Author Topic: Falcon 9 Q&A  (Read 5618 times)

Offline Zaum

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Falcon 9 Q&A
« 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?

Offline nadreck

Re: Falcon 9 Q&A
« Reply #1 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.
« Last Edit: 01/31/2016 06:52 PM by nadreck »
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Zaum

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Re: Falcon 9 Q&A
« Reply #2 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.
« Last Edit: 01/31/2016 07:28 PM by Zaum »

Offline Jim

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Re: Falcon 9 Q&A
« Reply #3 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.

Offline Raj2014

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Re: Falcon 9 Q&A
« Reply #4 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.

Offline Jim

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Re: Falcon 9 Q&A
« Reply #5 on: 03/05/2016 11:39 PM »
Nets on the barge would only cause more problems.
« Last Edit: 03/05/2016 11:39 PM by Jim »

Offline Coastal Ron

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Re: Falcon 9 Q&A
« Reply #6 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.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline jee_c2

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Transport from sea platform
« Reply #7 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?

Offline rocx

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Re: Falcon 9 Q&A
« Reply #8 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.
Any day with a rocket landing is a fantastic day.

Offline jee_c2

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Re: Falcon 9 Q&A
« Reply #9 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.

Offline Urx

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Understanding SpaceX pricelist
« Reply #10 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?

Offline rocx

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Re: Understanding SpaceX pricelist
« Reply #11 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.
Any day with a rocket landing is a fantastic day.

Online SmallKing

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Re: Falcon 9 Q&A
« Reply #12 on: 04/15/2017 09:53 AM »
Not a complicated question.
During the launch preparation, what is LOX drainback?
Some are bound for happiness, some are bound to glory, some are bound to live with less, who can tell your story?

Offline edkyle99

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Re: Falcon 9 Q&A
« Reply #13 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
« Last Edit: 04/15/2017 02:11 PM by edkyle99 »

Offline drunyan8315

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Re: Falcon 9 Q&A
« Reply #14 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.

Offline drunyan8315

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Re: Falcon 9 Q&A
« Reply #15 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.

Online ugordan

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Re: Falcon 9 Q&A
« Reply #16 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?

Offline Coastal Ron

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Re: Falcon 9 Q&A
« Reply #17 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.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline joncz

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Re: Falcon 9 Q&A
« Reply #18 on: 04/15/2017 04:24 PM »



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.


Offline drunyan8315

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Re: Falcon 9 Q&A
« Reply #19 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.

Offline drunyan8315

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Re: Falcon 9 Q&A
« Reply #20 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!

Offline Jim

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Re: Falcon 9 Q&A
« Reply #21 on: 04/17/2017 02:53 PM »
  A little-appreciated fact is that the rocket must generate aerodynamic lift

Not true at all. 


Offline Jim

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Re: Falcon 9 Q&A
« Reply #22 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.
« Last Edit: 04/17/2017 03:06 PM by Jim »

Offline Manabu

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Re: Falcon 9 Q&A
« Reply #23 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.
« Last Edit: 04/28/2017 02:45 AM by Manabu »

Offline envy887

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Re: Falcon 9 Q&A
« Reply #24 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.