A small satellite developed by MIT engineers has set a new record for data transmission between a satellite and Earth. The TeraByte InfraRed Delivery (TBIRD) system used a laser to beam huge amounts of data at up to 100 gigabits per second (Gbps).
This data transmission speed is far greater than most connections you’ll get between the sky and the ground. SpaceX’s Starlink satellite internet offers up to 500 Mbps to Premium customers, and even the International Space Station’s data transmission tops out around 600 Mbps. That makes TBIRD up to 200 times faster.
The key difference is that most satellites communicate with ground stations via radio waves. TBIRD, on the other hand, uses laser light, which can carry up to 1,000 times more data in each transmission. Lasers come with their own hurdles though – the beams are much narrower, requiring more precise alignment between transmitter and receiver. And the light can be distorted by the atmosphere, leading to data loss. So TBIRD was designed to overcome these issues.
The satellite contains three main off-the-shelf components – a high-speed optical modem, an optical signal amplifier and a storage drive – all packed into a container the size of a shoebox. To tackle the data loss problem, the team developed a new version of what’s called an Automatic Repeat request (ARQ) protocol. This allows a ground station receiver to alert the sender to specific packets of data (frames) that it missed, so the satellite can just re-send those.
“If the signal drops out, data can be re-transmitted, but if done inefficiently – meaning you spend all your time sending repeat data instead of new data – you can lose a lot of throughput," said Curt Schieler, TBIRD system engineer. “With our ARQ protocol, the receiver tells the [satellite] which frames it received correctly, so the [satellite] knows which ones to re-transmit.”
As for alignment, TBIRD doesn’t bother with a gimbal to point the laser beam. Instead, it uses a custom error-signaling system that adjusts the entire satellite itself to point precisely towards the receiver. This, the team says, allows the optical components to be miniaturized.
Having achieved the TBIRD’s original mission of transmitting huge amounts of data quickly via lasers, the team now plans to attempt to double that.
“Next, we plan to exercise additional features of the TBIRD system, including increasing rates to 200 gigabits per second, enabling the downlink of more than 2 terabytes of data – equivalent to 1,000 high-definition movies – in a single five-minute pass over a ground station,” said Jade Wang, TBIRD program manager.
Source: MIT
