The Phoenix Mars Lander will land tomorrow. The article below explains Delta's small contribution to the Controlled Descent System testing. Basically, it is a hydraulic brake that allow simulating martian gravity and air resistance. This was done by taking difference the non-linear differential equations from earth and mars and using that to compute the drag on the hydraulic brake as a function of velocity. From the generated motion profile a cam table was made to get the desired motion profile. They had to take into account the stretch of the cable when figuring the altitude. Dennis Ritola did most if not all the math for this part of the test. This project did not use our latest controller so the calculations had to be done ahead of time.
See the article
http://pdf.aiaa.org/preview/CDReadyMADSTC07_1443/PV2007_2537.pdf
The AIAA is the aerospace equivalent of ISA or IEEE.
On page 4 you can see the velocity profile as a function of elevation. Notice the increase in speed at 500 m. This is where the Phoenix is separated from the parachute and free falls until the landing thruster start. The Phoenix must use its landing thrusters to stabilize the probe and control the descent.
This method of testing by using a helicopter and hydraulic brake is new. It gives the other engineers a better idea of how the probes radar will perform as the probe falls. There was a lot of testing even before dropping the mock up probe from the helicopter. This saved time and money later because the helicopter time cost about $2000/hour.
Dennis Ritola, our engineer that co-authored the article ( pages 10-12 ), will attend the landing party at JPL in Pasadena tomorrow evening.
Now lets hope the Phoenix lander lands and doesn't make a crater or it will be a glum party.

Peter;
I only Get one page 1/1 from your link.

Here is the full article
www.vertigo-inc.com/aiaa/AIAA-2007-2537a.pdf

I didn't realize the AIAA article was just a teaser. The full article is on the Vertigo website. Vertigo is our customer who bought the controller, hired Dennis's services and coordintated writing the article.

Note, this is winch or brake control just like the off shore well tethers at a basic level. One application is very fast and requires precise motion control. The other requires coording winches or brakes. The ocean oil applications don't need the precision or speed but but are still challenging in their own way because three or more tethers must be coordinstate.

Interesting !!!
It reminds me our Descent Rescue Device
enabling the controled free fall speed
from up to 300 meter height.
For a short video clip , visit last post:
http://www.hydrocad.blogspot.com/

quote:

Originally posted by Nahum Goldenberg:
Interesting !!!
It reminds me our Descent Rescue Device
enabling the controled free fall speed
from up to 300 meter height.

I am sure the general hydraulics are the same. Difference is the degree of control and the math required to make the motion profile. That is a big difference.