Hack Chat Transcript, Part 1

A event log for AMSAT CubeSat Simulator Hack Chat

Making sure your bird will fly

LutetiumLutetium 12/04/2019 at 21:030 Comments

alan.b.johnston11:58 AM
Hi everyone!

Josh11:58 AM
Hi Alan

RoGeorge11:58 AM
You guys don't have audio?


Dan Maloney11:58 AM
Hi @alan.b.johnston! We'll kick off in just a minute or two

Applied Ion Systems11:59 AM
hi alan, looking forward to the chat!

Spehro joined  the room.11:59 AM

Joe Latrell joined  the room.12:00 PM

Joe Latrell12:00 PM
Good Afternoon everyone.

Dan Maloney12:01 PM
OK everyone, let's get started! Thanks for your patience with the lack of Hack Chats during the Supercon break. But we're back today with a great one - @alan.b.johnston is here to tell us all about simulations for CubeSats.

Alan - can you tell us a little about your background and how you came to the CubeSat world?

JamesDavid joined  the room.12:01 PM

Dan Maloney12:01 PM
And welcome, BTW!

alan.b.johnston12:01 PM
Thanks, Dan. Sure! Welcome everyone! Thanks for joining

alan.b.johnston12:02 PM
I got my start in electronics and radio as a teenager when he got his ham radio extra class license, call sign KU2Y. He built satellite antennas, and tracked satellites, and communicated using the AMSAT OSCAR-8 satellite. Since 2018 he has served as AMSAT’s Vice President for Educational Relations. I am also an Associate Teaching Professor of Electrical and Computer Engineering at Villanova, University.

alan.b.johnston12:02 PM
The AMSAT CubeSat Simulator is a functional model of a satellite for use in education and demonstrations. A proof-of-concept prototype was shown at the 2018 AMSAT Space Symposium, and the CubeSat Simulator program was officially “launched” at the AMSAT Update Forum at Hamvention 2019 in Dayton, OH.

alan.b.johnston12:02 PM
It is Raspberry Pi Zero W-based, 3D-printed frame structure, functional model of a “1U” CubeSat and is designed to act, as reasonably as possible, as though in Low Earth Orbit (LEO).

alan.b.johnston12:03 PM
Runs on rechargeable “flight” NiMH battery power and body-mounted solar cell panels.

alan.b.johnston12:03 PM
Transmits housekeeping telemetry on the 70 cm band using AO-7 format using AFSK AX.25 modulation

steve.bossert joined  the room.12:03 PM

alan.b.johnston12:03 PM
Lots of info at

alan.b.johnston12:03 PM
I have a live demo running in my office right now

alan.b.johnston12:03 PM
I'll try pasting a photo, see if it works

RoGeorge12:04 PM
you need to click the image button first

Dan Maloney12:04 PM
So that's interesting - do flight-qualified CubeSats used NiMH batteries routinely? Guess I always assumed something more "modern" like LiPo

alan.b.johnston12:05 PM

alan.b.johnston12:05 PM
Lets see if that worked!

alan.b.johnston12:05 PM
Yes, the battery design choice always generates questions :-)

Paul E Wogg joined  the room.12:06 PM

Joe Latrell12:06 PM
So what battery did you use and what is the total system power usage?

alan.b.johnston12:06 PM
Most CubeSats today use LiPO, yes, and they provide much higher capacity than nickel metal hydride

alan.b.johnston12:06 PM
I chose the NiMH for two reasons:

alan.b.johnston12:06 PM
1. The simulator was designed to be easy to ship to classrooms and events. So being able to answer "No" to the LiPO question when shipping is big benefit

Chinna12:06 PM
Hi Alan, great introduction. I am relatively new into the satellite things. Your Cubesat simulator looks great. I would like to build a even simpler cube sat. Is it possible to build one with just some kind of Arduino (I mean one Uno, not too many like Ardusat) and an antenna that is connected to RX and TX ports of the Arduino??

