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Using WOD graphs in class

PostPosted: Fri Dec 06, 2013 4:51 pm
by g0mrf
Hi all.

I've been looking at the graphs available in the WOD and have created some examples of how information about FUNcube can be derived from the graphs.
For example, the following fits into the UK yr9 - yr 11 (14 - 16yrs) Physics/maths. - Sorry to copy and paste, but this was part of a note sent to a colleague who wants to organise a 'gifted and talented' satellite activity.
Interestingly, there was more interest in the internet availability of data, rather than direct reception in the school field. - Seems that direct reception may need to be done in a small group
whereas there are no limits on numbers for a classroom activity with a demo (globe and model) some video and audio clips and a laptop based investigation. (personally I think the cold British winter put them off)

.............The live data changes as you watch, but it stores the last 104 minutes as whole orbit data. –As below.

It could be possible, perhaps with a model of the satellite and a globe to visualise what’s going on 600km above us, to create a class exercise. We could give them a graph or CSV file and after a suitable introduction, get them to interpret the data from a graph. It would show how telecommunications and graph plotting is invaluable to ‘space science’. We do have recordings of the satellites telemetry downlink to listen to and can put that into a program that displays the data in the recording. Also, we can put text messages into the satellite on request, so if the students look at the live data they could see. “Hello Mr / Miss xxxxx and the students at xxxxx school, London UK” or something similar (200 character limit per message)

For example: This is a graph of data received in South Africa this morning, but available a few seconds later via the internet.

WOD graph 5_Dec_13.jpg
WOD graph 5_Dec_13.jpg (49.64 KiB) Viewed 6721 times

This graph shows total current from the solar panels (black) and the temperature of a chrome plated bar of Aluminium mounted on the outside

of the satellite (Red). The X axis is time from 0 to 104 minutes. New data would appear at the right end of the graph.

The graphs are available as downloadable jpg or pdf fles. The data is also available as a CSV file, so the students can plot on Excel.

What can you learn from the graphs?

1) From the ‘photo current’ graph in black, can you see when the satellite is in the Earth’s shadow (eclipse)?

The satellite is in the sun from t= 0 – 42 minutes. It then passes into eclipse. - Solar panel current drops to zero

2) How long is the satellite in eclipse? - Data is taken at 1 min intervals. There are 35 samples of current at zero, so 35 minutes is spent in eclipse.

3) When the satellite is illuminated its temperature increases. Does it reach equilibrium? – Yes. At t= 30 minutes the temp settles around 26 degrees.

At this point, the amount of energy absorbed by the spacecraft equals the amount of energy radiated into space.

4) Why is the temperature curve in eclipse smooth, but ‘jagged’ when illuminated by the sun?

In eclipse heat energy is lost by radiation in all directions. But when the satellite Is in the sun (most visible between t=30 and 40 minutes) the

metal bar has many small variations in temperature. This is due to satellite rotation. When facing the sun, energy is absorbed from the Sun’s radiation,

but as the satellite rotates and the bar faces The Earth or deep space, it loses some of its energy and the temperature drops a few degrees.

5) Assuming this graph is repeated each orbit, can you estimate the time taken for the FUNcube satellite to complete one orbit of the Earth?

The red plot of temperature has a value of 10 degrees near the start. It also has 2 samples at 10 degrees near the end of the graph. By counting the

samples between repeating points we can measure the period of the waveform which equals the time of one orbit. – The 10 degree samples are at

3 minutes and then at 98 and 100 minutes. If we take 3 minutes and then find the average of 98 and 100 to get 99, we can determine that one orbit takes

99 – 3 = 96 minutes.

6) Given the radius of the Earth is 6371km and the altitude of FUNcube is 630km, can you calculate the velocity of the satellite?

As the satellite is orbiting 630km above the surface of the Earth, the orbital radius is 6371 + 630 = 7001km

The total distance travelled in one orbit is equal to the circumference of the orbit. Circumference = 2 x Pi x radius.

Therefore circumference = 2 x 3.142 x 7001km or 43,989km

So, velocity = 43,989 / 96 = 458km per minute

or Velocity = 43,989 / 96 x 60 = 27,480 km/hr

Or perhaps most dramatically……………. 43,989 / 96 / 60 = 7.63 kilometres every second.

