Ground Sphere Test Transmitter - Initial Questions v0.1

Project Background Questions

BQ1. Why are we making this?

BA1. There are two reasons for building this test transmitter. First, it helps to have an initial "smoke test" for the Ground Sphere Ground Station. What this means is that when someone assembles a copy of the Ground Sphere hardware, they should be able to easily test it to make sure that nothing major is wrong. Second, there are very few other 915 MHz satellites in orbit that are useful for testing the Ground Sphere Ground Station at the time of this project's inception. Having a test apparatus like this allows us to simulate satellite reception through terrestrial tests and possibly even High Altitude Balloon launches.

BQ2. Who is this for?

BA2. The Ground Sphere Ground Station is for SkyCube backers, students, teachers, scouting troops, space enthusiasts, and anyone who wishes to directly participate in the SkyCube mission. Therefore, this test transmitter is intended for the same audience.

BQ3. How will this be used?

BA3. Ground Sphere Ground Station operators will use the test transmitter to:

  • Do an initial test to make sure that the Ground Sphere hardware is capable of receiving 915 MHz transmissions in a laboratory environment.
  • Do an initial test to ensure that the Ground Sphere hardware is capable of receiving 915 MHz transmissions at a receive signal strength equivalent to a satellite on orbit.

BQ4. Who's going to build this?

BA4. The designs will be open so that anyone, without necessarily a technical education in amateur radio or satellite operations, would be able to build and operate a Ground Sphere Test Transmitter.

Technical Requirement Questions

TQ1a. What features does it need to have (now)?

TA1a. The test transmitter needs to:

  • Transmit radio signals at 915 MHz
  • Be mobile so that the terrestrial tests can be done by adding distance between the transmitter and Ground Sphere receiver
  • Be easy to assemble from kit components and only require simple tools (screw drivers, pliers, wrenches, etc) for assembly
  • Have low shipping costs for the packaged kit
  • All software required to operate the test transmitter must run on a Windows PC
  • The test transmitter must connect to the test transmitter programming computer through a commonly available port (for example: USB)
  • The test transmitter hardware should minimize the opportunity for mechanical failures (from things such as broken connectors or a lack of strain relief)

TQ1b. What features does it need to have (later)?

TA1b. In the future, the project (or related projects) may need to:

  • Have all software required to operate the test transmitter must run on Windows, OS X, and Linux
  • Transmit BPSK-modulated, unencrypted AX.25 data packets sent at 9600 baud
  • Have the capability to transmit on the 433 MHz (ISM) band

TQ2. What are the legacy requirements?

TA2. To maintain compatibility with other projects, the system should:

  • N/A

Project Requirement Questions

PQ1. How many do we want to make?

PA1. As an open source hardware kit, the long term objective is to promote and sell as many ground station kits to as large of an audience (schools, scouting troops, makerspaces, space enthusiasts, etc) as possible. However, the narrow focus on supporting SkyCube operations with the Ground Sphere may limit the number of kits which will be sold for this specific ground station, especially since the SkyCube is going to be on orbit for a very limited period of time. The sales lifetime of this specific kit (and in turn the number of kits we will want to sell) will depend on how many other satellites there are to observe in the same frequency range as the SkyCube.

PQ2. What is the budget?

PA2. The materials cost should be kept under $75 to limit the retail cost of any kit versions.

PQ3. What is the timeline?

PA3. The timeline for this project is dictated by the SkyCube launch and deployment timeline. SkyCube is currently scheduled was launched in January 2014, with deployment from the ISS in Q1 or Q2 of 2014. Southern Stars has stated they would be comfortable with a February 2014 delivery date for the kits.

PQ4. What waste products will be produced by the manufacture and/or operation of this?


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