sevenperforce

The Layman Physicist's Dictionary: Force: How hard was the push? Impulse: How big was the push? Momentum: How much was it pushed? Kinetic Energy: How hard was it pushed, and how far? Speed: How fast is it moving? Velocity: How fast is it moving in that direction? Weight: How hard is it to pick up? Mass: How hard is it to push? Acceleration: How fast are you pushing it faster?

Yeah, "force released" is like saying "degrees of applesauce"; it's nonsense. I'm sure he was thinking of impulse, not force. Isp is the amount of impulse produced (change in momentum) per unit of propellant. If you are measuring the propellant in units of mass, then you end up with a "specific impulse" given in distance/time, which happens to be the average exhaust speed of your propellant. If you are measuring the propellant in units of weight, then you'll end up with a "specific impulse" given in units of time, which happens to be the amount of time it would take to burn through a weight of propellant equal to what the engine can lift.

I may tackle this. Promising.

In the webcast for Sunday's NS launch, they showed an updated NG model with the BE-3 upper stage and 5m fairing. BO also took a shot at SpaceX by explaining that a moving ship (as opposed to a "barge") can match wind and weather conditions and thus can allow New Glenn to be recovered in much higher sea states, ensuring higher launch cadence and launch opportunity use.

The question then presents, what's the minimum realistic size for a solar-powered tether-based propulsion system large enough to overcome its own drag in LEO, and how far would you need to scale it up in order to have an infinite-persistence LEO robotug? I am sure that if I do a little digging I will find whitepapers that have already been written about this.

Hear, hear!

The CoM of the MEM is way low and there are no reaction wheels so everything is FUBAR. I just throw a solar panel on the side and a reaction wheel on top and clip the reaction wheel down. Works wonders.

Not when they're being told to do everything BUT go to Mars. But yes, $20B/yr is more than enough if that's all they were supposed to do. Hell, if Elon had been given $20B/yr starting when Falcon 1 first flew, he could have taken the entire NASA staff to Mars and back by now.

**headdesk**

Was just thinking... Magnetic field lines produce a measurable force perpendicular to the velocity vector of a charged particle. This is the Lorentz force. As explained in this paper, care must be taken that geostationary comsats do not acquire net-positive or net-negative electrical charge, as their orbital motion through the magnetic field of the Earth can cause perturbations if they are charged, which can change their apsides. Earth's magnetic field protects us from high-energy charged particles because they are deflected to the poles and to the Van Allen Belts via Lorentz forces. A rail gun is fired at high velocity when the DC electron flow through the projectile is traveling perpendicularly to the magnetic field lines produced on the rails. This is perhaps the most violent exhibition of the Lorentz force. If the magnetic field at geostationary differences is enough to perturb the motion of comsats, would it be possible to build an effectively-reactionless drive using either properly-oriented current flow across long wires, or by using counter-rotating charged wires in low earth orbit? Obviously it is not truly reactionless; it's pushing against Earth's magnetic field. And obviously the effective thrust would be quite low because Earth's magnetic field is so weak. But it might be enough for station-keeping or spiraling between orbits, right? I will need to break out an old textbook or two in order to work out the maths....

By "everyone is infected", I mean that everyone is carrying the zombie virus, but it is dormant. It won't hurt you and only activates after death. The reason it makes things dicey for the military is that you can't cordon off the zombies and slaughter them. The zombies can appear anywhere. There's no containing them because any time anyone in the world dies, for any reason, they will come back. But you can still survive and rebuild civilization. You just have to make sure that everyone knows to stab dead people in the head right after they die. And don't walk around outside in the open, except in groups, well-armed, because you never know when a straggler might shamble by.

Walking Dead zombies are a bit more troublesome because the problem is not containable. Everyone is infected; everyone is reanimated postmortem whether bitten or no.

...to which Shotwell probably replies, "If you want us to fly our reusable boosters expendable, that's fine. Just pay a 50% upcharge...and, hey, you'll still be paying less than you'd pay ULA."

Not a good comparison because the LM+CSM combo was far, far more capable than the Gemini capsule.

Of course. Until their separation/catching makes more headache than taking them to the surface, which requires just more fuel (and barrels). If your reentry capsule weights like LEM cabin and has, say, an inflatable heatshield, will you really add the complexity and risk of its catching near another celestial body? Or you will just take a little moar fuel and make the capsule unary, if the whole ship will mass 40 t? Inflatable heat shield saves volume, not mass. Inflatable heat shields are not significantly less massive than their rigid equivalents. The Moon isn't small enough to just require "a little moar fuel". It requires a lot. Well, that's certainly the more mass-efficient approach. And if your dV requirement is high enough (as it is with the Moon) and your Isp is low enough (as it is with chemical bipropellant fuels), then you need the mass-efficient approach. Iron Man has infinite Isp so obviously that's not a problem. Actually, because the landing engine needed high thrust to lower gravity losses along with deep throttling capability, it was more mass-efficient to use separate engines. I ran the numbers on this once. Using a crossfed drop-tank landing stage with a single engine ended up being less mass-efficient than using a separate non-throttled ascent engine, at that time.

