Category Archives: Amateur Science

Converting Microsoft Lifecam Cinema HD Webcam for Telescope Use

Before computers, my first love-affair with geekiness was an interest in telescopes and astronomy. For the past few years, I’ve slacked off considerably in my telescope making activities, but every once in a while I see something that piques my interest. Gary Honis has a fascinating webpage that details several conversions of digital SLR cameras and webcams into a form which allows them to be used for astrophotography. I found the following link to be particularly interesting for planetary photography, since the webcam is a reasonably high resolution and shoots at 30fps. For bright objects like the moon and planets, this means that you can capture moments of good seeing, and use them to generate nice pictures. Archived for future perusal:

Instructions for Converting Microsoft Lifecam Cinema HD Webcam for Telescope Use -by Gary Honis.

The camera is actually very reasonably priced (only $54.03 via Amazon).

Moon Bounce Day (Where do I aim the antenna?)

A few years ago when the amateur satellite AO-51 transmitted a beacon message on the 50th anniversary of Sputnik, it was enough to rekindle my interest in amateur radio (which had lain dormant for nearly a decade) and got me working amateur satellites. On April 16, 17 and 18, there is an Echoes of Apollo/Moonbounce day scheduled, which is a celebration of all things radio-lunar. EME or Moonbounce communications has always fascinated me, but has seemed very far out of reach of the small HOA limited antennas that I might be able to deploy. But this year, the radio observatory at Arecibo, Puerto Rico will be active, and its a really, really big antenna. There has been some traffic on the Moon Net mailing list that people have successfully received these signals using smallish yagi antennas, so I think I am going to give it a try.

K1JT posted the predicted hours of operation for Arecibo, so the question became “where will the moon be at that time?” My idea is to tripod mount an 10 or 12 element Yagi and aim it in the rough direction, and try to do some field recording using my FT-817 and a laptop. I was curious as to what elevation I would need, and it would be good to make sure that no buildings obscured my view.

I could have used any of a number of astronomy software programs, or even Google Earth (and Sky) or the Microsoft World Wide Telescope. But I’m a bit of a homebrewer when it comes to calculation, and I like having nice tabular data. So, I rapidly coded up this little python program which uses the PyEphem library:

#!/usr/bin/env python

import sys
import os
import optparse
import ephem
from math import degrees

from datetime import date, datetime

h = ephem.Observer()
m = ephem.Moon()

# K1JT mentioned these as likely times for moonbounce operations
# from the Arecibo Radio Observatory in Puerto Rico...

datetimes = [('2010/4/16 16:45', '2010/4/16 19:30'),
             ('2010/4/17 17:40', '2010/4/17 20:20'),
             ('2010/4/18 18:40', '2010/4/18 21:25')]

# I'm currently in grid CM87ux, which is centered here.

me = ephem.Observer()
me.lat, me.long = ('37.979166666666671', '-122.29166666666666')

moon = ephem.Moon()

print " MOON LOCATION ".center(55, "=")
print ("Observer at %.2f, %.2f" % (degrees(me.lat), degrees(me.long))).center(55, '-')
print

for sd, ed in datetimes:
    sd = ephem.Date(sd)
    ed = ephem.Date(ed)
    me.date = sd
    print "Time (UTC)           Time (Local)            Alt   Az  "
    print "--------------------+---------------------+-----------+"
    while me.date <= ed:
        moon.compute(me)
        print "%02d/%02d/%02d %02d:%02d:%02d |" % me.date.tuple(),
        lt = ephem.localtime(me.date)
        print "%02d/%02d/%02d %02d:%02d:%02d |" % (lt.year, lt.month, lt.day, lt.hour, lt.minute, lt.second),
        print '%4.1f %5.1f|' % (degrees(moon.alt), degrees(moon.az))
        me.date = ephem.Date(me.date + 5 * ephem.minute)
    print "--------------------+---------------------+-----------+"
    print

Running this produced the following table for my home location:

==================== MOON LOCATION ====================
---------------Observer at 37.98, -122.29--------------

