Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)  (Read 609585 times)

Offline cppetrie

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #80 on: 10/09/2017 03:20 pm »
So far the biological route regens the O2 but creates biomass which does not seem to have much use.
On Mars? It will be very useful indeed.
A one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.
https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.html

This could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.

So it is possible to get the consumables down to 2kg/day per person. Mostly food and some water with a little bit of O2 to replace losses in the recycling system. A water tank will be needed to store the excess water generated over time because this is where some of the losses in the regen system for O2 will end up. Also a tank to store the waste sludge to be useful in farming at a latter date.

At this rate stored consumables for 1 year for 1 person comes to 730kg. For 100 persons 73mt/yr. The weight of the person plus 400kg for personal baggage would make up the full weight capability of a BFR long duration flight and have enough consumables for their support for 1 year to handle any contingencies a 4X over supply of consumables for the expected duration of the trip. For the initial manned landings that 73mt of supplies must last 2X times the expected duration before an assured resupply event occurs. This duration is posited at being ~6.5 years or 3 synods. A 2X supply would be enough supplies for each person for 13 years. so that 73mt results in a crew size of 7.

If the assumption is only 2 synods for max time for resupply then a crew size of 11.

If the assumption is only 1 synod for max time for resupply then a crew size of 23.

Remember in all cases the available supply is 2X needed to handle unforeseen contingencies and losses.
Is that all on just one ship? The current plan is send 2 crew and 2 cargo on the second wave. Could some of those supplies be on a cargo vessel? Also, would some of it be preservable enough that it could be pre-staged by a cargo ship in the first wave so you know it landed safely and is ready and waiting for you?

Online ZachF

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #81 on: 10/09/2017 03:29 pm »
By the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t).  Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC.  (!)
I've been trying to rocket-equation this, with little success. 

Here are the "knowns".
GLOW 4400 t
Thrust Liftoff 5400 t, ISP = 330/356 sec
Ship dry mass 85 t
Ship Mp 1100 t
Ship Thrust 775 t (4 engines) ISP 375 sec
Ship Thrust 347 t (2 SL engines) ISP 330/356 sec

These imply a first stage mass = 4400 t - 1185 t = 3215 t
Unknown is first stage propellant mass fraction. 
When I plug the known numbers into the rocket equation, I get a first stage PMF required to be 0.97938 to get 250 tonnes to 9,200 m/s ideal delta-v (LEO).  That's unrealistic because the first stage ends up with 20 tonnes lighter dry mass than the second stage "Ship".  With PMF1 a more "reasonable" 0.96, I get total ideal delta-v = 9061 m/s, not usually good enough for LEO, but it depends on the details of the ascent.  To get 9200 m/s with PMF1 = 0.96, payload maximum is 235 tonnes.

S1:  3215 t > 128.6 t, ISP 347.4 sec, delta-v = 3734 m/s
S2:  1185 t > 85 t, ISP 375 sec, delta-v = 5479 m/s
PL:  235 t, delta-v total = 9217 m/s

When I try to model the reusable alternative, assuming 10% propellant saved for first stage flyback landing and 6% for second stage retro and landing, I get only 105 tonnes of LEO payload, as follows.

S1:  3215 t > 437 t, ISP 347.4 sec, delta-v (ascent) = 3265 m/s
S2:  1185 t > 151 t, ISP 375 sec, delta-v (ascent) = 5446 m/s
PL:  105 t, delta-v total = 9211 m/s

Rough guesses, obviously, but I've yet to match the SpaceX charts.  When I try to model the 20 tonne GTO mass, the numbers don't converge at all.  I get no payload to GTO.

 - Ed Kyle
A big incorrect assumption here: that 9.2km/s is required. Technically the absolute minimum energy for a 200km orbit (i.e. Including the potential energy from 200km altitude) above the equator (so using Earth's spin to maximum effect) is just 7.5-7.6km/s.

BFR doesn't use hydrogen, so it should get lower aero losses and higher averaged thrust to weight ratio (since your tanks empty sooner). Therefore the benchmark 9.2km/s need not apply, and I am nearly certain I've seen a legitimate estimate for BFR that shows a trajectory of 8.9something km/s to orbit.

If you use the exact same mass fraction as last year's ITS booster (slightly better than 96%) and your numbers for Isp and stage mass, then you get 250 tons expendable to LEO at about 8.99km/s. That fits perfectly with all the rest of the info we have.

No mystery. If you try to mess with SpaceX's numbers to fit more conservative assumptions, then of course you'll not be able to recreate their figures. That's not a mystery, either.

I can get it to work for 9.3Km/s, anyway.

In fact, after further review, I think the payload numbers listed for the BFR are for the spaceship variant, not the cargo variant. I think the cargo variant will be capable of ~190 tonnes to LEO and ~55 tonnes to GTO with no refuel. Here is a Delta V chart estimate for Spaceship, Cargo, Tanker, and expendable with a list of notes.

