Since Outer space is such a hot topic here. (1 Viewer)

[Ricardo C]

I meant as a means to getting rid of a stray asteroid

 

[Max Leung]

Part of the job of being a scientist is to handle criticism gracefully and with an open mind.

You want to help solve the world's problems? Become a scientist - IMHO you can do the greatest good for the least rhetoric (skip the name-calling, suppress the ego, and don't take it personally if someone questions your methods and results).

Unfortunately, I wish it were that easy - people tell me they spend more time writing research proposals, chasing research grants rather than doing any actual science. Wasting their time hob-knobbing with the bureaucrats and committees. Blah.

(I'd like to be a scientist, but damn it is too much fun arguing or lurking in public forums. )

 

[Andrew Testa]

Jack,

There isn't much info on the station-based tile repair scenario out there. It's still in development here at JSC by a rather small community, and the test on STS-114 still isn't in any of the official flight timelines. I tried to find a reference to point you to but there's nothing on any of the external websites. Hell, there's nothing on any of the NASA internal websites that I could find either. All the information is in the emails we keep sending back and forth as we try to integrate more disciplines into the development of the maneuver. It'll be a while before it matures to where it becomes official. There are still a lot of questions about the margins on the arm during something like this. A big problem is that usually the attitude control system has to be disabled whever the arm is in use, since the induced loads can cause the joints to slip and the payload to move uncommanded. But this maneuver takes about six hours, and the station must be under active control the whole time. So the arm has not only the mass of the station to deal with but the station's jets are firing too. There are a lot of flight rules that are going to have to be waived or rewritten for this to work. And it HAS to work, since it's a requirement set out by the CAIB before flights can resume. We've got a ton of work to do. IF I can find a graphic I'll post a link. unfortunately I know of a movie file showing the whole thing but it's on an internal server that I can't even get to unless I go onsite.

Andy

 

[Zen Butler]

That was strange

 

[Holadem]

But fun.

 

[Jack Briggs]

Andrew, anything you can and are free to link please do. Here I am, a layperson (albeit an "authoritative" one), and what you describe strikes me as edgy, seat-of-the-pants stuff. Which calls for some genuine right-stuff astronautics and engineering and navigation. I could not be more impressed. Best of luck on the hard work you and your colleagues are doing.

Zen, the situation on which you're commenting has been handled, so to speak.

For those new to HTF and its little subset of space enthusiasts, Julie K is a longtime member who is working as a navigator on the current Mars Exploration Rover missions. Yet she is obsessed with H.P. Lovecraft and with movies featuring flesh-eating zombies. (Meaning there's a certain current film remake for which, given her time constraints, she will have to wait for on DVD. )

 

[BrianW]

I'm sorry, Andrew, but that just doesn't sound possible to me. Before, it sounded like balancing a refrigerator on top of a fence post by nudging it with a two-inch length of burned cigarette ashes. But with the station under active control, now the fence post is mounted on the back of a pickup truck travelling down the highway.

If I may ask, why must the shuttle be attached to the station for this maneuver? Why can't you just use the shuttle's maneuvering thrusters?

Ashley: Yeah, I ducked.

 

[Mary M S]

Andrew; laugh for the day. Just thinking about this sentence. “A big problem is that usually the attitude control system has to be disabled whenever the arm is in use, since the induced loads can cause the joints to slip and the payload to move uncommanded.” Are you talking about being able to flip the shuttle (via its own arm and this manuver itself required 6 hrs to complete?) when docking for station line of sight to shuttle to review for damage and acess for repair? And the shuttle arm joints not built to hold the shuttle to the station during station fired attitudinal jets maneuvers?

I’m lost on the config of the station Vs the shuttle (and the costs of material payloaded up must be astronomical) But if a cradle of some sort could be permanently attached to the station, Loosely based on a in-flight refueling drogue (shuttlecock shaped) which could lock/dock the shuttle at any point on 90 degrees rotational axis of the shuttles centerline to the station. Station jets rotating the entire mass of station and shuttle once docked. Leaving whichever quarter of the shuttle requires viewing right side up to line of site and maintenance. Arm attached to station just used to payload materials to and around the exposed quarter of the shuttle without the inert mass of the shuttle itself hinging on an arm also used for coupling?

