Author Topic: Refuelable Spacecraft  (Read 9391 times)

Offline Nathan

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Refuelable Spacecraft
« on: 04/20/2008 07:06 AM »
NASA should be directed to work on refuelable spacecraft.

Earth to orbit should be refuleable - whether one, two or threee stages. This implies reusability.
LEO to LLO craft should be refuelable. this implies the existance of a propellant depot in LEO serviced by commercial operators on contract to NASA.

LLO to Lunar surface should be refuelable. This implies reusability - no crasher stages or drop tanks. This may lead to the development of lunar propellent depots.

LEO to Asteroid should be refuelable. This implies resuability and could prove an economical way to fill the LEO propelent depot as well as spur mining projects.

LEO to mars orbit should be refuelable.

Mars orbit to Mars surface should be refuelable - implying reusability and the manufacture of propellants on the surface.


If NASA requires that all of it's crewed spacecraft are to be refuelable we will, by default, spur the development of space infrastructure and space utilisation. Commercial interests will have a greater role to play if NASA requires that such infrastructure be commercially operated.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Nathan

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RE: Refuelable Spacecraft
« Reply #1 on: 04/20/2008 08:01 AM »
And not just NASA - but all nations, groups, companies etc. They should all be building refuelable systems.
Given finite cash, if we want to go to Mars then we should go to Mars.

Online Eerie

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Re: Refuelable Spacecraft
« Reply #2 on: 04/20/2008 08:47 AM »
And who is going to REFUEL?

Offline Analyst

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RE: Refuelable Spacecraft
« Reply #3 on: 04/20/2008 12:32 PM »
And why should all this happen? I mean, in a larger sense. Why spaceflight? And why didn't have anybody else this idea?

Analyst

Offline A_M_Swallow

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RE: Refuelable Spacecraft
« Reply #4 on: 04/20/2008 04:39 PM »
Quote
Analyst - 20/4/2008  1:32 PM

{snip}And why didn't have anybody else this idea?

Possibly because rockets were developed as weapons.  War time ammunition is only used once.

Refuelability is a cost trade off.  The cost of the larger fuel tank, extra motors, stronger structure, spares, repair work extra equipment such as heat shields and possibly smaller payload has to be traded against the cost of building a second rocket.

If the fuel is being lifted from the Earth's surface it can be cheaper to build a new fuel tank than to launch a now empty tank from the Moon's surface.

On the other hand building and launching 3 spacecraft with 3 lots of fuel is very expensive.  Using one big spacecraft and 2 refill tankers may be cheaper.  Particularly in a continuing programme.

High ISP electric propulsion means that fuel can be moved from LEO to say lunar orbit without having to lift twice the mass of fuel.

Offline Nathan

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Re: Refuelable Spacecraft
« Reply #5 on: 04/20/2008 09:01 PM »
Refuelability implies reuse which will push costs lower.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #6 on: 04/20/2008 11:33 PM »
Quote
Nathan - 20/4/2008  10:01 PM

Refuelability implies reuse which will push costs lower.

Hopefully but do remember that the reusable Space Shuttle is being replaced by an expendable Ares-I.  NASA suspects that launching the Ares-I will be cheaper.

Offline Nathan

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Re: Refuelable Spacecraft
« Reply #7 on: 04/21/2008 09:05 AM »
Quote
A_M_Swallow - 21/4/2008  9:33 AM

Quote
Nathan - 20/4/2008  10:01 PM

Refuelability implies reuse which will push costs lower.

Hopefully but do remember that the reusable Space Shuttle is being replaced by an expendable Ares-I.  NASA suspects that launching the Ares-I will be cheaper.

Space shuttle can't really be considered refuelable. Reusable is even a push. It's just easier to refurbish than build fresh.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline gospacex

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RE: Refuelable Spacecraft
« Reply #8 on: 04/21/2008 12:05 PM »
Quote
Nathan - 20/4/2008  3:01 AM
And not just NASA - but all nations, groups, companies etc. They should all be building refuelable systems.