1.) The yellow numbers are known numbers. They provide the foundation for this estimation.

2.)The original ITS had a payload of 300 tonnes, and a weight of 150 tonnes. There was no cargo variant listed, but there was a tanker variant that weighed 90tonnes. A theoretical cargo variant would have probably weighed ~100 tonnes and had a payload of >350 tonnes to LEO.

3.) The original ITS Spaceship had a landing tank of 50 tonnes. This was obtained by taking its 1,950 tonne fuel tank, subtracting 5x380 tonne tanker load required for refill, and correlating it measurements of the physical tanks from the CAD drawing.  Both seem to suggest a 50 tonne landing tank in the original ship, which would have provided a 920m/s dV for landing, this is what forms the basis for landing requirements of the upper stages. It is likely that with the addition of the delta wing, and a smaller ship having a greater sectional density, that this requirement is less in the new iteration.

4.) The original booster used 7% of it's fuel load to land, which provided ~320m/s less delta V than the booster imparted on the stage itself. This provided the basis to estimate landing fuel requirements for the various models. The weight of the booster is based on posted mass fractions of the previous ITS booster.

5.) The original ITS tanker variant had a 380 tonne to LEO payload, this was accomplished by having a larger fuel tank than the spaceship, even when accounting for the transfer. The original Tanker had a 2,400 tonne fuel tank, with 380 tonnes delivered to LEO. This means that it has 2,020 tonnes of fuel compared with 1,950 tonnes in the spaceship. The extra 70 tonnes is used to push up the higher payload. The BFR tanker will need to have a LEO payload of excess fuel around 210 tonnes in order to refill a BFS in 5 launches. I have estimated the tank, therefor, for the tanker variant to be around 1,400 tonnes. The empty weight of the tanker is based on the ratio of the previous iteration (90t vs 150t)

Im sure I'll think of more notes later
I've uploaded the XLS file if you want to play around with the numbers
« Last Edit: 10/09/2017 03:31 pm by ZachF »
artist, so take opinions expressed above with a well-rendered grain of salt...
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Offline oldAtlas_Eguy

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #82 on: 10/09/2017 03:47 pm »
Using the posited 2kg/person per day values:

A Lunar mission using the Lunar mission scenario encompassing a 6 month stay would be comprised of:
NOTE I do not think SpaceX actually specified how much payload for this scenario.

If 20mt payload to surface with 50% supplies for crew ->13 crew and 5.5mt of cargo to be left on surface.

If 50mt payload to surface with 50% supplies for crew ->34 crew and 13.5mt of cargo to be left on surface.

If the full 150mt payload to surface with 50% supplies for crew -> 100 crew (full complement) and 41mt of cargo to be left  on surface.

Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #83 on: 10/09/2017 04:35 pm »
A one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.
https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.html

This could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.
How intriguing. It recalls the "SolChem" project of the US Navy in the early 80's. Essentially the NRL's effort to work out what it would take to keep the USN on the high seas if the US was cut off from external oil supplies, using solar thermal conversion and molten salt conversion heat storage built entirely from resources found in the US.

Those guys thought on a very large scale.

However this will be a very hard sell as this TRL1 or 2 level at best.  A catalyst better matched to the solar spectrum moves things along a lot.

It certainly suggests other options are possible. That said a fully closed cycle ECLSS system would carry everything it brought from Earth to Mars. Long term it would be better if that had been converted into something that was usable on the surface.
« Last Edit: 10/09/2017 04:58 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline oldAtlas_Eguy

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #84 on: 10/09/2017 04:59 pm »
A one step process to remove the CO2 and process some of the recovered water to produce CH4 and O2.
https://phys.org/news/2016-02-proven-one-step-co2-liquid-hydrocarbon.html

This could be used to recycle the O2 and then make a useful and easily stored byproduct CH4 which can be liquefied and stored in the large LCH4 tank. Excess O2 can be liquefied and stored in the LOX tank. But there is unlikely to be any excess O2.
How intriguing. It recalls the "SolChem" project of the US Navy in the early 80's. Essentially the NRL's effort to work out what it would take to keep the USN on the high seas if the US was cut off from external oil supplies, using solar thermal conversion and molten salt conversion heat storage built entirely from resources found in the US.

Those guys thought on a very large scale.
Which is what should be thought of when trying to design a system to regen for a crew size of 100 or several 1,000s in a base or colony. Tiny systems designed for crew sizes of 6 is not what is needed.

This also brings up thoughts on regeneration of packaging. Plastic packaging including aluminum coated plastic can be ground into a fine powder melted to remove the plastic then the remaining aluminum melted to produce ingots of 3D printer blanks for a plastic and aluminum 3D printers. But this would not be done on the BFR but at an established base or colony.

