Author Topic: ASDS fly-back recovery  (Read 27812 times)

Offline Lars-J

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Re: ASDS fly-back recovery
« Reply #20 on: 04/10/2016 02:06 am »
Shouldn't this thread be in the "reusability" SpaceX sub-forum, and not here in the "missions" forum?

And there already are existing threads there for this discussion.

Offline drzerg

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Re: ASDS fly-back recovery
« Reply #21 on: 04/10/2016 02:08 am »
and you need to put nose cap on top if it is not side FH booster, where it already installed. with other activities related to rapid reflight such as refueling, folding legs, using hold downs and possible abort launch you need some mobile launch platform which could catch and rotate horizontally whole booster. its weight after drain RP will be less then 20 tons. not big deal.

so in this cas reflight will look like:

1. land on droneship
2. drain lox
3. move mobile launch platform from support ship to drone ship (or where it will be)
4. secure booster with platform. fold legs
5. move whole thing and then rotate horizontally
6. check all you need, install nose cap, fuel tubes and all other needed for launch.
7. put it vertical, refuel and launch with possible abort. 


Online meekGee

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Re: ASDS fly-back recovery
« Reply #22 on: 04/10/2016 02:17 am »
and you need to put nose cap on top if it is not side FH booster, where it already installed. with other activities related to rapid reflight such as refueling, folding legs, using hold downs and possible abort launch you need some mobile launch platform which could catch and rotate horizontally whole booster. its weight after drain RP will be less then 20 tons. not big deal.

so in this cas reflight will look like:

1. land on droneship
2. drain lox
3. move mobile launch platform from support ship to drone ship (or where it will be)
4. secure booster with platform. fold legs
5. move whole thing and then rotate horizontally
6. check all you need, install nose cap, fuel tubes and all other needed for launch.
7. put it vertical, refuel and launch with possible abort.

My list is similar except:
- The "Mobile launch mount" is parked on a deck extension to the side
- Everything stays vertical.  I know, nose cap and all.   Still though.
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Offline ChrisWilson68

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Re: ASDS fly-back recovery
« Reply #23 on: 04/10/2016 02:58 am »
However, keeping pretty big volume of LOX and RP-1 where hot rocket is coming in is a pretty dangerous proposition. Ensured loss of barge in cases, similar to SES9...

Nobody seems to think they would try this until they're flying at least once a day.  When they're flying once a day, they'd better have made SES-9-style crashes very rare.

Offline ChrisWilson68

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Re: ASDS fly-back recovery
« Reply #24 on: 04/10/2016 03:04 am »
One potential issue with "gas and go" from the drone ship is that you don't have hold down clamps. You also have no payload, so the stage is relatively light - even when fuelled - that means even partial engine thrust will possibly give you >1.0 thrust2weight (depending on how many engines are used)

I don't think this is a problem.  There are no hold-downs for the second stage.  There are no hold-downs for the boostback burn.  There are no holddowns for the re-entry burn.  There are no holddowns for the landing burn.  So a lack of holddowns for the burn to launch from the ASDS is not going to make the whole system much more likely to lose a stage.  And no customer payload is at risk.

With lots and lots and lots of launches, the engines will have to be very reliable, or they'll never make lots and lots of launches economically viable.  There's no fundamental reason that with lots of experience they can't make the engines very reliable.

Offline sanman

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Re: ASDS fly-back recovery
« Reply #25 on: 04/10/2016 04:39 am »
Hypothetically, under such a fly-back scenario, wouldn't you no longer really have need for a barge, and could just make it a fixed immobile oil rig or similar platform sitting at a fixed position out at sea? I thought the whole reason it's a barge is so that it can travel with booster back to shore. Otherwise, isn't a fixed rig better - especially if it's acting as a landing pad for many rockets?

Offline Hauerg

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Re: ASDS fly-back recovery
« Reply #26 on: 04/10/2016 04:48 am »
Different flight profiles require different landing coordinates.

Offline sewebster

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Re: ASDS fly-back recovery
« Reply #27 on: 04/10/2016 05:13 am »
Different flight profiles require different landing coordinates.

Would a significant number of flight profiles allow the stage to reach a small number of positions though? For example, could you have one for GTO, one for ISS (or the next space station) and have that cover a lot...?

Offline Impaler

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Re: ASDS fly-back recovery
« Reply #28 on: 04/10/2016 07:00 am »
I have to agree that an oil-rig like structure (specifically the semi-submersible type) would be preferable if their is a high rate of such fly-back launches.  It would be considerably larger landing target, VERY stable and can have the hold-down mechanism and cranes that would likely be necessary for actually readying a core for the fly-back.

