[X] My Assistant

[Guest_PhilCo126_*]

The Near-Earth Asteroid 99942 Apophis ( former designation 2004 MN4 ) was headline news again this week both in Newspapers & TV news. Observations pointed out that the Asteroid climbed a bit higher on the Torino impact hazard scale ( equivalent cosmic ‘Richter’ scale ) and could hit the Earth ( Southern Hemisphere ) on April 13, 2036 ( a Friday 13th I believe ).

Anyway, Apophis should pass between the Moon & Earth ( distance 250.000 KM ) in April 2029 … an amazing sight visible from Europe!
Interesting to know is the fact that European Space Agency ESA plans a mission to find out if an asteroid could be deflected from its course ( Don Quichote mission: Hidalgo is an impacter & Sancho is the observer probe ). American astronauts LU & LOVE wrote a paper in NATURE about a tug-rocket and NASA is making plans for a mission called ‘ The Son of Deep Impact ‘ … to be continued…



More on the Asteroid at:
http://www.esa.int/gsp/ACT/mission_analysis/asteroid.htm


Philip

[RNeuhaus]

I have read a paper about "Gravitation Tractor for Towing Asteroids" It takes many years to deviate the asteroid's path. As an example:

if the asteroid is 200 meters diameter, with a density of 2g/cm^3, provided it can maintain a total thrust T = 1 N. The velocity change imparted to the asteroid per year of hovering is Δv = 4.2×10−3 (m/ 2×104 Kg)(d /100m)−2 (m/ s)( yr)−1. Because Δv is largely independent of the asteroid’s detailed structure and composition, the effect on the
asteroid’s orbit is predictable and controllable, as needed for a practical deflection
scheme.

The mean change in velocity required to deflect an asteroid from an Earth impact
trajectory is ~3.5×10−2 / t m/s where t is the lead time in years. Thus, in the example
above, a 20 ton gravitational tractor can deflect a typical 200m asteroid, given a lead time of about 20 years. The thrust and total fuel requirements of this mission are well
within the capability of proposed 100kW nuclear-electric propulsion systems, using
about 4 tons of fuel to accomplish the typical 15 km/sec rendezvous and about 400 Kg
for the actual deflection.

For a given spacecraft mass, the fuel required for the deflection scales linearly with the asteroid mass. Deflecting a larger asteroid requires a heavier spacecraft, longer time spent hovering, or more lead time. However, in the special case where an asteroid has a close Earth approach followed by a later return and impact, the change in velocity needed to prevent an impact can be many orders of magnitude smaller if applied before the close approach.

For example, the asteroid 99942 Apophis (2004 MN4), a 320m asteroid that will swing by the Earth at a distance of ~30000km in 2029, has a small 10−4 probability of returning to strike the Earth in 2035 or 2036. If it indeed is on a return impact trajectory, a deflection Δv of only ~10−6m/s a few years before the close approach in 2029 would prevent a later impact (Carusi, personal communication). In this case, a 1 ton gravitational tractor with conventional chemical thrusters could accomplish this deflection mission since only about 0.1 Newtons of thrust are required for a duration of about a month. Should such a deflection mission prove necessary, a gravitational tractor spacecraft offers a viable method of controllably steering asteroid 99942 Apophis away from an Earth impact.

We are still on time to catch it up.

Rodolfo

Attached File(s)

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