I Detecting Asteroid Collisions: 'Oumuamua & Radio Telescopes

[websterling]

How fundamental is that narrow beam limitation, in terms of being a current technological barrier? Isn't it possible to develop a radar-radio-telescope, which encodes its transmitter signals just like internet packets and then not waiting with the whole apparatus for the round trip time, rather having a receiver that listens at a much wider returning beam-width, so any signal that returns is already encoded and thus will be known, to what region of transmission that signal belongs?

It's not uncommon to have the receiver and transmitter on different antenna. And they could be separated by some distance- radars for observing meteors are typically done this way. I think any encoding would probably be scrambled by a reflection from an irregular surface. You might be able to use different frequencies rather than an encoding. Still, considering transmitted power and beamwidth constraints, I don't think you could make a very efficient system.

 

[roineust]

It's not uncommon to have the receiver and transmitter on different antenna. And they could be separated by some distance- radars for observing meteors are typically done this way. I think any encoding would probably be scrambled by a reflection from an irregular surface. You might be able to use different frequencies rather than an encoding. Still, considering transmitted power and beamwidth constraints, I don't think you could make a very efficient system.

If some new SETI collaboration programs claim, that they will be able to hear an encoded signal as low as 100W in power, from a distance of up to 50 light years, isn't it possible to have Earth transmitters strong enough, to decode an asteroid hit round trip of up to a few hours?

 

[websterling]

they will be able to hear an encoded signal as low as 100W in power, from a distance of up to 50 light years

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

 

[roineust]

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

Yes, sorry, i read the whole article but missed the laser part when returned to quote, what about laser scanning then? (-:

It looks like LIDAR telescopes are used for atmospheric research. In what ways would it be different to scan much further away to a distance and object size of an asteroid 2 light hours from earth?

 

[mfb]

You misrepresented the project you cited, claiming it was to search for PHAs when it was actually searching for NEOs.

Uh, what?
"They looked for A and B."
"How often did they find A?"
"I said they looked for A and B, not only for A!"

Here A=PHAs, B=NEOs that are not PHAs just in case it was not clear.

NASA was established in 1958, and yet 40 years later they had only discovered ~10% of the NEOs larger than 1 km. Yet since Congress ordered NASA to locate NEOs larger than 1 km NASA has managed to find more than 98% of them in less than 20 years. Which clearly demonstrates that NASA was not specifically looking for NEOs (of any size) until ordered to track them by Congress.

No it does not demonstrate this, and even if it would, it would miss the point because I was asking about a different time frame. Telescopes and data analysis are improving rapidly, with or without congress orders.

Gaia alone is expected to roughly double the number of known asteroids in the solar system (and measure most of the discovered ones as well, of course). Without any congress order, and without NASA at all, because it is an ESA mission.

Yes, sorry, i read the whole article but missed the laser part when returned to quote, what about laser scanning then? (-:

You can't "laser scan" for asteroids. They are not nice retroreflectors that would reflect the lasers. Even with the Moon, which is nearby and where we have actual retroreflectors, we just get something like 1 photon per shot back with the best combination of ground stations and mirrors. You have to know precisely where the mirror is and you need a good estimate for the distance already, otherwise you wouldn't even find the Moon with that approach.
To get a detectable signal back from radar astronomy, the beam has to be very narrow. You cannot scan the whole sky, or even a relevant fraction of it, like that.

I expect attempting to achieve surface blast. (Subsurface would be even better, but it requires development of a penetrating warhead).

Ivy Mike's 10Mt explosion on a small coral reef island resulted in 1.9km diameter, 50m deep crater. You can fit about a hundred Oumuamua's into a crater of these dimensions.

You are still missing the atmosphere.

 

[roineust]

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

What are the basic technical and scientific hurdles for this 1km and less than 1 AU range/size limit?

 

[websterling]

What are the basic technical and scientific hurdles for this 1km and less than 1 AU range/size limit?