Well reading back that’s a whole newly configed space station requiring construction and lift up to orbit, not Lego brick additions that can be delivered and snapped into installation on site. Considering an astronaut turning one screwdriver on one bolt in freefall is such a laborious production.

What terrifying excitement it must be to try to engineer what you need to do with resources available. Best wishes in your current endeavor.

 

[RobertR]

I'm somewhat envious of Andrew and Julie. They work on the kind of stuff I dreamed about doing when I was a kid. My environmental engineering job does have its rewards, though.

 

[Andrew Testa]

Robert,

Thanks. Most of the time it feels like working in the bowels of any other disfunctional government agency, but once in a while you can step back from obsessing about whether the simulator is outputting the correct variable and why you get a different answer than last time, and realize you are standing in a shuttle cockpit mockup with a full projection dome around you, running a live simulation of a station assembly scenario, showing the exact scene the crews see, and yeah it's pretty cool.

Mary,

Yes, you've got it right. It takes somewhere around 6 hours for the shuttle arm to flip the orbiter around, mostly because we have to go really slow, and the move requires some gymnastics on the part of the arm to avoid hitting anything with the orbiter's tail. The reason this is being considered is that it has to be in place before we can fly again. It's definitely an emergency maneuver. You are quite correct the a station based cradle would be more effective, and we have proposed a long term solution involving an L shaped crane attached to the station truss. The truss would telescope out past the orbiter while docked, and the L part would telecope out along the belly of the shuttle, rotating so that it can cover the entire surface area. But something like that wouldn't be ready for a couple of years.

The scenario right now is like this:
1) as the orbiter approaches the station, it does a slow 360 degree pitch-over while the crew photographs the entire thermal protection system.

2) The crew performs the normal activities for the flight while the photos are sent to ground and analyzed for any damage.

3) If no damage found, the orbiter leaves as usual.

4) If damage is found that requires a repair, then at the very end of the mission, when the orbiter would normally depart, the arm flip maneuver is performed, and the station crew goes EVA on the station arm to fix the damage.

5) The shuttle arm lets go of the station and returns.

There are still a lot of problems to be worked out. But so far nothing has come up that's a showstopper.

Andy

 

[Jack Briggs]

Still, it's a breathtaking concept -- one I hope you never have to use.

Back to the Moon To Mars Program: You're right, Andrew. The initiative is not exactly polling well, which explains the reluctance on the administration's part to champion the cause. Without such lobbying, there won't be much support in Congress. But if the program could be sold as an incremental one based on a general-purpose vehicle that can establish the infrastructure for deep-space travel in the longterm and as a replacement for the STS in the nearterm, that might go some distance in helping silence the nonsensical talk in the commercial media about "$500 billion Mars programs."

We could establish the fact of the CEV and, as time and money and political will allow, expand its horizons to lunar flight and beyond. But, first, we call the CEV our "lower-cost replacement for the Shuttle."

 

[Andrew Testa]

Brian,

I completely understand your scepticism. When I was first told about this option I wondered what the tiger teams had been smoking. Then I saw the presentations where no idea was discarded and anything that could possibly be done was considered, and I decided it was crack laced with PCP. This is one of less insane ideas!

It does have a good chance of working though. Years ago in the days of the Freedom station there were plans to use the shuttle arm to dock the two vehicles. In those cases it would be a short straight line maneuver to bring the docking adapters together. In preparation the arm's joint firmware was upgraded to strengthen the wrist joints, which were only speced to handle a 32K pound payload. We also have in our favor the fact that the Russian control jets are very low thrust, only about 27 lbs, so they aren't a problem in usual cases.

