Author Topic: Manned Mars mission using SpaceX Falcon 9 Heavy?  (Read 83000 times)

Offline simonth

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #240 on: 06/06/2010 07:42 PM »
2. It has nothing to do with not carrying "return propellant". Propellant for use of VASIMR is not a big factor anyway. Of the total spacecraft, propellant would only be a small fraction.

That's what I was trying to say before.

Assuming someone can develop a multi megawatt nuclear or solar electric power source with suitable kg/kw ratio, then a VASIMR powered Mars Transfer Vehicle could easily decelerate back to LEO.  No need for the extra complexity of EML 1/2.

This is true if you discount the effects of long exposure to radiation in the Van Allen Belts. We currently do not have the technology for a SEP powered MTV that would pass more than once through the Van Allen Belts and still have somewhat working solar arrays. All other instruments on board also can be effected, even if radiation hardened, if they are exposed to hard radiation for weeks.

EML 1/2 isn't really a complication, it yields several benefits compared to a return of the whole ship to LEO. Time, some propellant for the MTV use not required, no hard radiation exposure etc.

Offline A_M_Swallow

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #241 on: 06/06/2010 08:05 PM »
Low-thrust departure from & return to LEO (eg SEP) probably involves unacceptably long transits through the Van Allan belts. As well as physiological effects, this also degrades Solar cells.
VASIMR is high thrust - 39 day trip to Mars.

The 39 days is err optimistic.  It only applies if the spacecraft does not carry return propellant.  A SEP powered VASIMR also needs to carry about 84 mT of solar arrays.

1. 39 days is optimistic, but not for the reasons you state. 39 days is the time quoted by Ad Astra for a 200MW nuclear powered VASIMR spacecraft.

2. It has nothing to do with not carrying "return propellant". Propellant for use of VASIMR is not a big factor anyway. Of the total spacecraft, propellant would only be a small fraction.


This has all been covered on other threads.
See around http://forum.nasaspaceflight.com/index.php?topic=1139.msg599320#msg599320

An actual 200MW nuclear power plant including cooling radiators is probably going to mass more than those solar arrays.

The propellant may be a small fraction but it is still weighs several tons.

Quote
3. where do you get 84mt of solar arrays? Nobody in the world knows how massive a solar array for a VASIMR based human spacecraft would be. It all depends on how powerful the engine is supposed to be, what type of solar cells are used, what the array will look like etc. If we assume 200W/kg (including structure) of a future SEP array, a 10MW VASIMR spacecraft would require a 50mt solar array structure. If there is a technological breakthrough and thin film solar arrays are possible, the whole spacecraft can be smaller, the VASIMR engine less powerful for the same flight path and you may end up with a 5MW VASIMR propelled spacecraft with a 1000W/kg solar array clocking in at a mere 5mt for the solar arrays.

We do however know the mass of 12MW of solar arrays if we started building them this month.

    Solar cell mass
    http://www.spaceflightnow.com/news/n1006/01vasimr
    "The Pentagon and Boeing Co. are developing a next-generation solar array aimed at reaching a weight-to-power ratio of 7 kilograms per kilowatt, according to the Defense Advanced Research Projects Agency."

12MW * 7 kg/kW = 12000 * 7 = 84,000 kg or 84 mT

200MW * 7 kg/kW = 200000 * 7 = 1,400,000 kg or 1,400 mT

Where they are the biggest mass the design of solar arrays will need re-optimising every 2 or 3 years to keep up with solar cell technology.

Offline Dave G

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #242 on: 06/06/2010 08:14 PM »
This is true if you discount the effects of long exposure to radiation in the Van Allen Belts. We currently do not have the technology for a SEP powered MTV that would pass more than once through the Van Allen Belts and still have somewhat working solar arrays. All other instruments on board also can be effected, even if radiation hardened, if they are exposed to hard radiation for weeks.

What percentage of the trip would be in the Van Allen belts?  What kind of trip time are you assuming?

From this article:
http://www.spaceflightnow.com/news/n1006/01vasimr/
"Even if 39-day trips to Mars are still a distant dream, Ad Astra officials are confident the journey time for smaller missions can be cut by more than half by the 2020s with imminent breakthroughs in solar array technology."

EML 1/2 isn't really a complication, it yields several benefits compared to a return of the whole ship to LEO. Time, some propellant for the MTV use not required, no hard radiation exposure etc.

