SpaceX Falcon 9 / Dragon 2 : SpX-DM2 : May 30, 2020 : DISCUSSION

[kevinof]

So it was interesting to hear their comments today to Benji @Spacex. Trying to remember their words:

S1 was smooth but they could really feel the stage throttle up and down - knew even before the call out. Felt like a real flying machine. How sensitive they were to the throttle - it was really neat. Very pure flying machine.

S2 right after MECO - Real kick in the pants when MECO happened and for an instant you got zero G, then the S2 fired - Neat event and highlight of the flight for Doug. The entire S2 (8+ mins) felt like driving very fast on a gravelled road. Not much vibration but you knew there was a powerful engine behind you.

[Oersted]

For what it is worth there was discussion during the ARES-1 program in modelling that the ride could be potentially so filled with vibrations and low frequency noise that the astronauts might have trouble with seeing screens and pressing keys and/or screens. I wonder if the test pilots were alluding to this kind of noise and/or vibration with yesterdays ascent ?

The crew reported that the ride was smooth. Falcon 9 uses liquid fueled engines, which don't have much vibration.

The Ares I was essentially a Shuttle SRB, which is a solid rocket booster, and solid rocket engines are notorious for having a lot of vibration due to the uneven burning of the solid fuel, and as the SRB casing is emptied of fuel the casing oscillates. Here is an article about what they were trying to do to mitigate the vibrations on Ares I.

But if you watch the capsule video you'll see that the ride inside the capsule is pretty smooth.

During the PAO event when Bob and Doug were welcomed into ISS and answered questions from the ground, Bob did say they were a bit surprised at how smooth the first stage burn was, compared to Shuttle.

But he went on to say that they had expected the stage 2 burn to get a lot smoother, but in fact the rocket was "huffing and puffing" all the way to orbit, and "we were definitely riding a dragon," that it was "not quite the same smooth ride as Shuttle" during the stage 2 burn.

The "huffing and puffing" sounds like a reference to chugging or pogo oscillation, probably for reasons suggested upthread  (much lower vehicle mass than Shuttle, one engine vs. multiple engines, etc.)

So apparently stage 2 was an unexpectedly bumpy ride as compared to Shuttle (after SRB sep).

I think you misheard. The "huffing and puffing" comment was about Dragon, not stage 2. That's the Dragon RCS firing.

Wrong, Behnken was definitely referring to the second stage ride:

No Dragon RCS firings before 2nd stage MECO.

[Oersted]

I was disappointed in NASA's post docking ceremony.  Far too many politicians taking up valuable time making the ceremony more about them and their politics than the accomplishment and hard work of NASA and SpaceX.  Bob and Doug didn't even get a chance to give a speech other than general responses to questions.  Cruz was too long-winded.  I gagged when the JSC Congressional House rep asked what "SECO" was and was mostly clueless.  At least the last rep had the decency to just say "congrats" and let them mostly be.  There was no mention of the capture-the-flag prize.  Doug really should have symbolically touched the flag at a minimum during the ceremony.  When the ceremony ended and the NASA livestream stopped, I had to do a double take and ask "was that it?!?!?"

I agree. In addition, the first media event from Bob and Doug - shortly after LEO insertion - came at the exact same time as the post-launcg press conference with Bridenstine, Musk and others. Couldn't they have organized that a bit better? - Just seems like the public outreach operation dropped the ball several times and in general wasn't up to the level of professionality of the rocket scientists and astronauts.   

The post-docking briefing questions were mostly terrible.  I think people really did run out of questions to ask at this point.  I'm all for equal justice, but the NASA administrator isn't going to solve the issue and wasting everyone's time with variations of the same question over and over again is counter-productive.  Bridenstine was already asked several times about the protests and the mission within the context of America's current events and answered as well as could be expected.  No need for reporters to keep asking variations on the same question just to hear themselves talk.

Many of the reporters and news organisations obviously wanted to downplay the positive space news and make launch day all about the civil unrest across the US. A sign of these fractured times, unfortunately...

[ugordan]

In addition, the first media event from Bob and Doug - shortly after LEO insertion - came at the exact same time as the post-launcg press conference with Bridenstine, Musk and others.

Well, orbital mechanics determining SpaceX ground station availability for onboard video tends not to wait for managers and big shots to gather up.

[Oersted]

Any other images from ISS of the ascent?

