01-20-2017, 04:06 AM
No worries about asking questions or being out of the loop. We all have lives outside of OA, after all.
That said, and just because these issues both jumped out at me in the article mentioned and were not (IIRC) mentioned in the earlier article that Rynn pointed to. Specifically:
a) The article mentions putting the 'Dyson Cap' in front of the bow of the ship - which would be the front. How that is supposed to translate into forward moment is not explained.
b) The Dyson Cap is said to need to be 20mi away from the BH to avoid melting. The mini-Dyson Shell that is also mentioned would presumably also need to be 20mi in radius to avoid the same fate. Which would seem to require:
1) A method of magnetically (or otherwise) grabbing onto something massing as much as 'two Empire State Buildings' that is 'smaller than a proton' - from 20 miles away. And then presumably dragging said super massive tiny thing along at an acceleration of about 1/5G without tearing the containment shell apart. That all seems likely to increase the mass far above the number the article gives.
2) The article talks in terms of a heat engine - while ignoring the fact that no heat engine is 100% efficient. This isn't my area of expertise, but I seem to recall reading something to the effect that a heat engine tops out at about 40 efficiency - maybe 60% if an MHD system is used. So a good chunk of the output of the BH is going to be lost to waste heat rather than going into propelling anything. And at these output levels, that waste energy is likely to be sufficient to fry your shell all by itself. Which would require active cooling systems - which ups the mass of the shell by some amount.
3) Something that this article seems to ignore - BHs do not radiate energy at a constant rate. Instead, they get 'hotter' as they lose mass, with the rate of Hawking radiation production increasing, until finally the hole 'tips over' and evaporates in a final blast (about 10 million megatons IIRC from a book I read many years ago on the subject). The upshot of this is that while it make take a distance of 20mi to keep the shell from evaporating at the start of the trip, the hole will radiate an every increasing amount of energy and the shell is going to likely melt/vaporize long before the ship has finished its boost phase. Plus the ship would need to actually release the hole and get some considerable distance from it before the final 'bang' or be destroyed.
4) The article ignores just how the energy of the BH would be converted to thrust. Presumably (in the heat engine version), the ship would need to carry reaction mass or else convert all the energy into a photon drive - which has its own challenges.
On a somewhat different note - BH based space drives were actually a moderately common feature of SF right after Hawking 'invented' small BHs. However, what Hawking giveth, Hawking also taketh away - and the advent of Hawking radiation made most of these stories non-viable.
Anyway - my 2c worth,
Todd
That said, and just because these issues both jumped out at me in the article mentioned and were not (IIRC) mentioned in the earlier article that Rynn pointed to. Specifically:
a) The article mentions putting the 'Dyson Cap' in front of the bow of the ship - which would be the front. How that is supposed to translate into forward moment is not explained.
b) The Dyson Cap is said to need to be 20mi away from the BH to avoid melting. The mini-Dyson Shell that is also mentioned would presumably also need to be 20mi in radius to avoid the same fate. Which would seem to require:
1) A method of magnetically (or otherwise) grabbing onto something massing as much as 'two Empire State Buildings' that is 'smaller than a proton' - from 20 miles away. And then presumably dragging said super massive tiny thing along at an acceleration of about 1/5G without tearing the containment shell apart. That all seems likely to increase the mass far above the number the article gives.
2) The article talks in terms of a heat engine - while ignoring the fact that no heat engine is 100% efficient. This isn't my area of expertise, but I seem to recall reading something to the effect that a heat engine tops out at about 40 efficiency - maybe 60% if an MHD system is used. So a good chunk of the output of the BH is going to be lost to waste heat rather than going into propelling anything. And at these output levels, that waste energy is likely to be sufficient to fry your shell all by itself. Which would require active cooling systems - which ups the mass of the shell by some amount.
3) Something that this article seems to ignore - BHs do not radiate energy at a constant rate. Instead, they get 'hotter' as they lose mass, with the rate of Hawking radiation production increasing, until finally the hole 'tips over' and evaporates in a final blast (about 10 million megatons IIRC from a book I read many years ago on the subject). The upshot of this is that while it make take a distance of 20mi to keep the shell from evaporating at the start of the trip, the hole will radiate an every increasing amount of energy and the shell is going to likely melt/vaporize long before the ship has finished its boost phase. Plus the ship would need to actually release the hole and get some considerable distance from it before the final 'bang' or be destroyed.
4) The article ignores just how the energy of the BH would be converted to thrust. Presumably (in the heat engine version), the ship would need to carry reaction mass or else convert all the energy into a photon drive - which has its own challenges.
On a somewhat different note - BH based space drives were actually a moderately common feature of SF right after Hawking 'invented' small BHs. However, what Hawking giveth, Hawking also taketh away - and the advent of Hawking radiation made most of these stories non-viable.
Anyway - my 2c worth,
Todd