Josh12:07 PM
Is it possible to purchase 1U frame are there instructions(?) for a more realistic 1U frame if I don't want to 3D print?

alan.b.johnston12:07 PM
2. I like to show the battery discharging and charging during demos, and LiPO batteries take too long! With a low capacity NiMH battery, you can see it change voltage over a few minutes

alan.b.johnston12:08 PM
Which is great for demos. So this is a choice because it is for the classroom.

alan.b.johnston12:08 PM
Hi Chinna! Sure, you could build something with an Arduino. We also have a Simulator Lite which only requires any Raspberry Pi

alan.b.johnston12:08 PM
Even the Zero will work for this low-cost Lite version

Dan Maloney12:08 PM
Hadn't thought about the lithium and shipping issue. Funny that you can put it on a rocket but not on a freight plane

J12:09 PM
I had a play with the lite. Good fun :)

alan.b.johnston12:09 PM
Hi Josh, you can order a print of the 3D frame on Thingiverse if you don't have a printer

Joe Latrell12:09 PM has a kit you can buy as well.

R. Scott Coppersmith12:10 PM
What's the difference between a CubeSat and a CubeSat simulator?

alan.b.johnston12:10 PM
There's a link to the 3D files on GitHub

alan.b.johnston12:10 PM
Hi Scott - this is a functional model for the classroom

alan.b.johnston12:10 PM
The 3D printed plastic frame wouldn't work in space very well at all!

alan.b.johnston12:11 PM
All components are as cheap as can be to make it easy to build. It is designed to show off satellite, STEM, and radio principles

Chinna12:11 PM
Hi Alan, could you please point me towards any Arduino based simple cubesat model? I am more comfortable with that than the Raspi platform

alan.b.johnston12:12 PM
I have a Web SDR running here is a link if you want to receive the signals from demo in my office:

alan.b.johnston12:12 PM
Only 20 of you can join at a time, perhaps fewer, depending my bandwidth ;-)

alan.b.johnston12:13 PM
I can see people joining!

billybob12:13 PM
And then the poor 1u melts :)

Jurist joined  the room.12:13 PM

alan.b.johnston12:13 PM
Hi Chinna, sorry, I don't have one at hand, but maybe someone else does

Joe Latrell12:14 PM
I can help out if you want to make one using Arduino.

Anass Wifak joined  the room.12:14 PM

Dan Maloney12:14 PM
FYI, I'll post a transcript at the end so you can go back and revisit those links. After Alan puts out the fires, lol

steve.bossert12:14 PM
im routing your audio from your webSDR via a virtual audio cable and everything seems to be decoding just fine in my telemetry software.

RoGeorge12:14 PM
How do you simulate the low temperatures during dark side of orbiting?

alan.b.johnston12:14 PM
Here's a screenshot from the live SDR

alan.b.johnston12:14 PM

home joined  the room.12:14 PM

Chinna12:15 PM
Hi Jeo, please let me know where to find more info regarding Arduino based Cubesat

Naeem Altaf12:15 PM
Hi Alan, do you recommend, raspberry pi 4 for a real 3U cubesat to LEO ? thanks

alan.b.johnston12:15 PM
Steve, that's great. My data isn't interesting right now. Let me take out the Remove Before Flight pin and "launch" it

home12:15 PM
Alan, will your simulator survive a balloon launch?

steve.bossert12:15 PM
how are you creating signal fade locally?

alan.b.johnston12:16 PM
OK, that is real data now

Naeem Altaf12:16 PM
hi steve, what telemetry software are u using to decode data ? thanks

alan.b.johnston12:16 PM
I have the Simulator on a turntable so it rotates

Josh12:16 PM
okay... frankly, the web sdr may be my favorite part of the whole chat :)

alan.b.johnston12:16 PM
That also makes the solar panels activate in sequence, like a spinning cubesat

Anass Wifak12:16 PM
Hi alan, have you experimented with the max distance of communication with the SDR?

steve.bossert12:17 PM
so rotating on just one axis and not 2? would be cool to replicate true planar spin

Josh12:17 PM
do you simulate doppler shift too?

alan.b.johnston12:17 PM
Hi Anass, well, my web SDR is just an RTL-SDR with a rubber duck antenna. My SatNOGS station is connected to an outside antenna, so that receives much better!

alan.b.johnston12:18 PM
Hi Steve, I tilt the Simulator to simulate off-axis rotation sometimes

