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Big Hopes for Tiny Satellites
shelflife writes: "ST5, according to NASA, will usher in a new era of small, smart spacecraft. Why send a human into space when you can send a computer? And why send something almost as heavy as a UNIVAC if a laptop will do? Compact nanosatellites will have everything you'd want in a full-size, luxury satellite. They will have the attitudinal and navigational capabilities needed to maintain proper orbits, and they will be capable of complex, high-bandwidth communications functions."
This isn't entirely new. There were "microsats" flown in the 1980s, some sponsored by the Amateur Satellite Corp. (AMSAT), and some university sats like Webersat (from Utah).
With today's smaller and more powerful chips, of course, it's a lot easier to do more in a small package.
That would have made Apollo 11 a really boring movie: write(nasafd,"houston, we have a problem",31)
Solar radiation is an extremely serious problem for any computer in space. To be rad-hard, chips need to be made of silicon on sapphire, which means a $1 embedded processor suddenly costs twenty thousand dollars. This is not material cost, it's because the economies of scale in production of terrestrial processors are what drives the cost down. Nobody can afford sapphire RAM banks, and thus memories get a flipped bit per orbit, in general. The only way they keep working is that there is a "washing" process that scans memory and does ECC correction continuously. Shielding is simply too heavy to be practical (send up a lead-clad satellite, and your rocket becomes 10 times as large to boost the weight).
Because it's available in sapphire and is flight-proven, the microprocessor of choice for controlling satellites is the 1802. Remember the RCA Cosmac Elf? Most of you weren't born when that was a popular hobby computer
I was surprised to find that the Phase 3D satellite boots up with no ROM. Hardware loads RAM directly from a radio modem. They couldn't afford a ROM they could trust.
Heat is a problem, too. Heat sinks don't work so well without an atmosphere to carry away heat. You have to pipe heat around with heat-pipes filled with a phase-change gas, and then radiate the heat away.Bruce
Bruce Perens.
Why send humans? Because there's more to life than just knowing new things. We're an expansive race, and for better or for worse (in my opinion for better) we need to grow. Robots, while they can give us a lot of information, are no substitute for actually being there and experiencing it for ourselves.
Narrative
With the growing amount of space detritus, another good point in favour of smaller satellites is less statistical risk of a collision.
This would go both ways -- less risk of debris colliding with satellites, and less risk of a rogue satellite colliding with something else. The odds are minimal anyway, but it can't hurt that much.
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It's called Brilliant Pebbles, guys. Sheesh!
OK, they mentioned funding is a consideration in the development.
A complete fluff piece.
Larger satellites tend to be plagued by little dints and holes in their solar sails because of these flecks of paint and whatnot. Smaller satellites would be harder to hit (because there's less volume up there in the first place,) HOWEVER the greater density of the devices could make a single unfortunate hit rather catastrophic because it could knock a whole bunch of things out at once.
It's like of like an ultra-powerful shuttlecraft compared to a borg cube. Small centralisation versus big generalisation. Comments anyone?
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Lower launch cost.
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Cheaper makes for cheaper still
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Smaller is simpler is more reliable
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It's much cheaper to scale up on the ground
The current satellite design philosphy is largely to engineer from a reliability-first perspective, which is guaranteed to produce an expensive solution. If satellites were built by consumer-technology companies (Sony, Philips, Dell, VolksWagen) they'd be cost-engineered first (without reliability being at such a premium) - and our solar system would soon have another planet with a ring round itRocket cost proceeds geometrically as payload size increases only linearly, so big satellites are much more expensive to launch than are smaller ones. Build a satellite small enough, then there's a real chance it can be put into orbit by an ambitious amateur rocket.
If a satellite is cheaper (by which I mean total cost = system cost + launch cost) then you're more able to throw it away and replace it. The more inclined you are to throw it away, the less you worry about its maintaining an orbit - in the extreme case you don't build in any altitude maintainance and only gyroscopic attitute maintainance - then you don't need orbital control jets (and fuel, and all the associated systems) - so your satellite becomes cheaper and cheaper yet. So the satellite size reduces and reduces until its stopped by another parameter (e.g. mass of electronics, transponders etc.) which doesn't shrink in this way.
