3 ms·

1. Not sure what you mean by significant delta-v. An 8km/s vehicle meeting a 6km/s warhead coming from the opposite direction will kill it just as surely as a 1

1. Not sure what you mean by significant delta-v. An 8km/s vehicle meeting a 6km/s warhead coming from the opposite direction will kill it just as surely as a 10km/s one. If you mean delta-v to go laterally, for that 1km/s is probably more than enough. A vehicle with 1km/s delta-v is, in the worst case scenario, twice as heavy than one with 100m/s delta-v, not 100 times as heavy. 2. 9 minutes is plenty. A ballistic missile takes about 30 min to go from one continent to another. The difference between 4 min and 9 min is not a make or break thing. 3. Everything has a price. If a single GBI booster costs north of $50 mil, then you can afford to spend a few tens of millions to keep fully fueled Starships on the launchpad, 24/7/365. From time to time you'd have to empty them, and move them an give them a thorough inspection. It can be done. 4. (bonus) If things get tense, a Starship could also carry a few hundred MIRVs. China thinks it can sprint forward in the arms race at a certain point. They'll find out it's not going to be that easy.

jltsiren 4y ago
1. This is just basic orbital mechanics. Multiple missiles are launched from different locations at different targets. The launches are not fully simultaneous. Each kill vehicle must be at the right place at the right time to intercept its target. If you launch all kill vehicles from the same location at the same time, the differences between the required velocity vectors are easily several km/s. 2. The midcourse phase typically takes ~20 minutes. You can't predict the trajectory accurately during the boost phase, and you have the wrong kind of missile for intercepting the target during the terminal phase. If your boost phase is 9 minutes instead of 4 minutes, you have 11 minutes instead of 16 minutes for political and tactical decisionmaking. 3. What is the price of a fully disposable Starship? How many of them do you need to have one ready to launch at any time? Because if you have them on standby, you can't use them for any other purpose, and they are effectively disposable.
- credit_guy 4y ago
  > What is the price of a fully disposable Starship? Musk aims to get the cost of building one Starship to $5 million [1]. That sounds insane, I know, but he also aims to build about 1000 of them. When you get to this scale of mass production, efficiencies of scale kick in. Could he be wrong. I suppose so, but even if he's wrong by a factor of 10 or 20, it would still provide a tremendous value proposition for an Anti Ballistic Defense system. [1] https://arstechnica.com/science/2020/03/inside-elon-musks-plan-to-build-one-starship-a-week-and-settle-mars/ https://arstechnica.com/science/2020/03/inside-elon-musks-pl...
rocqua 4y ago
The delta-v is not needed to get a big enough impact. The delta-v is needed to be able to maneuver into an intercept orbit. In case you don't know, for rockets the fundamental limit of their fuel is expressed in delta-v. Your kill vehicle doesn't need much delta-V if you can launch it close enough to an intercept course. But if all warheads are launched in very different directions, and all your kill vehicles need to start from a central starship point, they can't all be launched 'close enough' to an intercept course.

jltsiren 4y ago

1. This is just basic orbital mechanics. Multiple missiles are launched from different locations at different targets. The launches are not fully simultaneous. Each kill vehicle must be at the right place at the right time to intercept its target. If you launch all kill vehicles from the same location at the same time, the differences between the required velocity vectors are easily several km/s. 2. The midcourse phase typically takes ~20 minutes. You can't predict the trajectory accurately during the boost phase, and you have the wrong kind of missile for intercepting the target during the terminal phase. If your boost phase is 9 minutes instead of 4 minutes, you have 11 minutes instead of 16 minutes for political and tactical decisionmaking. 3. What is the price of a fully disposable Starship? How many of them do you need to have one ready to launch at any time? Because if you have them on standby, you can't use them for any other purpose, and they are effectively disposable.

credit_guy 4y ago
> What is the price of a fully disposable Starship? Musk aims to get the cost of building one Starship to $5 million [1]. That sounds insane, I know, but he also aims to build about 1000 of them. When you get to this scale of mass production, efficiencies of scale kick in. Could he be wrong. I suppose so, but even if he's wrong by a factor of 10 or 20, it would still provide a tremendous value proposition for an Anti Ballistic Defense system. [1] https://arstechnica.com/science/2020/03/inside-elon-musks-plan-to-build-one-starship-a-week-and-settle-mars/ https://arstechnica.com/science/2020/03/inside-elon-musks-pl...

rocqua 4y ago

The delta-v is not needed to get a big enough impact. The delta-v is needed to be able to maneuver into an intercept orbit. In case you don't know, for rockets the fundamental limit of their fuel is expressed in delta-v. Your kill vehicle doesn't need much delta-V if you can launch it close enough to an intercept course. But if all warheads are launched in very different directions, and all your kill vehicles need to start from a central starship point, they can't all be launched 'close enough' to an intercept course.