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21
Advanced Concepts / Re: Zubrin's Dipole Drive
« Last post by Proponent on Today at 04:27 PM »
OK, after reading Paul Gilster's article on Centauri Dreams, I think I understand where the mass-flow rate of 65.2 μg/s comes from  Taking, like Zubrin, the example of a thruster with a 500-W power source, Gilster assumes an 80% efficiency of conversion of electrical power into jet power.  Assuming, further, a grid potential of 64 V, Gilster calculates a jet current of (400 W)/(64 V) = 6.25 A.  Since a proton's mass-to-charge ratio is (1.67e-27 kg)/(1.60e-19 C) = 1.04e-8 kg/C, that current corresponds to a mass flux of (6.25 A)(1.04e-8 kg/C) = 6.51e-8 kg/s, which is what Zubrin "requires."

The grids' charge will tend to leak away over time.  Counteracting that will require electrical power, but why that power would be approximately equal to the jet power is a mystery to me.
22
Commercial Space Flight General / Re: EXOS aerospace
« Last post by Craftyatom on Today at 04:24 PM »
They've just uploaded a pair of high-quality videos from (opposite sides of) the rocket - another benefit of recovering it!
Definitely got some roll going on late in the burn, though nothing a payload couldn't handle.
Great audio!
[EDIT: And a third one, of liftoff!]

23
Russian Launchers - Soyuz, Progress and Unmanned / Re: FAILURE: Soyuz MS-10 - October 11, 2018 - Baikonur (DISCUSSION)
« Last post by eeergo on Today at 04:23 PM »
Here is another version of the above:

Soyuz MS-10 Failure extended (stabilization, zoom 2x, slow motion 25% with frame interpolation)

AstronautiCAST
Published on Oct 14, 2018

Original footage courtesy of Roscosmos

In these videos it's very noticeable which one is the booster that failed to separate properly.

It's the one on the right of the rocket as seen from the camera. Watching the whole launch it is clear that's the one lying on the pitch/-Z axis (Soyuz FG launches from a rotated launch mount so there is no roll to confound things), which means the defective booster should be Block V.
24
SpaceX BFR - Earth to Deep Space / Re: Should the BFR have a launch escape system?
« Last post by Rocket Science on Today at 04:22 PM »
25
SNC Dream Chaser Section / Re: Sierra Nevada Corporation - 2018 Capabilities Overview
« Last post by TrevorMonty on Today at 04:16 PM »
We can add US engine designer and manufacturer to SNC capabilities.

26
Space Science Coverage / Re: JAXA Hayabusa2 Mission : General Thread
« Last post by mcgyver on Today at 04:04 PM »
...well, after all it looks like that raising at 0.70m/s was a scheduled operation... but I still don't understand how it can be called a "touchdown rehearsal", it looks more like a "touch&go", which is a totally different thing.
http://www.hayabusa2.jaxa.jp/en/topics/20181014e_TD1-R1-A/
27
Space Science Coverage / Re: JAXA Hayabusa2 Mission : General Thread
« Last post by mcgyver on Today at 03:59 PM »
Altitude profile analysis and comparison to MASCOT mission;

28
SpaceX BFR - Earth to Deep Space / Re: Power options for a Mars settlement
« Last post by meekGee on Today at 03:56 PM »

SSPs assume a large enough receiver, which jn the case of laser is very practical in size.

QD PV is 6.5 g / m2, for max ~ 60 W on Mars.

I was asking what the inverse square law has to do with anything.

And when comparing systems, use watt-hours per day avg, or else the numbers are meaningless.

SSP is a better idea on Mars than it is on Earth, but still loses out to ground power.

It cuts received power density with the square of distance, naturally.

If you calc the mass required to get 60 W / m2 out of your rectenna, you'll see why areosat and geosat SSP systems aren't competitive.  Then you can calc Wh too.
You mentioned it with respect to laser too.

On earth, given the possible wavelengths and height of GEO, SSP is a non-starter.

On Mars, with a lower orbit, and using a laser or short wavelength RF, receivers that capture the entire beam are practical, and so the inverse square law is completely moot.

It's still a losing proposition because of transmission losses and most importantly the batshit insane system complexity, but the fundamental law you're looking for is diffraction limit, not inverse square law.

