SpaceX Raptor Engines

SpaceX Raptor Rocket Engines
Engine for atmospheric operation on the left
Engine for vacuum operation on the right

This picture shows how much bigger the nozzle on the vacuum engine is. The mechanical bits at the top are very similar, if not identical.


How SpaceX's New Raptor Vacuum Engine Is Different From Previous Raptors (and Other Stuff)
Scott Manley

In this video Scott Manley gives a pretty good explanation of the issues involved in designing rocket engine nozzles for different conditions.

SpaceX Dragon simulator

How To Dock With ISS in SpaceX's Free Dragon Docking Simulator
Very cool.

SpaceX Dragon simulator Via The Unwanted Blog

Space Bearings

Scientists May Have Figured Out Why So Many Spacecraft Were Failing
I knew that you could use flywheels driven by electric motors to control the attitude of a spacecraft, and I sort of knew that it was being done. It didn't seem like a really great idea because if you don't want the spacecraft's attitude to change, you need to make sure you aren't exerting any torque on the flywheels, except that won't work unless you have frictionless bearings and I'm pretty sure those don't exist. I suspect that even super low friction bearings like magnetic, or air, or fluid exert some drag, so you are going to need a motor that can supply the very low amount of torque needed to counteract that drag. So as long as you want the spacecraft to point in a specific direction (maintain the correct attitude: stand up straight, chin up, suck in that gut), you are going to need to supply the motor with power. It won't need much, but it will be a constant drain on your supply. Won't matter so much if you have solar panels, but for voyages out to Jupiter and beyond, solar panels won't cut it. Those guys use nuclear power mostly, so maybe it isn't an issue.

Anyway, Scott does a good job of explaining the issue and what may have caused it. The thing I don't get is just what impact a big solar flare would have if you were to encounter it. For people it can be very bad, but for mechanical devices? I wouldn't think it would have much effect. But maybe I'm wrong.

I remember reading an science fiction story once upon a time where big spaceships used reaction wheels to control their attitude. One spaceship set down on a planet, but one of its three landing legs did not deploy, but it had these powerful reaction wheels, so it was able to continue standing up straight even though it only had two legs. The pilot should have noticed this, but he was riled up over some disagreement and went charging off to resolve it. The reaction wheels kept the spacecraft standing for a while, but the strain was more than they were designed for so in short order the bearings froze and the spacecraft went cartwheeling across the landscape. Oops.

LOX

How Israel's Lander Crashed Into The Moon, And How Falcon Heavy Flew  Except I've skipped over the Lunar Lander story to get to the LOX.
Just the coolest thing I've seen in a while. Bonus: starting around 17:30 we have an animation of a large space telescope being loaded on the BFR, now known as Starship.

Far Side of the Moon

Chang'e 4 Lunar Landing In Detail
Mr. Manley does a good job here. But how is it that we know any of this at all? When we sent Apollo spacecraft to the moon 50 years ago, they were cutoff from communication when they went behind the moon. So how are we getting these pictures? We have sent probes around the moon and they have taken pictures, but they had to come back into view before they could transmit their images. This Chinese probe is on the moon, it isn't coming back into view, ever. Have the Chinese invented a new kind of super-quantum-licious communications technique that allows them to transmit through a thousand miles of rock? No, they sent another satellite, a communications relay, out to Lagrange point 2 which is out beyond the moon.


Queqiao relay satellite enters L2 orbit
Notice that this satellite doesn't just sit at the 'point', the 'point', after all, is unstable. Any slight disturbance from this location will cause the satellite to fall away from the 'point', never to return. Also sitting at the 'point' wouldn't do us any good, as the 'point' is directly opposite the Earth and so is blocked from radio communications by the moon. Instead the satellite goes into a halo orbit where it never actually crosses the point, instead it orbits the 'point'. The James Webb Space Telescope will be using a halo orbit when it eventually gets launched, which is expected in a couple of years.

Rocket Science

Why Do Ion Thusters Use Xenon? KSP Doesn't Teach.....
Since I have been studying chemistry, I've started to take note of specific uses for specific elements. (It helps that Scott uses the word 'specific' in his video.) I mean it's kind of weird. We've got this periodic table of elements and supposedly elements that are adjacent in the chart have some similar properties, but it seems that those similarities are vastly overshadowed by their differences. Which makes the fact that we even have a periodic table pretty fricking amazing.


