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<blockquote data-quote="Ovinomancer" data-source="post: 7486613" data-attributes="member: 16814">Treating Earth as a fixed point completely ignores the geometry of the problem.&nbsp; The asteroid is essentially a bullet fired leading Earth, on a rendevous to meet it, not a bullet fired directly at a stationary Earth.There's a 6x difference in needed delta-v 1 hour out by treating the problem as an orbital one rather than a fixed Earth one (3.3 km/s vs 18 km/s).&nbsp; This was calculated as instantaneous delta-v at one hour out, so I have no idea where light sails come into that.&nbsp; Heck, at 5 mins out, ypu need to slow the object by 40km/s (80% of it's 50km/s speed!) to cause a miss, but you'd need 108km/s (216%!!) to generate the same miss by perpendicular thrust.&nbsp; Ignoring Earth's 30km/s speed and the fact this is a rendezvous problem not a fixed target problem is the oversight, here.The acceleration needed will vary by object mass, but the delta-v doesn't care.&nbsp; For the 1 hour out case, and assuming a 1EE14 kg mass at 50km/s (roughly the same as the Chicxulbub impact), let's look at a 10 minute burn application centered at 1 hour out.&nbsp; The needed delta-v to slow or speed the stroid is 3.3km/s.&nbsp; Over 10 minutes, the a is 5.5m/(s x s).&nbsp; The F needed is 5.5EE14 N.&nbsp; The lateral shove needs an a of 30m/(ss), and an F of 3EE15 N.&nbsp; An order of magnitude more force!So, no, no lightsails or slow accelerations here.</blockquote>

[QUOTE="Ovinomancer, post: 7486613, member: 16814"] Treating Earth as a fixed point completely ignores the geometry of the problem. The asteroid is essentially a bullet fired leading Earth, on a rendevous to meet it, not a bullet fired directly at a stationary Earth. There's a 6x difference in needed delta-v 1 hour out by treating the problem as an orbital one rather than a fixed Earth one (3.3 km/s vs 18 km/s). This was calculated as instantaneous delta-v at one hour out, so I have no idea where light sails come into that. Heck, at 5 mins out, ypu need to slow the object by 40km/s (80% of it's 50km/s speed!) to cause a miss, but you'd need 108km/s (216%!!) to generate the same miss by perpendicular thrust. Ignoring Earth's 30km/s speed and the fact this is a rendezvous problem not a fixed target problem is the oversight, here. The acceleration needed will vary by object mass, but the delta-v doesn't care. For the 1 hour out case, and assuming a 1EE14 kg mass at 50km/s (roughly the same as the Chicxulbub impact), let's look at a 10 minute burn application centered at 1 hour out. The needed delta-v to slow or speed the stroid is 3.3km/s. Over 10 minutes, the a is 5.5m/(s x s). The F needed is 5.5EE14 N. The lateral shove needs an a of 30m/(ss), and an F of 3EE15 N. An order of magnitude more force! So, no, no lightsails or slow accelerations here. [/QUOTE]

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