NASASpaceFlight.com Forum

General Discussion => Q&A Section => Topic started by: Zaum on 01/31/2016 05:49 pm

Title: Falcon 9 Q&A
Post by: Zaum on 01/31/2016 05:49 pm
Is any interplanetary probe (or other payload that needs an escape trajectory) set to be flown on a Falcon 9?
Title: Re: Falcon 9 Q&A
Post by: nadreck on 01/31/2016 06:52 pm
Is any interplanetary probe (or other payload that needs an escape trajectory) set to be flown on a Falcon 9?
No but one flew already DSCOVR - it needed to get to the Earth Sun L1 and that is as close to escape velocity as makes no real difference the same sized probe could have been thrown into a heliocentric orbit.

Oh and Musk, answering question at the hyperloop event at TAMU yesterday said the current F9 could put between 3 and 4t on a trajectory to Mars.
Title: Re: Falcon 9 Q&A
Post by: Zaum on 01/31/2016 07:28 pm
Indeed. The upper stage that launched DSCOVR is in heliocentric orbit, in fact.

I knew it has a pretty good capability (advertised in the User manual too), I was more wondering if there were plans on part of NASA or other space agencies to put it to use any time soon, with its low cost.
Title: Re: Falcon 9 Q&A
Post by: Jim on 01/31/2016 07:31 pm
Indeed. The upper stage that launched DSCOVR is in heliocentric orbit, in fact.

I knew it has a pretty good capability (advertised in the User manual too), I was more wondering if there were plans on part of NASA or other space agencies to put it to use any time soon, with its low cost.

Just look at the manifest or NASA's ELV manifest and you will see that there are none.
Title: Re: Falcon 9 Q&A
Post by: Raj2014 on 03/05/2016 10:22 pm
Does SpaceX have anything to solve the problem when the Falcon 9 has to carry extra payloads in to orbit? I know they will soon be building the Falcon Heavy. I find it surprising that since the payload was heavy than usual payloads and SpaceX knew about it, that they did not add extra fuel (only if the Falcon engines has enough thruster) or may be a booster stage or use more than 3 engines? Still an impressive achievement.

Has SpaceX thought of using flaps on the Falcon 9 to slow the first stage down? Since it is mentioned that the Falcon 9 1.2v was moving faster than usual. Why has SpaceX not added nets to the barge to catch the first stage in case it lands or close to landing but tilts overs like it has done before? May save them money and reduce the clean up.
Title: Re: Falcon 9 Q&A
Post by: Jim on 03/05/2016 11:39 pm
Nets on the barge would only cause more problems.
Title: Re: Falcon 9 Q&A
Post by: Coastal Ron on 03/06/2016 12:09 am
Has SpaceX thought of using flaps on the Falcon 9 to slow the first stage down?

Undoubtedly, yes.  And what they decided to use is propulsive speed retardation, while using grid fins for aerodynamic control.  See:

http://www.spacex.com/falcon9

Quote
Why has SpaceX not added nets to the barge to catch the first stage in case it lands or close to landing but tilts overs like it has done before? May save them money and reduce the clean up.

Expanding on what Jim said, among other things the Falcon 9 structure would have to be reinforced to survive being caught by nets.  That would reduce overall payload.

Instead they have chosen to perfect landing upright - which they have already demonstrated successfully.
Title: Re: Falcon 9 Q&A
Post by: jee_c2 on 04/09/2016 09:25 am
What are the plans for transporting the landed first stage of the Falcon9 back from the sea platform? Aerial transport, or by ship? Do we know, how much it will cost about?
Title: Re: Falcon 9 Q&A
Post by: rocx on 04/09/2016 09:30 am
Elon Musk answered this yesterday during the press conference, and it was in line with earlier announcements: the stage will remain upright on the drone ship, but will be welded to the deck. It will then go to Port Canaveral. At the port a large crane will lift the stage and put it on the shore. On the shore the same thing will happen as happened to the stage landed at LZ-1 in december: a stand will be attached to the octaweb (the base of the stage), then the legs will be folded up or taken off, and then the stage will be put horizontally on some kind of truck.
Title: Re: Falcon 9 Q&A
Post by: jee_c2 on 04/09/2016 09:36 am
Thanks for the quick answer! Transported on the platform itself was one of my tips, as I thought about.
Title: Re: Falcon 9 Q&A
Post by: Urx on 05/09/2016 12:36 pm
I'm trying to understand SpaceX's pricing page at http://www.spacex.com/about/capabilities
1) There seem to be two different amounts of payload listed to GTO for F9: 5.5 mT and 8,300 kg. What's the difference between the two?
2) Are the $62M hardware and logistics?
2a) If so, then by comparing F9 and FH prices, would it be correct to assume the cost for one F9 S1 to be about $14M including fuel?
Title: Re: Falcon 9 Q&A
Post by: rocx on 05/09/2016 12:47 pm
I'm trying to understand SpaceX's pricing page at http://www.spacex.com/about/capabilities
1) There seem to be two different amounts of payload listed to GTO for F9: 5.5 mT and 8,300 kg. What's the difference between the two?
2) Are the $62M hardware and logistics?
2a) If so, then by comparing F9 and FH prices, would it be correct to assume the cost for one F9 S1 to be about $14M including fuel?
1) $62M buys you 5500 kg to GTO. If you want more, you'll have to pay more, up to a maximum of 8300. Presumably 5500 kg is the limit where recovery is possible, expending the whole rocket will be more expensive in the future.
2) As I understand it this is the price for the launch service, with everything the standard option and no extra options such as spin-stabilisation.
2a) The stage may cost about that much, but maybe integration and launch costs are higher for Falcon Heavy because it consists of more stages.
Title: Re: Falcon 9 Q&A
Post by: SmallKing on 04/15/2017 09:53 am
Not a complicated question.
During the launch preparation, what is LOX drainback?
Title: Re: Falcon 9 Q&A
Post by: edkyle99 on 04/15/2017 02:06 pm
Not a complicated question.
During the launch preparation, what is LOX drainback?
Here's a description for STS.  Once LOX loading is complete, the fill and drain valve or valves in the rocket close(s) (there is probably one for each stage).  LOX in the lines then drains back to the ground support equipment.  For STS, a second "outboard" fill and drain valve closed after the drain back was complete.
https://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/prop/flowsequence.html

