Author Topic: EDS size requirements  (Read 16029 times)

Offline mmeijeri

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EDS size requirements
« on: 05/02/2009 11:26 am »
New thread so as not to hijack the 'Most likely CLV' thread.
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Offline mmeijeri

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Re: EDS size requirements
« Reply #1 on: 05/02/2009 11:41 am »
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Why do you insist on having the thrust of a J-2X?

That's what it takes to boost the Ares V EDS into orbit.  The stage will weigh something like 280 tonnes at ignition - more than an entire Delta IV Medium!  RL10 only produces something like 10-11 tonnes of thrust.  Imagine an EELV needing to be powered not long after liftoff by an RL10 cluster!   

OK, that's one way of looking at it. If you intend to used an EDS the size of Ares V, then getting the thrust you need is too much for RL-10's. But you could also look at it the other way and say having such a big EDS is the problem. Each option has its advantages and disadvantages. Why do we need such a big EDS? Because NASA chooses to do EOR-LOR instead of LOR-LOR, and chooses not to use hypergolic propellants on the Altair so it can't be dry-launched.

And this is among a long list of choices NASA has made that ensure maximum in-house development and minimal commercial synergies. NASA has chosen an incredibly expensive architecture that requires 2 new launch vehicles, two new upper stages, new 5 seg boosters, new 5.5 seg boosters, new RS-68B engines, new J-2X engines, new deeply throttleable cryogenic engines for Altair.

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If not Ares V and EDS, then some other big stage will be needed for the lunar mission, even for a dual-launch architecture, and it will still need a lot of thrust to make it into LEO.  If not 12 RL10s, then maybe 11 - and 22 or 24 total for a single dual launch mission (about as many RL10s as have flown in this entire *decade*).  If a TLI-only stage is used, which would mean less thrust for the TLI burn, another ascent stage would still be needed, again with lots of thrust but requiring the launch vehicle to carry even more expensive engines on even more stages, etc.. 

DIRECT proposes using an EDS with 6 RL-10s and you can still send something like 70mT through TLI together. With L1 rendez vous you can even make do with a DHCSS, with LOR-LOR you would need a slightly larger stage.
« Last Edit: 05/02/2009 02:03 pm by mmeijeri »
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Online edkyle99

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Re: EDS size requirements
« Reply #2 on: 05/02/2009 02:24 pm »

DIRECT proposes using an EDS with 6 RL-10s and you can still send something like 70mT through TLI together. With L1 rendez vous you can even make do with a DHCSS, with LOR-LOR you would need a slightly larger stage.

The DIRECT literature I can find talks about an upper stage with *two* J-2X engines to power a stage that weighs about 100 tonnes *more* than the Ares V EDS.  http://www.launchcomplexmodels.com/Direct/documents/DIRECT_Summary_v2.0.2.pdf

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Offline mmeijeri

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Re: EDS size requirements
« Reply #3 on: 05/02/2009 02:31 pm »
The DIRECT literature I can find talks about an upper stage with *two* J-2X engines to power a stage that weighs about 100 tonnes *more* than the Ares V EDS.  http://www.launchcomplexmodels.com/Direct/documents/DIRECT_Summary_v2.0.2.pdf

Since then they have switched to SSME as their baseline core engine, in part because it allows switching to RL-10 as an upper stage engine in case there isn't enough money to develop J-2X. The new configuration is called J-246.
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Offline Stephan

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Re: EDS size requirements
« Reply #4 on: 05/02/2009 03:07 pm »
RL-10 only apply to versions with SSME powered core.
Suborbital burn after staging is less important than with the RS-68 version, so less gravity loss and then less need for a high thrust engine on EDS.

Ross said :

3x RS-68B:   Core Stage Burnout @ ~T+298sec @ 5,335m/s.
3x RS-68 Regen:   Core Stage Burnout @ ~T+306sec @ 5,790m/s.
4x SSME:   Core Stage Burnout @ ~T+385sec @ 6,605m/s.
« Last Edit: 05/02/2009 03:08 pm by Stephan »
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Offline butters

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Re: EDS size requirements
« Reply #5 on: 05/02/2009 03:44 pm »
Why do we need such a big EDS? Because NASA chooses to do EOR-LOR instead of LOR-LOR

LOR-LOR means LSAM and CSM are each launched with their own EDS?  Sure, that would allow for a smaller EDS configuration, but the combined dry mass of the two stages through TLI would be higher.