Time (UTC)           Time (Local)            Alt   Az
--------------------+---------------------+-----------+
2010/04/16 16:44:59 | 2010/04/16 09:44:59 | 23.8  80.1|
2010/04/16 16:49:59 | 2010/04/16 09:49:59 | 24.7  80.8|
2010/04/16 16:54:59 | 2010/04/16 09:54:59 | 25.7  81.4|
2010/04/16 16:59:59 | 2010/04/16 09:59:59 | 26.6  82.1|
2010/04/16 17:04:59 | 2010/04/16 10:04:59 | 27.6  82.8|
2010/04/16 17:09:59 | 2010/04/16 10:09:59 | 28.5  83.4|
2010/04/16 17:14:59 | 2010/04/16 10:14:59 | 29.5  84.1|
2010/04/16 17:19:59 | 2010/04/16 10:19:59 | 30.4  84.8|
2010/04/16 17:24:59 | 2010/04/16 10:24:59 | 31.4  85.5|
2010/04/16 17:29:59 | 2010/04/16 10:29:59 | 32.4  86.2|
2010/04/16 17:34:59 | 2010/04/16 10:34:59 | 33.3  86.9|
2010/04/16 17:39:59 | 2010/04/16 10:39:59 | 34.3  87.6|
2010/04/16 17:44:59 | 2010/04/16 10:44:59 | 35.3  88.3|
2010/04/16 17:49:59 | 2010/04/16 10:49:59 | 36.2  89.0|
2010/04/16 17:54:59 | 2010/04/16 10:54:59 | 37.2  89.7|
2010/04/16 17:59:59 | 2010/04/16 10:59:59 | 38.1  90.4|
2010/04/16 18:04:59 | 2010/04/16 11:04:59 | 39.1  91.2|
2010/04/16 18:09:59 | 2010/04/16 11:09:59 | 40.1  91.9|
2010/04/16 18:14:59 | 2010/04/16 11:14:59 | 41.0  92.7|
2010/04/16 18:19:59 | 2010/04/16 11:19:59 | 42.0  93.5|
2010/04/16 18:24:59 | 2010/04/16 11:24:59 | 43.0  94.3|
2010/04/16 18:29:59 | 2010/04/16 11:29:59 | 43.9  95.1|
2010/04/16 18:34:59 | 2010/04/16 11:34:59 | 44.9  95.9|
2010/04/16 18:39:59 | 2010/04/16 11:39:59 | 45.8  96.7|
2010/04/16 18:44:59 | 2010/04/16 11:44:59 | 46.8  97.6|
2010/04/16 18:49:59 | 2010/04/16 11:49:59 | 47.8  98.5|
2010/04/16 18:54:59 | 2010/04/16 11:54:59 | 48.7  99.4|
2010/04/16 18:59:59 | 2010/04/16 11:59:59 | 49.7 100.3|
2010/04/16 19:04:59 | 2010/04/16 12:04:59 | 50.6 101.2|
2010/04/16 19:09:59 | 2010/04/16 12:09:59 | 51.6 102.2|
2010/04/16 19:14:59 | 2010/04/16 12:14:59 | 52.5 103.2|
2010/04/16 19:19:59 | 2010/04/16 12:19:59 | 53.4 104.2|
2010/04/16 19:24:59 | 2010/04/16 12:24:59 | 54.4 105.3|
2010/04/16 19:29:59 | 2010/04/16 12:29:59 | 55.3 106.4|
--------------------+---------------------+-----------+