Propellants can be stored in the under water pontoons of the structure and tankers can LNG and LOX.  Likewise personnel can shelter in a underwater chamber/escape pod which will be well protected from any landing mishaps.

A landed stage can be moved to an elevator like thouse on aircraft carriers which can take the stage down into a vertical silo where it will be both protected from salt spray and fully inspected.  If an aerodynamic nose cone is necessary for proper flight that can likewise be attached.  Finally the stage is returned to the deck, fueled and launched.  With multiple silos multiple stages can be at the facility so one stage can land while others are still being turned around and a stage deemed unfit to fly dose not block the facility cold.

Contrary to popular belief these things are mobile too, most semi-submersible rigs today use the same dynamic positioning as the current Drone ships and don't even use anchoring cables and they can be towed at around 5 knots which should be comparable to the current Drone ships.  Still I would suspect several such platforms would be needed to accommodate such a high rate of launches.

Lastly platforms of this size are what you would need to land a BFR core on as the current Drone ships are just barely able to accommodate F9.  Their are considerable performance gains in down-range landing over RTLS and BFR needs all the possible performance it can get.

Offline Roga

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Re: ASDS fly-back recovery
« Reply #29 on: 04/10/2016 02:39 pm »
Aerodynamic stability would make flyback difficult. You need to maintain powered flight in the atmosphere to maintain control, and keep dynamic pressure low so you don't need a nosecone, and to limit fatigue cycles on the airframe. But you do need to go exoatmospheric in order to flip add accelerate for crossrange. So you need to ballast for ascent and probably do staged shutdowns as you burn fuel to keep t:w near 1, then throttle up once exo to get ballistic crossrange, then flip the stage and deploy fins for reentry. Additionally you need to constrain the terminal ballast so as not to crush the legs when you land. It seems like an overconstrained problem which may not be tractable without a nosecone or some provision to precision-dump propellants during exo coast.

Online meekGee

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Re: ASDS fly-back recovery
« Reply #30 on: 04/10/2016 02:56 pm »
Aerodynamic stability would make flyback difficult. You need to maintain powered flight in the atmosphere to maintain control, and keep dynamic pressure low so you don't need a nosecone, and to limit fatigue cycles on the airframe. But you do need to go exoatmospheric in order to flip add accelerate for crossrange. So you need to ballast for ascent and probably do staged shutdowns as you burn fuel to keep t:w near 1, then throttle up once exo to get ballistic crossrange, then flip the stage and deploy fins for reentry. Additionally you need to constrain the terminal ballast so as not to crush the legs when you land. It seems like an overconstrained problem which may not be tractable without a nosecone or some provision to precision-dump propellants during exo coast.
I agree that launch back is no mean feat.

You'll launch with 2-3 engines and very partial fuel load.  Stability should be OK since you're under power.

Burn for a similar duration, until out of the atmosphere.  Coast for most of the 1000 km (400 up, 400 down?)

Reentry burn, landing burn.

So half way to a full launch, really.

Which is why this ONLY makes sense in a scenario when rockets are going up on a daily basis or faster, like a concentrated Mars launch campaign, and if there's practically zero service to turn them around.

Otherwise, if you can wait a few days, it's better to ship them back.
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Offline pmonta

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Re: ASDS fly-back recovery
« Reply #31 on: 04/10/2016 04:45 pm »
What might SpaceX be doing to protect the booster from salt spray?  A tarpaulin around the engine area, or perhaps a spray coating that could be removed easily with no residue?  An exposure of several days might not be an immediate issue, but many such might have a cumulative effect.

Offline Archibald

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Re: ASDS fly-back recovery
« Reply #32 on: 04/10/2016 04:57 pm »
I was just reading this
 https://www.nasaspaceflight.com/2015/06/spacex-augments-upgrades-drone-ship-armada/

Quote
In his first “drone ship” tweet, Mr. Musk held out the tantalizing possibility that the drone ships would eventually allow recovered stages to be refueled, launched from the deck, and fly themselves home. Time will tell if SpaceX can make this dream a reality.
So, ok, found this thread  - gimme a break !
 Launch from The Cape, fly to 4000 miles an hour 100 miles high, brake, land on the barge, refuel, lift-off, suborbital leap toward The Cape, landing, reuse.
Folks: this is better than any sci-fi.
« Last Edit: 04/10/2016 05:02 pm by Archibald »
Han shot first and Gwynne Shotwell !