 - Ed Kyle
Title: Re: Falcon 9 Q&A
Post by: BeamRider on 04/15/2017 02:58 pm
More on grid fins.  A little-appreciated fact is that the rocket must generate aerodynamic lift during at least part of its climb to orbit. Rather than do this by adding an angle of attack to the whole stack, would it make sense to launch with the grid fins deployed (presumably permanently) and use their lifting ability for that purpose? Using them might result in a lower lift/drag ratio than using the entire rocket body, and would eliminate some weight, complexity and a point of failure in the deployment mechanism. There might also be an opportunity to reduce or even eliminate the gimbal authority required on some of the main engines.

On the downside, it would certainly concentrate lifting stress at the fin location on the tube, rather than distributing it along the length of the tube. And it would do nothing for the second stage, since the fins would remain with the first stage when it separates, as they do now.
Title: Re: Falcon 9 Q&A
Post by: BeamRider on 04/15/2017 03:02 pm
And I should have added that the deployed grid fins could contribute to yaw and roll control, in addition to pitch (lift), further reducing engine  gimbal authority required.
Title: Re: Falcon 9 Q&A
Post by: ugordan on 04/15/2017 03:07 pm
A little-appreciated fact is that the rocket must generate aerodynamic lift during at least part of its climb to orbit.

Say what?
Title: Re: Falcon 9 Q&A
Post by: Coastal Ron on 04/15/2017 03:15 pm
...would it make sense to launch with the grid fins deployed (presumably permanently) and use their lifting ability for that purpose?

No.  Grid fins don't produce lift, they produce drag.

Quote
Using them might result in a lower lift/drag ratio than using the entire rocket body...

They are too small to affect the full mass of a launching rocket (i.e. most of the fuel & still carrying the 2nd stage), and the current design wouldn't be able to push the grid fins out into the air stream in any case.

SpaceX has shown to be full of a lot of smart engineers, and if this was something that was useful they would have tried it.
Title: Re: Falcon 9 Q&A
Post by: joncz on 04/15/2017 04:24 pm
https://www.youtube.com/watch?v=o0Yc81t732k


Note where he discusses that the grid fins at the rear of the MOAB move the center of pressure back and that enables controllability.  Now move those grid fins forward, moving the CP ahead of the CG and see what happens to your rocket.

Title: Re: Falcon 9 Q&A
Post by: BeamRider on 04/16/2017 04:07 am
A. Grid fins produce both lift and drag just like any wing. They are merely a novel configuration of a wing that packages a lot of lift area in a dimensionally small structure that is more suited to use at very high speeds than a single high-aspect wing of equal area.

B. There is nothing inherently improper with wings or fins located forward on the body of a missile, as they are on virtually every air-to-air missile in existence. The fact that they are located on the aft end of the MOAB is a design choice appropriate to their application in a minimalistic guidance system of a gravity bomb.

C. The concept was not that the grid fins would be extended against the slipstream, but that they would be fixed in the extended position and their angle of attack varied... sort of like a wing.

D. I am not convinced that Spacex engineers should be assumed to have considered all conceivable solutions. While I am sure they are exceptionally clever, so too were their Apollo predecessors, for example, who would have howled at the thought of boosters returning to the launch site and landing tail-first... an idea nearly as preposterous as putting control surfaces toward the front of a rocket.
Title: Re: Falcon 9 Q&A
Post by: BeamRider on 04/16/2017 05:25 am
I believe that Elon Musk mentioned the angle of attack required of the rocket body cylinder during the press conference after the most recent launch.

Rockets that are going to orbit cannot follow a purely ballistic trajectory like an artillery rocket intended to come back down to impact the ground. Prior to obtaining orbital velocity, an orbit-bound rocket must maintain a slight "nose high" attitude to develop a thrust vector upward, preventing it from descending below the desired trajectory, unless it has wings!
Title: Re: Falcon 9 Q&A
Post by: Jim on 04/17/2017 02:53 pm
  A little-appreciated fact is that the rocket must generate aerodynamic lift

Not true at all. 

https://www.youtube.com/watch?v=n4yYZh1U908
Title: Re: Falcon 9 Q&A
Post by: Jim on 04/17/2017 02:58 pm
I believe that Elon Musk mentioned the angle of attack required of the rocket body cylinder during the press conference after the most recent launch.


