Author Topic: Falcon Heavy SEP tug  (Read 14343 times)

Offline spacenut

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Falcon Heavy SEP tug
« on: 04/16/2015 07:45 pm »
What would be to heaviest cargo a SEP tug, using today's technology, launched from a Falcon Heavy be able tow to Mars and return?  Say a 50 ton SEP tug.   

Offline russianhalo117

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Re: Falcon Heavy SEP tug
« Reply #1 on: 04/16/2015 08:30 pm »
What would be to heaviest cargo a SEP tug, using today's technology, launched from a Falcon Heavy be able tow to Mars and return?  Say a 50 ton SEP tug.   
two main factors prop type and amount loaded, as well as amount of available power, type of solar cells and size of solar array wings and radiators for heat rejection generated by engine and SC operation. until you define that it makes it very difficult to answer your question.

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #2 on: 04/16/2015 09:01 pm »
I was thinking 50 tons would be for the tug, solar panels, but maybe not fuel.  Fuel could be launched from a single Falcon 9.  I would use argon since it is more abundant.  Then, based on the 50 ton size of the tug using say the best of today's technology.  How much cargo could this tow to Mars in say 6 months and return in 6 months?  I know very little about SEP technology so that is why I'm asking.  Say a 50 ton tug could carry 50 tons of cargo/lander, wouldn't this get some type of Mars colony equipment started before the BFR and MCT is built.  Several tugs could take a lot of cargo to Mars that isn't perishable if they could tow enough in the 18 months between MCT trips.  Just wonder what SEP tug capabilities are and if Falcon heavy could be a work horse for SEP cargo. 

Offline Impaler

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Re: Falcon Heavy SEP tug
« Reply #3 on: 04/17/2015 02:55 am »
Estimates are that current SEP tech would have a ratio of 1:1 with the stage and the payload for a trip one way to Mars slow 6 months, this compared with the 2:1 ratio for a HydroLox chemical system doing the same thing.  An advanced SEP system with very efficient solar and much higher ISP might push the ratio as high as 1:2 aka a 1 ton stage and 2 tons payload.

P.S.  Please use the correct nomenclature, argon is not a fuel, it is a propellent.

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #4 on: 04/17/2015 11:49 am »
So a 50 ton SEP could take 50 tons to Mars and return.  Not bad if it can be.  I suppose a 50 ton SEP would cost several billion.  Just wondering if using Falcon Heavy to transport cargo to Mars would be cost effective using SEP. 


Online philw1776

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Re: Falcon Heavy SEP tug
« Reply #5 on: 04/17/2015 02:39 pm »
One way.
50 ton SEP takes 50 tons to Mars.  One way
FULL SEND!!!!

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #6 on: 04/17/2015 02:44 pm »
So Falcon heavy could do a lot of Mars prep work with a SEP tug.  Same could be said for a moon infrastructure. 

So does anyone know what a 50 ton SEP tug would cost?  I think it would have to be able to return to be reused if it is expensive. 

Offline Jim

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Re: Falcon Heavy SEP tug
« Reply #7 on: 04/17/2015 02:56 pm »
So Falcon heavy could do a lot of Mars prep work with a SEP tug.

So could any other launch vehicle.  There isn't any really special about the heavy with SEP.

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #8 on: 04/17/2015 03:25 pm »
50 tons to LEO was what I was thinking about IF they get the Heavy launched soon.  ULA is at least 5 years away with Vulcan.  Since this is a SpaceX thread, just thought getting equipment to Mars for set up, testing, etc, would be in SpaceX's interest if they are going to build the BFR and MCT.  More cargo has to get to Mars before people can go, and it isn't so time sensitive so using Falcon Heave with SEP might be a way to do this. 

Offline guckyfan

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Re: Falcon Heavy SEP tug
« Reply #9 on: 04/17/2015 04:37 pm »
50 tons to LEO was what I was thinking about IF they get the Heavy launched soon.  ULA is at least 5 years away with Vulcan.  Since this is a SpaceX thread, just thought getting equipment to Mars for set up, testing, etc, would be in SpaceX's interest if they are going to build the BFR and MCT.  More cargo has to get to Mars before people can go, and it isn't so time sensitive so using Falcon Heave with SEP might be a way to do this.

