ACME Test

[tblaxland]

Essentially, a HASTOL pickup is the same as a lunar surface payload pickup except that the tether doesn't go all the way down to the ground. Also, the surface relative tether tip velocity, instead of being zero, is matched to the sub-orbital vessel's velocity.

 

[n0mad23]

Indeed,

Which does make sense, if we consider that the catcher reaching the bottom of its rotation, begins a retrograde swing in a prograde orbit.

Translation: the relative velocity of the catcher is decreased. Very useful to the fact that its purpose is essentially interception. Might as well get the relative tangential velocity as low as possible before making the grab.

Good point. Thanks for the feedback. It's feeling like it's finally taking on "a life of its own." A good sign in my estimation.

 

[Bullethead]

Which does make sense, if we consider that the catcher reaching the bottom of its rotation, begins a retrograde swing in a prograde orbit.

As I understand things, the catcher never moves retrograde at all as seen from the lunar surface, it just moves prograde at a slower forward ground speed during the upswing. The catcher is still tied to the center of mass of the lunar rig, which is zooming around the moon fast enough to maintain orbit. The prograde distance traveled by that center of mass in a give amount of time far exceeds the retrograde distance traveled by the catcher tip on the upswing at its relatively slow rotational speed.

Hence, if you were standing on the lunar landing pad, you'd see the catcher's tip streaking across the sky at high altitude as the whole rig approached. As it got closer, the tip would slow down in the prograde direction and would appear to dive down at you, fast at first and then slowing down, until for a few seconds it would be right beside you with very little relative velocity either vertically or horizontally. Then the cargo exchange takes place. After that, the catcher tip would appear to slowly ascend nearly veritcally for a little while, and then both the apparent vertical and horizontal velocities would increase for a while, with the horizontal (prograde) increasing faster.

Think of the classic experiment showing how a give point on a tire moves relative to the ground as the tire rolls down the road. Its path looks like a series of semi-ellipses with no backwards motion relative to the road at all.

 

[n0mad23]

He gets it! Bullethead, the first official convert to the Church of the Orbital Trebuchet!

Yup, this is exactly how it works. What's weird though, is in terms of perceived motion, the tether does seem to move in a retrograde motion while at the bottom of it's rotation. Perceived.

In other words, while the payload moves in its prograde orbit, the catcher swings backward toward the payload. Of course the tangential velocity doesn't come close to the orbital speed, but it is enough to greatly reduce the relative velocity between the catcher and the target.

Still digging for the info on conservation of angular momentum....

 

[Bullethead]

He gets it! Bullethead, the first official convert to the Church of the Orbital Trebuchet!

Just as long as I get royalties for thinking up the name .

BTW, on the subject of names, given that the moon (or at least parts of it and its surrounding orbits) in your universe is inhabited by hippy communes, how about this as their name for the lunar rig? I'm thinking "What-evator", as a play on the word "whatever", because they can't remember the official name, with all its arbitrarily placed capital letters, and don't care enough to find out.

 

[n0mad23]

I've called it the "Ananke" RotoVatoR[FONT=&quot]® from Plato's model of the universe. Ananke is like a cosmic spider (lit=necessity) who weaves webs of attraction, because they're necessary.

The name of the first novel (where ZTC and Titan Werks make their debut) is Arias in C Minor: Prelude to a Space Opera.


[/FONT]

 

[n0mad23]

I just realized that I should publicly nod at Urwumpe for the title of ACME Test Tether. Our own Wiley E. C. made a comment in a post about how ACME was screaming to be implemented in Orbiter.

So Urwumpe, if you should make it into this thread, I've given credit where it's due.

 

[n0mad23]

Overhand versus underhand -

The counter-clockwise .scn I posted does in fact provide the same velocity/altitude boost IF you release at the bottom of the rotation.

I'm going to play around tonight with the Test and try some different parabolic orbits. I'm guessing even with the 40 km cable, I can cut down the fuel consumption for a lunar transfer to less than 7 percent.

 

[NukeET]

I just realized that I should publicly nod at Urwumpe for the title of ACME Test Tether. Our own Wiley E. C. made a comment in a post about how ACME was screaming to be implemented in Orbiter.

So Urwumpe, if you should make it into this thread, I've given credit where it's due.

n0mad23:

Hope your ACME works better than it did in the cartoons!

 

[n0mad23]

n0mad23:

Hope your ACME works better than it did in the cartoons!

Nope. It's just as big and dumb. And, it's equally as non-fatal!

 

[n0mad23]

Well the mesh problems continue.

However, I can now make a single cable (multiple sections cause fatal crash) that's 99 kilometers long.

