SpaceX Falcon 9 / Dragon 2 : SpX-DM2 : May 27, 2020 : DISCUSSION

[rdale]

Thanks Herb - it's been a while but those stressful feelings came right back

What I don’t understand is why they’re targeting Saturday and Sunday when both have 60% POVs.

Yesterday had a 60% POV - and we missed the launch by 15 minutes.

15.

Had that storm complex formed just 15 minutes earlier off Melbourne, we would have launched.

That's why you don't cancel a launch opportunity in Florida until you have to.

That being said - and I'll wait for Chris to start a new thread before I post a forecast - but if you have to pick a day this weekend that looks better, I'd go Sunday.

[Kabloona]

What I don’t understand is why they’re targeting Saturday and Sunday when both have 60% POVs.

I feel they should wait longer and choose a date that has at most 25%.

Do your probability math. With POV = .60 on two days, the probability of a weather scrub on  both days is 0.36. Which means the probability of at least one day having favorable weather is 1-0.36, or 0.64.

So two attempts on not-very-favorable days still gets you better than even odds of launching.

[Norm38]

So did they announce the capsule name?  I must have missed it.

[rdale]

So did they announce the capsule name?  I must have missed it.

No.

[FutureSpaceTourist]

For the non-meteorologists among us, the 45th now have a helpful FAQ on launch weather forecasts.

I’ve put in a separate - non-SpaceX section - thread:

https://forum.nasaspaceflight.com/index.php?topic=51047.0

[webdan]

What I don’t understand is why they’re targeting Saturday and Sunday when both have 60% POVs.

I feel they should wait longer and choose a date that has at most 25%.

Do your probability math. With POV = .60 on two days, the probability of a weather scrub on  both days is 0.36. Which means the probability of at least one day having favorable weather is 1-0.36, or 0.64.

So two attempts on not-very-favorable days still gets you getter than even odds of launching.

Agreed. I'll be taking a drive over there with the g/f on both days if need be. It'll be reminiscent of the first FH launch

[FutureSpaceTourist]

What I don’t understand is why they’re targeting Saturday and Sunday when both have 60% POVs.

I feel they should wait longer and choose a date that has at most 25%.

Do your probability math. With POV = .60 on two days, the probability of a weather scrub on  both days is 0.36. Which means the probability of at least one day having favorable weather is 1-0.36, or 0.64.

So two attempts on not-very-favorable days still gets you getter than even odds of launching.

Strictly speaking that probability calculation is only valid if the weather on the two days is completely independent. For weather systems that persist it’ll have the effect of reducing the probability of favourable weather.

I’ve no idea how much though

[Kabloona]

What I don’t understand is why they’re targeting Saturday and Sunday when both have 60% POVs.

I feel they should wait longer and choose a date that has at most 25%.

Do your probability math. With POV = .60 on two days, the probability of a weather scrub on  both days is 0.36. Which means the probability of at least one day having favorable weather is 1-0.36, or 0.64.

So two attempts on not-very-favorable days still gets you getter than even odds of launching.

Strictly speaking that probability calculation is only valid if the weather on the two days is completely independent. For weather systems that persist it’ll have the effect of reducing the probability of favourable weather.

I’ve no idea how much though

Good point. That makes the range of probability of favorable weather on at least one of two attempts this weekend anywhere from 40% to 64% depending on how closely the daily weather is coupled. Hopefully closer to the latter.

[ugordan]

Why is the NASAspaceflight archived livestream not available? It says "This video contains content from NBC Universal, who has blocked it in your country on copyright grounds."

What?

[mn]

Dumb question about lighting risk constraints:

Many of the rules were built from experience of the past, but things change. Perhaps a new vehicle like falcon/dragon can be designed to handle lighting safely. Is that possible? (commercial airliners fly thru thunderstorms all the time?)

[rdale]

I suppose it could be possible - but that would be tremendously expensive. And I still wouldn't want to risk it Much better to wait a day.

[mn]

I suppose it could be possible - but that would be tremendously expensive. And I still wouldn't want to risk it Much better to wait a day.

I guess my question is really what would it take? How expensive would it be? (and I would measure the cost primarily in lbs/kg)

[Kabloona]

Why is the NASAspaceflight archived livestream not available? It says "This video contains content from NBC Universal, who has blocked it in your country on copyright grounds."

What?

