NASA space copter ready for first Mars flight | Hacker News Reader

NASA space copter ready for first Mars flight

phys.org

143 pointsdnetesn49 comments

"The current plan for the first-ever attempt at powered, controlled flight on another planet is [...] to take off from Mars' Jezero Crater on Sunday at 10:54 pm US eastern time (0254 GMT Monday) and hover 10 feet (3 meters) above the surface for a half-minute, NASA said."

Set your alarms :)

If the given time is actually take off, we can expect images from the flight at the earliest around 11:10pm (E(S?)T)/ 03:31 AM (GMT) as Earth and Mars are currently at a distance of 15 light minutes from each other.

If they don't have a live feed, I would watch their Twitter account just in case. Useful links:

https://mobile.twitter.com/NASAPersevere

https://mars.nasa.gov/mars2020/

Edit: see reply by samizdis for another, better link

I'm not sure there will be images that quickly, just the telemetry to confirm if it was successful or not.

The bitrate Earth/Mars is very low. It will take a lot more.

I hope there is a movie eventually.

The direct earth to rover comms is slow but it's a lot quicker via MRO as it has a higher gain antenna.

https://mars.nasa.gov/mars2020/spacecraft/rover/communicatio...

Would setting up 60 Starlink satellites in a line to transmit between the two help?

No. It’s not a power or signal quality problem. It’s a speed-of-radio waves problem.

Mars is really far away. And unfortunately we don’t have something like an Ansible to make communication instant.

I think this situation is a good illustration of latency vs bandwidth. Latency is unavoidable due to the speed of light, but there’s no physical barrier to bitrate aside from power consumption.

Seems like the best bitrate we have from Mars is MRO at ~5 megabits/s which is enough for standard definition video. I’m certain we have the technology to push it higher, but it would be expensive and it seems it’s not really needed for existing projects.

Nit, though I'm going a bit (pun status unspecified) beyond my paygrade here: bandwidth is ultimately limited by the frequency of the trandsmission channel, though multiple channels can be multiplexed. This is the heart of Claude Shannon's work.

For deep-space transmission, other factors apply, though if you're operating in the right frequencies, the background noise level is low (at least as compared to Earth where there are numerous competing signals of terrestrial origin). And whilst signal/noise ratio does impose limits, there's only so much that boosting volume dB will achieve before you hit the channel limits themselves.

To increase bandwith beyond channel limits, you'd have to multiplex channels, which would involve different frequencies, different transmission routes (say, to widely-separated relay systems), or both. For physical media (e.g., fibre) this is relatively easy. For broadcast, given mass and energy budgets of spacecraft, probes, and rovers, the problems are harder.

Encoding, redundancy, error-correction, and retransmit protocols can all increase the ultimate reliability of the signal, though these impose other costs, notably on bitrate or at least time until the transmission is confirmed.

The time from mars to Earth is 3-20 minutes depending on orbit. Perseverance to MRO is 2 mbits/sec but only when it's overhead of the rover. MRO to Earth is 0.5 - 4 mbits per second.

While it takes around 10 seconds to transmit an image at 2mbit/s, the whole system has several store and forward steps adding significantly more delay. And a bunch of starlink-like satellites in medium orbit would for sure help to bridge the gap.

Latency and bitrate are both affected by distance. Bitrate scales down roughly by 1/d squared. Latency scales up by o(d) obviously. In theory, multiple small hops could keep power high over a long distance. On practice, the different sun-centered orbits the relays would operate on mean you'd have a lot of them. That's spendy.

Also, there's a spectrum limit on Earth side or else we could blast signals back with very wide bandwidth

This is a really clean explanation, thank you! Is the O(1/d^2) decrease in bitrate due to the inverse square law for radiation intensity?

Going real wideband would run into antenna efficiency issues. Designing an antenna that can handle a massively large bandwidth has a hell of a lot of engineering trade offs involved.