Should I whip up ACME Tether Test II? I'm betting a 99 km radius is going to create a large orbital boost.

 

[Bullethead]

Well the mesh problems continue.

However, I can now make a single cable (multiple sections cause fatal crash) that's 99 kilometers long.

Should I whip up ACME Tether Test II?

Sure, let's see how much difference that makes.

BTW, I know nothing of making Orbiter add-ons, so I'm unclear on the nature of your problems. But from what I've gathered, the main 3D editor used for Orbiter mods is Anim8tor, which was designed to make cartoons, not detailed objects. Hence, the need for MeshWizard to put vertices into regular positions.

If that's true, then why not just make the models with Blender? Then all the vertices could be put directly into the desired locations from the start. No need for MeshWizard, and thus no worries about its limitations.

 

[n0mad23]

It's the learning curve.

I can make things on Anim8or because I've already done so. The best success I've had with Blender so far is importing a mesh (though I suppose that is something).

I guess it's probably time to suck it up and do it anyway. Blender, here I come!

 

[n0mad23]

I've got a 95 kilometer mesh of the ACME Tether done. I've got to hack together the configuration files, and calculate the rotation but we should have something to play with tomorrow.

Cheers!

 

[n0mad23]

The 95 km cable delivers escape velocity with the tangential speed of 1.5 km/s. I'm estimating 2.7 g's of force, which seems pretty manageable.

Getting the tether velocity and ApA and PeA to match those from the TUI documents is proving a little more challenging. Perhaps using Elements instead of RPOS and RVEL will be the key here.

 

[Bullethead]

The 95 km cable delivers escape velocity with the tangential speed of 1.5 km/s. I'm estimating 2.7 g's of force, which seems pretty manageable.

Yee-hah! Can't wait to try it.

The effect of 2.7Gs would depend on the orientation of the flung ship. This number is well below the blackout limit, but IIRC is pushing the redout limit. IOW, we'd have to ensure that the the crew faced this as positive G, not negative. But I think shuttle launches are a bit more strenuous than this, so it shouldn't be that much of a problem.

 

[n0mad23]

Yee-hah! Can't wait to try it.

The effect of 2.7Gs would depend on the orientation of the flung ship. This number is well below the blackout limit, but IIRC is pushing the redout limit. IOW, we'd have to ensure that the the crew faced this as positive G, not negative. But I think shuttle launches are a bit more strenuous than this, so it shouldn't be that much of a problem.

You're forecasting the inevitability of it's own eventual payload system. To really implement the Delta-G would/will require another mesh cradle built into the grapple system.

Since it's to be a cislunar transport system, the payload's going to have to be designed to be a lander. It really needs to be able to re-enter the atmosphere back on Earth as well.

In not, another option is to put said payloads into stable LEO orbits and do docking/transfer maneuvers. Personally, I like this scenario best.

Meanwhile, successful Delta-V's been achieved, and the quest for stable, repeatable ejection continues.

Stay tuned...

 

[n0mad23]

Alright Fans and Skeptics,

Just a little more patience please. I'm sitting down to test the latest 95 km scenario, and if all goes well, I'll post the latest ACME Tether Test later tonight.

Sling me to the Moon!

 

[n0mad23]

95 Kilometer ACME Test

Here's the 95 kilometer version. It will sling you to the Moon.

REQUIRES Vinka's Spacecraft3.dll

Instructions are simple:

Undock at the top of rotation - when you're looking straight at the ground.

IMFD's a good choice.

:beach:

Feel free to comment.

Update:

Now passes within 900 km of the Moon.
If you've already downloaded this test, please download the scenario file. It's now included in the current zip file.
​

 

[Bullethead]

This is even more of a Yee-Hah than the original. When you let go, the Earth just falls away unbelievably quickly. :speakcool:

I'm still experimenting with the timing of the release. Anywhere on the low side of the flinger's orbit will toss you out to the moon's orbit, it's just a question of how close the moon is when you get there. Do you have any suggestions? When the scenario starts, the flinger is already slightly past its Pe. Is it better to release as soon as you're pointing down, or wait an orbit until you're at or on the other side of Pe?

The only disappointing thing is that I can't ever see the whole flinger. I suppose this is a result of Orbiter's graphics engine not drawing any ship-type objects beyond a certain distance from you. Thus, when you're still fairly close to the thing, say where it's rotated about 45^ from where you left it, it appears to be cut off somewhere in the middle of its length, and the lump end is never visible. And by the time it's rotated 90^ and you're far enough away to maybe see its full length in side view, it's no longer being drawn.