Author Topic: F9 Second Stage Reusability  (Read 212795 times)

Offline tyrred

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Re: F9 Second Stage Reusability
« Reply #880 on: 07/16/2018 07:40 AM »
With the absence of information on recent S2 reusability tests, which of the upcoming missions look to be prime candidates for S2 reusability testing? 
Which missions look like S2 reusability testing would be off the table?
Fairing recovery efforts are showing much more visible progress, would it be more prudent to focus on nailing fairing recovery first and then going full steam ahead on S2 recovery techniques?
A highly orchestrated series of events has to happen for a fully recovered Falcon 9 launch to become a reality, I don't envy the people hard at work on this effort (the team in charge of orchestrating live coverage included).  I wish SpaceX the best in this effort, though, as it would be a spectacular event to witness when/if finally achieved.
« Last Edit: 07/16/2018 07:53 AM by tyrred »

Online speedevil

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Re: F9 Second Stage Reusability
« Reply #881 on: 07/16/2018 10:56 AM »
With the absence of information on recent S2 reusability tests, which of the upcoming missions look to be prime candidates for S2 reusability testing? 
Which missions look like S2 reusability testing would be off the table?
It is probably strong to say 'none' - which might be the case if they were willing to swap out FH for F9. Especially as not all customers would be willing to do that.

Payload trade is pretty much 1:1 - but it's possible initial testing may be with limited hardware with the stage not intended to survive.
For example, a trailing ballute and inflation system which might weigh 1000kg.

GTO missions are doubly questionable - they are a lot harder, and giving a near max weight satellite 300m/s less may not fly commercially.
A useful metric might be 'any mission that can do RTLS' has comfortable margin.

On the other hand - GTO missions are most missions, so not trying for those leaves a moderate amount on the table, unless it's not unreasonably decided it doesn't matter due to changing orbit mix as Starlink et al come on line.

Propellant transfer in some manner could also make GTO work with no (or negative) penalty at lower total cost to spacex, though raises its own issues.

Offline darkenfast

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Re: F9 Second Stage Reusability
« Reply #882 on: 08/24/2018 05:04 AM »
We have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast.  Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"?  Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?

Online Bananas_on_Mars

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Re: F9 Second Stage Reusability
« Reply #883 on: 08/24/2018 05:45 AM »
We have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast.  Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"?  Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?
Could well be, but what i have read is that it's for Dragon recovery, being pulled by Mr. Steven. Of course once you have a bouncy castle or a big net, S2 recovery can use that too. I think the most likely candidate for S2 recovery is a CRS mission. They recently deorbited a S2 after a CRS? mission over the middle of the atlantic, a lot of people said it was simply a longevity test for S2, i suspect it was a precursor to S2 recovery.

Offline darkenfast

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Re: F9 Second Stage Reusability
« Reply #884 on: 08/25/2018 06:17 AM »
We have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast.  Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"?  Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?
Could well be, but what i have read is that it's for Dragon recovery, being pulled by Mr. Steven. Of course once you have a bouncy castle or a big net, S2 recovery can use that too. I think the most likely candidate for S2 recovery is a CRS mission. They recently deorbited a S2 after a CRS? mission over the middle of the atlantic, a lot of people said it was simply a longevity test for S2, i suspect it was a precursor to S2 recovery.

Okay, but has anybody from SpaceX said the inflatable is for Dragon recovery?

Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #885 on: 08/25/2018 07:07 AM »
Okay, but has anybody from SpaceX said the inflatable is for Dragon recovery?

It comes from a Teslarati article. They usually base things like that on insider info.

Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #886 on: 08/25/2018 01:40 PM »
I donít know, I havenít seen as careful attention to detail and verification as I have with NSF articles.
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Online rakaydos

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Re: F9 Second Stage Reusability
« Reply #887 on: 08/25/2018 05:37 PM »
I donít know, I havenít seen as careful attention to detail and verification as I have with NSF articles.
By the name, I expect they're car nerds more than rocket nerds. they may be misunderstanding the insider info they get.

Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #888 on: 08/25/2018 07:20 PM »
I donít know, I havenít seen as careful attention to detail and verification as I have with NSF articles.
By the name, I expect they're car nerds more than rocket nerds. they may be misunderstanding the insider info they get.
Judging by the name, this forum is about NASA...

Judging by the contents, however, both sites are knowledgeable and careful about what is posted.

-----
ABCD: Always Be Counting Down
« Last Edit: 08/26/2018 02:59 PM by meekGee »
ABCD - Always Be Counting Down

Online Bananas_on_Mars

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Re: F9 Second Stage Reusability
« Reply #889 on: 08/26/2018 06:02 AM »
Well, the guy responsible for the articles in question is quite active on this forum too...

This is the article about the inflatable structure and other means of dragon recovery.

Offline Lar

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Re: F9 Second Stage Reusability
« Reply #890 on: 08/26/2018 02:19 PM »
Teslarati, IMHO are among the better techie sites giving significant coverage to Musk endeavours. I take what is written with a grain of salt, knowing some is speculation, but I beleive it to be informed and earnest speculation so am OK with it. Also Vaporcobra is always open to correction or amplifications.

What that trampoline skin writ large being towed around is anyone's guess though.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #891 on: 08/27/2018 04:09 AM »
Yeah, I know teslarati means well, but NSF has set the bar very high and Teslarati is still relatively new to covering space. Just saying we don't know for certain this giant rubber inflatable kiddie pool is meant for Dragon recovery.
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Offline Lar

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Re: F9 Second Stage Reusability
« Reply #892 on: 08/27/2018 05:01 AM »
Yeah, I know teslarati means well, but NSF has set the bar very high and Teslarati is still relatively new to covering space. Just saying we don't know for certain this giant rubber inflatable kiddie pool is meant for Dragon recovery.
They are among the best. This site is THE best.[1]

Back on topic, k?

1 - I might be biased.
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline jbenton

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Re: F9 Second Stage Reusability
« Reply #893 on: 08/28/2018 12:23 AM »

Physics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.


The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg.  Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.

edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.

Delta IV CBC: 8738 m/s
Atlas V CCB: 8851 m/s

Surprisingly close.
Look at earlier Atlas variants, and youíll see mass ratios closer to what I was saying.

Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.


(Also, look at falcon 9).

IF you want to look at sensitivity to propellant choice, you should control for other variables. Atlas V and Delta IV use similar aluminum isogrid tank construction. Falcon 9 uses Aluminum-Lithium while previous Atlas vehicles used steel balloon tanks that couldn't support their own weight.

Another example: S-IVB vs Falcon 9 upper stage: they have comparable wet mass, thrust, wet TWR, engine cycles, and the F9 US has slightly better delta-v with a 6000 kg payload (~8400 m/s vs ~8100). But the F9 US has less than half the dry mass, in a much smaller footprint of 3.7x12 m instead of 6.7x18 m. Both factors would make it much easier to return from space: everything related to control, entry, and landing can be smaller and lighter.

Granted, the F9 US is Al-Li alloy instead of Al alloy, and uses FSW instead of arc welding. But the S-IVB is still a good example of a excellent dry mass fraction among restartable LH2 upper stages, so new tech hasn't improved the SOA that much to date.

Using LH2 ties up a lot of dry mass in tanks, insulation, engines, and subsystems to support those larger and heavier components.

I saw this in the Stratolaunch thread, and was surprised to learn that the Falcon 9 upper stage has better delta-v than a S-IV (I guess it depends on the mass of the payload though)

I was under the understanding that the F9 US was "low-energy" because of it's low Isp (relative to a hydrolox stage) but I guess it makes up for it with low payload mass fraction.

So just how low-energy is it? I figured I'd ask on a dedicated Falcon 9 Second Stage thread so as to not derail the other thread; this one seemed the best place to ask.
« Last Edit: 08/28/2018 06:38 AM by jbenton »

Offline jbenton

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Re: F9 Second Stage Reusability
« Reply #894 on: 08/28/2018 12:25 AM »
We have seen Mr. Steven playing with a big circular inflatable toy off the Southern California coast.  Didn't Musk hint that recovery of the 2nd Stage (if it ever happened) might involved giant "bouncy castles"?  Could this inflatable be laying the ground work for an upper stage recovery test at some point in the future (as opposed to fairing or Dragon catching)?
Could well be, but what i have read is that it's for Dragon recovery, being pulled by Mr. Steven. Of course once you have a bouncy castle or a big net, S2 recovery can use that too. I think the most likely candidate for S2 recovery is a CRS mission. They recently deorbited a S2 after a CRS? mission over the middle of the atlantic, a lot of people said it was simply a longevity test for S2, i suspect it was a precursor to S2 recovery.

