This isn’t correct. The limit on specific impulse (I[SUB]sp[/SUB]) on nuclear (fission) thermal rockets (NTR) is about 1,000 seconds, and the I[SUB]sp[/SUB] on the NERVA system was theoretically 811 seconds. That would give a best case possible transit of about 14 to 16 weeks. Although NERVA or other NTRs give a larger impulse for a given mass of propellant by a factor of 2 to 3 over chemical propulsion systems, they are far from constant thrust; in essence, you might get a few hundred seconds of acceleration, followed by a pseudo-Hohmann transfer, followed by a deceleration; you get a higher, “flatter” trajectory. This is a somewhat faster transit and gives a greater range of time over which transit can occur instead of very narrow windows of a few hours, but it isn’t a miraculous improvement that allows transportation at any arbitrary time, and the enormous mass of a nuclear thermal system may dictate a minimum vehicle size that is impractical for a system that has to be launched from Earth and assembled piecewise.
Chemical propulsion systems, even constructed in orbit, will not significantly reduce transit times. This is because adding more propellant is only of marginal benefit because the vast majority of impulse is expended simply accelerating the additional propellant. In fact, once your payload to propellant ratio is less than 0.05, the benefit of adding more propellant in terms of a faster transit is essentially nil. The 8.5 to 9 month Earth-Mars transit for chemical propulsion systems is baked into the essential orbital mechanics and cannot be improved upon just because chemical systems are thermodynamically limited to how much temperature, and thus specific impulse, they can develop.
Developing a manufacturing capacity in space, and more importantly utilizing materials and energy sources that are in interplanetary space is a sine qua non of any self-sustaining extraterrestrial presence. Regardless of how cheap surface-to-orbit transfers may be, it will never be cheap enough to sustain a significant human presence on Mars (or even Earth’s Moon) by shipping vital materiel uphill from Earth, nor is there any likelihood of a fiscally viable trade between Earth and “colonies” on Mars without some miraculous advance in propulsion technology. Despite what you may hear from frenetic, acid-dropping billionaires with Randian aspirations to create a “second home for humanity” on Mars, there is really no viable path for a self-sustaining colony on Mars or any other planet without a robust resource extraction and manufacturing infrastructure in space. There is certainly to practical trade between Earth and Mars analogous to the “Age of Sail” paradigm that is often imagined in fiction and by a certain contingent of space enthusiasts simply because there no dichotomy of commodities to support such a market.
Yeah it takes about 3 minutes for a radio message from Earth to reach Mars and vice versus. That sort of interplanetary latency has all sorts of implications for not just communications and data transfers, but also any kind of payments or money movement.
Like if your money is in a Bank of Earth account and you go to a Space ATM on Mars:
3 minutes to send you pin to Earth and
3 minutes to reply
3 minutes to send the requested amount
3 minutes to reply with a confirmation that the funds are available
That’s 12 minutes just to pull out some cash.
So obviously real time payments and other standard convenient forms of exchange are out. Most likely it would have to be some sort of Space Wire Transfer technology.
I’ll let you have spacebucks for a 15% charge upon presentation of a cryptographically signed letter of credit. No need for (or possibility of) instantaneous transfer.
So obviously if you’re on Mars and have most of your wealth in an account on Earth, you transfer a decent amount (enough to cover your stay) to the Bank of Mars some time while you’re in transit. Or if you live permanently on Mars, then you keep most of your wealth at the Bank of Mars.
Right now, on Earth, if you’re in North America and want to buy some product in Australia, sure, you can send the payment nigh-instantaneously, but it hardly matters, because the thing you’re buying is going to take days or weeks to arrive, anyway. If monetary transactions take an extra hour to complete (allowing for multiple round-trips, as might be necessary for a cryptographic handshake protocol), they’re still going to be the fast part of any transaction.
That’s only when Earth and Mars are at their closest. It can be as long as 20 minutes. So, while at best you could do your money transfer in 12 minutes at other times it might take as long as 80 minutes.
But…
There was a time in history when messages could take weeks or even months to travel between countries yet there was thriving international trade, even some global trade.
So… there could definitely be trade between planets but it would probably resemble 18th Century commerce more than what we’re used to right now.
Yes, I was just thinking that. In the 1700-1800s, banks in North America often issued their own currencies for local use, which often made it hard to transport cash long distances. But they still managed it, using letter of credit and such things. Basically, if one bank trusted the other enough, they’d credit your account with the money indicated, and settle the differences later.
Mars vs. Earth would be similar, if a bit faster. Earth Bank Alpha would tell Mars Bank Prime, “Yes, that guy has money”, and then Mars Bank Prime would let you withdraw your Marsbucks, for local usage.
The one place where things could get complicated is, as I mentioned earlier, I doubt we will see settlement of Mars until we are living in space, period.
So fine, we have the First Planetary Bank of Mars and a host of Earth banks and those are good enough for Earthlings and Martians. But what about miners in the asteroid belt? What about astronomers at the observatory at the L3 Lagrange point? All those people need access to the Interplanetary Banking System don’t they?
It seems to me like there might be some monetary shenanigans you could get up to if you have two banks to contact and both are 40+ minutes away.
Yes, they would, and I imagine someone will, at some point, discover new and fascinating forms of fraud to engage in. But such things were ever thus, and I’m sure we’d evolve new ways of handling them.
Since the transactions would almost certainly involve computers talking to each other, you’d have to have compatible systems. Asteroid Bank One would know that you have 20 Marsbucks on account. If you tell it, “Okay, send 15 Marsbucks to Mars Bank Prime”, and then a minute later, “Okay, send 10 Marsbucks to Earth Bank Alpha”, it would call foul on that. It would put a hold on the first 15 Marsbucks until it received word back that it had been withdrawn or sent back, and so it would only allow you to access the unencumbered 5 Marsbucks in your account.
You could try using your Marsbucks as collateral for a short-term loan, but again, the computer would record a lien against that money, and not let your borrow more than it was worth.
I guess I was thinking of a situation where there is no Asteroid Bank (or even if there is a bank on Ceres, maybe you’re on the opposite side of the belt) and so you’re telling both Earth Bank and Mars Bank to fulfil a transaction using the same funds. But as long as the funds actually “live” in either Earth or Mars accounts the transaction would not clear until the banks communicated and spotted the discrepancy.
Yeah, you used to be able to do things like that when writing a cheque. If you currently lacked funds, but knew your paycheck would be deposited before the other cheques cleared, you could get away with it.
These days that’s harder to do.
Even if there wasn’t an Asteroid Bank, you’d need something to communicate with the other banks, and that system would be programmed to disallow the more obvious types of cheating. Even if you’re just sending an encrypted signal saying, “Use this money”, you’d have to have a system for doing the encryption, and checking relative balances would seem to be an easy addition to that system.
Mars here is taken as having a “somewhat self sufficient mars colony” which would indicate it’s a bit more then mining an asteroid or doing science at an interesting point in space. The former appears to have started permeant residence where people go to live, give birth, and die , while the latter seems more like a long term work project where one would be returning presumably to earth (and thus can work with earth currency) and be supported while in space by the interest that sent them. Though perhaps a informal system would come about there.
The somewhat self sufficient moon colony seems close enough to earth to be able to work with earth currency, again with maybe an informal system.