Author Topic: TSTO RLV, OTVs & propellant depots  (Read 10472 times)

Offline Hop_David

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TSTO RLV, OTVs & propellant depots
« on: 10/28/2011 08:08 PM »
Elon's attempt to recover stages were a failure.

In a video he hints future attempts will have re-entering stages shedding velocity propulsively with reaction mass in addition to aerobraking.

It is already very common for TSTO (Two Stage To Orbit) rockets to deliver sats to GEO.

What if the TSTO delivered the sat to LEO? Then an OTV (orbital transfer vehicle) could take the sat from LEO to GEO. Not having to haul the sat to GEO would save the TSTO 4 km/s from it's delta V budget.

Having an extra 4 km/s to help with re-entry would make a TSTO RLV  more plausible.

Of course a multiple use OTV would require propellant depots.
« Last Edit: 10/28/2011 08:08 PM by Hop_David »

Offline A_M_Swallow

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Re: TSTO RLV, OTVs & propellant depots
« Reply #1 on: 10/29/2011 04:38 AM »
A reusable OTV taking satellites from LEO to GEO will require about 2 * 4 = 8 km/s delta-V.  Close to a launch vehicle's delta-V.
Using a heat shield to slow down may reduce the round trip propellant delta-V to around 6 km/s.

The techniques of aerobraking will need applying to LEO based OTV.  A mini one to test the concept would be nice.

Offline Jim Davis

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Re: TSTO RLV, OTVs & propellant depots
« Reply #2 on: 10/29/2011 04:56 AM »
It is already very common for TSTO (Two Stage To Orbit) rockets to deliver sats to GEO.

Strictly speaking, this has only been done once, a few years ago, by an Atlas V with no solid strap-ons. GEO satellites are usually of such a size that 2 stage vehicles can't deliver them to GEO. That's why the Falcon Heavy has started development.

Quote
Of course a multiple use OTV would require propellant depots.

It will be quite some time before the GEO market, to say nothing of  SpaceX's share of it, will be large enough to justify development of an OTV and a propellant depot.

Offline Warren Platts

Re: TSTO RLV, OTVs & propellant depots
« Reply #3 on: 10/29/2011 11:43 AM »
Quote from: Jim Davis
It will be quite some time before the GEO market, to say nothing of  SpaceX's share of it, will be large enough to justify development of an OTV and a propellant depot.

Yeah, but if depots and OTV's were developed to support HSF missions to the Moon, then why not also use them to deliver satellites to GEO? Indeed, the DOD is interested enough in depots for this reason that they would probably share the development costs for depots and OTV's with NASA--at least that's what the latest ULA paper on depots suggests...

Quote from: Hop David
[Musk] hints future attempts will have re-entering stages shedding velocity propulsively with reaction mass in addition to aerobraking.

Not sure how this would work. If you're already at orbital velocity, to propulsively slow down from LEO would take quite a bit of propellant. Perhaps if the stage was refueled (possibly with Lunar propellant), I guess the thing could land vertically like the old Delta Clipper concept. It seems if you have to haul up the propellant from Earth as part of the payload, you're fighting a losing battle.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Hop_David

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Re: TSTO RLV, OTVs & propellant depots
« Reply #4 on: 10/29/2011 05:18 PM »
A reusable OTV taking satellites from LEO to GEO will require about 2 * 4 = 8 km/s delta-V.  Close to a launch vehicle's delta-V.

A nice place for lunar supplied propellant depots would be GEO.



Given depots at LEO and GEO, the OTV could get by with a 4 km/s delta V budget.

In another thread here, Isaac Kuo pointed to a Darpa proposal for salvaging sats. Without propellant, such a robot would be good for one antenna salvage. Given a propellant supply, it could rendezvous with many dead sats. GEO propellant would also enable multi-use satellite servicing robots. Some satellites die when station keeping propellant runs out, another reason to have propellant at GEO.

