Refueling EDS's In-Orbit
There's been a bit of discussion lately about the concept of using commercial vehicles to refuel NASA's Earth Departure Stage in-orbit for a Mars mission. Rand asks the question "if it's a good idea for Mars, why isn't it a good idea for the moon?".
I think it's a good question. Griffin first mentioned the idea of refueling an Ares V launched EDS in orbit as an eventual extension to the capabilities of the program, but I think that that's a rather flawed and inefficient way of going about things. Think about it. The actual EDS stage is probably going to be somewhere between 80-90+% propellants. If you already think there's going to be the capability to refuel half of an EDS, and you think that that isn't a logistical problem (I don't), then why is fueling the whole thing on-orbit a problem? You could easily make a decently large transfer stage for lunar or martian purposes whose dry mass would be light enough to be launched empty on an Atlas V, Delta IV, Falcon IX, or Zenit Sea Launch. There's nothing that says the lunar lander or any cargo has to be launched on the same launch as the transfer stage. Compared to developing and operating an HLV, rendezvous and docking (or better yet, berthing using something like a mini Canadarm) just aren't that hard.
I guess the big annoyance I have with a government-only vehicles like the Ares I and Ares V, is that regardless of the flight rate, you still have to pay all the payroll and infrastructure costs. These vehicles, like the Shuttle are going to cost NASA almost as much when they're not flying as they would when they are. Where are they going to get the money for any sort of expanded exploration program if they're sinking all of their money into operating a vehicle that goes away if they don't pay the upkeep cost every year? Where are they going to get money to buy all that propellant from an orbital depot if they're still using an Ares V to get the EDS into orbit in the first place? Unless they retire Ares V as soon as propellant depots become available, they probably aren't going to be able to afford using them! And if they're already looking at on-orbit refueling in the future I think they'd be far better off putting their money into developing those capabilities (on-orbit propellant storage and transfer, on-orbit assembly and checkout of vehicles, reuse of in-space transportation vehicles) than developing a set of boosters that are at best temporary stop-gaps until the real infrastructure gets built.
I think it's a good question. Griffin first mentioned the idea of refueling an Ares V launched EDS in orbit as an eventual extension to the capabilities of the program, but I think that that's a rather flawed and inefficient way of going about things. Think about it. The actual EDS stage is probably going to be somewhere between 80-90+% propellants. If you already think there's going to be the capability to refuel half of an EDS, and you think that that isn't a logistical problem (I don't), then why is fueling the whole thing on-orbit a problem? You could easily make a decently large transfer stage for lunar or martian purposes whose dry mass would be light enough to be launched empty on an Atlas V, Delta IV, Falcon IX, or Zenit Sea Launch. There's nothing that says the lunar lander or any cargo has to be launched on the same launch as the transfer stage. Compared to developing and operating an HLV, rendezvous and docking (or better yet, berthing using something like a mini Canadarm) just aren't that hard.
I guess the big annoyance I have with a government-only vehicles like the Ares I and Ares V, is that regardless of the flight rate, you still have to pay all the payroll and infrastructure costs. These vehicles, like the Shuttle are going to cost NASA almost as much when they're not flying as they would when they are. Where are they going to get the money for any sort of expanded exploration program if they're sinking all of their money into operating a vehicle that goes away if they don't pay the upkeep cost every year? Where are they going to get money to buy all that propellant from an orbital depot if they're still using an Ares V to get the EDS into orbit in the first place? Unless they retire Ares V as soon as propellant depots become available, they probably aren't going to be able to afford using them! And if they're already looking at on-orbit refueling in the future I think they'd be far better off putting their money into developing those capabilities (on-orbit propellant storage and transfer, on-orbit assembly and checkout of vehicles, reuse of in-space transportation vehicles) than developing a set of boosters that are at best temporary stop-gaps until the real infrastructure gets built.
posted by Jon Goff at 9:19 PM
7 Comments:
It also bugs me that they don't intend to use these vehicles very much. Weren't they planning to use the big one only four or so times a year? At least with commercial launchers, you know the rockets will see use outside of what NASA does with them. And that means lower prices through higher launch frequencies.
We should have started Shuttle-C in the '90s and we'd have a heavy launch capability now. Griffin is working hard at being the last NASA administrator to make that mistake. This whole fiasco is all smoke and mirrors. It is nothing more than a way to sole source development money to big aerospace companies.
A kind of approach that might work would be if for every dollar NASA spent on its own launch vehicle it had to offer a dollar worth of prize to the private sector. As required politically, this would retain the standing army – though they might have to do more of their launch vehicle in house to sustain their standing army, (which might be a useful learning experience). NASA would not have to depend on the private sector for a launch vehicle and the private sector would not have to depend on NASA for a launch vehicle. Maybe something like the Bigelow prize funded equivalently to half the Ares I but split into multiple prizes so as to encourage many entrants – including the usual suspects.
> The actual EDS stage is probably going to be somewhere
> between 80-90+% propellants. You could easily make a
> decently large transfer stage for lunar or martian
> purposes whose dry mass would be light enough to be
> launched empty on an Atlas V, Delta IV, Falcon IX,
> or Zenit Sea Launch.
That's an understatement. On-orbit assembly and refueling gives you a *lot* more architecture possibilities for an upper stage than just one tin can with an engine on the back. You could make the EDS tank a collapsable bladder, allowing you to launch a tank that's larger than the shroud. You could connect tanks (and engines) together on orbit to build larger stages. Depending on the mission, you could drop or stage tanks and/or engines, in parallel, in serial, or both. Or you could use a flotilla of smaller stages, with the possiblity of refueling and other buddy ops between them. Then, of course, there's the possibiltiy of non-chemical propulsion.
We should have never stopped using Saturn V's. Then we would have had heavy launch capability all along.
Karl,
It also bugs me that they don't intend to use these vehicles very much. Weren't they planning to use the big one only four or so times a year? At least with commercial launchers, you know the rockets will see use outside of what NASA does with them. And that means lower prices through higher launch frequencies.
Bingo. The best situation would be if the boosters NASA wanted to launch on were commercially useful enough that even if NASA couldn't order any on a given year, that the boosters would still be available the next year without NASA having to pay any fixed costs. That would give NASA a lot more flexibility, as well as freeing up a lot of capital.
~Jon
Ed,
That's an understatement. On-orbit assembly and refueling gives you a *lot* more architecture possibilities for an upper stage than just one tin can with an engine on the back.
Well yes. I've even been thinking about a lot of the others. Unfortunately, I've been working 70-90hr weeks the last month or so, so I was planning on leaving some of my personal thoughts on the best route for a later post.
But yeah, inflatable tank based tugs, and cluster tug combos are definitely interesting options. It'll be interesting though to see how things pan out over the next several years.
~Jon
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