Author Topic: A Minimal Architecture for Human Journeys to Mars (JPL)  (Read 49571 times)

Offline sdsds

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #200 on: 09/18/2016 11:26 PM »
Deep space qualification of pumped biprop stage with non-storable propellants would likely cost around ~1B. For a storable prop it would definitely be cheaper

Looking at engines with U.S. spaceflight heritage the LR-91 comes to mind. Gas generator. Twice the thrust of what this architecture requires (467 kN vs ~250 kN).  Specific impulse of 316 s when used with Aerozine. MON-25 with its freezing point of -55 deg. C should be "easily" possible?

Were there ever any in fight failures of this engine when used on Titan 3 or Titan 4 missions? Is there a reason to think a redesigned engine basically like this could not be rated for cold starts after weeks or months in space?

EDIT: added graphic showing engine/stage as used in a Titan 24B.
« Last Edit: 09/18/2016 11:46 PM by sdsds »
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Offline savuporo

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #201 on: 09/19/2016 01:50 AM »
Were there ever any in fight failures of this engine when used on Titan 3 or Titan 4 missions?
Some, apparently. Stuck valve, gas generator failure, turbopump failure, hydraulics failure, electrical malfunctions, low thrust, fuel line obstructions are some of the cited reasons. However, according to  Dr. Jeffery L. Emdee  of Aerospace Corp, who has written extensively on history of US rocket engine developments, the flight failures at the time were not well enough instrumented to trace it very conclusively back to particular propulsion subsystem failures.

Quote
Is there a reason to think a redesigned engine basically like this could not be rated for cold starts after weeks or months in space?
It'd be a newly designed engine. You can't simply take an engine from second stage and expect it to work reliably in deep space. Cold welds, materials degradation issues, etc. A full up review component by component would be required. Every bearing, gear, valve, lubricant, seal.

It's not impossible, but it's effectively a new engine development program, and just based on part count three-four times more complex than state of the art deep space pressure fed engines. And engine development programs like these unfortunately run for close to a decade.

It's worth repeating that the mechanical complexity of a turbopumped engine is significantly higher than state of the art deep space pressure fed engines. For reference, below is a high level overview of LR91 vs 'simplified' view of propulsion system diagram of Messenger spacecraft with designed in redundancy and monoprop+biprop mode operation.

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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #202 on: 09/19/2016 07:37 AM »
Chemical propulsion may be faster than SEP but it tends to have smaller payloads. So big things like planetary habitats and manned rovers should go by SEP.

If you look at the both the 1-month and the 1-year stay part of the architecture, you'll notice all the Mars landers are directly sent to Mars...WITHOUT SEP involved.  Even the crew's lander aerocaptures into HMO.  JPL's study favors a direct approach when it comes to Mars itself.  Only the orbital elements for the Phobos missions and the return to Earth have any involvement with SEP.

It appears that it's not so much the size/mass of the payload that matters, but whether or not the payload can aerobrake and land on Mars.  So the more you utilize the surface (and later ISRU), the less need there is of SEP.  Only missions orbiting Mars, such as for Phobos, have direct need of SEP.

SEP flight time depends on both distance and delta-v. SEP tug staying in high orbit may reduce the flight time by several months. Mars landers can use heat shields.

Correct on high orbits and heat shields.  What really needs to be eliminated is that need to boost the MAV from LMO to HMO.  The MAV should be mandated to fly directly to the same orbit as the ERVs/Habs, with or without ISRU.  If the strength of SEP is in high orbit, then high orbit should be the staging point.
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Offline sdsds

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #203 on: 09/19/2016 08:11 AM »
What really needs to be eliminated is that need to boost the MAV from LMO to HMO.  The MAV should be mandated to fly directly to the same orbit as the ERVs/Habs

Yes, but ascent from the Martian surface to any orbit using storable propellants you placed there with a storable propellant propulsive landing looks almost insane! Even with an optimistic Isp of 338 s.

