Starship Asterisk*

http://www.howardastro.org/archives/2013/APODLecture/APODLecture.php wrote:
Special HAL Meeting on Thursday, February 21st

HAL is pleased to have Dr. Jerry Bonnell, one of the founders of APOD, speaking at this month's meeting. The meeting will be held at 7:30PM on the lower level of the Robinson Nature Center. Due to the large anticipated audience we will be in Auditorium adjacent to our usual meeting room. Signs will point the way. Alternately, inquire at the front desk when entering the building.

Click to play embedded YouTube video.

(Open to the Public)

Driving Directions
to HAL Meeting:

The Robinson Nature Center
6692 Cedar Lane
Columbia, MD 21044

http://asterisk.apod.com/viewtopic.php?f=9&t=29032

metamorphmuses wrote:^ You're welcome to present a proof to the contrary.

Seriously, do we all not think this idea is hard enough to realize as it stands? Imagine how much money, resources, and potential for error would be involved in this project. If we had the capability to pull this off, we'd also have no trouble sending crewed spacecraft throughout the solar system, which I may remind us all is a technology we do not currently possess - not because we could not possess it, but because there isn't enough of a collective will to realize it.

Guest wrote:
-this is a joke-its not astronomical at all-its Fantasy and NON reality

http://en.wikipedia.org/wiki/Gravity_tractor wrote:
<<Let us suppose that a NEO of size around 100 m, and mass of one million metric tons, threatened to impact Earth. Suppose also that a velocity correction of 1 cm/s would be adequate to place it in a safe and stable orbit, missing Earth that the correction needed to be applied within a period of 10 years.

With these parameters, the required impulse would be: V × M = 0.01 [m/s]×10⁹ [kg] = 10⁷ [N-s], so that the average tractor force on the asteroid for 10 years, = 3.156×10⁸ s, would need to be about 0.032 newtons. An ion-electric spacecraft with a specific impulse of 10,000 N-s per kg, corresponding to an ion beam velocity of 10 km/s (about twenty times that obtained with the best chemical rockets), would require 1,000 kg of reaction mass (Xenon is currently favored) to provide the impulse. The kinetic power of the ion beam would then be approximately 317 W; the input electric power to the power converter and ion drive would of course be substantially higher. The spacecraft would need to have enough mass and remain sufficiently close to the asteroid that the component of the average gravitational force on the asteroid in the desired direction would equal or exceed the required 0.032 N. Assuming the spacecraft is hovering over the asteroid at a distance of 200 m to its centre of mass, that would require it to have a mass of about 20 metric tonnes, because due to the gravitational force we have:



Considering possible hovering positions or orbits of the tractor around the asteroid, note that if two objects are gravitationally bound in a mutual orbit, then if one receives an arbitrary impulse which is less than that needed to free it from orbit around the other, because of the gravitational forces between them, the impulse will alter the momentum of both, together regarded as a composite system. That is, so long as the tractor remains in a bound orbit, any propulsive force applied to it will be effectively transferred to the asteroid it orbits. This permits a wide variety of orbits or hovering strategies for the tractor. One obvious possibility is for the spacecraft to orbit the NEO with the normal to the orbit in the direction of the desired force. The ion beam would then be directed in the opposite direction, also perpendicular to the orbit plane. This would result in the plane of the orbit being shifted somewhat away from the center of the asteroid, "towing" it, while the orbital velocity, normal to the thrust, remains constant. The orbital period would be a few hours, essentially independent of size, but weakly dependent on the density of the target body.>>

• Note that the mass of the tractor goes with the square of the asteroid's diameter:
  • (; e.g., 30 meter 2012 DA₁₄ would require just a 1800 kg tractor
    whereas a 1 km asteroid would require a 2,000 tonne tractor).

mister T wrote:Wouldn't it be more efficient to land on the asteroid and use the thrust to push directly on the asteroid??

Chris Peterson wrote:This is much, much cheaper and easier to manage than manned expeditions around the Solar System.

Chris Peterson wrote:Sure its expensive, and sure there are technical challenges. But they are well within our financial and engineering means given a bit of incentive... like a massive collision a few years in the future.

CMatisse wrote:
Why didn't we practice on 2012 DA14? (As if I didn't know)

and the tumbling of 2012 DA₁₄

• . http://apod.nasa.gov/apod/ap070422.html

• . http://apod.nasa.gov/apod/ap120919.html

• . http://en.wikipedia.org/wiki/Apollo_17

• 1) locating all the dangerous asteroids and
  2) tagging the worst offenders with accurate tracking devices.

neufer wrote:

Guest wrote:

• Note that the mass of the tractor goes with the square of the asteroid's diameter:
  • (; e.g., 30 meter 2012 DA₁₄ would require just a 1800 kg tractor
    whereas a 1 km asteroid would require a 2,000 tonne tractor).

K1NS wrote:

neufer wrote:

• Note that the mass of the tractor goes with the square of the asteroid's diameter:
  • (; e.g., 30 meter 2012 DA₁₄ would require just a 1800 kg tractor
    whereas a 1 km asteroid would require a 2,000 tonne tractor).

Pardon me, but shouldn't the mass of the tractor be proportional to the cube of the asteroid's diameter. Or does my high school geometry fail me?

• The mass of the tractor's ion propellent must be proportional to the cube of the asteroid's diameter. Hence, for asteroids much larger than 100m the need for sufficient propellent quickly becomes the dominant issue.

Altair wrote:
Why not use existing supplies of space junk already in orbit for the mass component of a gravitational tractor? The ISS and HST could become tractors following the end of their main missions rather than being deorbited. This could greatly reduce the cost of making tractors. Just attach motors to tractors already in orbit.

CMatisse wrote:Why didn't we practice on 2012 DA14? (As if I didn't know)

Boomer12k wrote:2012 DA14 was discovered on Feb, 23, 2012....it came by almost 1 year later....would it have been enough time to divert in one year?

metamorphmuses wrote:

Chris Peterson wrote:This is much, much cheaper and easier to manage than manned expeditions around the Solar System.

Really? If that were the case, then all the better. I suppose it would be nice to see some cost estimates. I assumed the vessel would be manned or at least crew-serviceable.

henrystar wrote:
I've seen this illustration before, but an idea occurred to me on looking at it again: depending on how a solid asteroid was rotating, we could simply paint one side black and one side white, so that the changed differential strength of solar light pressure would alter the path so as to miss Earth. (If no one has thought of that, I'd like to patent it.)

http://en.wikipedia.org/wiki/Asteroid-impact_avoidance#Other_proposals wrote:
Asteroid impact avoidance comprises a number of methods by which near-Earth objects could be diverted, preventing potentially catastrophic impact events. Various collision avoidance techniques have different trade-offs with respect to metrics such as overall performance, cost, operations, and technology readiness. There are various methods for changing the course of an asteroid/comet. These can be differentiated by various types of attributes such as the type of mitigation (deflection or fragmentation), energy source (kinetic, electromagnetic, gravitational, solar/thermal, or nuclear), and approach strategy (interception, rendezvous, or remote station). Strategies fall into two basic sets: destruction and delay.

"Painting" or dusting the object with titanium dioxide (white) or soot (black) to alter its trajectory via the Yarkovsky effect.