Author Topic: LV Agnostic Prop Depot/Tank: Size and Design  (Read 9182 times)

Offline JohnFornaro

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #20 on: 01/16/2012 01:00 AM »
Here is a cost differential analysis just for the cost of the propellant delivered to L1 of Hydrazine and LH2/LOX. A small fully reusable lander L1 to lunar surface and back using 27mt of Hydrazine propellant or 10mt of LH2/LOX propellant (I said it was a small human lander on approximate scale to the LEM, size is used just to show costs differentials for the propellant used) that does 2 missions per year over 5 years of operations would experience for a cost of propellant delivered at L1 at the price range of $10,000-$20,000/kg (thatís equivalent to being able to put something in LEO for <$3,000-$6,000/kg) would have a cost difference of $1.7B to $3.4B.

I'm fine with the size, number of missions, and number of years, for purposes of discussion.  But how did you come up with $10k to $20K/kg of prop costs?  And that cost differential?
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Online oldAtlas_Eguy

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #21 on: 01/16/2012 04:54 PM »
Here is a cost differential analysis just for the cost of the propellant delivered to L1 of Hydrazine and LH2/LOX. A small fully reusable lander L1 to lunar surface and back using 27mt of Hydrazine propellant or 10mt of LH2/LOX propellant (I said it was a small human lander on approximate scale to the LEM, size is used just to show costs differentials for the propellant used) that does 2 missions per year over 5 years of operations would experience for a cost of propellant delivered at L1 at the price range of $10,000-$20,000/kg (thatís equivalent to being able to put something in LEO for <$3,000-$6,000/kg) would have a cost difference of $1.7B to $3.4B.

I'm fine with the size, number of missions, and number of years, for purposes of discussion.  But how did you come up with $10k to $20K/kg of prop costs?  And that cost differential?

The 10K to 20K cost of delivery of prop to L1 is actually optimistic of either a FH with LH2 EDS (the low value) or an SLS that is doing around 3 or more flights per year (the high value). Delivery of LH2 is actually simpler and has lower dry weight since the tanks for the delivered prop is just a stretched tank of the EDS itself. Other prop types require separate tanks which causes its own inefficiencies in dry weight for the delivery of prop.

For the lander you are correct in that lower density increases dry weight but so does an increases in total amount of propellant. The volume needed for pure Hydrazine vs LH2 to deliver a set delta V for a reusable lander is nearly the same for either. The advantage in used volume is only when you use the Hydrazine/LOX combo which I havenít calculated yet but it is not as much of an advantage as you are suggesting with at most an increase in tank dry weight by at most a factor of 2 but all other dry weights are constant (RP1 and CH4 have a tank volume advantage factor of only 1.5 each over LH2 lander solutions). The tank weight of a lander in these cases varies for 50% to 75% of the total lander dry weight based on design. So yes it makes a difference but how much is a question of design more so than propellant density.

The cost of propellant at L1 is currently extremely variable depending on how and who gets it there. The actual cost could be higher which would cause a higher delta between the costs of getting LH2/LOX vs a lower ISP prop combination. Youíre correct in that the lander and tanker dry weights drive up the costs for the low density LH2 or CH4 solutions operational costs because a higher dry weight for the lander needs more propellant lowering the delta costs unfortunately that also varies widely based on the solutions actual dry weight designs. The development costs of a solution based on prop type is also another highly variable item that varies widely based on how and who is doing the development. In all there is just too much variability to definitely say one prop solution will be better cost wise than another there is cost advantages and disadvantages for each solution. Here I was just pointing out just one aspect of that solution space of the costs of delivery of the propellant to L1 by propellant type.

So in the end if you have a sufficiently accurate set of by weight for the reusable lander propellant usage totals by propellant types given a set lander capability a more accurate cost delta just for the cost of propellant delivered to L1 can be estimated for each solution set.

Online AnalogMan

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #22 on: 02/15/2012 01:04 PM »
Thought this recently posted paper by NASA may be of interest to readers of this thread:

Space Transportation Infrastructure Supported By Propellant Depots
AIAA Space 2011 Conference and Exposition; 26-29 Sep. 2011 - 26pp

Abstract
A space transportation infrastructure is described that utilizes propellant depot servicing platforms to support all foreseeable missions in the Earth-Moon vicinity and deep space out to Mars. The infrastructure utilizes current expendable launch vehicle (ELV) systems such as the Delta IV Heavy, Atlas V, and Falcon 9, for all crew, cargo, and propellant launches to orbit

Propellant launches are made to a Low-Earth-Orbit (LEO) Depot and an Earth-Moon Lagrange Point 1 (L1) Depot to support new reusable in-space transportation vehicles. The LEO Depot supports missions to Geosynchronous Earth Orbit (GEO) for satellite servicing, and to L1 for L1 Depot missions. The L1 Depot supports Lunar, Earth-Sun L2 (ESL2), Asteroid, and Mars missions.