It is not "required" but minimized


B. There is nothing inherently improper with wings or fins located forward on the body of a missile, as they are on virtually every air-to-air missile in existence. The fact that they are located on the aft end of the MOAB is a design choice appropriate to their application in a minimalistic guidance system of a gravity bomb.


Look at your words:  missile, air to air, etc.  Launch vehicles are not missiles, especially ones that operate at less than 50kft.

Launch vehicles spend most of the time out of the atmosphere.

Prior to obtaining orbital velocity, an orbit-bound rocket must maintain a slight "nose high" attitude to develop a thrust vector upward, preventing it from descending below the desired trajectory, unless it has wings!

Wrong.  Launch vehicles don't flight with "canted" thrust vector to counter gravity.  The rocket is in free flight, there is no side gravity force.  An astronaut only feels the thrust of the engine and not a pull to the center of the earth and not to a floor like an airplane.  If an airplane had strong enough engines, it wouldn't need wings.
Title: Re: Falcon 9 Q&A
Post by: Manabu on 04/28/2017 02:44 am
I believe that Elon Musk mentioned the angle of attack required of the rocket body cylinder during the press conference after the most recent launch.
That angle of attack and aerodinamic lift from the rocket body cylinder were for minimizing the boostback fuel in RTLS manouvers, not to help in the ascending phase.
Title: Re: Falcon 9 Q&A
Post by: envy887 on 05/23/2017 02:41 pm
...
Launch vehicles spend most of the time out of the atmosphere.

Prior to obtaining orbital velocity, an orbit-bound rocket must maintain a slight "nose high" attitude to develop a thrust vector upward, preventing it from descending below the desired trajectory, unless it has wings!

Wrong.  Launch vehicles don't flight with "canted" thrust vector to counter gravity.  The rocket is in free flight, there is no side gravity force.  An astronaut only feels the thrust of the engine and not a pull to the center of the earth and not to a floor like an airplane.  If an airplane had strong enough engines, it wouldn't need wings.

Launch vehicles are absolutely under the pull of gravity - they must either fly with some component of the thrust vector countering gravity, or they must accelerate under gravity. What they don't do is counter gravity with aerodynamic lift, because (as Jim noted) there is no atmosphere for most of the vehicle's flight.

The idea that rockets need aerodynamic lift for anything is totally misguided. It's trivial to have a thrust component that is countering gravity but is not "canted" relative to the vehicle or its direction of travel -  you simply point the rocket varying amounts of "up" while always thrusting and traveling in the direction the rocket is pointed (i.e. angle of attack is always zero).

Any thrust component that is opposing gravity is not accelerating the vehicle downrange, and so is contributing to gravity losses.  At liftoff the rocket is entirely vertical, so a large fraction of the booster's thrust is countering gravity, with the rest accelerating the vehicle upward. So most gravity losses are incurred near liftoff.

To reduce gravity losses (or more precisely, to absorb them primarily with the heavy booster(s) and not a light upper stage) many vehicles loft the upper stage far outside the atmosphere, where it slows vertically and eventually starts falling back without attempting to thrust to counter gravity. But as it slows vertically, it is accelerating downrange so to reach orbital velocity before falling back into the atmosphere. Orbit, of course, is a free-fall that never reaches the ground.
Title: Re: Falcon 9 Q&A
Post by: nicp on 12/21/2017 08:05 pm
Forgive me if this is covered elsewhere, couldn't find anything.
I've just noticed that the SpaceX coverage of NROL-76 uses m/s (metres per second), but CRS-13 uses km/h (unit of the antichrist).

The former is a proper SI unit of speed (yes I know some of you want feet per second or furlongs per fortnight, but SpaceX went metric, don't blame me).

My problem is km/h. Really? The only time I have ever seen that is the speedometer in a car.
Ok, so I'm British and less than 60 so I use m/s for engineering. When I'm driving, it's miles/hr.

I would be willing to bet SpaceX use SI units (kg/seconds/metres) internally. So why on earth would they switch the coverage to use km/h?
Title: Re: Falcon 9 Q&A
Post by: envy887 on 12/21/2017 08:10 pm
Forgive me if this is covered elsewhere, couldn't find anything.
I've just noticed that the SpaceX coverage of NROL-76 uses m/s (metres per second), but CRS-13 uses km/h (unit of the antichrist).

The former is a proper SI unit of speed (yes I know some of you want feet per second or furlongs per fortnight, but SpaceX went metric, don't blame me).

My problem is km/h. Really? The only time I have ever seen that is the speedometer in a car.
Ok, so I'm British and less than 60 so I use m/s for engineering. When I'm driving, it's miles/hr.

I would be willing to bet SpaceX use SI units (kg/seconds/metres) internally. So why on earth would they switch the coverage to use km/h?

Km/h are what 90% of the world uses (http://chartsbin.com/view/5261) for measuring speed, and is only used on the hosted webcast targeted at a general audience.

The technical webcast (when it's broadcast, which is not every flight) only shows m/s.
Title: Re: Falcon 9 Q&A
Post by: nacnud on 12/21/2017 08:12 pm
They're either Canadian (or Mexican) or trolling all the KSP players out there.

