Author Topic: F9 Second Stage Reusability  (Read 193578 times)

Offline Lemurion

Re: F9 Second Stage Reusability
« Reply #340 on: 04/13/2017 03:55 PM »
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #341 on: 04/13/2017 04:02 PM »
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
Sure... You wouldn't need them to burn for long...
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Offline Robotbeat

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Re: F9 Second Stage Reusability
« Reply #342 on: 04/13/2017 04:02 PM »
Could SuperDracos be used for both retropropulsion and landing? If you want to use them for landing anyway it might make sense.
If in vacuum or close to it, then use Merlin Vac. Otherwise, use Superdracos.
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Offline ArbitraryConstant

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Re: F9 Second Stage Reusability
« Reply #343 on: 04/13/2017 05:38 PM »
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
« Last Edit: 04/13/2017 05:41 PM by ArbitraryConstant »

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #344 on: 04/13/2017 06:28 PM »
no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.
My point exactly. The payoff with this is no propellant needed for the de-orbit burn.

Quote from: hkultala
The problem is more about the reliability and orbit flexibility side than delta-v side. It might be beneficial to stay on the GTO for multiple orbits, not circulizing the orbit to GEO on the first orbit, to get to correct position on the GEO.
I think this is generically called a "phasing burn."
Quote from: hkultala
On a trajectory that has pegiree of under 100km this is not possible. And if there is some technical proplem delaying the circularization burn, re-entering after one orbit is also quite a bad thing.
I suggested it more for completeness than anything else, on the basis that Musk was suggesting something just now. Flying the US sub orbital simplified the de orbit problem, as not doing a full burn to orbit is not an add on, just a change in the mission flight program.

In fact it's likely they've been working on this since they discovered whatever it is that potentially puts US recovery back on the table.

It's true that the odds against whatever they've got planned leading to a successful US recovery of a stage in good enough condition are a "Hail Mary" but I doubt the hardware preparations will be anywhere near so spur of the moment.
« Last Edit: 04/14/2017 03:28 PM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Robotbeat

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Re: F9 Second Stage Reusability
« Reply #345 on: 04/13/2017 06:46 PM »
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
That miniature Raptor/methane/BFS idea is looking better all the time...
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline hkultala

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Re: F9 Second Stage Reusability
« Reply #346 on: 04/13/2017 07:40 PM »
Please fix your quotes. I did not say things that look like my quotes in your original post.

no. The delta-v difference between a GTO that has pegiree of 70km (goes through the atmosphere so re-enters) and a GTO that has a pegiree of 300km is very very small, something like some tens of meters/sec. If a payload can raise it's orbit from 300km pegiree-GTO to GEO it can also raise it's orbit from 70km pegiree-GTO to GEO(unless it uses electric propulsion). Delta-v is not the problem here.
My point exactly. The payoff with this is no propellant needed for the de-orbit burn.
No propellant needed is not a big win compared to something like "100 kg of propellant needed". Deorbiting from some 300 km-pegiree GTO requires only VERY small deorbit burn at apogee.

suborbital seconds stage is a solution to non-existing problem, introducing much worse problems.

Whatever engines they are using for landing burn, they can very cheaply use same engines for deorbit burn.
« Last Edit: 04/13/2017 07:42 PM by hkultala »

Offline JasonAW3

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Re: F9 Second Stage Reusability
« Reply #347 on: 04/13/2017 07:55 PM »
Would Kestrels would make good landing engines?  They don't use turbopumps, right fuel, thrust seems in the right range for landing, and they're already a proven technology for SpaceX.  Instead of using dead weight for ballast in the nose, that space could be a tank, fuel could be pumped between ballast and main tanks to shift center of gravity so your landing fuel is also your ballast.
The problem with a pressure fed engine is the additional mass for the propellant tanks, since they have to be at higher pressure than the combustion chamber.

Another option might be electric pumped. The Rutherford engine by Rocket Lab has similar thrust to Kestrel, is 3D printed, and uses kerolox. If SpaceX wanted another engine of this type it likely wouldn't much harder to develop than SuperDraco, or they might license Rutherford from Rocket Lab. SpaceX typically doesn't use 3rd party engines but I think that's mostly because 3rd party engines cost too much and don't do enough to optimize manufacturing, neither of which is true here.
That miniature Raptor/methane/BFS idea is looking better all the time...

The question I have is; how well can that setup be scaled?

       Obviously some design compromises would creep into the equation, but depending on whether or not the designed in a significant amount of additional tolerances, it might work.

        I suspect the square-cube law might be an issue here.  Would have to have someone with more time than myself to run the numbers to see if such a subscale idea is even possible.  (Yes, I DID suggest building a subscale version of the BFR/ITS, but that was strictly for testing, not achieving orbit).
My God!  It's full of universes!

Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #348 on: 04/13/2017 08:07 PM »
I think I like the modular approach.
One module which closely resembles the bottom half of dragon.
Heat shield, draco's, CH6N2 and N2O4 tanks, parachute optional.
Maybe grid fins near the S2 merlin engine.
One module to either include or not.
Grid fins to include or not.

Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Online stcks

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Re: F9 Second Stage Reusability
« Reply #349 on: 04/13/2017 08:09 PM »
Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?