They would still need to build a lander and the SEP-tug. I don't see them developoing something that complex and expensive before they have MCT. When they have MCT they will use that.

Offline Impaler

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Re: Falcon Heavy SEP tug
« Reply #10 on: 04/18/2015 12:14 am »
Well their could conceivably be a use for SEP tugs in raising GEO birds from low to high orbits, that would allow the satellite to conserve its own propellents while also being much more massive.  Thing is I don't think the current design, market or lifespans of satellites make this attractive YET. 

If someday a communication satellite in GEO is massing 50 MT then it would be simple to swap out Mars bound hardware in what ever delivery mechanism were using to put said satellite in place, and a SEP tug seams like a reasonable mechanism for that.

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #11 on: 04/18/2015 12:48 am »
I was thinking a 50 ton lander, say landing 20-30 tons of equipment.  The SEP tug could if it had enough fuel on board travel back to earth to pick up another lander with equipment. 

The other idea was to use the tug to bring GPS satelites to put them in orbit around Mars for future use.  A tug could do a lot of work before MCT. 

Offline go4mars

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Re: Falcon Heavy SEP tug
« Reply #12 on: 04/20/2015 04:52 am »
Well, they are out talking about SEP for MCT, and about mass producing Hall Effect Thrusters.  I've wondered since "before it was cool" whether an in-space power/propulsion module and argon tanks might get stuck onto whatever methane/oxygen people-can shape they end up with for the MCT.  That way it could get swapped out if a better system comes out in a decade or 3 (looking at you fusion).  I think sub-scale tech demonstrators using FH could be a really good plan.

I also think a downmass expansion pack should have an eventual place on MCT (specifically thinking of silane ramjets, argon flash heatshield, water transpiration heatshields, and microthruster heatshields).  Those would benefit the musings of this thread similarly - perhaps test early iterations on FH. 

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Offline Darkseraph

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Re: Falcon Heavy SEP tug
« Reply #13 on: 04/20/2015 05:22 am »
Given how efficient SEP tugs are, I am not sure why the entire payload capability of the Falcon Heavy is necessary at all. Presuming such a vehicle is something you reload with propellant..it can be pretty light. The payloads to be mated with it can probably be launched on any EELV class vehicle. There's nothing special about Falcon Heavy for this application and the 50 ton capability is not something that is coming very soon even when Falcon Heavy is successfully fielded. In fact, it might might never fly with cross feed at all and I suspect Space X will eventually transition to a reusable methalox heavy lifter that is similar in size to Vulcan, using fewer engines than the FH.

There's zero evidence for that speculation, but I would guess this is what will happen as I don't see a huge market in the next 10 years for a ~200mt to leo BFR which will need dedicated factories and infrastructure before even one launch, but that an engine of the specs of Raptor would work well on a relatively smaller vehicle so that the income from doing their commercial work helps keep the company open whilst it builds up to sending colonists. In fact, if the right tools are developed in space...I think several vehicles of this scale would be all we need to do initial human missions to the moon, mars and asteroids and that it will be cheap enough to do because of sharing with military and commercial. When it is proven that 10's of people can be sent safely without dying or breaking the bank and that there is demand, then they scale that up by putting more engines on a bigger vehicle. Combined with SEP, it is almost all we would ever need for a civil hsf program.
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Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #14 on: 04/20/2015 02:10 pm »
Yes, with the Raptor now in the 500k lb thrust range, and smaller BFR for 60-90 ton payloads, and a 3 core heavy version when needed for a 200 ton payload.  The single core could do a lot of work.  I also think an in space only nuclear EMP rocket traveling between earth and Mars can tow a lot of landers, and pick up empty one for return.  I was just thinking when the launch the Falcon heavy, to use it for scaled down SEP to haul some cargo, or satellite infrastructure to Mars.  They could also be used to assemble propellant depots for the larger MCT craft to refuel in earth orbit and maybe even in Mars orbit for travel between the planets.  I think either depots or SEP or Nuclear electric is going to happen to keep launch costs down. 

