Author Topic: A Minimal Architecture for Human Journeys to Mars (JPL)  (Read 51394 times)

Offline RonM

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #20 on: 07/02/2015 10:00 PM »
NASA's Mars DRA 5.0 from 2009 had eight launches, seven Ares V and one Ares I.

Boeing's "Mission to Mars in Six (not so easy) Pieces" study presented in 2014 has five SLS launches. It uses an EML-2 gateway station.

So six SLS launches isn't bad, especially since it doesn't require a gateway station.

Mars Direct and Semi-Direct are too minimalist.
Yes this is a "simple, cheap" Mars mission by NASA standards.  :)

Absolutely, by government standards.  ;)

Now we'll have to wait and see if the private sector and reusable rockets can lower the cost, but you have to plan on what you got. Right now, that's SLS.

Offline Profwoot

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #21 on: 07/03/2015 02:59 AM »
The authors gave a presentation on their proposal a month before publication. The slides (attached) include some additional info and visualizations.

Offline john smith 19

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #22 on: 07/03/2015 08:10 AM »
Absolutely, by government standards.  ;)

Now we'll have to wait and see if the private sector and reusable rockets can lower the cost, but you have to plan on what you got. Right now, that's SLS.
A while back I looked at what US launchers could launch as a salvo now. At that point both the F9 and Antares were available. With A Delta IV, Atlas V, F9 and Antares I estimated you could put about 64 tonnes into LEO within less than 2 week (apparently there is a lot of comm channels that need testing and re configuration on the necessary ranges, something I had never considered). My instinct is this could be brought down to 1 week with some effort.

That's most of a low end SLS with no new LV development (and certainly not the $35Bn+ that SLS/Orion has swallowed already).

What SLS gives you is that 10m payload fairing and that you can't get anywhere else.

How badly that's needed is another question. The key fact is by relying on existing hardware you are not at the mercy of future funding of key components, which Congress has been all too willing to cut.  :(

I do like their recognition that all the various factors have to align. There has to be political milestones (photo ops) during each presidency to give some sense that for the current President this is "their" baby as well.

James Webb probably recognized this sort of thing instinctively but it's been a long time since NASA had someone so well plugged into the political establishment.  :(
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #23 on: 07/03/2015 09:12 AM »
Absolutely, by government standards.  ;)

Ok then, how would you make it simpler? The landers are about as simple as it gets, the ascent vehicle as well. Those are probably the biggest cost factors, so it makes sense to minimize their complexity. You need to push those landers from HEO to Mars, so you take an EUS because that's availabe. Even without SLS, you need some kind of big stage to do this, and a lot bigger one from LEO (or SEP, but you need a lot more power than 100kw for that).

Then there's the habitat, NASA has plenty of experience with that and I'm sure they know what is needed here. They decide to resupply the habitat in HMO, in order to minimize the habitat's mass at departure from HEO and HMO. That helps keeping the MOI and TEI stages small. A 100kw SEP can pre deploy the TEI to HMO in a reasonable time frame, when launched with an SLS towards Mars.

One could debate whether it would make sense to go back to cis-lunar space and not take Orion with them, but I guess that's a close call.

For an expendable architecture with SLS available, I don't see it getting any simpler (short of Mars direct nonsense).

« Last Edit: 07/03/2015 09:31 AM by Oli »

Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #24 on: 07/03/2015 10:49 AM »
The authors gave a presentation on their proposal a month before publication. The slides (attached) include some additional info and visualizations.

Thanks for posting this.

I will acknowledge it's a start, albeit the kind of start a newborn giraffe has which involves a hard 5-foot plop followed by a half-hour of awkward walking.  I do appreciate how they break down each leg of the mission and basically explain what's sent aboard each SLS.  Some parts make sense and could work, but others seem unnecessary.  I'll make a complement sandwich up...