Huh. I'm getting the same message. Maybe the livestream inadvertently caught some NBC newscast running on a monitor in the background?

They own The Weather Channel, so if someone had it playing in the background to keep tabs on the weather, that might do it.

[rdale]

I guess my question is really what would it take? How expensive would it be? (and I would measure the cost primarily in lbs/kg)

You'd get better success starting a new thread in a general area.

[ugordan]

Dumb question about lighting risk constraints:

Many of the rules were built from experience of the past, but things change. Perhaps a new vehicle like falcon/dragon can be designed to handle lighting safely. Is that possible? (commercial airliners fly thru thunderstorms all the time?)

Tory Bruno's tweet is relevant to this:

"Lightning: I've designed rockets that can take a lightning strike.  Not worth the impact (at present) for SLVs.  Ground Winds: Ditto. Not currently worth it"

https://twitter.com/torybruno/status/1265769319566278658

[hootowls]

For reference, linked below are the Lightning Launch Commit Criteria published by NASA that are used for civil, national, and licensed launches flown by the US.  The LLCC are meant to protect the mission but they also protect the airborne flight safety systems, both for function when needed as well as against inadvertent activation.

https://standards.nasa.gov/standard/nasa/nasa-std-4010

[Vettedrmr]

Dumb question about lighting risk constraints:

Many of the rules were built from experience of the past, but things change. Perhaps a new vehicle like falcon/dragon can be designed to handle lighting safely. Is that possible? (commercial airliners fly thru thunderstorms all the time?)

Actually, airliners deviate around just about every thunderstorm they can, and if a departure path takes them through a t'storm they'll delay the takeoff.  They can survive a strike, but damage to the avionics systems is expected when that happens.

rdale, thanks so much for your information, it's one of the things I love about this forum.  Having studied meteorology a little bit in college (the math will make your eyes leak!), I have huge respect for y'all!

Have a good one,
Mike

[gtae07]

Dumb question about lighting risk constraints:

Many of the rules were built from experience of the past, but things change. Perhaps a new vehicle like falcon/dragon can be designed to handle lighting safely. Is that possible? (commercial airliners fly thru thunderstorms all the time?)

Actually, airliners deviate around just about every thunderstorm they can, and if a departure path takes them through a t'storm they'll delay the takeoff.  They can survive a strike, but damage to the avionics systems is expected when that happens.

In my experience, lightning strikes typically result in small, localized minor structural damage (small burn areas on composites, a few fried fasteners, etc.).  It’s very rare for us to see the avionics get taken out by a strike—or at least, it’s never reported to engineering if they do. 

The greater concern with thunderstorms, and the reason you fly around them instead of through them, is that they can be strong enough to physically damage or destroy the aircraft.  Microbursts, windshear, and just plain turbulence have caused many accidents; of relevance here would be Scott Crossfield, whose aircraft broke up inflight in a thunderstorm.

https://en.wikipedia.org/wiki/Delta_Air_Lines_Flight_191
https://www.planeandpilotmag.com/article/after-the-accident-two-cessna-210-thunderstorm-accidents/


I’d imagine making launch vehicles more lightning-resistant would probably not be worth the effort (at least till we get to SS/SH flight rates?) as there are so few launches and we can almost always afford to wait for good weather.  It would just add mass and expense in materials and testing.

[kevinof]

So just an update on this - Both Doug and Bob took the nametags from their "Ninjas" and were going to bring them to the IIS and back again. Little keepsake for the ground crew.

Both astros handed over their name tags to their assigned Ninja. Must be part of the ritual/process they have in place.

I picked up on this..it looked like Behnken handed ninja #6 back a Spacex name tag he had aboard Dragon...maybe he offered to fly it to space for her ?

[Zed_Noir]

Finally, my goodness... the procedure to re-open the capsule manually. Almost looked like an escape room from the outside. Many tools, different people and I am not sure whether they had practiced this before. Can imagine a loaded Falcon triggers different/extra safety mechanisms for the locks.

<snip>
The astronauts can get themselves out of Crew Dragon in less than 20 seconds if they really have to.

Thank you for that explanation.  Would I be correct in assuming that there is also a method for rescue personnel to get into the capsule in a hurry (either on pad or after a landing, in an emergency)?
 

Yes there is. By setting off the EEC that blows the hatch open. Of course doing so means the capsule is no longer flightworthy.