Boeing's plan for Mars

JCO · 2015-01-25 01:48:11

Not being an engineer I do not know enough to really judge the technology of Boeing's plan. What I do know is there are a couple differences between Boeing and SpaceX that will determine what can be expected from them. SpaceX is a small company with something to prove and a name to make. Boeing is a large establish company who long ago made their name. They are currently more interested in maintaining market share than expanding their horizons. SpaceX has a single man in control of what their mission statement. This allows them maintain longer range goals and take greater risks. Boeing is run by a board of directors that for the most part will always choose short term profits over long term growth.

Though this reality frustrates me I do not blame Boeing for it because I suspect the same may be true of SpaceX ten years after Musk has passed away. Here is hoping Elon Musk lives to be very, very old.

kbd512 · 2015-01-25 02:23:54

Impaler wrote:

kbd512: Your critique of SEP is completely baseless. You seem to think that the technology can only work at small scale. That is where it is currently being used because that is the size of our unmanned systems like satellites and probes, the performance of the SEP is currently being used to reduce the size of the launch rocket and add multiple destinations/lifespan to satellites because this is most cost effective first utilization. But that has nothing to do with what scale it CAN operate at, it's like saying in 1945 that Rockets would never scale to bigger then a V2 because that's all that had been done so far.

Solar technology isn't even close to nuclear technology in terms of power density. If putting weight in LEO weren't a problem, SEP would be an enabling technology. However, reality being what it is, it's awfully expensive to put anything into orbit.

Impaler wrote:

The only limiting factor to SEP scaling is the Solar, and we have a 40 year history of higher and higher power availability on every type of space vehicle. Electric propulsion systems and Solar arrays gain higher power-to-weight ratios as they scale up. This scaling up is not a simple as just making a bigger tank of fuel and a bigger rocket engine, we have to do significant redesign and optimization of lots of hardware but the direction has always consistently been towards a higher performance system that has positive scaling factors. It is just a matter of time and clustering of large numbers of solar arrays and electric thrusters into a single vehicle to create something that reach the size and pushing-capacity to move human spaceflight level masses.

And that might happen… In another 20 years or so.

Impaler wrote:

I'm all for Technology development, and NASA badly needs to be allowed to redirect all that 'launch vehicle' boondoggle money into tech as the Obama administration tried to do. But I disagree on all of the things you've point at as worthy of development, the current crop of tech that NASA is looking at such as Mars EDL, and mitigating propellent boil-off are the best choices, they just don't have the budget to do more then the top few choices, and slowly at that. All of the technologies your asking for are on the other hand dead-ends or unnecessary and wouldn't in my opinion be deserving of any development funding.

Artificial gravity is a dead end? For who? Certainly not the astronauts.

Nuclear propulsion and power are politically unpopular. The technology works.

Impaler wrote:

Nuclear rockets have always been pie-in-the-sky, they are impossible to develop incrementally on the ground due to radiation release, the ISP they offer is no longer remotely attractive compared to what a SEP system can offer right now, their is zero reason to invest in this technology and that's exactly what is being invested in it a big zero. I don't know why this forum is full of people who feel in love with Nuclear propulsion 20 years ago and never reconsidered that the mighty N might not be the ultimate solution to everything in space (I know the Hollywood movies certainly give this impression), but your ALL chasing a phantom that will never see the light of day.

Whereas those spacecraft with solar arrays the size of football fields are awaiting the next launch? Yeah, right.

I don't love nuclear propulsion, but I accept that splitting atoms produces more power than using photons to excite electrons. You seem to equate the efficiency of an electric propulsion system with the means of providing the electricity to it.

Impaler wrote:

Artificial gravity sounds nice, but we have enough ISS experience to send people up for 6 months and have them come down into Earth gravity and be good to go in a few days, they are not cripples as some people like to exaggerate. In other words we can get to Mars in ISS derived habs and just recuperate for a tiny fraction of the surface stay time upon landing in lander/habitat, a trivial operational constraint that allows us to dispense with all the engineering of spinning stuff.

That's just what I want. A group of astronauts who can't walk without fainting after they've landed on another planet thirty million miles from Earth. All the engineering of spinning a wheel is too complicated? Wow. Maybe we should just be content here on Earth.

Impaler wrote:

Radiation shielding against Solar Flares is basically a solved problem, we use a modest water tank 'storm shelter', every proposed Mars transit vehicle has included this for decades now and no one expects it to be a problem to built it or do it and it hardly adds any mass to the vehicle given crew water needs, this radiation presents NO barrier to NASA. Cosmic Rays are the radiation that is currently the show stopper and which NASA has no solution for because their is NO passive shielding solution short hundreds of g/cm^3 which is far beyond our mass budgets. Either we will find some kind of active shielding in space, discover that the dosages are less damaging then previously thought based on animal studies, focus on getting underground on Mars so the crew only gets the in-Space dosage, or just raise the chance of death threshold for astronauts. Radiation deserves study but we should absolutely NOT be down-selecting to 'passive shielding' at this time.