Time (UTC)           Time (Local)            Alt   Az
--------------------+---------------------+-----------+
2010/04/17 17:39:59 | 2010/04/17 10:39:59 | 24.9  78.1|
2010/04/17 17:44:59 | 2010/04/17 10:44:59 | 25.9  78.7|
2010/04/17 17:49:59 | 2010/04/17 10:49:59 | 26.8  79.4|
2010/04/17 17:54:59 | 2010/04/17 10:54:59 | 27.7  80.0|
2010/04/17 17:59:59 | 2010/04/17 10:59:59 | 28.7  80.6|
2010/04/17 18:04:59 | 2010/04/17 11:04:59 | 29.6  81.3|
2010/04/17 18:09:59 | 2010/04/17 11:09:59 | 30.6  81.9|
2010/04/17 18:14:59 | 2010/04/17 11:14:59 | 31.5  82.6|
2010/04/17 18:19:59 | 2010/04/17 11:19:59 | 32.5  83.3|
2010/04/17 18:24:59 | 2010/04/17 11:24:59 | 33.4  83.9|
2010/04/17 18:29:59 | 2010/04/17 11:29:59 | 34.4  84.6|
2010/04/17 18:34:59 | 2010/04/17 11:34:59 | 35.3  85.3|
2010/04/17 18:39:59 | 2010/04/17 11:39:59 | 36.3  86.0|
2010/04/17 18:44:59 | 2010/04/17 11:44:59 | 37.3  86.6|
2010/04/17 18:49:59 | 2010/04/17 11:49:59 | 38.2  87.3|
2010/04/17 18:54:59 | 2010/04/17 11:54:59 | 39.2  88.0|
2010/04/17 18:59:59 | 2010/04/17 11:59:59 | 40.1  88.7|
2010/04/17 19:04:59 | 2010/04/17 12:04:59 | 41.1  89.5|
2010/04/17 19:09:59 | 2010/04/17 12:09:59 | 42.1  90.2|
2010/04/17 19:14:59 | 2010/04/17 12:14:59 | 43.0  90.9|
2010/04/17 19:19:59 | 2010/04/17 12:19:59 | 44.0  91.7|
2010/04/17 19:24:59 | 2010/04/17 12:24:59 | 44.9  92.5|
2010/04/17 19:29:59 | 2010/04/17 12:29:59 | 45.9  93.3|
2010/04/17 19:34:59 | 2010/04/17 12:34:59 | 46.9  94.1|
2010/04/17 19:39:59 | 2010/04/17 12:39:59 | 47.8  94.9|
2010/04/17 19:44:59 | 2010/04/17 12:44:59 | 48.8  95.7|
2010/04/17 19:49:59 | 2010/04/17 12:49:59 | 49.7  96.6|
2010/04/17 19:54:59 | 2010/04/17 12:54:59 | 50.7  97.4|
2010/04/17 19:59:59 | 2010/04/17 12:59:59 | 51.6  98.3|
2010/04/17 20:04:59 | 2010/04/17 13:04:59 | 52.6  99.3|
2010/04/17 20:09:59 | 2010/04/17 13:09:59 | 53.5 100.2|
2010/04/17 20:14:59 | 2010/04/17 13:14:59 | 54.5 101.2|
2010/04/17 20:19:59 | 2010/04/17 13:19:59 | 55.4 102.2|
--------------------+---------------------+-----------+

