Author Topic: SpaceX to begin testing on Reusable Falcon 9 technology this year  (Read 693309 times)

Offline QuantumG

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Edit:  Although what you are saying was the plan for the reusable launcher in "The Rocket Company."  And I've asked before on this form for an expert who has read that book to give it a critical review.

It's so hard to give a critical review because it's such a fantastic read :)

New thread for anyone who cares to comment: http://forum.nasaspaceflight.com/index.php?topic=29119
« Last Edit: 06/09/2012 01:24 am by QuantumG »
Human spaceflight is basically just LARPing now.

Offline modemeagle

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I updated the sim with the new M1D data and therefore can't match previous data as since the performance has changed.  Attached are graphs from a one run.  The run performs a 180 degree burn and stays at that attitude until impact for ease of simulating.  The velocity listed is "flight path" velocity.  If you want velocity data from a point, then let me know which ones and I will supply that data.

Total Mass at staging: 69.5 tonnes
Total Mass after return burn: 31.2 tonnes
Total horizontal velocity after burn: -466.6 m/s
Apogee: 178.5 km

Regarding the engine forward impact.  The stage has the cross section of a dragon capsule, but almost 5 times the mass.


I still don't understand your simulation. It doesn't seem to take account of the dynamic pressure slowing down the falling stage. In the diagram at around 40-50 km the DP starts increasing, however the velocity curve doesn't flatten out till around 18 km when it drastically slows. The drag would slow the stage down significantly as it got below 50km.

At 30 km, the charts show a velocity of about 1700 m/s and Q of about 25kPa. Ignoring supersonic effects which would increase the drag, that means there would be a total force on the side of about 3.6mN, so an acceleration of about 117 m/sec^2 so it would be slowing down at about 107 m/sec^2. At 20 km, the charts show it speeding up to about 1750 m/s and Q of about 140kPa. The force would be about 20mN, and it would be slowing at about 620 m/sec^2. That can't be the case, it would have slowed to terminal velocity before it got to 20km.

My guess is that under those start conditions, the stage falling sideways would slow to terminal velocity at about 30km and 500m/s. Falling end on it would get to terminal velocity at 14km and 486 m/s. All that ignores supersonic drag effects, so it would probably slow down a lot faster.

WRT the Dragon. Since the drag goes up with the square of the velocity, a factor of 5 in mass just about doubles the terminal velocity at given altitude. That's not the difference between subsonic and 1900 m/s and anyway the terminal velocity keeps decreasing as it falls.



You're right about the drag.  My drag model is based on surface drag since during launch your out of the air stream by the time your high in mach.  I will see if my drag calculation source has the information needed for supersonic effects on drag.

My drag is calculated using dynamic pressure, live Cd calculations (not a constant), and area of cross section.  Dynamic pressure is from velocity and air density (nasa model).  Cd was fun to add into the model.

Offline RDoc

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You're right about the drag.  My drag model is based on surface drag since during launch your out of the air stream by the time your high in mach.  I will see if my drag calculation source has the information needed for supersonic effects on drag.

My drag is calculated using dynamic pressure, live Cd calculations (not a constant), and area of cross section.  Dynamic pressure is from velocity and air density (nasa model).  Cd was fun to add into the model.
But does it take account of ordinary frontal drag, that is Q * Area?

Offline aero

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There are too many sources of quite speculative specifications for the SpaceX's hardware (even Wikipedia) and it's confusing. Maybe we should start a thread collecting only the most reliable data.

Did we ever make any headway on this question? The Falcon 9 v1.1 data at the bottom of this reference
http://www.spacelaunchreport.com/falcon9.html
is internally inconsistant by many tonnes. It gives

Lift Off mass 480 tonnes
Stage 1 fuel mass 411 tonnes
Stage 1 dry mass 28 tonnes
Stage 2 fuel mass 73.4 tonnes
Stage 2 dry mass 4.7 tonnes.