As we said, smaller satellites don't need as much (or any) orbital maintainance equipment. That's one of the parts of a satellite that's most likely to fail (and thus leave the satellite useless because its pointing the wrong way). If you can get the platform + payload cost down far enough, it'll be cheaper (and more reliable) to launch 10 cheap sats than one delux biggie.
Sure, making a small satellite makes for poorer signal strength, but ground-based equipment (dishes, antennae, amps etc.) scale with a much flatter geometric curve than do the same improvements in orbit (when you've spent all that money shoving them up the gravity well). If the VLA can detect "a cellphone at Saturn", a bigger dish here can detect a cokecan in LEO.
## W.Finlay McWalter ## http://www.mcwalter.org ##
Why not just send the shuttle by to snag 'em with a big butterfly net and bring 'em home?
I see even classic Slashdot is now pretty much unusable on dial up anymore.
While it seems like a "cool" idea on the outside, it probably isn't. There are at least two problems I can think of, off the top of my head, as to why microsatellites would be a Bad Idea (tm)
First and foremost, tracking. Suppose your microsatellite fulfills its useful lifespan, and dies, like so many other satellites....Without any means to communicate, the object is too small (and its irregular orbit too unpredictable) to be reliably tracked from the ground. Your microsatellite now becomes a big danger to other spacecraft, and other satellites, as it joins the ranks of tens of thousands of other pieces of other untrackable space junk.
Secondly, suppose you to manage to get a microsatellite up into orbit. You're an amateur, of course, which means you arent really aware of the orbital paths of other satellites. It might just be a matter of time before your little science fair project interrupts communication to half a continent due to the radio noise it gives off from a poor design meant to maximize for space, and not function.
I think we'd be wise to leave space for the professionals and be content with ground-based communications like shortwave packet and slow-scan TV.
Cheers,
Bowie J. Poag
By coincidence, I happen to both be a grad student studying IC architecture and living about 20 feet from someone working on rad-hard space electronics.
:).
It turns out that the situation isn't quite as grim as the scenario you've painted.
Solar radiation is an extremely serious problem for any computer in space. To be rad-hard, chips need to be made of silicon on sapphire, which means a $1 embedded processor suddenly costs twenty thousand dollars.
Silicon-on-insulator chips are used because they aren't vulnerable to latch-up (triggering of parasitic SCR structures formed by the many regions of doped silicon in conventional chips). However, there are other approaches to dealing with latch-up.
A common approach is to just add enough substrate contacts and apply design rules conservatively enough to ensure that latch-up currents won't be immediately destructive, and to power-cycle the chip either on a regular schedule, or when you see a huge current spike, or both. Powering down the chip turns off the SCR, and when you power up, everything's fine again.
On the flip side of this equation, SiOI is slowly becoming more common. There was a Slashdot article about IBM rolling out a SiOI process a while back; while plain silicon is still cheaper, I doubt you'd be looking at a factor of 10,000 price difference. The main problem with spacecraft electronics is that any custom chips will be fabbed in very low quantities, so you don't get the economics of devoting a wafer run to them. This is true whether they're rad-hard or not.
Nobody can afford sapphire RAM banks, and thus memories get a flipped bit per orbit, in general. The only way they keep working is that there is a "washing" process that scans memory and does ECC correction continuously.
You get noise events affecting the processor's activities too. You can get around this either by running two processors back-to-back with HA hardware to compare outputs, or by living with occasional errors and resetting the chip every so often. An expensive solution isn't necessarily needed
Also, using SiOI doesn't save you from these noise events. It's only useful for latch-up. An ionizing event could still cause conduction through gate oxide or do any of a number of other fun things that cause errors.
Because it's available in sapphire and is flight-proven, the microprocessor of choice for controlling satellites is the 1802.