When I was speaking about better passive radiation shielding, I meant using better habitat materials than aluminum cans. Some of the mass estimates for active radiation shielding exceed the entire mass estimates for Mars DRM's, so without knowing which particular tech you're referencing, I'll leave it at that.

louis · 2015-01-25 15:00:46

kbd512 wrote:

Impaler wrote:
Artificial gravity sounds nice, but we have enough ISS experience to send people up for 6 months and have them come down into Earth gravity and be good to go in a few days, they are not cripples as some people like to exaggerate. In other words we can get to Mars in ISS derived habs and just recuperate for a tiny fraction of the surface stay time upon landing in lander/habitat, a trivial operational constraint that allows us to dispense with all the engineering of spinning stuff.
That's just what I want. A group of astronauts who can't walk without fainting after they've landed on another planet thirty million miles from Earth. All the engineering of spinning a wheel is too complicated? Wow. Maybe we should just be content here on Earth.

I doubt anyone is going to send people to Mars without an analogue mission to the moon. I agree with Impaler that AG is likely to prove a very expensive diversion in terms of both money and time.

We can establish how people will react by taking them to the Moon first in lunar orbit for 6 months, until landing on the lunar surface, where they can work in 1G weighted suits and their health can be assessed. The Mars habitat can be tested at the same time.

I think they will be able to cope. But we have to test it first without taking them to Mars would be my view.

kbd512 · 2015-01-25 18:47:19

louis wrote:

I doubt anyone is going to send people to Mars without an analogue mission to the moon. I agree with Impaler that AG is likely to prove a very expensive diversion in terms of both money and time.

Flying a transit habitat around the moon for six months won't tell us anything that we don't already know about microgravity.

AG is too expensive or complicated whereas active radiation shielding is some sort of requirement for a Mars mission? The tech for effective particle shields to deflect protons with gigavolt energies or better is guaranteed to be far more expensive and heavier than AG. All the concepts I've seen had impressive power requirements. Are we going to power the propulsion system with our solar panels or use it to deflect radiation?

If we stop using soda cans for habitats, that'd be a good first step towards reducing radiation exposure. There are lots of better materials for absorbing radiation than aluminum.

With respect to AG, humans weren't designed for microgravity environments and there's no getting around that. Microgravity poses actual health problems and just because someone is ambulatory doesn't mean the effects aren't real or lasting. All we need is for someone's corneas to be adversely affected on the surface of Mars to put all the ridiculous hand wringing about the effects of radiation into context.

louis wrote:

We can establish how people will react by taking them to the Moon first in lunar orbit for 6 months, until landing on the lunar surface, where they can work in 1G weighted suits and their health can be assessed. The Mars habitat can be tested at the same time.

We already have plenty of data to discern the health effects of microgravity and radiation. We don't need any more human guinea pigs to tell us what we already know.

louis wrote:

I think they will be able to cope. But we have to test it first without taking them to Mars would be my view.

I don't want to find out how well the crew fares when they're tens of millions of miles from home.

SpaceNut · 2015-01-25 19:52:51

We also know the radiational effects when inside the megosphere of Earth belts and that is what we need to create for the shielding we would want for a Mars journey even if we could get there in days we would still need it on the surface though not as agressively as compared to open vaccum of space.

As far as AG we do have data points for exercise and medications but when the ISS was concieved there was the centrifugal module which was deleted which could give value as to the amount one needs to compensate for micro gravity.

RobertDyck · 2015-01-25 20:09:59

We are going in circles; obsessing about issues discussed over and over. We need hard data, and actual equipment development. Not sitting on our ass(es) talking about things that just aren't happening. The concern with rotation is how to manoeuvre. Ok. Do it! Just do the experiment. Long ago I posted a simple suggestion: attach a Russian Soyuz spacecraft with crew onboard to a spent Progress cargo ship filled with garbage. The spent cargo ship is destined to de-orbit and burn-up in the atmosphere anyway. Attach them with a cable, then spin to produce artificial gravity. While rotating, them change orbit. Exactly what orbit is changed to doesn't matter, the point is to demonstrate you can achieve controlled manoeuvre(s) while rotating in tethered flight. If something goes wrong, cut the cable. The Progress is intended for disposal anyway. And this will be done when the Soyuz is destined to return to Earth.

Since the Ukraine thing, cooperation with Russians is questionable. Could we do the same experiment with a Dragon CRS spacecraft, and Dragon Rider? Dragon Rider, Crew Dragon, or Dragon Version 2; whatever they call it now. We'll have to wait for the first Crew Dragon to fly. That isn't scheduled until 2017.