Interesting. I am not a rocket scientist, but I think there’s a few fundamental problems with doing this:

1. You can’t keep the satellites in a “line” between Earth and Mars, as objects in orbits of larger radii travel slower and so have longer orbital periods. This is the reason why for example geosynchronous orbits are only possible at a particular distance. They would only align with some frequency, which I’d guess would be closer to a geologic timescale than a human one. I think the fact that Mars and Earth’s orbits are slightly eccentric only makes this harder.

2. A solution to the above could be launching way more. But launching so many satellites carrying enough fuel to escape Earth’s gravity well would be prohibitively expensive compared to cost of LEO of existing Starlink satellites.

3. Starlink satellites are only designed to transmit maybe a few hundred km? In any case that’s 5 orders of magnitude smaller than the distance between Mars and Earth. You’d need dramatically more power consumption to transmit effectively over those distances, which is why existing bitrates are so low.

Anyway this is pretty cool, I found a NASA dashboard that also shows bitrates for current spacecraft: https://eyes.nasa.gov/dsn/dsn.html

Those units, e.g., 24. 25. 26 for Goldstone, are bitrates? Bits/second?

I think those are just identifiers for the telescopes. If you click on the telescope to expand you can see what it’s communicating with and some info about the link, and the bitrates are closer to e.g. 20 Kbit/s - 1.0 Mbit/s.

Thanks. The dataviz is unclear.

It might help reduce the affect of attenuation at a cost of more latency in the processing chain. This could help, afaik it's only been tested to Mars and not in production https://en.wikipedia.org/wiki/Laser_communication_in_space

You can't fix latency. You could increase data rate though.

I'm working on a multi-sat huge data rate, huge latency idea under the NASA NIAC program at the moment. If we continue to be concerned mostly with latency, then data rate will always be severely limited.

Sorry, no permalink, it's right on my page:

https://josh.vanderhook.info/index#2021-03-niac-announcement

Hard drives? :)

Sounds like back to DVD Netflix days. What's cool is that Reed Hastings planned to use internet from the start, but also knew that the tech is not ready.

Eventually it is going to be laser communications, I think. They are going to test deep space laser communications on the upcoming "Psyche"-mission, launching in 2022. The target asteroid will be at a distance of approximately 15 lightminutes (according to Wolfram Alpha) from Earth in 2026 when the probe is expected to arrive there. This is as far from Earth as Mars currently is. They hope to increase the bandwidth by an order of magnitude or two (i.e. 10-100 times). The link is supposed to be bidirectional, so the spacecraft can receive optical transmissions as well. I assume this laser uplink is more proof of concept than actually needed?

https://en.wikipedia.org/wiki/Psyche_(spacecraft)#Science_pa...

https://en.wikipedia.org/wiki/Deep_Space_Optical_Communicati...

You're right that the future of deep space communications is optical. There's a forum on Reddit: https://reddit.com/r/lasercom

According to NASA [1]: Perseverance is expected to obtain imagery of the flight using its Navcam and Mastcam-Z imagers, with the pictures expected to come down that evening (early morning Monday, April 12, in Southern California). The helicopter will also document the flight from its perspective, with a color image and several lower-resolution black-and-white navigation pictures possibly being available by the next morning.

[1] https://www.nasa.gov/press-release/nasa-s-mars-helicopter-to...

They’re quite confident. 3m is pretty high. Is there a reason not to hover at 1m? Maybe the lower gravity makes it acceptable...

Ground effect? But I would assume with such low atmospheric density the effect is probably not so strong.

What risks would be reduced by dropping the max altitude from 3m to 1m?

Obviously not an expert here. But here on Earth I would happily jump 1m but I'd probably break a leg from 3m.

Somebody must have decided that a 3m test flight was the best option. Maybe it's because if something fails, at least they may collect 1 picture at 3m high, and that's better than 1 picture at 1m...

They had a software glitch, and the flight was pushed back a few days while they investigate.