PS I'd vote for m/s if I had a vote
Title: Re: Falcon 9 Q&A
Post by: nicp on 12/21/2017 08:17 pm
So all I'm seeing is a difference between the technical and hosted (non-technical) webcasts? I've watched many (all?) of both, never realized.

I do not get on with km/h (as you may have guessed). For some reason I have trouble converting that in my head to m/s, whereas feet per second, miles per hour are no problem.

Sigh. Another conversion constant to try to remember...
Title: Re: Falcon 9 Q&A
Post by: ugordan on 12/22/2017 07:40 am
The technical webcast (when it's broadcast, which is not every flight) only shows m/s.

Well, not really. Not consistently, anyway. The CRS-13 technical webcast showed km/h.
Title: Re: Falcon 9 Q&A
Post by: deruch on 12/22/2017 09:35 am
For some reason I have trouble converting that [km/h] in my head to m/s,

Divide by 4, then add 10% of your new total.  quick conversion.  It's obviously not perfectly accurate.  But the actual conversion is to multiply by (1000/3600)=0.277| (sorry that's supposed to be 7s repeating, not sure how to type a bar) and my way is the same as multiplying by 0.275.  If you need additional accuracy, you can keep taking and adding 10% of your previous 10%.  So, say the speed is 8000 km/h.  That gives 2000 +200 +20 +2 +..... and just keep adding 10% of the previous adjustment until you reach enough accuracy.
Title: Re: Falcon 9 Q&A
Post by: cebri on 12/27/2017 08:45 am
One question can't seem to find the answer for. Does F9 use Draco engines as RCS or just nitrogen thrusters? Thanks.
Title: Re: Falcon 9 Q&A
Post by: ugordan on 12/27/2017 08:47 am
Nitrogen.
Title: Re: Falcon 9 Q&A
Post by: koshvv on 12/29/2017 12:47 pm
My problem is km/h. Really? The only time I have ever seen that is the speedometer in a car.

I would be willing to bet SpaceX use SI units (kg/seconds/metres) internally. So why on earth would they switch the coverage to use km/h?
I would like they use km/s (or m/s, conversion is trivial). Something like 18000 km/h is absurd number. I never encountered such long distances in my life and have no slightest idea how fast 18000 km/h is.
In contrast, 5000 m/s (or 5 km/s) is the distance from my home to Auchan, covered in just one second. Wow, it's pretty fast!
Title: Re: Falcon 9 Q&A
Post by: deruch on 12/29/2017 01:03 pm
My problem is km/h. Really? The only time I have ever seen that is the speedometer in a car.

I would be willing to bet SpaceX use SI units (kg/seconds/metres) internally. So why on earth would they switch the coverage to use km/h?
I would like they use km/s (or m/s, conversion is trivial). Something like 18000 km/h is absurd number. I never encountered such long distances in my life and have no slightest idea how fast 18000 km/h is.
In contrast, 5000 m/s (or 5 km/s) is the distance from my home to Auchan, covered in just one second. Wow, it's pretty fast!

I provided a quick method of estimating a conversion from km/h to m/s in response to @nicp's original complaint.  It's very easy.

http://forum.nasaspaceflight.com/index.php?topic=39481.msg1762532#msg1762532
Title: Re: Falcon 9 Q&A
Post by: Hominans Kosmos on 02/22/2018 02:38 pm
My problem is km/h. Really? The only time I have ever seen that is the speedometer in a car.

I would be willing to bet SpaceX use SI units (kg/seconds/metres) internally. So why on earth would they switch the coverage to use km/h?
I would like they use km/s (or m/s, conversion is trivial). Something like 18000 km/h is absurd number. I never encountered such long distances in my life and have no slightest idea how fast 18000 km/h is.
In contrast, 5000 m/s (or 5 km/s) is the distance from my home to Auchan, covered in just one second. Wow, it's pretty fast!

km/h is the perfect unit of measurement for communicating with the general public. Suggestions of using any other unit of measurement is demanding the company adopt the policy of communicating with the general public in gibberish.
Title: Re: Falcon 9 Q&A
Post by: Oberon_Command on 02/22/2018 02:50 pm
For some reason I have trouble converting that [km/h] in my head to m/s,

Divide by 4, then add 10% of your new total.  quick conversion.  It's obviously not perfectly accurate.  But the actual conversion is to multiply by (1000/3600)=0.277| (sorry that's supposed to be 7s repeating, not sure how to type a bar) and my way is the same as multiplying by 0.275.  If you need additional accuracy, you can keep taking and adding 10% of your previous 10%.  So, say the speed is 8000 km/h.  That gives 2000 +200 +20 +2 +..... and just keep adding 10% of the previous adjustment until you reach enough accuracy.

Actually, there's an easier way - the conversion factor is 3.6. There are 3600 seconds in an hour; a kilometer is 1000 meters. Therefore, an object travelling 1m/s travels 3.6km in an hour. So, 18000km/h = 5000m/s, because 18000 / 3.6 is 5000, while 7000m/s = (7000 * 3.6)km/h = 25,200km/h.

