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STS-111 Canadarm 2 Enhancements
Question and Answer Board

Tarun frm Gaithersburg, Maryland
In what way is the Mobile Remote Servicer Base System an advantage to the station? What are the current methods to service the International Space Station?
I guess the best way to answer this is to start with the second part of the question, which is how we are servicing the International Space Station right now. Canadarm 2 was mounted on the International Space Station on one anchor point last year, in April of last year, and it has been operating within that radius of action from that anchor point. The Mobile Base System will give it now a new operating base from which it can do business, but not only is it giving it the new operating base, it's got four operating bases from that particular plate, and it's also a movable, transportable base that can move along the truss of the International Space Station. So, it will allow us to move the arm and do operations anywhere along the trust, and not only that, but that the base will also be able to carry payloads or truss segments when it's time to assemble that trust segment in the long run. And the base will also give us the ability as well to do EVA [Extra Vehicular Activity], or support EVA better along the trust segment. It's going to be a platform that astronauts will be able to rely upon to carry out EVAs.
Lee from Hong Kong
Can you explain the function of the Mobile Remote Servicer Base System, and may I have the poster, please?
Well, I can't answer the second portion about the poster, but the functions of the Mobile Base System are really anchored around the main components that we have on that base. I've already mentioned that there are four grapple fixtures, or four points, where Canadarm 2 can anchor itself to on that base, and there's one in each corner, if you've seen the presentation, the picture of the Mobile Base System. So the arm also can double grapple, both ends can be grappled to the Mobile Base System, and later on when we have the special dexterous manipulator, another robot that will do finer tasks on orbit, it can also be stored, will also be stored, on those grapple fixtures. Afterwards, the other components on the Mobile Base System are also some payload accommodation points. These are anchor points, there are two different types: one is a payload, that will be for large payloads, like a truss segment, let's say. And the other one is more for payloads like, would be, science experiments and so on, that would be anchored on the base system while it is in transit from the shuttle payload bay to where it's going to reside on the truss segment. So the base will provide these major functions. And also, another important feature is when payloads are sitting on the MBS, on the Mobile Base System, they can also receive power through the Mobile Base System in order to be thermally conditioned during the time that they will be transited to their intended destination.
Skyuen from Burnaby
How does the most recent modification to the Canadarm enhance the ability of the space shuttle?
Well, I read here that when we talk about the Canadarm is the Canadarm as we know it is the Space Shuttle Manipulator that has been going up with the space shuttle since the early 80's or so. And what I read in your question is what are, the new modification is really Canadarm 2, which is a totally new arm, built by the same company, MD Robotics in Brampton in Canada, but that arm is very much different, because it also brings new functionality. Canadarm 2 can work from either end, when Canadarm on the space shuttle is only anchored down at one location and it is fixed at that point. Canadarm 2 has seven joints, so seven degrees of freedom as opposed to six. Canadarm 2 is about four times as heavy as the shuttle arm, and that's because it now has a redundant capability, because it's going to be on orbit for the next 15 years and will not come back to Earth. When Canadarm 2 was designed it was designed with two motors in each joint, two electronic circuitry in each joint, and that added some weight to the arm itself. Obviously it will also carry heavier masses: Canadarm 2 can also carry the full space shuttle approaching the space station if that was required. And, as I said, Canadarm 2 will stay in space for a long time. It's a little longer, a little wider than Canadarm, but it brings the functionality that is absolutely required to continue to assemble the space station.
Robert from St. Petersburg, Florida
Why does the Canadarm 2 need repair, and what part of it is not working?
Well, first, let me say Canadarm 2 is working, we've got two systems, two redundant systems on board of each joint, or each portion of the arm, so the arm has been functioning very well. We've had an anomaly that manifested itself on the 5th of March of this year and Canada, or the Canadian Space Agency, and our contractor had to look at that, and redo a little bit the software on that channel in order to operate the arm without one joint, and so the arm was functioning on that channel with only 6 degrees of freedom, but the other channel is fully functional and was used to install the S-Zero truss segment during Mission 8A, and the arm has been functioning very well. However this anomaly, should, needs to be fixed, and we believe right now that we might have a short circuit in one of the joints, and this is what will be done during this mission. We're going to launch in mission STS-111 another joint, a replacement joint, and the crew of STS-111 will do a space walk, an EVA, to go, and remove the LEE [Latching End Effector] from the end of the arm, and then remove the joint, and the joint that has an anomaly is the last joint just attached to the end of the arm, or where the LEE is attached, and we'll remove the joint, replace it with the new one, bring the broken one, or the one with an anomaly back to the ground and will be, at that point, be able to determine what the exact cause of the anomaly is, fix that, and make it ready again to be launched as a spare joint if another joint needed to be replaced in the future. The arm was totally designed to be repaired in that fashion in space, because it will never come back to Earth, so that gives us a tremendous capability, this design is a tremendous design, in order to enable us to maintain the arm on orbit. So, we will be experiencing a first maintenance operation during mission STS-111, and we're really looking forward to seeing the arm being totally healthy on the two strings.
Arnie from Hickory
How much weight can the Canadarm handle on Earth?
That's a good question, and it's an ironic question, because, it was interesting to watch Canadarm 2 during testing, being mounted on supporting structures, and the arm components, the booms, were not attached to each other, because the arm on the ground can not sustain any major weights. But, on orbit it is able to maneuver a space shuttle, and that's the interesting part of why things are so different working in space than working on the ground.
NASA's John F. Kennedy Space Center