As you can read, that doesn't add up, not even close. I get 517.7 tonnes Lift Off mass by adding up the stage and fuel masses. What is a good guess for the lift off mass? I could use Stage 1 Thrust divided by Lift Off acceleration, if I knew what that was. If I guess about 1.15 g, I get the Lift Off mass to be about 520 tonnes.

Would someone with experience take a cut at these estimations? (oldAtlas_Eguy?) Without accurate knowledge of Lift Off mass it is hard to credit simulations that calculate velocity at MECO, 180.2 seconds into the flight.
« Last Edit: 06/09/2012 01:29 am by aero »
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Offline modemeagle

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You're right about the drag.  My drag model is based on surface drag since during launch your out of the air stream by the time your high in mach.  I will see if my drag calculation source has the information needed for supersonic effects on drag.

My drag is calculated using dynamic pressure, live Cd calculations (not a constant), and area of cross section.  Dynamic pressure is from velocity and air density (nasa model).  Cd was fun to add into the model.
But does it take account of ordinary frontal drag, that is Q * Area?

Yes, the drag is based on frontal area and dynamic pressure.


Offline baldusi

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There are too many sources of quite speculative specifications for the SpaceX's hardware (even Wikipedia) and it's confusing. Maybe we should start a thread collecting only the most reliable data.

Did we ever make any headway on this question? The Falcon 9 v1.1 data at the bottom of this reference
http://www.spacelaunchreport.com/falcon9.html
is internally inconsistant by many tonnes. It gives

Lift Off mass 480 tonnes
Stage 1 fuel mass 411 tonnes
Stage 1 dry mass 28 tonnes
Stage 2 fuel mass 73.4 tonnes
Stage 2 dry mass 4.7 tonnes.

As you can read, that doesn't add up, not even close. I get 517.7 tonnes Lift Off mass by adding up the stage and fuel masses. What is a good guess for the lift off mass? I could use Stage 1 Thrust divided by Lift Off acceleration, if I knew what that was. If I guess about 1.15 g, I get the Lift Off mass to be about 520 tonnes.

Would someone with experience take a cut at these estimations? (oldAtlas_Eguy?) Without accurate knowledge of Lift Off mass it is hard to credit simulations that calculate velocity at MECO, 180.2 seconds into the flight.
If I'm not mistaken, the single core Falcon 9 is under filled. They get full fill for the Falcon Heavy. That also explains how the Falcon Heavy is heavier that three Falcon 9 v1.1 even though it uses the same upper stage and fairing.

Offline modemeagle

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There are too many sources of quite speculative specifications for the SpaceX's hardware (even Wikipedia) and it's confusing. Maybe we should start a thread collecting only the most reliable data.

Did we ever make any headway on this question? The Falcon 9 v1.1 data at the bottom of this reference
http://www.spacelaunchreport.com/falcon9.html
is internally inconsistant by many tonnes. It gives

Lift Off mass 480 tonnes
Stage 1 fuel mass 411 tonnes
Stage 1 dry mass 28 tonnes
Stage 2 fuel mass 73.4 tonnes
Stage 2 dry mass 4.7 tonnes.

As you can read, that doesn't add up, not even close. I get 517.7 tonnes Lift Off mass by adding up the stage and fuel masses. What is a good guess for the lift off mass? I could use Stage 1 Thrust divided by Lift Off acceleration, if I knew what that was. If I guess about 1.15 g, I get the Lift Off mass to be about 520 tonnes.

Would someone with experience take a cut at these estimations? (oldAtlas_Eguy?) Without accurate knowledge of Lift Off mass it is hard to credit simulations that calculate velocity at MECO, 180.2 seconds into the flight.

My estimates are V1.1 498 tonnes, F9R 490 tonnes,  Difference in mostly payload.

F9 SII should be partial filled compared to the FH configuration.

Offline RDoc

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Yes, the drag is based on frontal area and dynamic pressure.
Then why does it show the stage accelerating at 30km when the drag produces a deceleration of over 10G.