So asking the storable propellant ascent vehicle to reach HMO seems doubly implausible. Even as it is, their descent vehicle looks ... intimidating. Six engines, each with a thrust of 250 kN. Oof.

See this:
http://www.ssdl.gatech.edu/papers/conferencePapers/AIAA-2016-0219.pdf

 The lower orbit for the MAV requires about 4.2 km/s of delta-V. [...] A specific impulse (ISP) of 338 s was used in the ascent analysis. [Also:] The trajectory design for the EDL concept was analyzed with the Dynamics Simulator for Entry, Descent and Surface landing (DSENDS) program developed at JPL for the MSL program. The entry altitude and velocity used for the 75 t vehicle was at a Mars radius of 3,522 km and a velocity of 4.9 km/s from a highly elliptical orbit.
« Last Edit: 09/19/2016 08:12 AM by sdsds »
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #204 on: 09/19/2016 11:57 AM »
What really needs to be eliminated is that need to boost the MAV from LMO to HMO.  The MAV should be mandated to fly directly to the same orbit as the ERVs/Habs

Yes, but ascent from the Martian surface to any orbit using storable propellants you placed there with a storable propellant propulsive landing looks almost insane! Even with an optimistic Isp of 338 s.

Correct.  Storable propellants don't have enough kick.  The Phobos mission, needing 4 SLS launches, is reasonable and obviously gets away with it because the spacecraft doesn't delve all the way through the Martian gravity well.  Storable could suffice for the orbital operations, and considering the habs and Earth return craft will be sitting for many months it makes enough sense to use it in HMO and even at the moons.

I don't wanna blare ISRU...but...yeah, they need it.  If they need 10 SLS rockets worth of material for a single mission, wiser idea to put it on the surface and not waste it in orbit.
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Offline Oli

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #205 on: 09/19/2016 02:11 PM »
Chemical propulsion may be faster than SEP but it tends to have smaller payloads. So big things like planetary habitats and manned rovers should go by SEP.

If you look at the both the 1-month and the 1-year stay part of the architecture, you'll notice all the Mars landers are directly sent to Mars...WITHOUT SEP involved.  Even the crew's lander aerocaptures into HMO.  JPL's study favors a direct approach when it comes to Mars itself.  Only the orbital elements for the Phobos missions and the return to Earth have any involvement with SEP.

It appears that it's not so much the size/mass of the payload that matters, but whether or not the payload can aerobrake and land on Mars.  So the more you utilize the surface (and later ISRU), the less need there is of SEP.  Only missions orbiting Mars, such as for Phobos, have direct need of SEP.

This is a "Minimal Architecture", meaning it minimizes the development cost (assuming SLS/Orion are developed and paid for). Hence there's no multi-100kw SEP, no HIAD, no ISRU and no methalox propulsion. This plan is unlikely the most cost-effective for the long-term exploration of Mars, but it gets the job done with minimal up-front investment.

SEP is certainly useful also for aerocaptured payloads. Mainly for the LEO-HEO part, but it can also do a Mars flyby and "drop off" the payload within reasonable time and with very little fuel use.

So asking the storable propellant ascent vehicle to reach HMO seems doubly implausible. Even as it is, their descent vehicle looks ... intimidating. Six engines, each with a thrust of 250 kN. Oof.

The high thrust is necessary due to the traditional EDL method. With HIAD it would get away with significantly less thrust. Mars ascent is certainly not implausible with storable propellant, 340s is not a lot less than 360s, which is usually assumed for methalox ascent. In this architecture the MAV is limited by the landed mass (26t) and the total lander mass is limited by how much 2 SLS can throw to TMI. With a larger MAV (e.g. 40t) an ascent to a higher orbit would be possible.

Offline DarkenedOne

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #206 on: 09/19/2016 02:44 PM »
What are our long term plans for human spaceflight?  - That is the central question here. 

