Party-pooper: Gravity Part 1

As promised, here's some rocket science for ya.

Now, although it's not true of all rocket scientists, in my particular career, I've made something of a specialty out of telling people stuff they didn't want to know, because, well, that's really what safety engineers do. If someone's excited about their work and progress, and it's all hunky dory, safety people don't have to say anything. But, if it's not, safety engineers get the (not surprisingly) thankless task of telling engineers that their baby is ugly and needs some sort of makeover.

That mindset, looking for flaws, either becomes engrained in some of us, or, as I suspect is true with myself, we gravitate to positions like that because we're natural pick-aparters, devil's advocates, skeptics. And, if we have a thick enough skin (I'm nearly a solid), and stick to our guns, we can actually do good things because many a design has been passed over by enthusiastic supporters (aka reviewers) only to fail cataclysmally in reality. Safety folks, if they have a vestige of a spine, help keep that from happening.

But I digress. What I'm here to do is rain on the parade regarding the science of the movie Gravity. Yes, there will be spoilers, so, if you don't want to read them, stop HERE. Now, of course, the first thing people will tell me is to let it go: it's just a movie. After all, I had a great time watching Iron Man III (and the first two Iron Man movies) and the science is quite thoroughly whacked, though just as pretty (I love watching him don/doff suits). I understand what you're saying, I really do, but there's a reason I don't just let it go for Gravity and actually enjoy the Iron Man nonsense, and I'll explain why at the end (which will probably be in a later post).

Gravity is a very pretty movie, with excellent effects, notably the space scenes, and some fairly effective acting. The zero-g footage was particularly spectacular and well-done. When the ISS broke up, the movements involved, including the way the oscillation caused bending moment effects was pretty cool and likely based on some fairly correct physics. Orbital debris is also a significant risk for space vehicles, particularly those in low earth orbit as all the space stations, Hubble Space Telescope and the Shuttle (when it flew) were tied to. In principle....more on that later.

Aside from that, there was almost nothing that was right.

First, I think the movie owes astronauts and the people who train them an apology. The main character, whose name I forgot, is a strong female protagonist and scrappy, etc., which is great, in theory. However, she is also far more ignorant of basic EVA protocol, space information, science, training, etc. than any astronaut I've ever met, including those who were never planning to go EVA. EVA, in particular, is my baby, so let me point out a few things.