1) There's a limit to the transmitter power available.
2) Signal strength falls off as $1/d^2$.
3) Dust covered rocky objects are poor reflectors.
4) 1km is rather small.
5) The return also falls off as $1/d^2$.

 

[roineust]

In the article they're talking about a signal from a 100W laser; entirely different physics involved.

With radar I think the limit for just detection of a 1km object is less than 1 AU, less than a 15 minute round trip time. For an object like Oumuamua it would be far less.

To which specific radar type, class or model were you referring to, which have these limits (1km 1 AU) and yet are the best currently available, for such an asteroid finding task? You meant hypothetical usable radars or ones that already exist as part of an asteroid detection system? You did mention that radars are already used to search for near Earth objects, you probably meant space derbies collision avoidance for the ISS or did you refer to other radars that search further away than space derbies? How come these radars are able to detect meteors, as you mentioned, while meteors are much smaller objects than asteroids? You meant only when meteors are as close to us as space derbies or less?

What i could find regarding radars and space derbies was Cobra Dane and EISCAT.

 

[russ_watters]

It also helps if you are actually looking for them, which NASA wasn't prior to being given a congressional directive in 1998.

You ignored @nikkkom 's point, so I'll expand/repeat: Robotic/automated sky surveys were at best difficult and at worst impossible until at least the 1980s. But the capabilities expanded so fast that starting in the 1990s, amateurs regularly discover comets and asteroids. Many do their own automated sky surveys, discovering dozens or even hundreds. These days, hunting for such objects is so easy it is practically a race.

Sure, there is a a bit of a chicken-or-egg issue here, but what is certainly NOT a component of it is the implication that we could have found these thousands of objects in the 60s or 70s if we had simply decided to look. We could not have. And conversely, whether Congress was the cart or horse, a significant fraction of these objects were going to be found either way.

[edit] A quick google tells me that the first commercial CCD camera (100x100 pixels) was released in 1975 and the first telescope with a digital camera (pointed down ;) ) was launched into space in 1976. So I think it is fair to say that digital sky surveys were impossible until at least 1976.

 

[glappkaeft]

You ignored @nikkkom 's point, so I'll expand/repeat: Robotic/automated sky surveys were at best difficult and at worst impossible until at least the 1980s. But the capabilities expanded so fast that starting in the 1990s, amateurs regularly discover comets and asteroids. Many do their own automated sky surveys, discovering dozens or even hundreds. These days, hunting for such objects is so easy it is practically a race.

Unfortunately (or not) those days have been over for years if you are talking about the amateurs due to the big automated surveys. It is only going to get even harder for the amateurs when LSST comes online and with GAIA's later data releases.

Most amateurs switched to followup observations or other areas like variable stars years ago. See for instance this article https://www.airspacemag.com/as-interview/aamps-interview-roy-tucker-112571/?all

 

[|Glitch|]

You ignored @nikkkom 's point, so I'll expand/repeat: Robotic/automated sky surveys were at best difficult and at worst impossible until at least the 1980s. But the capabilities expanded so fast that starting in the 1990s, amateurs regularly discover comets and asteroids. Many do their own automated sky surveys, discovering dozens or even hundreds. These days, hunting for such objects is so easy it is practically a race.

Sure, there is a a bit of a chicken-or-egg issue here, but what is certainly NOT a component of it is the implication that we could have found these thousands of objects in the 60s or 70s if we had simply decided to look. We could not have. And conversely, whether Congress was the cart or horse, a significant fraction of these objects were going to be found either way.

[edit] A quick google tells me that the first commercial CCD camera (100x100 pixels) was released in 1975 and the first telescope with a digital camera (pointed down ;) ) was launched into space in 1976. So I think it is fair to say that digital sky surveys were impossible until at least 1976.

@nikkkom 's point was irrelevant. I wasn't debating the efficiency of automated searches. You pretend as if nothing could be discovered prior to CCDs, when we know that is not true. Granted, it is not as "efficient" as an automated/robotic search, but we have taken photographs of the same part of the sky at different times and then compared them to see if anything moved. How do you think Pluto was discovered?