No, 1/r^2 must be factored in, regardless of EM frequency.  Short range lab tests (km scale) don't factor it in because they're short-range.  Any notional orbital SSP must factor it in explicitly, else the collector's output power will be badly overstated.

Very roughly speaking, with 1 mm RF shooting over 10,000 km, a 100 m transmitter can create a 100 m spot.

With a 1 um NIR laser, a 1 m transmitter can create a 10 m spot.

Subject to these sizes, which are diffraction limited, where and how exactly are you going to factor in 1/r^2?

Here's a riddle for you.  Two comm sats have antennas that cover the same footprint.  Both provide the same power level to the receivers within the footprint.  One comm sat is in LEO, the other is in GEO, 100x as far.

Do you think the GEO sat transmitter needs to operate at:

A) 100^2=10,000x as much power
B) 100x as much power
C) 1x as much power
29
Space Science Coverage / Re: JAXA Hayabusa2 Mission : General Thread
« Last post by mcgyver on Today at 03:52 PM »
I can't understand why they remained at such altitude for 2 seconds and then started an escape at ludicrous speed. Looks like an emergency command to save from crash, rather than a successful LRF testing or a "touchdown simulation"!
In last seconds H2 was still lowering altitude at 0.10cm/s rate, which means  over 200 meters in the 18+18 minutes between telemetry-on-earth and command-on-hayabusa instants.... which can be seen as the "equivalent" of 200 meters per second if you remove the time-delay from the equation.
30
SpaceX BFR - Earth to Deep Space / Re: Should the BFR have a launch escape system?
« Last post by ncb1397 on Today at 03:52 PM »
Actually, GA airplanes are the worst, by far, when compared to jetliners.  Probably including Concorde too.

And if you're going to include Shuttle, you may as well include cars.  Shuttle failed as a rocket, not as an airplane.

My 3 examples all had similar maintanence practices. Bringing up Uncle Tom's beater aircraft that he works on himself is just being argumentative.

The wing damage on Columbia was likely survivable if it wasn't going at the speed it was when it hit the atmosphere. Aircraft have lost entire wings and landed.

http://www.military.com/video/military-aircraft-operations/aviation-accidents/f-15-lands-on-one-wing/644325471001
All your airplane examples have pilots. BFS doesn't. So they are not equivalent.

Quote
Yes a plane can land by itself using a system that is often referred to as “autoland”. The pilots can program the auto pilot to carry out the landing automatically whilst the pilots monitor the aircraft. However there are limitations as to when the autoland system can be used.
Automatic landings probably account for less then 1% of all landings on commercial flights. Many pilots actually think it’s much easier to land the aircraft manually, as monitoring the auto pilot in the autoland stage of flight is itself very demanding with a very high level of vigilance required at all stages.
https://www.flightdeckfriend.com/can-a-plane-land-automatically

BFS possibly doesn't have a pilot because there is no BFS vehicle (currently). The differentiation between an airliner with autopilot/autoland and a BFS is splitting hairs. Okay, BFS doesn't have a pilot monitoring anything and that somehow makes it safer?
Auto-pilots (or FMSs, in modern jet liners) are very limited in what they do.

Given how many airplanes crash due to pilot error, I don't think you can credibly claim it's "hair splitting".

-----
ABCD: Always Be Counting Down

Is this considered pilot error?

Quote
Continental / Colgan Air Flight 3407 is a really troubling one. Flying into Buffalo/Niagara airport one cold night, a Bombardier regional jet carrying 49 passengers collected a fair bit of ice on the wing. As the plane descended on landing approach, the pilots failed to notice that the airspeed had fallen below the approach speed that was appropriate for ice buildup conditions. The plane stalled.
https://www.quora.com/What-were-the-worst-pilot-errors-in-airplanes-crashes

How realible is your computer going to be at measuring and understanding all conditions of flight? And if it was that good, it would be just as effective as an assistant warning the pilot that their air speed is too low due to ice build up (as an example).

I wouldn't expect the software to be that great to begin with. Cargo dragon didn't even deploy the parachutes after CRS-7 in flight break up. In an automated system, the programmer is the pilot. I wouldn't expect him to be immune to mistakes as seen by the recent failure of Ariane V. The wrong parameters were put into the autopilot system and BFS won't have a human level AI. Sorry...
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