Offline aero

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OK - so the fuel tanks are not full. Instead of 411 tonnes and 73.4 tonnes of fuel in the first and second stage at lift off, we have something less than that. Great. Two things, 1 - Why would they build a rocket if they didn't expect to fill the tanks, and 2 - How does that help me evaluate the "boost back to pad" requirements?
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Offline charliem

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There are too many sources of quite speculative specifications for the SpaceX's hardware (even Wikipedia) and it's confusing. Maybe we should start a thread collecting only the most reliable data.

Did we ever make any headway on this question? The Falcon 9 v1.1 data at the bottom of this reference
http://www.spacelaunchreport.com/falcon9.html
is internally inconsistant by many tonnes. It gives

Lift Off mass 480 tonnes
Stage 1 fuel mass 411 tonnes
Stage 1 dry mass 28 tonnes
Stage 2 fuel mass 73.4 tonnes
Stage 2 dry mass 4.7 tonnes.

That suggestion was mine but it seems there's not much interest. Only for us, geekest between geeks  ;D

About those weights, I said it before but there are few who agree with this: If we believe Elon Musk's statement that a FH booster has a mass ratio slightly above 30, that gives an important clue regarding the dry weight of a F9v1.1 first stage. Has to be MUCH lighter than 28 mT.
« Last Edit: 06/09/2012 04:36 am by charliem »

Offline charliem

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@modemeagle, my simulation of the boost-back is different than yours.

Initial conditions at MECO are:

Speed relative to the pad: 2,600 m/s
Angle of ascent: 23 deg
Altitude: 78,100 m
Distance from the pad: 111,000 m
Propellant unburned: 40.9 mT

I leave 25 secs for separation and maneuvers to reorient the stage to a 161 deg heading.

Ignition of 3 engines at 100% thrust for 77 secs, throttling down when necessary to keep the acceleration under 6 g.

That puts the stage in a ballistic trajectory that, without more corrections, would take it less than 10 km from the pad.

Apogee is 222 s after staging, at 243.000 m of altitude.

The stage crosses down the Karman line 400 s after staging, doing 1.780 m/s and accelerating.

These numbers are for an engines first trajectory, no try to slow down.

Max speed: 2,060 m/s at 33,600 m.
Max-Q: 295 kPa at 12,200 m.
Max-g: 136 m/s2, same altitude.
Subsonic at 1,400 m high.
Crashes at 187 m/s, 469 s after staging.

Both dynamic pressure and g load look difficult to survive.

EDIT: Max-Q is not, as previously posted, 2,542 kPa, but much less.
« Last Edit: 06/09/2012 01:32 pm by charliem »

Offline cordor

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@modemeagle, my simulation of the boost-back is different than yours.

Initial conditions at MECO are:

Speed relative to the pad: 2,600 m/s
Angle of ascent: 23 deg
Altitude: 78,100 m
Distance from the pad: 111,000 m
Propellant unburned: 40.9 mT

I leave 25 secs for separation and maneuvers to reorient the stage to a 161 deg heading.

Ignition of 3 engines at 100% thrust for 77 secs, throttling down when necessary to keep the acceleration under 6 g.

That puts the stage in a ballistic trajectory that, without more corrections, would take it less than 10 km from the pad.

Apogee is 222 s after staging, at 243.000 m of altitude.

The stage crosses down the Karman line 400 s after staging, doing 1.780 m/s and accelerating.

These numbers are for an engines first trajectory, no try to slow down.

Max speed: 2,060 m/s at 33,600.
Max-Q: 2,542 kPa at 12,200 m.
Max-g: 136 m/s2, same altitude.
Subsonic at 1,400 m high.
Crashes at 187 m/s, 469 s after staging.

Both dynamic pressure and g load look difficult to survive.


Can it somehow generate enough lift to stay at the same altitude? maybe fire multiple short bursts. Eventually the speed slow down and the pad caught up, by than F9 just need to descent.

Offline hrissan

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@modemeagle, my simulation of the boost-back is different than yours.

