Some of the data is transmitted to satellites while in flight.
This is not done for incident analysis, but mostly for maintenance. So if something fails in flight, the airline would know to have replacement parts ready for when it lands to quickly fix the issue. There are also some other in the data that would be helpful in this situation. I am unfamiliar with what engine and flight control data is transmitted, but things like landing gear position are in the message, so I would think things like fuel cutoff switch state and flaps position (maybe actual positon, maybe commanded, maybe both). Binary data is easier to get in the limited space than an analog value, so binary states is more likely in the satellite message. But that data is limited and at a lower frequency than will be in the flight data recorder, since it is expensive to transmit data by satellite. So they are generally not constantly broadcasting a signal with all the data. But generally, messages are sent at certain points in the flight and also if certain status message, cautions, warnings, or alerts are active.
I know airlines can choose if Boeing can see the data, but I don’t remember how much airlines can config when data is sent.
So if they got some data during the flight, people will have already looked at it and it may tell them some stuff, but you will need the flight data recorder.
There is a big push for live telemetry streaming ever since MH370, the Malaysian Airlines flight that disappeared. I don’t think bandwidth would be too much of an issue, but there are reasons that you would still want on-board flight recorders. You probably wouldn’t want to live stream the cockpit voice recorder for privacy reasons. You will also lose satellite links for a whole host of reasons like extreme attitude or latitude. So even if they did stream data, they would want to collect the black boxes as part of the investigation.
I would be really interested in what spacecraft could have more instrumentation than a 787. I doubt the space shuttle orbiter did. Unless there is a bunch of video, then yes I could see something generating more raw bits.
787 is kinda a special case here because it does have more instrumentation than any other Boeing commercial aircraft.
But yes, there would be bandwidth issues if you were transmitting the data at high rate. Although systems like starlink are going to make it less of an issue as show by spacex which transmits a bunch of high definition video using it.
A single video channel is going to require more bandwidth than a huge amount of other instrumentation.
On Orion there are several hundred thermocouples (low rate), numerous accelerometers (high rate), strain gages, pressure sensors, … Well into the thousands of channels. It’s always a negotiation with the avionics folks about what data must be real-time telemetry vs recovered post-flight. Heck, even ISS has a channel for every actuated bolt on the common berthing mechanisms, and there are 16 bolts per ACBM.
Years ago I was doing flight test support for X-38 at Edwards. Even for those test flights we had several thousand channels of data. We had physical strip charts outputting the accelerometer data. To be able to make sense of the frequency content, the roll paper was on high speed. Made a mess in the control room!
On-orbit software monitors approximately 350,000 sensors, ensuring station and crew health and safety.
In the International Space Station’s U.S. segment alone, more than 1.5 million lines of flight software code run on 44 computers communicating via 100 data networks transferring 400,000 signals (e.g. pressure or temperature measurements, valve positions, etc.).
The 787 produces, with the data from engines, something like 30 terabytes per hour, forgot the exact number but it is in the tens of terabytes per hour if you are recording data off the network from the flight test ports. With only a portion of that stored on the flight data recorder and a smaller portion transmitted to the gate through WiFi.
From your numbers, yes the ISS could have more data produced than a production 787. I think the 787 was under than 400,000 number, but in that ballpark. But an instrumented flight test 787 which could double that data rate, would probably be more.
Think about the 787, each window is putting out multiple data channels on the network, since they are electronically dimming. Coffee makers also. Cabin lighting could be a couple thousand channels, you have hundreds of individual modules all being able to vary intensity and color and reporting health and the power modules for each one reporting current and voltage and likely more data from the ground side. Those are the simple systems! The 787 network is sending an incredible amount of data around.