Actually, rad-hard 386 chips have been standard for many applications for quite a while now.
Heat is a problem, too. Heat sinks don't work so well without an atmosphere to carry away heat. You have to pipe heat around with heat-pipes filled with a phase-change gas, and then radiate the heat away
Heat is indeed a problem, but you can get away with using the spacecraft structure as a passive heat sink if your electronics are low-power enough. This is a common trick, because you're on a limited power budget and want low-power electronics anyways. That way you only have to worry about craft-wide climate control (well, that and instruments that require very stable temperatures).
It's an interesting field, in any event.
I know a few of us have long dreamed of the stars. The riches beyond our grasp. Sure, we can find a few more facts with a computer, but we can never have the same satisfaction as we would have had if we sent a person.
I'd like to [mis?]quote a line from the movie Contact: "This is so beautiful...words cannot describe...they should have sent a poet."
Ponder that for a while. And no CmdrTaco, the poem-producing engine you wrote doesn't count!
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They talk in this article about flying a bunch of small telescopes in formation as a surrugate to HST. This is _rediculously_ complicated. I have been at conferences where they talk about plans for the Terrestrial Planet Finder: a giant telescope array that will be space-based and fly in formation (slated, very optimistically, to fly in 2020). Just keeping the _distances_ accurate is hard enough, much less keeping all the instruments in the same plane. At least for Astronomical applications, these minis aren't going to replace the bigger guys any time soon.
I couldn't tell if you were experimenting with poor-man's cryogenics or looking for the orange sherbet.
Microsats would be cooler if there were cheaper ways of getting them into orbit. Even if you get the bird's weight down to as little as possible you still need a deployment module. Then you've got this thousands of pounds of rocket to get a little bird into orbit. Your launch cost will still be in the order of a thousand dollars a kilogram if not more (especially if your rocket is wasting all of its power getting a tiny 100kg bird into orbit). Nearly all of the work being done at Marshall SFC has to do with the reduction of cost with any and all ground launches including getting birds in the air for alot less than they currently cost. They changed their site around or I'd put some useful links from there like the magnetic linear accelerator. It looks like a fucking brochure now. Maybe if a couple of us donate ten bucks to them they'll put some useful information back there. One can only dream I suppose.
I'm a loner Dottie, a Rebel.
Now there's an amusing thought: astronauts waking in the middle of the ship's night to the clunking of dozens of microsats on the hull. Like a hailstorm in an automobile. *thump thump clunk thump* "What's that noise?" "Aww, just a couple GPS birds. Nothing to worry about."
In actuality, it's pretty hard to hit anything in orbit. There's a whole lot of space out there, and not a very large volume of space junk. And, at least for spacecraft which are still in the middle of their useful mission lives, the orbit of everything up there is calculated. I'm sure there is even a repository or tracking agency for random space debris. Collision avoidance has got to be largely a planning matter (adjusting the Shuttle's flight plan so its orbit never intersects with known random space crap).
I wonder...does the Shuttle even have a search radar operating, to watch the space around it for navigational hazards? I've never heard of such a thing...
The page says that the satellite is the size of a birthday cake, and also that it is "42 centimeters (17 inches) across . . . weighs about 21.5 kilograms (47 pounds)". I don't know about you, but on my last birthday I didn't get a cake that big ;-).
More seriously, this is cool stuff. My favorite item from the list of new technologies is the "electrically tunable coating that can change its properties from absorbing heat when the spacecraft is cool to reflecting or emitting heat when the spacecraft is in the sun by applying electrical power". When you look at conventional ways of managing heat on a spacecraft (such as large and heavy radiators on the Space Station), this is pretty exciting.
somewhat off topic, but this sort of idea has been around for a long time, have a read of rodney brook's paper "Fast, Cheap and Out of Control: A Robot Invasion of the Solar System" [www.ai.mit.edu] (Journal of the British Interplanetary Society, October 1989).
similar ideas, but with robots. v