History, Politics And Current Affairs

Scott Manley does a good job of doing a analysis of our options.

https://youtu.be/kK5IXX4p2d0?si=lJJf3HANd946esIZ

https://youtu.be/Esk1hg2knno?si=FqbDvPqM0APcyeaX

clancyphile wrote: ↑Mon Feb 17, 2025 8:59 pm

Poohbah wrote: ↑Mon Feb 17, 2025 5:32 pm

clancyphile wrote: ↑Mon Feb 17, 2025 3:49 pm

I was thinking use Starliner to get the B83 close enough to the asteroid to make it go away. No crew needed. Just insert the special store, and activate the physics package remotely.

Probably won't work. 1 B83 will deliver roughly 150KT of energy to the asteroid if detonated on the surface. (The asteroid occupies 1/8th of the volume of a 50-meter radius fireball; 1.2MT yield divided by 8 gives 150KT.) This is enough to theoretically vaporize about 25% of the asteroid. The actual amount vaporized will be considerably lower. Now, this may be useful: the vaporized rock will exert thrust against the non-vaporized portion of the asteroid and deflect its path, assuming that it remains largely unitary. The problem is that vaporized rock has a piss-poor specific impulse.

OK... what about a B53 or W53? Nine megatons.

Better, but the delta-V for shoving six tons out to an asteroid intercept isn't available.

NASA has revised the chance of earth impact to 3.1%.

clancyphile wrote: ↑Mon Feb 17, 2025 3:49 pm

kdahm wrote: ↑Mon Feb 17, 2025 2:51 am Starliner doesn't have the delta-v to do anything to the asteroid. It would take something a bit more powerful to handle it.

I was thinking use Starliner to get the B83 close enough to the asteroid to make it go away. No crew needed. Just insert the special store, and activate the physics package remotely.

Starliner can't do that, as mentioned. Even getting a naked B53 or W53 is pushing it.

Starliner weighs 13 tons. It can carry 4 people and 100 kg to the ISS or LEO. The Atlas 5 can launch 18,850 kg to LEO, or 8,900 kg to a geostationary transfer orbit. That's 11,300 kph. or 3.1 km/s. The B53 is 4,000 kg, while the W53 is 2,800 kg.

The asteroid is expected to have an impact velocity of 61,200 kph, or 17 km/s. Any device that is used on it will have to intercept well outside of the moons orbit, or the most like event is that a third of the asteroid impacts Earth as fragments and two-thirds as a one-piece Big Badaboom.

So that leaves only a few options. The 2028 visit would allow us to really refine the trajectory and decide what to do. In early 2031 (WAG) we would launch either a device with a physics package or a pusher probe into a heliocentric orbit that would intercept the asteroid several months before impact. That would give enough time for orbit deviations to occur. A device would be easier, but the direction of the resulting fragments is unpredictable. A pusher would have to deal with the rotation of the asteroid, amounting to a surface velocity of 0.15 m/s at the equator, and timing the pushes. Or hope that the axis is aligned such that a polar landing will push it the right direction.

We can do it. James Webb is about 6,500 kg, and is located at the Earth-Sun L2 point. Cassini-Huygens was 5,700 kg at launch and took six years to get to Saturn. If we want a payload of around 2,000 kg, we'd probably need a total mass budget of 8,000 to 10,000 kg, plus a route that goes around some planets and the sun. Fortunately, Starship Block 2 is supposed to have a mass to LEO of 100 tons, and for this it isn't a problem to launch and expend three to ensure one gets there. The Cold Equations

SLS is supposed to have a mass to LEO of 70 tons, or 27 tons to Lunar Transfer, but if it isn't cancelled I'm not sure if they can get the third launch vehicle built and readied by 2031.

I'd rather base the launcher on the Falcon Heavy since it works and so far, Starship isn't.

jemhouston wrote: ↑Tue Feb 18, 2025 9:56 pm I'd rather base the launcher on the Falcon Heavy since it works and so far, Starship isn't.

I was thinking Falcon Heavy.

Well, we have time... However, we have to come up with both the political will and the money to pay for whatever solution we come up with. At this point, we could probably reserve a launch with Falcon Heavy in the appropriate timeframe. While the weight of the weapons in question are large, my guess is that the physics package of each weapon weighs significantly less than the entire weapon. I would think we'd be able to cut down on the weight appreciably just by discarding the aerodynamic shell, right?

Not sure about the 1/3rd - 2/3rd conclusion. Yeah, there will probably be a lot of fragments. Most of them will end up burning up in the atmosphere. The larger chunks are likely to have their orbits altered a significant amount. Not sure the big badaboom is a foregone conclusion.

Have we figured out if its a condrite or a metal asteroid yet?

Belushi TD

jemhouston wrote: ↑Tue Feb 18, 2025 9:56 pm I'd rather base the launcher on the Falcon Heavy since it works and so far, Starship isn't.

Starship works well enough. Not enough right now to launch one payload, but enough to be reasonably sure that three launches will get one or two on the way. Falcon Heavy is also an option with 63,800 kg to LEO, 26,700 to GTO, and 16,800 kg to Mars. It's more a matter of deciding on the payload and method, then packaging it for the launch system. And there's reason to believe that Starship will be reliable by the end of 2026.

Belushi TD wrote: ↑Tue Feb 18, 2025 10:03 pm Well, we have time... However, we have to come up with both the political will and the money to pay for whatever solution we come up with. At this point, we could probably reserve a launch with Falcon Heavy in the appropriate timeframe. While the weight of the weapons in question are large, my guess is that the physics package of each weapon weighs significantly less than the entire weapon. I would think we'd be able to cut down on the weight appreciably just by discarding the aerodynamic shell, right?

Not sure about the 1/3rd - 2/3rd conclusion. Yeah, there will probably be a lot of fragments. Most of them will end up burning up in the atmosphere. The larger chunks are likely to have their orbits altered a significant amount. Not sure the big badaboom is a foregone conclusion.

The difference between the B53 and the W53, to my understanding, is that the W53 is the B53 minus the chutes and aerodynamic package. I don't think it can be stripped down much more without a redesign. The B83 is 1,100 kg, and so multiple devices can be more easily used.

I admit that I was estimating on the 1/3 -2/3 conclusion. Some will be vaporized, some will be fragmented, and a lot, I think, will be pushed away. The material from a crater is only partially vaporized, and a lot becomes chunks and debris in the mushroom cloud. A big solid chunk of material was the basis for the shield on the Orion drive, after all. I think a large, 1 MT warhead will destroy at least 25% of a 54m rock, and probably less than 50%. Ivy Mike was 10.4 MT and left a 50m deep crater. Trinity, at 21 kt, left an 8 ft deep crater. Unlike an 50m asteroid, the Earth can't move away from the blast.

The time between getting to the Earth-Moon distance and hitting the Earth is about 6 1/4 hours. For a chunk with a center-Earth strike, it would need a side velocity of 0.25 km/sec to get clear of the planet. Without some more detailed math and testing, I wouldn't want to bet my life on that happing with a single device. Also, all of the fragments broken off and about to hit the Earth in a shotgun pattern are irradiated and probably contaminated.

New revised odds of an Earth strike is now down to 0.0039%, or 1 in 26,000. Plus or minus a healthy margin of error.

Ars Technica article here: https://arstechnica.com/space/2025/02/a ... e-threats/