sevenperforce

If a Dragon 2 aborts, then it will no longer be connected to stage 2, so it will no longer be going to space today.

I wonder if Uranus or Neptune are lined up for a relative-velocity-cancelling slingshot.

Visible light does have a fair bit of energy. If there was a way to create a crystal with a sufficiently high refractive index and superconducting properties, you could create a lossless closed loop of visible light bouncing inside the crystal forever. It's not a fatal stretch of scientific imagination to suppose that some sort of photon interference within the refractory matrix could create a standing wave of photons which would propagate out of the surface of the crystal. The maths would be far beyond even what we can do at the cutting edge of optical physics, but it's at least conceivable. Force propagation (i.e., where two lightsabers bounce off of each other, or where a lightsaber bounces off of cortosis or beskar) is trickier. If the photon standing waves are themselves transferring inertia, then that's a pretty damn high photon density. But hey, you need a high energy density. Lasers with high enough energy to cause injury can zip right through stuff which would stop lower-level visible light. With a lot of heat involvement. Presumably the "laser" bolts involved in fiction are some sort of standing wave of light enclosed in a powerful magnetic field, and a superconducting magnetic deflector shield could cause it to bounce away. Calling that a "laser" isn't entirely out of the question, incidentally. A laser is formed by creating a standing wave of light in a crystal and then pumping that standing wave until it collapses and emits a confined, phase-standard beam of photons. Any system which involves the creation of a standing wave of light which involves an emission could be termed a laser.

Looks like there would be space along the spaceplane's fuselage for a pair of simple crossfed boosters.

That is what they did.

Not to mention that "force per volume" is a not-so-clever way of saying "specific weight" which is density times gravity. So they're saying they can make negative density, simply by putting two electrical fields at right angles to each other.

"A spacecraft having a triangular hull with vertical electrostatic line charges on each corner that produce a horizontal electric field parallel to the sides of the hull. This field, interacting with a plane wave emitted by antennas on the side of the hull, generates a force per volume combining both lift and propulsion." In other words, it is pulling itself up by its own boot straps....which is to say, it's not moving at all. Reactionless thruster. No combination of magnetic fields produces a reactionless force.

Gravel pile is the problem for sure. That's the reason to have an MMU.

That's what they pretended to do in Armageddon.

Sounds like dragonskin body armor. They made quite a bit deal of out it a few years ago. IIRC it degraded really quickly under high temperature fluctuations and couldn't handle grit or sand. May also have had a shrapnel effect with multiple hits to the same area -- i.e., plate fragmentation would end up sending ceramic shards through the inner lining if you got hit more than once.

@Mad Rocket Scientist So here's the kicker. Adding 100 m/s of dV adds 100 m/s of dV. That doesn't change. 100 m/s of dV is the same instantaneous change in velocity regardless of where it is applied, at that moment. However, if you add 100 m/s of dV to your velocity while your fuel is moving very very fast, then you end up leaving with far more velocity than if you added that 100 m/s while your fuel is moving relatively slow, because fuel that is moving fast has a greater amount of inertia/momentum/impulse than fuel that is moving slow. That's the way to think about it, conceptually. The math is...the math. The math works out on its own.

Good example by @FleshJeb above. Another, less mathy way of looking at it: Suppose you do a burn out in empty heliocentric space. You're pushing fuel out the back of your rocket, which slows the fuel down (relative to the sun) and speeds you up. You're throwing something in one direction and it pushes you in the other direction. It's an exchange of momentum. Makes sense so far, right? Now, suppose you do a burn deep in a planet's gravity well. This time, you're still doing an exchange of momentum (pushing the fuel in one direction which pushes you in the other direction), but this time, the fuel you're pushing away has much more momentum to begin with because it's been sped up by the gravity well. When you push it away, you're pushing against something that is, effectively, "heavier"; as a result, it gives you more of a kick, relative to the original heliocentric orbit. This doesn't violate conservation of momentum, because the momentum left behind is (essentially) added to the gravity of the planet.

The one nice thing about the MMU was that an astronaut could use it to "fly out" and grab a derelict spacecraft and push it inside the orbiter's payload bay for repairs. Or, you know, the orbiter could simply fly a little closer and grab the spacecraft with the Canadarm.

Concern would probably be getting the reactor to sit dormant for a decade then pop online autonomously and start working.

JWST won't have any orientation problems because the sunshade is symmetric with respect to the sun, but it does have a propellant budget for counteracting the outward thrust produced by the solar wind. It can be turned to the ecliptic, but that's not the primary goal.

Sunshade isn't large enough to run into solar wind problems. As far as survey is concerned, JWST will primary point toward polar objects. This, incidentally, is one of the reasons why TESS had a sky-survey designed to maximize the amount of time spent looking due north and due south.

Too bulky, not necessary, replaced with the SAFER jetpack.

Driving a rover from your computer is tricky with the 3-second lightspeed delay. Better to have a bunch of tiny autonomous rovers doing a Google Street View thing, and then you could have human people navigating the existing data and flagging stuff that way.

Y u no haz pictures?!

And just like that you would have 100 male organs drawn on the surface of the moon. Rover McRoverFace all over again.

Ah, very good point. I wonder if you could use an excess-hyperbolic Type I transfer out of LEO to Neptune, and then use a Neptune flyby to lower velocity to reach Pluto with lower excess hyperbolic velocity. Might lower intercept speed to something that a big hydrazine (or even hypergolic biprop) tank could handle.

On Pluto... If you want to do a Pluto mission, just wait until BFR is flying. Build a massive 30-tonne Pluto science robot spaceship with an orbiter, a lander, and a sample return capsule. Send up a BFS tanker and refuel it in LEO with two additional launches. Mate your Pluto spaceship to a 110-tonne hydrolox Earth Departure Stage (Vacuum New Shepard or the like) and shove the whole affair into a cargo BFS. BFS launches to LEO, rendezvouses with the tanker, refuels, and burns to Earth escape. Open the clamshell, release the payload, and then turn around and burn slightly so the BFS can re-enter after a single eccentric orbit. The hydrolox stage burns the rest of the way to Pluto intercept, no Jupiter flyby or ion kick stage necessary.

I underlined the difficult bit.

A rover might be asking for a bit much. There are decent transfer windows to Pluto (using a Jovian assist) every 12 years, with three of those in succession being "ideal" every 200 years. There are passable orbital transfers every 30 years using a Saturn assist if you miss the Jovian assist. You can do an inefficient Pluto transfer once every year, if you have dV to burn. A Falcon Heavy Plutonian orbiter mission would use a fully-expendable Block 5 Falcon Heavy carrying an ion kick stage, with hydrazine monoprop for desaturation and orbital insertion, and solar panels to run the ion kick stage early on and to run the reaction wheels and comms for the rest of the time. You'd need an RTG for redundancy, and you'd use Charon for a slight Oberth kick during the orbital insertion burn. I don't think you'd have enough mass for a lander. If you want enough mass for a lander, then you'd need to put it up into an eccentric Earth orbit using a reusable Falcon Heavy and then you'd send up a hydrolox Earth departure stage separately on a New Glenn, Atlas V, or Vulcan. That would give you the mass budget for a lander. Even then a rover would be really, really pushing it.