Author Topic: Hypergolic depots versus Cryogenic depots  (Read 65016 times)

Offline charliem

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Hypergolic depots versus Cryogenic depots
« on: 05/13/2012 02:06 pm »
According SpaceX's website Dragon carries about 1.3 mt of MMH/NTO propellants at lift-off. From that it gets a bit under 500 m/s of delta-v (fully loaded).

It seems one of the things that worries SpaceX for COTS2+ is fuel, given all the maneuvers they are going to try.

Standard flights should not need that much unless something goes wrong, but what if?

On the other hand future powered landings wont be safe unless there's propellant enough with a fair safety margin. And cant forget the reentry burn that Dragon does by itself (no service module).

I remembered having read some piece about non cryogenic fuel depots a few years back, and finally found it. It's this 2010's article by Ed Kyle.

One of the interesting things it says is that if we want to go back to the Moon on the cheap, or even start thinking about Mars (I'd add servicing satellites, and maybe tugs), LH2/LOX is not compulsory, not even RP1/LOX. Hypergolics might not be the most efficient but they are good enough for many things, and we've been space-storing them for years so we already know how to do it.

Moreover, looks like NASA is not taking fuel depots seriously for the time being, and what little they have done to date seems to be centered on cryogenics.

So, from all this I'm wondering. What'd be the pros and cons of a private MMH/NTO fuel depot in LEO? And how hard could the development be? How much could that cost? How much for a little demo?

Until now SpaceX has built on well proven ideas and hardware designs, but everyone knows they are aiming high. RLVs and Mars landings are not exactly conservative goals, and if they want to enhance Dragon range and flexibility, and insure a bit more de-orbit burns and power landings, this could be a way.

How about a small fuel depot co-orbiting some distance from ISS? Not only useful for Dragon but potentially others, ISS included.

Thoughts?
« Last Edit: 05/13/2012 08:55 pm by Andy USA »

Offline douglas100

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Re: Dragon range
« Reply #1 on: 05/13/2012 02:33 pm »
So is this thread is about hypergolic depots versus cryogenic depots rather than about Dragon or its derivatives? Or both?
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Offline kch

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Re: Dragon range
« Reply #2 on: 05/13/2012 02:43 pm »
So is this thread is about hypergolic depots versus cryogenic depots rather than about Dragon or its derivatives? Or both?

Something like that, yeah ... ;)

Offline charliem

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Re: Dragon range
« Reply #3 on: 05/13/2012 03:05 pm »
So is this thread is about hypergolic depots versus cryogenic depots rather than about Dragon or its derivatives? Or both?

It's about how SpaceX could or could not have the motivations to go forward with something that, possibly, would allow them to increase the flexibility and safety of their craft, and what that'd imply technically and financially.

That latter on it could also be beneficial for many other enterprises is just a bonus, or maybe further motivation, how knows. SpaceX's seems to be able to think ahead more than just next fiscal year, or presidential term.
« Last Edit: 05/13/2012 03:44 pm by charliem »

Offline sdsds

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Re: Dragon range
« Reply #4 on: 05/13/2012 06:05 pm »
I believe there are good exploration architectures in which hypergolic depots are filled in LEO and then sent elsewhere. For purely LEO missions, though, adding a mission-critical rendezvous event seems overall less safe than simply designing the mission to fit within the constraints of a single launch.
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Offline go4mars

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Re: Dragon range
« Reply #5 on: 05/13/2012 08:29 pm »
adding a mission-critical rendezvous event seems overall less safe than simply designing the mission to fit within the constraints of a single launch.
My impression from past presentations and youtube videos is that "direct throw" is Elon's style.  Just build a bigger rocket.  Perhaps now that they have a dragon with ISS rendesvous software getting proven out, it will be considered as an interim solution for specific missions. 
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Offline Andy USA

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Re: Hypergolic depots versus Cryogenic depots
« Reply #6 on: 05/13/2012 08:56 pm »
So is this thread is about hypergolic depots versus cryogenic depots rather than about Dragon or its derivatives? Or both?

Agreed. Thread title needed to be specific to the main question, and moved to in space section.

Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #7 on: 05/13/2012 09:10 pm »
I think the main advantage of hypergolic depots would be their early availability. This is not the only consideration, but in my opinion it should trump all others. Two optimisations can make this easier:

1) use them at L1/L2 initially, use (or at least allow use of) prefueled cryogenic stages to rendez-vous with a spacecraft in LEO and then to transfer it to L1/L2
2) offload most of the propellant from the spacecraft to reduce its weight and only fuel it at L1/L2

This gets rid of most (but not all) of the inefficiency of hypergolics and also allows early use of SEP (which could even be a net gain compared to all-chemical LOX/LH2, and would still require no new technologies). Under this scenario only the spacecraft would be refueled, not the transfer stages (at least not initially). This would allow another optimisation:

3) Let the spacecraft be its own depot

This would reduce the investment needed to get this going. Once you had such a system operational, you could then optimise for higher performance instead of early availability as budgets and traffic levels warranted.

I've been arguing in favour of this for a while, mainly because it would allow us to use exploration to establish a large market for launch services for low-cost and easily divisible payloads. This in turn would give a major boost to launch vehicle R&D, hopefully leading to radically cheaper space launch, which could enable large scale commercial manned spaceflight as well as being greatly beneficial to government-funded exploration. This is essentially the New Space prescription for cheap lift, except for their inexplicable insistence on using LOX/LH2.
« Last Edit: 05/13/2012 09:54 pm by mmeijeri »
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Offline charliem

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Re: Hypergolic depots versus Cryogenic depots
« Reply #8 on: 05/13/2012 10:48 pm »
Ok, lets talk it in the hardware section then.

What I'm trying to do is tie up two problems, suggesting a solution for the first that could also be beneficial for the second.

Doing some calcs on the numbers I have on Dragon (not many, and not very reliable I'm afraid) they indicate that, unless Dragonrider is quite different from Dragoncargo about fuel and delta-v capacity, the powered landing that SpaceX says they are after is going to depend on how well in-space operations go ... each time.

Less than 500 m/s of delta-v is enough for orbital maneuvers plus deorbit burn, but to land safely they'll need to reserve a good chunk from that, unless, of course, Dragonrider carries much more propellant than the cargo version (reducing the habitable volume).

A SpaceX's small depot in LEO could take the function of buffer. If a flight goes well and no extra delta-v is needed they don't have to touch it, or could even leave there a portion of the propellants they didn't burn and don't need for the way down either. But if things don't go that well and they spend more than expected, it could be handy.

The second problem is fuel depots. It's the chicken and egg paradox again.

Why no one plans missions involving fuel depots, neither commercial nor scientific? Because there are no fuel depots, and their development would complicate things quite a bit. They are not essential, and they'd constitute an expensive (and dangerous) detour.

And why no one builds a fuel depot? Well, what for? No present design requires one.

I'm trying to cut through this knot suggesting an use that could be beneficial straightaway, at least for SpaceX.

Once it is in space there are many things that become possible alright, but there has to be some hardware up there first to start rolling this stone.
« Last Edit: 05/13/2012 10:50 pm by charliem »

Offline sdsds

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Re: Hypergolic depots versus Cryogenic depots
« Reply #9 on: 05/14/2012 06:06 am »
A SpaceX's small depot in LEO could take the function of buffer.

Yes, particularly if the Dragon flights had a reason to go there anyway. Imagine a Falcon Heavy launch out of Texas putting a small, monolithic station into a convenient orbit. Each crewed Dragon that visited could leave behind some of its unused "margin" propellant. That propellant could be used by the station for its own orbit maintenance, or made available to a later Dragon flight that was low on propellant for whatever reason.

This is a scenario where having a depot combined with the station could arguably increase the safety of crewed missions that came to visit!
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Offline JohnFornaro

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Re: Hypergolic depots versus Cryogenic depots
« Reply #10 on: 05/14/2012 01:22 pm »
I think the main advantage of hypergolic depots would be their early availability.

^ What he said.
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Offline charliem

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Re: Hypergolic depots versus Cryogenic depots
« Reply #11 on: 05/14/2012 11:17 pm »
This is a scenario where having a depot combined with the station could arguably increase the safety of crewed missions that came to visit!

That's the idea. Good for SpaceX operations in the short term and a first timid step in a very promising area.


Offline Robert Thompson

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Re: Hypergolic depots versus Cryogenic depots
« Reply #12 on: 05/17/2012 12:59 am »
<= change of optimism. Do the hypergolic depots, warts and all. Pemmican and biltong.

