Ground Receiver

The ground receiver (ground_segment/receiver.py) is a TCP server that accepts downlinked image frames from the satellite's GroundCommsDriver component. It represents the ground-side endpoint of the simulated X-band radio link.

ORIO Frame Protocol

Each downlinked frame uses a simple binary protocol with an 8-byte header:

Offset	Size	Field	Description
0	4 bytes	Magic	0x4F52494F ("ORIO" in ASCII), network byte order
4	4 bytes	Payload length	Size of the raw image data in bytes, big-endian
8	N bytes	Payload	Raw pixel data (786,432 bytes for 512x512 RGB)

The receiver validates the magic bytes on each connection. Frames with invalid magic are rejected and the connection is closed. Each frame arrives on its own TCP connection (one-connection-per-frame model).

Output

Files are saved to ./orion_downlink/ as orion_frame_XXXX.raw. Each .raw file contains raw RGB pixel data - 786,432 bytes for 512x512 images.

Relationship to Flight Segment

GroundCommsDriver connects to the receiver using ORION_GDS_HOST and ORION_GDS_PORT (default 127.0.0.1:50050). It sends frames in two scenarios:

• Immediate downlink: HIGH-priority frames transmitted directly during DOWNLINK mode
• Queue flush: previously queued HIGH frames flushed when entering DOWNLINK mode

MEDIUM-priority files are downlinked separately via the F-Prime FileDownlink service (triggered by FLUSH_MEDIUM_STORAGE), which uses the F-Prime ground link (port 50000) and does not go through receiver.py.

Configuration

The receiver uses hardcoded values:

Setting	Value	Notes
Listen IP	0.0.0.0	Listens on all network interfaces
Listen port	50050	Must match the flight binary's ORION_GDS_PORT
Output dir	./orion_downlink	Created automatically if it does not exist
Backlog	5	Maximum pending connections
Chunk size	4096 bytes	TCP read chunk size for payload reception

For instructions on running the receiver, see the Receiver guide.