Role of NTR/BNTR/NEP in future architectures

[Robotbeat]

A 39-day trip could be made easier if the crew is launched to the MTV right as the MTV reached Earth escape velocity (or slightly after).

And yeah, you would want to pre-position just about everything you could (I think you ought to preposition lots of equipment at Mars's surface and Mars orbit no matter what architecture you choose), since otherwise your spacecraft would just be way too big (and 200MW wouldn't even be enough) for such a fast trip.

But I think such a fast trip is definitely unnecessary. Even stretching it to 80-days of transit would greatly decrease power requirements.

[A_M_Swallow]

Has the viability of a 4 month trip to Mars possibly using 12MW solar arrays VASIMR been checked?

Ref:
Mars missions
http://www.adastrarocket.com/aarc/ToMars

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."

[mlorrey]

Has the viability of a 4 month trip to Mars possibly using 12MW solar arrays VASIMR been checked?

Ref:
Mars missions
http://www.adastrarocket.com/aarc/ToMars

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."

What sized vehicle and payload? The test unit being installed on ISS in the next few years isn't sufficient to keep the station in orbit with 100kw of power available to it. You're going to need to declare some mission particulars if you want to use that equipment.

[Robotbeat]

Has the viability of a 4 month trip to Mars possibly using 12MW solar arrays VASIMR been checked?

Ref:
Mars missions
http://www.adastrarocket.com/aarc/ToMars

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."

The basic concept of an opposition-class mission to Mars with 10MW worth of SEP is viable, according to this:
http://www.astronautix.com/craft/stcemsep.htm
(although the robots servicing the array sounds like a kind of dumb idea... just make the array have enough EOL power to not require such servicing)

The 7kg/kW is a pretty easy goal to hit. 200W/kg (5kg/kW) can easily be done, and 1kW/kg is certainly possible with efficient thin-film arrays and solar-sail-like construction techniques.

[A_M_Swallow]

Has the viability of a 4 month trip to Mars possibly using 12MW solar arrays VASIMR been checked?

Ref:
Mars missions
http://www.adastrarocket.com/aarc/ToMars

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."

What sized vehicle and payload? The test unit being installed on ISS in the next few years isn't sufficient to keep the station in orbit with 100kw of power available to it. You're going to need to declare some mission particulars if you want to use that equipment.

Using the Ad Astra page I linked to:
Crew lander (61 mT Payload)
31 mT Habitat
13.5 mT Areoshell
16.3 mT Descent System

Solar arrays 12,000 kW * 7 kg/kW = 84,000 kg = 84 mT

The mass of the core including VASIMR thrusters, RCS and fuel tanks must be around somewhere.  Permitting calculation of the propellant mass.

Edit : correct units and mass of solar arrays

[stealthyplains]

What sized vehicle and payload? The test unit being installed on ISS in the next few years isn't sufficient to keep the station in orbit with 100kw of power available to it. You're going to need to declare some mission particulars if you want to use that equipment.

Isn't the test unit operated in pulsed mode because the station doesn't have enough power for a continuous run?

[93143]

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."

Solar arrays 12,000 kW / 7 kW/kg = 1,715 kg or 1.8 mT

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

[A_M_Swallow]

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

Correction applied.

[kfsorensen]

with the powerplant and VASIMR dry specific mass alpha = 0.50 kg/kWe to see if this example could close.

Yeah, that's the magic number right there.  That's not doable.  And without that power supply all the rest of the argument falls apart.  FCD is disingenuous for continuing to quote that number.  I've asked him to his face why he does it, and he waves his hands and looks away from me and claims that he gets it from Samim Anghaie and that I should believe him.  Which I don't.  But FCD leaves the public and the NASA leadership with the impression that it is "VASIMR" that can do this when it's really "VASIMR and a magic power source" that does this.

[isa_guy]

with the powerplant and VASIMR dry specific mass alpha = 0.50 kg/kWe to see if this example could close.

Yeah, that's the magic number right there.  That's not doable.  And without that power supply all the rest of the argument falls apart.  FCD is disingenuous for continuing to quote that number.  I've asked him to his face why he does it, and he waves his hands and looks away from me and claims that he gets it from Samim Anghaie and that I should believe him.  Which I don't.  But FCD leaves the public and the NASA leadership with the impression that it is "VASIMR" that can do this when it's really "VASIMR and a magic power source" that does this.

Chang-diaz believed to a guy that has been accused of fraud  http://abcnews.go.com/Business/wireStory?id=8961162 , hmm no offence but it  looks like a conspiracy .

[Robotbeat]

with the powerplant and VASIMR dry specific mass alpha = 0.50 kg/kWe to see if this example could close.

Yeah, that's the magic number right there.  That's not doable.  And without that power supply all the rest of the argument falls apart.  FCD is disingenuous for continuing to quote that number.  I've asked him to his face why he does it, and he waves his hands and looks away from me and claims that he gets it from Samim Anghaie and that I should believe him.  Which I don't.  But FCD leaves the public and the NASA leadership with the impression that it is "VASIMR" that can do this when it's really "VASIMR and a magic power source" that does this.

An MPD thruster could have an alpha this low, though its low efficiency means you need an even bigger power source (and it'd probably be glowing a dull red).

A really lightweight solar-power-sail could theoretically have such an alpha.

Doesn't seem worth it, though. Just learn to live in space for 400+ days. The Russians have already demonstrated that.

[isa_guy]

Why 400 days  shouldn't the NEP/SEP propulsion system shorten the trip time to mars ( compare to NTR or chemical propulsion ) ?

[Robotbeat]

Why 400 days  shouldn't the NEP/SEP propulsion system shorten the trip time to mars ( compare to NTR or chemical propulsion ) ?