Isn't the better criticism of the CxP mission profile that the EDS has to lift the LSAM to LEO and is therefore sized larger than if it had been launched on its own?

EOR-LOR isn't the problem.  The 1.5 launch is the problem.

Apollo 13 is Exhibit A in the case for EOR-LOR.  If the crippled CSM had to coast to cislunar space and perform an LOI burn before docking with the LM, then the crew would have been lost.  If the CSM and LM were to have docked in LEO for checkout before the TLI burn instead of after, then the failure would have occurred much closer to earth and the abort would have involved far less risk of crew loss.

If we had the booster to lift another single-launch lunar mission, it would still make sense to do EOR-LOR.  If we use two launches, EOR-LOR is practically imperative for manned missions.  We can't responsibly send the CSM beyond LEO without the spare life support vessel and propulsion stage provided by the LSAM.

DIRECT has the right approach to EOR-LOR.  CxP doesn't.

Offline mmeijeri

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Re: EDS size requirements
« Reply #6 on: 05/02/2009 03:56 pm »
LOR-LOR means LSAM and CSM are each launched with their own EDS?  Sure, that would allow for a smaller EDS configuration, but the combined dry mass of the two stages through TLI would be higher.

That is true, but that advantage is wiped out if you use L1 rendez-vous. You can then use slow but efficient trajectories to L1 for the lander, its propellant and its cargo.

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Isn't the better criticism of the CxP mission profile that the EDS has to lift the LSAM to LEO and is therefore sized larger than if it had been launched on its own?

Well, it's a criticism I agree with.

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EOR-LOR isn't the problem.  The 1.5 launch is the problem.

I'd say the DIRECT approach is better than Ares, but I prefer staging.

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Apollo 13 is Exhibit A in the case for EOR-LOR.  If the crippled CSM had to coast to cislunar space and perform an LOI burn before docking with the LM, then the crew would have been lost.  If the CSM and LM were to have docked in LEO for checkout before the TLI burn instead of after, then the failure would have occurred much closer to earth and the abort would have involved far less risk of crew loss.

This is a better argument in my opinion, though DIRECT also proposes L1 staging further down the line. One potential solution is to use a modified Altair ascent stage as a mission module. And note that the Orion RCS is sized to be able to function as a backup for the TEI. Or at least it was at some point.

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If we had the booster to lift another single-launch lunar mission, it would still make sense to do EOR-LOR.  If we use two launches, EOR-LOR is practically imperative for manned missions.  We can't responsibly send the CSM beyond LEO without the spare life support vessel and propulsion stage provided by the LSAM.

The Orion doesn't have a backup on the return trip, I don't see how no backup is acceptable during return from the moon, but irresponsible on the way to the moon.
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Offline butters

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Re: EDS size requirements
« Reply #7 on: 05/02/2009 04:58 pm »
The Orion doesn't have a backup on the return trip, I don't see how no backup is acceptable during return from the moon, but irresponsible on the way to the moon.

Yeah, I thought of that.  You can get the redundancy on the departure trip at very little cost (some extra consumables to operate the LSAM) because all of that mass is going to lunar orbit anyway.  So it's irresponsible not to provide all those added crew safety contingencies.  On the return trip, you'd have to push the ascent stage of the LSAM through TEI, so that's more of a performance vs. capability trade-off.

I was actually considering asking on the DIRECT thread about the feasibility of retaining the LSAM ascent stage through the bulk of the return trip.  I'm sure the crew would appreciate the extra cabin space.

Any way you slice it, a more-or-less healthy CM is required for reentry.  I can imagine some contingency plans involving an LEO rendezvous with either a LON rescue CSM or an ISS layover that could possibly save a crew that resorted to the LSAM lifeboat due to a CM failure that would preclude reentry.

Offline mmeijeri

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Re: EDS size requirements
« Reply #8 on: 05/02/2009 05:23 pm »
Yeah, I thought of that.  You can get the redundancy on the departure trip at very little cost (some extra consumables to operate the LSAM) because all of that mass is going to lunar orbit anyway.

