Re: 2004 MN4 risk fades away.

From: Hop David (hopspageHATESSPAaMmM_at_tabletoptelephone.com)
Date: 12/29/04 

Date: Tue, 28 Dec 2004 17:17:16 -0700

Ian Stirling wrote:
> Tkalbfus1 <tkalbfus1@aol.com> wrote:
>
>>>Current NASA ephimerides for 2029 are for a miss distance of
>>>63,000 km (0.00043 AU) at closest approach around 2200 UT.
>>>
>>
>>That is inside the orbit of the Moon. Do you think there is a chance that by
>>2029, we'll be able to slow it down and capture it in a circular orbit about
>>63,000 km high? If it's in such an orbit around Earth instead of the Sun, it
>>will never threaten Earth again, and if its 300 meters in diameter, there
>>should be enough material there to build a space colony and perhaps a few Solar
>>Power Satellites. What sort of asteroid is it?
>
>
> It would be technically possible for us to do this, but it's going to be
> a major undertaking.
> You're looking at a delta-v of around 10Km/s.

With a Vinf of 5.84 km/s and perigee of 76800 km above earth's surface,
I get 4.4 km/sec to capture to a circular orbit.

Just to capture (apogee 912000 km, right at the edge of earth's Sphere
Of Influence) takes 3.8.

>
> Comparing the task with making an asteroid miss the earth, if started on
> a year out, a task which needs a delta-v of around 0.5m/s, this is 1/20000th
> the speed, or enough to make an 8Km asteroid miss earth.

OTOH nudging it _towards_ the earth makes capture easier. At 200 km
perigee it only takes 1.55 km/sec to capture into an elliptical orbit.
At that altitude some of that might be provided by aerobraking.

The powers that be would be completely nuts to try such a stunt on an
asteroid this size. 

-- 
Hop David
http://clowder.net/hop/index.html

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