NASA is also a government agency that does what they are directed to do by both Congress and the President. It is not like they have the initiative (or an unlimited budget) to do whatever they please. If Congress does not direct NASA to locate NEOs, and does not provide funding for that purpose, then NASA will not locate NEOs. Which is what happened between 1958 and 1998.

 

[nikkkom]

@nikkkom's point was irrelevant.

I feel hurt, distressed and also don't care :D

 

[TeethWhitener]

Even if we assume you manage to break the asteroid apart: So what? Now you have several smaller components that still fly towards Earth with the same combined energy. But instead of one area with a massive impact crater you get many impact craters scattered over a large area. You might even increase the damage it does.

Not to mention these fragments are highly radioactive. You've traded a sniper rifle for a plutonium shotgun.

 

[DrStupid]

Not to mention these fragments are highly radioactive.

It would be low- or medium-reactive material, depending in the size of the warhead (the bigger the less radioactive). An explosion of the same size on Earth would produce more nuclear fallout and we had many of them in the past. The resulting increase of the background radiation would be an irrelevant side-effect of the impact. The main problem is in fact the fragmentation of the asteroid.

 

[nikkkom]

The main problem is in fact the fragmentation of the asteroid.

Non-fragmented asteroid is exponentially more destructive.
1-2 meter fragments will do no damage whatsoever.
20-meter fragments generally won't reach the surface too (a-la Chelyabinsk) but cause shockwave damage.
50-meter fragments can cause a city-scale destruction.
200-meter intact asteroid would leave about 5km diameter crater.

 

[mfb]

64 scattered city-scale destruction areas (hard to evacuate) vs. one larger focused spot of destruction (possible to evacuate).

 

[nikkkom]

230x35x35m asteroid can't be separated into 64 30m fragments. Maximum eight fragments.

Fragmentation at ~500km altitude means ~25 seconds to impact. If big fragments would have ~100m/s lateral velocities, they can drift apart by ~2.5 km only. The destruction will still be localized in about the same location, not spread across half a continent.

 

[mfb]

If you break it up that late it doesn’t matter anyway.

The number of fragments scales with the cube of the length scale. It doesn’t matter which shape you assume but be consistent - don’t switch in between.

 

[DrStupid]

The destruction will still be localized in about the same location

And so will be the energy. Just the type of destruction will change. The larger the fragments the higher the ratio of mechanical effects (e.g. shock waves or seismic waves). The smaller the fragments the larger the ratio of radiative effects (e.g. heat radiation or emp). It depends on the circumstances which of them are more destructive. A direct hit could kill a city in any case.

 

[nikkkom]

And so will be the energy. Just the type of destruction will change. The larger the fragments the higher the ratio of mechanical effects (e.g. shock waves or seismic waves). The smaller the fragments the larger the ratio of radiative effects (e.g. heat radiation or emp).

Exactly.
Energy in different forms has very different destructive potential.
For example, one kilogram of burning wood releases more energy than a hand grenade.

If you turn this asteroid into 1-5 meter fragments, on entry its energy will be converted almost entirely to light and shock waves in the air.
Light flash would be spectacular but won't be intense enough to do harm.
Shock waves would cause widespread window damage and may cause moderate structural damage in some buildings.

 

[DrStupid]

Light flash would be spectacular but won't be intense enough to do harm.

We are talking about several Gt TNT equivalent. That would be sufficient to raise the temperature of the entire atmosphere within a 10 km radius around ground zero by some hundred K. The temperatures in the upper atmosphere, where most of the energy is initially released, would be much higher. A major part of the resulting heat radiation would pass the atmosphere and reach the ground, resulting in a second temperature peak at ground level. I don't believe that this would be harmless until I see a corresponding calculation.

Shock waves would cause widespread window damage and may cause moderate structural damage in some buildings.

Even the Chelyabinsk meteor caused widespread window damage and moderate structural damage in some buildings in Chelyabinsk which is 40 km away from ground zero. A direct hit with several thousand times the energy would raze the city to the ground and let it go up in flames.