A servicing robot in GEO could fire a small prograde burn to enter a slightly slower orbit or a retrograde burn to enter a slightly faster orbit. Thus these robots could move about GEO and rendezvous with various sats with little fuel.

Offline Hop_David

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Re: TSTO RLV, OTVs & propellant depots
« Reply #5 on: 10/29/2011 05:26 PM »
Not sure how this would work. If you're already at orbital velocity, to propulsively slow down from LEO would take quite a bit of propellant. Perhaps if the stage was refueled (possibly with Lunar propellant), I guess the thing could land vertically like the old Delta Clipper concept. It seems if you have to haul up the propellant from Earth as part of the payload, you're fighting a losing battle.


Here's the Musk video:



If all the propellant is carried from earth's surface, I give him less than even odds of closing this design.

If there were propellant in LEO, I'd give him better than even odds.

Offline Jim Davis

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Re: TSTO RLV, OTVs & propellant depots
« Reply #6 on: 10/29/2011 05:41 PM »
Yeah, but if depots and OTV's were developed to support HSF missions to the Moon, then why not also use them to deliver satellites to GEO?

The market for manned missions to the moon is much smaller than that of satellites to GEO. We might wish it were otherwise but there you have it. I think it would be foolish to count on an existing market to piggyback off a non existing one.

I have nothing against depots but it is interesting to note that when Musk was confronted with the depots or heavy lift question when it came to servicing GEO markets he came down on the side of heavy lift.

Offline Hop_David

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Re: TSTO RLV, OTVs & propellant depots
« Reply #7 on: 10/29/2011 07:12 PM »
The market for manned missions to the moon is much smaller than that of satellites to GEO.

If there were enough public support for a lunar program, that could change.

What is the existing budget for HSF? $6 billion per year? What are we getting? I.S.S., a sortie mission to NEO, a brief stay on Mars are a few possibilities. None of those can hope to have an export. Operating costs would never be mitigated by export revenue.

After establishing a lunar base, you would already have the infrastructure for exporting propellant to various earth orbits. If the export revenue meets or even comes close to meeting base operating expenses, the base becomes sustainable.

If exports can exceed operating expenses, growth will follow.

If human spaceflight can lead to something sustainable, I'd favor continuing the investment.

But if it leads to dead end publicity stunts, it is better to cancel HSF. Perhaps OMB could be persuaded to use these savings to help NASA's planetary science program.

Offline Jim Davis

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Re: TSTO RLV, OTVs & propellant depots
« Reply #8 on: 10/29/2011 11:12 PM »
If there were enough public support for a lunar program, that could change.

Fair enough, but why will there suddenly be enough public support in the next few years when there hasn't been in the last 40 odd years? What changes?

Offline dks13827

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Re: TSTO RLV, OTVs & propellant depots
« Reply #9 on: 10/29/2011 11:56 PM »
If there were enough public support for a lunar program, that could change.

Fair enough, but why will there suddenly be enough public support in the next few years when there hasn't been in the last 40 odd years? What changes?
Part of the problem is that kids like my nephew, age 28, were taught to hate space flight and moon landings.  Waste of money that could be spent on welfare.  The schools did that and it's more common than we think.  They learned nothing of Apollo, maybe zero on the Shuttle.  It's true.
( Not in Clear Lake, I imagine ) but in many places that was the plan.... zero  !!!  That's a problem.
« Last Edit: 10/30/2011 12:02 AM by dks13827 »

Offline grr

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Re: TSTO RLV, OTVs & propellant depots
« Reply #10 on: 10/30/2011 04:50 PM »
Was just thinking about fuel depots and the fact that NASA is looking more into these. It has finally struck me that NASA has this backwards. Instead, they should focus on coming up with an automated berthing standard that allows for electricity/fluid transfers. Upon coming up with a standard to be used on their sats, then it would encourage commercial development of tugs for sats. originally, I would suspect that the tug would be disposable. However, they would quickly turn to refuelable (which would lead to depots and automated delivery attendants), as well as new ones such as ion engines, tether-based EMD, or even nukes.
That seems to be the smart approach.

