Japan’s Hayabusa2 spacecraft grabs close-up thirty feet above asteroid(cnet.com)
cnet.com
Japan’s Hayabusa2 spacecraft grabs close-up thirty feet above asteroid
https://www.cnet.com/news/japans-hayabusa2-spacecraft-snaps-close-up-just-30-feet-above-asteroid/
97 comments
I'm kinda surprised an orbit that low as been stable for a year. Is this an unusually circular asteroid or is there a fair bit of eccentricity?
The hayabusa spacecraft is not in orbit about the asteroid. It's in orbit about the Sun, in an orbit very, very close to the orbit the asteroid is in, so they stay close to each other for a long time (about a year and a half IIRC).
I couldn't find any information on the trajectory. The sphere of influence in which the gravitational attraction of the asteroid dominates over that of the sun has a radius of about 6km though. So as long as the probe moves inside this area, it has to orbit or spend fuel of the reaction control system (the ion thrusters are inactive in the vicinity of the asteroid, they'd also have only enough thrust to allow hovering in a distance of hundreds of meters (in the tens of milli-newtons)).
> The sphere of influence in which the gravitational attraction of the asteroid dominates over that of the sun has a radius of about 6km though.
It depends on what you consider "dominates" to mean. For example, the corresponding value for the Earth and the Sun is 924,000 km, and the Moon is only 400,000 km from the Earth, but the Moon's orbit is still always concave towards the Sun.
It depends on what you consider "dominates" to mean. For example, the corresponding value for the Earth and the Sun is 924,000 km, and the Moon is only 400,000 km from the Earth, but the Moon's orbit is still always concave towards the Sun.
I'm not sure what you mean?
If Earth wouldn't dominate the space in which the Moon moves, the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
If Earth wouldn't dominate the space in which the Moon moves, the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
> If Earth wouldn't dominate the space in which the Moon moves
My point is that "dominate" here could mean different things, and the Earth does not dominate all of them.
Specifically, the fact that the Moon's orbit is always concave to the Sun means that the "acceleration due to gravity" of the Sun on the Moon is larger than the "acceleration due to gravity" of the Earth on the Moon. In other words, the net "acceleration due to gravity" of the Moon is always towards the Sun, not towards the Earth. So the Earth does not dominate in this way.
The "sphere of influence" you mention is based on tidal forces: the tidal effect of the Earth on the Moon is larger than the tidal effect of the Sun on the Moon. So the Earth does dominate in this way.
> the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
No, that's not what I said. Whether you think of the Moon as orbiting the Earth or the Sun depends on how you define "orbit" and what you are trying to do. If you define "orbit" according to which body the Moon is accelerating towards, on net, then the Moon is orbiting the Sun, not the Earth (see above); in this sense, the Moon and the Earth are in two closely matched orbits about the Sun.
And my point about the Hayabusa spacecraft and the asteroid is that, if you calculate the "acceleration due to gravity", you find that it's similar to the Moon's--the spacecraft's net acceleration is towards the Sun, not towards the asteroid.
My point is that "dominate" here could mean different things, and the Earth does not dominate all of them.
Specifically, the fact that the Moon's orbit is always concave to the Sun means that the "acceleration due to gravity" of the Sun on the Moon is larger than the "acceleration due to gravity" of the Earth on the Moon. In other words, the net "acceleration due to gravity" of the Moon is always towards the Sun, not towards the Earth. So the Earth does not dominate in this way.
The "sphere of influence" you mention is based on tidal forces: the tidal effect of the Earth on the Moon is larger than the tidal effect of the Sun on the Moon. So the Earth does dominate in this way.
> the Moon wouldn't be in orbit around Earth at all and the Sun couldn't perturbe this orbit (as you even stated yourself)?
No, that's not what I said. Whether you think of the Moon as orbiting the Earth or the Sun depends on how you define "orbit" and what you are trying to do. If you define "orbit" according to which body the Moon is accelerating towards, on net, then the Moon is orbiting the Sun, not the Earth (see above); in this sense, the Moon and the Earth are in two closely matched orbits about the Sun.
And my point about the Hayabusa spacecraft and the asteroid is that, if you calculate the "acceleration due to gravity", you find that it's similar to the Moon's--the spacecraft's net acceleration is towards the Sun, not towards the asteroid.
The disclaimer was meant to say that it's just an idealized system of two masses at a given distance. I picked these values to show what speed an object orbiting around a 'light' object like an asteroid approximately has.