They should be building systems in whatever way turns out to be most economical.

If you think that refuelable spacecraft will bring economic benefits (which may be true, I don't know), you probably need to explain why do you think so.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #9 on: 04/21/2008 04:30 PM »
Note: Earth to LEO may have a different cost trade off than beyond LEO.

Online Lampyridae

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Re: Refuelable Spacecraft
« Reply #10 on: 04/22/2008 12:00 AM »
This is an old argument.

1. Reusable spacecraft will need to fly more than 20x a year to

2. There are other costs besides the booster flyaway price. Pad integration, range safety, staff costs. Even when given a reusable vehicle for free, flights will still cost millions.

3. What payload? Small payloads achievable but small market for them.

4. What level of safety? Most reusable vehicles will have to push the envelope and that reduces safety numbers. No good having a reusable spacecraft if it blows up every ten flights.

There is definitely an argument for reusable tugs from LEO to GEO and the moon, but not for launches from Earth. The demands just won't support it. SpaceX is aiming for reusability, but it is still notional and it is more economical to wreck a tank but recover the engines than build a fully reusable stage. That will have to come later.
SKYLON... The League of Extraordinary Gentlemen's preferred surface-to-orbit conveyance.

Offline Spacenick

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Re: Refuelable Spacecraft
« Reply #11 on: 04/26/2008 02:00 PM »
I think reusable, and refuelable makes most sense for pure orbit spacecrafts.A good example for this is the proposed Parom spacecraft, I think that absolutely makes sense because it pushes flexibility a lot and would allow cargo to be brought up as modules, than dock with it unmanned and bring it where it's needed. A nice version of this could also be built from ATV or HTV components with very few changes to the system, though it would be better to have stronger thrusters than ATV, than fill it up with refuelable oversized tanks and you get a pretty nice space tug.
I think in this scenario one could simplyfy other spacecrafts a lot, for example a crew vehicle would only need enough fuel for attitude control whiel waiting for docking with the tug and a reserve for emergency deorbit, while it should use the same fuel as the tug so they could work together for attitude control and fueltransfer between tug<->spaceraft<->spacestation / other tug or another spaceraft + tug combination.
For the way from ground to orbit refuelable and reusable in my opinion makes only sense for stages, like using a winged firststage or boosters because then there is no need for big heatshields and the crew/cargo would be launched with a classic second stage so that there is not dead mass in orbit as we have with the shuttle.

What would be interesting to know is how much fuel something like ATV would need to get 25 mT to the moon. I mean could one use 25 tons in LEO to get another 25 tons launched seperately into lunar Orbit, I think it should be possible at least when using Ion propulsion and big solar arrays like SMART-1 did, it would take to long for humans but it should be very easy way to get a lander, cargo or even abse modules to the moon for cheap, maybe such a Ion propulsion tug could do it even more than once, than one could take 50 mT to the moon with just 3 Ariane 5 launches that would be by far the cheapest solution.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #12 on: 04/26/2008 11:23 PM »
Quote
Spacenick - 26/4/2008  3:00 PM
What would be interesting to know is how much fuel something like ATV would need to get 25 mT to the moon. I mean could one use 25 tons in LEO to get another 25 tons launched seperately into lunar Orbit, I think it should be possible at least when using Ion propulsion and big solar arrays like SMART-1 did, it would take to long for humans but it should be very easy way to get a lander, cargo or even abse modules to the moon for cheap, maybe such a Ion propulsion tug could do it even more than once, than one could take 50 mT to the moon with just 3 Ariane 5 launches that would be by far the cheapest solution.

This is a report prepared for NASA on using a Solar Electric Propulsion ferry to land 22 tonne cargoes on the  Moon.
http://www.entechsolar.com/SPRAT-XX-SLA-SEP.pdf

Reusable

Dry SEP 7000 kg
Solar panels 2105 kg

Expendable

Dry lander 5000 kg
Lander fuel 17972 kg
Ion thruster fuel (Xenon) 25756 kg

Cargo 22000 kg


I will leave it to you to work out how Ariane 5s can be used to launch the 80 tonnes to LEO.