R. Scott Coppersmith12:18 PM
Have you flown it around attached to a quadcopter or drone?

alan.b.johnston12:18 PM
Here's the decoded data from my demo

alan.b.johnston12:18 PM

Joe Latrell12:18 PM
@alan.b.johnston , do you need a HAM license to use this simulator?

alan.b.johnston12:19 PM
You can see AMSAT's callsign W3ZM

alan.b.johnston12:19 PM
And the AFSK 1k2 decoded AX.25 info

alan.b.johnston12:19 PM
The "hi hi" is the old OSCAR greeting :-)

alan.b.johnston12:20 PM
Hi Joe, it is transmitting at 434.9 MHz which is inside the unlicensed ISM band, so it is OK. It is also only putting out 1uW or -30dBm ;-)

Chinna12:20 PM
Hi Alan, does any real cubesat uses the solarcells like the ones used in Cubesat simulator?

alan.b.johnston12:20 PM
Hi Scott, haven't tried it on a drone. No one has put it on a balloon yet, but that could be fun, too!

R. Scott Coppersmith12:21 PM
We have a tethered balloon here

alan.b.johnston12:21 PM
Hi Chinna, I use the best solar cells I can buy for $1.5, so they are 4V 160mA cells. Real CubeSats use much more powerful (and expensive) ones

billybob12:21 PM
@Chinna Yep! They use real cells. Though in-practice they are much more expensive. You need 28-30% efficiency for most power loads because of the more powerful radios needed.

alan.b.johnston12:22 PM
I only see 7 of you on the web SDR. Here's the link again - any browser will work:

alan.b.johnston12:22 PM
You have to click on the top to tune to 434.9 MHz then you can hear it. Works on phones too

J12:22 PM
When you visit schools, does it go down well? Where do you start explaining it to the kids? I imagine there is quite a lot to cover so they get a good understanding of what it is doing? Are there any hands on activities?

alan.b.johnston12:23 PM
@billybob yes, that's true. The Simulator acts like a "sick" CubeSat in that it can't run for too long without running out of battery. But someone could put expensive cells on the Simulator

alan.b.johnston12:23 PM
Yes, so far it has been used in high schools and universities so far

alan.b.johnston12:24 PM
In the high schools, it is with hams or teachers who are hams, so experienced people. we are slowly developing materials to bring it to a wider audience

Chinna12:24 PM
Thanks @Billybob and @alan, please suggest some real cells that are avilable within the budget

alan.b.johnston12:24 PM
I'm going to decode some of my data now

alan.b.johnston12:25 PM
OK, got some data!

alan.b.johnston12:25 PM
Here is a link

alan.b.johnston12:25 PM
I just copy and pasted the decoded telemetry into it and this spreadsheet decodes and graphs the data

Casey Halverson12:26 PM
what radio are you using for the simulator/

alan.b.johnston12:26 PM
I used to use an AX5043-based board

Casey Halverson12:27 PM
interesting choice. Ive looked at that chip a bit. Are you able to do AFSK with it?

alan.b.johnston12:27 PM
But now I just use the rpitx library - so I just use the Pi GPIO pins

alan.b.johnston12:28 PM
Yes, AFSK works. Other modes are more difficult

Joe Latrell12:28 PM

alan.b.johnston12:28 PM
Anyone else getting a signal on the SDR? I think our satellite just ran out of battery!

steve.bossert12:28 PM

Joe Latrell12:29 PM
This is a Space Rated PocketQube I have been working on.

alan.b.johnston12:29 PM

Casey Halverson12:29 PM
nice Joe!

alan.b.johnston12:30 PM
I just keyed up on my HT to make sure the web SDR is live :-)

alan.b.johnston12:30 PM
Is the Simulator alive again?

steve.bossert12:31 PM
seems back live RF now

alan.b.johnston12:32 PM
Yes, and now it is in a different mode

alan.b.johnston12:32 PM
Instead of just AFSK modulation, it is cycling through three different modes:

alan.b.johnston12:32 PM

J12:33 PM
ah was thinking it sounded different to the cubesat sim lite examples

alan.b.johnston12:33 PM

alan.b.johnston12:33 PM
Wow, it just jumped frequency, right?