Right. Constellation didn't plan on having any crew remain in Orion during the lunar mission on Altair. Everyone goes to the surface; Orion waits autonomously on standby. The 680 m/s of fuel isn't going away, even if you do away with the life support in orbit. The third companion waiting in lunar orbit isn't necessary. But keeping your fuel, heat shield, and anything else you can in orbit is always the more efficient option, compared to taking it down to the surface. The most mass-efficient mission profile, assuming that you're not depending on any permanent infrastructure like a lunar space station and you're returning to Earth, will always be some sort of lunar orbit rendezvous. The theoretically most mass-efficient mission architecture would be to have a single habitable capsule with its own vacuum engines and a docking port on the base, but with no heat shield or parachutes and only a minimal aeroshell. It would be paired with an "Earth entry module" consisting of a docking port, fuel tanks, parachutes, and a heat shield. Once in lunar orbit, the capsule would break away from the Earth entry module and descend to the lunar surface, then return and dock with the orbiting module for the homeward journey, using that module's fuel tanks for its own engine. Of course, the complexity of such a system would make it impossible to man-rate. You'd want Earth-Lunar orbit rendezvous like Constellation, not pure Earth orbit rendezvous like the original Saturn C-1 "Jaybird" approach.

Yet another advantage for ULA. "We throw ALL our boosters away so we can launch ANY time!"

Au contraire. The spacemen in suits still need fuel to get from LLO to LEO, and they need a heat shield, and they need parachutes. So it will always be more efficient to leave a bottle of fuel, the heat shield, and the parachute in LLO while they go down the the lunar surface and do their surface mission than it would be to drag the fuel, the heat shield, and the parachute down to the lunar surface and back.

Anything that would make Apollo smaller would just make LOR more efficient.

Unless you're already flying with a pretty high launch cadence, a two-launch scheme is extremely sensitive to timing and requires twice as many orbital rendezvouses. In the Apollo era, we hadn't yet gotten REALLY good at orbital rendezvous quite yet. Another issue with meeting up in lunar orbit is that you need two different lunar orbit insertion burns, one for each vehicle. Which means both vehicles (e.g., your unmanned lander and your manned return vehicle) need to have fuel tank capacity specifically for braking into lunar orbit, which makes both of them bigger than they need to be. Apollo used the return vehicle's (oversized) engine and tankage for the LOI burn, meaning the lander only had to perform the landing, while Constellation planned to use the lander's engine and tankage for the LOI burn, meaning the return vehicle only had to perform the return. Plus, as @Tullius said, you still need a big rocket but now you need twice as many. Which means either you need VERY fast pad turnaround, or you need multiple pads. There are several possible architectures for a flags-and-footprints moon mission: Direct ascent. Big rocket goes to Earth orbit, goes to lunar orbit, goes to lunar surface, and comes back, dropping stages all the way. See Nova. Earth orbit rendezvous. Small rockets construct a big rocket in Earth orbit, which then goes to lunar orbit, goes to lunar surface, and comes back, dropping stages all the way. Lunar orbit rendezvous. Big rocket goes to Earth orbit, goes to lunar orbit, and then a lander breaks off, goes to the lunar surface, comes back to lunar orbit, and the original vehicle comes back to Earth. See Apollo. Earth-lunar orbit rendezvous. Small rockets construct a big rocket in Earth orbit, which goes to lunar orbit and then does everything that the lunar orbit rendezvous would have done. See Constellation. Joint lunar orbit rendezvous. Two separate rockets go separately to Earth orbit and then to lunar orbit, meet up, and then do everything that the lunar orbit rendezvous would have done. This is possible now via distributed launch.

This is...perfect. Now to just get the list the way I want it.

Don't know how slow ISRU will be, but yeah, probably.

I doubt this is really NEW news, but: https://gizmodo.com/nasa-and-esa-are-getting-serious-about-bringing-martian-1825568599 Has there been any design into a MAV? Why not just have the MAV perform the sample collection?

Yeah, I saw that. But I'm not going to include ALL vehicles.

So I'm thinking of three categories: Historical Rockets Saturn V N-1 R-7 Mercury-Atlas Gemini-Titan Delta II STS Energia Black Arrow Falcon 1 Current Rockets Electron Falcon 9 + Dragon Falcon Heavy Delta IV Delta IV Heavy Atlas V 551 Soyuz-FG Ariane 5 Long March 3B PSLV GSLV Mk3 Proton-K Vega Future Rockets New Glenn SLS Block 1 BFR Vulcan For each rocket, I'll have the name, the notional LEO payload, and the space program it belongs to. I'll also have a helmet icon above manned or man-rated vehicles. I have a 5yo as well who reads well enough to make use of this. Any rockets I missed that you think I really should add? Or any that are so similar to others that I should take them out? Also, any thoughts on organization within each set?