I'll state what I dislike first.  While I endorse Phobos/Deimos exploration, setting up a Phobos base seems redundant.  The base and the crew's main habitat are the same vehicle (a DSH working in zero-to-micro-gravity)...if you need to physically land just include legs with the habitat; better to apply the mass toward the propulsion stages (especially without any form of ISRU).  Speaking of mass, secondly is the notion of dragging Orion to Mars: a flat-out terrible idea.  It's a life-boat to nowhere while at Mars and the propulsion stage dedicated to Phobos-to-HMO operation would do a better job than it's limited service module; keep it within Cislunar space if it's to be used at all.  Finally, and most obviously, four flights for an orbital mission and six for a surface one - in fairness the real x-factor will be how many SLSs can be built in a single year.  If we're nominally assuming 2, that means at least 3 years needs to be devoted to building just the rockets for a full-fledged landing party that's an extremely short one-shot deal; I know the government can be wasteful but this seems a lil much.

Now for what I like.  Obviously there's visiting the moons; seeing them during a long orbital stay makes sense and makes the most of what otherwise would be a long and dull visit.  Second, HEO, not anything lunar at all, seems implied - that translates to avoiding wasted fuel for 'parking' hardware near Luna and focusing the flight to Mars itself - even Zubrin himself would respect that.  Third, while the DAV isn't the lander I'd want it might be one that could work; if nothing else it would eventually serve a purpose as a one-way platform for Martian infrastructures.

What I'd suggest to improve this at least a little:

Orbital Mission
1) Drop the Phobos base
2) Leave Orion in Earth orbit
-Reduces flights to 3 SLSs and frees up mass for fuel and supplies instead of dragging out extra vehicles-

Lander Mission
1) Directly send the DAV to Mars via single SLS
2) Leave Orion in Earth orbit
3) Minimize number of rendezvouses in Mars orbit involving DAV
-Reduces flights at least to 5, possibly 4 SLSs


Especially for the lander mission, for better or worse they would need to send up a lot of propulsion stages, but just by leaving Orion behind at Earth you free up an easy 20 tonnes.  Likewise with the Phobos base - just have the crew hab double as a Phobos lander and you save the mission an entire SLS.  Overall, I'd agree with the orbital half of this scheme (sans the Phobos base) because of the lighter logistics with a chance of reusing the crew hardware.  Otherwise, however you take to this plan it does point to Martian EDL as the real challenge.  Once the SLS is operational, the next heavy duty should be developing a Mars lander (potentially as DAV).
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #25 on: 07/03/2015 11:52 AM »
Orbital Mission
1) Drop the Phobos base
2) Leave Orion in Earth orbit
-Reduces flights to 3 SLSs and frees up mass for fuel and supplies instead of dragging out extra vehicles-

Lander Mission
1) Directly send the DAV to Mars via single SLS
2) Leave Orion in Earth orbit
3) Minimize number of rendezvouses in Mars orbit involving DAV
-Reduces flights at least to 5, possibly 4 SLSs

Orbital mission:
- The Phobos habitat provides supplies for the crew, you'd have to add that to the transfer habitat, increasing its mass by maybe up to 10t (note the hab gets resupplied im HMO for the other missions). Also requires the hab to go down from HMO to Phobos orbit, increasing MOI and TEI stage mass. 100kw SEP would likely be too slow to do that for the crewed hab. Note commonality with the Mars landing missions is important.
- Requires more delta-v to break the habitat into cis-lunar space. Also would require an additional transfer vehicle from HMO to Phobos orbit (if the hab doesn't go there). But yeah, might not be a bad idea.

Lander mission:
- Not feasible. Lander entry mass is 75t. Block 2 TMI performance is how much? 40t? You would likely need HIAD and ISRU (for ascent fuel) to get away with such small entry mass, and you'd only save 3 SLS (of 10) per campaign.
- See above.

Overall not obvious improvements to me.

If we're nominally assuming 2, that means at least 3 years needs to be devoted to building just the rockets for a full-fledged landing party that's an extremely short one-shot deal; I know the government can be wasteful but this seems a lil much.

There won't be more missions anyway, so how is it wasteful? Or do you expect a mission every 2 years?
« Last Edit: 07/03/2015 12:04 PM by Oli »

Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #26 on: 07/03/2015 11:56 AM »
Overall not obvious improvements to me.

Saving a billion here and there would keep a Congressional ax at bay :P
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Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #27 on: 07/03/2015 04:30 PM »
The one thing I did like about their mission was just having a lander with a MSL heritage heat shield and plain old fashioned retro braking. I would not want to subject a crew to that, but it would be a nice basis for pre deploying equipment, rovers etc and you could and should test it with robotic precursors.

