed this way if the vehicle refuels not only but is able to carry water to other worlds..



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Post    Posted on: Thu Sep 08, 2005 1:04 pm
Ekkehard Augustin wrote:
Another reason to do object hoping may be propellant that is available at asteroids. At the largest asteroid Ceres there could be a large reservoir of water - larger than the earthian oceans according to the article "Largest Asteroid Might Contain More Fresh Water than Earth" ( www.space.com/scienceastronomy/050907_ceres_planet.html ).


Fresh water is not the water in the oceans. Objecthopping will only be rendable if the gravity is low, like on asteroids and maybe small moons. If you have a large enough ship with some sort of processing facility attached to it, you can process enough asteroids to have enough fuel for a long time. So it's a good idea, only problem is that nobody wants to test this before we have a base on the moon and mars.


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Post    Posted on: Thu Sep 08, 2005 2:38 pm
The use of asteroids to get propellant is an idea of SapceDev and their founder. My focus here was on Ceres especially and some similar sized asteroids because they are large enought to do even more there.

Most smaller asteroids I would prefer to keep intact as far as is possible to use them as natural carriers. If water is extracted from them then it should be replaced by something that keeps them intact.

But Ceres and a few are good places for stations I think.



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Post    Posted on: Fri Sep 09, 2005 5:21 pm
This is basically a variant of the concept of "skipping" across the upper atmosphere with a hypersonic launch vehicle to pick up speed and eventually reach/break orbit.

And yes, this is also similar to the kind of approach that primitive asteroid mining missions will use: send a ship out on an eccentric orbit, catch a few asteroids with it both on the way out and on the way back in, process them en-route, and return to the start point -- either Earth, the Moon, or Mars (the Moon or Mars are each far more likely than Earth) -- with a cargo bay full of ores.

Later missions will involve sending people out into the Belt for short durations, and eventually on a permanent basis -- but let's not get ahead of ourselves, here.

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Post    Posted on: Wed Oct 25, 2006 12:16 pm
There is an article under www.wissenschaft.de today sounding as if NASA is thinking about making reality of the idea of object hopping.

May be that I have mentioned such an idea in one or two other threads also.

But the reason why NASA seems to be thinkng this way is radiation protection during the journey to Mars.

The article says that astronauts could travel inside and asteroid to be shielded against space radiation by the material of that asteroid - then no heavy and workfull construction of shields would be required.

According to that article there is a group of proper asteroids that regularly pass close to Earth as well as close to Mars.

Astronauts arriving from Earth then could either dig their vehicle into the asteroid by digging a hole and closing it again or they could keep their vehicle aside the asteroid close to it and surround it by a shell they would make from the material of the asteroid.

One of the scientists is quoted literally to have said that there is nothing truning this impossible. The only constraint: the work mustn't have no effect on the path of the asteroid because otherwise it might fail to pass Mars or even collide with Earth.

Also it is not sure if all asteroids are like Itokawa - in case of massive rocks digging in or using material would be impossible.

Electrostatic charged stones etc. might be a problem because they might stay on the tools or the hull of the vehicle then.

If it works neither a massive shield would have to be launched from Earth and the according consumption of energy could be avoided nor a generator of a magnetic field would be required to be developed.

At present the consistency of 40 potential proper asteroids are under investigation for containing heavy elements because theses emit inhealthy particles under contact with cosmic radiation.

The article is quoting the american student Daniella Della-Giustina, University of Arizona in Tucson, Daniel Durda, Southwest Research Institute in Boulder and New Scientist, Online-Service ( http://www.newscientistspace.com/articl ... eroid.html ), 23rd of October 2006.

...

It might be possible to have a limited look into the costs of this by what I am doing in the Financial Barriers secton once I am ready with some Algebra and an Excel spreadsheet to process numbers.



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Post    Posted on: Thu Oct 26, 2006 6:26 am
Asteroid hopping for radiation protection or refueling is reasonable. But otherwise it gives no benefit.

You CANNOT save fuel by landing on an asteroid with an eccentric orbit, then getting off closer to your destination. The reason is simple:

In order to land on an asteroid, the spaceship has to be put in exactly the same orbit as the asteroid, after which it would follow the same path anyway, without using any fuel. Landing on the asteroid and taking off agin would use slightly more fuel than just following along.

Planet hopping, or gravity assist, works by using gravity to transfer angular momentum from a large planet to a very small spacecraft. Effectively you steal some energy from the planet, slowing it down infinitesimally, while speeding up the vehicle quite a lot.

PS: You can't 'spiral' down to an asteroid. Ask Peter if you don't believe me :lol:


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Post    Posted on: Thu Oct 26, 2006 6:45 am
There is one aspect that means a benefit beyond radiation protection or refueling: The path, the course of an asteroid is known and determined - the vehicle might not need as much course corrections and their necessity doesn't require that much and intense checks.

Another advantage I had in mind (and still see) is the firm ground the vehicle is placed on or in. The astronauts might leave the vehicle and could stand on something if they need to do work on the exterior of their vehicle.

Also It is a difference if the vehicle has to be accelerated by consumption of fuel or if it is flying at less speed than an approaching asteroid that might safely capture the vehicle while still being in the acceleration section of its orbit - which would be the case if the perihelion of that asteroid is close to the orbit of Earth and thus to the vehicle. In this case asteroid hopping (object hopping) saves propellant.



