HSF Review subgroup: Fuel depots are game-changers

One thing though, isn't there another paradigm that also has so many advantages that it ought to be have been and should be included in the baseline? Inflatable structures.

A 25 mT inflatable is a large structure and just as with propellant depots one can fill it up incrementally.

The BA 330 is supposed to come in at 23 mT for $100 million and as the name implies provides 330 cubic meters of internal volume comparable to the 358 cubic meters of the ISS.

With fuel depot logistics and inflatable structures one can add for example VASIMIR and everything is ready for Aldrin's Cyclers. In such a setting the human domain could quickly expand to include everything crossing within 0.5 AU of Earth.

Maybe this is all a bridge too far right now, I guess it's hard and challenging enough to get propellant depots accepted (and understood).

Posted by Habitat Hermit at 07/30/09 12:48:49

the orbital fuel depots never can be a good option until (old.space or new.space) costs will not fall to a fraction of today's $15+ million per ton to LEO

Posted by one at 07/30/09 13:17:14

"the orbital fuel depots never can be a good option until"

You need consumables in space, right?

That's fuel. Sorry, that's how these things work, you need to accept that.

I suggest you conserve your consumables as well. Unless, of course, you don't really want to go to and live in space.

Posted by Hey Zeus at 07/30/09 14:06:38

Not true, one. With depots implemented, spacecraft can be lifted "dry" to LEO on EELVs, meaning the high development costs of HLVs can be avoided.

Posted by Rick Boozer at 07/30/09 14:11:22

Oops! Should have said "without the high development costs of HLVs in some cases." But even projects using HLVs would benefit from depots because you can go with a smaller HLV to launch spacecraft.

Posted by Rick Boozer at 07/30/09 14:22:45

the price I've posted is for today's EELV

there is NO advantage to carry a "dry" vehicle and its fuel separately, it ONLY adds LOTS or risks to fail the mission

a rational fuel depot systems needs cargo launch costs in the range of 5-10 times less than today

Posted by one at 07/30/09 14:32:50

I don't understand what they mean by "minimum." Minimum launch size? If so, 25T seems huge.

Posted by Rand Simberg at 07/30/09 15:15:49

<i>it ONLY adds LOTS or risks to fail the mission</i>

You are still only making one launch with an expensive, possibly unique, payload. The other launch or launches are propellant. You lose a load of propellant, you just launch another.

Posted by Paul at 07/30/09 15:35:39

Wow, I'm so glad Jeff Greason would be on the committee. For a while I was afraid they were going to marginalize him, but it's really looking like his proposals will become a critical part of the final report.

Rand, if I recall correctly, when Jeff was talking about the 25mT minimum, he was referring to what the "smallest biggest chunk" (or how small they could make the biggest part) of the system they could manage was (I'm not sure if this was for lunar, Martian, or what). It sounded like he went in assuming 25mT would be more than enough, but now he's not so sure, pending further analysis.

Posted by Neil H. at 07/30/09 16:37:36

@Paul

the higher risk of mission failure is in the space-refuel operation, NOT in the launch of the propellent

I believe it's clear to everyone HOW SAFER AND EASIER IS "refuel a tank" on the launch pad...

Posted by one at 07/30/09 16:44:28

Hi Rand,
As Neil indicates, you can certainly use smaller rockets for delivering fuel and other tasks but you need at least one rocket in your stable that can launch the "smallest biggest chunk" required for efficiently designed deep space missions.

They haven't decided how massive that smallest biggest chunk is but Jeff thought there were good arguments for making it as large or larger than 25mT.
- Clark

Posted by TopSpacer at 07/30/09 17:18:28

I'd be interested to hear what they think the "smallest biggest chunk" is.

Posted by Rand Simberg at 07/30/09 17:43:01

<i>I believe it's clear to everyone HOW SAFER AND EASIER IS "refuel a tank" on the launch pad...</i>

And if you were following modern technical thinking on this, you would understand that most people are talking in terms of residual fuel, left over after rendezvous and not used for reboost operations. It's a cumulative effect, you stockpile extra consumables while you are engaged in other tasks.

Tasks like, for instance, testing long duration missions on the ISS, living on a space hotel, recovery and retrofit operations of upper stages and engines, the list goes on and on, years of work, and the moon and Mars aren't going anywhere anytime soon. Get over it.

Posted by Hey Zeus at 07/30/09 17:49:28

I'm quite literally (pleasantly) stunned by the serious suggestion that depots get added to the human exploration baseline.
Depots are a great concept and do take a lot of the burden off of HHLV development. If fully implemented literally as the baseline for NASA's architecture, yes, it will have the effect that many have been hoping for on the price/kg over time.

But I maintain this is one of those concepts, like the Stick, that seems like a great and cheaper concept at first glance but after serious analysis carries serious sticker shock and penalties. (maybe not the unsafe component that Ares 1 does though)

When serious analysis and budget planning takes place, it will become clear that depot "gas tank" flights would take up between a quarter to a third of the human spaceflight budget. Nevermind the several billion for research and developing a sufficiently sized depot in orbit, and the sloooooow buildup of experience,fuel transfer vehicles, increased production rates and flights (more pads in use too).

