Author Topic: A Minimal Architecture for Human Journeys to Mars (JPL)  (Read 52509 times)

Offline sdsds

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I think this approach deserves a discussion thread of its own....

Overview:
Humans to Mars: New Affordable Strategy Promoted
By Leonard David
June 29th, 2015

http://www.leonarddavid.com/humans-to-mars-new-affordable-strategy-promoted/

We Can Send Humans to Mars Safely and Affordably
By Scott Hubbard
New Space. June 2015
http://online.liebertpub.com/doi/pdf/10.1089/space.2015.28999.gsh

A Minimal Architecture for Human Journeys to Mars
Hoppy Price, John Baker, Firouz Naderi
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California.
New Space. June 2015: 73-81.
http://online.liebertpub.com/doi/pdfplus/10.1089/space.2015.0018?src=recsys

N.B.: Not all links are guaranteed to work forever.
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #1 on: 06/30/2015 08:01 AM »
I seem to recall Mars Direct being more minimalistic than this, and this pretty much follows what we've already been alluded to from NASA.  I like the idea of doubling an orbital mission as a Phobos one too.  I don't think dragging a dedicated Phobos base or an Orion is really necessary.  One surprise I notice is the lack of lunar orbit or Lagrange point use in any part of this scheme (save testing prototypes according to text); considering Bolden's constant reinforcement of DRO this is a curious departure.  Slightly interesting to read into, but again this doesn't 'feel' minimalistic.
« Last Edit: 06/30/2015 09:11 PM by redliox »
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #2 on: 06/30/2015 11:25 AM »
Thanks. There's also a presentation on that on youtube, but this is more informative.

...but again this doesn't 'feel' minimalistic.

You must have missed that part:

Quote

We refer to this architecture as minimal because it would minimize large new development efforts and rely largely on elements currently being developed or planned by NASA, such as SLS, Orion, a deep space habitat, and a 100-kWe-class SEP tug.

By that definition it certainly is a minimalist architecture. No inflatable heat shield, no ISRU for ascent fuel, no methalox propulsion/storage (all hypergolics), 100kw SEP.

At least the most minimalist architecture I've ever come across.
« Last Edit: 06/30/2015 11:25 AM by Oli »

Offline Profwoot

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #3 on: 06/30/2015 12:37 PM »
This seems very realistic to me, with the lander stages being the only scratch development (the use of hypergolics in everything would require new EUS development as well, but I don't see why already in-dev or extant upper stages couldn't be used).

I doubt this would actually save money in the long run over development of additional assets, especially prop depots and ISRU, and I'd be tempted to see about resizing some of the payloads to fit on Falcon Heavies rather requiring SLS for everything, but this plan seems very practical in catering to existing projects, and may therefore be more likely to find congressional support.

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #4 on: 06/30/2015 01:44 PM »
I'm just starting to catch up with this. Interesting lander. I've often made this point before but its interesting to see that they are trying to make use of what I call a "late braking" profile. Going as deep into the atmosphere as possible before using lift. Doing this exposes the crew to a nominal peak deceleration of 6.4g. And even with this it only reaches Mach 2 and can go into SRP at just over 2Km above ground level with less than 20 seconds of margin.

That would compare to a fully propulsive landing with peak g forces closer to 2.5g and passing Mach2 at over 10Km above ground level.

I'll have more to say when I read through.

Offline ClaytonBirchenough

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #5 on: 07/01/2015 07:53 PM »
I like this kind of architecture very much. It seems this is definitely the way to go, unless a LOT more funding is going to be provided...
Clayton Birchenough
Astro. Engineer and Computational Mathematics @ ERAU

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #6 on: 07/02/2015 01:50 AM »

I like their use of hypergolics for everything but Earth departure with EUS. Apparently a 23t Mars ascent vehicle with hypergolics can do the job, so why waste money on cryo storage and ISRU? Hypergolic propulsion is simple and reliable, exactly what is needed for a Mars mission.