So sorry: it's not in that orbit. I should have made that clear instead of talking about the probe, circling, ... which sounds pretty concrete.
(The asteroid is not spherical or homogenous and is even supposed to be a "rubble pile" with large holes inside which makes it highly questionable at best to treat it as point mass (you could if the probe were far enough away from it ... which it is not at all), but hey ... ¯\_(ツ)_/¯)
So sorry: it's not in that orbit. I should have made that clear instead of talking about the probe, circling, ... which sounds pretty concrete.
(The asteroid is not spherical or homogenous and is even supposed to be a "rubble pile" with large holes inside which makes it highly questionable at best to treat it as point mass (you could if the probe were far enough away from it ... which it is not at all), but hey ... ¯\_(ツ)_/¯)
I assume you calculated the average force and relative velocity experienced in the 450m circular orbit. At the perigee of the polar orbit (when the picture was taken) the force and the relative speed should be bigger. Also due to the small size of the asteroid the gravity should be quite uneven during the approach.
Hayabusa2 is such a cool mission! A veritable space Swiss Army Knife with tantalum bullets, deployable free-floating cameras, four small rovers that hopped around the asteroid in super low-G, and a 1.5kg kinetic impactor that blew a crater.
> It took a 180 million mile trip to deliver this image.
Yup, and you break my ability to zoom in or right click and view image on mobile.
Welcome to the future.
Yup, and you break my ability to zoom in or right click and view image on mobile.
Welcome to the future.
Wonder what material that greyish rock looking stuff on the surface is.
I went poking around Wikpedia. Ryugu's surface is mostly carbon. It's also a "rubble pile" and about 50% of its volume is empty space. There could even be large voids within because the force of friction between pieces is greater than the force of gravity holding it together.
Here's what it looks like when shot at with a "bullet"[0].
[0]https://www.cnet.com/videos/japans-hayabusa2-space-probe-fir...
[0]https://www.cnet.com/videos/japans-hayabusa2-space-probe-fir...
I would guess even operating the RCS system could launch some of those loose looking rocks to escape velocity. Imagine blowing on a rock that's been in place for thousands of years and watching it drift into space.
It's hard to get a sense of how big these features are. 30 feet is damn close, but it's still hard to say. How big is that big chunk of rock (?) near the bottom-right, casting a blocky shadow?
Given the distance to the sun and proximity to the asteroid, shouldn’t the vehicle and its shadow be essentially the same size?
I'd assume without an atmosphere to diffuse light, the sun is basically a point light for 95% of the Solar System.
Upon opening cnet, I had to block notifications request, click through cookies agreement and close video window, which started autoplaying.
Why are the pictures so fuzzy?
Insane Contrast ratio - ultra bright sunlight when the sun gets in the frame (no atmosphere to diffuse light) plus ultra dark hard shadows as the light source is millions of miles away, and again no atmosphere to diffuse the light.
Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
And incredible motion, the spacecraft is whipping by the asteroid quickly.. so you'd need a fast shutter speed to get sharp detail. Which is made difficult by the lighting conditions.
No human photographer on the shutter button. Way too far away for that.
Incredibly challenging photographic environment.
Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
And incredible motion, the spacecraft is whipping by the asteroid quickly.. so you'd need a fast shutter speed to get sharp detail. Which is made difficult by the lighting conditions.
No human photographer on the shutter button. Way too far away for that.
Incredibly challenging photographic environment.
> And incredible motion, the spacecraft is whipping by the asteroid quickly
No it's not. The whole point of the Hayabusa2 mission is to go to the asteroid and stay there. In fact it landed on it and grabbed a sample back in March.
No it's not. The whole point of the Hayabusa2 mission is to go to the asteroid and stay there. In fact it landed on it and grabbed a sample back in March.
> no atmosphere to diffuse light
Could the spacecraft—just in theory—introduce an atmosphere? Maybe not this spacecraft, but if we’re riding around in the starship Enterprise and want to get better snaps of asteroids, would it be a good idea to just send out a big pair of glass hemispheres, encapsulate the asteroid with them, pump them full of air, and then take a picture of the asteroid-capsule system?
Alternately, could you stick something really good at diffusing light—like a big block of aerogel—between the sun and the asteroid?
Could the spacecraft—just in theory—introduce an atmosphere? Maybe not this spacecraft, but if we’re riding around in the starship Enterprise and want to get better snaps of asteroids, would it be a good idea to just send out a big pair of glass hemispheres, encapsulate the asteroid with them, pump them full of air, and then take a picture of the asteroid-capsule system?
