back to article Edge Research Lab to tackle chilly LOHAN's final test flight

We're on final approach for the Low Orbit Helium Assisted Navigator (LOHAN) ballocket mission to touch down at Spaceport America. Since we're relocating Stateside, it seems appropriate that the final high-altitude test flight should be carried out by our US allies at Edge Research Laboratory. As we reported yesterday, we …

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"... a small heater running off a ..."

How much spare Ah capacity do you now have? Must be enough without exceeding the "I've given ye all she's got Cap'n" capacity limit?

On the other hand, trying to add further Ah may exceed the physical constraint "she canna take it Cap'n".

Further low temperature battery/servo testing required I feel.

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We really are going to have to define the "Scottie Scale" as an el-Reg unit of measurement, aren't we?

The question would be whether it's a unit of work, effort, achievement or probability...

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The Scottie Scale

"The question would be whether it's a unit of work, effort, achievement or probability..."

Answer: yes.

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Thermos

I guess it's a bit late in the day to replace the main body of LOHAN with a thermos flask ... ?

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Re: Thermos

Actually, maybe it's not too late. How about, when you have everything in place, you fill the remaining space in LOHAN with expanding polystyrene foam? That might be able to keep LOHAN's innard's from getting too cold too quickly as she soars skywards, no?

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Re: Thermos

Might be time to break out the Apollo 13 (mis)quotes: "... you're telling me what you need. I'm telling you what we have ..."

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The secret is...

... to prevent the batteries dropping below a certain critical temperature. So the batteries powering the heater must be inside the heated enclosure.

It's really a bit of a shame that the internal resistance of the batteries is not a bit higher. If it were, the act of powering the electronics may generate enough heat to keep the batteries warm, or at least slow down the cooling rate!

But according to the specs. Energizer Lithium should be good to around -40 C, so I'd be a bit surprised if they would be a problem for most of the ascent.

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Re: The secret is...

"....most of the ascent"

It's the bit at the end which matters.

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Mumble

http://www.energizer.com/batteries/performance-lithium/ultimate-lithium/Pages/aa.aspx

http://www.google.com/search?q=-40%C2%B0F

IIRC El Reg published an article about someone discussing -40F as being -40C and having to check themselves.

Have Energizer got a dirtydatashitsheet that details performance down at that temperature and 10 degrees below?

IIRC Arrhenius, may not apply, says 10 degrees halves performance.

Or.... Will Energizer get involved and help out with a solution, and perhaps a bit of cash, cough cough?

http://www.energizer.com/batteries/performance-lithium/ultimate-lithium/Pages/ultimate-lithium-partners.aspx

Hmm, no mention of the Rabbit Dildo.

Errr... Elsewhere it would seem you have a battery pack on the main launch platform to keep the rocket motor toasty. Floating a misshaped turd and going bang for buck/weight is there not some chymical method of keeping the internals warm?

Mumble. I believe it is some sort of two part goo that gets hot when you mix it. Not sure about how long it lasts.

Don't forget 'conformal coating'.

Blah Blah Blah.

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WTF?

Re: Mumble

One of us needs more coffee for that to make sense.

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Re: Mumble

Please do let me know how it goes with more coffee.

If it still does not make sense after more coffee then I assume we can conclude that more coffee is not the solution to the sense you were seeking in the first place.

Or perhaps my logic is flawed.

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Pint

Stuff a couple o' these in there

http://tinyurl.com/lz4x2qj

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Re: Stuff a couple o' these in there

Apparently beer works whereas coffee does not.

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Was the freezer test carried out with the electronics sealed inside a plastic container of dimensions similar to the avionics section of the LOHAN fuselage? I would have assumed that even the meager heat given off by both batteries and electronics in such a confined sealed unit would be enough to keep the internal temperature high enough so that external temp would be irrelevant for such a short duration.

If anything I would be worried about overheating.

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(Written by Reg staff) Gold badge

We are indeed worried about overheating, especially the BEC. The flight test will show what's what.

