NAV

Inter-Satellite Links Tutorial

Complexity: High
Payloads: 2 satellites with ISL & SABERTOOTH
Windows: LEASE_ISL & PAYLOAD_SABERTOOTH

Inter-Satellite Links (ISL) are enabled for some satellites. ISL links can be made between a single pair of satellites following the same orbit so that they can be in contact at any time, where there is little relative motion between them. Satellites that are in intermittent contact (i.e. when their orbits overlap) may also be used for ISL contacts, so long as their direction is similar enough for meaningful contact time as well as low doppler-shift.

To simplify calculating when to schedule the windows, for this example we will be assuming that the satellites are in synchronous orbit.

Prerequisites

All tutorials require the steps outlined in the Getting Started Guide. Additionally the zfec python module must be installed on the payload. See the In-Orbit Python Environment Setup instructions for more information.

Scripts

  1. deploy - run by the user on the ground to upload isl_tx_demo & isl_rx_demo, and schedule them to execute in a PAYLOAD_SABERTOOTH window
  2. isl_tx_demo - Runs on the transmitting payload/satellite to send data
  3. isl_rx_demo - Runs on the receiving payload/satellite to receive data

Upload & Deploy

The deploy script is run by the user and performs the following steps:

  1. Uploads isl_tx_demo & isl_rx_demo scripts to the respective satellites
  2. Schedules an ISL between 2 satellites in 24 hours
  3. Schedules a PAYLOAD_SABERTOOTH window to run on the transmitting satellite to send data
  4. Schedule a PAYLOAD_SABERTOOTH window to run on the receiving satellite to listen for & downlink data
$ ./deploy "[AUTH_TOKEN]" [SAT_ID_TX] [SAT_ID_RX]

Schedule LEASE_ISL

The LEASE_ISL is used to configure a one-way Inter-Satellite-Link using the S-BAND radio, providing a simplex IP link between the satellites. In this example UDP is used for data transfer as the protocol has no return acknowledgment and ideal for simplex links.

A single call to the Tasking API creates a LEASE_ISL in both satellites. For this example satellites FM1 and FM2 are scheduled for 5 minutes. Everything is scheduled 24 hours out when there are no conflicts with existing down-link contact windows.

Review

Once the window has completed and enough time has passed for the log to download, it can be reviewed in AWS S3 (see Hello World tutorial).

Next Steps