Offline Hop_David

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Re: TSTO RLV, OTVs & propellant depots
« Reply #11 on: 10/30/2011 11:05 PM »
Fair enough, but why will there suddenly be enough public support in the next few years when there hasn't been in the last 40 odd years? What changes?

For most the last 40 odd years I didn't support lunar exploration.

Here are my words from 2007: "Apollo astronauts landing on the moon found a desolate place drier than a bone. With no water or other volatiles, colonizing the moon is nearly impossible. Mankind's dreams of a dawning Space Age seemed to die still-born."

Here's the graphic those words come from:


I had regarded NEOs as the most plausible source of volatiles. I had even compiled of page of links to evidence or theories that suggest NEOs with icey cores exist: Asteroid Resources

In 2010 my opinion changed.

Offline Jim Davis

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Re: TSTO RLV, OTVs & propellant depots
« Reply #12 on: 10/31/2011 04:57 PM »
For most the last 40 odd years I didn't support lunar exploration.

In 2010 my opinion changed.

But for at least the last dozen or so years you have been a space advocate. You did advocate a manned program beyond low earth orbit? O'Neill type settlements and space solar power? Certainly I recall many discussions with you on the subject. The discovery of water at the lunar poles has merely changed your focus.

The discovery of water at the lunar poles has certainly excited space advocates but the general public has not even heard of the discovery and wouldn't care in the slightest if it did.

But we've wandered far from your original point. The geosynchronous market is far too small to support development of OTVs and propellant depots. Certainly Musk thought so.


Offline Bill White

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Re: TSTO RLV, OTVs & propellant depots
« Reply #13 on: 10/31/2011 05:36 PM »
All current markets are too small to support significant levels of human spaceflight. (Current ISS demand is not at a significant level, at least IMHO).

Facilitating new demand simply is the mission critical task.

However, a geopolitical race for lunar resources (or perhaps more accurately the prestige associated with such efforts) would generate significant demand for depots, RLVs and OTVs.



« Last Edit: 10/31/2011 05:37 PM by Bill White »
EML architectures should be seen as ratchet opportunities

Offline jongoff

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Re: TSTO RLV, OTVs & propellant depots
« Reply #14 on: 10/31/2011 06:55 PM »
But we've wandered far from your original point. The geosynchronous market is far too small to support development of OTVs and propellant depots. Certainly Musk thought so.

I think I have to agree with Jim, at least as things currently stand I haven't been able to close the case on depots purely commercially.  Too much risk, and too many technologies that need to be matured and demoed first.  The total cost in the scheme of NASA manned exploration is pretty small, but compared to what you can raise commercially, it's the kind of extreme long-shot that only a philantrocapitalist could really make work.  That's why Altius is focusing on a depot-enabling subsystem that addresses more near-term needs, instead of depots directly.

My hope is that as depot technologies get put on the shelf by different programs that have similar needs (and/or if NASA decides to actively start retiring depot technological risks), we can get to a point where the business plan clicks.  I just don't know how to make it work -- yet.

~Jon

Offline DarkenedOne

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Re: TSTO RLV, OTVs & propellant depots
« Reply #15 on: 10/31/2011 11:25 PM »
But we've wandered far from your original point. The geosynchronous market is far too small to support development of OTVs and propellant depots. Certainly Musk thought so.

I think I have to agree with Jim, at least as things currently stand I haven't been able to close the case on depots purely commercially.  Too much risk, and too many technologies that need to be matured and demoed first.  The total cost in the scheme of NASA manned exploration is pretty small, but compared to what you can raise commercially, it's the kind of extreme long-shot that only a philantrocapitalist could really make work.  That's why Altius is focusing on a depot-enabling subsystem that addresses more near-term needs, instead of depots directly.

My hope is that as depot technologies get put on the shelf by different programs that have similar needs (and/or if NASA decides to actively start retiring depot technological risks), we can get to a point where the business plan clicks.  I just don't know how to make it work -- yet.