Offline douglas100

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Re: Hypergolic depots versus Cryogenic depots
« Reply #13 on: 05/18/2012 10:47 am »
If you were thinking about using a hypergolic depot in LEO to refuel a vehicle going to L2 or points further afield there is the present situation that there are only two current vehicles which could benefit from it: Briz M and Fregat. Other users would have to be developed. This is another example of the chicken-and-egg problem that was mentioned earlier.

On the other hand, if you had a cryogenic depot in LEO you could potentially refuel the upper stages of Atlas, Delta, Ariane, HII, Long March 3 series. So in a restricted sense there is a greater potential market for cryogens.

This is a difficult trade to make, not knowing what the future demand might be. You could imagine both being developed.
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Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #14 on: 05/18/2012 11:07 am »
If you were thinking about using a hypergolic depot in LEO to refuel a vehicle going to L2 or points further afield there is the present situation that there are only two current vehicles which could benefit from it: Briz M and Fregat. Other users would have to be developed. This is another example of the chicken-and-egg problem that was mentioned earlier.

Or Ariane's EPS or the Delta II upper stage, or Soyuz / Progress / ATV / HTV / Dragon / CST-100. All of these would have to be modified for refueling of course.

But if you built a refuelable transfer stage that acted as its own depot (say a cross between the Orion SM and the Delta II upper stage), then you avoid the chicken-egg problem.

Quote
On the other hand, if you had a cryogenic depot in LEO you could potentially refuel the upper stages of Atlas, Delta, Ariane, HII, Long March 3 series. So in a restricted sense there is a greater potential market for cryogens.

Not necessarily greater. And the risk as well as the required time and money would be greater.

Quote
This is a difficult trade to make, not knowing what the future demand might be. You could imagine both being developed.

It's not that difficult a trade. Hypergolics (and only a refuelable spacecraft, not a dedicated depot) are the obvious place to start. Cryogenic depots are an obvious follow-on, when funding and traffic levels warrant it. Exactly when that will be is a difficult decision to make, and one best left to the market since it concerns economic viability, not just technical achievements.
« Last Edit: 05/18/2012 06:58 pm by mmeijeri »
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Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #15 on: 05/18/2012 11:25 am »
Another point is that LEO is not the best place for a hypergolics depot or refuelable spacecraft using hypergolics, L1/L2 is. It is accessible with existing launchers, even for manned applications, using two launches and EOR in LEO, just like Constellation or DIRECT would have done. It is also so close to the edge of the Earth's gravity well that the relative inefficiency of hypergolics is much diminished, especially if you use advanced trajectories and SEP. In the latter case, the tables might even be turned on all-chemical even on a kg for kg basis. Not that that is the decisive criterion (cost/kg is much more relevant), but it's a good thing to know.

Hypergolics are a much better fit for spacecraft than for upper stages, which is why hypergolics are being phased out for upper stages, but not for spacecraft. And if they are ever phased out for spacecraft too, they are likely to be replaced by SEP, not cryogenic chemical propellant.
« Last Edit: 05/18/2012 11:27 am by mmeijeri »
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Offline JohnFornaro

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Re: Hypergolic depots versus Cryogenic depots
« Reply #16 on: 05/18/2012 12:35 pm »
Another point is that LEO is not the best place for a hypergolics depot or refuelable spacecraft using hypergolics, L1/L2 is. It is accessible with existing launchers, even for manned applications, using two launches and EOR in LEO, just like Constellation or DIRECT would have done. It is also so close to the edge of the Earth's gravity well that the relative inefficiency of hypergolics is much diminished, especially if you use advanced trajectories and SEP. In the latter case, the tables might even be turned on all-chemical even on a kg for kg basis. Not that that is the decisive criterion (cost/kg is much more relevant), but it's a good thing to know.

Hypergolics are a much better fit for spacecraft than for upper stages, which is why hypergolics are being phased out for upper stages, but not for spacecraft. And if they are ever phased out for spacecraft too, they are likely to be replaced by SEP, not cryogenic chemical propellant.

Right on bro.

Something that just dawned on me as I read this:  You know how we have hybrid cars?  Why not extend the idea to spacecraft:  SEP/hypergolic?