SpaceNut · 2015-01-25 20:21:15

I do agree that we do need to do the experiment to prove which option is the best choice for AG: which are the cable spin from a booster stage to habitat area, end over end tumble as GW would have and the modified radial spin of a hub struture for the crew to be housed in that is along the main course of travel.

What even happened to the TEMPO 3 experiment?

Impaler · 2015-01-25 23:44:12

kbd512 wrote:

Solar technology isn't even close to nuclear technology in terms of power density. If putting weight in LEO weren't a problem, SEP would be an enabling technology. However, reality being what it is, it's awfully expensive to put anything into orbit.

Your information is woefully out of date, Solar easily exceeds Nuclear power density in the Inner solar system (for in-space power, planetary surfaces are a very different environment), you need to be somewhere past Jupiter for Nuclear to be superior now. NASA is developing 300+ W/kg Solar arrays and theoretical limits are in the 1000 W/kg range. Nuclear systems simply can't reach that power density because they are thermal and need massive radiators and a whole working-fluid/turbine systems. This is what people ignore about Nuclear, they look at the mass of a core and ignore the rest of the system which is 90% of the mass and it's this part of the system which faces fundamental Carnot efficiency limits that give us little hope of a breakthrough improvement.

kbd512 wrote:

And that might happen… In another 20 years or so.

Yes that's how long it would take with NO SUPPORT at all, the commercial and small funding deep-space probes Electric propulsion and solar panels would give us human-flight capable systems in that kind of time-frame. IF we actually invested heavily in developing it then that could be considerably faster. This is in contrast to nuclear systems which are moving at a rate of zero with zero funding. NASA should put it's money on accelerating something that is not completely dependent upon NASA, just like NASA should buy commercial launch rockets rather then build boondoggles that it is the only customer for.

kbd512 wrote:

Artificial gravity is a dead end? For who? Certainly not the astronauts.
Nuclear propulsion and power are politically unpopular. The technology works.

No the technology has never been competitive with Solar for power, or with Big Dumb Boosters for propulsion, the 'politics' stuff is a BS excuse that Nuclear proponents have used for decades to nurse their failure and bitterness. I should hardly be surprised this sentiment is rampant on these forums considering Zubrin himself is absolutely dripping in this kind of resentment for politicians and half-concealed self-flattery "If only they had listened to ME we would be on Mars now!".

kbd512 wrote:

Whereas those spacecraft with solar arrays the size of football fields are awaiting the next launch? Yeah, right.

Double standard much, where are the 10 MW space based nuclear reactors ready to launch? Our largest Arrays is the ROSA from Deployable Space System at 63 m^3, a dozen of these would be used to create a MegaROSA system of 750 m^3 and 300 kw, less then one order of magnitude short of the football field in area and enough power for things like Asteroid Redirect, so actually not that far off. The ROSA arrays are set to become the new industry standard on commercial satellites too.

kbd512 wrote:

I don't love nuclear propulsion, but I accept that splitting atoms produces more power than using photons to excite electrons. You seem to equate the efficiency of an electric propulsion system with the means of providing the electricity to it.

You 'accept' an error if you think nuclear systems are higher power density then solar. And everyone in the SEP system field acknowledges that the power density of the energy source is the Primary determinant of the overall vehicles performance because the mass of thrusters hardware is minimal and scales very well, and the propellent fractions are already wonderfully low, so low that we would generally want to trade that back for higher thrust and shorter duration, which requires more power. So yes it is all about the power source density.

kbd512 wrote:

That's just what I want. A group of astronauts who can't walk without fainting after they've landed on another planet thirty million miles from Earth. All the engineering of spinning a wheel is too complicated? Wow. Maybe we should just be content here on Earth.

Astronauts CAN WALK after returning from the ISS, as I said it is a myth that people are crippled by 6 months of zero-G, that kind of stuff only happened a decade ago when we did not have the present exercise schedules. It is a solved problem, the Astronauts will need 3 days of safety recuperation on the surface because of adjustment of the shape of the eye that makes vision blurry, this is the ONLY current restriction that Astronauts have now upon returning to Earth, they can't drive vehicles for 3 days after returning to 1 G, we would thus not expect them to make any EVA's for comparable period on Mars. They will be walking around in the Habitat just fine for thouse 3 days waiting to get out on the surface.

kbd512 wrote:

When I was speaking about better passive radiation shielding, I meant using better habitat materials than aluminum cans. Some of the mass estimates for active radiation shielding exceed the entire mass estimates for Mars DRM's, so without knowing which particular tech you're referencing, I'll leave it at that.

I don't know what the solution to radiation is either, active magnetic based shielding is just one of many ideas that may not work. I just know that the solution is NOT passive Mass of ANY kind, their is hardly any difference between aluminum and liquid hydrogen (the best shielding) when it comes to stopping GCR, you would need a 200 tons of Aluminum and 100 tons of Hydrogen, both are equally unfeasible even if the later is half as much.