Initial conditions at MECO are:

Speed relative to the pad: 2,600 m/s
Angle of ascent: 23 deg
Altitude: 78,100 m
Distance from the pad: 111,000 m
Propellant unburned: 40.9 mT

I leave 25 secs for separation and maneuvers to reorient the stage to a 161 deg heading.

Ignition of 3 engines at 100% thrust for 77 secs, throttling down when necessary to keep the acceleration under 6 g.

That puts the stage in a ballistic trajectory that, without more corrections, would take it less than 10 km from the pad.

Apogee is 222 s after staging, at 243.000 m of altitude.

The stage crosses down the Karman line 400 s after staging, doing 1.780 m/s and accelerating.

These numbers are for an engines first trajectory, no try to slow down.

Max speed: 2,060 m/s at 33,600.
Max-Q: 2,542 kPa at 12,200 m.
Max-g: 136 m/s2, same altitude.
Subsonic at 1,400 m high.
Crashes at 187 m/s, 469 s after staging.

Both dynamic pressure and g load look difficult to survive.


Awesome!

Do we have numbers on max-q, velocity and acceleration at max-q of the rocket going up? Then we would be able to calculate the force acting on the tank structure by taking into account the weight of the second stage and payload at max-q acceleration. Again on the way down we would be able to calculate the force acting on the tank structure roughly assuming the weight of the tank itself (we may improve calculation if we take into account the tank consists of 2 parts, because fuel mass in the upper tank can weight a lot in comparison to tank itself).

So you see the same pressure acting on the way down exerts much less force on the tank structure, because tank has not to support large additional weight.

The deceleration itself cannot cripple the structure, the force of weight does this.

To say if your result of 10g and 25atm dynamic pressure is survivable for the tank, please calculate the force acting on the tank and you will see! But it may survive.

The question now will be if the engines nozzles would survive 25atm acting on them when falling down? This forces are applied to the nozzles and the stage structure up in roughly the same way as if the engines are firing, so may be. But if you want to actually fire the engine in 25atm pressure environment, I doubt it will work.

When you simulate the engine firing on the part of way down where dynamic pressure is high, it has to overcome this pressure.

Offline modemeagle

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OK - so the fuel tanks are not full. Instead of 411 tonnes and 73.4 tonnes of fuel in the first and second stage at lift off, we have something less than that. Great. Two things, 1 - Why would they build a rocket if they didn't expect to fill the tanks, and 2 - How does that help me evaluate the "boost back to pad" requirements?

1.  The design was for the FH, they then took the core and second stage and checked to see how much payload they can get with that configuration for commonality.  I found the upper needed less fuel for the payload, or needed a higher thrust engine for more payload/fuel.

2.  With boostback, my model still uses the same reduced SII fuel, where the extra performance taken from SI for boost back is traded from payload.

Offline modemeagle

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Yes, the drag is based on frontal area and dynamic pressure.
Then why does it show the stage accelerating at 30km when the drag produces a deceleration of over 10G.

Its also multiplied by Cd, and at 30 km my Cd model is nearly zero.  What are you using the calculated Cd?

Offline modemeagle

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@modemeagle, my simulation of the boost-back is different than yours.

Initial conditions at MECO are:

Speed relative to the pad: 2,600 m/s
Angle of ascent: 23 deg
Altitude: 78,100 m
Distance from the pad: 111,000 m
Propellant unburned: 40.9 mT

I leave 25 secs for separation and maneuvers to reorient the stage to a 161 deg heading.

Ignition of 3 engines at 100% thrust for 77 secs, throttling down when necessary to keep the acceleration under 6 g.

That puts the stage in a ballistic trajectory that, without more corrections, would take it less than 10 km from the pad.

Apogee is 222 s after staging, at 243.000 m of altitude.

The stage crosses down the Karman line 400 s after staging, doing 1.780 m/s and accelerating.

These numbers are for an engines first trajectory, no try to slow down.

