Author Topic: SpaceX tanker variant  (Read 15909 times)

Online hkultala

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SpaceX tanker variant
« on: 10/16/2017 11:58 AM »
From the Reddit AMA:

"Q: Will the BFS tanker's payload section be empty, or include extra propellant tanks?

A (Elon): At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).
"

So, first just using same (cargo) BFS, with empty tanks it will have plenty of fuel left when it reacher orbit.


But the dedicated tanker:

The "cargo space" of current BFR is has much higher area than tanks needed for 150 tonnes of propellant.

No need for cargo hatch etc might save some weight, so the optimized tanker might be able to actually carry slightly more propellant than 150 tonnes. Let's say 160 tonnes.

So, the "trivial design" would be to just increase the tanks lengths so that it can carry 160 tonnes more propellant.
This would mean much shorter craft than the ordinary BFS.

What about the fins? Are they needed for the tanker?

The tanker would always be practically empty when landing, and it would always land on earth. Might not need the fins.

3 landing engines also not needed. Only 1 would be enough for the T/W, but maybe still have two for redundancy?

Not having the fins and third engine might save more mass. Maybe could carry even 170 tonnes of fuel?


Offline Peter.Colin

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Re: SpaceX tanker variant
« Reply #1 on: 10/16/2017 12:05 PM »
The new “kinda weird” tanker might be a big almost empty tanker.
More like the nose cone of a Falcon 9 (12-15 meter wide)
Without heat shield
Without landing legs
Without deep space engines
Without fins

It would be basically a depot-tanker which remains in orbit.
That’s the only thing that makes sense, that would have an extremely full to empty mass ratio.
The reduction in mass from launching it empty and stripped can be used to make it much bigger.

You could use the largest part of the 26 months between departures to launch the depot-tankers, and filling them up with regular cargo ships.
And than launch the spaceships, that are filled up by the depot-tankers.
Maybe 10 launches are needed to fill up a depot-tanker, could someone calculate this?

The Mars depot-tanker would need a heat shield.
But no landing legs.
« Last Edit: 10/16/2017 12:10 PM by Peter.Colin »

Offline Athrithalix

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Re: SpaceX tanker variant
« Reply #2 on: 10/16/2017 12:11 PM »
The question that jumps to mind for me is: are there other missions in planning that require refuelling in space? If it's only Mars missions then having propellant sit around in space for a year or so waiting for launch windows just seems like a waste of infrastructure and an opportunity for gradual wastage of propellant. In that case it would be better to have a BFS tanker that takes more fuel per launch to reduce the number of launches needed for each round of the colonisation fleet.

Offline Peter.Colin

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Re: SpaceX tanker variant
« Reply #3 on: 10/16/2017 12:23 PM »
The question that jumps to mind for me is: are there other missions in planning that require refuelling in space? If it's only Mars missions then having propellant sit around in space for a year or so waiting for launch windows just seems like a waste of infrastructure and an opportunity for gradual wastage of propellant. In that case it would be better to have a BFS tanker that takes more fuel per launch to reduce the number of launches needed for each round of the colonisation fleet.

It depends on how many Mars missions will there be in the future?
The gradual wastage of fuel is negleable if the heat isolated nosecone is pointed to the sun at all times.
Like will be done when traveling to Mars.
You could even reduce it to zero if there is a cryocondensor built in, that is planned for future ships.

« Last Edit: 10/16/2017 12:24 PM by Peter.Colin »

Offline corneliussulla

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Re: SpaceX tanker variant
« Reply #4 on: 10/16/2017 03:03 PM »
Remember BFS going to a lot more places than Mars, cis lunar space, lunar surface, potential lagrangepoint missions, possible contracted to asteroid miners. In fact as Mars only in place once every 2 Years BFS probably gets used a lot more to other destinations at first.

Offline philw1776

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Re: SpaceX tanker variant
« Reply #5 on: 10/16/2017 03:04 PM »
The question that jumps to mind for me is: are there other missions in planning that require refuelling in space? If it's only Mars missions then having propellant sit around in space for a year or so waiting for launch windows just seems like a waste of infrastructure and an opportunity for gradual wastage of propellant. In that case it would be better to have a BFS tanker that takes more fuel per launch to reduce the number of launches needed for each round of the colonisation fleet.

Not necessarily in planning however that's interpreted but Lunar surface missions require re-fueling as would very high payload to HEO and beyond Earth orbital and cis-lunar missions.
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Online Cheapchips

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Re: SpaceX tanker variant
« Reply #6 on: 10/16/2017 03:21 PM »
Did Musk mean that it literally looks weird or that it would seem weird?

