A lot of people ask us if/how we talk to COSI in flight. We actually have 4 different ways of communicating with our instrument, each with different ways of sending/receiving data and, most noticeably, different speeds. Here’s a summary of the different communications links.
Wired Ethernet (LAN) – 1Gbps
When we are physically next to COSI, we can hook up a normal Ethernet cable to connect it directly to our computers. Using this method, we can transfer lots of data quickly. The nature of the wired connection, however, means we cannot use this in flight.
L-Band Radio Link (Line-of-sight) – 1Mbps
In the first day of flight, we have a direct radio link between COSI and CSBF’s ground station here in Wanaka. As long as COSI is still in our line of sight, we can get a high-bandwidth downlink, but as soon as it goes behind some mountains, or past where we can see due to the curvature of the earth, we lose this link.
Being our fastest communications link in flight, we try to make the most of our time with this link operational and the team takes shifts to ensure COSI is being monitored 24/7 until we lose our line of sight.
Iridium OpenPort – up to 2x 134kbps
Iridium, a satellite phone network, offers the OpenPort Internet service which uses Iridium’s satellite network. Its Pilot device consists of antennas in a mushroom-shaped enclosure that sits on our antenna boom, and a modem/router device that acts just like the Internet routers we have in our homes. Attaching an Ethernet cable to these routers gives our flight computer Internet access.
We are flying two sets of the OpenPort Pilots. Internet speeds over the satellite network vary greatly, and at times we have trouble connecting at all. All this aside, OpenPort is great since it is a normal (albeit slow) Internet connection, and we can actually log in to our flight computer mid-flight to perform any diagnostic checks or download any particularly interesting data files that we don’t automatically transmit.
Slower Iridium Links – 0-2kbps
An older technology using the Iridium phone network can be more reliable, but gives us slower speeds. We can send a small batch of commands every minute, and receive a very small (255Bytes) amount of telemetry every 15 minutes.
CSBF can also create a ‘dial-up’ connection, much like dial-up modems over traditional phone lines. This gives us a data rate of 2kbps. That’s 28x slower than those old 56kbps modems from the 1990s!
Due to the low bandwidth of these links, we only use them for diagnostics.
Why do we have so many different links? You may think it would be for redundancy, but we actually have 2 OpenPorts and 2 of the slower Iridium links for that reason. The real reason is the speed and/or convenience of using the links. Check out the comparison of the different links below, along with the time it would take to download a 5MB MP3 file using each link.
|Ethernet||Before launch||1Gpbs||42 milliseconds|
|L-band||Line of sight||1Mbps||42 seconds|
|OpenPort||22+ hrs/day||268kbps (max)||2.5 minutes|
|170 kbps (avg)||6 minutes|
|Iridium Dial-up||On-demand||2kbps||6 hours|
|Iridium Short Burst||24/7||255 Bytes/15 min||214 days|