Also the waste sludge would also be processed at a base or colony and not on the BFR. The BFR would just store it and offload at destination where it becomes a useful commodity able to be processed by a large industrial size system.

Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #85 on: 10/09/2017 05:08 pm »
A packaging recycling machine that spits out 3D printer filament is being flown to Station soon.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #86 on: 10/09/2017 05:31 pm »
A packaging recycling machine that spits out 3D printer filament is being flown to Station soon.
That's a good start too.

It's pretty clear that any flights will continue to use a lot of packaging and being able to convert it into something useful will pay major dividends into the future.

The challenge of course is to see what (and how much) of the ships components can be resigned to use the parts that can be made.  Ideally you'd want them to be made on a bigger version of the same machine on Earth of the same material, but I don't see that happening much without a lot of effort.  :(
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Steve D

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #87 on: 10/09/2017 07:45 pm »
Organic waste from 100 people on board the BFR should produce a fair amount of methane on its own. Any thoughts on how much could be produced during a 4 to 6 month voyage and if it would be worth collecting?

Offline Johnnyhinbos

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #88 on: 10/09/2017 07:50 pm »
This is an interesting conversation. Perhaps it should be continued on the "BFS - the Human Factors - Updates and Discussion" thread. Regardless, I'll cross link over there...

https://forum.nasaspaceflight.com/index.php?topic=43884.0
John Hanzl. Author, action / adventure www.johnhanzl.com

Offline dror

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #89 on: 10/09/2017 08:13 pm »
...
Also if 3 tankers accompany the deep space mission into a 4.2km transfer orbit that returns the tankers back to Earth, the total DV for the Deep Space Mission could be as high as 12km/s. This can be done as well from LEO but since you loose nearly 4km/s by not leaving from L2 would be like the first case L2 deep space mission...

Is it possible to design a mission in  a similar manner, which could land on Mars with enough fuel for take off without ISRU?
Maybe another fueled tanker could wait at LMO.
How many flights will it require in total?
what payload could it take and bring back?

Space is hard immensely complex and high risk !

Offline maitri982

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #90 on: 10/09/2017 10:54 pm »
Since I could not reply to Ed's post on the prior thread and quote it here, i want to note that making extrapolations on Musk projects by looking back at what he said in 2005 is ridiculous really.

He was very new to running a rocket company and had a helluva lot to learn.  Couple that with his typical over enthusiasm for forecasting shorter than realistic time frames and you got things that turned out to appear to be wildly optimistic.

BUT...he is a veteran now of creating brand new rocket engines, air frames, spaceships, software, electronics, assembly lines, friction stirred tanks and on and on and the result is he is MUCH smarter nowadays.  I run a software company and i can say that my own ability to forecast project time frames is much better than it was in 2005 when i started the company since i have a bunch of experience to go on now.

We still have to take account for his aggressive nature for time frame predictions, but i would guess his margin for error is quite lower now than it was 12 years ago.  So before it was probably like add ~5 years onto estimates and now I would guess its add <~2 years.


Offline intrepidpursuit

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #91 on: 10/09/2017 11:42 pm »
My biggest concern with BFS is the heat shield. It covers a massive area. Nothing will fall on it and it shouldn't be in bird range while going fast enough to lose a battle, but MMOD damage seems like a real risk. It may be that because of its size and corresponding lighter heat load that it could take the inch or two damage that is likely from an MMOD strike and survive reentry. It certainly seems like a potential problem at really high flight rates.

It is also inevitable that the heat shield will have to be replaced fairly regularly. (It is PICA-X so it is ablative right? why was it rendered silver...) Whether it is 10 flights or 100 flights it will likely be a pacing factor in refurbishing the ship. Tiles seem like the most likely method considering they are being used for dragon. It would be hard to make a shield as difficult to maintain as shuttle's, but it will still require a huge number unique tiles to be removed and reapplied and in this case they have to be replaced with new tiles or remanufactured.

Are there any other technologies that may be helping them avoid these issues do they just consider them manageable?

Offline CapitalistOppressor

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #92 on: 10/10/2017 04:01 am »
My biggest concern with BFS is the heat shield. It covers a massive area. Nothing will fall on it and it shouldn't be in bird range while going fast enough to lose a battle, but MMOD damage seems like a real risk. It may be that because of its size and corresponding lighter heat load that it could take the inch or two damage that is likely from an MMOD strike and survive reentry. It certainly seems like a potential problem at really high flight rates.

