Latest prototype of Starship is fitted with Starlink satellite receiver. The SN11 prototype was destroyed during landing and the last seconds telemeteries before the explosion could not be monitored. Can satellite internet be used for monitoring online telemetries during rocket testing?
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$\begingroup$ The starlink connection will be great for exporting many multiple channels of , for example, video feeds. Stuff that is valuable to have, but not immediately-time-sensitive. Each StarShip launch has many little cameras on board, that provide useful engineering and PR data, way too much data to be collected live on the timing-sensitive true telemetry channels. Unfortunately, the typical StarShip landing makes recovery of recordings a bit problematic. $\endgroup$– CuteKItty_pleaseStopBArkingCommented Apr 17, 2021 at 19:05
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$\begingroup$ Is there any confirmation that all telemetry was delayed and lost with the loss of vehicle, or just the video stream? $\endgroup$– GremlinWrangerCommented Apr 18, 2021 at 4:55
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$\begingroup$ @GremlinWranger the stream host specifically mentioned they were still getting telemetry when the video feed cut out. I've seen nothing to support the claim that they lost telemetry before the explosion. $\endgroup$– Christopher James HuffCommented Apr 24, 2021 at 17:26
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2 Answers
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I was involved in a project that tried to gather some data from the reentry phase of spent stages. At this time, Iridium was the only available provider of data links via satellite. It was soon found however that the Doppler shift introduced by the vehicle's motion was big enough to cause rejection of the signal by the receiving satellite.
Technology has progressed since then (Iridium Next, Starlink, etc.), but the problem is fundamental: the faster you move, the more difficult it becomes to communicate with something that is not designed to track fast-moving things (Iridium for example had a band-pass filter designed to accommodate at most something at car speed, if I recall correctly).
So for tests at high speeds, commercial satellite internet is not suitable for telemetry transfer.
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$\begingroup$ Cool! Was the effect related to radio frequency shift or a shift in received data clocking rate? The Cassini/Huygens mission took the carrier frequency Doppler shift into account but there were challenges because the data-rate Doppler shift wasn't, so it was in danger of being clocked/sampled incorrectly. $\endgroup$– uhohCommented Apr 19, 2021 at 10:20
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$\begingroup$ @uhoh This was a radio frequency shift issue, but it's not unlikely that even if we had managed to "connect", that the data clocking rate would be off as well. Can't confirm though. $\endgroup$– LudoCommented Apr 19, 2021 at 13:40
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1$\begingroup$ @uhoh To clear: I was referring to "my" Iridium issue in the previous comment. I don't know much about the details of Cassini/Huygens, but your assertion of it being a data rate issue does sound familiar. $\endgroup$– LudoCommented Apr 19, 2021 at 13:50
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Can satellite internet be used for monitoring online telemetries during rocket testing?
Yes... But.
tl;dr: Starlink satellites are a lot farther away than ground tracking stations, and their antennas are a lot smaller than ground-based dishes, so this will be much harder.
Telemetry receiving from the ground can be done with dishes of several meters in diameter, and collecting areas of 10's of square meters that track the spacecraft. In this case a small transmitting antenna of a standard band can be easily placed at several locations around the rocket so that one is always exposed to the ground tracking stations.
- How does this fast-slewing SpaceX rocket-tracking dish track a moving spacecraft?
- Elon Musk tweet: At SpaceX Boca Chica launch site in Texas
The Starlink receiving satellites are able to receive data uplink from ground stations but transmitted from modestly-sized phased arrays, with an area of roughly 0.3 m^2. A launch vehicle needing near-continuous contact would have to always have a surface with such an antenna facing a Starlink satellite.
This sounds a lot harder.
above: screenshot from Starlink Teardown: DISHY DESTROYED! below: screenshot from TSP #181 - Starlink Dish Phased Array Design, Architecture & RF In-depth Analysis
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$\begingroup$ Thanks. The telemetry signal need not be received real-time, as latency is obvious, but can the data be analyze d later, like in black box? $\endgroup$– seccpurCommented Apr 17, 2021 at 10:59
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$\begingroup$ @seccpur The definition of telemetry excludes a black box recorder. $\endgroup$– uhohCommented Apr 17, 2021 at 13:20
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1$\begingroup$ @seccpur you may also be trying to solve the wrong problem, the missing data for SN11 is the video due to processing latency onboard (believe they are now encrypting video). No changes to the radio would help here, either you need to cut the latency in onboard hardware (faster/more CPUs) or use an armored black box (which probably exists, just nothing in it Elon wants to Tweet about). Or you can do what SpaceX are probably doing and send sensor data at high priority/low latency and accept that the less important video may be lost in an event like this. $\endgroup$ Commented Apr 18, 2021 at 4:53