 Here's the links: COMPARE OTHER ISS VIEWS OF LAUNCHES
http://satobs.org/seesat_ref/misc/Soyuz_launch_4.pdf

Observations of the Soyuz launch on December 3, 2018:
[plus obs of Soyuz launch abort, from ISS, a few months earlier]
http://satobs.org/seesat_ref/misc/181203-soyuz_launch.pdf

http://satobs.org/.../Russian_Missile_Launch_Viewed_from...
http://www.jamesoberg.com/ISS_crew_spots_second_russian...

Yes, this one:
<blockquote class="twitter-tweet"><p lang="en" dir="ltr">2 minutes before the #CrewDragon launch the @Space_Station passed Cape Canaveral. Captured some pictures of LC39A from where the Falcon 9 launched.

Congratulations to everyone and looking forward to seeing @Astro_Doug, @AstroBehnken! pic.twitter.com/UuleioMjI3</p>&mdash; Ivan Vagner (@ivan_mks63) May 30, 2020 <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>

[the_other_Doug]

Saturn's second stage has some known, and very scary vibration problems.   Google POGO to read more about it.   Fascinating stories about almost losing a couple of Saturn launches.

These days, I think that computational structural models would be able to identify vibrational issues and help fix the design.

I'm not talking about pogo.

I think I remember some of the astronauts saying the ride wasn't too great on the S-IVB especially during TLI.

Off-topic, but most crews said the second stage of the Saturn V was very smooth.  Mike Collins called it "smooth as glass".  The S-IVB was only reported to have enough vibration to alarm the crew on Apollo 10, with the recorded line from Young to Stafford "If you had said s**t I'd have shut it down!"  That was the messiest TLI of them all, I think -- the Earth entry angle resulting from its initial free return trajectory was something like 89 degrees from local vertical.  Short but intense fireball...

Collins called the Apollo 11 S-IVB "crisp and rattly" and that its vibrations felt good to him, so the problem -- a propellant flow rate issue related to, but not the same as, POGO -- was shown to have been fixed.

And yes, I know of the Apollo 13 S-II.  Sort of a one-off issue on that vehicle, not generic to the class.

[yg1968]

I was disappointed in NASA's post docking ceremony.  Far too many politicians taking up valuable time making the ceremony more about them and their politics than the accomplishment and hard work of NASA and SpaceX.  Bob and Doug didn't even get a chance to give a speech other than general responses to questions.  Cruz was too long-winded.  I gagged when the JSC Congressional House rep asked what "SECO" was and was mostly clueless.  At least the last rep had the decency to just say "congrats" and let them mostly be.  There was no mention of the capture-the-flag prize.  Doug really should have symbolically touched the flag at a minimum during the ceremony.  When the ceremony ended and the NASA livestream stopped, I had to do a double take and ask "was that it?!?!?"

I disagree. I think that it is very important to have politicians be involved in these things. Commercial crew was made possible because of the political support that it received from certain Senators and Representatives. If commercial Human Landing Systems (HLS) is going to happen, it will need strong political support in Congress. Hearing politicians praise commercial partnerships was music to my ears.

In terms of MECO, when speaking to a large audience, it is generally not advisable to use acronyms for people that are less familiar with space. Using the words "Main Engine Cutoff" would have been better. The reason that Bob Behnken apologized is because that he knows that he is not supposed to use acronyms when speaking to a large audience. In any event, it wasn't a big deal.

This article makes the point that I was trying to make:
https://aviationweek.com/defense-space/space/lawmakers-demo-2-success-could-fuel-nasas-lunar-initiative

[Oersted]

I find it interesting that Bob and Doug expressed surprise at some of the aspects of their Falcon ascent, since they supposedly got a lot of data (including audio recordings) from DM-1 fed into their sim sessions. I guess nothing can really capture that seat-of-the-pants sensation.   

[cebri]

Here Doug (02:30) says it was like going through a gravel road when 2nd stage kick in, not unpleasant but the feeling was there.



BTW, check the rest of questions they were very good.

[kdhilliard]

So it was interesting to hear their comments today to Benji @Spacex. Trying to remember their words: ...