Edit: Nonsense removed.

« Last Edit: 07/02/2015 04:59 AM by Oli »

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #7 on: 07/02/2015 08:16 AM »
I've had a first pass read over it and I'm impressed by the fact that they are using ideas that went into my own architecture.

For instance they are keeping the ascent vehicle minimal and docking with a booster stage in orbit (in my architecture that booster stage is a transit vehicle and provides more security but that's a work in progress.)

They also have figured out that leaving as much as possible in high Mars orbit helps a lot with overall energy costs.

I like the idea of using hypergolics for the lander/ascent vehicle but for two things. Firstly it does push the mass a lot relative to methalox. Secondly a mature, robust methalox engine design is needed for the transit stage. Thirdly I do not agree with exposing crew who have been in weightlessness for 6-8 months to a nominal 6.4g on reentry.

I do think they've got the entry configuration right at least for cargo.

And using SEP all the way to Mars. I need to study this further. It may be that what SEP does there is save mass notionally but simply end up making the project more expensive (I'll change my mind about this if anyone can explain how to build a 100KW class SEP vehicle for a few tens of megabucks).

Testing of some systems is minimal for my tastes. I'd prefer to have more bits tested on robotic missions. You can't expect not to run into unknown problems on the basis of a few tests. So its either much more testing, or full redundancy which is what my architecture has.

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #8 on: 07/02/2015 11:46 AM »
I like the idea of using hypergolics for the lander/ascent vehicle but for two things. Firstly it does push the mass a lot relative to methalox.

And using SEP all the way to Mars.

- Not really. Pump-fed hypergolics can have pretty good ISP. They mention the RS-72 (GG), which has an isp of 340. Further the delta-v that must be provided by the MOI and TEI stages is relatively small, so isp doesn't matter that much. The MOI stage is 30t and the TEI stage 26t by the way. Most of the delta-v in this architecture is provided by the EUS (launch to HEO+departure), which really shines here if you ask me.

But lets look at the Mars ascent vehicle just to have an idea. It must provide a delta-v of 4.1km/s, far more than the other 2 hypergolic stages. With a 5t payload and a 10% stage dry mass fraction we get to a total mass of ~23t as in the study. Now lets use methalox and we get ~20t. For methalox however a dry mass fraction of 15% might be more appropriate (with emphasis on might), in which case we're looking at a ~24t vehicle, of which around 16t is fuel which you could save with ISRU.

- Note they only use SEP for cargo that cannot aerobrake into Mars orbit. I guess they could launch that cargo in a similar fashion as the crew (i.e. attach a MOI stage to it and send it to Mars with an EUS), but that might cost them 2 additional SLS and MOI stages. 2 100kw SEPs are probably cheaper and help keeping the launch rate down.

« Last Edit: 07/02/2015 11:50 AM by Oli »

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #9 on: 07/02/2015 12:30 PM »
Ok just so I can get my head around it. My understanding is that their lander is 23 tonne total landed mass. That includes the ascent vehicle as only a portion of that 23 tonnes?

Also, what Isp were you counting on for the hypergolics, and do you know what figure they were working on?

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #10 on: 07/02/2015 12:53 PM »
Ok just so I can get my head around it. My understanding is that their lander is 23 tonne total landed mass. That includes the ascent vehicle as only a portion of that 23 tonnes?

Also, what Isp were you counting on for the hypergolics, and do you know what figure they were working on?

- 23t is the payload of the lander and at the same time the mass of the ascent vehicle (see the vehicle mass table on page 80, its also in the text). No coincidence of course.

