Some of the nuke types over on Twitter have been discussing this. It would have beaten Sputnik to space, but not to earth orbit.
Category Archives: Mathematics
Europa With Falcon Heavy
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.
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]
Commercial Supersonic
Here’s the latest entry. They seem to have persuaded Virgin into buying ten planes.
They don’t seem to be addressing boom, no mention of transcontinental flight. I have a lot of trouble believing they can do trans-Pacific non-stop. But I’d like to find out more.
Climate Prediction
What a concept. Read the concluding sentence.
The Pension Crisis
As I’ve said in the past, if the federal government bails out a state, it should be under the conditions that it revert to territory status until it has demonstrated fiscal responsibility over a long period of time. And in the case of California, it should not be allowed to come back in as a single state. If this requires a constitutional amendment, I’ll bet you could slam one through enough of the more fiscally prudent states pretty quickly.
Commercial Crew
“Building in safety from the ground up.”
Note the theme that safety is the highest priority, and no discussion of how much this is all costing, or how much it’s delaying ending our dependence on Russia (which is part of the cost) in addition to delaying an increase in ISS crew size (which is also part of the cost).
How Inevitable Is Trump?
Not as much as some want us to think.
#ProTip: If you want to have a high probability of stopping Trump, get behind Cruz. If you want to throw the dice, try to get to convention.
— Rand Simberg (@Rand_Simberg) March 7, 2016
[Late-morning update]
Kurt Schlichter has sympathy for the Donaldites.
So do I, but The Donald isn’t their (or anyone else’s) salvation.
Confident Idiots
A long but very interesting piece on the overconfidence of the incompetent, by David Dunning (of Dunning-Kruger fame). For some reason, I think it has some relevance to the Trump phenomenon, and politics in general.
For the record, I have never had a problem claiming my ignorance on a topic.
The Ignorant Idea That Won’t Go Away
No, we can’t “just” throw our trash into the sun.
But I hate when people use current launchers to demonstrate the cost of a massive space project. That’s not how it would be done. And I wish they’d simply say “the sun is the most expensive place to get in the solar system.” Because it is.
Linux Problem
I’m trying to format a micro-SD to install Fedora on my Raspberry Pi 2. I’m following the instructions here.
But when I get to the part about building the swap partition, I’m getting an error message. This is the output of fdisk:
Command (m for help): p
Disk /dev/sdd: 29.7 GiB, 31914983424 bytes, 62333952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0002ce31Device Boot Start End Sectors Size Id Type
/dev/sdd1 2048 264191 262144 128M b W95 FAT32
/dev/sdd2 264192 1312767 1048576 512M 82 Linux swap / Solaris
/dev/sdd3 1312768 62333951 61021184 29.1G 83 Linux
Now here’s what happens when I run mkswap:
[root@new-host-5 raspberry]# mkswap /dev/sdd2
mkswap: error: swap area needs to be at least 40 KiB
I’ve tried searching for a similar issue, but am coming up empty. Anyone have any ideas?
[Update a while later]
OK, I’ve decided that it’s a bad SD. But now I’ve got a new problem; I can’t mount the W95 FAT32 boot partition:
Disk /dev/sdd: 14.5 GiB, 15560867840 bytes, 30392320 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000Device Boot Start End Sectors Size Id Type
/dev/sdd1 2048 264191 262144 128M b W95 FAT32
/dev/sdd2 264192 772095 507904 248M 82 Linux swap / Solaris
/dev/sdd3 772096 30392319 29620224 14.1G 83 LinuxCommand (m for help): q
[root@new-host-5 raspberry]# mount -t fat32 /dev/sdd1 /tmp/rpi/boot/
mount: unknown filesystem type ‘fat32’
[root@new-host-5 raspberry]# mount -t auto /dev/sdd1 /tmp/rpi/boot/
mount: /dev/sdd1 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/sdd1,
missing codepage or helper program, or other errorIn some cases useful info is found in syslog – try
dmesg | tail or so.
It doesn’t work with “auto” or “vfat” either.
[Tuesday-morning update]
OK, not sure what the problem was, but after rebooting the machine, I managed to get it all to work. I haven’t actually tried booting the Pi, yet, though.