Starship Asterisk*

APOD Robot wrote: ↑Tue Nov 13, 2018 5:09 am Bennu's diamond-like appearance

neufer wrote: ↑Tue Nov 13, 2018 1:16 pm viewtopic.php?f=8&t=18688&p=287008#p287008

starsurfer wrote: ↑Tue Nov 13, 2018 5:03 pm
Also noticed this mistake in the last sentence: ORISIS-Rx

https://en.wikipedia.org/wiki/Medical_prescription wrote:
<<'℞' is a symbol meaning "recipe". It is sometimes transliterated as "Rx" or just "Rx". This symbol originated in medieval manuscripts as an abbreviation of the late Latin verb recipere, specifically the second person singular imperative form recipe meaning "take", thus: "take thou". Originally abbreviated Rc, the c was simplified and finally written as a straight stroke making it look like an x in combination with the right "leg" of R. Medieval prescriptions invariably began with the command to "take" certain materials and compound them in specified ways. Folk theories about the origin of the symbol '℞' note its similarity to the Eye of Horus, or to the ancient symbol for Zeus or Jupiter, (♃), gods whose protection may have been sought in medical contexts.>>

MarkBour wrote: ↑Tue Nov 13, 2018 4:55 pm Nice images. I love the boulders littered on the surface. Would this body qualify as a rubble heap? Perhaps easily crumbled? It is so small, I assume we have the capability to alter its trajectory with conventional propulsion ... should the need arise. And, if OSIRIS is going to go bump into it, take a scoop, and then push off of it, we may create the problem ourselves. But, I have confidence that NASA scientists already thought about that before launching this mission. Indeed, part of the mission objectives involve fine measurements of Bennu's orbit and small effects like the Yarkovsky effect. Bennu has a mass of about 60-80 billion kg.

BDanielMayfield wrote: ↑Tue Nov 13, 2018 10:18 pm

MarkBour wrote: ↑Tue Nov 13, 2018 4:55 pm Nice images. I love the boulders littered on the surface. Would this body qualify as a rubble heap? Perhaps easily crumbled? It is so small, I assume we have the capability to alter its trajectory with conventional propulsion ... should the need arise. And, if OSIRIS is going to go bump into it, take a scoop, and then push off of it, we may create the problem ourselves. But, I have confidence that NASA scientists already thought about that before launching this mission. Indeed, part of the mission objectives involve fine measurements of Bennu's orbit and small effects like the Yarkovsky effect. Bennu has a mass of about 60-80 billion kg.

It certainly is a rubble heap, and it's low gravity is barely able to hold it together I would guess.

Better not bump it too hard... Imagine the liability if it was accidentally pushed into an Earth intersecting orbit... The ultimate butterfly effect.

Chris Peterson wrote: ↑Wed Nov 14, 2018 1:14 pm

BDanielMayfield wrote: ↑Tue Nov 13, 2018 10:18 pm
Better not bump it too hard... Imagine the liability if it was accidentally pushed into an Earth intersecting orbit... The ultimate butterfly effect.

Of course, the tiniest bump could as easily prevent a collision with Earth. That's the thing about chaos theory. No way to tell.

https://en.wikipedia.org/wiki/101955_Bennu wrote:

1. Bennu will pass 0.005au from Earth on 23 September 2060. The close approach of 2060 causes divergence in the close approach of 2135.
   
   2. On 25 September 2135 the nominal approach distance is 0.002au from Earth, but Bennu could pass as close as 0.0007au.
   (There is no chance of an Earth impact in 2135.)
   
   3. The 2135 approach will create many lines of variations and Bennu may pass through a gravitational keyhole during the 2135 passage which could create an impact scenario at a future encounter. The keyholes are all less than 55 km wide.

gwarstadt wrote: ↑Wed Nov 14, 2018 8:07 pm
Is anyone else struck by the fact that the horizontal axis [sic...you mean radius ?] of this non spherical object is exactly half the vertical axis, and its so symmetrical that if you watch an edge as it rotates the profile hardly moves (except for the big rocks)?

https://www.syfy.com/syfywire/hey-bennu-have-we-met-i-never-forget-an-asteroid wrote:

101955 Bennu / 162173 Ryugu

---

Hey Bennu, have we met?
I never forget an asteroid.
Contributed by Phil Plait @BadAstron

Comparing two small asteroids: 550-m-wide Bennu (left), and 1-km-wide Ryugu (right) roughly to scale.

Credit: Ryugu: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.

neufer wrote: ↑Wed Nov 14, 2018 2:46 pm

Chris Peterson wrote: ↑Wed Nov 14, 2018 1:14 pm

BDanielMayfield wrote: ↑Tue Nov 13, 2018 10:18 pm
Better not bump it too hard... Imagine the liability if it was accidentally pushed into an Earth intersecting orbit... The ultimate butterfly effect.

