# wizzlebippi

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Spacecraft Engineer
1. ## Lifting body aerodynamics: chord length/airfoil area - how do I find it?

The fuselage is one awkward airfoil. On conventional aircraft, the fuselage is usually assumed to produce as much lift as the wing area it covers. Assume the chord is the length of the craft, and the area is what you see in your top down view. The easiest way to calculate area on that is to break it down into simpler shapes.
2. ## GPS navigator on a space station

It doesn't even need to be in space. Next time you fly on an airliner, have a navigation app open. Your phone will drop GPS shortly into the takeoff roll because it senses excessive acceleration. For entertainment, if you get the chance to fly on something smaller and slower like a skyhawk, open a navigation app and watch it try to figure out where you are.
3. ## For Questions That Don't Merit Their Own Thread

I might be a savvy engineer, so I'll take a crack at this. Engines work by using a heat source to cause a working fluid to expand as a means of transferring energy from fuel into mechanical energy. The problem is most working fluids don't hold much thermal energy at useful temperatures, limiting the energy output and efficiency of the engine. The solutions are either increasing the operating temperature or increasing the mass of the working fluid. Increasing operating temperature usually isn't an option, at least not by enough to make a difference, due to material properties and cooling. Increasing the size of the engine can dramatically increase energy output by increasing the volume of working fluid, but at the expense of efficiency due to difficulty heating all the working fluid. Compressing the working fluid increases the mass being heated while keeping the volume being heated reasonable, allowing more chemical energy to be captured as heat, resulting in increased energy output and efficiency of the engine.
4. ## Effects of hypoxia - interesting video (slightly disturbing - discretion advised)

The problem is transferring gasses to and from your blood relies entirely on pressure. If the pressure of oxygen in the air is less than the pressure of oxygen in your blood, then oxygen moves from your blood to the air in your lungs. Above about 35,000 ft, the ambient pressure is low enough, that the time of useful consciousness becomes constant. This is because there isn't enough air pressure to keep enough oxygen in your blood for you to remain conscious. It then becomes a race of you using oxygen vs. oxygen and other gasses escaping in your lungs. Holding your breath will not stop this because breathing also relies on relative pressure. If you have an FAA medical certificate, you can take a chamber ride for free at the Civil Aerospace Medical Institute.
5. ## Enable disabled reaction wheels

And now it magically works again. I'm not sure what I did to disable the reaction wheels and today they work again.
6. ## Enable disabled reaction wheels

I have a ship with an mk1-2 command pod that for some reason has had it's reaction wheels disabled. It has both power and a pilot, and the reaction wheel mode is set to normal. RCS works, but I already ran out of monoprop. How do I dock this ship with the station to salvage its science.
7. ## Wings without volume? (made from a single layer of foil)

It's not just chord length, but speed as well. Calculate your expected takeoff and cruise Reynolds Numbers. There's a transition around 250-300k, above which airfoil shape matters a lot more. As a point of reference, RC aircraft operate around this transition.
8. ## Wings without volume? (made from a single layer of foil)

How big will this glider be? If you want to build something large, a sheet or two of foil won't do it, but at the right scale it could get the job done. Also, for small enough wings, the shape of the airfoil doesn't matter as much because even airfoils behave like flat plates.
9. ## Contrail

The engine exhaust also needs to have the correct amount of soot and water vapor for contrails to form. Stealth aircraft have contrail detectors to help them avoid throttle settings that could help the enemy spot them.
10. ## Cannae/EmDrive

I think you're underestimating the cost of testing on earth. The cost of man hours spent designing away test interference has likely greatly exceeded the cost of launching a cube sat. NASA Eagleworks probably spent at least a million just on having independent test experts analyze their rig and findings. Bench testing, or basically all that has been done with the Cannae drive, is inherently flawed. There is always interference from the test setup, despite how carefully designed it may be. It takes a lot of time and money do design out flaws, and even then we can only account for known sources of error. The only way to truely eliminate error due to the test setup, it to put the Cannae drive in space. Yes, if it breaks we may never know exactly why, but if it produces the same amount of thrust in space, we will finally know it's not test error.
11. ## Cannae/EmDrive

Magnetrons have been around for decades and are pretty well understood. Some hardening will be necessary to ensure it survives the harsh conditions in space, but that shouldn't be too difficult. Since the Cannae drive is such a simple system, there aren't many ways for it to fail. If there was to be unexpected behavior from the drive, something should have presented its self by now on the test stand. I'm only advocating a prototype, not equipping a commercial satellite with Cannae drive station keeping thrusters.
12. ## Cannae/EmDrive

Do we really need to be able to explain the thrust it produces for it to have benefits? Proving the Cannae drive works in orbit is worth billions. Satelites could maintain orbit near indefinitely because fuel is no longer a concern, and safely deorbit or rendezvous with a craft for repairs/upgrades. Besides, it won't be the first time something is used when science has an incomplete understanding of how it works.
13. ## Embrittlement caused by liquid hydrogen and other materials effects of cryogenics temps

As far as I know, it doesn't have as much to do with temperature as pressure. A hydrogen molecule is small enough to slip through the crystal structure of the metal tank that contains it, which is why hydrogen is so hard to contain. Occasionally, the hydrogen gets trapped in the interstitial space. When force is applied to the crystal, the atoms that make up the crystal can realign around the hydrogen molecule, creating a defect. Eventually, these defects can cause cracks or failure of the tank. https://en.m.wikipedia.org/wiki/Hydrogen_embrittlement
14. ## "Dawn" Ion Engine Suggestion

Dawn is fine as is. Use a bunch of batteries, 12-15k EC, and you'll still be able to achieve a few minutes of run time at Eeloo with 7 Dawn thrusters. I only use 4 gigantor solar panels, ~3 EC/s at Eeloo, and one RTG incase I end up with no solar panels facing the sun during time warp. You still end up with 1.5'ish hour burn times and need to start from a very deep orbit to make the burn work. Bigger Xenon tanks and ISRU support would be nice though.
15. ## What's better, more low thrust engines, or fewer high thrust engines?

Aircraft aren't the best example. Engines have become more reliable mostly because fuel management and scheduling have been taken away from human hands (why some older airliners required a flight engineer). The odds of a mechanical failure really haven't changed. This is partly because engines are becoming more complex, and partly because they largely reuse the same core, give it a larger fan, and spin it faster. The real reason why aircraft like the 747 exist is because before ETOPS (Extended-range Twin engine Operations Performance Standards), the airlines were required to have aircraft with 3+ engines for direct routes. Basically, the aircraft was never allowed to be more than 1 hour away from an airport with a suitable runway unless it had more than 2 engines. Now, the FAA allows a twin engine aircraft to certify to whatever time it can sustain single engine flight after making it half way to its intended destination with appropriate reserves. There may still be a few routes inaccessible to a twin engine aircraft, but there can't be many left. For a rocket, none of this applies. Having more, smaller engines increases the odds of an engine failure, and any engine failure reduces TWR and can affect the rocket's ability to make the desired orbit. From that standpoint, you want the fewest number of engines possible. As previously mentioned, the only reason Space X's Falcon 9 has 10 Merlin 1D engines is it's cheaper to manufacture 1 engine with the ability to fit a longer engine bell.