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Tomáš “tomoxm” Martinove
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Doug Ellison @doug_ellison Feb 2
I’ve got to do a deep dive into the launch requirements of mission designs beyond LEO and compare F9 Arlas V 401, 551, FHeavy and FHeavy Expendable. I think a lot of people will be VERY surprised. Specific Impulse on the upper stage is everything.

David S. F. Portree @dsfpspacefl1ght Feb 2
I keep hearing the FH isn't that great when it comes to tossing things beyond LEO, and at a higher cost than competitors.

Doug Ellison @doug_ellison Feb 2
Basically a recovered FHeavy is out performed by the high end Atlas Vs, and an expendable FHeavy is probably more expensive than those Atlas Vs. the performance numbers are at https://elvperf.ksc.nasa.gov/pages/Query.aspx

Elon Musk‏ @elonmusk
Replying to @doug_ellison @dsfpspacefl1ght
The performance numbers in this database are not accurate. In process of being fixed. Even if they were, a fully expendable Falcon Heavy, which far exceeds the performance of a Delta IV Heavy, is $150M, compared to over $400M for Delta IV Heavy.
https://twitter.com/elonmusk/status/963076231921938432

- Both exhaust velocity (Isp) and mass ratio drive the rocket equation. Also thrust/mass matters a lot for Oberth effect. Delta upper stage Isp is good, but mass ratio and thrust are not.

- https://en.m.wikipedia.org/wiki/Oberth_effect

Davide @DavideDF_
How much does a Falcon Heavy cost if only the center core is expendable?

Elon Musk‏ @elonmusk
Replying to @DavideDF_ @doug_ellison @dsfpspacefl1ght
Side boosters landing on droneships & center expended is only ~10% performance penalty vs fully expended. Cost is only slightly higher than an expended F9, so around $95M.

Scott Manley @DJSnM
One thing a lot of people are curious of is the FH performance with an expendable center core since SpaceX sales page shows only full recovery, or full expendable numbers.

Doug Ellison @doug_ellison
Yup - I got a feeling that would be a huge increase in performance - maybe getting back half the performance cost of recovery. Outer cores RTLS or Outer Cores to Barge would be interesting as well.

Scott Manley @DJSnM
For full recovery to make sense over single stick expendable needs each booster to be reused multiple times. I’m also curious as to whether SpaceX would consider stretching Stage 2 if there was a market that made sense.

Elon Musk‏ @elonmusk
Replying to @DJSnM @doug_ellison @dsfpspacefl1ght
Under consideration. We’ve already stretched the upper stage once. Easiest part of the rocket to change. Fairing 2, flying soon, also has a slightly larger diameter. Could make fairing much longer if need be & will if BFR takes longer than expected.

Michael Baylor @nextspaceflight
Michael Baylor Retweeted Elon Musk
This would, of course, require two droneships. There is currently only one on each coast.

Elon Musk‏ @elonmusk
Replying to @nextspaceflight
A third is under construction

Robin Seemangal‏ @nova_road
Replying to @elonmusk @nextspaceflight
What are you going to name it?

Elon Musk @elonmusk
Replying to @nova_road @nextspaceflight
A Shortfall of Gravitas

Emre Kelly @EmreKelly
East Coast? West Coast? ...elsewhere?

Elon Musk‏ @elonmusk
Replying to @EmreKelly @nova_road @nextspaceflight
East, to support high flight rates for F9 and dual ocean landings for FH side boosters

David Legangneux @dlxinorbit
Replying to @elonmusk @doug_ellison @dsfpspacefl1ght
Just under $400M for Delta IV Heavy, not over. The cost of the Parker Solar Probe launch is $389.1M (contract announced in 2015).

Elon Musk‏ @elonmusk
That was three years ago, before ULA cancelled all medium versions of Delta IV. Future missions have all Delta fixed costs piled on, so their cost is now $600M+ for missions contracted for launch after 2020. Nutty high.

Sasamj @AngryPackOMeese
I think after 2020, the idea is to switch to Vulcan-centaur+ for heavy lift not stick with Delta

Elon Musk‏@elonmusk
Replying to @AngryPackOMeese @dlxinorbit and 2 others
Maybe that plan works out, but I will seriously eat my hat with a side of mustard if that rocket flies a national security spacecraft before 2023

Sasamj @AngryPackOMeese
Replying to @elonmusk @dlxinorbit and 2 others
can it be a boring company hat :P for the memes

Elon Musk @elonmusk
Of course :)

Jason @kerrbones
Any details as to why core stage “didn’t make it” last week?? Great discussion by the way... @elonmusk

Elon Musk‏ @elonmusk
Replying to @kerrbones @nextspaceflight
Not enough ignition fluid to light the outer two engines after several three engine relights. Fix is pretty obvious.



Image: https://space.stackexchange.com/questions/4229/oberth-effect-for-earth-vehicles
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Finding views in the view hierarchy

If you define your Android UI layout in XML, this video describes how to find each of those views in Java code. This is useful to make an interactive app where the UI can change while the app is running.

Excerpt from Udacity Android course (goo.gl/vc5VKs)
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First part of tutorials for building Root 3 CNC machine designed by "sailorpete" on thingiverse: https://www.thingiverse.com/thing:1750276
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Free and Secure software makes people happy, even if it comes with limitations
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Zajimavy slibny projekt. Az se mi chce jit hned vykuchat ty skenerotiskarny co jsem vylovil z odpadku. :-)
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