Last edited by Impaler (2015-01-25 23:57:31)

RobertDyck · 2015-01-26 01:05:11

Impaler: you guys have a nice argument going, but...
Nuclear Thermal Rockets are a lot further along than you appear to think. NERVA development was complete, in fact a second generation called NERVA 2, was developed in 1974. All that was left was a test firing in orbit. The early 1970s version wasn't powerful enough for ground launch, but was sufficient for TMI. In fact that's what it was designed for. After Apollo 11, the Russians talked about trumping that by going straight to Mars. So NASA started work on a Mars mission. They developed PICA heat shield material to allow an Apollo command module to return directly to Earth from Mars. And they developed the NERVA engine as the TMI stage. Of course they didn't have life support, so weren't ready. But Russia had their own problems. When Russia quit, so did NASA. But don't think NERVA wasn't ready. The Nova rocket was designed for Mars, but NASA also had short-term plans if necessary. They were working on a replacement 3rd stage for Saturn V that would use NERVA instead of J2. The entire 3rd stage the the spacecraft would have to be parked in LEO; the NERVA engine could only be fired up after it was safely parked in LEO. Could it have worked? Well, like I said, they didn't have life support. But the engine was ready.

Timberwind was designed with much greater energy density. Intended for ground launch, thrust to engine weight ratio was 30. The advantage with NTR is both high thrust and high Isp. That means you get to Mars quickly. With electric propulsion, launch mass is much lower, but you get there much slower. Expect SEP to take 2 years from LEO to Mars. Chemical will take 6 months. Spirit and Opportunity took 6 months, Curiosity took 8.5 months. With solid core NTR, you don't get there faster, instead launch mass is lower. It will still take 6 months, because that trajectory gives you a free return.

Radiation: there is research into mini-magnetosphere. One design is only 50kg of equipment, but requires significant electric power. Washington State University has done work on this. They claim with <1kW they can deflect 1 Newton plasma. How much power for heavy ion GCR? The problem is mini-magnetosphere requires vacuum, and expands too far for any test chamber on Earth. It needs to be tested in space. So do so. But it certainly isn't ready yet. The solution today is simple: get to Mars fast. Then land so you have atmosphere overhead.

Impaler · 2015-01-26 01:47:23

I know what the Technology Readiness level of NTR is and it only a 5-6, it was NOT completed because completion would be involve demonstration of a system in space to achieve TRL of 8 a 'flight qualified system'. SEP is already a 9.

The performance of the NERVA system is simply obsolete now, the mass sent through TMI is only 50% more then a chemical booster, that's not even worth investing in even if SEP did not exist.

SEP mission durations can be as short as any chemical mission, stop repeating this garbage based on unmanned probes. When we send robots to Mars chemical we send them as SLOW as possible for efficiency and for any single impulse event that is Holman transfer with is 8 months at most, low-thrust systems are capable of even slower and more efficient non-Holman trajectory but this is a WIDER RANGE that is being utilized. The only limit to speed is power density and the near term Solar power density that is already in the development pipeline will allow transits of comparable duration to any high thrust systems. The LEO to Mars period is not what we care about either, it is the High Earth Orbit To Mars that matters, the SEP vehicle goes to High orbit alone and then the crew take a fast Taxi of a few days to dock with it, THEN the relevant human mission duration begins. You know this so stop throwing out blatantly dishonest comparisons.

And you are blatantly wrong on Free return trajectory, thouse do NOT last 6 months and they occur incredibly infrequently, like once every decade, the total duration is space is close to two years and the radiation dose would be terrible. They are not a remotely practical for a mission to Mars that intends to land, only Tito's crazy flyby mission is aiming to for that trajectory.

For GRC protection Mars atmosphere is NOTHING, literally less shielding in it then the aluminum of the spacecraft you rode in. The Martian GROUND shields half a hemisphere and cuts your GCR dosage in half but that is it. If you want to shield yourself on Mars you need to get under neither several meters of regolith which is certainly possible but by no means trivial. Something like half of the total GCR dosage you get on a Mars mission is radiation on the surface because of the long 500 day surface stay, getting to Mars fast is not the ONLY solution to the radiation problem though every person with a 'fast' propulsion system to sell you pretends that it is.

Last edited by Impaler (2015-01-26 01:57:13)

kbd512 · 2015-01-26 02:27:38

Impaler wrote:

Your information is woefully out of date, Solar easily exceeds Nuclear power density in the Inner solar system (for in-space power, planetary surfaces are a very different environment), you need to be somewhere past Jupiter for Nuclear to be superior now. NASA is developing 300+ W/kg Solar arrays and theoretical limits are in the 1000 W/kg range. Nuclear systems simply can't reach that power density because they are thermal and need massive radiators and a whole working-fluid/turbine systems. This is what people ignore about Nuclear, they look at the mass of a core and ignore the rest of the system which is 90% of the mass and it's this part of the system which faces fundamental Carnot efficiency limits that give us little hope of a breakthrough improvement.