Easy conversions like that are one of the advantages of the metric system. :P
Title: Re: Falcon 9 Q&A
Post by: deruch on 03/01/2018 02:38 pm
For some reason I have trouble converting that [km/h] in my head to m/s,

Divide by 4, then add 10% of your new total.  quick conversion.  It's obviously not perfectly accurate.  But the actual conversion is to multiply by (1000/3600)=0.277| (sorry that's supposed to be 7s repeating, not sure how to type a bar) and my way is the same as multiplying by 0.275.  If you need additional accuracy, you can keep taking and adding 10% of your previous 10%.  So, say the speed is 8000 km/h.  That gives 2000 +200 +20 +2 +..... and just keep adding 10% of the previous adjustment until you reach enough accuracy.

Actually, there's an easier way - the conversion factor is 3.6. There are 3600 seconds in an hour; a kilometer is 1000 meters. Therefore, an object travelling 1m/s travels 3.6km in an hour. So, 18000km/h = 5000m/s, because 18000 / 3.6 is 5000, while 7000m/s = (7000 * 3.6)km/h = 25,200km/h.

Easy conversions like that are one of the advantages of the metric system. :P
Maybe you missed the part where nicp said, "in my head"?  Sure, multiplying and dividing by 3.6 is going to get you an accurate result and is simple enough with a calculator.  But the method I mentioned is much better for "in your head" math.
Title: Re: Falcon 9 Q&A
Post by: Slarty1080 on 03/30/2018 03:35 pm
What material is used for the Octaweb? It looks like a heavy piece of kit, just wondered if it was Aluminium, Aluminium alloy, Steel or even Titanium? I guess that even with 10 flights expected for the block 5's that that amount of Titanium would be too expensive?
Title: Re: Falcon 9 Q&A
Post by: envy887 on 04/01/2018 12:52 am
This is a good question. I always assumed it was titanium, but SpaceX published pictures of a worker welding (TIG?) on it in the open air, which doesn't really work with titanium. So I'd guess either Li-Al alloy or stainless steel.
Title: Re: Falcon 9 Q&A
Post by: su27k on 04/01/2018 05:12 am
From the reddit comment (https://www.reddit.com/r/spacex/comments/60d41s/official_spacex_glassdoor_image_falcon_9_octaweb/df6aibs/) of an ex-employee who welded the octaweb:

Quote
2219 aluminum/lithium alloy

This is from a year ago, but I doubt they'll change it for Block 5.
Title: Re: Falcon 9 Q&A
Post by: Bananas_on_Mars on 04/01/2018 12:55 pm
Somewhere along the way(Block 4ish?) they changed to an octaweb that's bolted instead of welded.
So the material might have changed.
Title: Re: Falcon 9 Q&A
Post by: LucR on 05/11/2018 06:49 pm
From Elon's Block 5 phone presser transcript:
Quote from: theinternetftw link=https://gist.github.com/theinternetftw/5ba82bd5f4099934fa0556b9d09c123e
But this is a much stronger octaweb structure. It's made of a much higher strength of bolted aluminum. A 7000 series instead of a 2000 series.
So they did change it for block 5.
Title: Re: Falcon 9 Q&A
Post by: kevinof on 05/11/2018 07:00 pm
Used to be welded together, now it's bolted which (according to Space X) makes building and refurb easier.
Title: Re: Falcon 9 Q&A
Post by: IanThePineapple on 11/12/2018 05:53 pm
Is it known which core F9R Dev2 is/was? I thought I read somewhere that it was core 1007, but I couldn't find any of this info again.

Thanks for the help!
Title: Re: Falcon 9 Q&A
Post by: Slarty1080 on 02/17/2019 01:57 pm
What are those short towers around the launch pad of Falcon 9 used for?
Title: Re: Falcon 9 Q&A
Post by: Orbiter on 02/17/2019 01:58 pm
Lightning protection.
Title: Re: Falcon 9 Q&A
Post by: Jim on 02/17/2019 03:09 pm
Leftovers from Titan IV
Title: Re: Falcon 9 Q&A
Post by: ugordan on 02/17/2019 03:26 pm
Plus, they're not exactly short. They're what, 250 feet tall just to the bottom of that white cylinder, which is another 150 ft high?
Title: Re: Falcon 9 Q&A
Post by: PM3 on 02/17/2019 04:38 pm
https://www.google.com/search?q=cape+canaveral+lightning+protection&tbm=isch
Title: Re: Falcon 9 Q&A
Post by: Slarty1080 on 02/17/2019 06:21 pm
Why not just a metal spike at the top? What's with the white cylinder bits?
Title: Re: Falcon 9 Q&A
Post by: ugordan on 02/17/2019 06:27 pm
Because the towers themselves are not meant to be isolated ligthning rods. If you look carefully at SLC-40 imagery, you'll see catenary wires going between all four towers and a middle grid inside that one. The purpose of the towers is to create a "net" by shielding the launch vehicle from high electric field tension when a lightning strike hits, sort of like a Faraday cage does. It's not supposed to *attract* lightning.
Title: Re: Falcon 9 Q&A
Post by: PM3 on 02/17/2019 07:12 pm
What's with the white cylinder bits?

"The big top rods are insulators  ... spun fiber in polymer matrix structure ... at the time the biggest such cylinder in the world."

