Falcon Heavy Assembly Underway

kbd512 · 2017-12-20 10:26:19

All,

Well, SpaceX is finally going to make this happen:

Elon Musk Unveils Falcon Heavy Rocket Photos Ahead of Maiden Flight

Yay!

Rusakov · 2017-12-20 11:29:30

Wasn't expecting that this morning. O.o

louis · 2017-12-20 11:44:16

Looking good, Houston!

SpaceNut · 2017-12-20 17:49:31

we have talked about the first mission in another topic....

Falcon Heavy's first payload will be his own midnight-cherry-red Tesla Roadster, launched on a trajectory aimed for Mars orbit. However, Musk has said that there's a fair chance the rocket could fail on its debut test flight.

To which its a tax write off if it makes it and an insurance payout for the failed payload loss.....

kbd512 · 2017-12-20 19:41:57

I'd rather they at least attempted to land a Red Dragon on Mars to get this ISRU and humans to Mars show on the road, so to speak, but it's Mr. Musk's money so it's his call. If it fails, so what. Go big or go home.

louis · 2017-12-20 19:59:20

I don't think Musk is really geared to doing things for show...he has been on a learning curve about what is the quickest way to get humans to Mars. I think the latest BFR proposals make a huge amount of sense and they have generally had good reviews. Better he focuses on those now. 5 years for a cargo BFR to Mars is not long to wait.

kbd512 wrote:

I'd rather they at least attempted to land a Red Dragon on Mars to get this ISRU and humans to Mars show on the road, so to speak, but it's Mr. Musk's money so it's his call. If it fails, so what. Go big or go home.

kbd512 · 2017-12-20 20:05:05

Louis,

Once BFS gets to Mars, then it has to get back home. An airliner is too expensive to build, fly across the world, and then leave it there because there's no gas to get back home.

louis · 2017-12-21 02:14:22

I am not sure whether he needs to fly back the initial two cargo BFSs but, the first human BFS he does. But Space X have all that worked out as regards how they will make the propellant. The major question or issue I think is identifying the water source. I have read so many conflicting things about the presence of water on Mars that I frankly admit to being confused. However, I think it very likely that a lot of water in large areas of the planet is bound up with the regolith as a permafrost layer not far below the surface. If so, then I think extracting it is doable.

kbd512 wrote:

Louis,
Once BFS gets to Mars, then it has to get back home. An airliner is too expensive to build, fly across the world, and then leave it there because there's no gas to get back home.

elderflower · 2017-12-21 03:08:25

I suspect that the water will be condensed from the atmosphere for the first couple of missions at least. This will mean a limited purification requirement and no prospecting or digging.
I do hope you all have a good festival period!

louis · 2017-12-21 03:51:20

Likewise Elderflower and all others who post here.

I did look into the figures for condensing out water previously...they didn't seem v. encouraging, given you will need hundreds of tonnes of water. There is also a seasonal fluctuation in the amount of atmospheric water available. But I agree that if it could be done, it make the most sense, to have that guarantee. However, I am pretty sure Musk has talked in terms of identifying a specific water source.

Edited to add:

On the basis of an assessment I read it seems a 885 Kg machine producing 3 kgs of water per sol at 25 degrees north in summer could supply 1800 kgs of water over six years which in turn would produce 1026 kgs of methane. So to produce approximately a 1000 tonnes of methane, you'd need 885 tonnes of condensing machinery over six years or 2,400 tonnes over two years. To do it in 2 years would also require an energy input of something like 15,000,000 Kwhes or 20,000 Kwhes per day or a constant of about 850 Kwes. I think the energy is doable but clearly the mass of the equipment at 2400 tonnes would not be feasible. Even if you go to 4 years, and 1200 tonnes, it's still too much for the cargo limit of around 300 tonnes. Whichever way you look at it, I think you have to find a water source in the Mars regolith - or a nearby glacier would be nice!

elderflower wrote:

I suspect that the water will be condensed from the atmosphere for the first couple of missions at least. This will mean a limited purification requirement and no prospecting or digging.
I do hope you all have a good festival period!

Last edited by louis (2017-12-21 05:22:22)

elderflower · 2017-12-21 07:19:56

Musk needs 1200 te of propellant but most of that is LOX. Even if he runs his rocket a bit methane rich, which will give more CO in the exhaust and therefore a better SI, he will still need mostly Oxygen in his tanks, by mass.
CH4 +2O2 >CO2 +2H2O
16 + 64 > 44 + 36.
So only a quarter of the propellant would be methane for stoichiometry.
Strictly speaking Mars Hydrogen is more massive than Earth hydrogen due to the relative excess of Deuterium so a bit more methane is needed for that, then if it runs methane rich we need more to cover for that- maybe it doesn't.
Any way Musk need only make 400 te max of methane in two years to allow him to get each machine home. If he runs the engines Oxygen rich he needs a lot less of it.

