POLL: Are you supportive of the Prop Depot Concept?

[Warren Platts]

Water and fuel cells as well.

[neviden]

The most important thing about space depot would be that it would allow REUSABILITY.

If you look at each space depot as a space station, then it becomes a focal point from or to where things go. One in LEO, One in EML1/EML2, One at Phobos, One at NEO,.. Make it modular and add things as needed Nautilus-x style.

They would be visited, supplied, docked with, would fuel and be refueled by Dragon, Orion, Soyuz, RLV, lunar landers, mars landers, NEO landers, SEPs, STPs,..

To allow all this, you would need lots of propellant. H2/O2 and water is present on the Earth, Moon, Phobos and NEOs. At first most of the propellant would come from Earth. Then it would come from either Phobos or from some low delta-V NEO. “mine” 1000s of tons of water from them, use solar thermal (in 10s – 100s of MW range) propulsion with concentrated solar energy to bring it back to earth’s orbit and you have enough (unlimited propellant for a price of one mission to NEO) propellant and technology to get anywhere beyond LEO.

All this would cost money to develop and build, but you can build it incrementally and at the end of program you have capabilities to build massive structures (things like O'Neill cylinders would become feasible) in space from space material (NEOs) and transport it around for very small cost.

[douglas100]

I think that depots are primarily an enabling technology with some hope of reducing the cost of missions beyond LEO. Re-usability is a byproduct of the architecture.

H2/O2 and water is present on the Earth, Moon, Phobos and NEOs.

I agree that water has been shown to exist on Earth(!) and the Moon. As far as I know it has only been hypothesised to exist on Phobos and NEO's. That's one reason why the loss of Phobos-Grunt was such a disappointment. I would be interested to know of direct evidence of water on these bodies. Without direct such evidence it is premature to consider a depot architecture which uses such sources.

At first most of the propellant would come from Earth. Then it would come from either Phobos or from some low delta-V NEO. “mine”

I don't agree. The logical source for the first extraterrestrial propellant is the Moon. The Moon is nearby and propellant can be delivered from it to destinations in cislunar space or LEO in days. The time from Phobos or NEO's is months. This is more important than any delta-V advantage which far away sources may have.

All this would cost money to develop and build, but you can build it incrementally and at the end of program you have capabilities to build massive structures (things like O'Neill cylinders would become feasible) in space from space material (NEOs) and transport it around for very small cost.

In the current financial and political world such grandiose schemes are well over the horizon. (Don't get me wrong, I like the idea of O'Neill habitats but I think they will not be realised for a long time.)

Nothing about space transportation is "a very small cost," not even launching cubesats.

[neviden]

I agree that water has been shown to exist on Earth(!) and the Moon. As far as I know it has only been hypothesised to exist on Phobos and NEO's. That's one reason why the loss of Phobos-Grunt was such a disappointment. I would be interested to know of direct evidence of water on these bodies. Without direct such evidence it is premature to consider a depot architecture which uses such sources.

The moon is the obvious source of water, but it requires rockets to get them from the surface. You can try to set up some kind of rail guns or slingshots from the surface, but it's tricky.

I don't agree. The logical source for the first extraterrestrial propellant is the Moon. The Moon is nearby and propellant can be delivered from it to destinations in cislunar space or LEO in days. The time from Phobos or NEO's is months. This is more important than any delta-V advantage which far away sources may have.

I agree that the first source would be Moon if we will go there. Or at least source of H2 if there is no water on the Phobos.

You can defenitly get O2 from Phobos/NEOs, but that would be trickier to achive since it is in the form of oxides and other complex minerals. Phobos posibly has water, but that we don't know. What we do know is that there are extinct comets out there that have lots of water..

Phobos/NEOs have a distinct advantage over the Moon in that you can transport massive amounts of mass to Earth orbit if you use even bigger amounts of propellant and large amounts of power over the long time. Something like ion drive only with STP in 100s of MW range that is relativly cheap.   