"The fiberglass (FRP) tubes on the top of the launch platforms are a part of a lightning protection system and are insulators with cables that form a cone of protection for the launch tower. They were designed by my former company CH2M HILL, (Gainesville,FL)an engineering firm, and were manufactured by Starline Fabricators, Astatula, FL"

https://space.stackexchange.com/questions/2958/what-are-the-towers-around-the-spacex-launch-pad-used-for
Title: Re: Falcon 9 Q&A
Post by: Slarty1080 on 02/17/2019 08:38 pm
thx - does that mean that Starship will need an even bigger set up? Or will that be different because its made of Stainless?
Title: Re: Falcon 9 Q&A
Post by: cebri on 05/26/2020 06:03 pm
Do we know how much thrust the RCS of the first stage of the falcon 9 produce?
Title: Re: Falcon 9 Q&A
Post by: gongora on 08/15/2020 11:20 pm
Ariane 5 just launched 3 satellites to GTO.  How many launches would it take the falcon 9 to launch them?

two
Title: Re: Falcon 9 Q&A
Post by: Lisa_R4 on 09/02/2020 03:49 pm
Amazing photos. Seems so surreal it can light engines on the way back when the forces must be pushing some plume back on to the engines themselves. Sorry for the newbie question, but how do they protect the bottom of the Falcon 9 from that?
Title: Re: Falcon 9 Q&A
Post by: CorvusCorax on 09/02/2020 05:26 pm
Amazing photos. Seems so surreal it can light engines on the way back when the forces must be pushing some plume back on to the engines themselves. Sorry for the newbie question, but how do they protect the bottom of the Falcon 9 from that?

The bottom of Falcon9 has a heat-shield for that reason. I's design changed a couple of times over F9's design iterations. The rigid parts are easy, they are simply coated in a sufficiently heat resistant material. But the engines gimbal and that makes it necessary that parts of this shield are flexible. In the past SpaceX used something that looked like asbestos cloth you find in furnace-mits and similar, but these have shown holes and other signs of burn through after booster-recovery. The block5 iteration has something better, but the exact design is probably a trade secret ;)


Nevertheless SpaceX has encountered heatshield failures on some extreme reentry recovery attempts. (B1057 - Falcon Heavy Center Core suffered from TVC failure on center engine after a heat shield burn-through -> aborted landing)

The nozzles themselfes don't need protection, they are designed to cope with rocket exhaust and have active cooling channels in their walls.
Title: Re: Falcon 9 Q&A
Post by: CorvusCorax on 10/12/2020 03:05 pm
I think Shotwell was quoting Musk though when she said [Re: Elon Musk criticized Grasshopper's test campaign as having been "not aggressive enough" as the test article ended up surviving all tests.]. I don't have the exact source/video, though.

Link/Reference anyone? It should be public, but I don't know where to look.
Title: Re: Falcon 9 Q&A
Post by: AS_501 on 04/22/2021 09:51 pm
I'm puzzled why Falcon 9 throttles down through Max Q.  I can understand why Falcon 9 Heavy (as well as Shuttle, Delta IV Heavy, etc.) does this to reduce aerodynamic loads on the booster attach points.  But F9 is single stick.  My best guess is that the vehicle velocity approaching Max Q dictates the need for throttle down.  Or this is required by Dragon, not the booster?  Or if Space X built Dragon and Falcon 'beefy' enough to endure full Max Q, there would be a weight penalties.

Sidebar coments:
-  I just watched the last Delta IV Medium (two SRBs) launch.  Didn't hear an RS-68A throttle down comment.
-  I think the Shuttle was first vehicle to utilize throtte down simply because it had the first throttleable engines.
-  The original Atlas rocket is an interesting case.  It was famous (or infamous!) for it's thin-skin construction.  As far as I know it survived Max Q every time with its fixed-thrust engines.
Thanks
Title: Re: Falcon 9 Q&A
Post by: Jim on 04/22/2021 10:29 pm
I'm puzzled why Falcon 9 throttles down through Max Q.  I can understand why Falcon 9 Heavy (as well as Shuttle, Delta IV Heavy, etc.) does this to reduce aerodynamic loads on the booster attach points.  But F9 is single stick.  My best guess is that the vehicle velocity approaching Max Q dictates the need for throttle down.  Or this is required by Dragon, not the booster?  Or if Space X built Dragon and Falcon 'beefy' enough to endure full Max Q, there would be a weight penalties.

Sidebar coments:
-  I just watched the last Delta IV Medium (two SRBs) launch.  Didn't hear an RS-68A throttle down comment.
-  I think the Shuttle was first vehicle to utilize throtte down simply because it had the first throttleable engines.
-  The original Atlas rocket is an interesting case.  It was famous (or infamous!) for it's thin-skin construction.  As far as I know it survived Max Q every time with its fixed-thrust engines.
Thanks

Delta IV and Atlas V (and so will Vulcan) also throttle down.  It has nothing to do with "booster attach points", but rather loads on the vehicle and payload.  The shuttle had an additional reason because of the aerosurfaces.  Throttling down prevents the vehicle from accelerating too fast through the lower atmosphere and keeps max q to less than 1000 psf (I think around 700, the same as the Saturn V).    Throttling also reduces the max g which is usually just before core burnout. 