Sure if you are only interested in Apollo style missions where you are only putting down a few people on the planet then such an architecture might be just fine.  If your are interested in actually establishing a long term outpost then an architecture that would essentially cost a few billion dollars per person is definitely a no go. 

Personally I want to see humanity become a truly space fairing species.  That means developing the technologies that make spaceflight affordable. 

Offline Khadgars

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #207 on: 09/19/2016 03:41 PM »
I still think the same thing I did before, way too many SLS launches for "minimal". Posit that Musk's plans work, then envision the campaign that could be constructed using *those* resources for the same cost...

Can we not get into this argument in every thread

Offline A_M_Swallow

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #208 on: 09/19/2016 04:53 PM »
Chemical propulsion may be faster than SEP but it tends to have smaller payloads. So big things like planetary habitats and manned rovers should go by SEP.

If you look at the both the 1-month and the 1-year stay part of the architecture, you'll notice all the Mars landers are directly sent to Mars...WITHOUT SEP involved.  Even the crew's lander aerocaptures into HMO.  JPL's study favors a direct approach when it comes to Mars itself.  Only the orbital elements for the Phobos missions and the return to Earth have any involvement with SEP.

It appears that it's not so much the size/mass of the payload that matters, but whether or not the payload can aerobrake and land on Mars.  So the more you utilize the surface (and later ISRU), the less need there is of SEP.  Only missions orbiting Mars, such as for Phobos, have direct need of SEP.

This is a "Minimal Architecture", meaning it minimizes the development cost (assuming SLS/Orion are developed and paid for). Hence there's no multi-100kw SEP, no HIAD, no ISRU and no methalox propulsion. This plan is unlikely the most cost-effective for the long-term exploration of Mars, but it gets the job done with minimal up-front investment.

SEP is certainly useful also for aerocaptured payloads. Mainly for the LEO-HEO part, but it can also do a Mars flyby and "drop off" the payload within reasonable time and with very little fuel use.

So asking the storable propellant ascent vehicle to reach HMO seems doubly implausible. Even as it is, their descent vehicle looks ... intimidating. Six engines, each with a thrust of 250 kN. Oof.

The high thrust is necessary due to the traditional EDL method. With HIAD it would get away with significantly less thrust. Mars ascent is certainly not implausible with storable propellant, 340s is not a lot less than 360s, which is usually assumed for methalox ascent. In this architecture the MAV is limited by the landed mass (26t) and the total lander mass is limited by how much 2 SLS can throw to TMI. With a larger MAV (e.g. 40t) an ascent to a higher orbit would be possible.


The Asteroid Redirect Mission will pay for the development of 30kW-50kW SEP by the early 2020s.

The SLS may only have a 70 mT payload.

Offline savuporo

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #209 on: 09/19/2016 05:16 PM »
Yes, but ascent from the Martian surface to any orbit using storable propellants you placed there with a storable propellant propulsive landing looks almost insane! Even with an optimistic Isp of 338 s.
~325 is the maximum you'll get with TRL=7
Anything more is TRL3, and optimistically 5-7 years away, likely more.

Note that this thread is over a year old, during that time the achievable deep space chemical propulsion ISP has gone up by exactly 0.

Source: http://www.nasa.gov/offices/oct/home/roadmaps/
« Last Edit: 09/19/2016 05:18 PM by savuporo »
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Offline MATTBLAK

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #210 on: 09/22/2016 11:18 PM »
What's the (ballpark) specific impulse for a Hydrazine/LOX pumpfed engine? Anyone able to work that out?
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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #211 on: 09/23/2016 07:51 AM »
What's the (ballpark) specific impulse for a Hydrazine/LOX pumpfed engine? Anyone able to work that out?

Is there a reason to do that  propellant combination? Sure, LOX eliminates the (truly awful) N2O4. But if you're going to maintain LOX, why not also maintain some fuel like CH4? The advantage of nitrogen textroxide and monomethyl hydrazine as a propellant combination is that both can survive "cold soak" in space (i.e. zero maintenance) for months/years and still perform upon demand.