Most depot advocates would point out the nation would be getting much more for its money than it is with the shuttle or Ares. I agree, but unfortunately that's not the way Congress or the Smartest Administration Ever will see it.

They'll see a third of the NASA budget that used to be sucked into the reliable civil servant pockets in Houston, Huntsville, and the Cape, suddenly sprayed willy nilly into Colorado, Texas, California, and Louisiana instead, and worse, into the hands of the private sector. (some maybe, even, gasp, into the hands of a private company owner)

And that will be the end of depots.

But then, I'm a pessimist lately on anything resembling capitalist methods from our current government.

Posted by tom at 07/31/09 00:07:43

25ton, including conservative factors of safety gives an inflated volume 20m diameter and 40m long ~12500m^3 or ~35 times larger than the ISS or Bigelow module and roughly equivalent to a say 5000m^2 living space. I would probably be inclined to use a couple of shells for redundancy (inflated one inside another) and one or two more for shielding. There are also some fairly trivial ways of clipping sections together to make larger volumes if desired.

I am not sure what the maximum sized chunk is for a Mars mission (a nuclear reactor?) but it is definitely not a habitat module. Note that the Bigelow module is designed as a fully furnished and functioning space station, not as an empty shell ready to be filled with utilities, internal walls, furnishings, provisions, equipment, etc.

Posted by Pete at 07/31/09 00:41:27

I can see how the minimum size of the largest module would easily exceed 25,000 kg. I believe the dry mass of a Zubrin "Mars Direct" four man crewed Hab module exceeds 25,000 kg (and even that much mass is more realistic for a crew of only three).

Posted by Brad at 07/31/09 01:01:27

Hi Tom,
Not sure if I agree with your exact scenario but I do agree with the general idea. There has always been this conundrum, regardless of the particular administration, that if you make NASA more efficient with its funding in ways that don't put the funding into the correct districts and states, then NASA could easily see that funding disappear. Not sure if the Augustine panel can solve that.

"..one of those concepts, like the Stick, that seems like a great and cheaper concept at first glance..." Did anyone but Griffin think that? I always thought it was a horrible concept but was resigned to the fact that it was impossible to stop. I was really surprised when all the serious technical problems started showing up. So it now looks quite possible that it will be stopped but only after a heart-sickening waste of money, time, and effort.

- Clark

Posted by TopSpacer at 07/31/09 01:15:06

I can easily see how the minimum size of the largest module could exceed 25 ton, I just can not see why it should exceed 25 ton. Not when a ready to furnish habitat module shell only need weigh a few ton and one is starting out from "home depot"...

Posted by Pete at 07/31/09 01:22:07

Rand, NASA should definitely hire you. This is a big chance.

I don't really know what the big chunks are. IIRC Orion is much less than 25 t without the TEI propellants. A good LSAM can't weigh much empty.

And you could build them differently anyway - if you have depots, all kinds of assumptions about needs become different. Since you have the possibility multiple launches, you can attach all kinds of pieces to a lunar exploration stak: a LOI stage, a TEI stage, an LSAM crasher stage, some combination etc etc...

It seems the space program is running on assumptions that are not logically built, on so many facets.

Posted by gravityloss at 07/31/09 05:59:37

The "smallest largest chunk" should be the size of the Falcon 9-Heavy payload capacity, until something cheaper comes along.

Posted by Stellvia at 07/31/09 08:35:36

"I always thought it was a horrible concept but was resigned to the fact that it was impossible to stop. I was really surprised when all the serious technical problems started showing up. So it now looks quite possible that it will be stopped but only after a heart-sickening waste of money, time, and effort."

Clark, it was many many people with little actual real world physics and engineering experience thinking just like that, which let the stick (Ares I) get as far as it did. If more real engineers would have spoken up, out and loudly from the start, then the severe technical problems which indeed were self evident from the very start, would have been obvious and more widely known.

You only have yourselves to blame.

Posted by Hey Zeus at 07/31/09 10:44:04

"The "smallest largest chunk" should be the size of the Falcon 9-Heavy payload capacity, until something cheaper comes along."

I completely agree, many people still seem to assume that the payload sizes the launch vehicle - instead of the other way around.

I am not quite sure where this false assumption came from, MIR and ISS modules were sized to the launch vehicles that the world had.

Posted by Pete at 07/31/09 10:53:58

Depot with a tweek to eliminate fuel launches:

1MW solar + Vasimr (= ~6500kg) at about 200km orbit, 45N thrust at 3000Isp.

Lower a tethered collector with a big vacuum pump down to ~100km altitude, tether tension is about 100kg with 7 tonnes on each end, or about 2.5mm dia at 2GPa tensile stress.

If half drag is tether then have enough thrust to overcome about 0.003 kg/s atmosphere being sucked up and compressed = 270kg/day, 90tonnes/year.

Power pump and compressors using power down tether or beamed power or solar on collector.

Ditch any gases you don’t want. Use about 25% of Nitrogen collected to fuel the VASIMR drive, pull tether up every week to offload collected atmosphere.