Time (UTC)           Time (Local)            Alt   Az
--------------------+---------------------+-----------+
2010/04/18 18:40:00 | 2010/04/18 11:40:00 | 25.8  77.7|
2010/04/18 18:45:00 | 2010/04/18 11:45:00 | 26.7  78.3|
2010/04/18 18:49:59 | 2010/04/18 11:49:59 | 27.6  79.0|
2010/04/18 18:54:59 | 2010/04/18 11:54:59 | 28.6  79.6|
2010/04/18 18:59:59 | 2010/04/18 11:59:59 | 29.5  80.3|
2010/04/18 19:04:59 | 2010/04/18 12:04:59 | 30.4  80.9|
2010/04/18 19:09:59 | 2010/04/18 12:09:59 | 31.4  81.6|
2010/04/18 19:14:59 | 2010/04/18 12:14:59 | 32.3  82.2|
2010/04/18 19:19:59 | 2010/04/18 12:19:59 | 33.3  82.9|
2010/04/18 19:24:59 | 2010/04/18 12:24:59 | 34.2  83.6|
2010/04/18 19:29:59 | 2010/04/18 12:29:59 | 35.2  84.2|
2010/04/18 19:34:59 | 2010/04/18 12:34:59 | 36.1  84.9|
2010/04/18 19:39:59 | 2010/04/18 12:39:59 | 37.1  85.6|
2010/04/18 19:44:59 | 2010/04/18 12:44:59 | 38.0  86.3|
2010/04/18 19:49:59 | 2010/04/18 12:49:59 | 39.0  87.0|
2010/04/18 19:54:59 | 2010/04/18 12:54:59 | 39.9  87.7|
2010/04/18 19:59:59 | 2010/04/18 12:59:59 | 40.9  88.4|
2010/04/18 20:04:59 | 2010/04/18 13:04:59 | 41.9  89.1|
2010/04/18 20:09:59 | 2010/04/18 13:09:59 | 42.8  89.8|
2010/04/18 20:14:59 | 2010/04/18 13:14:59 | 43.8  90.6|
2010/04/18 20:19:59 | 2010/04/18 13:19:59 | 44.7  91.3|
2010/04/18 20:24:59 | 2010/04/18 13:24:59 | 45.7  92.1|
2010/04/18 20:29:59 | 2010/04/18 13:29:59 | 46.6  92.9|
2010/04/18 20:34:59 | 2010/04/18 13:34:59 | 47.6  93.7|
2010/04/18 20:39:59 | 2010/04/18 13:39:59 | 48.6  94.5|
2010/04/18 20:44:59 | 2010/04/18 13:44:59 | 49.5  95.3|
2010/04/18 20:49:59 | 2010/04/18 13:49:59 | 50.5  96.2|
2010/04/18 20:54:59 | 2010/04/18 13:54:59 | 51.4  97.1|
2010/04/18 20:59:59 | 2010/04/18 13:59:59 | 52.4  98.0|
2010/04/18 21:04:59 | 2010/04/18 14:04:59 | 53.3  98.9|
2010/04/18 21:09:59 | 2010/04/18 14:09:59 | 54.3  99.8|
2010/04/18 21:14:59 | 2010/04/18 14:14:59 | 55.2 100.8|
2010/04/18 21:19:59 | 2010/04/18 14:19:59 | 56.1 101.8|
2010/04/18 21:24:59 | 2010/04/18 14:24:59 | 57.1 102.9|
--------------------+---------------------+-----------+

From this, I determined that I could probably mount the antenna at a fixed 30 degree elevation, aimed mostly east, and I’d likely (given the width of the main lobe of my proposed antenna) be good to go, without any additional guiding.

Now, I just need to get the antenna constructed.

Launching a rocket with hydrogen/oxygen combustion…

A recent issue of Make magazine had an article about launching water rockets via hydrogen/oxygen combustion: basically an electric current is used to break water into its constituent hydrogen and oxygen, which then bubbles up in the rocket, forcing out some additional water. To launch, this hydrogen is ignited, and recombines quickly into water vapor, but also generates a huge burst of pressure and launches the rocket.

And here was my question: how big of a burst of pressure does it really generate? Is it safe? 2 liter bottles have a burst pressure of around 120psi or so. That’s actually reachable with ordinary mechanical means, and it is pretty easy to understand and monitor: the pressure increases slowly, and can be monitored if necessary by an ordinary pressure gauge.

The chemical reaction isn’t so easy to wrap one’s head around. You actually need to know some physics. Sadly, I’m mostly self taught, so I have to work through these things slowly. A discussion with Michael and Tom over lunch the other day reminded me of the ideal gas law. One mole of hydrogen and one half mole of oxygen combine to create one mole of water vapor. But I must admit: I know very little about the realities of combustion physics.

So, I did what I always did: I googled. And I found this interesting page. It estimates the pressure to peak at around 160psi, well beyond the burst pressure of the common 2L bottle. To keep the rocket from bursting, it is vital then to dilute the reaction by the introduction of ordinary air. The nitrogen won’t combust, and should limit the overpressure.

I’ll have to muddle over the details more sometime, but it’s good reading.

Powering Water rockets with hydrogen combustion

The Science of Water Rockets

There has been a lot of publications lately about water rockets. These are rockets which are usually constructed of empty plastic soda bottles, pressurized by a bicycle pump and launched into the air. I haven’t done any of this, but it sounds like great fun. I even picked up a copy of Soda Pop Rockets by Paul Jarvis, which is a colorful if rather arts-n-craftsy book on the subject. While reading it, I couldn’t help but muse about the physics involved. How do things like diameter of the rocket, diameter of the exhaust nozzle, and the amount of pressure affect the height that the rocket might achieve?