Alternately, could you stick something really good at diffusing light—like a big block of aerogel—between the sun and the asteroid?
This shot was taken from 9m away. A powerful camera flash would have been sufficient. It fact it seems like a bit of a missed opportunity not to have a handful of powerful but tiny LEDs on the spacecraft and take shots with different lighting to try to get the most detail out of this as possible. Yes you need to be quick, but this can be designed.
As far as I know these things are designed for scientific value and not for producing cool pictures for viewers. I am sure they are getting the best possible value for their budget with whatever they designed.
> not for producing cool pictures for view
Science funding often needs some one's buyin.
Science funding often needs some one's buyin.
You'd need miles and miles of air to get the kind of blue sky environment we think of as diffuse light. If you wanted to try this trick, it would be easier just to deploy a big translucent sunshade over the frame.
Or just do the science with the camera you have and ignore the fact that human viewers don't like the results aesthetically.
Or just do the science with the camera you have and ignore the fact that human viewers don't like the results aesthetically.
It... might be easier to 3D-scan the asteroid and render it with the lighting conditions of your choice in a 3D program?
If your spaceship is sufficiently large you could just point a lot of lights from different angles at the smaller asteroid to get the same effect.
Alternatively point a light strong light at yourself, so it is diffused back at the asteroid evenly. Photographers have used this trick for ages.
Alternatively point a light strong light at yourself, so it is diffused back at the asteroid evenly. Photographers have used this trick for ages.
The gravity likely isn't strong enough to hold the atmosphere. Also, that's a lot of material. A large white solar sail style diffuser might work, or even easier a really really powerful flash (probably explosive based).
Well, yeah, that’s why I mention encapsulating the thing in a glass ball or somesuch first, to hold the air in as it’s pumped over. Make a gatcha/Kinder Surprise asteroid. Obviously impractical, but I really like the image of it.
Wouldn't it be immensely more practical to match course and speed, have the object perfectly still relative to you, then take multiple pictures at different exposures and assemble them into an High Dynamic Range picture? Then if you really feel like it you can apply a diffuse filter to it.
> Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
Is it so dark? IIUC the asteroids is almost at the same distance from the Sun than Earth (something like a 50% more) so the illumination should be similar (about a half, but a glass that blocks half the light looks totally transparent at sight, it's weird to measure it experimentally). Is the soil of the asteroid too dark? Like what? Grounded coffee?
Is it so dark? IIUC the asteroids is almost at the same distance from the Sun than Earth (something like a 50% more) so the illumination should be similar (about a half, but a glass that blocks half the light looks totally transparent at sight, it's weird to measure it experimentally). Is the soil of the asteroid too dark? Like what? Grounded coffee?
I’m surprised they didn’t house a mirror on the craft to aid in illumination
The camera was not a priority for this mission. The small monitor camera was built and installed on the spacecraft thanks to public donations. This mission is about chemical and physical properties of the asteroid. Having a camera on it is mainly for publicity. NASA did a similar thing with the Juno spacecraft, letting people vote on where to point the camera while the main mission was to map out Jupiter's magnetic and radiation fields.
Indeed, none of these cameras need to be super crisp, although DCAM-3 (the deployable camera) is both a navigational tool and expected to provide some scientific insight. It was used to monitor the impact from the crater they created for the next sample, while Hayabusa 2 was safely on the other side of the asteroid: https://twitter.com/haya2e_jaxa/status/1114112619844005889?l.... That thread also has a shot from one of their navigation cameras, which apparently has a flash.
I love how many deployable objects this spacecraft is carrying, the target markers included. The number of moving parts must be staggering! (I wonder if they charge over USB? :b). JAXA has really amazed me with how resilient their missions have been. (The first Hayabusa limped back with a sample after a bunch of engine failures; their Venus probe failed to enter Venus's orbit, spent 5 years orbiting the sun, then tried again and worked). There's clearly a mountain of potential over there, so it's a treat to see this one go so perfectly smoothly :)
I love how many deployable objects this spacecraft is carrying, the target markers included. The number of moving parts must be staggering! (I wonder if they charge over USB? :b). JAXA has really amazed me with how resilient their missions have been. (The first Hayabusa limped back with a sample after a bunch of engine failures; their Venus probe failed to enter Venus's orbit, spent 5 years orbiting the sun, then tried again and worked). There's clearly a mountain of potential over there, so it's a treat to see this one go so perfectly smoothly :)
Perhaps because of the conditions of space + limited power supply?