Offline The Amazing Catstronaut

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Re: Falcon Heavy SEP tug
« Reply #15 on: 04/20/2015 05:56 pm »
Yes, with the Raptor now in the 500k lb thrust range, and smaller BFR for 60-90 ton payloads, and a 3 core heavy version when needed for a 200 ton payload.  The single core could do a lot of work.  I also think an in space only nuclear EMP rocket traveling between earth and Mars can tow a lot of landers, and pick up empty one for return.  I was just thinking when the launch the Falcon heavy, to use it for scaled down SEP to haul some cargo, or satellite infrastructure to Mars.  They could also be used to assemble propellant depots for the larger MCT craft to refuel in earth orbit and maybe even in Mars orbit for travel between the planets.  I think either depots or SEP or Nuclear electric is going to happen to keep launch costs down.

Smaller BFR is just conjecture right now. Single stick BFR is what SpaceX claims to be working on and they have not publicly reconsidered that yet. Not the thread topic though - this is about SEP tugs for Fal Heavy specifically.

To play devil's advocate, why use an SEP tug for Mars satellites, when Falcon heavy could already throw smallsats to mars by itself? SpaceX is in favour of small and light as far as we've seen. SpaceX is already looking to put hall effect thrusters on their sats, so they'll have a fair degree of delta-V leeway once they're at mars and will be able to push themselves into graveyard orbits, assuming planetary protection in the 2030s isn't particularly fond of SpaceX (or any other hardware operators in martian orbit) dropping their sats into the atmosphere.
« Last Edit: 04/20/2015 05:57 pm by The Amazing Catstronaut »
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Offline joek

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Re: Falcon Heavy SEP tug
« Reply #16 on: 04/20/2015 05:57 pm »
One way.
50 ton SEP takes 50 tons to Mars.  One way

Good point, but depends on what you mean by "to Mars".  At reasonably approachable TRL in the not-so-distant future... assuming ~10t SEP tug dry mass + ~40t of propellant + ~50t cargo carrier (inclusive of usable cargo), starting in LEO, and aerocapture of the cargo carrier into Mars orbit.

So all-up, ~100t IMLEO to get a ~50t cargo carrier in Mars orbit.  Not going to get 50t of anything on the Mars surface with that.  Not going to get the SEP tug into Mars orbit with that (couldn't survive aerocapture), only the cargo carrier.  Not going to get the SEP tug back with that (not enough propellant).

This has been discussed in several threads, most recently in the Getting to Mars - 420 tons or less? thread.
« Last Edit: 04/20/2015 06:14 pm by joek »

Offline Jimmy Murdok

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Re: Falcon Heavy SEP tug
« Reply #17 on: 04/20/2015 09:00 pm »
Given how efficient SEP tugs are, I am not sure why the entire payload capability of the Falcon Heavy is necessary at all. Presuming such a vehicle is something you reload with propellant..it can be pretty light.

You would spend most of the weight with solar panels to power the engines. As soon as you want something electric relatively fast you need huge amounts of energy. So I would expect a huge solar panel structure with several small hall thruster and some tankage. This tug could be used for several things.

Offline Impaler

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Re: Falcon Heavy SEP tug
« Reply #18 on: 04/21/2015 02:42 am »
starting in LEO, and aerocapture of the cargo carrier into Mars orbit.

The estimate I provided earlier was assuming propulsive capture into Mars orbit, that is the baseline for most SEP system mission profiles.  It is thus not quite apples-2-apples with the chemical stage and the 2:1 ratio as they would need as that assumes direct entry.

Offline spacenut

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Re: Falcon Heavy SEP tug
« Reply #19 on: 04/30/2015 02:21 pm »
So several Falcon heavy launches to build a large enough SEP tug with enough propellant to travel from earth to Mars and back and land 50 tons on Mars with say a disposable lander.  If the SEP tug is taking a re-usable lander that can land and take off from the Mars surface and re-dock with the tug to be hauled back to earth.  The tug will probably weigh 200-300 tons in itself. 

I was just wondering if Falcon heavy could do Mars colonization using a large SEP tug, or several large SEP tugs.  The main idea was to get ISRU equipment to Mars to deploy solar panels or a small nuke power plant to begin to make methane, oxygen, and water for future colonists, say several years ahead of the BFR and MCT, just to get started. 

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