 

[nikkkom]

>> Light flash would be spectacular but won't be intense enough to do harm.

We are talking about several Gt TNT equivalent. That would be sufficient to raise the temperature of the entire atmosphere within a 10 km radius around ground zero by some hundred K.

...if all of it is absorbed. Which does not happen.

A direct hit with several thousand times the energy

This particular asteroid would not have "several thousand times the energy" of Chelyabinsk event. More like about 50 times more energy. (Chelyabinsk bolide estimated to be ~20m, Oumuamua is ~230m x 35m x 35m).

 

[mfb]

..if all of it is absorbed. Which does not happen.

The energy is still there - if it doesn't get absorbed by the atmosphere that just means it directly reaches the ground and heats that.

230*35*35/20³=35. If we give the asteroid 3 times the speed it has 315 times the energy. If we give it 8 times the speed it has 2200 times the energy. Not necessarily thousands of times, but the difference is still huge.

 

[nikkkom]

The energy is still there - if it doesn't get absorbed by the atmosphere that just means it directly reaches the ground and heats that.

Half of the energy which has been converted to light goes up straight to space and has no effect. The other half shines onto the ground, and part of that (on average 30%) gets reflected.

 

[DrStupid]

This particular asteroid would not have "several thousand times the energy" of Chelyabinsk event. More like about 50 times more energy. (Chelyabinsk bolide estimated to be ~20m, Oumuamua is ~230m x 35m x 35m).

With 230m x 35m x 35m Oumuamua has a volume of about 2.8·10⁵ m³ and with a density of 1500 kg/m³ a mass of 4.2·10⁸ kg. With a speed of 50 km/s this results in a kinetic energy of 5.3·10¹⁷ J which corresponds to 1.3 Gt TNT eqivalent. That's like 25 Tsar bombs (50 Mt) or 2500 times the energy of the Chelyabinsk meteor (500 kt). What makes you think the resulting destructions at ground zero would be similar to a single Chelyabinsk meteor in a distance of 40 km?

 

[nikkkom]

What makes you think the resulting destructions at ground zero would be similar to a single Chelyabinsk meteor in a distance of 40 km?

Nothing makes me think so. I said no such thing.

I said that nuking this asteroid in space is (a) probably possible even with today's tech, and definitely possible if we'd finance a R&D program for nuclear-tipped asteroid interceptors; and (b) does significantly reduce the effects. The effects will still be severe, but many times less so than if we just let it impact the ground intact.

 

[Drakkith]

This paper, which studies the deflection and fragmentation of a near-Earth asteroid, may be of interest: http://web.gps.caltech.edu/~sue/TJA_LindhurstLabWebsite/ListPublications/Papers_pdf/Seismo_1621.pdf

Note that "fragmentation" here refers to the strategy of breaking up the asteroid so that the majority of its fragments are either too small to pose a threat to Earth or miss Earth completely. Interestingly, the paper claims that a surface burst is not more effective than a "stand-off" burst, which is detonated at a distance from the asteroid.

I said that nuking this asteroid in space is (a) probably possible even with today's tech, and definitely possible if we'd finance a R&D program for nuclear-tipped asteroid interceptors;

A short search on google netted me this paper: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150011479.pdf
It discusses the suborbital interception and fragmentation of an asteroid with very short warning times using modern ICBM's. Interception of an asteroid at further distances is probably not possible without a specialized launch vehicle. I don't think ICBM's have enough fuel to escape Earth's orbit and reach their target. We certainly have the technology to create a launch vehicle and weapon system capable of intercepting and deflecting/fragmenting potential threats, we just haven't had the push to do so.

 

[OCR]

...google netted me this paper:

Lol, not bad... .

Intended... ?

 

[Drakkith]

Lol, not bad... .

Intended... ?

Sorry, I'm not sure what you're asking me.

 

[OCR]

Sorry, I'm not sure what you're asking me.

No worries ... I thought you might have made an intended pun. .