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MankindsError t1_itm2g94 wrote

Say someone spots a planet killer, how much time would we need to put up a fight? Now that we know its entirely possible to deflect. Obviously the bigger the object the bigger we would need the craft to be for deflection, right?


KitchenDepartment t1_itmczjs wrote

Designing interplanetary probes takes years. You could probably speed that up in an emergency. But there are no manufacturer out there that are prepared to build probes rapidly.

Then you need to travel to the asteroid, and you want to hit it years in advance of the impact. Adding all that up you probably need something like 5-10 years of early warning. Depending on how devastating the impact would be.

If you want to be serous about planetary defense you should have one of these probes ready in advance in case we ever need it. A new falcon 9 rocket is launched every week. There would be no problem swapping out a payload in the event of a emergency. You could launch the probe in a matter of weeks instead of years.


bjornbamse t1_itn714n wrote

Designing interplanetary probes takes years because if can take years and you put time and effort into designing experiments. If there is time pressure it can be done faster.


Verbose_Code t1_itn9w10 wrote

Yeah I’d imagine if there was an extinction sized asteroid people (and money) would be mobilized very rapidly.

We also would not be aiming to do anything fancy. New solar panels that we want to raise the TRL on? Nope, we’re using a 2 decade old design. New engine with potentially 5% efficiency gain? Nope, just build a bigger spacecraft.


Hypamania t1_itpj62g wrote

But if we simply let it land we can mine all of the resources!


RandoCommentGuy t1_itnlpin wrote

Exactly, just look at climate change, people with money are flocking to fix the problem..../s


Verbose_Code t1_itnmrl7 wrote

Climate change is a much slower and easier to ignore problem. Big difference between “in 100 years we will see sea levels rise by x amount” and “this asteroid will impact the earth in 714 days and will kill everyone”

There are also a lot of people making money on us not fixing climate change. There isn’t the same economic force preventing us from reacting to asteroid threats


JUYED-AWK-YACC t1_ito0wqx wrote

From an engineer’s standpoint, a mission with no science instruments would be awesome. You could really get stuff done!


KitchenDepartment t1_itr1i93 wrote

Yes. And because it takes years to figure out the science part. The industry that produces the rest of the spacecraft is set up to also work on year long timelines. Producing the thrusters for a satellite in a few weeks would just be a waste of resources. You would spend most of the year without a job.

It is possible to do things faster. If things are truly desperate I am sure the US military's would just snatch up every satellite engineer they can get ahold of and give them blanket checks to whatever they need to manufacture a probe as soon as possible. But probes require a lot of highly specific components. And if only one of them is missing the entire program grinds to a halt.


kcahmadi t1_itnjvlz wrote

with companies like spaceX and rocketlab pumping out launches more than once a month now. they probably have inventory on hand where enough money and government priority will let them dedicate a rocket to it immediately

all you would need now would be trajectory analysis and a payload which could very well just be a warhead or even just have the rocket itself collide


Alan_Smithee_ t1_itndvkc wrote

That’s assuming an impacter/kinetic probe is the only type; there’s also the Gravity Tractor, which offers more precision, but probably needs more lead time (the closer the asteroid is to earth, the more you have to deflect it.)


burtzev OP t1_itm4x18 wrote

I'd agree that size is a great factor. There's , however, another thing about this that lurks in the background. Simply 'moving' an object isn't the same thing as moving the object to a precise and planned place. The mission did change the orbit of a smaller asteroid around a larger one. I suspect such a system was chosen precisely because the degree and even direction of movement was unknown and unpredictable. Nobody would want to 'accidentally succeed' by pushing a harmless target onto a dangerous (and once more unpredictable) trajectory.

I've read about the numbers associated with the success ie it changed the orbital period of the target around its babysitter. But I've seen no evidence that the precise change was predictable. After showing that it is possible to hit a small target very far away and move it there's still the steep hill of moving it where you want to left to climb.


MankindsError t1_itm5v1i wrote

I guess that's where distance and velocity come in? So if you only move it a small amount, over a great distance it would be enough to make a hit a miss? Say we have 18 months a millions upon millions of miles before impact. We push it successfully a short distance which makes its trajectory a miss for earth. We could then plan out where it will be in the future and in necessary do it again? I don't know much about the subject or the math that goes into something like this. It's just really interesting


bestest_name_ever t1_itn8b87 wrote

Yes, this is pretty much spot on. Accuracy isn't actually important, because in a theoretical mission where we're saving earth, well, it was already going to hit. We can't accidentally make it double hit, so the only thing that matters is changing the orbit enough so it no longer hits. And because asteroids are inert, it doesn't even matter if the new course isn't perfectly safe and would still hit earth next time it comes around, because when we know of an asteroid we can track it, so that case would buy sufficient time to do another deflection mission.


