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drasnor Icrontian


Hawthorne, CA
Last Active
Invited by
April 13, 1984
Hawthorne, CA
Rocket Scientist
  • Re: Falcon Heavy!

    Who knew that was going to work?!? It did though, holy shit!

  • Re: Nintendo is delightfully weird.

    I once built a 12" x 3" x 3" hollow pillar out of 20 lb bond paper that weighed ~4 oz and supported an 80 lb compressive load. It was disqualified from the competition because the footprint was slightly too small; in which young drasnor learned about manufacturing tolerances.

  • Re: SpaceX - Falcon 9 Rocket Launch

    @aspieRommel said:
    How was the rocket able to “glowworm” like that? What conditions were just right for it to happen?

    TL;DR, the rocket condensation trail is illuminated by the sun which had already set at ground level but had not yet set at the altitude that the rocket flew through. The Fox newscaster in the original post discusses this briefly.

    1. The Earth is round.
    2. The Earth rotates about its north-south axis once per day.
    3. Other laws of physics (particularly relating to chemistry) are valid.

    At local sunset, the light from the sun seems to be traveling exactly parallel to local observers on the ground. However, in actuality it is traveling tangent to the round surface of the Earth as shown in the figure below (Wikipedia).

    The time of sunset as a function of altitude can be determined trigonometrically knowing the radius of Earth (R ≈ 6370 km) and its rotation rate (15°/hr). The conditions of sunset suitably match the small angle approximation for sine though such that sunset is 1 minute later for each 1.5 km of altitude gained for relatively small altitudes (h ≪ R).

    Local sunset at Lompoc, CA near the launch site was 4:56 PM on the day of the launch and liftoff occurred at 5:27:34 PM or roughly 30 minutes after sunset. As such, Falcon would fly out of twilight and into direct sunlight at an altitude of roughly 45 km. Lets take a look at the webcast:

    It takes a couple more minutes for the rocket to reach 45 km altitude so by then the rocket must reach an altitude of ~50 km before hitting daylight. It's pretty evident in the webcast when this happens at ~00:02:15 into flight. When we tune into Stage 2 following stage separation we can see it's in daylight. It's still dark on the ground though so anything in the sky lit by daylight is going to appear brilliant (i.e. like the moon).

    Now that we've established the lighting conditions, let's turn our attention to the thing being lit. According to publicly-available information, Falcon 9 Stage 1 converts 2.5 metric tons of liquid kerosene and liquid oxygen per second into mostly steam and some carbon dioxide, soot, and other random organic molecules. Stage 2 does the same thing at roughly an order of magnitude lower rate (9 engines vs 1 engine with all else being equal). Steam is nothing more than hot water vapor and is being exhausted from Merlin at a fairly high temperature and pressure into a fairly cold vacuum. Chemistry tells us that these sorts of conditions cause the expelled vapor to condense and form clouds. I'll leave the exercise of working through steam phase transitions as an exercise for the reader. The generic name for clouds formed this way is "condensation trails" or "contrails".

    So, now we have high altitude clouds lit up by daylight seen by observers in the Earth's shadow.


  • Re: Niantic announces a Harry Potter AR game

    @GHoosdum said:
    “But if it matters to you, you'll be able to choose Hufflepuff over Slytherin."


  • WPA2 is fallen, winter is here

    Proving once again that hackers security researchers are the reason we can't have nice things, the Key Installation Attack (KRACK) is loose in the wild and exploits an intrinsic weakness in the WPA2 protocol to let unsavory sorts do unsavory things.

    How screwed are you?

    That depends on who lives near you and how much you've pissed them off because as usual hacking WiFi networks requires the attacker to be physically close. On the down side, the short story is that there are no more secure wireless protocols.

    • WPA2 GCMP, WPA2/WPA TKIP: attackers can decrypt your packets, steal your network key, and spoof your clients to switch to their access point for other nefarious man-in-the-middle attacks
    • WPA2 CCMP/AES: attackers can decrypt your packets and spoof your clients to switch to their access point but can't steal your network key.
    • WEP: completely cracked years ago, you are better off using WPA2 CCMP/AES.

    The industrial and national espionage opportunities are more compelling than Eve going after Alice and Bob's home network traffic so some of you are more screwed than others. Authenticated WPA2 Professional still relies on the same underlying technology that has this intrinsic flaw. Additionally, some implementations are more susceptible to certain classes of attacks than others.

    Problematically, the extremely-vulnerable wpa_supplicant implementation is at the heart of any Linux-based system including and especially embedded ones such as consumer WiFi routers, smart TVs, and pretty much any Internet of Things device. For a lot of these things you'll be lucky to ever see a firmware update.

    The good news

    This can be fixed by a minor revision to the WPA2 specification that's backwards-compatible with existing devices/software/whatever. Network traffic that's designed to operate over unsecure links is unaffected (e.g. https://, encrypted VPN). Read a Mickens about security and feel better.

    The bad news

    Any fix will require a patch, a lot of stuff won't get patched, and any unpatched device/software/whatever is an attack vector. Unsecure network services (e.g. everything not designed to operate on the raw Internet) are exposed to attackers on your network. An attacker on your network can turn all your stuff into zombies, access your open network shares, and otherwise do anything that someone you've given your network password can do.

    Closing thoughts

    Have a nice day, patch all your stuff, and don't forget to use AES.



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