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Spain’s First Open Source Satellite

posted by Fnord666 on Saturday August 17 2019, @06:25AM   
from the circling-the-globe dept.

MrPlow writes:

Submitted via IRC for TheMightyBuzzard

[Fossa Systems], a non-profit youth association based out of Madrid, is developing an open-source satellite set to launch in October 2019. The FossaSat-1 is sized at 5x5x5 cm, weighs 250g, and will provide free IoT connectivity by communicating LoRa RTTY signals through low-power RF-based LoRa modules. The satellite is powered by 28% efficient gallium arsenide TrisolX triple junction solar cells.

The satellite's development and launch cost under EUR 30000, which is pretty remarkable for a cubesat — or a picosatellite, as the project is being dubbed. It has been working in the UHF Amateur Satellite band (435-438 MHz) and recently received an IARU frequency spectrum allocation for LoRa of 125kHz.

[...] The satellite is being built in a cleanroom at Rey Juan Carlos University and has undergone thermovacuum and vibration testing at the facility. The group has since developed an educational satellite development kit, which offers three main 40×40 mm boards that allow the addition of modifications. As their mission states, the group is looking to develop an open source project, so the code for the satellite is freely available on their GitHub.

Source: https://hackaday.com/2019/08/15/spains-first-open-source-satellite/

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Original Submission

• Not sure what they are meaning by RTTY Not sure what they are meaning by RTTY (Score: 3, Interesting) by janrinok on Saturday August 17 2019, @07:59AM (2 children)

  by janrinok (52) on Saturday August 17 2019, @07:59AM (#881466) Journal

  When I was active in Ham radio (DL5YZ) the abbreviation RTTY meant radio teletype. The data rate of LoRa is very slow which is how they achieve the long range at low power. Typically you might get 90 seconds of transmission every 24 hours. From https://arxiv.org/pdf/1607.08011 [arxiv.org] page 2:

  The LoRa physical layer uses Chirp Spread Spectrum (CSS) modulation, a spread spectrum technique where the signal is modulated by chirp pulses (frequency varying sinusoidal pulses) hence improving resilience and robustness against interference, Doppler effect and multipath. Packets contain a preamble (typically with 8 symbols), a header (mandatory in explicit mode), the payload (with a maximum size between 51 Bytes and 222 Bytes, depending on the SF) and a Cyclic Redundancy Check (CRC) field (with configurations that pro-vide a coding rate from 4/5 to 4/8). Typical bandwidth (BW) values are 125, 250 and 500 kHz in the HF ISM 868 and 915 MHz band, while they are 7.8, 10.4, 15.6, 20.8, 31.2, 41.7 and 62.5 kHz in the LF 160 and 480 MHz bands. The raw data rate varies according to the SF and the bandwidth, and ranges between 22 bps (BW = 7.8 kHz and SF = 12) to 27 kbps (BW = 500 kHz and SF = 7) [2]. Frequency hopping is exploited at each transmission in order to mitigate external interference [10].

  TheThingsNetwork [thethingsnetwork.org] has the following restrictions on usage "30 seconds uplink and 10 messages downlink per day Fair Access Policy". Now that is the limits that they as an entity impose upon their users but they are also not too different to those imposed by law i.e. there are restrictions. There are also slight differences between geographical areas; the USA, Europe and Asia are all slightly different but essential the same.

  The limit on how much one is permitted to transmit in a given time period is not dependent on how much transmission power one has available but is restricted to ensure that all users have the opportunity to use the same spectrum in any given period of time. Several of my devices are configured to only transmit 4 or 5 bytes per hour. The relationship between bandwidth, spreading factor and data rate is explained in https://docs.exploratory.engineering/lora/dr_sf/ [docs.exploratory.engineering]. So even at the fastest data rate of 50kbs the maximum payload will be limited to about 230 characters.

  As I am sure this project is being run by people who know what they are doing I am obviously missing something. I suspect that is the use of the term RTTY to reflect that they will be using frequency shift keying rather than anything really related to radio teleprinters. I'll have to delve deeper to confirm what that 'something' is.

  Starting Score:	1		point
  Moderation		+1
  Interesting=1, Total=1
  Extra 'Interesting' Modifier		0
  Karma-Bonus Modifier		+1
  Total Score:		3

• Problem Solved Problem Solved (Score: 3, Interesting) by janrinok on Saturday August 17 2019, @01:36PM (1 child)

  by janrinok (52) on Saturday August 17 2019, @01:36PM (#881517) Journal

  They are using a special frequency allocation inside the Ham radio band and therefore do not have to comply with the same limitations as other LoRa users.

  Parent

  • Re:Problem Solved (Score: 0) by Anonymous Coward on Saturday August 17 2019, @04:19PM

    by Anonymous Coward on Saturday August 17 2019, @04:19PM (#881548)

    I'm curious about the next installment of this conversation ;)

    Parent