~Jon

Well the problem is demand IMHO.  No one is going to develop a depot system without a knowing someone will have use for it. 

In the commercial market there exists no potential users at the moment.  However it robotic servicing turns out to be a success than they might be able to build a market around them.

There is definitely a potential market on the military side.  They have expressed a great deal of interest in satellites that can inspect other satellites, refuel satellites, perform upgrades and repairs, and etc.  The problem is that these technologies are not at the top of their priority list at the moment. 

While man spaceflight is possibly the biggest beneficiary of fuel depots, there is no way any private company would be willing to develop these systems without a promise from NASA that NASA will purchase the fuel.  Of course if NASA did make such a promise than it might make sense. 

That is one thing that NASA could do at practically zero cost.  They could promise to buy a certain amount of fuel at a certain cost. 

 

Offline aero

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Re: TSTO RLV, OTVs & propellant depots
« Reply #16 on: 10/31/2011 11:54 PM »
The problem I see with NASA as the customer for a commercial fuel depot is the year-to-year uncertainty of the budget and even more, the lack of the political will to carry major projects through to completion. That uncertainty could easily result in a commercial fuel vendor being hung out to dry, no matter that NASA had committed to multi-year purchases.

If NASA cancelled a contract, it would probably pay the cancellation penalty but it is doubtful that it would cover the vendor's cost of the commercial investment needed to win the contract. Or, if so, the cancellation penalty wouldn't pay the lost opportunity cost to the vendor. IMO the military would be a much more reliable customer.
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Offline Hop_David

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Re: TSTO RLV, OTVs & propellant depots
« Reply #17 on: 11/01/2011 12:08 AM »
But for at least the last dozen or so years you have been a space advocate. You did advocate a manned program beyond low earth orbit?

Yes.

O'Neill type settlements and space solar power? Certainly I recall many discussions with you on the subject.

I recall no such discussions.

I don't think SPS could be competitive with nuclear. I've held that opinion for some time.

The discovery of water at the lunar poles has merely changed your focus.

Indeed it has. I used to regard NEAs as the most plausible near term target for settlement, but a long shot.

Since the discovery of water, I see the moon as the most doable goal. And I don't think its a long shot.

But we've wandered far from your original point. The geosynchronous market is far too small to support development of OTVs and propellant depots.

Given routine travel between earth orbits, LEO to GEO sat delivery is just one of many possible applications. As I've mentioned.

When you add to it the substantial exploration of the moon, it becomes a much better bargain than flags and footprints on an asteroid.

Offline grr

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Re: TSTO RLV, OTVs & propellant depots
« Reply #18 on: 11/02/2011 09:44 PM »
The problem I see with NASA as the customer for a commercial fuel depot is the year-to-year uncertainty of the budget and even more, the lack of the political will to carry major projects through to completion. That uncertainty could easily result in a commercial fuel vendor being hung out to dry, no matter that NASA had committed to multi-year purchases.

If NASA cancelled a contract, it would probably pay the cancellation penalty but it is doubtful that it would cover the vendor's cost of the commercial investment needed to win the contract. Or, if so, the cancellation penalty wouldn't pay the lost opportunity cost to the vendor. IMO the military would be a much more reliable customer.

That is why NASA, and private space, should focus on an automated docking system standard that allows for various transfers (fluid, electricity, etc). In doing that, it will encourage tugs that can be attached to various cargo( sats/ space stations/ and yes, fuel or water depots). 
By groups focusing on fuel depot, they put the cart first.  Instead, with the docking, once a new form of propulsion  or other enhancements are created, they can be substituted quickly.  For example, I suspect that a common tug up front would be a unit to push a sat to GEO (or higher).  The first generation will no doubt be simple chemical engines. However, I would think that we would quickly get into ion, or even tethers to move sats up to GEO.  The reason would be costs. The tether is going to be cheap compared to chemicals.

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