Offline Spacenick

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Re: Refuelable Spacecraft
« Reply #13 on: 04/27/2008 12:07 PM »
Do I interpret those numbers correctly? It seems to me the lander needs >17 mT of fuel, that sound realy heavy. Also the needed Xenon mass sound too much, Smart-1 flow to the moon with just 82 kg. On the other hand i would say it's possible with the Ariane, in junks of 25 mT each.
1. launch a 4 mT Tug with an aditional 21 mT solar panels and the bare minimum of  Xenon for an Earth orbit docking
2. launch the  22 mT Xenon fuel in a big fuel tank tih a minimal docking adapter on it's back let the Ariane upper stage make it spin a little to prevent tumbling and then dock the tug with it (it's a a tough docking but it's unmanned so the risk is low and docking with inertial stations has been done with Salyut 7 and should be absolutely doable with a high-tech automatic docking system)
3. launch the lander or cargo container and dock it with the tug then let them spiral to the moon, because there are no humans aboard we don't care whether this takes months.
When using an unmanned lander with no return stage just to put cargo on the moon I guess it's fuelmass could be reduced a lot maybe even give it a rough landing and some nice airbag system.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #14 on: 04/27/2008 08:26 PM »
Smart-1 did not land on the Moon, it crashed into it at high speed.  That takes about 1/3 of the fuel.  The probe was also very small.

You appear to have halved the size of the tug and using 10 times as many solar panels as in the report.

Offline Spacenick

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Re: Refuelable Spacecraft
« Reply #15 on: 04/27/2008 08:57 PM »
Ups, made a mistake reading the solar panel mass. For the tug I assumed that a lot of the structural mass was to support the fuel tank and other stuff that would be attached to the inertial fuel tank system launched on my proposed second launch, I don't know but 7 mT seems to be a lot for a few Ion engines, especially since my proposal doesn't need to have strong ones like VASIMIR or anything special because it doesn't matter much how long it takes to bring the cargo into lunar orbit, anything < 1 year seems ok.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #16 on: 04/29/2008 01:40 AM »
The example SEP ferry took about a year to do the round trip.

An alternative design is for each launch to put 6 to 7 tonne on the Moon.  The Ariane 5 lifting the payload, SEP propellant, lander and lander fuel.

Working back from the final payload pay permit a SEP Ferry weighing less than 9 metric tons to be used.

SEP ferries can be used to lift cargoes to GEO and, with larger solar panels, to Mars.

Offline hmh33

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Re: Refuelable Spacecraft
« Reply #17 on: 05/12/2008 01:58 AM »
Something you may not be considering-- Xenon propellant runs about $10m per tonne at the moment, and I believe world annual production is in the range of 2 tonnes.

Offline A_M_Swallow

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Re: Refuelable Spacecraft
« Reply #18 on: 05/12/2008 02:29 AM »
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hmh33 - 12/5/2008  2:58 AM

Something you may not be considering-- Xenon propellant runs about $10m per tonne at the moment, and I believe world annual production is in the range of 2 tonnes.

Then use Argon as the propellant.
Price $0.50 per 100g = $5 000 per tonne
http://www.chemicool.com/elements/argon.html

Can be made on both the Earth and Mars.

Offline Andy USA

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Re: Refuelable Spacecraft
« Reply #19 on: 05/13/2008 12:01 AM »
Quote
Nathan - 21/4/2008  4:05 AM

Quote
A_M_Swallow - 21/4/2008  9:33 AM

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Nathan - 20/4/2008  10:01 PM

Refuelability implies reuse which will push costs lower.

Hopefully but do remember that the reusable Space Shuttle is being replaced by an expendable Ares-I.  NASA suspects that launching the Ares-I will be cheaper.

Space shuttle can't really be considered refuelable. Reusable is even a push. It's just easier to refurbish than build fresh.

Shuttles are mainly reusable, apart from the ET.

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