工程师故事：打造一颗业余卫星(5)

Chips in Space: Design challenges, intrigue and solutions

Steve Bible

We’ve covered a lot of ground in the past seven blog posts. The story had a beginning of an idea (hey, let’s fill a suit with electronics and toss it out of the International Space Station!). Twists and turns (we lost the suit, now what?!). Heroic recovery (that’s a nice aluminum space frame you got there!). And a happy ending (We have liftoff! ARISSat-1 is successfully operating in space!).

With every project large or small, there are challenges the designers face—the unknown. What problems did we encounter, and how did we find solutions? Let’s explore in this blog post some stories of design challenges, intrigue and solutions.

ARISSat-1 was conceived, designed and produced entirely by volunteers. We started with an idea and we called upon people with the necessary talents. Thus, the team grew over time as the project scope widened. There is so much truth to the statement, “If you want to get something done, ask a busy person to do it.” – Lucille Ball.

Sergey Samburov (RV3DR) had the idea, but more than 50 people worked on ARISSat-1. You could say that almost all of the volunteers are technical in some fashion, at work and play: electrical, mechanical, scientists, technicians, information technologists, programmers, and educators. In the words of Phil Karn (KA9Q), we don’t get enough during the day. I like to say that during the day I do what the customer needs me to do, and during the night I do something new I would like to learn.

Early SuitSat-2 Control Panel/Radio/Antenna Concept (from left to right Cosmonaut Alexander Kaleri, Mark Steiner (K3MS) and Sergey Samburov (RV3DR))

I’m sure the other volunteers share my sentiment that, ‘The payment is that you get to work on something that is way cool!’ On a scale of one to ten, this project was an eleven. However, it was no cake walk—it was hard work. Lou McFadin (W5DID), ARISS Hardware Manager, recalls, “Volunteers have great enthusiasm at the beginning of the project. As time goes on, people lose interest or have other obligations.”

Vibration Testing ARISSat-1 (from left to right Lou McFadin [W5DID] and Gould Smith [WA4SXM])

Volunteers did come and go. A project this large and complicated can burn people out. The project will move at its own pace. People do have a life and family. However, for the people who stuck with it, this was an incredibly satisfying experience. Here’s a great story about the camaraderie of the development team by Tony Monteiro (AA2TX), AMSAT Vice President of Engineering:

“The Software Defined Transponder (SDX) first came to life around midnight on April 4, 2009. The development work had been going on for several months, and the team had all gathered at Microchip to integrate the hardware and software for the first time. It had been a pretty intense couple of days and we were all getting a little punchy by then. We were intently focused on getting the Morse-code beacon working. This was to be the first signal generated by the SDX and, when it finally spit out absolutely perfect Morse code, we had high-fives and huge smiles all around. That is, until Lou pointed out that the perfect signal from the SDX did not sound at all like real Morse code; the kind you hear on the air. Without saying anything, I added a few more lines to the software and reloaded the SDX. When run, the Morse beacon chirped like an old WWII AN/ARC-5 tube transmitter, and the hilarious scene of grown men laughing uncontrollably and acting like a bunch of silly kids is one I will certainly never forget. Although commented out of the flight code, you can still find the few extra lines in the CW beacon source file; left there for good luck!”

Hardware went through several revisions. Three to five revisions were the rule. There was much to learn from the prototypes—especially from the hardware fit checks and interconnections. Jerry Zdenek on the camera logic:

“[It was a challenge to get] all the logic gates to fit in the CPLD. The video capture went from being a simple SPI interface to a parallel host port, and then we added image data analysis into it, too. Occasionally, it would just stop fitting for no good reason. I fought it for a while, but we ended up spinning the board to put a bigger, newer CPLD on that was a more flexible architecture.”

Each of the subsystems had a microcontroller and there was much programming—including the iterations over the serial communications links. Here is Jerry again, telling the tale of getting all the code to fit inside the 8-bit PIC16F887 microcontroller on the Power Supply Unit (PSU):

“I had to keep iterating, adding and removing code and data, and optimizing it until it worked. Debugging was fun too, because it's real-time I2C? talking to the IHU running on another processor. There was no debug serial port available on the PSU. So, until the I2C was up and running reliably enough that I could send out debug data over it, I had to use two computers and single-step each processor alternating. The USB logic analyzer would burp and lose the data stream at the worst times, too. Lots of Fun!”

The SDX subsystem, CPLD camera circuitry and the PSU subsystem were all covered in Post #5.

How was it paid for? Volunteers provided their time, work benches, and test equipment. But there are still materials to be bought and travel arrangements—airfare and hotel—for the weekend work meetings and safety reviews with NASA. The answer is much of the cost was covered by AMSAT. AMSAT is a non-profit, amateur satellite research and development organization that subsists largely on membership dues and donations. AMSAT is still taking donations for ARISSat-1 and future projects. Donations can be made from the AMSAT Web site.

Group photo from one of our weekend work meetings (from left to right, Bob Davis (KF4KSS), Jim Johns (KA0IQT), Tim Moffat, Joe Julicher (N9WXU), Larry Brown (W7LB), Phil Karn (KA9Q), Steve Bible (N7HPR), Bill Reed (NX5R), Jerry Zdenek (N9YTK), Lou McFadin (W5DID), and Tony Monteiro (AA2TX))

There you have it, a tale of challenge, intrigue and solutions. It is by no means a fairy tale. This project was hard work—all on volunteer time. And it was not free! What was the payback? The chance to work on an über cool project, work with some great engineers, learn new things, and make new friends. But most of all, to see and hear the enjoyment from people around the world working with ARISSat-1.

Next week, I’ll answer some of the most frequent and interesting questions that engineers have been asking me about this project.