(there’s probably more than the just the above if we think about it)



'Steps' in cooling curves

PostPosted: Mon Feb 03, 2014 12:01 pm
by g0mrf
Hi all.

For a few weeks there have been some questions about the shape of the cooling curves when the satellite is in eclipse.- It seems reasonable that it should just be an exponential curve. Or does it?
I may have a possible answer.

Until today I had only looked at the WOD on the warehouse but since I managed to get my FC dongle working, I can now see the pattern more clearly on the dashboard display
If you look at the central area of the graph below there are 3 steps in the cooling curve. One is very easy to see, while the others are shallower.

Now count the time between each 'step' in minutes......
Answer - 7 or 8. Which happens to be the present rotational rate of the satellite.

Capture bumps.JPG
Solar panel cooling curve
Capture bumps.JPG (37.01 KiB) Viewed 6634 times

The reason the steps are so prominent in the central area is because the satellite is near the equator.
At that point the attitude control (magnet) keeps the X and Y panels in parallel with the surface of the Earth. - The satellite's attitude follows the magnetic field lines of the Earth.
As the satellite rotates, the panels turn away from deep space and face the planet, which is an infra red source at about 290 Kelvin. Because of this, the panels radiate or absorb energy at a different rate, so the slope of the graph changes.

The steps above and below the central one, have a different slope because the satellite is no longer near the equator and the panels now 'see' part of the Earth but also partly deep space.

Sound reasonable?


Re: Using WOD graphs in class

PostPosted: Tue Feb 04, 2014 3:10 pm
by wa8sme
I am going to go out on a limb here and state from what I have observed, the slowing rotation rate of the FC seems to have turned around and the bird is spooling back up:

Improving Rotation Rate.jpg
Improving Rotation Rate.jpg (35.22 KiB) Viewed 6616 times

A couple of days ago (Jan 30-31), I observed the minimum rotation rate at around 8.5 minutes/revolution, then there has been a steady increase to 7.4 today. It is kind of difficult to capture the rotation rate from the data since it is so slow, but I think the trend is pretty consistent now.


Re: Using WOD graphs in class

PostPosted: Wed Feb 05, 2014 5:32 pm
by g3vzv
Hi Mark,

Thanks for your observations and for the fine graph...your views agree with yours...what we are not sure is - "what will happen over the next few days/weeks." We are not at all certain so would appreciate any ideas:)

Exciting times ahead but lets hope not too exciting...



Re: Using WOD graphs in class

PostPosted: Thu Feb 06, 2014 12:03 am
by wa8sme
Hi Gram,

I am just "hanger flying"...what I think is going to happen. I anticipate that the bird will slowly spool up until such time as the rotational force is equal and opposite to the braking forces of the hysteresis materials. At some point the rotation rate will stabilize at some rate (until the next thing that bumps into the bird).

Could you fill in some configuration details? I know that two of the vertical support members (the cube corners and part of the MSE) are anodized metal, and the other two are chrome or silver colored, please correct me if I am not interpreting the photographs correctly. My question is are there any other Kapton tapes (of dark and light color) mounted on the cube surfaces to impart some rotational force?


Re: Using WOD graphs in class

PostPosted: Thu Feb 06, 2014 3:43 pm
by wa8sme
Hi Gram,

The signs continue to be positive, the rotation rate this morning was 6.75 minutes per revolution and the MSE temperatures are following consistently.


Re: Using WOD graphs in class

PostPosted: Thu Feb 06, 2014 5:33 pm
by g3vzv
Hi Mark,

Thanks - you are indeed correct. The standard ISIS structure has four machined aluminium parts in the corners of the structure that are exposed to space in flight. Usually they are black anodised I believe. For FUNcube-1 we arranged for two of them to be silver anodised instead. Both have a matt finish. One of the black and one the silver ones have thermistors fixed to the back of them and form the "structure" MSE channels. These support the "panel" MSE strip which are surface mounted. Again they thermistors mounted on the inside/back of them. One is polished chrome plated aluminium and the other is black anodised matt aluminium.

We have no kapton or other colour differences between the faces.

During integration we made a requirement that the wiring between the solar panels and the EPS should be routed so as to prevent any regular torque being created between the array currents and the earths magnetic field.