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Perseverance Rover lands on Mars [video]

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Re: Perseverance Rover lands on Mars [video]

#311

Post by theelous3 »

WJW wrote: post #131
tectonic wrote: post #14

You can also watch an EDL visualization in your browser: https://eyes.nasa.gov/apps/mars2020/#/home And read about how it will use Terrain Relative Navigation to find a safe landing spot: https://www.jpl.nasa.gov/news/a-neil-armstrong-for-mars-land... Perseverance is phenomenally complex, its Sample Caching System alone contains 3,000+ parts and two robotic arms. So exited for all the sciencing this nuclear-powered,…

> is this what NASA calls 'weights'? Well no, the Cruise Mass Balance Devices are intended to Balance the Mass of the spaceship during Cruise conditions. That these Devices are single-part and constructed out of a single chunk of metal each should not be construed as merely being 'weights'. :)

What I'm getting from this, is that you can use weights to balance the mass of the spaceship during cruise conditions.

Re: Perseverance Rover lands on Mars [video]

#312

Post by frabbit »

Daho0n wrote: post #224

I stopped watching videos like these when they started chanting like some crazy cult when things went well (USA! USA! USA!). No wonder we can't just get along.

Certainly took away from the experience for me. Also the constant clapping was irritating along with the guy going "yes, yess" towards the end.

Not enough info, too much "personality" and "team work". Waste of time watching it really.

Re: Perseverance Rover lands on Mars [video]

#313

Post by science4sail »

aaron695 wrote: post #304

I don't get why they had to bring the children into this asking questions constantly. Do we really want to reinforce this is just for children? SpaceX doesn't do this. They are always top quality. Adults doing professional things in space, that to me is more inspiring to children and young adults. Can't they have an adult stream and one dumbed down for the children if they really think these things should be dumbed d…

I wonder if it's a case of misaimed audience?

Even though "children asking questions" may be less appealing to children than "adults asking questions", the former might get aired anyway because it's more appealing to the adults that make children's programs.

Re: Perseverance Rover lands on Mars [video]

#314

Post by Dylan16807 »

amelius wrote: post #211
theNJR wrote: post #200

Earlier quoted context omitted.

Came here to suggest The Order of Time by C Rovelli, which explains this in such a captivating way.

I think this video explains the issue quite well in only two minutes: https://www.youtube.com/watch?v=wteiuxyqtoM

But that only happens with sufficiently high relative velocities. Earth and Mars are effectively in the same reference frame.

Re: Perseverance Rover lands on Mars [video]

#315

Post by heisenzombie »

mulmen wrote: post #310
Melkman wrote: post #307

Earlier quoted context omitted.

Consistency is not the only value of a system of units. Convenience is also of importance. And that is where the metric system shines. Having all measures of a unit in multiples 10 combines perfectly with our decimal calculations. Having as few as possible magical numbers to convert and combine between units makes making mistakes harder. How many calories in kinetic energy has a pound going 10 miles per hour ? I know…

If working with simple units of ten is beneficial then every mission should redefine units in terms of expected velocities and vehicle size so they are optimized for the actual calculations at hand. That's not realistic, obviously, so we just pick one. The units in the system are arbitrary, really. In reality regardless of the system you choose every calculation is going to end up with fractions of something. You are…

Physicists are quite fond of redefining units so that the constants they care about are all just 1. (https://en.wikipedia.org/wiki/Natural_units).

For example, you could define mars units where the gravitational acceleration on mars is 1. Now your velocity in freefall is just equal to the time you've been freefalling! You don't even have to do a calculation!

(note: Don't actually do this. Gravitational acceleration isn't a constant when you're doing orbital mechanics.)

Re: Perseverance Rover lands on Mars [video]

#316

Post by iexplainbtc »

0_____0 wrote: post #73
iexplainbtc wrote: post #49

That live stream was epic! It was great to see them so happy :)

Hard for me to imagine what it's like to spend years of your life working on a singular launch project. So much riding on what happens in a handful of moments, whether that's launch or EDL. Pretty sure I'd just start sobbing in the control room if that were me regardless of outcome.

These live streams are anxiety inducing for us, I can only imagine how they must feel!

Re: Perseverance Rover lands on Mars [video]

#317

Post by m4rtink »

dmurray wrote: post #128
hedgehog wrote: post #122

I read that the design life of the helicopter is five flights. Does anyone know what the limiting factors are? The brutal cold and abrasive dust both seem like they could contribute but I am curious what the real answer is.

The "design life" figure is something like the 5th percentile, if previous rovers are anything to go by. As in, they can estimate a 95% chance it makes it through 5 flights. I'd bet on it making 20+ at evens.

If we go by MER Opportunity standards (surviving 55x times its design timespan) we might go up to 275 flights! :D

Re: Perseverance Rover lands on Mars [video]

#318

Post by xarope »

theelous3 wrote: post #311
WJW wrote: post #131

Earlier quoted context omitted.

> is this what NASA calls 'weights'? Well no, the Cruise Mass Balance Devices are intended to Balance the Mass of the spaceship during Cruise conditions. That these Devices are single-part and constructed out of a single chunk of metal each should not be construed as merely being 'weights'. :)

What I'm getting from this, is that you can use weights to balance the mass of the spaceship during cruise conditions.

Ships do this all the time (ballast), and anybody who's ever flown on a light aircraft or helicopter also knows the importance a pilot places on weight distribution.

I guess what's surprising is that they needed that much weight (140+kg seems like a lot?) and couldn't redistribute existing componentry; guess the knapsack algorithm wasn't good enough, or that they just couldn't break up enough pieces?

And yes, Cruise Mass Balance Devices sounds like the type of name a tired engineer would come up with to convince upper management...lol

Re: Perseverance Rover lands on Mars [video]

#319

Post by xarope »

theelous3 wrote: post #311
WJW wrote: post #131

Earlier quoted context omitted.

> is this what NASA calls 'weights'? Well no, the Cruise Mass Balance Devices are intended to Balance the Mass of the spaceship during Cruise conditions. That these Devices are single-part and constructed out of a single chunk of metal each should not be construed as merely being 'weights'. :)

What I'm getting from this, is that you can use weights to balance the mass of the spaceship during cruise conditions.

Surely you mean: "What I'm getting from this, is that you can use devices to balance the mass of the spaceship during cruise conditions"...j/k

Re: Perseverance Rover lands on Mars [video]

#320

Post by m4rtink »

FrojoS wrote: post #163
raphaelj wrote: post #47

NASA's ability of succeeding at landing things successfully on the first try on foreign bodies since 1969 is mind-blowing. Meanwhile, SpaceX takes half a dozen tries before managing to do the same on a fully known environment on Earth.

Rediciolous comparison. The size of the objects that SpaceX is landing is much larger. The approach that was used here for Perseverance (Skycrane) would not work for larger ships, like those required for a human mission. Just like the previous approaches, e.g. Lithobraking with Spirit and Opportunity, would not have worked for Perseverance. Larger objects are much more difficult to land. Simply put, while mass will i…

The Mars atmosphere is at a tricky spot where you can't ignore it like when landing on the Moon (also Mars gravity is higher than on the Moon) yet it's not thick enough for survivable landing with parachutes or wings (as envisioned in the earliest Mars mission plans) only.

That's why you always see parachutes + something else for Mars EDL - parachutes + rockets, parachutes + airbags, parachutes + skycranes. And in Starship case, high speed glide and speed shedding with propulsive landing at the end.

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