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By my way of thinking it's going to be an interesting race to see how much it cools off as it ascends and how much it heats. As the pressure drops on ascent so too will the majority of the cooling ability but there is that little bright spot in the sky radiating large amounts of heat and it's pretty hard just to keep up with it. Part of the problem is that the internals may be poorly thermally coupled to the fuselage so while the skin gets warm the innards may stay quite chilled.

It might be worth sending up a small test cylinder about the size of the relevant portion of the fuselage painted in LOHAN's colors to get some thermal data ahead of time if you've got a flight planned or someone is willing to let you hitch a ride. Heck, thinking about it now I'm worried about the plastic deforming and jamming up the controls.

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Yeah... Lets do this thing. One more corporate sponsor and it's practically a go.... Have you considered popping off something at Lindsey Lohan.. like a tweet. Maybe she'll drop you a grand to sponsor her namesake :-) (that is a joke... please don't)

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Aerogel and space blanket.

Trying not to harp on this too much - but the physics should not be too hard.

The dominant heat loss mechanism will be radiative. Wrapping the battery pack in a loose layer of space blanket material may well be enough. Whilst, as noted above, the inherent self heating from the internal resistance of the batteries will be small, it will be a contributor. Between them, radiative insulation and self heating could do the trick.

And to reiterate the point. Space blanket only works when it is not touching anything else. If it is covered by some other layer it ceases to work. This is why all the spacecraft you see are covered in wrinkly blanket, or the insides of them are so covered. The wrinkles mean that almost all the blanket isn't touching anything on either side.

A proper aerogel could be used to kill off any remaining convective losses. At the air pressures involved when the air gets cold the mean free path of the air molecules is long enough that an aerogel will essentially have zero thermal conduction. Even a thin wrapping of aerogel, and then a loose layer of space blanket would get you to a point where over the time period of the mission the batteries might simply stay warm all by themselves.

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Less than £1000 to target...

...it's been years in the planning and R&D, and now we've put real money in too! It's getting exciting!

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Energizer Ultimates are specifically designed for low temps (down to -40, F or C), they should be fine with ambient heat from all the gear and waste from the motor jacket. Leave the poor guys alone on this, they have a good solution in hand. Molykote grease on the other hand, sounds like a good idea regardless.

Edit: Hm, this is interesting - apparently there's an "advanced" energizer cell that are NOT the good ones. So long as you're using L9x series cells, you should be golden, or at least as golden as it's possible to be - nothing sold works colder than that:

For many years Energizer only sold the L91 and L92 lithium AA and

AAA cells. Recently (maybe a year or two ago?) Energizer added the

EA91 and EA92 "Advanced Lithium" AA and AAA cells and started calling

the L91 and L92 "Ultimate Lithium" cells. The data sheets for these

no longer include temperature range information. The "Advanced

Lithium" AA cells should be avoided as their price is about the same

as the Ultimate Lithiums, but their performance is significantly

lower at the higher current loads used by most digital cameras.

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(Written by Reg staff) Gold badge

Yes, the "advanced" are not the same beast.

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Cold and colder...

This reminds me of a time (long ago) where I was helping out in the inner workings of a propane powered thermocouple. Due to its position (a very southern point) it was quite cold, and the propane didn't gas out as is normal. To "start" the process the parts needed to be "pre-heated" to make vapor. So, there I was with a propane torch only to find out that it too wasn't up to making vapor. The next step was to get ANOTHER propane torch, and hold it next to a warm object (my body) and use it to heat up the second torch to let it make vapor to heat up the thermocouple(s). I think it worked for a while while things got started. The "backup" power source was much more reliable, being a nice RTG the size of an oil drum that was mostly concrete and lead. Sadly I don't think this solution will work for LOHAN.

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Flame

Pocket warmers

http://www.amazon.co.uk/Magic-Gel-Reusable-Hand-Warmer/dp/B000MU4IJ2

might do the job

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