- They mention the RS-72, so I assumed an isp of 340s. I do not know what figure they were working with.
« Last Edit: 07/02/2015 12:53 PM by Oli »

Offline john smith 19

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #11 on: 07/02/2015 01:43 PM »
This seems very realistic to me, with the lander stages being the only scratch development (the use of hypergolics in everything would require new EUS development as well, but I don't see why already in-dev or extant upper stages couldn't be used).
Raise the risk level, changes the development profile. Stuff already developed (or being developed in a known way) was a design ground rule.
Quote
I doubt this would actually save money in the long run over development of additional assets, especially prop depots and ISRU, and I'd be tempted to see about resizing some of the payloads to fit on Falcon Heavies rather requiring SLS for everything, but this plan seems very practical in catering to existing projects, and may therefore be more likely to find congressional support.
It's affordable Mars exploration from the NASA perspective, using tools NASA is developing.

In the same way I doubt an SX initial Mars mission will base line the SLS as part of its hardware.

Incidentally is it just my impression but are some of the most innovative ideas for human exploration coming out of JPL, the part of NASA that does not do human exploration.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Russel

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #12 on: 07/02/2015 01:47 PM »
That bit that confuses is the text

"The lander would have about a
75-ton entry mass and deliver a
useful landed payload mass of
about 23 t"

That suggested to me that what actually lands on mars is 23 tonnes. Yet the lander is quoted as 56 tonnes.

If so what they are saying is that they hope to land a 56 tonne mass on Mars with a 75 tonne entry mass. That's a 75% ratio of landed mass to entry mass. That's so high that I assumed I was reading it wrongly.

How much is a 12 metre heat shield and backshell going to mass? They said it was a scaled up version of the MSL heat shield but its nearly 3 times larger. Possibly 7 times more massive. Then how much landing propellant do they need?

Edit: If you assume that the lander has to brake from Mach 2 and then have a tiny bit left for maneuvering then you figure it needs 0.7Km/s worth of thrust. With the Isp of 340 that means a mass ration of 1.23. So the 56 tonne landed mass (dry) equates to 68 tonnes with fuel. That leaves 7 tonnes for absolutely everything else. And no margins.

I would also love to have details on the ascent vehicle. The mass of the crew cabin part for one thing. And 4.1Km/s is a commonly quoted figure for the delta V from mars surface to low Mars orbit but its assumed that you ascend from the equator into equatorial orbit and there's no margin. I'd allow at least 4.5Km/s and in my own design I allow 5Km/s.

With 4.1Km/s the 23 tonne ascent vehicle would have a mass of 6.8 tonnes dry (why so high?).

That little tin can is the core of a whole bunch of multipliers. Obviously they've chosen to give it life support to survive to high mars orbit and then quite a lot of waiting. But I would imagine they don't intend their crew to spend a week in it. So I'm left puzzled where their basic structural mass figures come from.

« Last Edit: 07/02/2015 01:52 PM by Russel »

Offline ThereIWas3

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #13 on: 07/02/2015 01:51 PM »
Thirdly I do not agree with exposing crew who have been in weightlessness for 6-8 months to a nominal 6.4g on reentry.

There is some data on this.  On those Soyuz flights where there modules did not come apart properly and it did a ballistic re-entry, weren't the astronauts subjected to at least that much G?   After being in space for some months..   What shape were they in on landing?

Even on a normal Soyuz reentry, they look pretty limp coming out of the capsule.
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #14 on: 07/02/2015 02:50 PM »
That suggested to me that what actually lands on mars is 23 tonnes. Yet the lander is quoted as 56 tonnes.

If so what they are saying is that they hope to land a 56 tonne mass on Mars with a 75 tonne entry mass. That's a 75% ratio of landed mass to entry mass. That's so high that I assumed I was reading it wrongly.

How much is a 12 metre heat shield and backshell going to mass? They said it was a scaled up version of the MSL heat shield but its nearly 3 times larger. Possibly 7 times more massive. Then how much landing propellant do they need?

