Category Archives: Technology and Society

Business, Economics, Political Commentary, Space, Technology and Society

Rethinking SLS

17 Comments

In the course of working on my Kickstarter project over the past several months, I’ve been examining the arguments in favor of the SLS program. In the course of doing so, I’ve finally come to realize that they aren’t just compelling, but irrefutable, really.

Dumbacher, Griffin, Cooke, Cook and King are right. It does take a lot of mass in orbit to get to Mars, and bigger rockets are clearly better. Sure, each flight will cost billions, but how can we put a price on national pride, and jobs in Huntsville, Promontory, Michoud and Titusville? The more I think about the hazards and complications of launching a lot of dinky rockets, and all that orbital assembly, the more I realize how risky it is, not just for our precious astronauts’ lives, but for the mission itself. And really, NASA just wouldn’t be NASA if it’s not building and launching its own giant rocket.

So I want to go formally on record as being fully supportive of this program, and I can’t wait for President Trump to come in next January to make space great again, with a yuuuuuuuge rocket, not those little dummy loser rockets that are always exploding on barges. #MakeSpaceGreatAgain

Mathematics, Space, Technology and Society

Europa With Falcon Heavy

12 Comments

I was running some numbers, and just got a surprising result. I’m wondering if someone can check my work.

The AIAA paper by Boeing, presented in Pasadena last fall, has a reference mission of 8.3 MT thrown at Jupiter for the fast trip with no gravity assists with the Block 2 cargo version. They specify a C3 of about 85 km^2/s^2. Here’s the table I’m looking at.

Europa Reference Table

When I back that out, I end up with a departure velocity from LEO of about 6.5 km/s. With a stage fraction of 0.1 (that is, the ratio of the stage dry weight to loaded weight) and an Isp of 465 (referencing RL-10), and sixty tonnes in LEO (that’s the latest I’m hearing for FH with the upgraded cores), I can do that mission with a single flight. If we do two flights, I can throw 24 MT. Here’s my spreadsheet. Am I getting something wrong? Because that implies that they could do an even bigger mission with a 130 MT SLS. Here’s my spreadsheet.

[Update a few minutes later]

OK, I do see one slight problem, but I don’t think it affects my results much. I sized the “rubber” stage to the 2nd-stage requirement, so it’s probably a little undersized for the first stage. That is, when I change the payload mass, I get a slightly different propellant load in the first stage, though in actuality it should be independent of that.

[Update a few minutes later]

I’m wondering if the problem they have is that the EUS is oversized for the mission, so it wastes a lot of propellant shoving the parasitic stage mass? If so, that would be kind of hilarious.

But it is also possible that I’ve done the calculation wrong, which is why I’d like more eyes on my work.

[Update a couple minutes later]

D’oh!!

I do see an error. I double the potential energy as well as the kinetic when solving for departure velocity in line 13. BRB.

[Update a few minutes later]

OK, I guess I was wrong when I said I was wrong. Still not seeing the problem, if there is one.

[Update a while later]

I should note that the numbers don’t look obviously wrong, or bother me intuitively. I’m just trying to understand the disparity with the SLS mission, which supposedly has twice the throw weight.

[Late-afternoon update]

Looking at the Wikipedia page for EUS (I know, but it’s usually not a bad source for things like this), mass properties are pretty scarce. All it says is that it can carry 129,000 MT of propellant, which makes no sense, since that’s the throw weight of the SLS, and leaves no margin for structure. So huh. It’s almost like the whole program is a Bravo Sierra jobs program.

[March 28th update]

I just had an email exchange with one of the paper’s authors. They are using the Block 1B configuration, which only has 105 tonne capability. So my numbers seem to be right.

[Bumped]