6 ms·
The Doppler stuff is new (as of the 24th). What I had understood before was that the airplane carried an Inmarsat satellite transceiver which remained active,
by cynwoody 13y ago
The Doppler stuff is new (as of the 24th).
What I had understood before was that the airplane carried an Inmarsat satellite transceiver which remained active, even though certain subsystems that use it (notably ACARS) were disabled. While active, the transceiver communicates with the satellite once an hour (the "pings" at 11 minutes past), even if it has no traffic to send. Failing to disable the transceiver in addition to the other systems would have been an oversight on the part of the plane's hijackers, assuming it was hijacked.
Apparently, Inmarsat had available accurate ping timing data. Combined with knowledge of turnaround delays, this would enable them to calculate the plane's distance from the satellite during each ping. That defines an imaginary sphere in space, which intersects with the earth's surface to form a circular locus of where the plane could have been at the time. Presumably, there were eight such ping interactions, ending with the one at 0811 Kuala Lumpur time. There was no 0911 ping, meaning the plane had either crashed or landed and powered off before that time.
And so we had the northern and southern arcs. These were obtained by cropping the circle based on factors such as how far the plane could have flown in the available time, whether or not military radars, if any, had detected the plane, etc.
Now comes the Doppler data. Apparently, Inmarsat also has an accurate read of the plane's transmit frequency. The extent to which this frequency differs from the nominal frequency would indicate the plane's velocity towards or away from the satellite at the time of the ping.
Today, Chris McLaughlin revealed that Inmarsat had studied the Doppler patterns of normal flights in the same region and concluded that the Doppler data for MH370 indicated that the southern arc was the right one. Hopefully, Inmarsat has it right, and the black boxes will be found before their beacon batteries run out.
- brador 13y agoIs the data on the black boxes dependent on continual power? That seems strange.
- bteitelb 13y agoThe data is persistent, but the beacons only transmit for 30 days or so.
- nakedrobot2 13y agoIt seems very clear that these airplane blackboxes are ridiculously under-specced and underpowered. Yes, I know these things have to be hardened, debugged, tested, and paid for. Still! Why 30 days only? Why not have an atomic (nuclear) battery that will be able to send out sonic pings for a year? Why can't the damn thing record audio (and lots of other data) from the entire flight, rather than only two hours? I think after this crash, blackboxes are going to be redesigned....
- ddeck 13y agoWhy can't the damn thing record audio (and lots of other data) from the entire flight, rather than only two hours? I commented on this on a prior thread [1]. There has been push back from the Airline Pilots Association against longer recording duration on privacy grounds: The Air Line Pilots Association (ALPA) did not support the proposal to increase CVR recording time because the FAA did not propose any increase in the privacy protections regarding the access and use of information recorded on a CVR. The ALPA stated that existing protections are inadequate despite years of its attempts to change the standard. [1] https://news.ycombinator.com/item?id=7434130 https://news.ycombinator.com/item?id=7434130
- XorNot 13y agoAtomic batteries are not at all powerful enough. Microwatts. Running anything on batteries for days takes a lot of batteries. A Raspberry Pi for 2 days for example takes somewhere from 1.5 to 2 kg of li-ion batteries. That sort of weight starts to be really problematic for a device which needs to survive a plane crash - since every bit of extra mass increases the force with which it hits.
- mikeash 13y agoThey don't have to be microwatts. Galileo, for example, used 17 pounds of plutonium to generate 570W of power at launch, with a half life of about 88 years. Not that you'd want to carry 17 pounds of plutonium around on an airliner all the time, but power output is not an insurmountable problem by itself.
- spc476 13y agoI don't think so, but having the beacon on will make finding the black box easier.
- khuey 13y agoNo. Persistence of the data does not require continuous power. But the black box has a battery-powered "pinger" that produces sound to make it easier to find. The batteries for that is only required to last for 30 days.
- antocv 13y agoWhy does it produce sound? Why not infrared or something easily detectable?
- bodhi 13y agoI think they often end up underwater? In that case, sound seems to be the more used medium, unless hollywood stories about sonar have led me astray...
- emillon 13y agoUnder water, I assume that sound is easier to detect than IR.
- masklinn 13y agoInfrared doesn't work underwater, water covers most of the earth surface and it's where the hardest to find crashes are located.
- rcxdude 13y agoFor communication under(salt)water, you're pretty much screwed with every part of the electromagnetic spectrum apart from visible light, and even that won't work in cloudy conditions or if the emitter is occluded. Sound is really the best option.
- cynwoody 13y agoBecause infrared doesn't work very well in water, and crashes in water are the biggest challenge for finding wreckage. Airliners also carry emergency locator transmitters† (ELTs), which, when activated by a crash, transmit radio signals which can be triangulated via satellite. However, ELTs do not work underwater. No ELT signals from MH370 were heard. †http://en.wikipedia.org/wiki/Emergency_Locator_Transmitter http://en.wikipedia.org/wiki/Emergency_Locator_Transmitter
- Shivetya 13y agothe second biggest issue with the data is that it will have written over some of the information that would have occurred at the time the flight deviated from the assigned course. It used to be that voice recorders with 30 minute loops, I am not sure if that is still the case.
- ibmthrowaway218 13y agoThe voice recorder only records the last 120 minutes. The data recorder will cover the entire flight.
- masklinn 13y agoDepends on the model (and how much you pay for it). Honeywell's SSVCR[0] is available in 30 minutes and 120 minutes. [0] http://www.sea-avionics.com/lc/cart.php?target=productDetails&model=SSCVR&substring=sscvr http://www.sea-avionics.com/lc/cart.php?target=productDetail...
- Fuxy 13y agoThat's odd with today's technology we should be able to record hours of voice on to an a usb stick. Granted that is a lot more fragile then a plane black box but still. There should be a way to record a lot more then 120 minutes.
- roc 13y agoI suspect the answer is similar to "why don't they stream FDR-data, live, for all flights?". That being: the airlines feel the cases in which extra measures matter are only a small subset (flights with problems in incredibly remote areas) of a small subset (flights that have any problems at all) and thus not worth the extra cost/complexity/risk to all the other flights.
- sigkill 13y agoI don't know why I haven't seen this linked before here, but this is a very informative teardown of an FDR by Mike of MikesElectricStuff https://www.youtube.com/watch?v=mQehX0rVYuY https://www.youtube.com/watch?v=mQehX0rVYuY Check out his other videos as well. He is really good at what he does, and his videos still retain the hackery feel.
- hga 13y agoOne minor correction, which I'd seen an indication of and had suspected from an architectural design point of view: the plane was getting pinged, it wasn't producing the pings. Per The Aviation Herald, which has lots of details today (and isn't behind a pay wall who's visits per month I used up yesterday): http://avherald.com/h?article=4710c69b&opt=0 http://avherald.com/h?article=4710c69b&opt=0 "During the flight the ground station logged the transmitted and received pulse frequencies at each handshake." That's in the middle of a huge paragraph describing how they did it in quite some detail, e.g. compared data to other 777s flying that day.