Thursday, December 01, 2005

Galileo's Success is due to Redundancy & Flexibility in its Design


Photo Courtesy NASA/JPL-Caltech

Wow! I'm impressed with the Galileo Group's research into the Galileo mission.

Here a picture of the surface of Europa (second closest major moon of Jupiter). Apart from other evidence, this image shows why scientist believe there's an ocean beneath Europa's surface. What do you think it shows?

This may be beyond the scope of the Lego Ocean Odyssey challenge, but its something you may want to think about when you are designing your robots.

The success of the Galileo mission at Jupiter was due to 2 important design elements that everyone should try to plan into their robot designs. Galileo had redundant systems for critical functions and a versatile computer that was capable of being reprogrammed from Earth.

The Galileo mission was designed to send high volumes of data over its high gain antenna from Jupiter. This antenna was suppose to unfold like an umbrella, from its stowed position after the spacecraft was on its way to Jupiter. However, a few of the pins that held the ribs of the umbrella-shape antenna became permanently stuck and thus the antenna could not open. Fortunately, Galileo also had a redundant low gain antenna, but the rate of data sent back to Earth was only a trickle. The comparison is like the slow drip of a faucet to buckets full of data being sent back to Earth.

To make use of this 'slower' antenna, engineers had to redesign the entire mission with this lower data rate in mind. They programmed algorithms to compress or shrink the size of the images without losing too much information. This helped Galileo send thousands of pictures which otherwise would have been impossible. Furthermore, with the high gain antenna, the spacecraft would essentially relay the images to the ground as they were being shuttered. However, this would not work with the low gain antenna. For the low gain mission, engineers made good use of Galileo's tape recorder. Data from the close observations of the Jupiter's moons were compressed and recorded on the tape recorder. Then the data was read out into the telemetry stream and modulated onto the radio signal sent back to Earth. So the tape recorder was essentially a redundant system for handling the data and its return to Earth.

Now, with the tape recorder becoming a vital part of the redesigned mission, we could not let it fail. Our precise navigation requirements for entering into orbit around Jupiter required us to take optical navigation images of Jupiter's moons. But on the final approach to Jupiter, the tape recorder's tape became stuck. I believe it was pretty much like glued to the tape head. Without these images, Galileo's orbit insertion did not meet the requirements needed to stay on our planned orbital tour of Jupiter. Faced with this possibility beforehand however, we came up with a plan to change the first orbit around Jupiter according to the miss distance from our target and eventually reconnect the orbit to the planned tour. A few months after orbit insertion, the engineers were able to figure a way to unstick the tape and get it working again. They had to be very careful since it would have been very easy to break the tape. Luckily, they had a spare tape recorder at JPL to verify the problem, test their ideas on and verify the fix. According to my memory, this problem happened 3 or 4 more times during Galileo's mission.

I won't go on and on, but there were a few other major problems that Galileo experienced. Despite these problems, engineers and scientists were able to overcome them by making use of Galileo's redundant systems and by reprogramming it from many 100's of millions of miles away. When you can only afford to build one spacecraft and send it to Jupiter, you need to provide your spacecraft with backup systems and allow flexibility in the design of its computer and how it interacts with all its subsystems to control the vehicle.

7 comments:

Gabby said...

I was amzed when i read this post.It was very informative.I learned alot from it.

Fred Wright said...

Dr. Antreasian,
I am truly amazed. First of all, the photograph looks like someone spent a couple of hours in PhotoShop doctoring up a photo but then I remeber it from the galaxy somewhere. I lose my car keys around my small house and then I consider that your team has to find a moving target in the solar system! That kind of perspective is tough to wrap your haed around!

The crystal-looking striations make me very curious. I am thinking , "What is that?" They give me a vague feeling that I have seen them before or that I should recognize what they are but I know that is impossible. I wonder if it is frozen metal or stained ice. The possibilites are fun to consider. Thank you for adding it to your text.

I really appreciate the time you take to explain these concepts about the redundancy in the design of Galileo and undoubtably other projects. I have read stories over the years how a system will fail in space and the teams manage to figure out how to do "work around" to get the job done. Now you have given a first-hand account of how multiple-occurring problems were handled by both planning and innovation. Bravo!

Honestly, my biggest concern is that my students actually get what you do. It is so abstract to them that when you say "many millions of miles" and other comments like that, they just nod and go on. I am really going to have to focus on your postings. I think I may have to create additional lessons just for your posts.

I have read your post over and over. It is just facinating and I feel privileged to have you contribute to our tech blog. You wrote you had a reservation about how your comments might not be appropriate, I assure you they are dead on! We can not neccessarily build in redundant systems per se, but planning strategy and having a back-up plan at different levels is exactly what we need. I guarantee the whole team will stop and consider how to best take advantage of the flexibility and redudancy concepts you have put forth here. We are in your debt.

We will post some examples this week to share.
FW

Dr. Antreasian said...

I should have pointed out the scale of the Europa surface picture: the area shown is about 34 kilometers by 42 kilometers (21 miles by 26 miles) and one of the largest 'structures' is about across 13 km (8 miles). The surface of Europa is extremely cold, but this picture shows evidence that Europa may have an internal heat source at its core due to Jupter's massive gravity pulling and tugging on it. These structures are very similar to things seen on Earth from airplanes or from space. So that should be enough clues to give you on what scientists think it shows.

Nicholas719 said...

I am not sure, but I think that the picture you posted shows streams and bodys of water that might have existed on that planet. I would also like to say that I found your post very interesting and informative.

Daniel said...

Wow, Dr.Antresian! I am amazed of your success with the Galileo project. I can guess that you are proud!

By the way, that is a very strange looking photogragh! I think that it is some kind of a mixture of elements. Probably a compound. Looks a little like mercury(a very poisonous element), and a mixture of other elemnts. Looks alot like a metal/semi-metal substance.

I hope everybody else understood what you meant by redundency and flexibility. It is basically to be able to do alot of stuff using the same design,and if you were to try to accomplish a mission with ten tries, you are supposed to get there 110% of the time!

Dr.Antresian, thank you for mentoring us! You just can't imagine how much we appreciate your help! I would compare this moment to a dream come true. I hope you helpme toward my path of becoming an engineer when I grow up!

Good Luck to everyone, and Goodbye!

Gary said...

WOW! This picture is amazing. It looks like parts from other robots that tried to explore here. I hope to see more pictures from missions you have worked on!

Robert said...

It's Robert from 719 again. Thank you for this information it will prove very usefull when we are building our robots. I think that the picture shows erotion created by bodies of water that may have existed in the past on Europa.