It is also inevitable that the heat shield will have to be replaced fairly regularly. (It is PICA-X so it is ablative right? why was it rendered silver...) Whether it is 10 flights or 100 flights it will likely be a pacing factor in refurbishing the ship. Tiles seem like the most likely method considering they are being used for dragon. It would be hard to make a shield as difficult to maintain as shuttle's, but it will still require a huge number unique tiles to be removed and reapplied and in this case they have to be replaced with new tiles or remanufactured.

Are there any other technologies that may be helping them avoid these issues do they just consider them manageable?

IIRC in his most recent presentation Elon made a fairly strong claim that the heat shield would only experience noticible ablation during a Mars Entry, and would not do so when entering Earths atmosphere.

Offline oiorionsbelt

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #93 on: 10/10/2017 04:14 am »
(It is PICA-X so it is ablative right? why was it rendered silver...)
IIRC the silver lining is a layer put on to prevent moisture intrusion prelaunch. It wasn't used on the first few launches, again IIRC.

Offline intrepidpursuit

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #94 on: 10/10/2017 04:18 am »
My biggest concern with BFS is the heat shield. It covers a massive area. Nothing will fall on it and it shouldn't be in bird range while going fast enough to lose a battle, but MMOD damage seems like a real risk. It may be that because of its size and corresponding lighter heat load that it could take the inch or two damage that is likely from an MMOD strike and survive reentry. It certainly seems like a potential problem at really high flight rates.

It is also inevitable that the heat shield will have to be replaced fairly regularly. (It is PICA-X so it is ablative right? why was it rendered silver...) Whether it is 10 flights or 100 flights it will likely be a pacing factor in refurbishing the ship. Tiles seem like the most likely method considering they are being used for dragon. It would be hard to make a shield as difficult to maintain as shuttle's, but it will still require a huge number unique tiles to be removed and reapplied and in this case they have to be replaced with new tiles or remanufactured.

Are there any other technologies that may be helping them avoid these issues do they just consider them manageable?

IIRC in his most recent presentation Elon made a fairly strong claim that the heat shield would only experience noticible ablation during a Mars Entry, and would not do so when entering Earths atmosphere.

I heard him say, "It is a multi-use heat shield, but unlike for Earth operations, it's coming in hot enough that you really will see some wear of the heat shield." But that passing reference isn't enough for me to believe that a heat shield would get more use in mars' thin atmosphere than earth's atmosphere. Bleeding off the speed propulsively makes reusability sense, but would use an incredible amount of fuel. Hard to believe that is the plan.

Offline intrepidpursuit

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #95 on: 10/10/2017 04:21 am »
(It is PICA-X so it is ablative right? why was it rendered silver...)
IIRC the silver lining is a layer put on to prevent moisture intrusion prelaunch. It wasn't used on the first few launches, again IIRC.

If they are planning to put that on BFS that is a huge project every launch by itself. It is shown on the booster too. That seems very unlikely.

Offline KelvinZero

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #96 on: 10/10/2017 05:56 am »
Hi, any thoughts what goes into the top two windowless levels of the BFS?

Link to image from presentation here:

...

Offline Torbjorn Larsson, OM

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #97 on: 10/10/2017 06:37 am »
How much and how big would all the ECLSS equipment be for the support of 100 people for a couple of years?
Turn the question on its head.

The NASA baseline for crew consumables is 5Kg/person/day, of which maybe 3.5Kg is water.

So is that part of the ECLSS solution for the trip? If 150 mt ascent and 50 mt descent cargo mass is the generic load (but is it?) then the BFS "has to" get rid of 100 mt during travel. For Mars with 6 months travel that is about 1 mt/person, or 100 mt for the fully crewed ship.

Venting used consumables would remove some heat as well (~ 0.5 kWh/day if superheated steam, I think) but I guess not enough to take care of the cooling needs.

EDIT: Clarified wording.
« Last Edit: 10/10/2017 06:41 am by Torbjorn Larsson, OM »

Online Cheapchips

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #98 on: 10/10/2017 07:16 am »
Organic waste from 100 people on board the BFR should produce a fair amount of methane on its own. Any thoughts on how much could be produced during a 4 to 6 month voyage and if it would be worth collecting?

I did a cursory look into this a while ago. Human digestion produces very little methane.  In terms of sold waste, we produce around 127kg a year.  I'm sure it'll be useful for something on Mars, but it's not going to contribute to ISRU.

Offline HVM

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #99 on: 10/10/2017 07:29 am »
(It is PICA-X so it is ablative right? why was it rendered silver...)
IIRC the silver lining is a layer put on to prevent moisture intrusion prelaunch. It wasn't used on the first few launches, again IIRC.

Does the Big frakking Sponge ohhh, I mean spacecraft need to be painted after every reentry? BFS really need real reusable thermal protection system; Toughened Uni-piece Fibrous Reinforced Oxidation-Resistant Composite or other similar solution.
« Last Edit: 10/10/2017 07:30 am by HVM »

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