Or am I missing something?
« Last Edit: 09/23/2016 07:51 AM by sdsds »
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #212 on: 09/23/2016 09:21 AM »
What's the (ballpark) specific impulse for a Hydrazine/LOX pumpfed engine? Anyone able to work that out?

Is there a reason to do that  propellant combination? Sure, LOX eliminates the (truly awful) N2O4. But if you're going to maintain LOX, why not also maintain some fuel like CH4? The advantage of nitrogen textroxide and monomethyl hydrazine as a propellant combination is that both can survive "cold soak" in space (i.e. zero maintenance) for months/years and still perform upon demand.

Or am I missing something?

Actually it's simple.  Hydrazine is a common, hypergolic fuel and LOX production is easier than full methalox production.  It's an attempt at combining storeable fuels with the simplest version of ISRU, which in this case would be by the fuel cell technology the 2020 Rover's MOXIE experiment will test on Mars.
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Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #213 on: 09/23/2016 09:47 AM »
What's the (ballpark) specific impulse for a Hydrazine/LOX pumpfed engine? Anyone able to work that out?

I heard it mentioned before, but I also know the combination is never used in modern rocketry.  Here are 2 sets of the listings I found, with the later listing it as a very-high energy bipropellant: https://en.wikipedia.org/wiki/Liquid_rocket_propellant http://history.nasa.gov/conghand/propelnt.htm
Overall I think it is at least 300 Isp, although not quite as high as methane or certainly hydrogen/oxygen.

I'm under the impression using the 2 is too toxic, too oxidizing, and far less tested than methane.  If you could make it work, it would make ISRU easier to integrate by following MOXIE-derived tech.
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Offline DOCinCT

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.  :)

Besides the time line:
They propose a long-term, stepwise series of missions to Mars that would begin with a crew landing on Marsís moon Phobos in 2033, and followed by a short-stay mission in 2039 and a year-long landing in 2043
The is the scope:
A one month stay for 2 astronauts (or 6 days for 4) requires 6 SLS launches spanning 3.8 years  with 2 landings on Mars. with multiple LEO and LMO/HMO rendezvous.
A one year stay for 4 would require 10 SLS launches  over a 5.5 year period, with 3 landings on Mars and the multiple orbital rendezvous.

Not exactly a simple, minimalist approach.  Might be easier, and less expensive, to send a single STS Spaceship (5-6 launches all with LEO rendezvous before the Phobos mission even takes off. 

Offline redliox

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Re: A Minimal Architecture for Human Journeys to Mars (JPL)
« Reply #215 on: 10/05/2016 06:02 PM »
The is the scope:
A one month stay for 2 astronauts (or 6 days for 4) requires 6 SLS launches spanning 3.8 years  with 2 landings on Mars. with multiple LEO and LMO/HMO rendezvous.
A one year stay for 4 would require 10 SLS launches  over a 5.5 year period, with 3 landings on Mars and the multiple orbital rendezvous.

Not exactly a simple, minimalist approach.

Indeed, or at least depends on whether you mean 'minimalist' by NASA definition...which is hardly minimalistic to begin with.

Might be easier, and less expensive, to send a single STS Spaceship (5-6 launches all with LEO rendezvous before the Phobos mission even takes off.

Assuming you meant Single-Stage-To-Orbit, maybe.  Mars Direct essentially was following this philosophy.  The SLS (which I also think you may have implied), in its block 2 form if not block 1B, could likely send sizeable payloads to Mars in the Mars Direct manner.

LEO may or may not be the best spot; if you have to do orbital rendezvous it has the most support thanks to Earth proximity.  There may be an inevitable need to rendezvous in Mars orbit since a habitat or otherwise return vehicle would be wise to include; it just depends on whether that should be low versus high Mars orbit.
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