LOHAN lays mitts on second Iridium sat comms kit

We're pleased to announce that the Low Orbit Helium Assisted Navigator (LOHAN) team has got its grubby mitts on a second Iridium satellite comms unit, courtesy of Rock Seven. Click here for a bigger version of the LOHAN graphic Those of you who've been following our audacious spaceplane mission will recall we took delivery …

[David Given]

Live piccies!

I wonder if it's occurred to anyone that, given 4-colour greyscale, you can fit a 25x25 image into a 160-byte text message. (That assumes eight usable bits per character. I don't know how much of the SMS character set is usable.) You'd probably be able to get more with compression, but I don't know of any compression schemes that would work on datasets that small.

That doesn't sound like much, and indeed it's not, it's crap; but it would still let you stream live footage of the ascent (and descent) at the rate of one picture every 10 to 30 seconds. You'd at least get to see the curve of the Earth and see the vehicle attitude. Place the camera properly and you'd get to see whether the aircraft had detached, for example...

[Mage]

Re: Live piccies!

Hmm... 25 x 25 using 4 bit greyscale is moderately useful. If converted to 256 shades and upscalled x300 % it is a little better than simple pixel zooming by x3

[David Given]

Re: Live piccies!

Actually, a bit of fiddling shows that WebP images compress down really, really small. I can get a colour 48x48 image down to 156 bytes. That's got about 20 bytes of fixed size header that would be trivial to strip off. That's at 7% quality so it's fuzzy as hell, but what are you expecting?

If you're willing to use *two* text messages, for a grand total of 320 bytes, you can either increase the quality to 50%, or increase the resolution to a rather fuzzy 64x64 at 20% --- in both cases, in that CHAV thumbnail, you can make out the parachute. That uses twice the bandwidth, of course. What does an Iridium text message cost these days?

Given the CPU in a Raspberry Pi, it would be trivial to write a script that takes a picture and then tries various cwebp options to crunch it down as small as possible before sending.

[daveake]

Re: Live piccies!

Well, we already have the option of sending images over the radio link, and even though we won't have so many radio listeners as usual that will probably still be the best option.

[Parax]

Sounds like all your UK flights could do with a cut-down to avoid the channel in future. Perhaps GPS if no SMS iridium device is available.

[Monkey Bob]

Most importantly...

If there's going to be some ground-based manual kill switch it has to be something suitably Bond-villian-esque, the sort of switch that would look fitting on some instrument panel in an extinct volcano-based lair.

Can it have a cover that you need a key to open?

And red, lots of red. Flashing.

[daveake]

Re: Most importantly...

I like this :-)

[Lester Haines]

Re: Re: Most importantly...

I agree. We need to get a volcanic lair rented for a week and get busy on the abort box.

[Jon Green]

LOHAN shouldn't suck wet caps!

You've got a monster electrolytic capacitor on that module - but wet caps aren't a great idea in near-vacuum; they've a tendency to pop. For space hardware, we don't spec electrolytics, and replace them on COTS hardware with solid equivalents.

If it's being used for power storage and smoothing, which seems likely, you might want to work out a battery-based replacement.

[John Brown (no body)]

Re: LOHAN shouldn't suck wet caps!

You've got a monster electrolytic capacitor on that module"

You're not kidding! 3.0F!!

Are we sure it's a cap? 3 Farads seems awfully big.

[daveake]

Re: LOHAN shouldn't suck wet caps!

It's a super-cap. It's there so the device can be run from USB. When transmitting it uses a lot more than the 500mA that USB can manage.

In our case power comes from some Lithium Energizer cells so the supercap isn't needed.

[John Brown (no body)]

Re: LOHAN shouldn't suck wet caps!

It's there so the device can be run from USB. When transmitting it uses a lot more than the 500mA that USB can manage."

OIC. It's a long, long time since I last got my hands dirty with a soldering iron. "Big" caps were 2200uF and nearly the size of an HP11 ("B" cell" in the stuff I dealt with.

[daveake]

Re: LOHAN shouldn't suck wet caps!

Yeah, I remember at school accidentally blowing up a 5000uF cap. Which I was holding at the time. Fortunately the top of the cap was facing away from my hand, otherwise A&E would have been required! It took some time for the cloud of white dust to settle.

[Morrie Wyatt]

Warranty void if broken

The seal on the side states "Warranty void if broken"

I wonder what the warranty has to say about dropping it from 113,000 feet?

I can also picture the following scenario:

Lester: Hey, I want a new one because this one is not working!

Sales Droid: Sorry, you obviously didn't read the label. "Warranty void if broken."... Next!