various OTs

I have been warned by an Indian project manager working in Bangalore that the Indian culture explicitly believes that miracles happen.

Couple that with other factors common to many cultures, and optimistic underbidding is certain to happen.

The one cubesat company that I know well is making money profiling the atmosphere and maybe doing some shipboard services. Another is doing high-res worldwide synthetic apearture radar, which sounds like a great thing to have.

Radar doesn't need a transmitter; there's tons of RF around already. All it needs is a lot of antennas and a lot of DSP.

Natural language can be a killer. ESA uses English to specify the ICDs (Interface Control Documents), but the language usage is highly structured according to a 500+ page standards document which dictates the structure, sentence construction, glossary and interpretation. Each ICD defines the entire monitoring and control interface between a satellite module and the central computing, and is the primary artefact to specify the supply contract.

I have worked with the main author of this standard on software which is now capable of *generating* the structured English from the logical model (more below).

Every ESA mission in the last decade, and decreasingly so for a decade before that, applied the discipline of Fact-Based Modeling in creating these logical models. FBM is a first-order logic, so all the logical proof theory of Russell and Whitehead applies to ensuring semantic consistency. This has avoided the re-occurrence of expensive in-flight failures which had occurred a couple of times earlier (despite extensive ground testing), which were blamed on the use of industry standard techniques including UML and XML. These have no complete basis in mathematical logic, and so they sometimes allow multiple interpretations. Such core failures could not be fixed by updating the software in-flight.

My "Constellation Query Language" is one implementation of an FBM language that conforms to the draft Exchange Schema, see . Some might be interested in the fact that CQL is itself a controlled natural language (English, with incomplete implementations for French, German, Italian, Spanish and Mandarin). It allows use of *open vocabulary* in sentences that conform to particular linguistic structures which map unambiguously to the underlying logic. The sentence structures and open vocabulary are designed to facilitate correct interpretation by anyone fluent in that natural language, whether or not they are already familiar with the technology being defined. That means they can understand the model, and perhaps detect errors or omissions in the intended behaviour.

What remains now is the further promulgation of *other* tools that comply with the new model exchange standard, so that the supply contracts can start to migrate to using the models themselves, not just the generated English.

Clifford Heath.

Yea...magnetic bearings were old-hat back then (~40+ yrs old). Maybe it is so old,,,'twaz fergotten?

You're thinking of "magnetorquers".

Mike

There is an exception...

Cheers

I don't think that is an exception. AFAIK no-one uses those commercially because of their obvious flaws.

NT

Yes, it was intended to be a humorous comment, m'lud.

However, when this first appeared in Wireless World (how I miss those well-crafted circuit diagrams!) it did give rise to all sorts of crackpot theories involving magnetic fields.

Of course, it's all just a load of expanding balls.

Cheers

it gets in a spin because its balls swell up.

NT

No, that's the official term. I have a friend who has designed a bunch of t hem. There are some tricks, as I understand it. The bearings have to withstand l aunch vibrations (cubesats are often not stuck in the prime locations too..)

It's basically just a motor with a flywheel (and a controller). Change the angular momentum and you generate a torque. Of course you can only go so fa r in one direction before you run out of available RPM so some other method is used to balance that out, such as using the earth's magnetic field.

--sp

I sat through a (moderately) technical presentation by one of the Huawei engineers last week. Very impressive company.

--sp

I wonder if people use hard drives in satellites. That would sure complicate these issues.

he

f them.

d launch vibrations (cubesats are often not stuck in the prime locations

he angular momentum and you generate a torque. Of course you can only go so far in one direction before you run out of available RPM so some other met hod is used to balance that out, such as using the earth's magnetic field.

more weight, slower performance, more power...

NT

Voyager is still going on its original tape(s).

Tim

Nah, just use two of them, RAID 1 mirrored, mounted antiparallel. ;)

Cheers

Phil Hobbs

Use SSD. Hard drives require atmospheric pressure to float the heads. There is a small vent to equalize pressure. They will crash in a vacuum. Helium drives will eventually leak and crash.

SSD in RAID is another idea. Much lighter, faster, lower power consumption, redundant backup. There are many options:

One problem is cosmic radiation flipping bits. ECC could help recover data.

Flash chips are another option. How much storage does a satellite need? Why keep hundreds of gigabytes when you have to download it anyway?

Orbit does not always allow you to download, dish time, pointing of antennas.

Flash .. I think you get a lot of bit errors.

Even on earth at ground level here some cosmic radiation is incredibly strong. Basically the smaller you make storage cells the more vulnerable those are. Same goes for multi-level FLASH, more levels more problems.

Memristors? Those are in the news every now and then, else back to magnetic core memory ;-)

Data corruption is already a problem in normal aircraft systems.