I'm very tempted here to use hypergolics instead of methalox for the non manned landers. Does mean more engine development but not a hell of a lot.

A couple of questions. Can you get away with battery powered pumps for the hypergolic engines (see for instance the Rutherford engine). Secondly what about two SpaceX Falcon 9 heavy rockets being launched not a week apart but simultaneously? Doesn't seem to be too much of a stretch.

Also, as far as mass to earth orbit goes, I don't mind using up lots of dumb "upper stages" if you can launch them cheaply on a SpaceX rocket. What I don't get is that this mission relies exclusively on SLS which is going to absolutely bleed money.

Offline RonM

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #28 on: 07/03/2015 04:55 PM »
Absolutely, by government standards.  ;)

Ok then, how would you make it simpler? The landers are about as simple as it gets, the ascent vehicle as well. Those are probably the biggest cost factors, so it makes sense to minimize their complexity. You need to push those landers from HEO to Mars, so you take an EUS because that's availabe. Even without SLS, you need some kind of big stage to do this, and a lot bigger one from LEO (or SEP, but you need a lot more power than 100kw for that).

Then there's the habitat, NASA has plenty of experience with that and I'm sure they know what is needed here. They decide to resupply the habitat in HMO, in order to minimize the habitat's mass at departure from HEO and HMO. That helps keeping the MOI and TEI stages small. A 100kw SEP can pre deploy the TEI to HMO in a reasonable time frame, when launched with an SLS towards Mars.

One could debate whether it would make sense to go back to cis-lunar space and not take Orion with them, but I guess that's a close call.

For an expendable architecture with SLS available, I don't see it getting any simpler (short of Mars direct nonsense).

Yes, for an expendable architecture with SLS, it really can't get simpler than this. But I think you missed my point about the private sector, especially since you removed it from my quote. I was trying to avoid turning this thread into another "the company that shall not be named" thread. You know, NASA isn't the only group designing a Mars architecture.

Also, remember that SLS was mandated by Congress, not suggested by NASA. While this is a great architecture for using SLS, we might have something better if NASA got to spend five years doing research before designing an HLV. That was President Obama's plan. But, we got SLS instead, so we might as well try to figure out what to do with it.

Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #29 on: 07/04/2015 12:03 AM »
Yes, for an expendable architecture with SLS, it really can't get simpler than this. But I think you missed my point about the private sector, especially since you removed it from my quote. I was trying to avoid turning this thread into another "the company that shall not be named" thread. You know, NASA isn't the only group designing a Mars architecture.

I think the commercial sector could be very useful between module-like craft ala Cygnus or emerging retropropulsion ala Dragon 2.  Furthermore, while the SLS might be the most useful it shouldn't be exclusive since we are talking both a big and expensive rocket - supplement it by sending up the smaller payloads to LEO via smaller rockets.

Also, remember that SLS was mandated by Congress, not suggested by NASA. While this is a great architecture for using SLS, we might have something better if NASA got to spend five years doing research before designing an HLV. That was President Obama's plan. But, we got SLS instead, so we might as well try to figure out what to do with it.

NASA would have been needing this whether it continued on the Lunar Constellation route or the Mars Direct route; it just sadly took poor Columbia falling apart to give the wake-up call that we needed to move beyond STS.
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Offline john smith 19

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #30 on: 07/04/2015 09:32 AM »
Also, remember that SLS was mandated by Congress, not suggested by NASA.
True.
Quote
While this is a great architecture for using SLS, we might have something better if NASA got to spend five years doing research before designing an HLV. That was President Obama's plan. But, we got SLS instead,
Probably, but now we'll never know.
Quote
so we might as well try to figure out what to do with it.
Exactly.  Which is what this is.

If you didn't work for NASA and weren't convinced more than 4 SLS's would ever be produced you would choose a different architecture. But they do work for NASA and SLS is the designated standard NASA launch vehicle.
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #31 on: 07/04/2015 10:03 AM »
Quote
so we might as well try to figure out what to do with it.
Exactly.  Which is what this is.

If you didn't work for NASA and weren't convinced more than 4 SLS's would ever be produced you would choose a different architecture. But they do work for NASA and SLS is the designated standard NASA launch vehicle.