Edit: If you assume that the lander has to brake from Mach 2 and then have a tiny bit left for maneuvering then you figure it needs 0.7Km/s worth of thrust. With the Isp of 340 that means a mass ration of 1.23. So the 56 tonne landed mass (dry) equates to 68 tonnes with fuel. That leaves 7 tonnes for absolutely everything else. And no margins.

With 4.1Km/s the 23 tonne ascent vehicle would have a mass of 6.8 tonnes dry (why so high?).

According to the vehicle mass table the "Mars lander descent stage" weights 52t. Judging by the picture that is everything but the backshell and the heat shield which I guess are being dropped before the retropropulsion phase. The payload is clearly 23t, the lander itself is not counted as payload.

That gives me 8.8t for backshell/heat shield for a delta-v of 0.7km/s (we don't know the actual dv value here).
Is that unrealistic? Well, in the case of MSL backshell+heat shield had a mass of 731kg. A 12m diameter blunt-body has ~7.11 times the area of MSL with its 4.5m diameter. So 5198kg. Its obviously going to be more than that but around 9t doesn't seem particularly unrealistic to me.

Regarding the ascent vehicle. I assumed a 5t payload (the "habitat" for the crew plus crew), so (~23.4-5)*0.1= 1.84t dry mass for the "stage".
« Last Edit: 07/02/2015 02:53 PM by Oli »

Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #15 on: 07/02/2015 03:00 PM »
For those interested in the presentation.

[youtube]https://www.youtube.com/watch?v=nsyUP68fEwU&feature=youtu.be[/youtube]

Offline tea monster

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #16 on: 07/02/2015 05:48 PM »
You wouldn't really have a solid deck on that lander would you? It would be tubes and struts connecting thrusters and engines together with contact points for the aeroshell at strategic places.

Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #17 on: 07/02/2015 05:56 PM »
...but again this doesn't 'feel' minimalistic.

You must have missed that part:

Quote

We refer to this architecture as minimal because it would minimize large new development efforts and rely largely on elements currently being developed or planned by NASA, such as SLS, Orion, a deep space habitat, and a 100-kWe-class SEP tug.

By that definition it certainly is a minimalist architecture. No inflatable heat shield, no ISRU for ascent fuel, no methalox propulsion/storage (all hypergolics), 100kw SEP.

At least the most minimalist architecture I've ever come across.

True regarding technology, but I also look at the chart itself.  Any 7 year old space camper would be able to say "It looks complicated."  Apollo required one launch per mission, Mars Direct two, Mars Semi-Direct three; this "simple" setup wants six.  In back of my mind when I figure the amount of SLS launches and Congressional patience together...you'll hear a long riiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiight.  Also, presuming Trumph becomes president, I picture him pointing a finger at the NASA administrator (Bolden or otherwise) and delivering his classic "You're fired!" with extreme prejudice.
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Offline RonM

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #18 on: 07/02/2015 06:10 PM »
...but again this doesn't 'feel' minimalistic.

You must have missed that part:

Quote

We refer to this architecture as minimal because it would minimize large new development efforts and rely largely on elements currently being developed or planned by NASA, such as SLS, Orion, a deep space habitat, and a 100-kWe-class SEP tug.

By that definition it certainly is a minimalist architecture. No inflatable heat shield, no ISRU for ascent fuel, no methalox propulsion/storage (all hypergolics), 100kw SEP.

At least the most minimalist architecture I've ever come across.

True regarding technology, but I also look at the chart itself.  Any 7 year old space camper would be able to say "It looks complicated."  Apollo required one launch per mission, Mars Direct two, Mars Semi-Direct three; this "simple" setup wants six.  In back of my mind when I figure the amount of SLS launches and Congressional patience together...you'll hear a long riiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiight.  Also, presuming Trumph becomes president, I picture him pointing a finger at the NASA administrator (Bolden or otherwise) and delivering his classic "You're fired!" with extreme prejudice.

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.

Offline john smith 19

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #19 on: 07/02/2015 09:45 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.  :)
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

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