I mentioned this to Loren over lunch the other day, since I know that he has done his fair share of water bottle rocket launches, usually using liquid nitrogen as the propellant. He had a few interesting insights, namely that the nozzle design which is common in ordinary rockets isn’t really useful in water rockets, as water is essentially incompressible. This means that you can use Bernoulli’s equation to compute the force generated. Of course, the mass of the rocket is continuously dropping as water is expelled, but that’s not too hard to deal with in the simulation.

What wasn’t clear to me was that after the water is exhausted, there is still residual air pressure in the rocket, and this pressure is significant and must be dealt with differently since the air is compressible. A bit of research led me to this rather nice website:

Rocket Science.

He has an interesting example of a 2 liter bottle which is pressurized to 100 psi and filled 20% with water. It’s fascinating: the “water burnout” (when all water has left the rocket) occurs only 0.042 seconds after launch, when the rocket has an altitude of only 3.2 feet (!). It continues to accelerate though as the air pressure equalizes. In this example, one third of the velocity of the rocket is obtained after water burnout.

It might be fun to make an implementation of this.

Addendum: Here’s another link to a water rocket simulator.
Addendum2: Another simulator.

Internet Archive: The telescope by Louis Bell

Poking around on archive.org, I found that Louis Bell’s classic work The Telescope was available for download. It is a pretty nice book, well worth reading if one has an interest in astronomy and telescopes. It is part history, part engineering, and part user’s guide. It also includes some great illustrations such as the one below of Newton’s first reflecting telescope. Enjoy!

Internet Archive: Free Download: The telescope.

BookReaderImages.php

HO-68 in SSB mode

I don’t really have the hardware to effectively transmit to satellites in linear transponder mode. To really make it straightforward, you probably would like to have a computer to handle the Doppler tracking and antenna pointing, and a full duplex SSB transmitter (or a pair of ordinary ones). That’s more than I am willing to invest at the moment, but with my little FT-817, you can actually receive these birds pretty easily, using my ever present Arrow antenna and just tuning by hand. So, that’s what I did this morning: here is my recording of HO-68. It begins with a bit of the CW beacon, then shows me tuning around to try to find SSB signals. Sometimes, the tracking is pretty good, but later in the recording, my next door neighbor began mowing his lawn and running a leaf blower, and it was hard to hear (I need to use my over the ear headphones instead of these earbuds I’ve used for FM passes). Anyway, here’s the recording:

2009-12-30-HO68-SSB, recording by K6HX in CM87 using an FT-817 and hand tuning

AlgaeGeek.com

I have a bizarre fascination with algae. There is a lot of science going on with algae for use in food stuffs, in detoxifying industrial waste, and even as food. But my geek-itude is vastly exceeded by Jared Bouck, whose created an entire site about the cultivation of algae. I’m bookmarking this for later fun.

AlgaeGeek.com – Site News


httpv://www.youtube.com/watch?v=RSeHW_tV65k

Addendum: While reading the algae page on Wikipedia, I found a link to this book on identifying freshwater algae in the United States.

An annotated key to the identification of commonly occurring and dominant genera of algae observed in the phytoplankton of the United States

IRIDIUM 33 + COSMOS 2251 = BOOM

It was reported that an Iridium satellite and an “non-functional Russian satellite” collided yesterday. I was curious, so I did a bit of digging, and found out that NASA had reported that it was Iridium 33 and COSMOS-2251. A bit more work uncovered orbital elements for both objects, so I was able to plug in their numbers and determine the location of the collision. A bit more of scripting, and I had GMT generate the following map (click to zoom in some more):

world

According to my calculations, they passed within 100 meters of one another (but my code gives an uncertainty much greater than that.) Each satellite is travelling about 26,900 km/second hour (sorry for the typo, but the math holds). I don’t have the mass numbers for the satellite, but even if you think they are travelling at perfect right angles, each kilogram of the mass generates about 28M joules of energy. According to this page on bird strikes, a major league fastball is about 112 joules, a rifle bullet is about 5,000 joules, and a hand grenade is about 600,000 joules. This collision generated 28M joules per kilogram of mass. Ouch!