Out of curiosity about long can a S2 last?

Offline jbenton

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Re: F9 Second Stage Reusability
« Reply #895 on: 08/28/2018 12:27 AM »
Also, how what's the dry mass of the S2? That would help us better speculate if the "bounce house"/"kiddie pool" can support a Second Stage recovery, I'd think

Offline WTF

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Re: F9 Second Stage Reusability
« Reply #896 on: 08/28/2018 06:22 AM »
Re: 'dry mass of Stage 2' ...

Wikipedia (as of May, 2017) indicates the second stage full thrust Falcon 9 ...

"Mass (without propellant)" is 4,000 kg (8,800 lbs).

Vertical descent velocity is a pertinent question.

EDITED punctuation.
« Last Edit: 08/28/2018 06:24 AM by WTF »
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Offline jbenton

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Re: F9 Second Stage Reusability
« Reply #897 on: 08/28/2018 06:37 AM »
Re: 'dry mass of Stage 2' ...

Wikipedia (as of May, 2017) indicates the second stage full thrust Falcon 9 ...

"Mass (without propellant)" is 4,000 kg (8,800 lbs).

Vertical descent velocity is a pertinent question.

EDITED punctuation.

Thanks! I was asking, 'cause there is talk of using the floating pad thing for Dragon-catching, and I figured that the mass was similar for both - coming from re-entry velocity, they would be coming down with similar momentum.

Wikipedia says that Dragon 2 has a Dry Mass of 6,400 (odd that I didn't notice that in the Falcon article, better use Ctr-F next time! ;D)

Online Semmel

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Re: F9 Second Stage Reusability
« Reply #898 on: 08/28/2018 07:03 AM »
S2 can last at least 6 hours, as demonstrated multiple times. First at the FH launch if I remember correctly. 6h is required for direct GSO insertion. (following numbers from spaceflight101) It has an estimated propellant mass of 107500 kg with an ISP of 348. Lets say we have a payload of 2000kg, then the dv would be
dv = ISP * g * ln ( (drymass + payload + propellant) / (drymass + payload) )
dv_S2 = 348s * 9.81m/s^2 * ln((4000kg + 2000kg + 107500kg)/(4000kg + 2000kg)) = 10036 m/s.

If it sits on a F9, the first stage might induce a dv of about 4000 m/s (same computation, different numbers) if it is expanded. Together, F9 has a dV of roughly 14000 m/s for a payload of 2000kg. I have no idea how to do the computation for FH.

For reaching LEO, about 9000m/s are required (I know its more complicated than that). With rough numbers and estimates, the second stage might be able to put 5000m/s additional dV into the 2000kg payload after LEO.
« Last Edit: 08/28/2018 07:40 AM by Semmel »

Online speedevil

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Re: F9 Second Stage Reusability
« Reply #899 on: 08/28/2018 10:24 AM »
S2 can last at least 6 hours, as demonstrated multiple times. First at the FH launch if I remember correctly. 6h is required for direct GSO insertion.
Demonstrated, but it's unclear how much of the oxygen boils off.

If you put the numbers in for a 3.5km/s burn (tesla injection final), with the second stage at 5000kg and the tesla at 2000, you end up with some 13 tons of propellant remaining before the burn, after a coast and a 1.2km/s burn post LEO to get it to a 7000km apogee.
The initial 1.2km/s burn takes another nine tons.
This would put the LEO mass at 29 tons.
This is pretty close to the upper mass limit of FH in fully reusable mode that anyones come up with.
Which implies not much boils off.

If you assume this is true, this comes out to for a 5 ton S2 and a 2 ton payload, 4.7km/s over LEO.

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