Edit: Thank you to all the other posters who wrote way better answers with more information!
Edit: Thank you to all the other posters who wrote way better answers with more information!
30 feet = ~9.14 meters
30 feet = 10 meters at this level of accuracy. 9 if you want to be a pedant. Significant figures matter.
I know this thanks to playing DnD. Otherwise my entire life has been always metric.
It bothers me (too much) that we are going to space and still using 'feet' as a unit of measurement.
"Eschew flamebait. Don't introduce flamewar topics unless you have something genuinely new to say. Avoid unrelated controversies and generic tangents."
https://news.ycombinator.com/newsguidelines.html
https://news.ycombinator.com/newsguidelines.html
We don't use the imperial system for space, but the American readers do.
https://www.space.com/3332-nasa-finally-metric.html
I'm just as guilty as the next person when I post numbers. Occasionally, I'll also show metric. However, as an old(er) dog, my first instinct is to use feet, miles, etc.
Perhaps we should agree to use only the metric system on HN?
https://www.space.com/3332-nasa-finally-metric.html
I'm just as guilty as the next person when I post numbers. Occasionally, I'll also show metric. However, as an old(er) dog, my first instinct is to use feet, miles, etc.
Perhaps we should agree to use only the metric system on HN?
As a younger person who predominantly uses metric - as long as there's a conversion I don't see the issue. Just list both. I'm not sure why the sight of imperial units makes some people irrationally angry.
He’s probably referring to the time NASA lost the $125 million spacecraft because teams used different systems.
https://www.wired.com/2010/11/1110mars-climate-observer-repo...
It’s helpful when there’s only one system. In the US, it’s too costly to switch. HN readers are global and we’re technical so there’s no reason not to simply use metric.
https://www.wired.com/2010/11/1110mars-climate-observer-repo...
It’s helpful when there’s only one system. In the US, it’s too costly to switch. HN readers are global and we’re technical so there’s no reason not to simply use metric.
> In the US, it’s too costly to switch.
What is the estimated cost out of curiosity?
What is the estimated cost out of curiosity?
I estimate the cost to be 1 unit of national pride.
Everything has a cost. NASA estimated their cost was $370 million to switch to metric.
https://www.cnbc.com/2015/06/04/why-the-us-hasnt-fully-adopt...
The cost of switching road signs alone was quite expensive. Exit numbers, for example, are often the mile marker number.
https://www.cnbc.com/2015/06/04/why-the-us-hasnt-fully-adopt...
The cost of switching road signs alone was quite expensive. Exit numbers, for example, are often the mile marker number.
Oh yeah, I'm not saying there's zero monetary cost. I'm saying the blocker isn't affordability.
Honestly. Communication is about clarity, not about arbitrary 'correctness' in word-choice. Put both so everyone can understand it.
95% of the world officially uses metric.
https://www.reddit.com/r/theydidthemath/comments/2cjiau/self...
Do they still teach the metric system in US schools? I learned it over 40 years ago. Metric is the official system for science.
It’s hard to believe that we’re so close but we still have holdouts. It’s not an arbitrary choice at this point.
https://www.reddit.com/r/theydidthemath/comments/2cjiau/self...
Do they still teach the metric system in US schools? I learned it over 40 years ago. Metric is the official system for science.
It’s hard to believe that we’re so close but we still have holdouts. It’s not an arbitrary choice at this point.
It's a mistake that sometimes even Americans do, but the USA uses the US customary units system, which is closely related, but slightly different to the British imperial system.
Americans also call US customary units "imperial units", even though they're not the same as the British ones.
Imperial pints are bigger than customary pints, for example.
...the sad fact of which rears its head in American drinking establishments nationwide.
In my country, NZ, we refer to beer as pints, and order them as such, but a pint isn't a legal unit of measurement, so it's accepted that your pint will vary. The good establishments have a chart on the wall explaining how many millilitres map to their "pint". And a pint of high alcohol beer will often be less than a pint of average alcohol beer. 473mL vs 568mL typically.
It's not illegal to serve someone a "pint" if they ask for one, but it is illegal to offer a "pint" for sale.
It's not illegal to serve someone a "pint" if they ask for one, but it is illegal to offer a "pint" for sale.
So at the same establishment you could order two pints of beer and the high ABV one would be smaller in volume? That would really bother me or anyone calculating the unit cost of ethanol.