Working against us is that it is very easy to backdrive the arm's joints, and even with the brakes on it only takes about 400 ftlbs to slip them. Normally the station can deal with being in free drift for the short times the arm moves payloads, but many of the systems can't function if out of position for 6 hours. The normal docked position is an unstable gravity gradient pose, so as soon as the maneuver begins and the mass matrix changes, the whole system wants to begin rotating to a stable attitude. The station has to keep controlling the attitude at the original position to prevent the uncontrolled motion and keep other systems working. Normally the attitude is controlled by the gyros, which are very benign as far as the arm is concerned. But with the orbiter moving and the inertial properties of the system changing, they saturate very quickly and require frequent firings of the Progress jets to desaturate them. It's these desaturation burns that we are concerned with, and we're just beginning detailed sims to understand how the arm will respond.

As for using the orbiter jets to get into position, there are two showstoppers that eliminate that option. First, the crew flying the orbiter has no view, even through cameras, of their postion relative to the station. If the crew can't see where they're going, they will refuse the operation. They've refused to do simple arm operations in the simulators because they had insufficient views (not refused to cooperate, but said they would not perform the operation on orbit under the same conditions).

Second, the orbiter jets themselves become dangerous to the station. When approaching the station in the normal manner, a mode of firing the jets is used where any command to fire a jet that points toward the station is redirected to a jet that fires to the side and a little bit up. This is to prevent the jet exhaust from washing over the station as the orbiter approaches. This plumimg effect is hazardous due to the toxic reactants which would contaminate the station, and ultimately any crewmember whose suit touched it and brought it inside. It's also hazardous due to the force it applies to the station components. The plume could damage the solar panels or other delicate systems. So the alternate firing is used even though it wastes fuel by dumping most of the force vector to the sides, but has a small upward component to allow control without pluming the station.

Unfortunately, there is no such alternative for the jets which face downward. Should the orbiter approach with it's belly forward, the jets face right at the station and pluming cannot be avoided. So that option is not possible.

As crazy as it sounds, the orbiter arm option is the most workable solution so far, and there are still plenty of opportunities for a showstopper to crop up. We'll see.

I did start out by saying it was pants-wetting scary, didn't I? I wasn't kidding.

Andy

 

[Andrew Testa]

Jack,

That's exactly how the CEV should be sold. If the administration would aggressively sell the incremental and modular concept, and emphasize that each part is low cost and valuable in its own right, there might be less of the pundit blather that focuses only on this being a lunar and Mars mission program. There are so many boats being missed on this it's a wonder there's any room left on the dock.

Andy

 

[Andrew Testa]

Jack,

Yes, but we will have to use it on the very first flight. Not the entire maneuver, but we have to perform enough of it to prove that it can be done. So on our first flight we will be moving the orbiter around with the arm, to what extent we still don't know, but it'll be several motions through several waypoints involving different combinations of translation and rotation. This will be the only time I can think of where I'll be anxious about something we do with the arm.

Andy

 

[Jack Briggs]

Well, here will be a media spin on STS-114: Since Eileen Collins is the mission commander, she will be showing the guys that women too are possessed of the Right Stuff. Makes me wonder what's going through her and her crew's heads when I'm reading about this maneuver. Wow. Impressed.

 

[BrianW]

Andrew, just because I think it's impossible doesn't mean I don't think you can do it. Things are impossible only until they're not.

Thanks for taking the time to answer my question.

 

[Mary M S]

“Since Eileen Collins is the mission commander” JB Very often, Female pilots are known for greater delicacy and less heavy handedness during initial flight training. Arriving much earlier than their male peers to the realization that small inputs are always to be greatly desired over large abrupt inputs which then necessitate major corrections. I’m not sure if this advantage edge of ‘finesse’ tends to evaporate between the sexes after years of seat time. But it would be nice to think each sex has its special talents. Which crewmember is responsible for articulating the arm?

“but many of the systems can't function if out of position for 6 hours. The station has to keep controlling the attitude at the original position to prevent the uncontrolled motion and keep other systems working.”AT

Solar panels powered systems? Oriented to the proper [degree?] for panels to keep providing power?