Addendum: It’s been a long time since I took basic physics. If you care, you shouldn’t trust my math, you should do it yourself and send me corrections. 🙂

Antenna Design

I’ve been reading up a bit on antenna design, particularly the design of Yagi style antennas, and decided to give it a whirl. In particular, I decided to try to design a Yagi that actually is supposed to work on 137.62 megahertz, to see what is possible. I actually am not displeased with the paper specs for the resulting four element 137Mhz Yagi. I designed it using the suite of programs written by David Kirkby, G8WRB. Here’s the resulting pattern at the design frequency.

Pattern for a 137Mhz 4 Element Yagi

Here is the specification for the resulting design…

NOTES Optimised with the genetic algorithm
FREQUENCY 137.620000
MIN_FREQUENCY 137.000000
MAX_FREQUENCY 138.000000
STEP_FREQUENCY 0.020000
ELEMENTS 4
DRIVEN 1
PARASITIC 3
ANGULAR_STEP   2.000000
#DATA_DRIVEN        x         y       length     diameter voltage(r) voltage(i)
DATA_DRIVEN     0.38625    0.00000    1.02524    0.00475    1.00000    0.00000
#DATA_PARASITIC     x         y       length     diameter
DATA_PARASITIC
                0.00000    0.00000    1.08740    0.00475 reflector
                0.95210    0.00000    0.94818    0.00475 D1
                1.78574    0.00000    0.92937    0.00475 D2

And here is the analysis over the entire 137-138 Mhz band.

