Author Topic: SpaceX Falcon 9 : CRS-16 (Dragon SpX-16) : December 5, 2018 - DISCUSSION  (Read 219955 times)

Online Danny452

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Testing booster recovery equipment is not like testing other equipment as booster recovery is of no advantage to the customer.  If you test the fins and they fail the test what do you do?  You have to choose between delaying the customer's launch (if possible) and expending the booster.

Offline CorvusCorax

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Testing booster recovery equipment is not like testing other equipment as booster recovery is of no advantage to the customer.  If you test the fins and they fail the test what do you do?  You have to choose between delaying the customer's launch (if possible) and expending the booster.

Still useful. If SpaceX had known that the Gridfins were inoperational, they would have chosen a contingency approach in cooperation with the customer. Either:

- stand down and fix the issue
or
- forgo recovery. No boostback burn, splashdown in NOTMAR/NOTAM designated exclusion zone


We wouldn't have seen the scary imagery of a booster tumbling out of control over the cape, nor its unexpected but highly impressive recovery and water landing.


Offline llanitedave

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Testing booster recovery equipment is not like testing other equipment as booster recovery is of no advantage to the customer.  If you test the fins and they fail the test what do you do?  You have to choose between delaying the customer's launch (if possible) and expending the booster.


Once you set your pricing under the paradigm of recovery and reuse, then booster recovery IS an advantage to the customer, and scrubbing a launch on a threat to recoverability makes perfect sense.
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Offline llanitedave

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The grid fins deploy when S1 is in free fall, and they are also carry some not insignificant mass.  I wonder if the hydraulics do not have power to deploy them when under 1g, therefore they can’t be ground checked when S1 is vertical under its own internal power.  Deployment also looks s bit non linear, like it is spring loaded or something.  Actual control inputs are rotational, and give 2 axis control only.

Afair, Falcon9 used to retract the fins on its own after landing, during saving procedure. They also extended them under 1 G on F9RDev1 flights, although those were lighter aluminum fins and a dev vehicle.

It could be something mundane like physically being in the way of the TE that prevents a full actuation test on the pad. Or they just didn't bother since the system wasnt mission critical until now.


Maybe that check could be done after the partial retraction of the TE?
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Offline Stan-1967

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Maybe that check could be done after the partial retraction of the TE?

I think it is possible the only time they could do a hydraulic check ( for RTLS ) is the short span of around 3 minutes between the end of the boostback burn, and just prior to the re-entry burn.  I think it is an unknown trade as to the power budget needed to keep the hydraulics active for an extra 3 minutes, but operationally, I think it only makes sense to do any testing before re-entry.  Furthermore, the failure was with the hydraulics that actuate the grid fins, not with the deployment of the fins.  It is being assumed by many that these events are controlled by the same sub-system.  I do not think they are, so ground testing is not enabled by adding redundancy to the hydraulics if the systems are separate.

The rest of this post is a bit lengthy, but I'll try to explain why;

1.  If an anomaly is detected in the grid fin hydraulics before re-entry, the flight software can divert to a safer distance offshore during the entry burn.  It makes no sense to stop RTLS while SpaceX investigates this, the overall record is still very good, & other precautions can be done.

2.  This is not an issue that concerns customers, with the exception of when your customer also owns the launch range.  It concerns CCAFS, & as demonstrated with the last launch from Vandenberg, that customer weighed risk & said no too RTLS coming anywhere near their pads & other payloads.

2.  I think video of past RTLS missions suggest grid fin deployment is done with springs, not hydraulics. ( note SpaceX does use springs for S1/S2 separation, & fairing sep.  They like springs.) 

3.  If the size & weight of a spring that deploys in zero g vs. under 1 g is a significant weight penalty.  The prudent rocket engineer will size for zero g & this choice is why it can't be ground tested. 

4.  Using springs vs. hydraulics for fin deployment is likely a weight trade against the hydraulic reservoir, piston stroke, & needed force duration for translating the grid fin joint in a rotational axis that changes roll/pitch only vs. adding what would basically be yaw control in the deployment translation mode.

5.  This is not comparable to F9Dev, New Shepard, or an airplanes pre-flight.  F9Dev & New Shepard do not have the weight priorities of an orbital booster.  Both had a T/W that could throttle on either side of 1.0, so both had margin for more robust systems than would be included on an orbital booster.   Airplanes have payload mass fractions no rocket will ever touch, so the built in safety features are not comparable.

Here are some YT clips showing what I am talking about.  I have tried to cut/paste at the relevant time stamp, but YT wants to show you commercials first.  I have included the clock time in comments so you can forward to the relevant time.

