Reaction wheels and gyros can integrate up speed without limit, so rotational thrusters are sometimes used to reset the gyros now and then. They use up gas or fuel so have to be used sparingly.
Orbital velocity thrusters are a different animal, and need a huge amount of fuel.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Resetting a reaction wheel is quite another matter.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Put graphite in the grease? (They've obviously thought about things like that.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
ISS will probably be abandoned soon, certainly if we kill another crew. It wasted around a trillion dollars to basically demonstrate that space is too hostile for humans.
The outsourcing trend turned out to be mostly bad business. D's tax and tariff changes also encourage doing things here in the USA.
I don't see a lot of engineering innovation happening in China or India or even much in Europe.
Doubt it.
Stock markets are emotion-driven and noisy. That started with spice ships and tulip bulbs. Nothing new there. The long-term outlook for sensible investments has been good.
Some from schools, some poached from competitors, some imported, some developed on site. They will do it. It's a cool place to work for.
I'm hoping they will stay with their core competances and continue to outsource electronics. Big aerospace companies (and national labs, and others) used to have in-house electronic design groups, but haven't replaced them as they retired.
No, you don't sound cheerful.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
That's within reasonable PCB design rules. What's scary will be heat sinking the thing.
It's obviously intended to drive the EPC GaN fets (fig 15) which took us getting some used to too.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yeah, maybe. Or, add a bit of contaminant so the grease conducts. I'd worry about chemical stability of oxide ceramics (zirconium oxide, for instance) in space; it's like a reducing atmosphere, and you're gonna be there for years, and care about microinches of surface finish. Metal should hold up well. If ZrO turns to Zr, though, it's gonna lose the smooth surface.
Insulating bearings will make the Van de Graaf problem worse. Pity you can't use corona points in a vacuum.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Carbon nanotubes!
-- John Larkin Highland Technology, Inc lunatic fringe electronics
ZrO's binding energy is higher than that of Fe.
You might as well consider transmutation of Fe or Zr due to high energy spallation, too, but you'll only be that much further down in the noise. Or Wigner energy. Bulk effects are an extremely small priority. It would have to be in orbit for a very long time indeed.
I don't know that asteroids have these problems after billions of years. And common minerals, like olivine, aren't as stable as zirconia.
Photoemission is the only mechanism with a plausible risk factor -- showers of charged particles exiting a surface, multiplied by the energy of the impacting particle.
There should be ions in there, too, but again, that's a bulk effect manifest at the surface. Sure, it'll roughen the surface, atomically. The surface is already microscopically rough. Drops in the bucket.
I'd worry much more about chemical breakdown of the grease. If it's carbon or silicone based, expect fragmentation and cross-linking. If it can be dry (graphite, MoS2 or PTFE?), that helps, but a purely dry lubricant would only stay in place by van der Waals forces.
Material composition is critical inside a fission reactor, say. But that's not an environment that humans can sit in for years with mainly just an elevated cancer risk. That's an environment that liquifies biological tissue in -- minutes, hours, days?
And that's in the mSv for casual (days-long) missions, comparable to a PET scan, or CT of the more sensitive areas, so as long as you don't make a habit of, say, space tourism, it's not going to affect your long-term risk.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
How about a magnetic design - -no surface-to-surface friction?
They did that already 10-20 years ago.
field emission? photo-electric effect? nanotube brushes?
-- Notsodium is mined on the banks of denial.
That takes enormous electric fields.
Good idea. Plate something with photoemmisive stuff and shine a UV led on it now and then.
Or real brushes.
It's tough to get stuff to work in space. Probably even tougher to figure out what went wrong.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
As I understand, gyros use sealed gas bearings and very thin conductors to drive the motors. Here's some more information (old)
Apparently the new mems gyros would be more reliable:
Apparently some models are super-sensitive and require recalibration due to changes in G due to the moon's gravity.
Hey John, here's an idea to make you the most popular guy on the planet.
Why not call up Elon Musk and propose a joint venture to replace the failing gyros on the Hubble. You can supply the new mems gyros and he can supply the rocket.
There is nothing to replace the Hubble. The photos it supplies have entranced the entire world. We need it.
Your risk is low. You are good at integrating extremely powerful electronics with precise mechanics. You could also get NASA to underwrite your work and hold you harmless in any case of failure. They are good at that.
This needs to be done before NASA decides to de-orbit Hubble. Please give it your utmost consideration. Then do it!
Apart from those two that NRO decided not to launch,
Dunno how they'd launch 'em though.
-- Notsodium is mined on the banks of denial.
Ha, I ran a test with the MEMS with a very precisely controlled temperature to see if I could see correlation with the moon phases... Published that in some related group few years ago. The idea was to replace GPS with an inertia based system. Did not get to see the effect of the moon, but noted daily variations very likely due to chip expansion and board expansion caused by minuscule temperature changes. concluded that I needed a better oven. Then somebody at some university repeated it with a better oven. It is out there can search for the graph, lemme see
The spike is where I opened the box to check some switches... At least when those sats fail I know where to pick up...
Its fun. so many things to get into...
Hubble is about 11T and 13m by 4m. Time spent slewing between objects is wasted so they plan its observing list very carefully. Even so if a transient target of opportunity comes up they want to get onto it ASAP.
Most of the serious so called microsatellites* built today are dustbin sized and around 30-100kg. You can't do that much interesting science in orbit without either a decent sized antenna or a big lens. eg.
If you are launching a toy satellite the size and weight of a good textbook you might just as well spin stabilise it by bulk rotation. Hyperbole means they are called nano satellites (actually sub milli).
Cubesats might be interesting when they get to the stage of being self assembling Lego but for the moment they are fun toy research projects that are relatively cheap for universities to play around with.
The $25 parts cost credit card sized sprites might sometimes be interesting as disposable probes - though the first launch was a failure as they didn't get properly deployed by their parent vessel.
-- Regards, Martin Brown
Jasen Betts wrote in news:pq1a8t$40d$ snipped-for-privacy@gonzo.alcatraz:
The JWST will replace it, but will not have the same speed of maneuverability due to its larger size.
It is worth it to invest in a way to do a repair on it without our shuttle program. I wonder how big each gyro axis unit is. For a mass the size of the HST, They are likely pretty big. Remember the huge IBM hard drives?
Anyway, short of getting up there pretty soon, it will fall hopelessly out of any serviceable orbit. I suppose they could boost it one more time to some higher orbit to give more time to get to it to service it.
On Oct 12, 2018, John Larkin wrote (in article):
I recently read that the root cause of gyro and reaction-wheel failures in space had been uncovered: Electric currents passing through the balls in ball bearings were destroying the bearings, causing premature failure (compared to testing on the ground).
I has been known for a century of electric motor experience that electric currents passing through bearings is a bad idea. (Commutators are not bearings.)
This was a big mystery - nobody could figure out what was different between space and ground, and nobody could imagine where such currents could be coming from. It turns out to be space weather and the solar wind, by a mechanism I have not studied and so cannot explain.
The solution was to use ball bearings with ceramic balls, so no current can flow. Such bearings are catalog items, and have been for some time. It?s just that nobody thought it necessary to pay the added cost.
.My immediate question is why anyone was surprised. Today?s programmers are typically innocent of any hardware knowledge or instinct, and have no idea how the system they are working on actually works.
Joe Gwinn
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