Agate

Musk's business plan has an extra step that makes all the difference: 1) Start with ridiculous amounts of money.

They've been selling these since I was a kid: http://www.abundantearth.com/store/ecosphere.html

There's not all *that* many cosmic rays, the Sun's and Earth's magnetic fields offer quite a bit of protection, and many of them go right through you.

Service bays cause spontaneous explosions of spaceships. If any part of the spacecraft is anywhere near the doors when they open, kaboom. Goes double for parts that also move. If a part is attached to the outside of a service bay, or really anywhere near the bay, the game may treat it as being *inside*, rendering it unusable at best, kaboom at worst. And objects attached inside the bay but in the wrong place may rattle continuously, causing control difficulties at best, kaboom at worst.

To my mind, it looks like they've got a bare concept that they've thrown some 3-d graphics at, but there's no engineering design yet. This concept is based on Ariane 5: the distinguishing feature of Ariane 5 is that it's got an oversized "main stage" that provides propulsion from liftoff almost all the way to orbit. (SpaceX drops its first stage at about V = 1.8 km/s; Ariane 5 keeps the main stage running until about 7 km/s). That makes the main stage engine big, expensive and worth recovering, BUT it means that the mass of your recovery hardware (wings, landing gear, propellers) has a much bigger impact on payload, since it must be carried almost all the way to space. In addition, re-entry is a lot harsher at this speed. That means there are a bunch of possible showstoppers: 1) Turboprop and turbofan engines are very heavy compared to rocket engines with similar thrust. Often, that doesn't matter because the savings in fuel and tank mass makes the engine mass negligible, but the plan here is to ditch the tanks, so engine mass matters. (Especially given the flight profile of Ariane 5, see above.) 2) The turboprop engines are going into space, so you're going to need to design them to be vacuum tolerant. A space-rated jet turbine is not exactly off-the-shelf technology. 3) The wings on this thing are very short and stubby, and the payload (a ginormous rocket engine) is pretty heavy. Also, the wings have to be flat boards rather than a classic asymmetric airfoil shape, or they'll throw off the rocket during launch. Odds are good it's going to fly like a brick, with a high stall speed that will make landing an exciting challenge. 4) The video shows folding propellers that deploy in flight. Designing props that fold when you want them to and not when you don't is a challenge. There are a few aircraft (motor gliders) that do this, but they operate under much less stressful flight conditions. 5) The nose of the return vehicle needs a heat shield to protect it during re-entry. But the nose also needs to have ginormous pipes and clamps running through it to mate the engine unit to the fuel tank during launch. This is doable: the Space Shuttle has a bunch of doors in its heat shield to solve this problem. But I think we can all agree that the ideal number of holes you want in your heat shield is zero. And none of this is shown in the video. The upshot: this may be doable, and hell, it might work better than SpaceX's plan. But the final design would involve a lot more careful design than the "strap some wings onto the side of an Ariane 5 engine" concept shown in the video. Which makes me suspect they haven't even started doing their homework yet. SpaceX will either succeed or prove its design impossible long before this concept ever flies. SpaceX and Ariane 5 launch videos, to compare staging design:

This one goes out to the amazing service bay. Convenient storage system for small parts, destroyer of space ships. Post your service bay fails here!

I spent some time this week doing this. Well, not intentionally using asteroids for heat shielding, but aerobraking asteroids in Kerbin's atmosphere. Rthsom's right: while asteroids look like space rocks, they're actually made of styrofoam, and no amount of torque could keep my space tug from flipping around engine-first as soon as it hit atmo. Your spacecraft will act as a heat shield for your asteroid, unfortunately.

The rules should definitely be: on Kerbin, no torque wheels, no thrusters, nothing but wheel power.

The fact that "seconds" is the only unit metric and American units have in common is not a good reason to use Isp. I mean, I could tell you that my own mass is 2 seconds, if by that I mean the period I would bob up and down at if tied to a certain bungee cord. But that would be ridiculous, and Isp is exactly that same ridiculous. But we're stuck with it, so sigh.

Found a pretty impressive Half Dome northeast of KSC. Cliff's about two and a half miles tall. I never liked the Mun's polar mountain. It was obviously a mapping glitch rather than a real mountain.

Ladies and gentlemen, the heavier-than-air zeppelin. The bad news is, it's just as slow. The good news is, it's still full of explosive hydrogen, but for a completely different reason.

I'm a physics professor, and when I teach this stuff, I teach the exhaust velocity form Rune listed. I figure if I don't tell students about "specific impulse", maybe eventually it'll go away.

Best part about that suit is the crotch-window, so you can see where you're stepping. Genius.

Hacked my save to get rid of the Pol exploration, so no new Pol missions, but I do have a Pol milestone that I can't cancel. Is it safe to edit the save to remove this milestone contract, or will that mess everything up?

Yeah, now that I've solved the Pol problem, I've picked up that one. It so happens that I've got a spare segment of my near-Kerbin-orbit station I'm not using... (it was intended to be the central hub, but I didn't realize that a Radial Attachment Point is nothing like a Clamp-O-Tron Docking Port until I tried to dock with one.)