Agree with both of you.  NASA's gonna use this thing, SLS in itself could be useful, and we just need a proper plan.  The minimal architecture could be a starting point because it uses current tech, although there's room for improvement as I stated.  As for the SLS, so long as we can use block 1B my only concern is how many can be built and launcher cost.
« Last Edit: 07/04/2015 10:05 AM by redliox »
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #32 on: 07/04/2015 10:41 AM »
Orbital mission:
- The Phobos habitat provides supplies for the crew, you'd have to add that to the transfer habitat, increasing its mass by maybe up to 10t (note the hab gets resupplied im HMO for the other missions). Also requires the hab to go down from HMO to Phobos orbit, increasing MOI and TEI stage mass. 100kw SEP would likely be too slow to do that for the crewed hab. Note commonality with the Mars landing missions is important.
- Requires more delta-v to break the habitat into cis-lunar space. Also would require an additional transfer vehicle from HMO to Phobos orbit (if the hab doesn't go there). But yeah, might not be a bad idea.


As far as TEI and HMO-Phobos masses, those payloads are already being delivered by SEP-tugs.  If you leave the weight of the Orion behind at Earth a 40 mt DSH with a 40 mt stage could break into HMO.  Dragging the Orion's weight around is the main thing that would limit a hab's function.  Capturing into and then maneuvering between HMO and Phobos orbit (with Deimos in between) is on the order of 3 km/s for a round trip.  If the hab arrives with 40 tonnes of hypergolic fuel that's enough for MOI and rendezvousing with Deimos.  The delivered stages could readily be used for Phobos operations and returning to Earth.  Also, why are you complaining about the hab increasing TEI mass?  The plan clearly shows the hab returning to Earth.

The number for consumables has always varied with architectures; for Mars Direct it was 7 mt, for DRM 5.0 it was 13 mt.  A hab's weight could easily include this with a budget totaling 40 mt; most plans for DSHs put their dry weight in the area of 25 mt.  That gives 15 mt not devoted to hardware for crew needs.

The lander half is going to be the hard part.  The orbital half could reasonably be trimmed down while drawing on existing technology.
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #33 on: 07/04/2015 05:23 PM »
Orbital mission:
- The Phobos habitat provides supplies for the crew, you'd have to add that to the transfer habitat, increasing its mass by maybe up to 10t (note the hab gets resupplied im HMO for the other missions). Also requires the hab to go down from HMO to Phobos orbit, increasing MOI and TEI stage mass. 100kw SEP would likely be too slow to do that for the crewed hab. Note commonality with the Mars landing missions is important.
- Requires more delta-v to break the habitat into cis-lunar space. Also would require an additional transfer vehicle from HMO to Phobos orbit (if the hab doesn't go there). But yeah, might not be a bad idea.


As far as TEI and HMO-Phobos masses, those payloads are already being delivered by SEP-tugs.  If you leave the weight of the Orion behind at Earth a 40 mt DSH with a 40 mt stage could break into HMO.  Dragging the Orion's weight around is the main thing that would limit a hab's function.  Capturing into and then maneuvering between HMO and Phobos orbit (with Deimos in between) is on the order of 3 km/s for a round trip.  If the hab arrives with 40 tonnes of hypergolic fuel that's enough for MOI and rendezvousing with Deimos.  The delivered stages could readily be used for Phobos operations and returning to Earth.  Also, why are you complaining about the hab increasing TEI mass?  The plan clearly shows the hab returning to Earth.

The number for consumables has always varied with architectures; for Mars Direct it was 7 mt, for DRM 5.0 it was 13 mt.  A hab's weight could easily include this with a budget totaling 40 mt; most plans for DSHs put their dry weight in the area of 25 mt.  That gives 15 mt not devoted to hardware for crew needs.

The lander half is going to be the hard part.  The orbital half could reasonably be trimmed down while drawing on existing technology.

Sorry but I don't see the architecture closing with a 3km/s Phobos round trip for the habitat (is it that much?).

Edit: Never mind the calculation, you meant 3km/s for capture plus lowering to Phobos orbit. I would say its about 0.9-1.9km/s to HMO (1 sol orbit) (depending on the opportunity) and 0.8km/s for HMO to Phobos orbit.