For the record, from @06:25:

Benji Reed: What did it feel like riding on Falcon 9?
Doug Hurley: It never gets old talking about riding on Falcon 9. From the time the engines lit, the first two and a half minutes to staging was about like we expected, except you can never simulate the Gs, so as the Gs built you could certainly feel those.  Also, what I thought was really neat was how sensitive we were to the throttling of the Merlin engines.  That was really neat.  You could definitely sense that as we went transonic and broke Mach 1 we could definitely feel that.  In fact I said it to Bob and then the next thing you know the call was made, and we didn't even need to look at the speed.  You could tell just by how the rocket felt.  It's a very pure flying machine.
The next thing that really stood out for me was first stage separation with the engine cutoff and that separation event.  Going to zero G for split second and then the Merlin vacuum engine lighting.  That was a pretty neat event.  That was a highlight of the ascent for me.  And then once the M-vac started, then it was that kind of driving fast, very fast, on a gravel road, is how it felt the rest of the way up.  A little bit of vibrations, not anything that was really unpleasant, but you certainly knew that there was a powerful engine behind you at the time, and that obviously took us all the way to orbit about six minutes later.  And one again the Gs and how the engine throttled to control the Gs and then straight to cut off, and then just like with Shuttle, you go from three, actually in this case we were more than three Gs, to zero Gs instantaneously, and we knew we made it to orbit.

It is such a pleasure to see the rapport the crew has with the SpaceXers, but it's a shame we didn't have a cabin view for either MECO or SECO.

_{Edit: Fixed quotes}

[Lars-J]

I think you misheard. The "huffing and puffing" comment was about Dragon, not stage 2. That's the Dragon RCS firing.

Dragon RCS is not activated until it has separated from the upper stage.

[Oersted]

Benji Reed of SpaceX is one heck of a communicator. Empatic, sharp, positive. He really shone in the pre-flight press conferences as well. Hope to see more of him.

[daveglo]

So it was interesting to hear their comments today to Benji @Spacex. Trying to remember their words: ...

For the record, from @06:25:

Benji Reed: What did it feel like riding on Falcon 9?
Doug Hurley: It never gets old talking about riding on Falcon 9. From the time the engines lit, the first two and a half minutes to staging was about like we expected, except you can never simulate the Gs, so as the Gs built you could certainly feel those.  Also, what I thought was really neat was how sensitive we were to the throttling of the Merlin engines.  That was really neat.  You could definitely sense that as we went transonic and broke Mach 1 we could definitely feel that.  In fact I said it to Bob and then the next thing you know the call was made, and we didn't even need to look at the speed.  You could tell just by how the rocket felt.  It's a very pure flying machine.
The next thing that really stood out for me was first stage separation with the engine cutoff and that separation event.  Going to zero G for split second and then the Merlin vacuum engine lighting.  That was a pretty neat event.  That was a highlight of the ascent for me.  And then once the M-vac started, then it was that kind of driving fast, very fast, on a gravel road, is how it felt the rest of the way up.  A little bit of vibrations, not anything that was really unpleasant, but you certainly knew that there was a powerful engine behind you at the time, and that obviously took us all the way to orbit about six minutes later.  And one again the Gs and how the engine throttled to control the Gs and then straight to cut off, and then just like with Shuttle, you go from three, actually in this case we were more than three Gs, to zero Gs instantaneously, and we knew we made it to orbit.

It is such a pleasure to see the rapport the crew has with the SpaceXers, but it's a shame we didn't have a cabin view for either MECO or SECO.

_{Edit: Fixed quotes}

THANK YOU for this, and the earlier quotations.  I knew I had heard some mentions about G levels, and was happy to see Hurley corroborated the subjective G forces with Onespeed's great graphs.  Wanted to cite, but could NOT find those quotes.

Of course it was something the astronauts could handle, but the quality of the ride will be important to future commercial opportunities.  I'm thinking more as a feature!

[Kabloona]

So it was interesting to hear their comments today to Benji @Spacex. Trying to remember their words: ...

For the record, from @06:25:

Benji Reed: What did it feel like riding on Falcon 9?
Doug Hurley: It never gets old talking about riding on Falcon 9. From the time the engines lit, the first two and a half minutes to staging was about like we expected, except you can never simulate the Gs, so as the Gs built you could certainly feel those.  Also, what I thought was really neat was how sensitive we were to the throttling of the Merlin engines.  That was really neat.  You could definitely sense that as we went transonic and broke Mach 1 we could definitely feel that.  In fact I said it to Bob and then the next thing you know the call was made, and we didn't even need to look at the speed.  You could tell just by how the rocket felt.  It's a very pure flying machine.
The next thing that really stood out for me was first stage separation with the engine cutoff and that separation event.  Going to zero G for split second and then the Merlin vacuum engine lighting.  That was a pretty neat event.  That was a highlight of the ascent for me.  And then once the M-vac started, then it was that kind of driving fast, very fast, on a gravel road, is how it felt the rest of the way up.  A little bit of vibrations, not anything that was really unpleasant, but you certainly knew that there was a powerful engine behind you at the time, and that obviously took us all the way to orbit about six minutes later.  And one again the Gs and how the engine throttled to control the Gs and then straight to cut off, and then just like with Shuttle, you go from three, actually in this case we were more than three Gs, to zero Gs instantaneously, and we knew we made it to orbit.