They make it clear what size they serve it in on their beer menu, so it's not too bad.
Japan's Hayabusa2 spacecraft grabs close-up 9.6652e-16 light-years above asteroid
https://www.mediamatters.org/video/2019/06/05/tucker-carlson...
Tucker Carlson: God bless you, and that's exactly what it is. Esperanto died, but the metric system continues, this weird, utopian, inelegant creepy system that we alone have resisted.
Tucker Carlson: God bless you, and that's exactly what it is. Esperanto died, but the metric system continues, this weird, utopian, inelegant creepy system that we alone have resisted.
...I had to look up Tucker Carlson to discover if this was satire or not.
At least it wasn't...
Japan's Hayabusa2 spacecraft grabs close-up 1/10th of an American football field above asteroid
Japan's Hayabusa2 spacecraft grabs close-up 1/10th of an American football field above asteroid
Japan doesn't if that helps.
You should be happy that they don’t measure it in “baseball fields” or something like that. That’s how usually things are reported.
Who's "we"? This article is about Japan. The Japanese do not ever use "feet" as a unit of measurement.
It's only Americans who still use feet and other imperial units, which is why they lost a Mars probe.
It's only Americans who still use feet and other imperial units, which is why they lost a Mars probe.
You mean the British-built one?
I think us Brits are the worst of the worst when it comes to mixing units. Fuel is sold in litres but consumption measured in miles per gallon. Milk is sold in 1 pint or 2/4/6 litre bottles. Road signs to towns are in miles but in roadworks are in metres. And so on.
I think us Brits are the worst of the worst when it comes to mixing units. Fuel is sold in litres but consumption measured in miles per gallon. Milk is sold in 1 pint or 2/4/6 litre bottles. Road signs to towns are in miles but in roadworks are in metres. And so on.
Yeah, the strange half-transition to metric in the UK is really odd. I'm from Australia, another Commonwealth country, and we're -entirely- metric here. The only thing I can think of is that people still talk about height of people in feet and inches, but on official forms it's in centimetres.
I wonder why the UK couldn't quite make the jump over?
At least the US has agreed that the Moon is a metric only zone! https://science.nasa.gov/science-news/science-at-nasa/2007/0...
I wonder why the UK couldn't quite make the jump over?
At least the US has agreed that the Moon is a metric only zone! https://science.nasa.gov/science-news/science-at-nasa/2007/0...
> I think us Brits are the worst of the worst when it comes to mixing units.
McLaren recently failed to qualify for the Indy 500 (McLaren!) due in part to a unit conversion problem made prior to the last day of qualifying.
https://autoweek.com/article/indy-500/mclaren-ceo-zak-brown-...
McLaren recently failed to qualify for the Indy 500 (McLaren!) due in part to a unit conversion problem made prior to the last day of qualifying.
https://autoweek.com/article/indy-500/mclaren-ceo-zak-brown-...
To be fair, from my reading of the article, this was a metric-to-imperial conversion problem, meaning McLaren was used to working in metric, but the Indy 500 is in the USA, which uses the backwards and archaic US customary units, so someone screwed up in converting to those. This could have happened to any non-American racing team, and doesn't serve at all as an example of Brits sticking with obsolete units, but rather the opposite.
It does seem that McLaren made a lot of boneheaded mistakes here, but this example just doesn't go with the "Brits are still using imperial units" theme of this thread at all.
It does seem that McLaren made a lot of boneheaded mistakes here, but this example just doesn't go with the "Brits are still using imperial units" theme of this thread at all.
To add to the mix, some signs are in yards - who even knows what one of those equals these days?!
And even then it's only the American public; NASA development is in metric.
(Part of the Mars orbiter fiasco was that it was being developed during the transition.)
(Part of the Mars orbiter fiasco was that it was being developed during the transition.)
Not really. The problem with the Mars lander (not orbiter, it was a lander that crashed) was that they got some data from a defense contractor (Lockheed Martin I think) which was in imperial units, and then NASA assumed it to be in metric units. Both sides made a stupid mistake here: the contractor didn't even provide any units at all on the data sheet they provided, and NASA didn't bother to ask, and just assumed some units. IIRC, these weren't some simple 1-dimensional unit like meters or liters, they were some compound unit (like lb-ft/N-m), so it was a stupid mistake, because even if you have metric units, you don't know if, for instance, there's some prefix, such as kilograms instead of grams, kiloNewton-meters instead of N-m, etc. It was really unbelievable IMO that they just took a bunch of bare numbers and assumed them to have some units associated.