What would fall into either interpretation?

I'd have thought that's it's a given that it's reusable and derived from the regular BFS.  That's cheapest and every landing counts towards crew rating /passenger rating.

Offline philw1776

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Re: SpaceX tanker variant
« Reply #7 on: 10/16/2017 03:23 PM »
A future low dry mass tanker could simply be a 2nd stage with only 2 SL Raptors and a very short, nearly nil "cargo" volume.  Extra propellant tanks pretty much fit in the nose volume.  Or simply stretch the std propellant tanks by just a couple meters and have zero cargo volume/length. 

So the BFS Custom Tanker would be very short & stubby and "look weird".

Ironic that the shorter BFR tanker would deliver more mass to LEO than the "standard" taller config.
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Offline aero

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Re: SpaceX tanker variant
« Reply #8 on: 10/16/2017 03:32 PM »
That's likely it. Elon likes his rockets to be tall and slender, so he might describe rocket that is not tall and not slender as "looking weird."
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Offline Lars-J

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Re: SpaceX tanker variant
« Reply #9 on: 10/16/2017 03:56 PM »
That's likely it. Elon likes his rockets to be tall and slender, so he might describe rocket that is not tall and not slender as "looking weird."

Yep, that's what I expect... An optimized tanker would be a shorter and more squat looking BFS.

Some here seem to think that it would been a larger diameter BFS or something even weirder. No. Propellant is HEAVY. There is a practical limit to what the BFR booster can lift. If anything it will be smaller. And certainly not expendable.

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Re: SpaceX tanker variant
« Reply #10 on: 10/16/2017 04:10 PM »
I'm fully on board for the 'Stumpy the Weird Tanker' being the most likely thing. 

How blunt can you go with the nose cone on a 9m vehicle?


Offline envy887

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Re: SpaceX tanker variant
« Reply #11 on: 10/16/2017 05:48 PM »
I'm fully on board for the 'Stumpy the Weird Tanker' being the most likely thing. 

How blunt can you go with the nose cone on a 9m vehicle?

No need to blunt it, the same ogive shape as the cargo ship is fine.

Offline tea monster

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Re: SpaceX tanker variant
« Reply #12 on: 10/16/2017 06:02 PM »
This is with the same shaped nose as the manned/cargo version.

Offline Peter.Colin

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Re: SpaceX tanker variant
« Reply #13 on: 10/16/2017 06:51 PM »
This is with the same shaped nose as the manned/cargo version.

It doesn’t really qualify, “warning: it will look kinda weird”
« Last Edit: 10/16/2017 06:53 PM by Peter.Colin »

Online nacnud

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Re: SpaceX tanker variant
« Reply #14 on: 10/16/2017 07:07 PM »
I think you are reading far too much into that one comment, bear in mind that the whole comment was.

'At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).' - Elon

Offline philw1776

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Re: SpaceX tanker variant
« Reply #15 on: 10/16/2017 07:11 PM »
This is with the same shaped nose as the manned/cargo version.


Shorter yet.  Nose atop just a few meters of expanded tankage.
Zero crew or cargo space.
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Offline GalacticIntruder

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Re: SpaceX tanker variant
« Reply #16 on: 10/16/2017 07:34 PM »
It might look weird because the BFR is 9m in diameter, and the tanker variant could be larger, more bulbous. Say 12m (ITS) or even 15m. 
Watch out for those pesky corners, they have teeth.

Offline meekGee

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Re: SpaceX tanker variant
« Reply #17 on: 10/16/2017 07:41 PM »
I'm going with "spherically short".

On a different question, Musk referred to cylindrical tanks as having "even acceptable" mass ratios, still with some disdain..

I'm thinking it'll almost look like a flying beach ball.

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Offline Lar

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Re: SpaceX tanker variant
« Reply #18 on: 10/16/2017 07:47 PM »
This is with the same shaped nose as the manned/cargo version.

Wouldn't it still need the delta for reentry?
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Online nacnud

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Re: SpaceX tanker variant
« Reply #19 on: 10/16/2017 07:56 PM »
There is not going to be any spherical tanks or wider stages for the tanker version. The payload for the BFR is 150 tonnes, the propellant load for the second stage is 1100 tonnes.

All they need to do is stretch the tanks by 10% and lop off the payload section. They may not even need to stretch the tanks. It's going to look a little weird because the tanker version is going to be half the length of the normal BFS.
« Last Edit: 10/16/2017 07:58 PM by nacnud »

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