If we assume 5t of "consumables" are used up at Mars arrival, the MOI stage (30t) has to break (30+19-5)=44t into HMO. With an isp of 340 and smf of 10% that gives me 1.5km/s.

Just the emphasize it again, the architecture's elements are meant to be used for the Mars landing campaign, so it makes little sense to optimize them for the Phobos mission. There will likely be only one anyway.

The number for consumables has always varied with architectures; for Mars Direct it was 7 mt, for DRM 5.0 it was 13 mt.  A hab's weight could easily include this with a budget totaling 40 mt; most plans for DSHs put their dry weight in the area of 25 mt.  That gives 15 mt not devoted to hardware for crew needs.

Totally depends on the time spent in the Hab, everything I read so far suggest that 5-10kg per crew member per day is a reasonable range. Some super-ambitious ECLSS isn't going to be cheap either.

« Last Edit: 07/04/2015 05:44 PM by Oli »

Offline Impaler

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #34 on: 07/04/2015 05:44 PM »
Doesn't this mission length FAR exceed the life-span of an Orion, even when powered-down?  Orion is a cis-lunar taxi-capsule, any architecture that brings it to Mars is flawed right from the start, I can kind of forgive the old all chemical mission plans for using it as they come in to Earth fast and will need something like Orion (but much smaller) as an Earth entry capsule.  But as soon as your using SEP and your returning vehicle is not being destroyed but rather capturing to high Earth orbit the logic of sending a FRESH retrieval capsule up from Earth is inescapable.

Overall I find the mixing of SEP and Chem in this architecture to be very poor, the SEP is underpowered as it reflects zero improvement on ARM which is ridiculously conservative.  The Chem stages don't make use of oberth effects and are big and bulky.  This proposal is almost Zubrin like in it's rejection of tech development, even the technologies already under development by NASA right now like HIAD.  Did their sand charts assume NASA's tech development budget gets zeroed out and all the money dumped into their program?

Lastly the presenters make the absurd claim that "by being specific with out plan our international partners can see themselves IN the plan and will come on board", which would makes sense if your specifics weren't composed of ALL AMERICAN VEHICLES.  After taking out the sole launch vehicle SLS, Orion, and ARM derived SEP theirs not much left for anyone else to do.  The habitat module is the only part I could see ESA or Roscosmos doing, the chemical kick-stages are grunt-work that no ones would be interested in.  Lastly the landers, everyone knows JPL would produce that, they have ALL the Mars EDL experience and this is unequivocally the most dangerous part of the mission.  None of our partners would want the PR risk that would entail.  Lastly the crew size of 4 is too small to include enough international astronauts to make the mission attractive, no nation will contribute if their nationals don't get a ticket, on the FIRST flight.

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #35 on: 07/04/2015 06:28 PM »
Overall I find the mixing of SEP and Chem in this architecture to be very poor, the SEP is underpowered as it reflects zero improvement on ARM which is ridiculously conservative.

The Chem stages don't make use of oberth effects and are big and bulky.

This proposal is almost Zubrin like in it's rejection of tech development, even the technologies already under development by NASA right now like HIAD.  Did their sand charts assume NASA's tech development budget gets zeroed out and all the money dumped into their program?

Lastly the presenters make the absurd claim that "by being specific with out plan our international partners can see themselves IN the plan and will come on board", which would makes sense if your specifics weren't composed of ALL AMERICAN VEHICLES.

- The SEP for ARM has 50kw, this one 100kw. SEP for ARM is expected to launch in 2020, and SEP for the Phobos mission in 2029. There is not a lot of time. Then there's the question of cost. An additional SLS might cost as little as $500m, if you stay within 2 launches per year (which this architecture does, more or less). A 100kw SEP is unlikely to be cheaper (a comsat can already cost as much), ARM costs $2.6bn, development included. I would like to see more powerful SEPs though, especially the hybrid approach which can return within 4 years is very interesting.

- The chem stages are 30t respectively 26t and hypergolics are dense, they're going to be "tiny".

- Zubrin assumed heavy lift more powerful than SLS, a deployable heat shield, methalox storage/propulsion, ISRU, artifical gravity (optional) and some ridiculously lightweight Earth return hab + reentry vehicle. It was and still is extremely ambitious technology-wise.