In the current financial and political world such grandiose schemes are well over the horizon. (Don't get me wrong, I like the idea of O'Neill habitats but I think they will not be realised for a long time.)

Nothing about space transportation is "a very small cost," not even launching cubesats.

It will be expensive as long as we need to watch for every gram of weight. If you don't have to use latest and most bleading edge technology, then the costs come way down. Sure, it costs a lot to get it to LEO, but once you have ready access to propelant and bulk materials, then your costs go way down. Especially if you don't throw everything away since it is made for one use only, becouse the propelant comes from (expensive) Earth.

There is nothing inherently expensive in melting big chunks of metalic iron, making big slabs of it, welding those slabs together to make crude but usefull objects in space and then delivering it to Earth's orbit by steam rocket. Why does it sudenly cost hundreds of billions of dollars just because it is in space?

[douglas100]

The moon is the obvious source of water, but it requires rockets to get them from the surface. You can try to set up some kind of rail guns or slingshots from the surface, but it's tricky.

So you agree that if we wish to exploit extraterrestrial water to make propellant we should go first to the Moon. You also agree that there is no current evidence that there is water on Phobos. So let's forget about Phobos as a first step, OK?

You don't need rail guns to get propellant from the Moon. You use lunar produced hydrogen and oxygen to transport the propellant using conventional rockets to whatever depot needs it. Have a look around the forum. There has been plenty of discussion of this.

Something like ion drive only with STP in 100s of MW range that is relativly cheap.

It will be expensive as long as we need to watch for every gram of weight. If you don't have to use latest and most bleading edge technology, then the costs come way down.

I think you have contradicted yourself with these two quotes. Ion propulsion that size is currently leading edge technology since nothing like it exists and developing it will be very expensive.

But this thread is about propellant depots and not about space habitats. It is more about what could realistically be done in the coming decades. And realistically the Moon has to be the first source of propellant beyond Earth.

[qti]

I am supportive of propellant depots.  But like anything a good idea can be turned into a disaster.  While a fully capable way station that combines propellant storage, living quarters, an servicing capabilities may appear attractive I believe it will overly complicate the depot to the point where the cost is unsustainable.  A simple depot, maybe even a temporary depot, is a more appropriate way to demonstrate the technology and utilize it to enable early missions.

[muomega0]

I am supportive of propellant depots.  But like anything a good idea can be turned into a disaster.  While a fully capable way station that combines propellant storage, living quarters, an servicing capabilities may appear attractive I believe it will overly complicate the depot to the point where the cost is unsustainable.  A simple depot, maybe even a temporary depot, is a more appropriate way to demonstrate the technology and utilize it to enable early missions.

JSC did study depots awhile ago:Developing a Safe On-Orbit Cryogenic Depot

The depot concept has been refined over the last decade.

It is not clear what is meant by "simple" or "temporary" however, maybe *evolvable* is a better adjective, if this is cost effective.  Also, not sure if living quarters would be *close* to the depot for any significant time.

So what does *close* mean?  Since the depot spins initially to separate liquid and gas, suppose someone hooked a tether to the depot to conduct variable gravity research?  This could be great length (900m) to avoid sickness.  This could be facilitated by locating the depot near ISS.

The other option is having the depot part of ISS, but if the technology is that risky, would one want to risk 100B?  Probably not.

For most operations of propellant delivery, the crew is not present.  But regardless, eventually the crew is on top of a transfer stage of cryogenic fluids, and a depot in simple terms is just a stretched tank version of a transfer stage with power and some pumps.  Many of the same safety concerns would exist, as well as many new ones.

Perhaps the depot will require maintenance, then crew may need to be present.  One option is to do maintenance when the depot is empty.

Or to change out a component/assembly to "evolve" the depot, or just launch a new one.  For example, adding different LADs to study if the liquid and gas can be separated without spinning.

Perhaps the transfer stage is launched first and fueled, then meets up with the crew at the depot or away from the depot, to avoid having the crew present during the transfer?