As we have seen the Martian Atmosphere gets saturated with water at night as the temperature falls. Capturing the water by compressing atmospheric gas, condensing the water and then expanding it to recover power is fairly straight forward, or perhaps an adsorption method might be used, heating the adsorbent with focussed sunshine during the day and exposing it during the night.

louis · 2017-12-21 10:30:51

My understanding that it is only during summer that you get the water saturation in the atmosphere, and - as the atmosphere is so thin - that is a relatively. The figure of 885 Kg machine to produce 3kgs of water per sol in summer was not mine but from a study paper, admittedly a few years back now. What mass of equipment do you think would require to produce the 1200 tonnes of propellant?

elderflower wrote:

Musk needs 1200 te of propellant but most of that is LOX. Even if he runs his rocket a bit methane rich, which will give more CO in the exhaust and therefore a better SI, he will still need mostly Oxygen in his tanks, by mass.
CH4 +2O2 >CO2 +2H2O
16 + 64 > 44 + 36.
So only a quarter of the propellant would be methane for stoichiometry.
Strictly speaking Mars Hydrogen is more massive than Earth hydrogen due to the relative excess of Deuterium so a bit more methane is needed for that, then if it runs methane rich we need more to cover for that- maybe it doesn't.
Any way Musk need only make 400 te max of methane in two years to allow him to get each machine home. If he runs the engines Oxygen rich he needs a lot less of it.
As we have seen the Martian Atmosphere gets saturated with water at night as the temperature falls. Capturing the water by compressing atmospheric gas, condensing the water and then expanding it to recover power is fairly straight forward, or perhaps an adsorption method might be used, heating the adsorbent with focussed sunshine during the day and exposing it during the night.

Oldfart1939 · 2017-12-21 10:43:02

kbd512 wrote:

I'd rather they at least attempted to land a Red Dragon on Mars to get this ISRU and humans to Mars show on the road, so to speak, but it's Mr. Musk's money so it's his call. If it fails, so what. Go big or go home.

I suspect that the heavy hand of NASA was waiting in the wings to tell Musk he could NOT land his Red Dragon on Mars because it would violate their planetary protection policy. The rejection of retro-propulsive landing of the Dragon 2 here on Earth by NASA as being "too risky," probably influenced that decision as well. The heavy hand of NASA lurks behind the scenes.

RobertDyck · 2017-12-21 11:57:14

elderflower wrote:

CH4 +2O2 >CO2 +2H2O
16 + 64 > 44 + 36.

I'm going to be picky. Using the numbers you provided, 16 + 64 = 80 total. So methane is 16 / 80 = 1/5 total propellant mass. Not a quarter.

However, the Raptor engine developed by SpaceX runs with a ratio of 3.8. That means 3.8 mass units of oxygen per unit of fuel. So methane is 1 / (3.8 + 1) = 0.2083333 or 20.83333%.

If you want to add up atomic mass, here is an excellent periodic table: www.webelements.com
Hydrogen 1.00794
Carbon 12.0107
Oxygen 15.9994

so CH4 = 12.0107 + 4 * 1.00794 = 16.04246
O2 = 2 * 15.9994 = 31.9988, so 2 * O2 = 63.9976
CO2 = 12.0107 + 2 * 15.9994 = 44.0095
H2O = 2 * 1.00794 + 15.9994 = 18.01528, so 2 * H2O = 36.03056

This means a perfect stoichiometric fuel ratio is 63.9976 / 16.04246 = 3.98926349. So raptor runs a little fuel rich, but not much.
In rocketry, precision matters. Extra digits do matter.

Last edited by RobertDyck (2017-12-22 05:14:27)

Oldfart1939 · 2017-12-21 13:24:37

The rationale given for running slightly fuel rich is to keep an oxidizer rich condition from damaging the metal in injectors and various other segments of the motors. It has been called oxidative erosion. With methane, there doesn't seem to be an issue w/r coking, or the buildup of carbon deposits. Better rocketry through chemistry.

Oldfart1939 · 2017-12-21 15:13:00

Musk is really playing it very cagy on this project by using 2 previously flown cores for the 2 side booster stage elements. As he has said in interviews, the central core required a lot of re-engineering. This is probably an order of magnitude more difficult than even he had imagined. The structural loads imposed by the 2 boosters are huge, and undoubtedly required major changes in construction and materials incorporated.

RobertDyck · 2017-12-21 22:22:20

In hope that someone from SpaceX is reading this, could I make a suggestion? Since Falcon Heavy is so greatly modified from Falcon 9 anyway, could they please restore propellant cross-feed? This would result in separating side boosters earlier, and the central core booster would be full at separation. This would reduce inert mass earlier, resulting in greater payload mass to orbit. The reason cross-feed was cancelled was to use standard Falcon 9 cores. But since Falcon Heavy requires modification anyway, that's no longer a consideration.

