Re: [Paparazzi-devel] question about paparazzi on sounding rocket

[Chris Gough]

Wow Bernard.

Do you use civilian GPSs in those rockets? MEMS IMUs?

Chris Gough

On Tue, Feb 14, 2012 at 10:34 PM, Bernard Davison
<address@hidden> wrote:
> Hi Florin,
>
> Sorry I haven't had chance to read this whole thread yet... But I will do.
>
> There is a currently active development effort to improve the hardware for
> use in sounding rockets.
> The rockets that I work with pull >70Gs and can get up to Mach 4.
>
> I'll read the rest of this thread and get back to you with more details.
> You might also like to join in on the skype conversation.
>
> Cheers,
> Bernie.
>
>
> On 14/02/2012, at 10:25 PM, Florin Mingireanu wrote:
>
> It works well.
> Here are some photos obtained on a high altitude balloon mission that I
> directed:
>  
> http://www.stiintasitehnica.com/imagini-i-mai-uimitoare-delta-dunarii-i-marea-neagra-vazute-din-stratosfera_803.html
>
> We used the altitude branch of the problem... :-)
>
>
>
> On Tue, Feb 14, 2012 at 1:21 PM, Chris Gough <address@hidden>
> wrote:
>>
>>
>> I believed that for an accurate and fast estimation, the GPS system
>> required ASIC/FPGAs "expensive" propietary architectures, more than one
>> receptor along the fuselage (allowing for measuring Euler angles), etc.
>>
>>
>> I don't know much about that. I thought they used fancy ASIC/FPGA stuff in
>> satellites so they could fix them over the wire when the chips got holes
>> punched through them by very fast dust.
>>
>> I believe carrier-phase correction (in dgps) is more much harder at speeds
>> greater than 1/2 a wavelength per message duration. By Shannon-Nyquist,
>> there's not enough information to disambiguate the direction of the phase
>> error, so you have to mix in more information from somewhere. Maybe that's
>> what fancy dual antenna systems are doing.
>>
>> One off-topic question, is the hardware is not a limit, why some GPS
>> modules are limited to about 20km of altitude? is this done deliberated? and
>> this is not an actual limitation in firmware/hardware? I can not see why the
>> system could work at 13km of altitude and not at 20km, the atmosphere layer
>> is the same, the signal/line of sight should be better, etc.
>>
>>
>> Section 11, part (c)
>>
>> Global Positioning System (GPS) or similar satellite receivers; (1)
>> Capable of providing navigation information under the following operational
>> conditions; (i) At speeds in excess of 515 m/sec (1,000 nautical
>> miles/hour); and (ii) At altitudes in excess of 18 km (60,000 feet)
>>
>> Note the "and"; logically I guess that means one or the other is ok, just
>> not both. I don't know how that works out in practice.
>>
>> Chris Gough
>>
>>
>>
>> On Tue, Feb 14, 2012 at 11:29 AM, Chris Gough
>> <address@hidden> wrote:
>>>
>>>
>>> About GPS measuring Ground Speed and ECEF Position at high velocity, I
>>> really do not know about how the accuracy is affected, Doppler effect, etc.
>>>
>>>
>>> It's not physics, it's firmware. Limits are result of treaties.
>>>
>>> Http://armscontrol.org/documents/mtcr
>>>
>>> See section 11.
>>>
>>> But it seems that you need an expensive GPS module.
>>>
>>>
>>> The firmware/hardware isn't more expensive, only the paperwork. You have
>>> to prove you won't pass it on, among other things.
>>>
>>> Chris Gough
>>>
>>> Héctor.
>>>
>>>
>>>
>>> On Tue, Feb 14, 2012 at 2:34 AM, Chris Gough
>>> <address@hidden> wrote:
>>>>
>>>> > Does the paparazzi code accomodate velocities as large as Mach 2- Mach
>>>> > 3?
>>>>
>>>> I don't know, sorry (don't see why not though, try it in
>>>> simulation...). Maybe someone else can comment on that.
>>>>
>>>> Do I understand you correctly:
>>>>  * the rocket will go directly where you aimed it, it's not actively
>>>> "navigated'
>>>>  * the autopilot is not responsible for maintaining vertical attitude
>>>>  * your instruments require a constant orientation (roll in the
>>>> rocket's frame of reference) during the preiod between boost and apex.
>>>>  * your experiments require position and attitude logging during the
>>>> same flight phase.
>>>>
>>>> Chris Gough
>>>>
>>>>
>>>> > Best regards,
>>>> > Florin Mingireanu
>>>> >
>>>> >
>>>> >
>>>> > _______________________________________________
>>>> > Paparazzi-devel mailing list
>>>> > address@hidden
>>>> > https://lists.nongnu.org/mailman/listinfo/paparazzi-devel
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>> .
>>>>
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>>>
>>>
>>>
>>>
>>> --
>>> Héctor
>>>
>>>
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>>
>>
>>
>> --
>> Héctor
>>
>>
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>
>
>
> --
> Florin Mingireanu
> Romanian Space Agency
> Str. Mendeleev 21-25, et. 5, sector 1, 010362 Bucuresti, ROMANIA
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