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Perseverance- Computational Systems & Software, technical discussion of all things digital
nprev
post Mar 21 2021, 10:49 PM
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A member requested a thread dedicated to this topic, so here it is. Please review recently-added rule 1.4 & keep it in mind (as well as the rest of them). Enjoy! smile.gif


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Brian Swift
post Mar 24 2021, 03:47 AM
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Technically it's still part of Perseverance...

There was discussion today during the Ingenuity preview press conference that the helicopter's CPU was 100s of times faster than all previous planetary mission flight computers combined. Someone also mentioned/thanked Qualcom as a partner.

Internet search says Ingenuity CPU is a Qualcomm Snapdragon 801.
Specs at https://www.qualcomm.com/products/snapdragon-processors-801

I started to wonder if that chip's Wi-Fi/Bluetooth would be used to communicated with Perseverance, but wikipedia say comm is via 900 MHz Zigbee.
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pospa
post Mar 24 2021, 08:37 AM
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QUOTE (Brian Swift @ Mar 24 2021, 04:47 AM) *
I started to wonder if that chip's Wi-Fi/Bluetooth would be used to communicated with Perseverance, but wikipedia say comm is via 900 MHz Zigbee.

That's correct. Here is a bit more details about Ingenuity telecommunication system:

"Once separated from the host spacecraft (lander or rover), the Mars Helicopter can only communicate to or be
commanded from Earth via radio link. This link is implemented using a COTS 802:15:4 (Zig-Bee) standard 900 MHz
chipset, SiFlex 02, originally manufactured by LS Research. Two identical SiFlex parts are used, one of which is an
integral part of a base station mounted on the host spacecraft, the other being included in the helicopter electronics.
These radios are mounted on identical, custom PC boards which provide mechanical support, power, heat distribution,
and other necessary infrastructure. The boards on each side of the link are connected to their respective custom antennas.
The helicopter antenna is a loaded quarter wave monopole positioned near the center of the solar panel (which also
serves as ground plane) at the top of the entire helicopter assembly and is fed through a miniature coaxial cable routed
through the mast to the electronics below. The radio is configured and exchanges data with the helicopter and base
station system computers via UART.
One challenge in using off-the-shelf assemblies for electronics systems to be used on Mars is the low temperatures
expected on the surface. At night, the antenna and cable assemblies will see temperatures as low as -140 C. Electronics
assemblies on both base station and helicopter will be kept “warm” (not below -15 C) by heaters as required. Another
challenge is antenna placement and accommodation on the larger host spacecraft. Each radio emits approximately
0.75 W power at 900 MHz with the board consuming up to 3 W supply power when transmitting and approximately
0.15 W while receiving. The link is designed to relay data at over-the-air rates of 20 kbps or 250 kbps over distances of
up to 1000 m.
A one-way data transmission mode is used to recover data from the helicopter in real time during its brief sorties.
When landed, a secure two-way mode is used. Due to protocol overhead and channel management, a maximum return
throughput in flight of 200 kbps is expected while two-way throughputs as low as 10 kbps are supported if required by
marginal, landed circumstances."
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mcaplinger
post Mar 24 2021, 04:30 PM
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A citation for the above quoted text: https://trs.jpl.nasa.gov/bitstream/handle/2...L%2317-6243.pdf I believe.

A more detailed reference for the telecom system with some good detail about the helicopter in general is https://trs.jpl.nasa.gov/bitstream/handle/2...L%2318-3381.pdf


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JRehling
post Mar 24 2021, 04:45 PM
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Hundreds of times faster is an eye-catching claim. It seems that Ingenuity's CPU's clock speed is about 14x that of the Curiosity rover, which is a considerable difference, and it has four cores, and apparently twice the bus width of the former, and 14 * 4 * 2 is indeed over 100. It's not straightforward to compare computing power in objective units, but it seems like the claim is at least approximate if not literal.

Moore's "law," holding that CPU speeds increase exponentially over time more or less held true from the 1950s through 2010. Spacecraft computers tend to be about 10 years older than the launch date, so here we are ~10 years after Moore's law ran out of steam. This might make Perseverance part of the last generation of spacecraft with computational power much greater than its predecessors. N.B., virtually every part of what I just said merits at least one grain of salt.
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fredk
post Mar 24 2021, 05:14 PM
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QUOTE (JRehling @ Mar 24 2021, 05:45 PM) *
Hundreds of times faster is an eye-catching claim.

It's worth pointing out that the Ingenuity computer wasn't required to last long on the surface so didn't need to be rated for the environment as the rover's was, so could be newer hardware.

I wonder if the image processing demands of Ingenuity are greater though, and maybe that factored in. The rover handled the EDL image processing, but I'd guess that the timescales are shorter for Ingenuity flights so the computational requirements greater.
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mcaplinger
post Mar 24 2021, 05:27 PM
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QUOTE (JRehling @ Mar 24 2021, 08:45 AM) *
It's not straightforward to compare computing power in objective units...

Indeed. "Lies, damn lies, and benchmarks", to paraphrase Twain.

Who cares how fast anything is if it's fast enough to do what it needs to do? All the MSSS embedded processors on Mars are 40 MHz IPC=1 RISCS with 128Kbytes of SRAM.


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MahFL
post Mar 24 2021, 11:03 PM
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They said Ingenuity is a tech demo so they pretty much could use what they wanted, long term survivability was not an objective, so hence the capability of using a modern processor. Also Ingenuity's nav cam takes 30 frames per second pictures for flying navigation purposes. I think they said they did do a little hardening of the CPU, but not the amount a processor would get designed to last a decade or more on Mars.
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