F9Dev vehicle:
Deployment of fins at altitude takes less than 1s, ( 14'12" mark) &  folded down immediately after landing. Quick motions indicate excess hydraulic power margins.  F9DEV purpose was to make powered landings work by learning the control laws for low speed flight regime, it was not to engineer the systems.



CRS-13 webcast:
Grid fin deployment at 19:38, ends by 19:49, so around 10s deployment time. Deployment is uneven & jumpy ( like an under damped spring) .  Fins bounce at end of deployment & then presumably lock into place or bounce is dampened out.



CRS-16 webcast:
Deployment starts at 18:41, ends at around 19:10.  Deployment is symmetrical fin to fin, but jumpy in deployment. Aero forces start roll at around 22:05, a 3'30" interval where hydraulics could be tested before re-entry burn.


Another take-away is that the grid fin hydraulics look like they are evolving.  That is expected from F9Dev into block 1.0, 1.1, FT, but even comparing CRS-13 ( block FT) against CRS-16 ( Block 5) , they do not perform the same.  The system is changing.  No surprise given this is SpaceX.


Offline mn

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...
. ( note SpaceX does use springs for S1/S2 separation, & fairing sep.  They like springs.) 
...


I'm pretty sure stage separation is pneumatic. (High pressure helium if I'm not mistaking)

Offline Stan-1967

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...
. ( note SpaceX does use springs for S1/S2 separation, & fairing sep.  They like springs.) 
...


I'm pretty sure stage separation is pneumatic. (High pressure helium if I'm not mistaking)

You are correct.  Section 2.3 of the F9 users guide confirm S1/S2 separation is driven by a high pressure pneumatic helium source.  So is the fairing separation.

I'll defend myself a bit & say I think it's fair to consider a pneumatic pusher as a type of spring. :-) 

My original thinking was however that it was mechanical, so I erred in that.  To the points I made, using the existing high pressure helium to deploy the heavy grid fins seems consistent with a favorable trade against oversizing the hydraulics for ground test or deployment under gravity.

Online gongora

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Thorlabs in orbit: Space station hosts optical fiber experiment
Quote
Inside that 21-inch-by-18-inch-by-11-inch box is a self-contained factory using the near-weightlessness of space to pull high quality optic fiber from highly technical glass.
...
As Saad talked about the project last week on the upper floors of Thorlabs' headquarters on Sparta Avenue, more than 250 miles higher still, astronauts were installing the third box in a series of four that make up this stage of experiments.

The third box was delivered to the ISS on Dec. 8, aboard the SpaceX-16 mission and returns to Earth early next year when the docking vehicle leaves the station. A fourth box will be delivered aboard SpaceX-17, due to launch in March.

Saad heads up the Thorlabs team that is working with a team from a California-based company, Made in Space, which is providing the mechanics of the glass-pulling "factory" in the box.
...
The glass being used in the ISS experiments is made from a group of fluoride compounds.

The difference between glass fiber made from silica and fiber drawn from fluoride is the wavelengths of light that can be transmitted along the fiber.
...
Saad said the first two flights of the production box on ISS did not produce any fiber because of mechanical issues.
...
The result was blobs of glass, rather than strings of glass.

In this third box, the glass is pulled along and it's hoped strands of fiber will result. The box has three "pre-forms," specific size, shape and weight pieces of pure glass, which can be pulled into a total of 1.5 kilometers (0.93 miles) of optic fiber.
...
« Last Edit: 12/26/2018 07:08 pm by gongora »

Online Comga

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(Snip)
I'll defend myself a bit & say I think it's fair to consider a pneumatic pusher as a type of spring. :-) 

My original thinking was however that it was mechanical, so I erred in that.  To the points I made, using the existing high pressure helium to deploy the heavy grid fins seems consistent with a favorable trade against oversizing the hydraulics for ground test or deployment under gravity.

Titanium grid fins are not “heavy” in free-fall. 😉
They are massive, but the power to deploy them is inverse to the speed of deployment. (Even under 1g)
However, the power to actuate them against the airstream must be huge.
The scaling of the hydraulic actuation system is unlikely to be effected by deployment.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Stan-1967

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Titanium grid fins are not “heavy” in free-fall. 😉
They are massive, but the power to deploy them is inverse to the speed of deployment. (Even under 1g)
However, the power to actuate them against the airstream must be huge.
The scaling of the hydraulic actuation system is unlikely to be effected by deployment.

Is it a known fact that deployment is by hydraulics? 