Oldfart1939 · 2017-12-21 23:31:25

There was also an earlier proposal for a Falcon Super Heavy which incorporated 4 booster stages rather than only 2. The problem of starting 27 engines seems bad enough, and 45 engines all at once is probably why we've heard no more about this proposal for 6 years. The concept of cross feed is a great one, but that's probably not going to happen for a while. As they began working on the current model of Falcon Heavy, the idea of cross feed was simply too complicated. Another order of magnitude more difficult?

Last edited by Oldfart1939 (2017-12-21 23:33:58)

kbd512 · 2017-12-21 23:39:40

Louis,

If SpaceX has this figured out, then great. My point is that SpaceX or NASA needs to test a Sabatier reactor design on Mars to ensure that the dust doesn't interfere with production of LOX from CO2. Falcon Heavy could land Red Dragon there with the ISRU experiment aboard. We just need to know with certainty that the machinery will continue to produce over the course of 2 years under Mars surface conditions. If that works without any major failures, then the technology can be scaled up afterwards to produce more propellants. Perhaps Sir Dyson's work can help "spin" the dust out of the inlet before it reaches the SOXE unit. This unit basically has to be "walk-away" safe in operation and utterly reliable.

Oldfart1939,

What would be required to produce Hydrazine or HydroxylAmmonium Nitrate on Mars?

Obtaining LOX from CO2 is not as much of a problem as obtaining water in the requisite quantities. If we could get water, we may want to use that for drinking, farming, thermal control, and radiation shielding. The density impulse of LOX/Hydrazine is approximately 35% greater than LOX/LCH4, the Isp is slightly better than LOX/LCH4, and the O/F ratio is only .74, so less cryogenic propellant storage is required. Are there any energy favorable methods for manufacturing Hydrazine or HAN that might work on Mars?

If we only had to keep the oxidizer cold, that would be a major plus. I understand that the Raschig process for manufacturing anhydrous Hydrazine is quite a bit more complicated than making Methane, but Hydrazine requires less thermal stabilization than LCH4 and far less LOX.

If Hydrazine storage poses a significant risk to humans, then what about HydroxylAmmonium Nitrate (AF-M315E)?

LOX is 1.14g/cm^3
Hydrazine is 1.021g/cm^3
HydroxylAmmonium Nitrate is 1.84g/cm^3
Ammonium Perchlorate is 1.95g/cm^3

I've no idea what the O/F ratio for LOX/HAN should be, as I was never all that interested in chemistry, but the bulk density would undoubtedly be impressive. The propellant tanks would be rather small in comparison to a LOX/LCH4 fueled rocket.

louis · 2017-12-22 05:30:17

Kbd,

Well I don't think Space X plan any pioneer experimental missions. The plan appears to be to go straight into propellant manufacture beginning 2022.

I presume the dust factor can be tested for over the next four years using Mars analogue facilities (Mars analogue dust, atmosphere and temperature).

kbd512 wrote:

Louis,
If SpaceX has this figured out, then great. My point is that SpaceX or NASA needs to test a Sabatier reactor design on Mars to ensure that the dust doesn't interfere with production of LOX from CO2. Falcon Heavy could land Red Dragon there with the ISRU experiment aboard. We just need to know with certainty that the machinery will continue to produce over the course of 2 years under Mars surface conditions. If that works without any major failures, then the technology can be scaled up afterwards to produce more propellants. Perhaps Sir Dyson's work can help "spin" the dust out of the inlet before it reaches the SOXE unit. This unit basically has to be "walk-away" safe in operation and utterly reliable.

elderflower · 2017-12-22 08:40:04

The military have the dust question sorted for helicopter engines operating in desert conditions. An unreliable helicopter is a very bad thing if you are putting troops into theatre or evacuating them. And that is without a water scrub.
Sorry for my silly error, Louis. Of course stoichiometry requires approx. 20 % methane not 25%.

Oldfart1939 · 2017-12-22 11:10:20

In one of my earlier mission architectures, I suggested bringing along adequate MMH for the return to Mars orbit, and manufacturing just the LOX from the atmosphere by means of a massive moxie /liquefaction unit. Hydrazine-type fuels are nicely energy-dense, and don't require the large tanks associated with lH2 and lCH4. The weight savings w/r tankage size can be thus utilized by bringing fuel to the Martian surface.

elderflower · 2017-12-22 13:36:10

Then you need a different engine for the second stage of your BFR as hydrazine derivatives are not popular for first stages and boosters.

Oldfart1939 · 2017-12-22 16:54:44

Elderflower-

Only here in the USA. The Russian Proton rocket is all hydrazine/NTO powered. Not sure which hydrazine, but either MMH or UDMH. I like Aerozine 50 for my architecture. Any hydrazine + LOX is a surefire winner.

SpaceNut · 2017-12-22 17:51:48

If we are making oxygen on the surface of mars how will the boiloff rates be altered.... Lox is bad enough

Storeables do not have the issue, so we will need to determine which ones can be made on mars?

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#1 2017-12-20 10:26:19

Falcon Heavy Assembly Underway

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Re: Falcon Heavy Assembly Underway

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