The S2 attaches to the trunk, which attaches to the dragon with the attachment points on the bottom: http://i.imgur.com/s7yORbX.jpg
« Last Edit: 04/13/2017 08:11 PM by stcks »

Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #350 on: 04/13/2017 08:36 PM »
Question how does S2 attach to dragon capsule now? With the heat shield sort of in the way? Maybe around the edges?

The S2 attaches to the trunk, which attaches to the dragon with the attachment points on the bottom: http://i.imgur.com/s7yORbX.jpg

I was wondering how the trunk attaches with the heat shield in the way. Your picture shows circular (maybe 6") things around the outside. Maybe 6 of them. So would the Payload Adapter attach to these points in the modular approach? Are these circular things heat resistant?
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline CharlieWildman

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Re: F9 Second Stage Reusability
« Reply #351 on: 04/13/2017 11:49 PM »
CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!

To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.
A small amount of knowledge can be a dangerous thing.

Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #352 on: 04/14/2017 12:02 AM »

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

Would the almost existing titanium grid fins be good enough for reentry velocity. The front picax should break the front and reduce the heat on the back? For peak heating keeping the stage straight into the blast would be best. After peak heating grid fins should be able to steer it a lot. Elon said on the S1 a L/D of 1.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #353 on: 04/14/2017 12:09 AM »
1 kg and the size of a dinner plate...

https://linuxacademy.com/blog/space/comparing-heat-shields-mars-science-lab-vs-spacex-dragon/

Quote
One improvement that PICA-X represents is greater ease of manufacturing. Like many things at SpaceX, PICA-X is made in-house and at a fraction of the cost of NASAs PICA. Produced in large pieces and then cut into tiles about the size of a cafeteria tray they are placed, in a similar fashion to the MLS shield, on to a carbon-composite mold. The tiles are about 3 in (8 cm) thick, and weigh about 2 lbs (1 kg).
« Last Edit: 04/14/2017 12:10 AM by rsdavis9 »
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #354 on: 04/14/2017 06:38 AM »
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm or close, really that light.

Online docmordrid

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Re: F9 Second Stage Reusability
« Reply #355 on: 04/14/2017 07:03 AM »
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm or close, really that light.

I've seen 0.35 and 0.38g/cm, but that was PICA-X 1.0 and Dragon 2 is 3.0. If it's as black as portrayed how should we interpret that, more carbon / less phenolic? What does that do to density?
DM

Offline Elmar Moelzer

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Re: F9 Second Stage Reusability
« Reply #356 on: 04/14/2017 07:19 AM »
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm or close, really that light.
This and other sources I have seen claim 0.27g/cm3
https://solarsystem.nasa.gov/docs/13_Stackpoole-Poster.pdf
« Last Edit: 04/14/2017 07:20 AM by Elmar Moelzer »

Offline Lar

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Re: F9 Second Stage Reusability
« Reply #357 on: 04/14/2017 11:40 AM »
Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.

I saw it mentioned a few days ago. But my poor memory has only slightly denser than balsa wood. I am pretty sure it is 0.38g/cm or close, really that light.
This and other sources I have seen claim 0.27g/cm3
https://solarsystem.nasa.gov/docs/13_Stackpoole-Poster.pdf
How does that compare to shuttle tiles? Not AS good I think?

Quote
The HRSI tile was composed of high purity silica fibers. Ninety percent of the volume of the tile was empty space, giving it a very low density (9 lb/cu ft or 140 kg/m3) making it light enough for spaceflight.
[1] .... which is .14g/cm3 if I got my math right[2]

From the same article here are the other densities. To convert to g/cm3 shift the decimal point 3 places leftward

Quote
While RCC had the best heat protection characteristics, it was also much heavier than the silica tiles and FIB blankets, so it was limited to relatively small areas. In general the goal was to use the lightest weight insulation consistent with the required thermal protection. Weight per unit volume of each TPS type:
RCC: 1986 kg/m (124 lb/ft)
LI-2200 tiles: 352 kg/m (22 lb/ft)
FRCI tiles: 192 kg/m (12 lb/ft)
LI-900 (black or white) tiles: 144 kg/m (9 lb/ft)
FIB blankets: 144 kg/m (9 lb/ft)

1 - from https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
2 - well, if Google did...   https://www.google.com/search?q=convert+140+kg%2Fm3+to+g%2Fcm3
« Last Edit: 04/14/2017 11:47 AM by Lar »
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Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #358 on: 04/14/2017 01:05 PM »
Found this:

Here's what I have....

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36039.0;attach=621091;sess=43050

Quote
PICA-X heat shield material boasts a density of only 0.27 g/ cm3, near the density of solid cork (0.24 g/cm3) [22]. The material needs only be a few centimeters thick (typically around 6 cm)


With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #359 on: 04/14/2017 01:17 PM »
CG with out nose weight looks quite scary to this untrained eye.  Adding 5 tons of nose weight  gets it looking possible.

Maybe it wont take 5 tons.  Maybe just 3 tons... But still...  Yikes!

To me it looks better than expected. Instead of ballast at the top drag devices at the back will be much lighter and get it stable as well. Drag and steering plates folding out at the bottom are quite simple and lightweight. They need to be covered with PicaX heatshields.

Planning to add drag 'flaps' to the model in the next couple days to see how it looks and get an idea how much the flaps will weigh.   Is PicaX density known?  Couldn't find it searching the web.
Charlie, your drag flap components and actuators are going to impact your CoG much more significantly than any TPS estimates due to their relatively low densities...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

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