• First of all, you DON'T go out spacewalking while nauseous because puking in the suit=dead astronaut. That's why they don't do spacewalks the first few days after launch so they can get acclimatized to the zero g (which sets many a tummy a-flutter), which means, if they were late in the flight, as they were supposed to be, if she were still so nauseous they would not LET her go out and would probably be worried she had something else wrong with her. 
• Secondly, one doesn't send out three astronauts at the same time without desperate need. Sending three astronauts out would have to be for a heckuva a reason (only once, in the entire history of spacewalking, has anyone (US, Russia or China) sent out three spacewalkers at once [STS-49 to try to retrieve IntelSat IV F-3 - which they managed to do]). We don't send out three at once for the very good reason that everything is designed for a pair. There are connections for two suits in the airlock (which has to hold a suit tech and two suited crewmembers and is probably smaller than your shower stall). We don't send out just one person any more either, but pairs have managed to get the job done over and over again.
• If one were desperate enough to have to send out three EVA crewmembers, it certainly would not be to piddle-poo around with a jet pack that looks amazingly like the Manned Manuevering Unit, that stopped flying before I started working in the space industry in 1989 - (flew in 1984 only). And certainly not on a Hubble Servicing Mission, given that those are always wall-to-wall back-to-back EVAs (where, interestingly enough, no one has enough free time to go bouncing up and down on his safety harness - shudder). They do those missions with a staff of four EVA astronauts that go out in pairs on alternating days (because doing EVAs on successive days is tremendously tiring - EVAs are hard physical labor working against the pressurized suit, mean usually 16 hour days [at least], and are taxing to hands in particular). And, on HST, much like they do on ISS, EVA crewmembers work their tails off each EVA and have half a dozen other tasks to do if they miraculously get finished early. 
• EVA crewmembers are drilled continuously and at great length, both on safety requirements, contingencies and actual tasks in the Neutral Buoyancy Lab. Preferably 10 hours in the water for every one on orbit. This is particularly true on something like HST where they EVAs are packed, challenging, gruelling and frequently run into snags.  The crews that perform EVAs (and I know it from personal experience with HST) are smart as hell, driven, capable, knowledgeable and professional. I personally was a little offended on their behalf at the behavior of the crewmembers in the movie.
• And, no, crewmembers do not bounce back and forth on their tethers for entertainment, because (a) that's stupid, (b) they don't have time, and (c) most importantly, it's not safe. Crews count on the tethers to save them if they get separated, but bouncing on that puts forces on them, adds to the risk of them rubbing on something (and failing when you need it) and also imparts forces on the ship you're attached to, which is trying to hold the arm and HST still at the same time. 
• You don't manipulate computer boards on EVA for a couple of reasons, not the least of which is that pressurized gloves don't have that kind of dexterity. The gloves are ballooned out and you have to work against them without being able to really feel what you're manipulating. But, far more importantly, circuit boards are covered with sharp edges, those little solder-tipped spots where ICs poke through. In a suit where glove material can be torn open with anything even vaguely sharp, no way you'd handle a circuit card or slide it into a card cage with all those resultant pinch points. I might add the HST folks that design those challenging EVAs are very cognizant and work very hard to make all the unusual equipment they send up EVA friendly and safe. But, if they had managed to send this contraption, it would never have gotten past the crewmembers or me or any other EVA Safety Engineer.
• When they tell you to come in because there's danger, you do it. No one is more cognizant of how close to death they are than an EVA astronaut. Space is completely unforgiving and there's no second chance if your suit fails catastrophically.
• Even if the airlock wasn't sound (and with the catastrophic damage to the shuttle, I wouldn't trust it either), the system to provide power and oxygen to the suit via umbilical in the airlock might still have worked. Given how low her oxygen was, I would have tried that before setting forth for the station (if that were viable, which it isn't - more on that later). Still, there is an emergency oxygen supply, intended to provide oxygen in case of a "hole in the suit" scenario. Not saying you want to use it, but this is probably sufficient emergency to justify it. It's not unnexpected, with the hyperventilating, that her oxygen went low first, but the CO2 would also also likely gone up since CO2 scrubbing capability and oxygen supply are generally about the same capability.
• As has been noted by others, crewmembers do not don the suit in just their skivvies. They have socks and diapers, and, most importantly, a liquid cooling garment, necessary to keep from dumping a liter of sweat out when they doff the suit (as happened on EVAs before we had the liquid cooling garment). No argument, though, that the skivvies look better on the big screen.
• Orlans, the Russian spacesuit presumably stored in the Soyuz capsule, would be plenty heavy to sink like  stone in water (120 kg), but doffing it, since you slide out the rear swifter than most spacesuits, rather than peeling them off like long johns, still would take five minutes, even if you could get it open in the pressure of underwater.

There's more, of course. I haven't even touched on the orbital mechanics involved, the orbital debris scenario and the issues with communications satellites. Sigh. Still, this should be enough for one post. Several of you are already having your eyes roll into your heads at the stuff I tossed at you. So, next time, how far can you go with an MMU? Not nearly as far as they showed, seriously. 

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The Last Hubble Mission Part 4

I know it's supposed to be a writing exercise on Wednesday but, hey, HST SM-4 is a big topic so I'm continuing. Yesterday, of course, I talked about all the work they had to do to get the complement of instruments up and running, but the instruments are dependent on the spacecraft for pointing, power, communication, data handling, thermal protection and structure. And HST needed a bit of work, too. You can see a layout of the key HST systems here.

First off, there is the long put off battery replacement. HST's batteries have done a heck of a job over the last 18 years. A change in plan on the battery left them with some circuit mismatches (that have been corrected over past flights) but they are slowly but surely degrading now. All the new batteries are also Nickel Metal Hydride, but they are an improved setup and have a nifty little safety feature: an isolation switch.

Then there are the gyros. They've been problems before and HST-SM3 was broken into two missions as a result of an earlier failure. HST can fly and point with two of the six gyros (when it used to require three). The gyros are described as fantastic, but we've had to replace them several times. These new ones are supposed to be new and improved, but one of the units wouldn't fit (Rate sensor units=two gyroscopes) so a refurbished one from a previous mission was installed.

But wait, there's more. There's also the thermal blankets that have deteriorated thanks to the rough environment. HST SM-4 installed a number of New Outer Blanket Layers (NOBLs - because you can't have too many acronyms).

