SFS News: ARCA - Haas Orbital Rocket Launcher for Google Lun

Thanks

The launch will be soon but there is no set date yet. What I can tell you is that we are ready for the launch. Monday morning we will have a final meeting with major stakeholders, there are still some security details to be set.

We are well aware of the risks associated with this stabilization system. It was not used before, but it is not the same thing as the pendulum rocket fallacy that everyone has in mind. There is a torque that is applied to the first stage that tends to stabilize the rocket. This torque is applied only when the system is accelerated, this is obvious. Forget about "g", the rocket is in free fall and the acceleration "a" is all that matters. The torque is generated only when there is an angle between the first stage and the direction of alignment of the system below. Fortunately for us, the system below is perfectly aligned vertically at t0. The 4 cables that converge to a point below are attached on the outside of the structure, not at the center - that is why that stabilization torque is created. The tension in the cables is different if there is a misalignment. Since it is applied at a distance "d" from the center, we get that stabilization torque. Of course there is another torque due to the fact that the direction of the thrust is not colliniar with the center of mass. There is no such perfect rocket. Still, there is an overall stabilization in our system. Because the system is very complex, we only have some approximate values for the trajectory.

BTW, there are lots of very nice presentations about torque and angular momentum. An example: http://videolectures.net/mit801f99_lewin_lec20/ ...and many others.

A pendulum has inertia. If, for a while it will apply a stabilizing, good force, on the rocket after it passes the other side of the symmetry axis it will act with a destabilizing, bad force, trying to bring the rocket back into its inclined position.

You can not suppose the pendulum will act in such a way that it just points the nose of the rocket to the sky and after that it stops, waiting quietly to correct a new misalignment when it appears.



On the other side, a pendulum does not know, in general, which way is down, otherwise pendulums would have been used as gyroscopes.

Inside an accelerating metro train, and you can test it when the metro leaves the station, a pendulum will not swing left and right with respect to the vertical but with respect to an inclined line which has the direction of g+a_metro (both of them vectors).

Source : http://www.googlelunarxprize.org/forum- ... &start=120

Good luck never the less!
Cant wait to see what happens!

Rob

This is what will happen:




More details here:
http://www.googlelunarxprize.org/forum- ... =5812#5812

New poll:

viewtopic.php?f=45&t=10779&start=0&view=viewpoll

If we ignore air resistance and the rocket exhaust slamming against the tethered stages, then the problem becomes easier to understand. The intended purpose of tethering mass below the rocket motor is to correct for any off-center thrust. If the tethered mass is much higher than that of the rocket motor, then the motor exhaust will end up pointing toward the tethered mass. This will cause the rocket to travel straight along the initial line defined by the tether.

However, if the tethered mass is not much greater than the rocket motor mass any off-center thrust will not be fully corrected. This would cause the rocket to slowly rotate around its center of mass. Normally, the mass of the first stage is much greater than the mass of the second stage, and so on. So this method of stabalizing the rocket wil not work well.

Now if we include air resistance and the fact that the exhaust will be hitting the tethered stages, we have real problems. Even if this worked there is still a problem with pointing the rocket at the correct initial angle. Before the first motor is ignited the tethered stages will hang directly below the first stage due to gravity. When launching from a balloon at 100,000 feet the optimal angle is going to be many degrees from vertical. I'm not sure how this would be accomplished with a tethered rocket.

Dave

It is totally possible to get to orbit without ANY moving parts or vanes or gimbals. Spin stabilization is the only requirement. There are several ways to do that! I don't see any fins but the launcher could spin it up or thrusters.
An optical sensor and electronics would fire an orbital stage when the rocket reaches the right angle during apogee. An inferred telescope could easily discern the earths horizon. The waveform created from the spin would determine the angle to fire the engine.
The final stage is mounted with the nozzle facing forward under the nose cone because of the spin stabilization the motor will fire the engine on a timer exactly halfway around the world (with the engine now facing the right direction) to circularize the orbit and prevent re-entry. Do you get that?

Monroe

That could be a tough one a freebe from Team Prometheus.

Sorry guys my last post was an answer for page one. Did not see page 2!

"One question though: did I miss something? how are they going to steer that thing? I don't see any gimbals/vanes/differential throttling abilities/reaction control system (thrusters)?"

Also the nozzle idea seams sound to me one inside the other with a release mechanism. However don't forget about heat dissipation and take a lesson from Falcon 1.

Monroe

Dave's really sharp about the pendulum fallacy his Quad Pod is Really Cool.

That's nice. But you have two images, please make up your mind How is this launch going to fail?

I wonder, do you have a backup plan if you are wrong? Oh, you will change the username, right

ARCA is silent. Possible, something wrong happened.
I am afraid of big delays, months.

ARCA may be waiting for good weather conditions. However, it seems like today would have been a good day to launch. The weather forecast doesn't look good for the next several days. It could be weeks before they get the ideal weather conditions.

But it will crash in a crazy interesting way. I only wish they'd do it at a low enough altitude so that there would be good video of the sequence.

Something went wrong from the beginning… when they started another project without finishing any of they’ve started before.
I just ask myself why they keep showing in their webpage the same guy, doing the same thing (talking…). When will they show him listening? Well, maybe that’s not part of their PR strategy…



What makes you think they will show something like a total failure?

chandrayaan, you are simplex!

The ARCA rocket will launch soon. There is good weather approaching. Are you ready to change your bets?