“as the maneuver begins and the mass matrix changes, the whole system wants to begin rotating to a stable attitude.”AT

“Stable attitude” when orbiter is docked keeps the station with its new mass at the incorrect [degree?] for ISS to properly function? If I’m understanding this correctly it would have been nice if the ISS had been set up ‘for stable’ orient to its (heading? -not the proper word) desired degree as normally maintained by gyros using some sort of adjustable ballast which reflects the mass/weight/inertia of a docked orbiter. Shifted at docking so that the orbiter mass when in residence does not present an “unstable gravity gradient pose.”

Is there any discussion surrounding the future design of CEV, to engineer into the initial unit an allowance for refitting (if more than one CEV are in future constructed) which could accommodate a CEV to CEV docking? Expanding greatly the severely limited resources of currently available options for unforeseen contingencies. (Or) are the payload restrictions on fuel GMW so critically close to the upper envelope for normal mission operations as to not allow for the reserves required for such emergency maneuvering?

“5) The shuttle arm lets go of the station and returns.” And everyone remembers to draw breath again

 

[Rex Bachmann]

RobertR wrote (post #31):


Indeed. All this brings to mind the oft heard pronouncement from the early '70s, "If they can land a man on the moon, why can't they . . . .?" where the most frequent complement to the statement was the naming of some social problem or other, which means that the speaker didn't understand it was an "apple-to-oranges"-comparison. Some "problems" are mainly technical in nature while others have to do with the very nature of the human condition.

Still, if the choice has to come down to fixing or preventing an unviable ecosystem within a century or exploring the galaxy---not that it ever would be so clear cut---I wouldn't hesistate to go with the former. Going into space isn't going to stop the need for better management of our earthly resources, no matter how many "colonies" may be established elsewhere. That's all I thought either of us was trying to get across.

 

[BrianW]

Once Andrew's done with this task, instead of saying, "If they can put a man on the moon..." I suspect we'll be saying, "If they can present the belly of a space shuttle using an articulated arm with 400 ft-lb joints..."

Andrew, is there a specified period of time that the underside needs to be visible to the ISS for inspection? If it's just posing for a few cameras, would it be possible for the shuttle to use a set of compatible thrusters (compatible as in not harmful to the station) to begin a slow pirouette, have the ISS cameras snap pictures of the underside at the appropriate time, and then use the opposing set of thrusters to halt the pirouette after a full turn? This would require thruster fire only when the top of the spacecraft is facing the ISS.

Yeah, I know. It's like my mother asking me why I don't just use bytes with eleven bits in them to get more computer memory. I'm sure there's a good reason, so don't bother answering if it keeps you from your work. All I really know about space station/space ship mechanics I learned from reading Clarke and watching Babylon 5.

 

[Andrew Testa]

Mary,

I don't know who'll be flying the arm on STS-114. Since we'll be trying so many new things that take such a huge chunk of crew time, I suspect that there will be two or three operators working in shifts. You are quite correct about the attitude stability. The very early station designs were focused on a stable position, but in all the redesigns and competing requirements that got lost. But an unstable point is ok so long as you don't add too many perturbations. Most orbiter dockings have little effect on the control system. It's only because we'll be moving so much mass in ways the control system wasn't designed to handle that we now are taxing the ability to maintain attitude.

Almost every system on the station has temperature limits and /or exposure limits that have to be factored into whether we can just drift or not. The solar arrays are a big part of that, since they can't track the sun as we drift. Also the cooling system must be shaded from the sun to radiate away excess heat. Add to this that some pieces can't get too cold or too hot, and you wind up with a large number of systems demanding that the station stay in a particular orientation.

As far as the CEV goes, right now it's just a few words on paper. Nobody know yet what its requirements are going to be, so there's no way to tell what it will or won't be capable of. We have to wait and see.

Brian,

Actually, that pirouette is exactly what is planned. Unfortunately it can't be done uncommanded. The pitch axis of the orbiter likes to twist , and orbital mechanics would quickly move the orbiter away from the station. The means that jets are firing frequently during the pirouette to maintain both position and orientation. The plan now is to perform this at 600 feet below the station, then maneuver up and in front for a normal docking.

You should hear some of the questions my family asks. Sometimes I have no idea where to start. "Okay, you know how gravity likes to pull things down right?, well..."

Andy