This should be studied and worked out.  The economic benefits appear significant to be traded against the risks.  Quite a bit of work to do:)

[Longhorn John]

One sided poll!

[JohnFornaro]

I am supportive of propellant depots.  But like anything a good idea can be turned into a disaster.  While a fully capable way station that combines propellant storage, living quarters, an servicing capabilities may appear attractive I believe it will overly complicate the depot to the point where the cost is unsustainable.  A simple depot, maybe even a temporary depot, is a more appropriate way to demonstrate the technology and utilize it to enable early missions.

I'm quite the fan of a rotating ring station, but the approach you suggest here is spot on.  Start small, and enlarge it as time goes on.  Were I in charge, I'd plan for the ring station.  But the first thing built would be a simple hub with slowly rotating prop tanks, to ease the prop transfer with a bit o' centripetal force.  Later, two tethers with habs could be added, slowly rotating to provide at least partial gee.  Years and years later, the station would resemble the "2001" station, complete with a hotel and gift shop.

By that time, the old original hub would have long ago been swapped out.  Same with the tethers and early habs.  The location would remain the same, EML-1; the functions would slowly and methodically grow, as the cis-lunar economy grew.

[mmeijeri]

While not directly depot focused, the use of integrated vehicle fluids may enable elimination of helium and hydrazine from in-space stages.  This would certainly ease the use of depots.

I don't think having helium and hydrazine in addition to LOX/LH2 is much of a complication for in-space stages. If anything, it's LOX/LH2 that leads to the complications. Of course, we'll want LOX/LH2 eventually, but getting rid of the helium and hydrazine isn't important. Getting rid of them does yield more important benefits on upper stages, which is where ULA intends to apply IVF first.

That said, I think the IVF proposal is in fact aimed squarely at depot applications, even though it is being pitched differently. ULA know that zero boil-off in LEO is both very difficult and unnecessary, and they are trying to make the best of the situation. When life gives you lemons, make lemonade.

IVF entails a massive redesign of ULA's upper stages, one that could not be justified on its own merits just for upper stage applications. Still, if your launch rate leaves your skilled scientists and engineers less than fully occupied, it makes sense to invest some of their remaining time in IRAD. And if that R&D results in some limited but tangible benefits to upper stage use (as IVF does), it can still be a sound business decision.

More importantly for the rest of us, it can lead to great rewards when we finally do transition towards a depot-based architecture.

[A_M_Swallow]

I don't think having helium and hydrazine in addition to LOX/LH2 is much of a complication for in-space stages. If anything, it's LOX/LH2 that leads to the complications. Of course, we'll want LOX/LH2 eventually, but getting rid of the helium and hydrazine isn't important. Getting rid of them does yield more important benefits on upper stages, which is where ULA intends to apply IVF first.
{snip}

On Earth nitrogen is much easier to make the helium.  So the designers of in-space stages need to think carefully about which gas they use for pressurisation.

[douglas100]

On Earth nitrogen is much easier to make the helium.  So the designers of in-space stages need to think carefully about which gas they use for pressurisation.

Neither nitrogen nor helium are "made." They are both chemical elements and are extracted from their sources and purified.

[A_M_Swallow]

On Earth nitrogen is much easier to make the helium.  So the designers of in-space stages need to think carefully about which gas they use for pressurisation.

Neither nitrogen nor helium are "made." They are both chemical elements and are extracted from their sources and purified.

Both need processing.  A difference is a difference only if it makes a difference.

[QuantumG]

Neither nitrogen nor helium are "made." They are both chemical elements and are extracted from their sources and purified.

"made" is a perfectly cromulent word.

[Avron]

Voted NO..

1) I don't see how this will move us forward..
2) too many if's .. it's not clear, it it was great, it would be simple.. I am reading 17 pages of not simple.. not clear..
3) We refuel fighters in the air as there is a clear need, an a unlimited budget.  How come we don't do the same for airliners.. cost a lot to refuel on the ground.. etc..