Classic Atlas and Saturn V had lower T/W and accelerated slower through the lower atmosphere.
Title: Re: Falcon 9 Q&A
Post by: AS_501 on 04/22/2021 10:39 pm
Thanks Jim.  Your breath and depth of knowledge is worth umteen times my NSF subscription price.
Title: Re: Falcon 9 Q&A
Post by: DaveS on 04/22/2021 10:51 pm
keeps max q to less than 1000 psf (I think around 700, the same as the Saturn V).
The 700 lbs/ft2 Max Q came later for shuttle. It was a Performance Enhancement. Earlier was around 670/ft2.
Title: Re: Falcon 9 Q&A
Post by: ZachS09 on 05/24/2021 03:21 pm
Why does the SpaceX Launch Director give his GO for every Falcon launch at T-45 seconds? Shouldn’t it be earlier in the count?

Also, I noticed before the Falcon Heavy Test Flight, the Launch Director gave his GO at T-25 seconds. That’s cutting it close, right?
Title: Re: Falcon 9 Q&A
Post by: Jim on 05/24/2021 04:07 pm
Why does the SpaceX Launch Director give his GO for every Falcon launch at T-45 seconds? Shouldn’t it be earlier in the count?

Also, I noticed before the Falcon Heavy Test Flight, the Launch Director gave his GO at T-25 seconds. That’s cutting it close, right?

The range gives him a go late in the count.    As long as there is a place to safely stop the count, it isn't too late.
Title: Re: Falcon 9 Q&A
Post by: Lucjusz on 11/03/2021 09:53 pm
Hi,
is there any paper/video on YouTube/anywhere else describing what happens if you rotate one/two/all grid fins on Falcon 9 booster? Any video/paper about control authority? I'm just wondering what would have happened if you rotated for example two opposite fins, etc.
Title: Re: Falcon 9 Q&A
Post by: penguin44 on 09/17/2022 02:41 am
With the recent weather scrubs of Falcon it got me wondering, is there a limit on how many tankings it can do?
Title: Re: Falcon 9 Q&A
Post by: markbike528cbx on 09/17/2022 05:08 pm
With the recent weather scrubs of Falcon it got me wondering, is there a limit on how many tankings it can do?
Since Elon has said there are no obvious limits to Falcon 9 reuse, then tankings should be included.
The number is high, but not infinite. My guesstimate is about 100?
Title: Re: Falcon 9 Q&A
Post by: AmigaClone on 09/17/2022 10:58 pm
With the recent weather scrubs of Falcon it got me wondering, is there a limit on how many tankings it can do?
Since Elon has said there are no obvious limits to Falcon 9 reuse, then tankings should be included.
The number is high, but not infinite. My guesstimate is about 100?

I can see the design limits to be above 100 tankings. On the other hand, I can see a much lower number (10?) for the number of times SpaceX would fill the Falcon 9 with propellants and detank before pulling the rocket down to conduct some inspections.
Title: Re: Falcon 9 Q&A
Post by: ddunham on 01/16/2023 07:11 am
It appears the external cameras on the first stage have some method of clearing the view after entry burn fouling.  I can think of a few ways this might be accomplished, but not sure what is used.  Rotating shield that moves to a clean spot?  That would require a servo or similar which seems odd to me.  Is there a reference for how this is done?
Title: Re: Falcon 9 Q&A
Post by: edzieba on 01/16/2023 11:32 am
It appears the external cameras on the first stage have some method of clearing the view after entry burn fouling.  I can think of a few ways this might be accomplished, but not sure what is used.  Rotating shield that moves to a clean spot?  That would require a servo or similar which seems odd to me.  Is there a reference for how this is done?
No cleaning methods other than the supersonic airflow blasting the camera fairing window that can impinge once the burn ends.
The 'wipe' is shadowing and internal glare from the vehicle moving relative to the sun. The effect of the airflow is most visible for RTLS landings (as the trajectory is more vertical the the time between end of the entry burn and hitting the denser lower atmosphere at speed is much shorter than for the shallower downrange landings) and more dramatic for Falcon Heavy due to the heavy fouling from the separation and boostback (the deposits are visible long before the entry burn starts).
Title: Re: Falcon 9 Q&A
Post by: Citabria on 01/31/2023 07:07 pm
Does SpaceX ever put previously flown engines on unflown expendable cores?
Title: Re: Falcon 9 Q&A
Post by: whitelancer64 on 02/08/2023 05:59 pm
Does SpaceX ever put previously flown engines on unflown expendable cores?

I presume you are really asking if SpaceX puts older engines they are willing to lose onto new, expended Falcon Heavy cores. There is no way to know this outside of someone at SpaceX explicitly saying they installed older, previously flown engines on an expended core.

However, SpaceX does engine swaps all the time, and there is no particular reason why a previously flown engine could not be installed on a new booster. The Merlin engines are effectively interchangeable and can be installed on any first stage.

Unless the customer specifies that they want completely new engines to fly on their booster, SpaceX can assign engines to that launch as they please.
Title: Re: Falcon 9 Q&A
Post by: deltaV on 03/28/2023 02:46 am
Why does NASA Launch Services Program's Launch Vehicle Performance Website (https://elvperf.ksc.nasa.gov/) not show Falcon performance for many orbits? For example the orbits (i) 200 km 28.5 degree LEO and (ii) C3 = -2 km^2 / s^2 high energy show performance numbers for other launchers but not for Falcon 9 or Falcon Heavy.