Are solar panels near that kW/kg threshold yet? Because that's where GCNR's operate at.

The heat has to go somewhere, but generally you want to convert that heat to power or heat propellant. If you start radiating the thermal energy from the reactor into space, you reduce efficiency.

A single Falcon 9 can lift an entire GCNR. The type of SEP transfer vehicle that Boeing wants to build to go to Mars with would require a SLS launch of its own.

Impaler wrote:

Yes that's how long it would take with NO SUPPORT at all, the commercial and small funding deep-space probes Electric propulsion and solar panels would give us human-flight capable systems in that kind of time-frame. IF we actually invested heavily in developing it then that could be considerably faster. This is in contrast to nuclear systems which are moving at a rate of zero with zero funding. NASA should put it's money on accelerating something that is not completely dependent upon NASA, just like NASA should buy commercial launch rockets rather then build boondoggles that it is the only customer for.

I never said that NASA shouldn't pour money into the technology. I firmly believe that the benefits are worth the development funding.

Impaler wrote:

No the technology has never been competitive with Solar for power, or with Big Dumb Boosters for propulsion, the 'politics' stuff is a BS excuse that Nuclear proponents have used for decades to nurse their failure and bitterness. I should hardly be surprised this sentiment is rampant on these forums considering Zubrin himself is absolutely dripping in this kind of resentment for politicians and half-concealed self-flattery "If only they had listened to ME we would be on Mars now!".

A failure of what? The people who developed nuclear power and propulsion for NASA didn't fail at anything. You can't fail at what you're never given a chance to attempt.

Resent politicians for acting like politicians? I think a good number of them can be pretty short-sighted but I don't resent them.

If funding for the space nuclear power and propulsion development effort had continued, we'd have visited Mars in the early 1980's, long before Zubrin ever started his rants about how we could go to Mars "DIRECT". That's all history, though, and I don't really care that much about the past since it can't be changed. Just because we wasted a lot of development funding in the past doesn't mean we have to continue to do so.

Impaler wrote:

Double standard much, where are the 10 MW space based nuclear reactors ready to launch? Our largest Arrays is the ROSA from Deployable Space System at 63 m^3, a dozen of these would be used to create a MegaROSA system of 750 m^3 and 300 kw, less then one order of magnitude short of the football field in area and enough power for things like Asteroid Redirect, so actually not that far off. The ROSA arrays are set to become the new industry standard on commercial satellites too.

It's hard to develop a program when funding is pulled or never made available.

Impaler wrote:

You 'accept' an error if you think nuclear systems are higher power density then solar. And everyone in the SEP system field acknowledges that the power density of the energy source is the Primary determinant of the overall vehicles performance because the mass of thrusters hardware is minimal and scales very well, and the propellent fractions are already wonderfully low, so low that we would generally want to trade that back for higher thrust and shorter duration, which requires more power. So yes it is all about the power source density.

I accept that gas core reactors have power densities that are at the theoretical limits of solar technology and don't have the limitations of solar technology. We keep going round and round on this point. The tech hasn't been developed because it hasn't been funded. I think solar tech is great and we could conceivably use it to explore the inner solar system, but that's about it.

Impaler wrote:

Astronauts CAN WALK after returning from the ISS, as I said it is a myth that people are crippled by 6 months of zero-G, that kind of stuff only happened a decade ago when we did not have the present exercise schedules. It is a solved problem, the Astronauts will need 3 days of safety recuperation on the surface because of adjustment of the shape of the eye that makes vision blurry, this is the ONLY current restriction that Astronauts have now upon returning to Earth, they can't drive vehicles for 3 days after returning to 1 G, we would thus not expect them to make any EVA's for comparable period on Mars. They will be walking around in the Habitat just fine for thouse 3 days waiting to get out on the surface.

Bone decalcification doesn't disappear in three days and not all of the eye problems disappear in three days, either. If the astronauts don't have to go anywhere after they land then that may be fine. Alternatively you could simply avoid the situation altogether with artificial gravity. I have a feeling that if artificial gravity is a costly or insurmountable engineering challenge that lots of other aspects of the program would prevent us from moving forward.

Impaler wrote:

I don't know what the solution to radiation is either, active magnetic based shielding is just one of many ideas that may not work. I just know that the solution is NOT passive Mass of ANY kind, their is hardly any difference between aluminum and liquid hydrogen (the best shielding) when it comes to stopping GCR, you would need a 200 tons of Aluminum and 100 tons of Hydrogen, both are equally unfeasible even if the later is half as much.