Max speed: 2,060 m/s at 33,600.
Max-Q: 2,542 kPa at 12,200 m.
Max-g: 136 m/s2, same altitude.
Subsonic at 1,400 m high.
Crashes at 187 m/s, 469 s after staging.

Both dynamic pressure and g load look difficult to survive.

Charliem, why point at 161 degrees instead of 180 to cancel all of the horizontal thrust.  At 161 your adding more to the apogee which will kill the reentry conditions.

Offline aero

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oldAtlas_Eguy posted some numbers here. Masses, etc.

http://forum.nasaspaceflight.com/index.php?topic=28882.msg914108#new

It would be more convenient to have the data posted in a sticky, but at least it is posted.
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Offline charliem

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Can it somehow generate enough lift to stay at the same altitude? maybe fire multiple short bursts. Eventually the speed slow down and the pad caught up, by than F9 just need to descent.

Yes, certainly. In that simulation the burn to start the ballistic way back doesn't consume all the propellants, 4.6 mT remain so there's the possibility of slowing down using them.

I'm still thinking about what would be the best way to do reentry because if you start one engine above the atmosphere there might not be enough fuel to reach the surface and do the landing, and if we wait until latter then there's the difficulty of ignition against a supersonic flow.

And you can't wait till the stage is subsonic (1.400 m) either, because then there's not enough time to brake, even at max thrust (one engine).

I see two ways. First, reorient the stage sideways to do reentry so the atmospheric drag slows it down much higher. Second, deploying a supersonic parachute at about 10 km up (mach 3).

Do we have numbers on max-q, velocity and acceleration at max-q of the rocket going up?
...
The question now will be if the engines nozzles would survive 25atm acting on them when falling down?

For the going up max-Q was 30 kPa and max acceleration about 5.5 g.

About max-Q on the way down I made a mistake on my previous post, was not 2,542 kPas but only 295 kPa (3 atm). I just edited the post.

Charliem, why point at 161 degrees instead of 180 to cancel all of the horizontal thrust.  At 161 your adding more to the apogee which will kill the reentry conditions.

You are right about the reentry conditions, but that trajectory was the one that burned less fuel, having also the best range.

Offline modemeagle

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Can it somehow generate enough lift to stay at the same altitude? maybe fire multiple short bursts. Eventually the speed slow down and the pad caught up, by than F9 just need to descent.

Yes, certainly. In that simulation the burn to start the ballistic way back doesn't consume all the propellants, 4.6 mT remain so there's the possibility of slowing down using them.

I'm still thinking about what would be the best way to do reentry because if you start one engine above the atmosphere there might not be enough fuel to reach the surface and do the landing, and if we wait until latter then there's the difficulty of ignition against a supersonic flow.

And you can't wait till the stage is subsonic (1.400 m) either, because then there's not enough time to brake, even at max thrust (one engine).

I see two ways. First, reorient the stage sideways to do reentry so the atmospheric drag slows it down much higher. Second, deploying a supersonic parachute at about 10 km up (mach 3).

Do we have numbers on max-q, velocity and acceleration at max-q of the rocket going up?
...
The question now will be if the engines nozzles would survive 25atm acting on them when falling down?

For the going up max-Q was 30 kPa and max acceleration about 5.5 g.

About max-Q on the way down I made a mistake on my previous post, was not 2,542 kPas but only 295 kPa (3 atm). I just edited the post.

Charliem, why point at 161 degrees instead of 180 to cancel all of the horizontal thrust.  At 161 your adding more to the apogee which will kill the reentry conditions.

You are right about the reentry conditions, but that trajectory was the one that burned less fuel, having also the best range.


Try a run where you burn 4 engines for the return maneuver at 180 degrees.  The video showed 3, but if they do an octagonal arrangement, then 4 would be more optimum and then igniting the center engine for final braking and landing.

Offline MikeAtkinson

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I'm not sure, but I think that thrusting back along the trajectory will give better results (i.e. a gravity turn in reverse).

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