Edit: Falcon 9 and Falcon Heavy do show up for some orbits, e.g. C3 = -1.5 km^2 / s^2.
Title: Re: Falcon 9 Q&A
Post by: markbike528cbx on 04/05/2023 07:43 pm

What is the use of a entry burn for RTLS, especially FH boosters?

The RTLS entry burn start speed (4000km/hr) is less than the ASDS (barge) landing entry burn end speed (~6000km/hr).


Info I've gathered from webcast telemetry.

RTLS One Web 16  Jan 9 2023
Payload mass kg   5900      40x 147.5 = 5900 plus dispenser (1000kg??)

Entry Burn start speed 4473
Entry Burn end speed  2926

FH side booster RTLS  USSF-67  Jan 2023
Payload mass kg  ??? to GEO

Entry Burn start speed 4472
Entry Burn end speed  3690

F9 RTLS ISI EROS C-3 Dec 29 2022 Vandenburg
Payload mass kg 470

Entry Burn start speed  4651
Entry Burn end speed   2616



F9 ASDS  Starlink  Dec 17th 2022  Cape
Payload mass kg

Entry Burn start speed  8152
Entry Burn end speed   6074   

Distance to ASDS km est 656

F9 ASDS  Starlink 5-1  Dec 28th 2022  Cape
Payload mass kg 16200   54x300kg Starlink 1.5

Entry Burn start speed  8026
Entry Burn end speed   5627

Distance to ASDS km  660
Title: Re: Falcon 9 Q&A
Post by: John Santos on 04/05/2023 08:36 pm

What is the use of a entry burn for RTLS, especially FH boosters?

The RTLS entry burn start speed (4000km/hr) is less than the ASDS (barge) landing entry burn end speed (~6000km/hr).


Info I've gathered from webcast telemetry.

RTLS One Web 16  Jan 9 2023
Payload mass kg   5900      40x 147.5 = 5900 plus dispenser (1000kg??)

Entry Burn start speed 4473
Entry Burn end speed  2926

FH side booster RTLS  USSF-67  Jan 2023
Payload mass kg  ??? to GEO

Entry Burn start speed 4472
Entry Burn end speed  3690

F9 RTLS ISI EROS C-3 Dec 29 2022 Vandenburg
Payload mass kg 470

Entry Burn start speed  4651
Entry Burn end speed   2616



F9 ASDS  Starlink  Dec 17th 2022  Cape
Payload mass kg

Entry Burn start speed  8152
Entry Burn end speed   6074   

Distance to ASDS km est 656

F9 ASDS  Starlink 5-1  Dec 28th 2022  Cape
Payload mass kg 16200   54x300kg Starlink 1.5

Entry Burn start speed  8026
Entry Burn end speed   5627

Distance to ASDS km  660

Entry burns are to reduce velocity and therefore aerodynamic heating of the booster during re-entry.  This is needed whether the booster is heading for a drone ship landing or an RTLS landing.  The altitude and duration of the entry burn is carefully calculated to use the least possible amount of fuel while keeping the heating of the rocket below the safe limit.
Title: Re: Falcon 9 Q&A
Post by: markbike528cbx on 04/13/2023 07:04 pm
The previous answer deftly avoided the question.

WHY does Spaces even bother with a RTLS entry burn since the ENDING velocity of an ASDS is greater than the START velocity of an RTLS entry burn.

Quote
The altitude and duration of the entry burn is carefully calculated to use the least possible amount of fuel while keeping the heating of the rocket below the safe limit.
This doesn't hold water since the entry burn time is identical and altitude  is very close between RTLS and ASDS.



                                                                          Entry Burn start   Entry burn end   Entry burn time   Altitude at End of Entry burn
                                                                       km/hr                      km/hr                       seconds                km
F9 RTLS One Web 16  Jan 9 2023                        4473                       2926                            19                      32.4
FH side booster RTLS  USSF-67  Jan 2023             4472                     3690                            21                       34.5
F9 RTLS ISI EROS C-3 Dec 29 2022 Vandy             4551                    2616                            21                       31
Average RTLS                                                     4499                    3077                             20                       33
            
F9 ASDS  Starlink  Dec 17th 2022  Cape                 8155                       6074                            18                      36.1
F9 ASDS  Starlink 5-1  Dec 28th 2022  Cape           8026                       5627                            23                      41.6
F9 ASDS Starlink  January 19 Vandy                       8110                       5843                            19                      35.8
Average ASDS                                                     8097                        5848                            20                      38
            
Difference                                                             3598                        2771                               0                        5


Entry burn starts range from 6:07 to 6:51 with RTLS starts tending to be a little earlier.

Speculation on reasons for this, in the hopes of invoking Cunningham's Law https://en.wiktionary.org/wiki/Cunningham%27s_Law

Commonality of Operations?
Doesn't make sense, SpaceX seems to have a pretty darn good grasp on writing real-time adaptive control software.

Vehicle control ? 
But the same question applies to the relative ENDING velocity.

RTLS is probably more nearly vertical than ASDS?

Perhaps just making the later entry less stressfull for RTLS, as in you might be able to have lesser structural and heating loads. 

Reducing cold-gas RCS thruster requirements?

An on a non-sequitor note:  Does anybody have suggestions for a good way to insert spreasheet tables that you don't have to  hand-tweek?  A PM and or a pointer to an answering thread would be appreciated.