Active shielding for GCR mitigation isn't a critical technology for a Mars mission and that's the point I've tried to make. The better materials are for shielding from SPE's, not GCR's. I have no idea how a 400t-1600t active radiation shielding system would play into the SLS cost-per-launch equation, but I'm guessing it wouldn't be too helpful.

kbd512 · 2015-01-26 02:50:30

Impaler wrote:

I know what the Technology Readiness level of NTR is and it only a 5-6, it was NOT completed because completion would be involve demonstration of a system in space to achieve TRL of 8 a 'flight qualified system'. SEP is already a 9.
The performance of the NERVA system is simply obsolete now, the mass sent through TMI is only 50% more then a chemical booster, that's not even worth investing in even if SEP did not exist.

So NASA is spending what little funding it puts into nuclear propulsion to re-create a solid core reactor that isn't worth the investment. Makes perfect sense.

Impaler wrote:

SEP mission durations can be as short as any chemical mission, stop repeating this garbage based on unmanned probes. When we send robots to Mars chemical we send them as SLOW as possible for efficiency and for any single impulse event that is Holman transfer with is 8 months at most, low-thrust systems are capable of even slower and more efficient non-Holman trajectory but this is a WIDER RANGE that is being utilized. The only limit to speed is power density and the near term Solar power density that is already in the development pipeline will allow transits of comparable duration to any high thrust systems. The LEO to Mars period is not what we care about either, it is the High Earth Orbit To Mars that matters, the SEP vehicle goes to High orbit alone and then the crew take a fast Taxi of a few days to dock with it, THEN the relevant human mission duration begins. You know this so stop throwing out blatantly dishonest comparisons.

I've never had any problem with the length of the mission, but the throw to LEO for the proposed chemical solutions and the type of SEP vehicles being proposed is substantial. If we can afford heavier throws, I'd put the money into the payload.

Impaler wrote:

And you are blatantly wrong on Free return trajectory, thouse do NOT last 6 months and they occur incredibly infrequently, like once every decade, the total duration is space is close to two years and the radiation dose would be terrible. They are not a remotely practical for a mission to Mars that intends to land, only Tito's crazy flyby mission is aiming to for that trajectory.

I have no idea why so much is made of the free return trajectory nonsense. Once you get to Mars you're not coming home for awhile.

Impaler wrote:

For GRC protection Mars atmosphere is NOTHING, literally less shielding in it then the aluminum of the spacecraft you rode in. The Martian GROUND shields half a hemisphere and cuts your GCR dosage in half but that is it. If you want to shield yourself on Mars you need to get under neither several meters of regolith which is certainly possible but by no means trivial. Something like half of the total GCR dosage you get on a Mars mission is radiation on the surface because of the long 500 day surface stay, getting to Mars fast is not the ONLY solution to the radiation problem though every person with a 'fast' propulsion system to sell you pretends that it is.

You accept the radiation dose, don't do the mission, or put far more funding into lowering the incredible mass of the proposed active shielding. I think it's a solution in search of a problem. Short of burying the habitats and limiting surface stays, I don't see any other feasible solutions.

RobertDyck · 2015-01-26 02:56:26

Flight to Mars: Calculations

...orbital period T in years...
For Mars, r = 1.523691, T2 = (1.523691)3 = 3.53745
T = 1.8808 years
Assuming 365.25 days per (Julian) year:
T = 1.8808 years = 686.96 days

That's orbital period. Divide in half for one-way trip to Mars: 686.96 / 2 = 343.48 days = 11.28 months.

That is a strict Hohmann ellipse, also known as a Hohmann transfer orbit. Increasing fuel by just a tiny bit can reduce trip time to 8.5 months. Or 8 months, depending on relative positions of Earth and Mars in their orbits, and exactly how much fuel. Remember Mars' orbit is significantly more eliptical than Earth's. Increasing fuel by about 10% reduces trip time to 6 months. Reducing trip time further takes significantly more fuel. And more important, the 6 month transit arrives at Mars with the perfect velocity for a free return to Earth.

Total trip time Earth-Mars-Earth is significantly longer than 6 months. However, to use a free return, you must arrive at Mars with a certain velocity. That velocity corresponds to a 6 month one-way transit to Mars.

True, the Russian company Energia came up with a mission plan to send humans to Mars with SEP. It involves 3 month spiral out of Earth orbit, then 8 month transit to Mars, then 1 month spiral down to Mars working orbit, then 1 month in Mars orbit and men on the surface, then 1 month spiral out of Mars orbit, then 7 month transit to Earth, 3 month spiral down to LEO.

To do that, the vehicle is 700 metres wide. That meansures solar arrays along the diagonal. Based on the image, each solar array appears to be 230m x 230m. And 600 tons (tonnes?) at launch is rather heavy.

