Perseverance rover’s descent and touchdown on Mars [video] • Hacker News Board

Re: Perseverance rover’s descent and touchdown on Mars [video]

#131

Post by manicdee » Tue, Feb 23, 2021, 2:15 AM UTC

kbaker wrote: post #104

giantrobot wrote: post #59

Earlier quoted context omitted.

Nothing about "interplanetary streaming" needs to be invented. The limiting factor is the size and power of the transmitter on Mars (or wherever). The MRO orbiter for instance is the highest bandwidth probe we've sent to Mars and it maxes out at about 4Mbps when Mars is closest to Earth. When Mars is farther it can only do about 500Kbps. That relatively prodigious rate requires the use of 34m receiving antennas on Ea…

Maybe that's what Elon has planned for the back side of the Starlink v2.0 satellites - to create an Earth-sized massively distributed phased array and get a super-high-bandwidth downlink from Mars.

Don't need particularly large antennas at the Mars end. Basically if you double the size of the antenna at the Mars end you can halve the size of the antenna back here on Earth.

So to establish a link comparable to the Earth-MRO link which has 35m dish here on Earth and 3m antenna at Mars, you could have a 11m antenna at both ends. The hard part is lofting that 11m antenna into Earth orbit in the first place (shipping it to Mars from Earth orbit is easy in comparison).

As an example you could cut the 11m antenna into two pieces, each being a half of a circle with 5.5m radius. That would easily fit into the SpaceX Starship cargo hold. Loft that into orbit, assemble it in orbit, then send it on its way to Mars. The only technical challenges there are flying a spaceship which hasn't reached orbit yet, and performing orbital assembly of a spacecraft (which hasn't been done yet).

Then for completeness put two more of those relay satellites at the leading and trailing Lagrange points for Mars so that we have communication with Mars even when it's on the other side of the Sun.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#132

Post by rsj_hn » Tue, Feb 23, 2021, 3:32 AM UTC

Kudos, NASA. This is why we love you.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#133

Post by snarf » Tue, Feb 23, 2021, 4:41 AM UTC

polishdude20 wrote: post #128

donarb wrote: post #108

Earlier quoted context omitted.

They use explosive bolts that attach the tether to the deck of the rover. They're almost 100% fool proof. Here's a Wikipedia entry, they're called pyrotechnic fasteners and NASA uses a lot of them. https://en.wikipedia.org/wiki/Pyrotechnic_fastener

But the image of the cables show what looks to actually be a literal cut cable. Not just a connector being disconnected but a clean slice.

From today's Reddit AMA with the NASA team, they use pyrotechnics to set off a guillotine like device to cut the cables. Possibly something like https://psemc.com/products/pyrotechnic-cable-cutter/

Source: https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

Re: Perseverance rover’s descent and touchdown on Mars [video]

#134

Post by jonnycomputer » Tue, Feb 23, 2021, 4:46 AM UTC

spookthesunset wrote: post #31

As it got closer to the ground, it seemed really hard to get a sense of scale with that downward camera. It felt like the ground just kind of "appeared" right before the sky crane did its thing. How big are the rocks under it? It felt like they were either big (1+ meter) or just little pebbles. I really couldn't tell. Either way, this is seriously the coolest video I think I've ever seen. I cannot wait for more.

Yeah, geology often seems self-similar at many different scales. I also was completely surprised when it was suddenly so close to the ground.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#135

Post by nier » Tue, Feb 23, 2021, 5:08 AM UTC

andyzweb wrote: post #109

GeorgeTirebiter wrote: post #105

Earlier quoted context omitted.

What if you had $ 2.7B? Would that help? (I'm not suggesting Percy is anything but a near miracle; only that they did have at least some non-trivial resources.)

Was that the budget for the whole thing? If that’s what it cost to put that thing up there why aren’t we doing this once a month.

NASA’s budget is not what it used to be during the cold war and specifically during the race to the moon. The budget for 2020 was $22.6 billion.

Source: https://www.planetary.org/space-policy/nasa-budget

Re: Perseverance rover’s descent and touchdown on Mars [video]

#136

Post by easton_s » Tue, Feb 23, 2021, 6:29 AM UTC

midasuni wrote: post #91

joeyh wrote: post #53

This was recorded by a computer running Linux, using ffmpeg. Embedded Intel system with fairly stock cameras. "the first open source linux box running on the surface of Mars" "thank you to the open source community for allowing us to use your amazing software" Per their press conference today, in the Q&A section. https://youtu.be/gYQwuYZbA6o?t=4025

30 years ago “ I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones. This has been brewing since april, and is starting to get ready” I think it’s more than a hobby now...

I know Linux is way more then just one man, but holy hell what one person can inspire.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#137

Post by easton_s » Tue, Feb 23, 2021, 6:35 AM UTC

udev wrote: post #24

There is this emotion, not sure it has a name, which I am sure many engineers know -- when you prepare your system for a long time and then send it into the real world and watch it work... You can feel it in this video, e.g when you see the crane fly away after accomplishing the mission. If we don't have a name for this emotion yet, I hope the japanese or the germans invent one. :)

It feels like watching your kids accomplishing something difficult on their own. The fear of mortality is loosened a bit.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#138

Post by skc » Tue, Feb 23, 2021, 6:54 AM UTC

soheil wrote: post #92

The way and the speed by which the sky crane moves away is just like any sci-fi movie, totally unreal [0] [0] https://youtu.be/4czjS9h4Fpg?t=188

Yes! It looked exactly like a B-Grade sci-fi film shot.

Beautiful.

I'm now sitting here wondering where it decided to crash land.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#139

Post by CompuHacker » Tue, Feb 23, 2021, 6:59 AM UTC

giantrobot wrote: post #122

kbaker wrote: post #104

Earlier quoted context omitted.

Maybe that's what Elon has planned for the back side of the Starlink v2.0 satellites - to create an Earth-sized massively distributed phased array and get a super-high-bandwidth downlink from Mars.

Wow. That's not how any of that works.

Oh, do explain a little more about why that doesn't work; wavelengths, total power, distances, etc.

Re: Perseverance rover’s descent and touchdown on Mars [video]

#140

Post by ranguna » Tue, Feb 23, 2021, 7:52 AM UTC

udev wrote: post #24

There is this emotion, not sure it has a name, which I am sure many engineers know -- when you prepare your system for a long time and then send it into the real world and watch it work... You can feel it in this video, e.g when you see the crane fly away after accomplishing the mission. If we don't have a name for this emotion yet, I hope the japanese or the germans invent one. :)

Joy?