Below is a summary of technical information, with links to further reading and data sheets that should prove useful and interesting to everyone keen to know more about KickSat and Sprites.
Our next action is to programme our Sprite, and therefore links are provided for downloading the Sprite schematics, programming tools and code examples.
More information about ground stations will be provided at a later date.
BIS members can add comments and ask questions below by logging in to the website. Check the website regularly for details of Sprite programming sessions and other events being planned in the near future, and become a BIS member to participate.
The Sprite antenna is a V-shaped half wave dipole with a 50 ohm impedance, which doesn’t require a matching network, and is nearly isotropic.
The Sprite microcontroller is a Texas Instrument MSP430, which is an ultra-low power 16-bit RISC mixed-signal microprocessors, ideal for solar power devices where continuous power cannot be guaranteed. Download the data sheet from http://www.ti.com/lit/sg/slab034v/slab034v.pdf
Each Sprite has a UHF (437 MHz) transceiver capable of transmitting at a maximum power of 10 milliwatts.
The Sprite signal will have around 120 attowatts of power when received on the ground around 500 kilometres away. For a comparison, GPS signals are broadcast with about 50 Watts of power from about 20,200 kilometres away. Ignoring variations in antennas and other smaller effects and just taking into account free-space loss, a GPS signal received on the ground will have a power of about 28 attowatts. The Sprite signal is actually four times more powerful than a GPS signal when received from Earth!
Magnetometer & Gyroscope
Both the gyroscope and magnetometer are vector sensors, meaning they each have three sensors, one along each of the x, y, and z axes, to give data in three dimensions.
- The gyroscope will give the Sprite’s rotation rate, allowing study of nutation and how small perturbation torques (due to atmospheric drag and solar pressure for example) affect each Sprite over time. Click here for the Invensense ITG-3200 data sheet.
- The magnetometer will provide a measurement of the Earth’s magnetic field, which we can actually learn a lot from. The magnetometer measurements from a number of Sprites could also be combined to produce a local map of the Earth’s magnetic field.
By combining the information from the gyroscope and magnetometer, a Sprite’s attitude determination can be calculated (i.e., which way it is pointing).
TASC (Triangular Advanced Solar Cells) are made from the offcuts of larger square and octagonal solar cells and are constant voltage, so if they are illuminated the MCU will run. Download the datasheet from http://www.spectrolab.com/DataSheets/PV/PV_NM_TASC_ITJ.pdf
Full hardware schematics can be downloaded from GitHub at the following address https://github.com/zacinaction/kicksat/wiki
During tests, signals from two Sprites were received using a Yagi antenna at a distance of 37 kilometres with an additional 23 dB of attenuation between the antenna and LNA (low noise amplifier). This equates to an equivalent distance of about 532 kilometres, or approximately the same as listening to an orbiting Sprite at 38 degrees elevation above the horizon.
- The basic theory behind the radio is matched filtering – read more at http://en.wikipedia.org/wiki/Matched_filter
- Forward Error Correction (FEC) will be used to correct signal errors due to noise. Read more at http://en.wikipedia.org/wiki/Forward_error_correction
- Each Sprite is assigned a unique identifier known as a Gold Code, which the radio correlator will use to pull the required signal while rejecting the rest. Read about Gold Codes at http://en.wikipedia.org/wiki/Gold_code
Two frequencies have been assigned for the KickSat mission:
- 437.240 MHz for the Sprites
- A swathe of S-band near 2.4 GHz for communicating with KickSat itself.
Programming is using Energia – a modified version of the Arduino IDE for the MSP430 Launchpad.
- Download Windows: https://dl.dropbox.com/u/19178351/Energia-KickSat/Energia-KickSat-Windows.zip
- Download Mac: https://dl.dropbox.com/u/19178351/Energia-KickSat/Energia-KickSat-Mac.zip
- Code examples can be found on GitHub: https://github.com/zacinaction/kicksat/wiki/Code-Examples
The Sprite Deployer’s main goal is to ensure the Sprites come out facing the Sun enabling them to harvest enough power from their solar cells to function.
After KickSat leaves the launch vehicle, communications will be established and its subsystems checked. Once everything reports as OK, KickSat will be turned so that the deployer end is pointing at the Sun.
- By monitoring the current from the panels on each side of KickSat, the side facing the sun can be determined at any time.
- KickSat will use magnetic torque coils (magnetorquers) capable of turning the satellite. Magnetorquers are essentially just electromagnets – big coils of wire that generate a magnetic field when an electric current runs through them. Torque is produced by the interaction between the magnetorquer’s magnetic field and the Earth’s magnetic field. Basically, the satellite will spin like the needle in a compass so that the magnetorquer’s field lines up with the Earth’s field.
KickSat’s magnetorquers will then be used to spin KickSat like a gyroscope to counter disturbances like atmospheric drag and solar pressure that can slowly nudge satellites away from their desired attitude.
Finally, once KickSat is pointing at the Sun and spin-stabilized, deployment will be triggered. A spring will push the deployer out and a combination of spring force and centrifugal acceleration will make sure the Sprites make it out of KickSat. If all goes well, the Sprites will inherit the spin-stabilized Sun-pointing attitude of KickSat and have plenty of solar power.
The intention for receiving signals from the Sprite fleet is to have a network of ground stations. Individuals and groups are encouraged to have their own ground station, the best options for which are still being tested but will be a based on a GNU Radio (http://gnuradio.org/redmine/projects/gnuradio/wiki) – a radio written in software. A potential antenna is the FUNcube Dongle (http://www.funcubedongle.com/) that a user can simply plug into a USB slot on a computer.
KickSat is confirmed as a payload in the ELaNa 5 / CRS 3 mission. This will be the third Commercial Resupply Service flight to deliver supplies to the International Space Station aboard a Space X Falcon 9 rocket. KickSat, along with five other CubeSats, will be hitching a ride as a secondary payload thanks to NASA’s ELaNa program.
Check the latest launch date at http://spaceflightnow.com/tracking/
KickStarter KickSat page: http://www.kickstarter.com/projects/zacinaction/kicksat-your-personal-spacecraft-in-space
Zac Manchester Vimeo web seminar: http://vimeo.com/34892231
Zacinaction GitHub: https://github.com/zacinaction