I question that assumption because the deployment does not look like it is done with hydraulics, & if it is hydraulic, it appears to be an unreliable system when you look at the uneven & unrepeatable deployment.  (see my video links a few posts back)

Why does it matter in regards to the thread topic "CRS-16 Discussion"?  If it is done with pneumatics ( or springs), it means that ground testing, or testing on the pad as part of the preflight, may not be possible.  This is where the weight of the Ti grid fins matters if you want to test under 1g, and it addresses the previous discussion of what solutions are possible to fix the failure mode.

Online zubenelgenubi

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Re: CRS-16 splashdown and return to port at nearly the same time as...
Iridium Next Flight 8 1st stage return to port:

Are both assets returning to the same dock or dock area?  If so, might they be there simultaneously?
That would be a great photo-op!
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Offline Joey S-IVB

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As Chris mentioned in the updates section, is this the first night-time splashdown? I can't remember a previous SpaceX night splashdown.

Online ejb749

The last line in the article should really say:

CRS-17 is the next Dragon ONE mission to the ISS, currently scheduled for March.

Offline ugordan

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The last line in the article should really say:

CRS-17 is the next Dragon ONE mission to the ISS, currently scheduled for March.

I like your optimism.

Online Rondaz

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Dragon Back on Earth as Crew Revs Up Station Science

Mark Garcia Posted on January 14, 2019

The SpaceX Dragon cargo craft is back on Earth after splashing down in the Pacific Ocean Sunday night loaded with critical space research and International Space Station hardware. Four spaceships remain parked at the orbital lab including Northrop Grumman’s Cygnus resupply ship from the United States.

Today, the three-member Expedition 58 crew is exploring a wide array of microgravity science to improve life for humans on Earth and in space. The orbital residents also worked on life support systems and upgraded computer hardware.

NASA astronaut Anne McClain set up a specialized microscope in the morning for the Biophysics-5 study to research the production of protein crystals. Afterward, she deactivated Dragon communications gear then swapped out hard drives on several laptop computers.

Flight Engineer David Saint-Jacques of the Canadian Space Agency opened up the Combustion Integrated Rack and replaced optics gear inside the flame and soot research device. He later swapped a hydrogen sensor inside the Oxygen Generation System before inspecting and cleaning some of its parts.

A pair of tiny internal satellites, better known as SPHERES, were set up by Commander Oleg Kononenko today inside the Kibo laboratory module. High school students write algorithms and submit them in a competition to control the SPHERES to demonstrate spacecraft maneuvers and formation-flying for future space missions.

https://blogs.nasa.gov/spacestation/2019/01/14/dragon-back-on-earth-as-crew-revs-up-station-science/

Offline tyrred

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The last line in the article should really say:

CRS-17 is the next Dragon ONE mission to the ISS, currently scheduled for March.

I like your optimism.

Will DM-1 be the next splashdown for SpaceX?  Is CRS-16 the last Dragon1 splashdown before the first Dragon2 splashdown?  If so, what a sweet 16.

Edit: optimism
« Last Edit: 01/15/2019 05:36 pm by tyrred »

Offline rpapo

Will DM-1 be the next splashdown for SpaceX?  Is CRS-16 the last Dragon1 splashdown before the first Dragon2 splashdown?  If so, what a sweet 16.
You need to add the two test flights plus the pad abort test, but then subtract CRS-7, which had a rather harder splashdown than usual.

So there have been 18 good splashdowns and one not so good so far.  Not counting the various parachute tests, of course.
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Offline CorvusCorax

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Will DM-1 be the next splashdown for SpaceX?  Is CRS-16 the last Dragon1 splashdown before the first Dragon2 splashdown?  If so, what a sweet 16.
You need to add the two test flights plus the pad abort test, but then subtract CRS-7, which had a rather harder splashdown than usual.

So there have been 18 good splashdowns and one not so good so far.  Not counting the various parachute tests, of course.

yeah, I think even Dragon2 had a few splashdowns already, at least the parachute qualification test articles did ;)

Online zubenelgenubi

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Re: CRS-16 splashdown and return to port at nearly the same time as...
Iridium Next Flight 8 1st stage return to port:

Are both assets returning to the same dock or dock area?  If so, might they be there simultaneously?
That would be a great photo-op!

Tweet in NSF forum post here contains video of such a view!
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Offline tyrred

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Re: CRS-16 splashdown and return to port at nearly the same time as...
Iridium Next Flight 8 1st stage return to port:

Are both assets returning to the same dock or dock area?  If so, might they be there simultaneously?
That would be a great photo-op!

Tweet in NSF forum post here contains video of such a view!

That is so nice  8)  Recovery and re-use is a lot sexier than expendable... Even if it gets dirty.

Tags: CRS-16 
 

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