Adeldor t1_itm7t8u wrote

> I suspect such a system was chosen precisely because the degree and even direction of movement was unknown and unpredictable.

This target was chosen because the orbital parameters of Dimorphos about Didymos were precisely known, and its short orbital period of hours made it relatively quick and easy to determine the magnitude of change.

ETA: Also, Dimorphos' relatively small size made the changes larger, thus easier to measure.


burtzev OP t1_itmirq1 wrote

I'm sure that there has to be more than one factor in choosing an appropriate target when there are thousands of possible choices. The size and orbital period of Dimorphos certainly come into play - once you have first decided to look at binary systems as the safest bet. Here's what Science Magazine had to say about the mission. I quote the relevant paragraph:

>NASA chose to conduct the test on a binary asteroid system for two reasons. First, even though the pair was not on a course to hit our planet, the 780-meter-wide Didymos served as a gravitational anchor during impact, ensuring that Dimorphos wasn’t inadvertently ricocheted toward Earth. And second, having a pair of space rocks locked in orbit made it easier for scientists to measure the asteroid’s deflection relative to its partner.

Ease of measurement is reason number 2. Safety is reason number 1. Like the old slogan says, "Safety First". Space missions aren't always planned so responsibly.


Adeldor t1_itmwtun wrote

Curious. That doesn't gel with what I've read. For example, in this Wikipedia entry:

> "The Didymos system is not an Earth-crossing asteroid, and there is no possibility that the deflection experiment could create an impact hazard."

Further, in this preliminary presentation (PDF) by the planners of the DART mission, and in their subsequent paper (PDF), there's no mention of the system's binary nature being selected specifically for safety. The ease of measurement afforded by it being binary and its well understood parameters are the reasons given.

It's a shame Science Magazine didn't include a reference for the claim:

> "Didymos served as a gravitational anchor during impact, ensuring that Dimorphos wasn’t inadvertently ricocheted toward Earth."

To avoid future misunderstanding, I'd love to see a more direct reference for that if you know of one!


Xaxxon t1_itmhwc3 wrote

> the bigger the object the bigger we would need the craft to be for deflection, right?

Bigger or sooner. Either one is ok.

The earlier you change its course the less you need to change its course.


hawklost t1_itmxsjb wrote

You are forgetting other major factors. Angle of approach. Speed of approach. Even composition of the object drastically changes requirements.

You could have an object the side of Texas and if it is heading at the perfect angle to hit directly, would be far far harder to actually redirect than something 5x bigger but is coming at a different angle.


iqisoverrated t1_itpb7gf wrote

Depends on size, speed and how 'central' it would hit. Possibly also on composition (if it's very 'loose' then there's less effort to disperse it). All of these would determine how difficult it is to deflect...or whether it's possible at all. Beyond a certain size there's just nothing we can do.

But the idea is to detect them early and then have several years (5+) to stage a deflection mission. The further out you deflect the less change in its path is needed.


FaufiffonFec t1_itmpai6 wrote

> Now that we know its entirely possible to deflect.

I don't think that the DART mission has shown that we have the ability to deflect a large asteroid.

If a planet killer shows up, we're dead.


JBLeafturn t1_itn0j9n wrote

Planet killers are pretty easy to catch, though. Large bodies like that reflect more light. They've been mapped out and a planet killer is less that 1 in 12 billion chance in the next 100 years. The gap we have right now is bodies around 80-180M which would impact with the force of a few nuclear bombs, but are not enough to end civilization. It wouldn't be great if one of those hit, but it wouldn't end humanity. That's why DART was so important, it showed that we can give bodies in that range a pretty good shove in a short period of time.


Bensemus t1_itr9yuf wrote

It 100% did. Any impact on any body will move it. The greater the difference between the two objects the less change there will be.

With a planet killer asteroid it will be much larger so a DART sized craft will change its orbit much less but it will still change it. So for such an asteroid we ether need to hit it years out for that tiny change to have time to propagate or we hit it with something with more energy.


Schyte96 t1_itpju3k wrote

I would say a decade of warning minimum. Getting any space mission off the ground takes years, and you want your deflection event to be as far out as possible. The flight time from launch to impact is also probably around a year on top as well.

But the good thing is that we don't necessarily need to scale up in size for a bigger rock. One impactor of a size we can launch on a current rocket can't get it done? No problem, send 10, or 100. The cost of the craft is going to be negligible on these, all it needs to have is a chunk of mass, some avionics, and an engine for course adjustments. All of these already exist, so you don't need to invent anything new. The biggest cost item is going to be the launch vehicles.