I'm not following you here.  You just said that VASIMR propellant mass is not a big issue.  How does returning to EML1/2 vs. LEO affect time or radiation exposure?  Hauling 2 years worth of consumables to EML1/2 would certainly be more complicated than LEO.  And since EML1 is beyond the Earth's protective influence, long term storage could be an issue.

Offline savuporo

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #243 on: 06/07/2010 04:48 AM »
    "The Pentagon and Boeing Co. are developing a next-generation solar array aimed at reaching a weight-to-power ratio of 7 kilograms per kilowatt, according to the Defense Advanced Research Projects Agency."

You mean like the UltraFlex arrays on Phoenix ?
Orion - the first and only manned not-too-deep-space craft

Offline simonth

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #244 on: 06/07/2010 05:25 AM »

I'm not following you here.  You just said that VASIMR propellant mass is not a big issue.  How does returning to EML1/2 vs. LEO affect time or radiation exposure?  Hauling 2 years worth of consumables to EML1/2 would certainly be more complicated than LEO.  And since EML1 is beyond the Earth's protective influence, long term storage could be an issue.

The trip back from Mars orbit to EML1/2 requires a lot less delta-v than the trip from EML1/2 to LEO. I said propellant wasn't a significant factor in the equation for a VASIMR based MTV, however it's still a factor. Adding 7km/s delta-v for no reason at all, complicating the whole mission by adding months to the timeline and the whole radiation problem to it, is a problem.

2 years of cargo to EML1/2 is no complication at all, we are talking one HLV launched cargo ship or a few EELV-type launches every mission. Also, who says we need 2 years of cargo for a VASIMR based trip? The whole point of a Mars program with VASIMR would be the shorter trip times to and from Mars.

Offline Sen

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #245 on: 06/07/2010 07:41 AM »
      I hate to be a killjoy but half this thread has nothing to do with spacex or a flacon 9 heavy architecture for a manned mars mission. To the point the conversation has evolved into vasmir viablilty/EELVs/HLV.

Offline simonth

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #246 on: 06/07/2010 10:13 AM »
      I hate to be a killjoy but half this thread has nothing to do with spacex or a flacon 9 heavy architecture for a manned mars mission. To the point the conversation has evolved into vasmir viablilty/EELVs/HLV.

Well, an architecture for Mars using F9H by definition can't be using chemical propulsion, which means people have to discuss advanced propulsion concepts, particularly VASIMR. With F9H, no HLV would be available, which is the second big difference to all the Mars mission studies out there.


Offline Nathan

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #247 on: 06/07/2010 10:44 AM »
      I hate to be a killjoy but half this thread has nothing to do with spacex or a flacon 9 heavy architecture for a manned mars mission. To the point the conversation has evolved into vasmir viablilty/EELVs/HLV.

Well, an architecture for Mars using F9H by definition can't be using chemical propulsion, which means people have to discuss advanced propulsion concepts, particularly VASIMR. With F9H, no HLV would be available, which is the second big difference to all the Mars mission studies out there.


Nonsense. F9H can use the Mars4less architecture which is all chemical. It can also use propellant depots to build up fuel over the two year period between launch windows.

The problem with alternative propulsion methods is:
1: they assume slow trajectories through the van allen belts - such trajectories are harmful to humans without massive shielding.
2: They need power supplies whose mass plus fuel outweighs the mass of a chemical stage. The increased development costs puts them far into the future.

Truth is - if we want to go tomorrow, we use chemical stages.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline A_M_Swallow

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #248 on: 06/07/2010 11:00 AM »
      I hate to be a killjoy but half this thread has nothing to do with spacex or a flacon 9 heavy architecture for a manned mars mission. To the point the conversation has evolved into vasmir viablilty/EELVs/HLV.

That is the Mars side of the thread title.  For the full title the talk becomes how do we build and resupply a VASIMR Mars Transfer Vehicle (MTV) using Falcon 9 Heavies?

A MTV, including Mars lander, would probably be built in LEO and flown to Earth-Moon Lagrange point 1 or 2 (EML1/2).  At the EML1/2 space-dock the MTV would be fuelled, stocked with the other consumables and the crew would board.

At the end of the mission the MTV would return to EML1/2.  The crew will need returning to the Earth.  The MTV would then be cleaned, repaired, refuelled, given a replacement set of consumables and the new crew boarded.  The MTV then flies off on its next mission.

Which company will manufacture the MTV has yet to be determined.

Possible LEO work for the SpaceX Falcon 9 - lifting the MTV in say 30 metric ton (mT) sections, the parts of the spaceship dock, the workers with capsule(s) and the MTV fuel to get to EML1/2.