Of course, the tiniest bump could as easily prevent a collision with Earth. That's the thing about chaos theory. No way to tell.

https://www.youtube.com/watch?v=6a6rAa34H9Y

https://en.wikipedia.org/wiki/101955_Bennu wrote:

1. Bennu will pass 0.005au from Earth on 23 September 2060. The close approach of 2060 causes divergence in the close approach of 2135.
   
   2. On 25 September 2135 the nominal approach distance is 0.002au from Earth, but Bennu could pass as close as 0.0007au.
   (There is no chance of an Earth impact in 2135.)
   
   3. The 2135 approach will create many lines of variations and Bennu may pass through a gravitational keyhole during the 2135 passage which could create an impact scenario at a future encounter. The keyholes are all less than 55 km wide.

In order to move Bennu by ~0.001au before its next encounter with Earth Bennu's velocity must be sped up or slowed down by ~11 cm/sec.

This would require a momentum impulse of ~7,500,000,000 kg m/sec.

The Paris Gun used to bombard Paris during World War I generated a momentum impulse of ~175,000 kg m/sec.

Hence, a Bennu/Paris Gun would have to discharge over 40,000 times to have a significant effect for the near future.

gwarstadt wrote: ↑Wed Nov 14, 2018 8:07 pm Is anyone else struck by the fact that the horizontal axis of this non spherical object is exactly half the vertical axis, and its so symmetrical that if you watch an edge as it rotates the profile hardly moves (except for the big rocks)?

https://www.syfy.com/syfywire/hey-bennu-have-we-met-i-never-forget-an-asteroid wrote:

101955 Bennu / 162173 Ryugu

---

Hey Bennu, have we met?
I never forget an asteroid.
Contributed by Phil Plait @BadAstron

Comparing two small asteroids: 550-m-wide Bennu (left), and 1-km-wide Ryugu (right) roughly to scale.

Credit: Ryugu: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.

MarkBour wrote: ↑Thu Nov 15, 2018 8:22 pm
I just stumbled upon the site: https://cneos.jpl.nasa.gov/ which I find really wonderful. They have a nice set of data and you can run the data in animations for many near-earth objects. I could learn a lot from that site, if I were to give it the time it deserves. What I did learn is that 101955 Bennu has an elliptical orbit similar to Musk's roadster -- running from just a little inside Earth's orbit to nearly Mars' orbit. But I don't think it ever has close encounters with Mars, it is probably not in Mars' orbital plane when it approaches. It can get arbitrarily close to Earth, crossing our orbit, and the close encounters should be about once every 6 years or so.

Back to your momentum calculation. I'll gladly accept that you did the math to determine that it would take an impulse of about 7.5x10⁹ Ns to slow Bennu enough to displace it by 0.001 AU. I assume you figured this displacement in a period that would be about 5 orbits for Bennu = 6 orbits for Earth. (?) And that much displacement ought to be enough to avoid an encounter.

• Bennu has an orbital period of ~436.65 days or ~104/87 years
  
  After 5 Bennu orbits (~6 years) the Earth lags by ~0.12 au (too far to matter).
  
  After 87 Bennu orbits (~104 years) the Earth leads by ~0.03 au.

• Note: Bennu's orbital period of ~436.65 days changes after each relatively
  close approach making the next close approach after just 75 years (in 2135).

MarkBour wrote: ↑Thu Nov 15, 2018 8:22 pm
The first stage of the Saturn V, I believe, could deliver 9x10⁹ Ns impulse, so that would mean we must have the capability, in theory, to give such a push with conventional tech. Of course it is a lot easier to build and launch a Saturn V from Florida than to deliver a working Saturn V to an object in space, fully loaded with fuel. So this would require a lot more rockets and would beg a myriad of other questions as well.

MarkBour wrote: ↑Thu Nov 15, 2018 8:22 pm
(Examples: When would be the best time for such a mission. I assume it would be most efficient to try to intercept it at perigee #(n-1), if we wanted to push it with something between then and perigee #n? If we wanted to move such a pile of rubble, we might rather separate all of the engines of a Falcon-Heavy-like rocket and place them all in a large array. Build something more like a rocket-powered girdle. I wonder if nudging such an object out of our orbital plane is easier than nudging it backward or forward? It would seem a more permanent solution, upon first consideration. Then again, adjusting its perihelion to be > Earth's aphelion is another idea.

neufer wrote: ↑Thu Nov 15, 2018 11:22 pm ...
However, I was primarily interested with any possible perturbation with current OSIRIS-Rex activities
affecting the next close approach in 2060 (~104 years after the last relatively close approach in 1956).
...
Actually, a catapult that could launch 0.1% of Bennu rocks at 110 m/s makes a lot of sense.
(Or having Bruce Willis bury a nuclear charge to blow off the front or back 0.1% of Bennu into space.)
...
All plans on moving asteroids involve having it sped up or slowed down in order to throw the timing off.