I think there are three tasks involved.  Launch to LEO or EML1. LEO to EML1.  EML1 to lunar surface.  Hypergolics, at first, can do the last leg.  But could a hybrid craft do the second leg, LEO to EML1?
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Offline douglas100

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Re: Hypergolic depots versus Cryogenic depots
« Reply #17 on: 05/18/2012 12:38 pm »

Or Ariane's EPS or the Delta II upper stage, or Soyuz / Progress / ATV / HTV / Dragon / CST-100. All of these would have to be modified for refueling of course.

But if you built a refuelable transfer stage that acted as its own depot (say a cross between the Orion SM and the Delta II upper stage), then you avoid the chicken-egg problem.

Knew you would come back Martijn!  :)

Delta II isn't going to be around for much longer. Apart from EPS all the others vehicles are already part of what is already almost a hypergolic depot--the ISS itself. So in a sense, what you are proposing has already started to happen.

Your second point can apply just as well to cryogenic vehicles. This is precisely what ULA is proposing with ACES or even an improved Centaur. Technically and financially cryogenic is harder, of course. But I think for exploration applications, in the long term, cryogenic is superior.

(Don't you get a sense of deja vu about this thread already?  :))
Douglas Clark

Offline Archibald

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Re: Hypergolic depots versus Cryogenic depots
« Reply #18 on: 05/18/2012 12:46 pm »
(deja vu encore !)
Quote
Something that just dawned on me as I read this:  You know how we have hybrid cars?  Why not extend the idea to spacecraft:  SEP/hypergolic?

A-MMO-NIA ! NH3 works with arcjets and every future advanced SEP system (PIT-thruster, VASIMR, many others) and it is close enough from hydrazine (N2H4 vs NH3) minus the toxicity. Together with menthanol, it is the only "green" fuel that can replace gasoline in Internal combustion, piston engines. The modifications to the engine are rather straightforward - although both methanol and ammonia have only half the mileage of gasoline. Range remains superior to electric cars (not too difficult).
« Last Edit: 05/18/2012 12:46 pm by Archibald »
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Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #19 on: 05/18/2012 01:04 pm »
Delta II isn't going to be around for much longer.

Probably true, and that's not a problem, but I'd love to see the Orion SM / Delta II merger.

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Apart from EPS all the others vehicles are already part of what is already almost a hypergolic depot--the ISS itself.

Yeah, and even EPS is closely related to all this as it's currently only used for ATV (but may be used for Galileo too as was suggested in another thread).

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So in a sense, what you are proposing has already started to happen.

True, but the ISS consumes only relatively little propellant, which is either a bug or a feature, depending on your point of view. It certainly doesn't provide enough demand in the easily divisible, cheap category to give us cheap lift through demand-pull.

I'd rather see a spacecraft that consumes much more propellant, as it would if it travelled beyond LEO.

However, LEO to L1/L2 isn't the best match for a hypergolic stage. It would work, but it might need a new pump-fed engine for manned applications. That is not a show-stopper (especially if you allow the use of non-US engines), but it does take away from the main benefit of hypergolics: early availability.

L1/L2 to beyond on the other hand works much better, both for manned and unmanned applications. A fully fueled Delta II upper stage or EPS at L1/L2 has a lot of oomph. If HEOMD provided this at no cost to SMD (and got to keep their budget as a result), then SMD would no doubt find ingenious ways to make use of it. The trick would be to focus on classes of mass-intensive or propellant-intensive cheap spacecraft and to maximise science value. I can think of a couple of plausible ways to do this, and SMD could likely come up with better ones.

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Your second point can apply just as well to cryogenic vehicles.

Do you mean using L1/L2 as the first location for a depot / propellant transfer point or using a refuelable spacecraft instead of a dedicated depot?

L1/L2 is indeed easier than LEO for LOX/LH2, just as with hypergolics, though for different reasons. For hypergolics the main benefit is minimising the Isp-penalty, whereas for cryogenics lower boil-off is more important. SEP would of course benefit both.

As for refuelable cryogenic spacecraft, those are possible too of course, but having a cryogenic stage / spacecraft be its own depot is more difficult (and expensive in terms of mass for thermal insulation) and less practical than for a hypergolic spacecraft.

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But I think for exploration applications, in the long term, cryogenic is superior.

Agreed, though there may be some deep space applications for which hypergolics (or more generally non-cryogenic propellants) will remain important for a long time to come.

Quote
(Don't you get a sense of deja vu about this thread already?  :))

 ;)
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