Picaxe-based Satellite: PongSat-18X

[MFB]

This certainly sounds like an interesting project, with the low noise signal circuitry being especially challenging. My only concern is the count rate forms such a small detection area. Do you have an estimated count rate? Many years ago, whilst at Bristol University, I was involved in the design of instrumentation for a large balloon-borne cosmic ray detector that was flown from Palestine Texas. It used a gas scintillater that was about four metres in diameter and used 25 photomultipliers!

[kranenborg]

The challenges are indeed significant:

- Noise generation: The Maxim low-noise amplification circuit as presented in my last post should be adequate regarding just the amplification part (have just ordered the parts today and will start testing soon) but I think that the real challenge is the noise generation at the input, since a voltage of 12V for the PIN-diode needs to be generated using a PWM signal and voltage quadruple circuit, and there the PWM circuit could be a real noise generator in practice, with the noise generated on-chip in the PWM module (maybe use a PWM frequence as low as possible). Testing will show to which extent this is a real problem.

- Strong depence of PIN diode sensitivity on temperature

- Strong depence of battery voltage on temperature, and consequently also difficulties to generate a 12V diode voltage over a large temperature range, maybe the FVR can be used here (assuming that it is reasonably temperature stable over a large range, needs to be tested as well)

- Like MFB remarked, the small size of the PIN-diode detector area

There is however one single reason why I think this project may be successful in showing that radiation levels will increase with height, and that is that the temperature decreases monotonically below the tropopause and then increases again above it (as is very clear form the NLSE-1 results), allowing results to be compared with the same temperature levels at two different heights. I am thinking of implementing the maxim app note circuit using an 18M2 and using its internal comparators (see my note on using 18M2 comparators in the snippets section of the forum). If this all works after testing at ground level then this will become the NLSE-2 PongSat.

Regards,
Jurjen
http://www.kranenborg.org/electronics

[kranenborg]

Another PongSat application that may be interesting is to investigate whether electrical charge differences occur while traveling the atmosphere. We all know about charge differences in thunderclouds (I guess that it will be difficult to persuade JPAerospace to do a launch directly into such a storm ...) but it seems probable to be that even in clear skies considerable differences in electrical charge levels might occur. I could not find much relevant literature about it, so this somehow seems like an interesting research subject. I came to the idea when considering the new touch sensor features of the PICAXE-18M2 indicating capacity/charge changes: when wrapping the PongSat in aluminum foil both inside and outside the pongsat surface (i.e. creating a capacitor, the inside foil connected to GND of the electrical circuit) and taking a reference value at ground level and recording charge changes for each interval using the touch16 command, one should maybe get an impression? Is this something to pursue or is it total nonsense?

/Jurjen
http://www.kranenborg.org/electronics

[eatabean]

First post on this forum... I am totally new to the Picaxe, but hope to make a contribution here anyway!

I use a device called the Sun and Sky Station, made in the US by Radio Shack, to measure sunlight directly and indirectly, in 4 different wavelengths. The developer, demigod Forrest Mims III came up with a cheap and effective device that is also very stable over long periods of time.

I have not read anywhere on this thread anything about the wavelengths your diodes are most sensitive to. Have you taken this into consideration? Perhaps even more experiments could be performed by simply duplicating the device in different wavelengths. I have also read where the diodes give slightly different outputs, and should be matched and tested.

Another question: do you check your recorded data against a known reference? There should be some sort of zero to calibrate against. Perhaps I have missed this info. I am very impressed with the project and your ability, as shown here. In fact the entire group should be commended!

Perhaps most interesting... I live in Västerås ( about an hour's drive from Uppsala!)
Jim

[MFB]

The current edition of Elektor has an article about using a general purpose BPW34 photodiode to detect radiation. This looks worth considering for a pongsat project...

http://www.elektor.com/uploads/pagef..._uk/index.html

[a.a.mcmahon]

Fantastic use of your time! I'm sure your inspiring a lot of others to do similar projects... as for the extreme low temperatures... a simple handwarmer placed in the device? Just a tiny tiny one near the battery would do, as the extreme cold hits the device that tiny, yet high, thermal energy will be very quickly conducted to the coldest parts of the device. There are some equations (Look at specific heat capacity equations) that can help you determine the theoretical amount you would need. It wouldn't be hard at all to make sure the device is warm but not so much so as to cause damage. Some sort of chemical reaction would be best for this very short experiment. Let me know if you need any more help!