And the last minute problem that manifested only days before the first scheduled launch: the failure of one side of the Science Instrument Control and Data Handling system. We moved to the unused B side, but it was definitely something to fix if we could. Fortunately, this was one of those systems that was designed to be replaced. Be just had to blow the dust off our stored spare (figuratively speaking; Goddard has a great big clean room) and make sure it was still working. And stuff.

Then, it was just a matter of installing a Soft Capture and Rendezvous Fixture on the spacecraft (so we can send a robot deorbiting aide on it for a controlled reentry), wipe the windshield, check the dipstick and give her tires a last kick.

It was a heck of a lot of work, a real challenge, but thanks to some good planning and lots of old fashioned elbow grease, she's in as good a shape as we can manage. Hopefully, she'll be giving us more gorgeous pictures and cool data for years to come.

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The Last Hubble Mission Part 3

So, what exactly did all that hard work buy us on the Hubble Space Telescope?

Today, let's talk about the science instruments.

Well, the Hubble Space Telescope was in pretty tough shape. You can see a layout of the key HST systems here.

NICMOS
The Hubble's science instrument complement included a NICMOS (Near Infrared Camera and Multi-Object Spectrograph). Installed originally on SM-2, an unexpected thermal expansion required the cooler installed on SM-3B. This cooler was a non-trivial task, effectively squeezing a complex system into a space that wasn't expecting anything. The clever and innovative design worked, though.

Unfortunately, a required shutdown for a software upgrade in September of last year still hasn't been recovered as the NICMOS has stubbornly refused to restart for any appreciable time. Another attempt after SM-4 will likely be attempted. This unit was not repaired during SM-4 and its future is uncertain.

STIS
The STIS (Science Telescope Imaging Spectograph) which was installed when the NICMOS was installed, had a recent failure of a 5 volt power supply. One task set (and accomplished) for SM-4 was the replacement of the computer board with the 5 V power supply. An EVA computer board repair was another of those repairs that were never envisioned for the HST. Computer boards are inherent sharp edges and opening the the cover to get to the board required removal of 111 screws - non-captive fasteners.

Now, for those of you that don't know, captive fasteners are generally used for EVA because, even when you remove an item, the fastener stays in place. That way bolts and screws and nuts and what-have-you don't float out into space to return later as projectiles and make sure that all the fasteners needed for a piece of hardware are available during reinstallation.

In order to perform this repair, a special plate was designed that would allow capture of all the screws. Then the board was replaced and a modified cover was installed in the original cover's place, one that required only two levers for installation instead of 111 screws. I think you begin to see the advantages of the work done on the ground to make these EVAs easier. This EVA was performed and tests are ongoing to hopefully allow this valuable instrument, the first instrument to detect the spectrum of the atmosphere of an extrasolar planet, return to work.

ACS
The ACS (Advanced Camera for Surveys) also had failed. Electronic issues on both redundant sides left the ACS with only a single channel and two of its modes unavailable. Since there isn't time to replace the failed electronics, the hope is that the wiring is intact and a new power supply will be tied to the existing system. The intent is to replace four computer boards with new ones. The new boards are pre-installed into a cartridge that will go into the spot vacated by the removed boards. The cartride simplifies installation and the smaller boards are of a new type that can be reconfigured remotely to tweak the system for the best use of the ACS instrument. The integrated circuit board design is the same sort of system planned for the James Webb Telescope.

COS
Replacing the corrective optical package (that none of the instruments currently need) will be a new instrument, COS (Cosmic Origins Spectrograph). Intended to complement the STIS (if the repair is successful), this is one of the more straight-forward EVA tasks as these instruments were intended to be replaced and, in fact, this was installed on HST SM-1.

FGS
The Fine Guidance System (FGS) has been replaced repeatedly and will be replaced with an refurbished and upgraded unit. This unit is not only an astronomical instrument, it is also part of the fine pointing system for the complex spacecraft. It's a tricky and bulky instrument to replace, but it was also designed for EVA and replacement was done with existing tools and procedures.

WFC-3
Finally, the primary camera, the Wide Field Planetary Camera-2 will be replaced with a lovely new instrument, the Wide Field Camera-3, that is more accurate and stunning than the two previous versions. It's a tricky activity to replace this camera, much like replacing the FGS, but it was also designed for replacement and the task was readily done.