For GCR, the science team for the MARIE instrument on Mars Odyssey calculated heavy ion GCR on Mars surface. Their result showed heavy ions are blocked the most, medium ions a medium amount, and light ions much less, and protons the least. Click [ here ], and look at the 3D chart on page 20. You can look at the chart for solar maximum or solar minimum. Compare 8km altitude with 0km, and notice the scale is logarithmic. It shows roughly 90% blocked. And the implication is any altitude below the datum would have even more blocked. So Mars atmosphere is the most effective shielding against heavy ion GCR. Not so much with light ions, and practically no protection against protons. But they can be blocked with regolith (sand bags).

Last edited by RobertDyck (2015-01-26 03:04:24)

kbd512 · 2015-01-26 11:21:36

It is possible, although never demonstrated that the tech can scale up, as Impaler has noted, but my understanding is that even in LEO the Space Shuttle was and ISS is routinely peppered with debris.

What happens if one of these arrays or the truss supporting it is hit with something the size of a marble?

I would presume that the likelihood of simply damaging a panel is far higher than damaging a support structure, but is any of that been baked into the hardware design and mission planning?

RobertDyck · 2015-01-26 13:22:35

Assuming Russia's plan has the size I calculated from their image, total size is 105,800 square metres. An American football field is 120.0 yards × 53.3 yards or 6400 square yards = 5,351.215104 square metres. So the solar array area is 19.77 American football fields.

kbd512 · 2015-01-26 14:00:56

RobertDyck wrote:

Assuming Russia's plan has the size I calculated from their image, total size is 105,800 square metres. An American football field is 120.0 yards × 53.3 yards or 6400 square yards = 5,351.215104 square metres. So the solar array area is 19.77 American football fields.

Yes, but our solar tech is better than their solar tech.

Maybe Impaler can tell us how big a vehicle we're talking about to move the mass of the tug and a 110t payload from L1/L2 to Mars.

I don't recall seeing exactly how much area Boeing envisioned for their SEP tug or what the mass would be, but perhaps I didn't read carefully enough. I've gone through various proposals from Boeing, NASA, ESA, and others. All of the SEP powered transfer vehicle proposals I've seen are fairly substantial and require heavy lift.

I don't give two hoots about using chemical, solar electric, nuclear electric, or nuclear thermal to get to Mars. There are problems and benefits associated with each solution. I've already stated the reasons why I think nuclear propulsion, done the right way and with the right tech, is preferable and won't belabor the point any further.

I just want to figure out what our chances of shooting ourselves in the foot are with whatever tech we use to get there.

If we fly a vehicle with a large enough surface area through as much space as we're going to cover to make the transit, we're bound to hit something along the way. If we use SEP, will the damage be catastrophic or does it merely degrade performance? I'm curious to know what our options are for damage control to maintain a powered transfer when that happens.

Is there a way to deploy a lesser portion of the total surface area of the solar panels to move the tug away from what little remains of Earth's atmosphere in LEO? These solar arrays have substantial surface area, so I presume that's been factored into their design.

I have reservations about the size of these things and how delicate they are, but if it works reliably then it serves the requirement and removes another reason for NASA to stall the mission.

Impaler · 2015-01-26 18:01:14

kbd512 wrote:

Are solar panels near that kW/kg threshold yet? Because that's where GCNR's operate at.
The heat has to go somewhere, but generally you want to convert that heat to power or heat propellant. If you start radiating the thermal energy from the reactor into space, you reduce efficiency.
A single Falcon 9 can lift an entire GCNR. The type of SEP transfer vehicle that Boeing wants to build to go to Mars with would require a SLS launch of its own.

For crying out loud, a GCNR is a science fiction engine, TRL of 1, you have NO BLOODY CLUE what it's power density would be of IF it could even be built, or what mass it would be and what launch vehicle it would need, you might as well be talking about the power density of anti-matter. Solar technology is mature and scalable the engineering to make the array level power density higher is just engineering of deployment structures and trusses the theoretical limits are what the cells alone would produce, this is dirt simple engineering compared to any kind of nuclear system. The ROSA array was developed with a NASA grant for a few MILLION dollars, the power density is 200-400 W/kg at the wing level according to the manufacturer. Their difference in the nearness and cost to get more power and more power density from solar vs nuclear is just staggering, the nuclear stuff is Billions of dollars and decades vs millions and a few years for solar, how are people so grossly misinformed, who is spreading all this garbage?

I'm talking about actual hardware that's either exists now or is about to come out of the lab, if your going to talk science fiction nuclear systems then I'll come back with Fusion powered Magnetoplasmadynamic thrusters that could theoretically put a Megawatt of power through a device the size of a 5 gallon bucket and produce 200 N, and these things have actually been made and operated in labs.