20 tonnes in LEO would go a long way towards getting this all working, and could just about eliminate propellant launch. Gets more efficient as scale up due to reduced tether drag.

Posted by Robert Lynn at 07/31/09 12:20:01

Pete I wouldn't mind being wrong but I thought and still think the BA330 (like Genesis I and II) will only have "rudimentary" internal stuff like life support systems, axial structural support, a sufficiently sized satellite bus (power, c&c etc.), and gas/"atmosphere" sources. The reasoning is the comparatively limited available space in the deflated configuration (launch).

Is there some publicly available information contrary to this somewhere?

Separately about ("micro") nuclear power plants just as a reference point the Hyperion design is meant to come in at or below 20 mT: http://en.wikipedia.org/wik...

Posted by Habitat Hermit at 07/31/09 14:42:37

Habitat Hermit, indeed, calculating the approximate mass of an inflatable pressure vessel is fairly trivial, and is what I did. The mass of such a double wall pressure vessel is only a few percent of the weight of the BA330, adding insulation and impact protection one might get up to 5% of the total mass of the BA330. These numbers seem approximately correct for the materials used in the transhab module (there was a paper somewhere), note this ignores the mass of foam which should not have been there anyway...

~95% of the mass of the BA330 is not in the inflated structure but in the integrated rudimentary internal stuff. The BA330 is a bit like a camping trailer with a tent built around it, unfortunately the design is perhaps a little over constrained in this regard. I am simply advocating erecting a much larger tent shell and then furnishing it with following launches.

As the rudimentary internal structure mass of the BA330 scales mostly with the number of people, one could in theory increase the shell volume tenfold for around a fifty percent increase in overall mass. This could not support any more people, but it would give them ten times the room. With this scaling relationship in mind, there is also little financial reason why people in space should be cramped.

Posted by Pete at 07/31/09 18:58:16

Another approach for collecting propellants from the Earth's atmosphere might be to use a ram scoop vehicle on a lunar gravity assist highly elliptic orbit. Using the moon to pump the orbit back up after each atmospheric skim. But I have not yet analyzed it.

Posted by Pete at 07/31/09 20:13:26

"The "smallest largest chunk" should be the size of the Falcon 9-Heavy payload capacity, until something cheaper comes along."

That is a bad idea. Nothing should be planned around an unproven and unflown design by a relatively unproven firm. Falcon 9 is not a given.

Why to people assume it is? It is not logical or objective

Posted by me at 08/01/09 16:06:41

"Nothing should be planned around an unproven and unflown design by a relatively unproven firm. Falcon 9 is not a given.

Why to people assume it is? It is not logical or objective"

It would be far less logical to plan around the Ares V considering that NASA now has a far worse track record of developing launch vehicles than SpaceX and there would be no alternate launch vehicles of a similar size.

Not that you were necessarily advocating Ares V, though I am not sure where one would otherwise find the two or more heavy launch vehicle providers necessary to plan a heavy lift based space program around. No one else has even started developing the required back up heavy launch vehicle to the Ares V as far as I am aware.

Posted by Pete at 08/01/09 17:23:09

"That is a bad idea. ... It is not logical or objective"

Problems could certainly occur with the F9 just as happened with the F1. However, the problems will most likely be solved in a similar straight forward manner. After all, manned liquid fueled rockets have been flying since the early 1960s. There is nothing fundamentally new about the F9. It has passed design reviews by independent panels of experienced engineers who have not found any major flaws or areas where unobtanium is required.

After fixing any initial design flaws, successful operation of the F9 will just be a matter of execution on SpaceX's part, e.g. keeping quality control consistently high.

I believe that rocket engineering has progressed to a level where it is highly unlikely, though not impossible, that the F9 at this point in the development and testing process has some deep profound flaw of the sort that the Ares I is experiencing. (Note that the F1 has also tested components that are identical to those on the F9, e.g. the Merlin engine, as well as components that differ in scale but were made in same way, e.g. the tanks.)

Yes, the Ares I turned out to have serious flaws but these were in fact discovered during the detailed design process as well as in the reviews before any test flights. So rocket engineers successfully spotted these problems even in the case of a radical design on which humans have never flown before. This only increases my confidence in the state of rocket engineering.

For cargo the F9/Dragon will have cost NASA all of $300M. For manned another $300M. The sum of that is still less than the cost of single Shuttle flight. Even if there were overruns of several hundred percent to fix an F9 design problem (this is theoretical since the COTS contract doesn't allow for overruns), it would still be a bargain in comparison to the Ares I.

I'm all for having multiple service providers, e.g the EELVs, both to drive prices lower through competition and to allow for continued service in case one vehicle type is grounded for some period to fix a problem. So I'm not saying that all the eggs should be put in the F9 basket so to speak. However, I do find it quite logical and objective for NASA to base an exploration architecture on the assumption that the F9 will be usable for both manned and unmanned operations. Nothing is absolutely guaranteed but this is not supposed to be a business where zero risk is required. Certainly compared to the current architecture with the Ares I, the F9 risk is far lower.

- Clark

Posted by TopSpacer at 08/01/09 23:49:59

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