# Driven=1 parasitic=3 total-elements=4 design=137.620MHz
# Checked from 137.000MHz to 138.000MHz.
  f(MHz) E(deg) H(deg)  R     jX    VSWR   Gain(dBi)     FB(dB)    SideLobes(dB)
  137.000 58.1  79.6  28.25  -4.35  1.790      9.202     26.440      0.000
  137.020 58.1  79.6  28.24  -4.22  1.789      9.205     26.547      0.000
  137.040 58.1  79.6  28.23  -4.08  1.788      9.209     26.650      0.000
  137.060 58.1  79.5  28.23  -3.95  1.788      9.212     26.750      0.000
  137.080 58.1  79.5  28.22  -3.81  1.787      9.216     26.845      0.000
  137.100 58.1  79.5  28.21  -3.68  1.786      9.219     26.936      0.000
  137.120 58.0  79.4  28.20  -3.55  1.786      9.222     27.023      0.000
  137.140 58.0  79.4  28.20  -3.41  1.785      9.226     27.104      0.000
  137.160 58.0  79.4  28.19  -3.28  1.785      9.229     27.179      0.000
  137.180 58.0  79.3  28.18  -3.14  1.784      9.233     27.250      0.000
  137.200 58.0  79.3  28.17  -3.01  1.784      9.236     27.314      0.000
  137.220 58.0  79.3  28.16  -2.87  1.784      9.240     27.371      0.000
  137.240 58.0  79.2  28.16  -2.73  1.784      9.243     27.423      0.000
  137.260 57.9  79.2  28.15  -2.60  1.783      9.247     27.467      0.000
  137.280 57.9  79.2  28.14  -2.46  1.783      9.250     27.505      0.000
  137.300 57.9  79.1  28.13  -2.33  1.783      9.254     27.535      0.000
  137.320 57.9  79.1  28.12  -2.19  1.783      9.257     27.558      0.000
  137.340 57.9  79.0  28.11  -2.05  1.783      9.261     27.574      0.000
  137.360 57.9  79.0  28.10  -1.92  1.783      9.264     27.582      0.000
  137.380 57.9  79.0  28.09  -1.78  1.783      9.268     27.582      0.000
  137.400 57.8  78.9  28.08  -1.64  1.784      9.271     27.575      0.000
  137.420 57.8  78.9  28.07  -1.51  1.784      9.275     27.561      0.000
  137.440 57.8  78.9  28.06  -1.37  1.784      9.278     27.539      0.000
  137.460 57.8  78.8  28.04  -1.23  1.784      9.282     27.509      0.000
  137.480 57.8  78.8  28.03  -1.10  1.785      9.286     27.473      0.000
  137.500 57.8  78.8  28.02  -0.96  1.785      9.289     27.429      0.000
  137.520 57.8  78.7  28.01  -0.82  1.786      9.293     27.379      0.000
  137.540 57.7  78.7  28.00  -0.68  1.786      9.296     27.322      0.000
  137.560 57.7  78.6  27.98  -0.55  1.787      9.300     27.258      0.000
  137.580 57.7  78.6  27.97  -0.41  1.788      9.304     27.189      0.000
  137.600 57.7  78.6  27.96  -0.27  1.788      9.307     27.114      0.000
  137.620 57.7  78.5  27.95  -0.13  1.789      9.311     27.034      0.000
  137.640 57.7  78.5  27.93   0.01  1.790      9.315     26.948      0.000
  137.660 57.6  78.4  27.92   0.15  1.791      9.318     26.858      0.000
  137.680 57.6  78.4  27.91   0.29  1.792      9.322     26.763      0.000
  137.700 57.6  78.4  27.89   0.43  1.793      9.326     26.664      0.000
  137.720 57.6  78.3  27.88   0.56  1.794      9.330     26.561      0.000
  137.740 57.6  78.3  27.86   0.70  1.795      9.333     26.455      0.000
  137.760 57.6  78.3  27.85   0.84  1.796      9.337     26.345      0.000
  137.780 57.6  78.2  27.84   0.98  1.797      9.341     26.233      0.000
  137.800 57.5  78.2  27.82   1.12  1.799      9.345     26.118      0.000
  137.820 57.5  78.1  27.81   1.26  1.800      9.348     26.000      0.000
  137.840 57.5  78.1  27.79   1.40  1.801      9.352     25.881      0.000
  137.860 57.5  78.1  27.78   1.55  1.803      9.356     25.760      0.000
  137.880 57.5  78.0  27.76   1.69  1.804      9.360     25.637      0.000
  137.900 57.5  78.0  27.74   1.83  1.806      9.364     25.512      0.000
  137.920 57.4  77.9  27.73   1.97  1.807      9.367     25.387      0.000
  137.940 57.4  77.9  27.71   2.11  1.809      9.371     25.260      0.000
  137.960 57.4  77.9  27.70   2.25  1.811      9.375     25.133      0.000
  137.980 57.4  77.8  27.68   2.39  1.812      9.379     25.005      0.000
  138.000 57.4  77.8  27.66   2.54  1.814      9.383     24.876      0.000

This was mostly just an exercise, to understand how the software works. It’s kind of silly to use a linearly polarized antenna for the circularly polarized polar orbiting satellites (3db mismatch), but I’d still be interested in hearing any comments about this design from knowledgeable antenna design people.

Volksat

I keep wondering if the whole KISS principle (a personal favorite of mine) might be sensible to apply more thoroughly. Diane, VA3DB pointed me at a satellite design I hadn’t seen before: a picosat that would carry aerogel ultracaps as well as traditional nicads. It was dubbed Volksat. I think there are lots of sensible and good ideas contained here.

Plan 13, in Python

Well, I’ve made some headway on a project that I thought would be cool to write: porting G3RUH’s Plan 13 Satellite Prediction algorithm to a more palateable language than BASIC. I chose python, and it appears to be mostly working. It reads in the TLE orbital elements (same ones I use in “predict” or “gpredict”) and then allows you to create a bunch of satellite objects, and query their positions over time.

Here’s a screendump of a simple test program that I was running this morning:

Monitoring Satellites Using Python Plan13

Satellites which are above the horizon are marked in bold. They are sorted by elevation. The datafields displayed are elevation, azimuth, latitude and longitude of the subsatellite point, velocity, the Doppler velocity, and the frequency of a signal Doppler shifted from 435.845Mhz (just a value I did to check, since I was using PolySat CP3 at the time, which has APRS telemetry downlinked on that frequency). The code requires some additional cleanup, and once I have it all ready to go and documented, I’ll make it available. I think it will have a lot of uses.