Possible EML1/2 work for the SpaceX Falcon 9 - getting a EML1/2 rated capsule(s) to the EML1/2 space-dock.  Lifting the parts of the space-dock, replacement MTV parts, fuel, consumables, workers and new crew.  How much cargo a Falcon 9 Heavy can lift to EML1/2 needs calculating - there are fast flight routes and minimum propellant flight paths.

The number of Falcon 9 and Falcon 9 Heavy launches is dependent on the mass of the MTV including solar arrays, mass of the spaceship yard, mass of the space-dock, manned Dragon flights to the spaceship yard, LEO consumables for the construction workers, LEO fuel, EML1/2 fuel, flight consumables and manned EML1/2 capsule flights.

The EML1/2 capsule will need designing, possibly an enhanced version of the Dragon with extra consumables, radiation protection and an Earth Departure Stage.

The MTV's main engines will be ion thrusters such as VASIMRs or HiPEP.  It will also need a chemical RCS probably made by a different firm (SpaceX?).

The spaceship yard and space-dock will need designing.

The total mass to be lifted to each location needs calculating.

Offline A_M_Swallow

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #249 on: 06/07/2010 11:08 AM »
{snip}
Truth is - if we want to go tomorrow, we use chemical stages.

If we go tomorrow we may have to use chemical stages, however in 6 years time there will be space tested large electric thrusters such as the 200kW VASIMR.

Offline simonth

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #250 on: 06/07/2010 11:11 AM »
Nonsense. F9H can use the Mars4less architecture which is all chemical. It can also use propellant depots to build up fuel over the two year period between launch windows.
Sorry, it is not nonesense at all. If anything, the DRM 5.0 tells us that a Mars surface mission requires 1200mt IMLEO if chemical propulsion is used. Even if we discount all the assembly problems with a 28mt to LEO rocket, and assume cryogenic LEO depots were readily available, the sheer amount of launches for a single mission are prohibitive. We are talking approximately 50-60 launches for fuel alone. This is not a viable Mars architecture.

Alternative concepts to Design Reference Missions have been literally fallen apart when NASA looked closer at them (e.g. Zubrin's Mars reference architectures).

Quote
The problem with alternative propulsion methods i:
1: they assume slow trajectories through the van allen belts - such trajectories are harmful to humans without massive shielding.
2: They need power supplies whose mass plus fuel outweighs the mass of a chemical stage. The increased development costs puts them far into the future.

ad 1. no they don't. They assume EITHER a high orbit assembly or EML1/2 assembly of the MTV OR a single crossing through the Van Allen Belts. In no instance whatsoever would humans be aboard the ship while it crosses the Van Allen Belts.

ad 2. no, untrue. In contrast to politically infeasible 1200mt reference missions (due to costs infeasible), we are talking about MTVs with a gross weight of 150-200mt. And I have no idea what you mean with "increased development costs". A 200mt solar array VASIMR based 8MW MTV doesn't require much development effort at all, VASIMR is know to work and 150W-200W/kg solar arrays are in development and use with upcoming robotic missions. The power structure for a 8MW advanced propulsion craft with current SEP technology clocks in at about 40mt. Contrast that with more than 1000mt of fuel for DRM 5.0 per mission (where all hardware is thrown away during each mission).

Quote
Truth is - if we want to go tomorrow, we use chemical stages.

Actually, the truth is, we can't go tomorrow because only chemical propulsion is available and we don't have 500 billion available for a Mars program relying on chemical propulsion, nor do we have working cryogenic fuel depots in LEO, nor a 25-30mt to LEO vehicle that can sustain a 50 launch flight rate per year etc.
« Last Edit: 06/07/2010 11:16 AM by simonth »

Offline A_M_Swallow

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Re: Manned Mars mission using SpaceX Falcon 9 Heavy?
« Reply #251 on: 06/07/2010 11:15 AM »
    "The Pentagon and Boeing Co. are developing a next-generation solar array aimed at reaching a weight-to-power ratio of 7 kilograms per kilowatt, according to the Defense Advanced Research Projects Agency."

You mean like the UltraFlex arrays on Phoenix ?

And even more like the UltraFlex arrays on the Orion.  The new UltraFlex solar cells are 30% efficient but I do not know the new power:weight ratio.  The MTV solar arrays are so big that they are unlikely to be round.
http://www.emcore.com/news_events/release?y=2010&news=237

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