It is such a pleasure to see the rapport the crew has with the SpaceXers, but it's a shame we didn't have a cabin view for either MECO or SECO.

_{Edit: Fixed quotes}

Thanks for that transcript.

Since Bob and Doug mentioned the engine, Tom Mueller and the propulsion team are no doubt rightfully proud of the Merlin engine. At a reported cost now of less than $1 million per unit ( more for Mvac), the cost of all ten engines on the Falcon 9 is probably in the ballpark of $10 million, which is an astonishingly low number for such a capable vehicle.

Of all SpaceX's technical achievements on F9, making such a robust, low cost, high performance (for kerolox) engine like Merlin ranks near or at the top of the list in my book.

PS: Good time to check out Tom Mueller's twitter account. He has a bunch of photos and reminiscences about previous (homebuilt) engines and rockets. All leading up to Merlin...(and check out the "original" BFR...)

https://twitter.com/lrocket?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor

[rdale]

Decoding Crew Dragon Demo-2

https://destevez.net/2020/06/decoding-crew-dragon-demo-2/

[lonestriker]

A brighter version of the last image, lots of nice details in there...

Zooming in, I thought I saw some stars in the black sections. But I suspect they're just bad pixels on the sensor due to radiation/cosmic ray damage.

[argjlg]

Question:   As noted by the SpaceX announcers several times, the four thrusters at the front of the Dragon pointing forward were used for the orbital adjust burns to reach the ISS.  Does that mean the astronauts would be feeling like they were being thrown 'forward' towards the display screens during the burns?

[Lars-J]

Question:   As noted by the SpaceX announcers several times, the four thrusters at the front of the Dragon pointing forward were used for the orbital adjust burns to reach the ISS.  Does that mean the astronauts would be feeling like they were being thrown 'forward' towards the display screens during the burns?

Yes, but the combined thrust of those thrusters is pretty low, so it should be a very small force. But it would be interesting to hear them discuss the sensation.

[Steven Pietrobon]

Yes, but the combined thrust of those thrusters is pretty low, so it should be a very small force. But it would be interesting to hear them discuss the sensation.

Total thrust would be 1600 N (400 N per thruster) and assuming a mass of 12 t gives an acceleration of 0.13 m/s² or 0.013g.

[CorvusCorax]

This Spiegel article linked in the schedule discussion thread

https://www.spiegel.de/wissenschaft/weltall/spacex-chefingenieur-zum-stat-des-crew-dragon-wilde-party-kommt-noch-a-998ff592-1071-44d5-9972-ff2b73ec8fb6

From an article in Spiegel:
SPIEGEL: Die erste Raketenstufe ist kurz nach dem Start auf einem ferngesteuerten Schiff gelandet. Was passiert jetzt mit ihr?

Königsmann: Sie wird inspiziert und startet dann wieder, nach aktueller Planung mit einem internationalen Satelliten.

So 1058-2 will be launching an international satellite...

Not too surprising, but maybe anyone here can figure out which one that will/must be?

has some other interesting  tidbits. Hans Königsmann was asked about the risk associated with the DM-2 mission:

Königsmann: Es gibt Anforderungen der Nasa zum Design des Transportsystems. Demnach darf das Risiko, die Crew zu verlieren, über die gesamte Mission gerechnet nur bei 1 zu 270 liegen. Wir liegen etwas besser, bei einem rechnerischen Wert von 1 zu 276. Und da ist noch nicht einmal das Rettungssystem berücksichtigt, das die Kapsel bei Startproblemen absprengen und wegtransportieren kann. Berücksichtigt man das, ist das reale Risiko für ein katastrophales Ereignis noch deutlich geringer.
...
Die Zahl haben wir nie im Detail ausgerechnet. Aber sicher bei 1 zu mehreren Tausend. Das sollte passen.

Too lazy for manual translation.

Königsmann: There are Nasa requirements for the design of the transport system. According to these, the risk of losing the crew over the entire mission may only be calculated at 1 in 270. We're a little better, with a calculated value of 1 in 276, and that doesn't even take into account the rescue system, which can eject the capsule and transport it away if there are launch problems. If you take that into account, the real risk of a catastrophic event is even lower.
...
We never calculated the number in detail. But certainly at one in several thousand. This should be right.

Translated with www.DeepL.com/Translator (free version)