Big Hopes for Tiny Satellites 152
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."
Lots of advantages to being small (Score:5, Interesting)
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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.
Computers in space... (Score:1, Interesting)
Solar Powered airplanes (Score:2, Interesting)
Space-qualified electronics. (Score:5, Interesting)
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.
micro satilites (Score:1, Interesting)
Hey, I'm serious.
Formation Flying (Score:3, Interesting)
Re:Space-qualified electronics. (Score:4, Interesting)
What about latch-up and RAM? Use dynamic RAM and power it down between refresh cycles?
Rad-hard '386? Is it a static version? I was aware that Harris did a fully static '286. AMSAT flew an ARM, and that probably has the most MIPS per mA, but due to the problems with P3D I don't think they've gotten much chance to test it.
Bruce
Re:And... (Score:5, Interesting)
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...
That's a pretty big birthday cake (Score:4, Interesting)
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 [nasa.gov] 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.
small is nice (Score:4, Interesting)
similar ideas, but with robots. v