I wouldn't say at little cost, because the JUS is very expensive to develop.

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  So it's irresponsible not to provide all those added crew safety contingencies.  On the return trip, you'd have to push the ascent stage of the LSAM through TEI, so that's more of a performance vs. capability trade-off.

I think it's a trade-off anyway. Using L1 rendez-vous pretty much requires a hypergolic lander in the short term, which has its own safety benefits. A gateway station would also have some safety benefits.

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I was actually considering asking on the DIRECT thread about the feasibility of retaining the LSAM ascent stage through the bulk of the return trip.  I'm sure the crew would appreciate the extra cabin space.

With hypergolic refueling at L1, this wouldn't be a problem.

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Any way you slice it, a more-or-less healthy CM is required for reentry.  I can imagine some contingency plans involving an LEO rendezvous with either a LON rescue CSM or an ISS layover that could possibly save a crew that resorted to the LSAM lifeboat due to a CM failure that would preclude reentry.

This only works on the outbound journey, since propulsive braking to LEO is too expensive. Intriguingly, a return to GEO would be different, provided you use L1 refueling.

I've become fond of an architecture that uses hypergolic refueling at L1 anyway. L1 is such an excellent staging location and depots are so powerful that even with the low Isp of hypergolics, cargo missions are actually more efficient than current plans. And once boil-off mitigation is developed and cryo depots become operational, it would become even more efficient. And L1 is not only useful for trips to the moon, but also to other locations in near-Earth space.

I had been thinking about using Orion for that, but an Altair ascent stage (or AS+Orion) is even more interesting. It already has a delta-v of 2 km/s, enough to get back to GEO. You would want to use it in conjunction with an Orion, for satefy. Because the Orion is so much heavier than the ascent stage, you would have to use its propulsion system too. A more elegant solution would use a bigger ascent stage or perhaps a completely hypergolic lander as a shuttle.

Now, I haven't done all the calculations yet, but it looks as if a reusable hypergolic shuttle between GEO and L1 is perfectly feasible and not ridiculously expensive. You would need to have a way to get the Orion to GEO of course, and you may need a bigger EDS / JUS for that. In this way you could have a completely reusable transport system between GEO and the lunar surface. The Orion could also be reused. The only thing you'd be throwing away is the Orion SM (though that could also be saved too if it is cost effective) and the Jupiter cores.
« Last Edit: 05/02/2009 05:29 pm by mmeijeri »
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Offline butters

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Re: EDS size requirements
« Reply #9 on: 05/02/2009 05:45 pm »
Yeah, I thought of that.  You can get the redundancy on the departure trip at very little cost (some extra consumables to operate the LSAM) because all of that mass is going to lunar orbit anyway.
I wouldn't say at little cost, because the JUS is very expensive to develop.

You need the JUS to push both spacecraft through TLI anyway.  It's just a question of whether Orion docks with Altair before or after TLI.  And when I said cost, I meant payload efficiency, not development cost.

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I've become fond of an architecture that uses hypergolic refueling at L1 anyway. L1 is such an excellent staging location and depots are so powerful that even with the low Isp of hypergolics, cargo missions are actually more efficient than current plans. And once boil-off mitigation is developed and cryo depots become operational, it would become even more efficient. And L1 is not only useful for trips to the moon, but also to other locations in near-Earth space.

I'm only vaguely familiar with the practical usage of Lagrangian points as rendezvous locations for space exploration.  This is something I should read more about.

Offline mmeijeri

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Re: EDS size requirements
« Reply #10 on: 05/02/2009 06:04 pm »
You need the JUS to push both spacecraft through TLI anyway.  It's just a question of whether Orion docks with Altair before or after TLI.

To get back to the main topic of the thread, it is true that you need some kind of EDS, but not necessarily one as large as the JUS. The DIRECT team plans to use the Delta IV Heavy upper stage, also known as DHCUS, also known as DHCSS, as a temporary upper stage for an Apollo 8 style mission even before the JUS is developed. You could also use a Centaur, but it can put less mass through TLI.