MarkBour wrote: ↑Fri Nov 16, 2018 2:49 am

neufer wrote: ↑Thu Nov 15, 2018 11:22 pm ...
However, I was primarily interested with any possible perturbation with current OSIRIS-Rex activities
affecting the next close approach in 2060 (~104 years after the last relatively close approach in 1956).
...
Actually, a catapult that could launch 0.1% of Bennu rocks at 110 m/s makes a lot of sense.
(Or having Bruce Willis bury a nuclear charge to blow off the front or back 0.1% of Bennu into space.)
...
All plans on moving asteroids involve having it sped up or slowed down in order to throw the timing off.

Thanks for the answers!

RE: A catapult. If Bennu is truly rubble, I really like the simplicity of the idea, and it would be able to do a little at a time until it got the job done, perhaps not needing fuel? So, it is a brilliant plan on those features, at least.

A catapult would not change the total net momentum, of course. It sounds like it would effectively turn it into a disintegrating "comet". And the way I'm picturing this, it would just make a huge mess out of the launched chunks, as a sort of discrete cometary tail, right? I suppose some of those pieces would have to hit Earth, even as they would allow Bennu's main body to miss. On the bright side, maybe there is something worth mining and trying to get into Earth orbit. Or to even crash into the Moon. Would anyone ever want to play that dangerous game with large chunks? I can scarce imagine the possible long-term effects of such actions.

Anyway, if you send Bruce Willis to do the job, keep in mind that you're going to need to send his whole crew. Non-negotiable. They needed Ben Affleck ("A.J. saved us. He did."), and even more importantly, they needed Steve Buscemi for comic relief.

• 1) Bennu would be moved by ~0.001 au by 2060 and
  2) the ejecta would all be moved by ~1.00 au in the opposite direction by 2060.

MarkBour wrote: ↑Fri Nov 16, 2018 2:49 am

neufer wrote: ↑Thu Nov 15, 2018 11:22 pm ...
However, I was primarily interested with any possible perturbation with current OSIRIS-Rex activities
affecting the next close approach in 2060 (~104 years after the last relatively close approach in 1956).
...
Actually, a catapult that could launch 0.1% of Bennu rocks at 110 m/s makes a lot of sense.
(Or having Bruce Willis bury a nuclear charge to blow off the front or back 0.1% of Bennu into space.)
...
All plans on moving asteroids involve having it sped up or slowed down in order to throw the timing off.

Thanks for the answers!

Chris Peterson wrote: ↑Fri Nov 16, 2018 5:20 am

neufer wrote: ↑Thu Nov 15, 2018 11:22 pm ...
However, I was primarily interested with any possible perturbation with current OSIRIS-Rex activities
affecting the next close approach in 2060 (~104 years after the last relatively close approach in 1956).
...
Actually, a catapult that could launch 0.1% of Bennu rocks at 110 m/s makes a lot of sense.
(Or having Bruce Willis bury a nuclear charge to blow off the front or back 0.1% of Bennu into space.)
...
All plans on moving asteroids involve having it sped up or slowed down in order to throw the timing off.

In reality, however, you don't necessarily need anywhere near that impulse... or, you need a lot more. We don't know where Bennu will be a few orbits from now. A trivially small impulse now could have a dramatic effect on its position in 100 years. We wouldn't be able to do anything until a collision was much nearer in time, and then we'd have to do more, of course.

neufer wrote: ↑Fri Nov 16, 2018 1:26 pm My own plan is to talk Bennu to death.

BDanielMayfield wrote: ↑Fri Nov 16, 2018 4:53 pm

neufer wrote: ↑Fri Nov 16, 2018 1:26 pm My own plan is to talk Bennu to death.

In furtherance of neufer's (laudable,laughable?) plan I'll pose a hypothetical question, to wit:

Given two asteroids of equal mass and Earth impacting trajectory, one of which is a loose rubble pile and one is a solid body, which poses the greater threat, and which threat would be easier to ward off?

BDanielMayfield wrote: ↑Fri Nov 16, 2018 4:53 pm

neufer wrote: ↑Fri Nov 16, 2018 1:26 pm My own plan is to talk Bennu to death.

In furtherance of neufer's (laudable,laughable?) plan I'll pose a hypothetical question, to wit:

Given two asteroids of equal mass and Earth impacting trajectory, one of which is a loose rubble pile and one is a solid body, which poses the greater threat, and which threat would be easier to ward off?