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PS: By the way - I think it is very clear that I never will ask Peter something...


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Post    Posted on: Thu Oct 26, 2006 8:43 am
Aside from the shielding an asteroid might provide I see very little point in trying to hop from one to another during a journey. Going to an asteroid to extract raw materials makes sense but hitching a lift is a waste of effort and IMO would complicate any journey unnecessarily.

I did think that it might be worth stopping off at an asteroid to extract fuel from ice deposits which would allow craft to a have additional boosts once in space or arrive at a destination with extra fuel. But arn't most of the asteroids in the inner solar system (I'm talking about out to Mars) devoid of ice due to the sun boiling it off?

Ekkehard

I think your point about astonauts having something to "stand on" would require a very large asteroid (10s of miles across) to generate enough gravity otherwise the first step would create enough DeltaV to launch the astronaut into space.

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Post    Posted on: Thu Oct 26, 2006 8:53 am
Hello, Andy Hill,

regarding the opportunity to stand on something I hadn't in mind gravity but merely the asteroid as a substitute for the end of the Canadarm an astronaut was standing on when Discovery was repaired at the ISS.

Regarding boiling off water I suppose this concerns asteroids with perihelions closer to the sun than that of Earth rather than asteroids with perihelions outside the orbit of Earth.

And to clarify the idea of acceleration by the asteroid a bit - of course the asteroid is going to decelerate after it has passed its perihelion but the vehicle could have a velocity below that the asteroid has and fly in front of it. Then the asteroid would approach the vehicle until the two get in touch to each other - the vehicle would touch down on the asteroid that moment. This could occur similar to the landing on eros or to the design of the landing on Itokawa (that failed due to handling errors and problems). From that moment on the vehicle would be travelling faster by being carried by the asteroid than it has been before the touch down. The difference wouldn't require propellant that would have to be carried and consumed if the asteroid wouldn't be used. ...



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

EDIT: Not to forget - if this is done to return to Earth then the vehicle would touch down on the asteroid during its acceleration phase because it is approaching its perihelion then...


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Post    Posted on: Thu Oct 26, 2006 11:20 am
Are you suggesting playing cosmic snooker using asteroids as cue balls? :)

Not sure I like the sound of that, you never know which pocket you could end up in. Besides if you parked your craft in front of an oncoming asteroid and fired the engines so that it touched down on the surface relatively gently then you would use as much energy as just accelerating.

touching down at 1.5m/sec basically means that you will have accellerated your craft by that much more than the speed you were travelling at anyway. Take into account the extra fuel used to manouvre into position and later escape the asteroids pull when you take off again and I cant see any advantage.

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Post    Posted on: Thu Oct 26, 2006 1:57 pm
Hello, Andy Hill,

I only had in mind a difference in velocity established before touch down. In that case no firing of the engines would be required to decelerate the vehicle.

The velocity of the asteroid is known well previously because the orbit is known well. The velocity of the vehicle can be calculated prior to the launch as is done for unmanned missions also and thus can be adjusted well.

What might be required is firing of RCS - which are short firings only.

There is one alternative I sometimes think about but looks more difficult to me: The vehicle could be moving tangentially to the asteroid... But I didn't think into details.

There also might be another method. The vehicle could use a web or net or so that the asteroid moves into. That web could be made of materials that can withstand large stresses. Then the vehicle itself doesn't need to be in the path of the asteroid but the web only would be deployed so that it is. When the asteroid moves into the web it pulls the vehicle with it and the vehicle could wind up those sections of the web that are behind the asteroid by electromotors...

What is required is that the difference of the velocities is neither too large nor too small.



In between there is an article at www.space.com reporting what I read under www. wissenschaft.de - "Harnessing Asteroids and Comets to Travel the Solar System" ( www.space.com/businesstechnology/techno ... 61026.html )

The article is linking to two other interesting articles reporting about another Mars-related student-project also that merely seems have to do with Terraforming.



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Post    Posted on: Thu Oct 26, 2006 3:01 pm
Ekkehard,

An asteroid and a spacecraft cannot be in the same place at the same time with no appreciable difference in velocity, unless they are in the same orbit around the Sun. The same forces act on them, they must move in the same direction.

An asteroid has no way to 'capture' a spacecraft except by smacking into the back of it at thousands of km/h. If you want to save a relatively small amount of deltaV, say 500 m/s, the collision will be at 1800 km/h.

Deploying a net to 'lasso' an asteroid sounds good, but the weight of the equipment to handle even a small deltaV difference (see above) is going to reduce the Mass Ratio so much that many times as much deltaV will be lost.


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Post    Posted on: Thu Oct 26, 2006 3:12 pm
What might work is permanently attaching a rotating tether to the asteroid. If the tip speed was 1000 m/s, you could gain a total of 2000 m/s from pickup near Earth and release further out.

Solar panels could supply power to maintain the rotation, and you get artificial gravity as a bonus. A 102 km tether at 1000 m/s provides 1 g.


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Post    Posted on: Thu Oct 26, 2006 3:24 pm
Forget asteroids, instead put a series of rotating tethers in circular orbits around the Sun at radial intervals where the orbital velocity differences equal double the tether tip speed.

A sub-orbital rocket could be picked up from Low Earth Orbit and slung from one tether to another to just about anywhere! Without having to use much more than RCS and course correction fuel. 8)


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