[kranenborg]

Hello,

It has been a few years since our NLSE-1 (Pongsat-18X) near-Space Satellite was launched by JP Aerospace (www.jpaerospace.com) and sucessfully operated, as reported in this thread.

In order to have a cool summer project activity we have enrolled in the upcoming flight, planned for 22 September, now with three Picaxe-based satellites (and two of my sons taking part in their design):

- NLSE-2: Gamma ray detection using a reverse-charged PIN-diode as detector (see also posts #51 and 52 in this thread for background info). Furthermore we want to study the picaxe's behaviour at very low temperatures (internal RC clock drift as compared to watch crystal oscillator, we are open to discussion of more interesting experiments for testing semiconductor behaviour at low temperatures)
- NLSE-3: "Atmospheric sensing" Pongsat with temperature, pressure, tilt/vibration (= wind speed measure)
- NLSE-4: An alternative - fun but somewhat crazy - way of measuring pressure decrease with height using a marshmallow-based home-brew pressure sensor! (since marshmallow is the most popular material flown in pongsats). We have an idea on how to do it, using a lemonade straw, marshallow filler in it, a miniature potentiometer and some stiff wire ... .

The one that is technically most challenging is of course the NLSE-2 (but in a sense also NLSE-4). For the gamma radiation circuit we plan to use a variant of the one presented in the Maxim Application Note AN2236, and our circuit then looks as follows:

NLSE-2.JPG

The circuit front-end part with the PIN-diode detector and subsequent amplifiers IC1a-b and IC2a is identical with Maxim's AN. However, I altered the end stage containing the IC2b stage and IC3 comparator: we use a programmable noise canceler circuit using the Picaxe-14M2 internal comparator, DAC and SR-Latch as discussed elsewhere recently on this forum (will post the final version of the noise canceler in the code snippets section soon). Since the PIN-diode sensitivity is very temperature dependant we include a DS18B20 temperature sensor, and all data needs to be stored in an EEPROM as well. There are a number of questions we have and which we would like to discuss here, all related to the power delivery for this satellite:

1. The circuit above shows two variants: either a 3.6V special Lithium battery (same as NLSE-1 which worked very well) or a solar cell based solution. Since the PIN-diode needs a higher voltage (>=12V) and a sensitive 4-stage amplification circuit is used, I am a lttle afraid that the step-up coverter circuit as shown in the right-upper part of the circuit will generate too much switching noise. Would it still be possible to make it work? (we will start buiding a prototype soon and check it with Womai's oscilloscope) If so we still may get everything into a pongsat if Womai's offer of providing an industry-grade PCB still stands.

2. We may however also opt for a MiniCube version (a new offering by JP Aerospace, see their website), a 5x5x5 cm box which provides for space to fit solar cells on its surface. I guess that this then would allow a very smooth power provision (also shown in the circuit). I expect that due to the high efficiency of solar cells at low temperatures there would not be a need for any MPPT-like circuit for boosting their efficiency. With an effective area per side of 20 cm2 and five areas I would presume that such a setup would provide for enough power. Any opinions here?

Any suggestions, critical remarks etc. are most welcome

Enrollment in JPA's upcoming launch by sending John Powell a mail and one's own PongSat or MiniCube is still possible for other forum contributors as well ...

Best regards,
Jurjen

[kranenborg]

Hello,

We have come so far as to have a working prototype version of the 14M2-based NLSE-2 (radiation detection). We're quite close to the deadline now (has been put forward one week). It will not be seated in a pingpong ball but in a MiniCube instead (which we got for free from JPA due to our NLSE-1 in 2008 being such good propaganda for them, it pops up at several places on their website ...). The included picture shows the prototype circuit, the photodiode and the Minicube (5x5x5 cm), the latter two covered with several layers of black paint in order to avoid light on the photodiode.

The prototype is functioning currently (with Womai's 2-channel DPSCope as an indispensable tool!), but does not have a RF-protective shell around it yet (which is definitely needed because of its extraordinary sensitivity). My goal is to tightly wrap the assembled minicube in aluminum foil all around. The foil helps in blocking most of the light as well.
I have two questions regarding this RF-shielding approach:
1. would one aluminum foil layer be sufficient?
2. Does it need to be connected to GND of the circuit (not so easy actually, but not impossible)

Best regards,
Jurjen
http://www.kranenborg.org/electronics

[boriz]

AARG! It's one of those cubes from Dr Who!