I once witnessed a person take their brand new electric rc helicopter place it on the ground and before I knew it the thing flipped over and smashed itself on the ground. I have a lot of respect for them taking their time; this could work incredibly well or for some unforeseen reason smash into the ground. In my situation it was the loss of signal that caused the accident when the pilot admitted to accidentally shutting off his controller right at that moment.

RC helicopter flying has evolved into something really insane

https://www.youtube.com/watch?v=AXSfFLGeVZA&t=156s

https://www.youtube.com/watch?v=E24JIetETAE&t=91s

Thanks for links. I had no idea. I tried flying an RC copter some time ago (piston engine) and getting it to hover was a nerve-wracking triumph. These folks and electric motors have taken it into another dimension.

Not just electric motors but cheap, high quality flight controllers. That and kickass batteries.

The nitro helis are no slouches either, they're all capable of insane 3D maneuvers in the right hands.

The exhaust plume of a nitro doing the same things is kind of more interesting IMHO, it's like a telltale in a wind tunnel test. I'm surprised they don't put a smoke bomb on the electrics during these demos.

Oh wow, can a full size helicopter do that? Would be amazing to see at an air show.

I don’t think so, engines on RC aircraft are quite powerful compared to their weight which isn’t a case with “real” aircraft. There’s a number of issues that can happen (and probably kill the crew) but it’s the most fundamental issue.

Only event I know of is this: https://www.reddit.com/r/nextfuckinglevel/comments/jmtvch/tu...

I think that's a few too many Gs for human pilots.

Delayed until no later than April 14

https://mars.nasa.gov/technology/helicopter/status/291/mars-...

Isn't "space copter" a bit of a misnomer? Isn't a copter a device with whirring blades tilted just so to cause thrust through a fluid medium (to wit, a propeller)? And isn't space defined often as that place where there is no such fluid like medium? So wouldn't it make more sense for it to be called a "Mars Copter"?

i guess i skim read news too much because i thought this happened last week.

Last week I almost thought it flew, but then it actually said "survived first night" not "survived first flight". And now I spot "first Mars flight" in the headline and thought it again but... nope, now it's "ready to fly". Like, great, let me know when it does.

The solar panel on the YouTube thumbnail looks quite dusty.

I wonder if the rotor wash will clean them off or kick up more dust and make them worse.

"Musk, get to tha choppa!"

When I read such articles I imagine SpaceX dropping their own rover in a few years that will autonomously drive around and gather more data in 30 days than NASA had in 30 years.

However, it will also manage to get stuck/kill itself within the 30 days ;-)

This is my concern about SpaceX applying its superpower to Mars. Rapid prototype iteration on Mars is orbital time: you wait 2 years for the next launch window and then ~7 months for travel, blow something up and learn lessons, repeat next window.

Hopefully they do some rapid iterating on Starship Moon missions and get some of the blowing up out of the way early.

I expect SpaceX to be prepped to launch multiple rockets per window.

In production, of course yes.

In iterating development, you would expect one at a time so a bug would not affect a whole fleet.

One thing spacex seems to do better is “eye candy”. They’d make sure that copter would transmit high quality video of its flight... constraints be damned.

Eye candy is very important for getting the public excited about these missions. More public excitement == more money and easier recruiting.

Musk said SpaceX would have a mars mission (not manned) on every earth/mars rendezvous starting in 2018. He originally said it was going to use dragon. And then he said manned missions starting in 2024.

https://en.wikipedia.org/wiki/SpaceX_Mars_program#2016_plans

They backed out of that but are still claiming they will do the manned around-the-moon trip in 2023 using Starship, and haven't backed down from point-to-point earth passenger travel by 2028 for cheaper than a business class flight.

https://www.vox.com/2018/4/11/17227036/flight-spacex-gwynne-... ("Shotwell estimated the ticket cost would be somewhere between economy and business class on a plane ")

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