- I agree with that, but that's a problem with most Mars architectures, especially those using SLS. Even the hab will probably be based on SLS tanks. NASA has most experience with ECLSS, Mars entry etc.

« Last Edit: 07/04/2015 06:33 PM by Oli »

Offline john smith 19

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #36 on: 07/05/2015 12:00 AM »

- The SEP for ARM has 50kw, this one 100kw. SEP for ARM is expected to launch in 2020, and SEP for the Phobos mission in 2029. There is not a lot of time. Then there's the question of cost. An additional SLS might cost as little as $500m, if you stay within 2 launches per year (which this architecture does, more or less). A 100kw SEP is unlikely to be cheaper (a comsat can already cost as much), ARM costs $2.6bn, development included. I would like to see more powerful SEPs though, especially the hybrid approach which can return within 4 years is very interesting.
In the talk the authors point out that SEP is being designed to support 2x the current number of thrusters IE 100Kw, and 2x the amount of propellant, IE 32tonnes of Xenon.

So it's a case of ordering additional tanks and thrusters, along with a couple of more SEPs to begin with.

That's about as "low risk" as it gets.
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Offline qraal

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #37 on: 07/05/2015 04:05 AM »
One problem with wanting to use xenon as an SEP propellant for large vehicles is that only tiny amounts (i.e. tons) are currently produced per year, due to its extreme scarcity. Needing ~32 tons would represent several years worth of the world's total production. Doesn't give any scope for multiplying the flight rate. Another gas or element is clearly needed for the propellant.

http://www.rsc.org/education/eic/issues/2009Jan/xenon-noble-gas-inert.asp

...this source says 6 tonnes a year production back in 2009.
« Last Edit: 07/05/2015 04:11 AM by qraal »

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #38 on: 07/05/2015 05:51 AM »
Krypton can be substituted for Xenone at very little cost in performance, and it is 10 times as abundant (and 1/10th the cost).

ARM costs $2.6bn

That's not to cost to manufacture the SEP, that's the combined cost of all development, an Orion and the SLS that launches it, and ground operations through the course of the mission.  The SEP stage development is a pittance of that total and comes out of the NASA tech development budget.

The version they are proposing uses the exact same bus and tanks (just full rather then half full) and twice the panels and thrusters.  It's like taking an after market car and putting a supped up carburetor and exhaust system on it and another gas tank, not remotely the cost of developing a vehicle from scratch.  This is 'no risk' not low risk.

As for 9 years between ARM and their Phobos mission date, that is ages in the SEP world.   That's the amount of time between Deep Space 1 and the Dawn Probe which was a huge leap forward in capabilities.  It is absurd to think that our SEP would stagnate so much that 9 years after ARM we can't do any better then that.  Even the ARM SEP developers say it can scale to 300 kw.


Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #39 on: 07/05/2015 12:40 PM »
That's not to cost to manufacture the SEP, that's the combined cost of all development, an Orion and the SLS that launches it, and ground operations through the course of the mission.  The SEP stage development is a pittance of that total and comes out of the NASA tech development budget.

As for 9 years between ARM and their Phobos mission date, that is ages in the SEP world.   That's the amount of time between Deep Space 1 and the Dawn Probe which was a huge leap forward in capabilities.  It is absurd to think that our SEP would stagnate so much that 9 years after ARM we can't do any better then that.  Even the ARM SEP developers say it can scale to 300 kw.

- Well yes obviously. A more informative figure would be $1.25bn, which is the cost of the robotic craft without launch and operation. Still, I doubt the manufacturing of the SEP is less than $500m. Either way, the reason I was comparing it to SLS was because you could possibly safe some SLS launches (3-4 of 10 for the landing campaign) by making the landers less heavy and/or using (a lot) more powerful SEPs. My point is, the development and fixed cost of SLS are payed for, so you get SLS at marginal cost. In that case you might as well use it. If you go for a reusable architecture, if that is worth it, you'd want more powerful SEPs though.

- Well I'm not saying it couldn't be scaled to 300kw or more. However, according to the paper the program cost in the 20s already doesn't fit into the budget (ISS 2028). I guess there's a lot to develop in that time period for the Phobos mission. Further, there is no need for more powerful SEP beyond human spaceflight.

Just saying, I guess they have their reasons. Of course we could end up with a completely different architecture.



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