What is Hall Effect and How Hall Effect Sensors Work
Hall Effect Thruster sounds like something I should understand, after all Hall Effect Sensors are everyday items. Shoot, the ABS in our 1995 Ford Windstar used Hall Effect Sensors for measuring wheel speed. Your keyboard probably uses Hall Effect Sensors to determine when you have pressed a key, assuming of course that you are even using a real keyboard. I dunno how many people are reading this on their smart phones, but what am I gonna do about it? Yell at the kids? Tell them to
'get off of my lawn'? Yeah, like that's gonna work.

Anyway, I didn't really understand the Hall Effect until I watched this video. I also watched another half a dozen videos on the subject and while the audio track on this one isn't Hollywood perfect, the video is still better than all the others I sampled.

The Hall-effect thruster aboard the European Space Agency’s SMART-1 mission. Launched in 2003, this became the first Hall thruster to be utilized beyond geosynchronous orbit. Photo Credit: ESA

The Hall-effect thruster in the above image is from Experimental Design Bureau (EDB) Fakel of Kaliningrad, Russia. That's twice Russia got mentioned today. Three times if you count the link in my post about cocaine production. The link pointed to a story that came from RT (formerly Russia Today).

Scott Manley (the video up top) has appeared here before.

How much energy would it take to blow up a planet?

How Much Power Do You Need To Destroy A Planet?
Remember when Darth Vader used the Death Star to blow up Princess Leia's home planet of Alderaan in the original Star Wars movie? I got to wondering about this the other day. In particular I was wondering if the Death Star would be big enough to generate the required energy. I'm thinking we could use microwave radiation to heat the interior of the planet to the point that it would boil and then vaporize. Who knows why this returned to my attention tonight, but it did. A little surfing turned up a story on Science Alert that features a video by Scott Manley (above) and an article in Popular Mechanics that offers a selection of ideas on how the job might be accomplished. I like Manley's explanation best, mostly because he put together this cool video.

Manley has graced these pages before.

Nukes in Space

Most Kerbal Spaceship Ever
This video reminded me of my post on the subject and prompted me to do a little digging. The biggest problem mentioned, neglecting the whole getting a zillion tons of steel into orbit thing, is getting rid of excess heat. I'm pretty sure all spacecraft have that problem and I'm likewise sure that NASA has a solution. Getting rid of the waste heat from a large nuclear power plant would require an extra large heat sink*, but a nuclear submarine is a large object, with acres** of outside surface area where heat sinks could be mounted. It might not be hydrodynamic any more, but that wouldn't be a problem, would it?

Anyway, I'm poking around and I came across this synopsis of the early years of nuclear propulsion. It still astounds me that the US Government committed billions of dollars to the construction of a uranium enrichment facility before they knew whether they could make an atomic bomb that would work. And then they start on new projects:

Rethinking Submarines as Spaceships
Part One
Once the A-bomb was developed physicists turned to harnessing the new mode of power in other ways. The US Air Force decided that it wanted an atomic powered bomber that could reach anywhere in the world non-stop without refueling. It dreamed of giant planes that could stay in the air on indefinite patrol, possibly only coming down every few weeks for crew rotation. Obviously an impossible dream, but they set to work toward that goal. Two B-36 bombers were dedicated to be modified to carry experimental reactors.
As the saying goes, the air force went off half-cocked in their efforts. As an experimental unit, the reactor was hung under the belly of the B-36. It provided no power for propelling the plane. It was for demo purposes and perhaps a PR show more than anything. The Air Force gave up the effort after two flights of that contraption. They concluded that the required shielding for the reactor made the concept impractical. Probably more important to the dismissal was that they never got seriously involved in a design for a nuclear-powered type of jet engine for such an aircraft.
The jealous rival of the Air Force, the Navy, picked up the idea in 1947 of using nuclear energy to propel machinery and asked industry to provide a design for a submarine reactor. Nukes were perfect for their submarines. It would be able to stay on patrol indefinitely without refueling or surfacing. And so the transition started as the submarines and bigger naval ships were designed for the new mode.
The design for the world’s first operational atomic powered ship, a submarine, was accepted and the keel laid in 1952. lt was named the USS Nautilus. It was launched in 1954 and commissioned later that year. 

Nine years after the end of the war the US Navy launched their first nuclear powered submarine. They designed and built a nuclear power plant, installed it in a submarine, launched the submarine, and it worked. That is phenomenal.

The first nuclear power plant came alive in 1951.

*   the whole heat in space is a real problem. I haven't found a good explanation of how it is handled.
** Okay, it's only about 1.5 acres.