Now the Orion has enough propellant to get into lunar orbit, but not enough to do both that and the TEI to get back home. The DIRECT team has figured out that they do have enough fuel to get into a highly elliptical orbit and still have enough fuel to do the TEI to get back. Similarly, you can use the DHCSS to get the Orion to L1, with enough fuel to do both the final insertion into L1 and the TEI to get back. You don't have a whole lot of margin, but it just about works. In other words, if you use L1 staging, you don't need a JUS.

Of course, if you do have a JUS, you can still do staging and DIRECT is planning to do that as a later evolution.The disagreement is over what is more important and should be done first, lunar landings or gateway stations and depots. And since I'm in favour of synergy with commercial activities, I prefer the approach that doesn't need a big launcher that is inaccessible and far too expensive for commercial applications.

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I'm only vaguely familiar with the practical usage of Lagrangian points as rendezvous locations for space exploration.  This is something I should read more about.

They are very interesting. A lot of progress has been made in astrodynamics recently. It turns out there are very interesting low-energy routes between L-points and between L-points and other destinations. For instance you can get from LEO to L1 for 3.2 km/s using such an efficient route, as opposed to 3.8 km/s for a more conventional route.

These routes are very slow (>100 days) and therefore only useful for cargo/propellant. But since cargo and propellant are most of your mass anyway (especially if you use hypergolics), these routes generate a lot of savings, even with the low Isp of hypergolics.

For interplanetary travel the Sun-Earth Lagrange points are even more efficient. See http://iaaweb.org/iaa/Studies/nextsteps.pdf for a well thought-out proposal that uses SEL-2 staging.

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And when I said cost, I meant payload efficiency, not development cost.

This is more than compensated for by the efficient routes.
« Last Edit: 05/02/2009 06:20 pm by mmeijeri »
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Offline MP99

Re: EDS size requirements
« Reply #11 on: 05/02/2009 06:16 pm »

DIRECT proposes using an EDS with 6 RL-10s and you can still send something like 70mT through TLI together. With L1 rendez vous you can even make do with a DHCSS, with LOR-LOR you would need a slightly larger stage.

The DIRECT literature I can find talks about an upper stage with *two* J-2X engines to power a stage that weighs about 100 tonnes *more* than the Ares V EDS.  http://www.launchcomplexmodels.com/Direct/documents/DIRECT_Summary_v2.0.2.pdf

 - Ed Kyle


Ed,

that was their J-232 vehicle (with 3x RS-68 engines).

DIRECT has now baselined 4xSSME for the Lunar mission, although they have left choice of upper stage engine open at the moment, since several options close CxP requirements with plenty of margin.

Their LV-41 version of their J-246 config (6x RL-10B-2) claims 100mT+ TLI propellant (after 4 days boiloff @ 0.35% per day) in an EDS massing ~13mT. This can push 79.7mT thru TLI.

If J-246's EDS massed another 13mT (still slightly less than AVUS, IIUC), that would increase DIRECT's thru-TLI fuel requirement by well over 13mT.

If J-246's EDS also had to operate at 445s (per Ross's comments re the J-2X programme), that would add a further 4-5mt to the fuel required to push CxP's 71.1mT requirement thru TLI (a bit more for 79.7mT, obviously).

Note that these are my calculations based on simple rocket equation considerations, not DIRECT-provided figures.

cheers, Martin

Offline MP99

Re: EDS size requirements
« Reply #12 on: 05/02/2009 06:32 pm »
One potential solution is to use a modified Altair ascent stage as a mission module.

The ascent stage is extremely light ~3.3mT burnout. This is partly achieved by leaving the life support system behind in the lander. The crew can survive for some hours on stored consumables, then things get a bit sticky...

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And note that the Orion RCS is sized to be able to function as a backup for the TEI. Or at least it was at some point.

RCS & MPS share the same propellant, and similar Isp's. By routing prop through the RCS system, similar gross delta-V can be achieved. Since thrust is only a few percent of MPS, though, gravity losses will be much higher, and the thrusters will have to burn for a very long time.

cheers, Martin

Offline mmeijeri

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Re: EDS size requirements
« Reply #13 on: 05/02/2009 06:35 pm »
The ascent stage is extremely light ~3.3mT burnout. This is partly achieved by leaving the life support system behind in the lander. The crew can survive for some hours on stored consumables, then things get a bit sticky...