New vehicle design concepts are presented that can be launched on current 5-meter diameter ELV systems. These new reusable vehicle concepts include a Crew Transfer Vehicle (CTV) for crew transportation between the LEO Depot, L1 Depot and missions beyond L1; a new reusable Lunar Lander for crew transportation between the L1 Depot and the lunar surface; and a new reusable Deep Space Habitat (DSH) with a CTV to support crew missions from the L1 Depot to ESL2, Asteroids, and a Mars Orbital Depot. The LEO Depot, L1 Depot, and Mars Orbital Depot are based on International Space Station (ISS) heritage hardware.

Data provided includes the number of launches required for each mission utilizing current ELV systems (Delta IV Heavy or equivalent) and the approximate vehicle masses and propellant requirements. Also included is a discussion on affordability with ideas on technologies that could reduce the number of launches required and thoughts on how this infrastructure might be implemented incrementally over the next few decades.

The potential benefits of this propellant depot infrastructure include competitive bidding for ELV flights and propellant services, development of new reusable in-space vehicles, and development of a multiuse infrastructure that can support many government and commercial missions simultaneously.


http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120001435_2012001131.pdf

Offline JohnFornaro

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #23 on: 02/15/2012 02:12 PM »
Thanks for posting.  Promises to be an interesting read.
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Offline A_M_Swallow

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #24 on: 02/15/2012 02:39 PM »

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120001435_2012001131.pdf

Is the journey from L1 Depot to the Lunar surface really '~2-3 week' or should it say '~2-3 days'?

I like this plan.

Offline deltaV

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #25 on: 02/15/2012 04:02 PM »
Is the journey from L1 Depot to the Lunar surface really '~2-3 week' or should it say '~2-3 days'?

All of the other missions in Figure 1 appear to give time and delta-vee for a round-trip. I think the error in the lunar mission is not the 2-3 weeks, which is reasonable for a round trip including time spent on surface, but the delta-vee, which is only one-way.

Offline JohnFornaro

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #26 on: 02/16/2012 01:34 PM »
All of the other missions in Figure 1 appear to give time and delta-vee for a round-trip.

Wait a sec.  Delta-v from Earth to Leo is readily rounded from 9.8 to 10 km/s.  That's one way.  From Wiki:

http://en.wikipedia.org/wiki/Delta-v_budget

The values shown at Wiki don't seem to jive with this chart on this thread.


Earth to LEO-Ken     9.3-10
LEO-Ken to GEO       4.33
LEO-Ken to L1        3.77
L1 to Moon           2.52


The chart shows one way these values:

Earth to LEO          10
LEO to GEO (total)    6.5
(I presume "total" means round trip?)
LEO to L1 (total)     4.1
L1 to Moon            2.52


Again, what is it that I'm not getting about delta-v?
« Last Edit: 02/16/2012 04:13 PM by JohnFornaro »
Sometimes I just flat out don't get it.

Offline Robotbeat

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #27 on: 02/16/2012 02:53 PM »
All of the other missions in Figure 1 appear to give time and delta-vee for a round-trip.

Wait a sec.  Delta-v from Earth to Leo is readily rounded from 9.8 to 10 km/s.  That's one way.  From Wiki:

http://en.wikipedia.org/wiki/Delta-v_budget

The values shown at Wiki don't seem to jive with this chart on this thread.


Earth to LEO-Ken   9.3-10
LEO-Ken to GEO      4.33
LEO-Ken to L1      3.77
L1 to Moon      2.52


The chart shows one way these values:

Earth to LEO      10
LEO to GEO (total)   6.5
(I presume "total" means round trip?)
LEO to L1 (total)   4.1
L1 to Moon      2.52


Again, what is it that I'm not getting about delta-v?
The trip back can brake non-propulsively using the atmosphere. I.e. aerocapture/aerobraking.
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Offline JohnFornaro

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Re: LV Agnostic Prop Depot/Tank: Size and Design
« Reply #28 on: 02/16/2012 04:15 PM »
The trip back can brake non-propulsively using the atmosphere. I.e. aerocapture/aerobraking.

I know that aerocapture/aerobraking is theoretically available, but it would have an associated delta-v "charge" as it were, on the return trip.  This is not specified in the chart in any case.
Sometimes I just flat out don't get it.

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