So, how much of this science upgrade, repair was completed on SM-4? All of them. The WFC-3 was installed on EVA-1. The COS was installed and the ACS repaired on EVA-3. STIS was repaired on EVA-4 and the Fine Guidance Sensors were installed on EVA-5.

And, hey, that's not even counting all the other spacecraft repairs they did. I'll tell you about them tomorrow.

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The Last Hubble Mission Part 2

Someone mentioned on my first post that protecting the crew was most important but that saving the Hubble Space Telescope was also important - that it's loss would also be terrible.

This mission was a balancing of these two risks and, hats off to NASA and the crew, they pulled it off so that we lost neither one. Given the challenge, and, as taxpayers, we were paying for it, I think it worth while to detail what exactly we bought with this last mission and what kind of shape our telescope is in now.

There was a great deal of work involved so this might take a few posts.

Today: Prep work

I have a quote in my collection from Abraham Lincoln: "If I had eight hours to chop down a tree, I'd spend six sharpening my axe." NASA is generally the living embodiment of this sentiment and never more so than working with Hubble.

The folks from Goddard Space Flight Center figure out the priority of tasks, build the tools and all of the support hardware. Hubble has more unique tools developed than probably any other EVA [EVA=extravehicular activity] project since we landed on the moon. As for the support equipment, that's a pretty impressive feat in and of itself. Not only to we have to safely bring up huge items like replacement instruments and solar arrays, we have to make them so that they can be readily retrieved by suited crewmembers and also cart back the big items we are pulling off to replace - and they aren't always the same size. And, of course, bring all the tools in an accessible way.

EVAs are generally practiced ahead of time in an environment as close to zero-g as we can manage, in this case, the Neutral Buoyancy Laboratory. The actual choreography is worked by Mission Operation personnel who run test after test where the activities are worked on representative models under water (and, yes, safety watches too). In general, one wants to do 10 water runs for each EVA, but Hubble missions can push it even farther, including developmental runs and runs to test various tools thatmight be developed specific to the mission objectives. For instance, on the last mission (SM-3B), they had to develop a special tool to replace the Power Control Unit (which was not designed to be replaced on-orbit) where the connectors were too close together for the pressurized gloves to remove them. So they made a tool to grip them.

If we didn't do the exhaustive (and exhausting) water runs, if we didn't have such responsive and capable folks handling tool and hardware development, these servicing missions wouldn't be nearly as successful as they have been. And some of what the Hubble has accomplished would never have been.

More to come...

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Ah, Thieving Thursday. This time, finally, it's a comment from Relax Max' blog Clarity 2009. Someone asked me about extravehicular tools on a post about a different science experiment. The question was if EVA tools were gold plated to prevent oxidation/binding.

I told the questioner, “no.”. There is gold on the sun visor because it's such a good reflector for a wide spectrum of light, but not any of the tools (they are generally reworked Snap-On tools, often with holes cut into the handles to make them lighter, with special tether points added or made to be pressurized-glove friendly). I have never seen one gold plated (the socket wrenches I have seen are clear anodized - they look like metallic silver). Gold would not wear well. There's a PDF document describing some older EVA tools here.

Now, EVA handholds are anodized yellow or gold so they can be differentiated from handholds that are not rated for human mass and loading (which are generally white or silver - you can tether a load to them but not a crewmember). However, they are not gold plated. EVA requirements can be found here and here.

In fact, most metal surfaces are anodized, alodined or painted to (a) protect against corrosion (which isn't an issue for gold) and (b) reduce overheating in the massive thermal extremes, where a gold or other bare metal surface would be bad. (I had mentioned previously in the same comment thread that cold temperatures were a particular concern for EVA crewmembers because they were less likely to detect a dangerously cold surface by touch than a dangerously hot surface).

EVA tools are cool, and there's a great deal to say. There are only two power tools, the Pistol Grip Tool (pictured) and the Power Ratchet Tool. The rest are variations of hand tools, some standard and some completely new. We have tools for cutting, though those must be handled careful to preclude cutting the suit. Tools must be actuated and have handles large enough that using a pressurized glove is (a) possible and (b) not too tiring. Sometimes tools have holes cut in them to facilitate handling an reduce mass. They must pass stringent dimensional tolerance requirements because of the thermal extremes. Most have tether points or bayonet interfaces or velcro (if not all three).

Seriously, if you're a tool junkie or like neat stuff, pay attention to the next Hubble Servicing Mission. No missions use cooler EVA tools than Hubble Servicing Missions.

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