Calm down. I clearly understood that as we humans, a collective whole.
Humans, in general, do not use "feet" for measurement. It's only dumb Americans. They don't represent humanity: they're only a small fraction of all humans (around 4%). Don't blame humanity for something that only Americans do.
I went all metric when we started the new millennium. I try to do all my personal measurements in metric. It has been my own personal battle to make progress, every little bit helps..
It's funny how life fights with you though. My wife and I share a scale in the bathroom, it's a fitbit wifi thing and she finally laid down the law, it uses pounds now. Chasing 130lbs is somehow more satisfying than 58.9 or 59Kg. Our electronic outdoor thermometer is in Fahrenheit now too; this one sort of pisses me off, metric is simple, below 10 you need a coat, 10 to 20 probably want a light jacket, 30+ is shorts because it's hot. Mind you, she is an actual scientist, a real deal scientist that works on viruses and immunology, which is somewhat frustrating. You wouldn't believe the fit she had when our electronic human thermometer was found to be metric... When you call the doctor because your child has a fever, it is better to use whatever units the doctor uses.
I suspect that major new papers could probably start using metric units with translation in parens and only the wingnuts that think the papers already harbor a liberal bias would say anything about it. Other than temperature and like human height, you can toss out metric measurements to most folks when they ask something and they seem to absorb it well; from time to time you get a question or push-back, rarely I'll translate the unit for them. We're at the point where people just need to see it more. It would be an interesting experiment if some media organizations started to make metric more prominent. Hell the US military uses it, mostly for NATO reasons... we could probably somehow put a patriotic spin on it.
It's funny how life fights with you though. My wife and I share a scale in the bathroom, it's a fitbit wifi thing and she finally laid down the law, it uses pounds now. Chasing 130lbs is somehow more satisfying than 58.9 or 59Kg. Our electronic outdoor thermometer is in Fahrenheit now too; this one sort of pisses me off, metric is simple, below 10 you need a coat, 10 to 20 probably want a light jacket, 30+ is shorts because it's hot. Mind you, she is an actual scientist, a real deal scientist that works on viruses and immunology, which is somewhat frustrating. You wouldn't believe the fit she had when our electronic human thermometer was found to be metric... When you call the doctor because your child has a fever, it is better to use whatever units the doctor uses.
I suspect that major new papers could probably start using metric units with translation in parens and only the wingnuts that think the papers already harbor a liberal bias would say anything about it. Other than temperature and like human height, you can toss out metric measurements to most folks when they ask something and they seem to absorb it well; from time to time you get a question or push-back, rarely I'll translate the unit for them. We're at the point where people just need to see it more. It would be an interesting experiment if some media organizations started to make metric more prominent. Hell the US military uses it, mostly for NATO reasons... we could probably somehow put a patriotic spin on it.
> Chasing 130lbs is somehow more satisfying than 58.9 or 59Kg.
I mean, chasing 60kg is more satisfying than 132.2lbs. There's nothing intrinsically important about 130lbs except that it's a round number in base 10. In metric you just pick a different round number to chase.
I mean, chasing 60kg is more satisfying than 132.2lbs. There's nothing intrinsically important about 130lbs except that it's a round number in base 10. In metric you just pick a different round number to chase.
I just want to go 15 miles per second (54000 mph/86904.6 Kph/46925 knt).
The solar system is moving at about 143 miles per second.
Does knots even make sense outside of the context of being located on a sphere?
According to https://en.wikipedia.org/wiki/Nautical_mile, nautical mile used to be defined as 1/60 of a degree of latitude, but is now defined as exactly 1852 metres. So feasible to use even in space, although unusual.
They are not particularly tied to spheres -- it's just nautical miles per hour, no? As such it can be a totally abstract unit, regardless of the origin (the same way feet can be used to measure something that doesn't involve a walk).
Aviation also uses them (though they still fly above a sphere).
Aviation also uses them (though they still fly above a sphere).
We could talk radians per second.
Perhaps we could use leagues... or furlongs :P
Relative motion is smaller though: The gravitational force between the probe (660kg) and asteroid (4.5 * 10^11kg) is just 0.1 N. The probe has therefore to be circling the asteroid with about 0.25m/s or just 1km/h (0.57 mph for american readers).
And how else could it be: the asteroid was assumed to be a point mass and the probe in a circular orbit of 450m around it.