Online CameronD

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Re: ASDS fly-back recovery
« Reply #33 on: 04/11/2016 01:32 am »
I agree that launch back is no mean feat.

You'll launch with 2-3 engines and very partial fuel load.  Stability should be OK since you're under power.

A question on reliability then:  Assuming it's the same 2-3 engines that are used for the landing burn, presumably that means those 2-3 engines will wear out faster than the other 6-7 and require earlier swap-out.  Doesn't having engines with significantly different run-hours decrease the reliability of the re-used stage on the way back up??


What might SpaceX be doing to protect the booster from salt spray?  A tarpaulin around the engine area, or perhaps a spray coating that could be removed easily with no residue?  An exposure of several days might not be an immediate issue, but many such might have a cumulative effect.

I don't see there's anything they can do about it, aside from the usual acid-anodising during manufacture and a fresh-water hose down.  A tarpaulin might actually make things worse by concentrating salt water exposure in a few particular areas.

With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Online meekGee

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Re: ASDS fly-back recovery
« Reply #34 on: 04/11/2016 02:08 am »
I agree that launch back is no mean feat.

You'll launch with 2-3 engines and very partial fuel load.  Stability should be OK since you're under power.

A question on reliability then:  Assuming it's the same 2-3 engines that are used for the landing burn, presumably that means those 2-3 engines will wear out faster than the other 6-7 and require earlier swap-out.  Doesn't having engines with significantly different run-hours decrease the reliability of the re-used stage on the way back up??


What might SpaceX be doing to protect the booster from salt spray?  A tarpaulin around the engine area, or perhaps a spray coating that could be removed easily with no residue?  An exposure of several days might not be an immediate issue, but many such might have a cumulative effect.

I don't see there's anything they can do about it, aside from the usual acid-anodising during manufacture and a fresh-water hose down.  A tarpaulin might actually make things worse by concentrating salt water exposure in a few particular areas.

Yup - except this problem already exists with the reentry and landing engines.
So whatever they do, they have to look at engines individually.

I wouldn't get too far into it until launch rates really go up.  The hardware now is still in the state they later refer to as "we barely knew what we were doing"...   Who knows what other rabbits are going to show up before then.
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Offline Impaler

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Re: ASDS fly-back recovery
« Reply #35 on: 04/11/2016 07:40 am »
Engine usage could be evened out by alternating between two groups of 4 engines in the outer ring of the octo-web.  Alternate these for each launch and everything will be getting similar utilization.

Offline sevenperforce

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Re: ASDS fly-back recovery
« Reply #36 on: 04/11/2016 03:55 pm »
Engine usage could be evened out by alternating between two groups of 4 engines in the outer ring of the octo-web.  Alternate these for each launch and everything will be getting similar utilization.
Especially if they can manage to pull off two-engine landing burns reliably.

Would the first stage really need to go exoatmospheric?

Online envy887

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Re: ASDS fly-back recovery
« Reply #37 on: 04/11/2016 11:42 pm »
Engine usage could be evened out by alternating between two groups of 4 engines in the outer ring of the octo-web.  Alternate these for each launch and everything will be getting similar utilization.
Especially if they can manage to pull off two-engine landing burns reliably.

Would the first stage really need to go exoatmospheric?

It has to flip 180 degrees to land, so the apogee needs to be well above the majority of the atmosphere. A 500 to 1000 km crossrange also requires a lot of ballistic coasting. Basically, the flyback will be a launch in reverse.

Online envy887

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Re: ASDS fly-back recovery
« Reply #38 on: 04/12/2016 12:04 am »
Leasing a cargo ship that has an internal hold big enough for several F9s seems like a logical interim until the flight rate is multiple times per day. A shipboard crane could easily pick the S1 of the barge, drop it on blocks for delegging, and lower it into the hold where it would be protected from salt spray and even inspected and cleaned. A ship could travel 2-3 times faster than a barge while also carrying multiple F9s aboard, substantially increasing throughput over the towed-barge return scheme.

Offline joek

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Re: ASDS fly-back recovery
« Reply #39 on: 04/12/2016 12:43 am »
More likely IMHO is that SpaceX will muddle through with slow-boat return until the next generation LV.  For that next generation LV, RTLS will be the only non-expendable option (as I hope and expect will be the approach for BFR/MCT).  Barge fly-back may seem cool, and lots of interesting challenges... but really... just make the LV so it can always RTLS for the expected range of missions.

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