Yeah, or it could allow you to bring more mass. Or have greater margins. Or both.

[mlorrey]

with the powerplant and VASIMR dry specific mass alpha = 0.50 kg/kWe to see if this example could close.

Yeah, that's the magic number right there.  That's not doable.  And without that power supply all the rest of the argument falls apart.  FCD is disingenuous for continuing to quote that number.  I've asked him to his face why he does it, and he waves his hands and looks away from me and claims that he gets it from Samim Anghaie and that I should believe him.  Which I don't.  But FCD leaves the public and the NASA leadership with the impression that it is "VASIMR" that can do this when it's really "VASIMR and a magic power source" that does this.

Chang-diaz believed to a guy that has been accused of fraud  http://abcnews.go.com/Business/wireStory?id=8961162 , hmm no offence but it  looks like a conspiracy .

Lets see, they committed "Fraud" because the work was done on campus and in Russia rather than at NE facilities?

There's been some iffy prosecutions lately by the government, they recently tried to go after a pshrink at Dartmouth Hitchcock who did work at the VA across the river and managed some grants that he happened to do the work on and paid himself (shockers!). The jury found him innocent and said afterwards the governments case was baseless.

Part of the problem with these contracting prosecutions is that the investigators and prosecutors get a cut of the money and assets recovered, which encourages fake prosecutions.

[kfsorensen]

I don't really care if Samim Anghaie is a crook but his 0.5 kg/kWe number is a fantasy.  Why FCD builds his VASIMR sales case on that number when all other reputable electric-propulsion researchers have rejected it (even though it makes their thrusters look incredible too) is beyond my understanding.

[mmeijeri]

Why FCD builds his VASIMR sales case on that number when all other reputable electric-propulsion researchers have rejected it (even though it makes their thrusters look incredible too) is beyond my understanding.

Because he sees VASIMR as a precursor to fusion powered propulsion and hopes to get that precursor funded? Not the most honest sales strategy...

[Star-Drive]

The best supportable dry mass specific mass figure for the current VASMIR and a Polywell based aneutronic fusion reactor in the 100 MWe output power class was 1.70 kg/kWe plus structure + Tanks + H2 Propellant.  That doesn't make Franklin's 39 day one-way to Mars trip time doable, but it does allow pushing a manned 52 mT payload from Earth GEO to Mars Phobus orbit, stay for 30 days around Mars, and then go back to Earth GEO all in just under 12 months round trip time.  To me that makes a lot of Mars mission senarios very doable as compared to the current 900 day (30 monts) Mars round trip times still baselined by NASA. 

[Robotbeat]

The best supportable dry mass specific mass figure for the current VASMIR and a Polywell based aneutronic fusion reactor in the 100 MWe output power class was 1.70 kg/kWe plus structure + Tanks + H2 Propellant.  That doesn't make Franklin's 39 day one-way to Mars trip time doable, but it does allow pushing a manned 52 mT payload from Earth GEO to Mars Phobus orbit, stay for 30 days around Mars, and then go back to Earth GEO all in just under 12 months round trip time.  To me that makes a lot of Mars mission senarios very doable as compared to the current 900 day (30 monts) Mars round trip times still baselined by NASA. 

Those longer Mars missions are Conjunction-class missions, though. Though they have a long trip time, they stay at Mars for over a year, potentially getting more done. I hope we can quickly transition from Opposition-class 400-500 day missions to those Conjunction-class 900 day missions. Heck, rotate crew every couple years. But that's probably dreaming.

[KelvinZero]

Hey, just another throwaway idea..

As I understand it, the biggest technical problem with NTR is that you cannot make the gas arbitrarily hotter than a chemical rocket because you are still limited by the materials of the chamber which must contain this heat.

However, as I understand it, initially this heat is in the form of extremely hot fragments of nuclei and gamma rays. I imagine these have so much energy that they ionise whatever they bang into, and the results of these collisions might also have enough energy to ionise whatever they bang into.

So if you could use magnetic fields to separate out these ions before their energy is defused into mere heat, you could use them for thrust immediately and at the same time greatly reduce the amount of heat you have to deal with, because you have expelled it while it was still in a low entropy state.

In short I guess I am talking about a nuclear powerplant/ VASIMR hybrid, where the powerplant produces the usual amount of heat for electricity, but also is a source of hot ions which do not count towards this heat and are fed directly into the VASIMR

[Star-Drive]

The best supportable dry mass specific mass figure for the current VASMIR and a Polywell based aneutronic fusion reactor in the 100 MWe output power class was 1.70 kg/kWe plus structure + Tanks + H2 Propellant.  That doesn't make Franklin's 39 day one-way to Mars trip time doable, but it does allow pushing a manned 52 mT payload from Earth GEO to Mars Phobus orbit, stay for 30 days around Mars, and then go back to Earth GEO all in just under 12 months round trip time.  To me that makes a lot of Mars mission senarios very doable as compared to the current 900 day (30 months) Mars round trip times still baselined by NASA. 

Those longer Mars missions are Conjunction-class missions, though. Though they have a long trip time, they stay at Mars for over a year, potentially getting more done. I hope we can quickly transition from Opposition-class 400-500 day missions to those Conjunction-class 900 day missions. Heck, rotate crew every couple years. But that's probably dreaming.

You have to remember that neither the Russians nor the USA have ANY long term (greater than a week) human flight experience outside of the Earth's geomagnetic field.  The proposed long term stays (~900 days) in the cosmic ray shooting gallery and the radiation issues associated with solar flare events that is encapsulated in interplanetary journeys have many crew safety question marks still unanswered.  So longer missions to Mars poses more risk to the crew than NASA is willing to take at the moment.  Shorter stay and trip times are better if you don't want dead or dying crew members coming back to Earth...