Ah, I had wondered how its dry mass could be so low. In that case, one of the required modifications would be to add full-size life support systems...

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RCS & MPS share the same propellant, and similar Isp's. By routing prop through the RCS system, similar gross delta-V can be achieved. Since thrust is only a few percent of MPS, though, gravity losses will be much higher, and the thrusters will have to burn for a very long time.

I don't have the details, but I think the RCS was believed to be powerful enough for that. Any expert opinions on that?
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Online edkyle99

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Re: EDS size requirements
« Reply #14 on: 05/02/2009 08:42 pm »
The DIRECT literature I can find talks about an upper stage with *two* J-2X engines to power a stage that weighs about 100 tonnes *more* than the Ares V EDS.  http://www.launchcomplexmodels.com/Direct/documents/DIRECT_Summary_v2.0.2.pdf

Since then they have switched to SSME as their baseline core engine, in part because it allows switching to RL-10 as an upper stage engine in case there isn't enough money to develop J-2X. The new configuration is called J-246.

'Kinda hard to discuss something that keeps changing - and for which nothing seems to be presented on the Direct web site.

 - Ed Kyle
« Last Edit: 05/02/2009 08:44 pm by edkyle99 »

Offline mmeijeri

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Re: EDS size requirements
« Reply #15 on: 05/02/2009 08:44 pm »
'Kinda hard to discuss something that keeps changing.

Good thing Constellation is so stable. ;)
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Online edkyle99

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Re: EDS size requirements
« Reply #16 on: 05/02/2009 09:31 pm »
'Kinda hard to discuss something that keeps changing.

Good thing Constellation is so stable. ;)

Ares program hasn't resorted to mass RL-10 clusters.

How, by the way, do six RL10B-2 engines fit?  They need a lot of clearance for  those big French nozzle extensions. 

 - Ed Kyle
« Last Edit: 05/02/2009 09:31 pm by edkyle99 »

Offline mmeijeri

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Re: EDS size requirements
« Reply #17 on: 05/02/2009 09:46 pm »
How, by the way, do six RL10B-2 engines fit?  They need a lot of clearance for  those big French nozzle extensions. 

Yikes, that looks big! BTW what do you mean by French nozzle extensions? I'll leave the DIRECT people to defend the J-246 concept as I'm moderately enthusiastic about J-130, but opposed to a JUS. I'm very curious what you think of L1 rendez vous and DHCSS as an EDS.
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Offline Kaputnik

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Re: EDS size requirements
« Reply #18 on: 05/02/2009 09:52 pm »
Ah, I had wondered how its dry mass could be so low. In that case, one of the required modifications would be to add full-size life support systems...

Every gram added to the LSAM ascent stage has a massive multiplier throughout the whole system. It's the most mass-critical part of the whole mission- you'd be better off building in the required margin in Orion, and then not taking it down to the surface and back.
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Offline mmeijeri

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Re: EDS size requirements
« Reply #19 on: 05/02/2009 10:09 pm »
Every gram added to the LSAM ascent stage has a massive multiplier throughout the whole system. It's the most mass-critical part of the whole mission- you'd be better off building in the required margin in Orion, and then not taking it down to the surface and back.

Yes, if you are constrained by the size of your EDS. And if you insist on putting everything through TLI together you are, even if you use a giant EDS. That's a logical enough choice, but there are alternatives. With refueling it is much less of a problem. Of course you still need a lot of propellant, but if you save the cost of a brand new Altair for every landing, you can afford to launch more propellant. Unless my calculations are very wrong (and they could easily be), the extra cost is on the order of hundreds of millions, similar to the cost of an Altair.

You'd need a monolithic lander of course, which means you'd have to lift more mass back to L1, but it also means you could remove common systems, which would save some mass. I think I read somewhere in a ULA paper that a single stage lander wouldn't be much heavier than a two stage one. It would of course be considerably heavier than just an ascent module.
« Last Edit: 05/02/2009 10:13 pm by mmeijeri »
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