SEP tug stages, solar + thrusters + propellent + tank are expected to be about the same or LESS mass then the payload and will move the payload from LEO to LMO with a stop at L2 if you wish, add a bit more propellent and you can move your payload BACK to LEO/L2. They beat NTR in payload fraction even for the simplest TMI in which the payload has to make a direct (dangerous) entry to Mars atmosphere, but the SEP can give you soooo much more, a parking orbit without a heat-shield, return to Earth and then reusability of both the tug AND the payload. Will the SEP tug need Heavy-lift? If your monolithic payload already needs heavy-lift then it would be stupid not to use it for lifting the stage too, EVERY TMI stage ever proposed have been comparable in mass to the payload it pushes through TMI so it has commonality with the launch vehicle that puts the payload in LEO, the question is how MANY TMI stages you need, SEP has by far the best ratio at 1:1 with the potential for 1:2 if we can get into the 20-30k ISP ranges.

Last edited by Impaler (2015-01-26 18:04:51)

JCO · 2015-01-26 18:11:29

I think the biggest danger entailed with using nuclear is the potential of budget cuts. There will be a significant number of people who will appose any program using nuclear propulsion. We will also likely also face international pressure as some other countries will view the program as a possible weapon, especially if it is assembled in orbit. To be honest the chances of anything on this scale getting funding soon are low and nuclear propulsion could cut the chance in half. I think this will continue to be the case until we are able to mine the radioactive materials off Earth.

RobertDyck · 2015-01-26 18:44:58

I have a better idea: full size upper stage of SLS with a pair of J-2X engines, LH2/LOX.

Mars: Get on with it.

SpaceNut · 2015-01-26 20:11:21

Yes and men are there in less than 6 months not 13 making them unable to even do the work to explore mars....Then the extra exposure to cosmic radiation levels....
This method is fine for cargo but not for man.

Something else to think of with an array so large is the solar wind effect as well as removing the accelerations effect on slowing the ship due to the large area surface with ion drive.

kbd512 · 2015-01-26 20:29:45

Impaler wrote:

For crying out loud, a GCNR is a science fiction engine, TRL of 1, you have NO BLOODY CLUE what it's power density would be of IF it could even be built, or what mass it would be and what launch vehicle it would need, you might as well be talking about the power density of anti-matter. Solar technology is mature and scalable the engineering to make the array level power density higher is just engineering of deployment structures and trusses the theoretical limits are what the cells alone would produce, this is dirt simple engineering compared to any kind of nuclear system. The ROSA array was developed with a NASA grant for a few MILLION dollars, the power density is 200-400 W/kg at the wing level according to the manufacturer. Their difference in the nearness and cost to get more power and more power density from solar vs nuclear is just staggering, the nuclear stuff is Billions of dollars and decades vs millions and a few years for solar, how are people so grossly misinformed, who is spreading all this garbage?

I was going to stop talking about this, but given your insistence on this nonsensical idea that everything that hasn't fallen into our laps must necessarily cost billions or take decades…

LANL designed, built, and tested a reactor, yes a real working nuclear reactor, for small spacecraft power in less then a year and for less than a million dollars. I'm certain that if we had involved some defense contractors we could make the project cost billions and last for decades… Kinda like STS and SLS.

By your logic a SEP tug is science fiction because it's never been built. We DO HAVE A BLOODY CLUE about what the power density would be because real research was funded by the same organization funding SEP technology because at one point in time in this country real people were really interested in going to Mars. You want to talk about spreading garbage? That's garbage.

We can have a SEP tug for a few million dollars? In what universe? Certainly not this one because the SLS launch it requires is forecasted to cost billions, never mind the fact that SLS has never flown, which also makes it science fiction by your logic.

Nobody has ever built an anti-matter rocket engine. We have videos of the nuclear rocket engines developed in the 1960's and 1970's. I guess if you didn't see it with your own eyes then it never existed.

Impaler wrote:

I'm talking about actual hardware that's either exists now or is about to come out of the lab, if your going to talk science fiction nuclear systems then I'll come back with Fusion powered Magnetoplasmadynamic thrusters that could theoretically put a Megawatt of power through a device the size of a 5 gallon bucket and produce 200 N, and these things have actually been made and operated in labs.

As long as you're talking about nonsense, by all means, keep going.

Impaler wrote:

SEP tug stages, solar + thrusters + propellent + tank are expected to be about the same or LESS mass then the payload and will move the payload from LEO to LMO with a stop at L2 if you wish, add a bit more propellent and you can move your payload BACK to LEO/L2. They beat NTR in payload fraction even for the simplest TMI in which the payload has to make a direct (dangerous) entry to Mars atmosphere, but the SEP can give you soooo much more, a parking orbit without a heat-shield, return to Earth and then reusability of both the tug AND the payload. Will the SEP tug need Heavy-lift? If your monolithic payload already needs heavy-lift then it would be stupid not to use it for lifting the stage too, EVERY TMI stage ever proposed have been comparable in mass to the payload it pushes through TMI so it has commonality with the launch vehicle that puts the payload in LEO, the question is how MANY TMI stages you need, SEP has by far the best ratio at 1:1 with the potential for 1:2 if we can get into the 20-30k ISP ranges.

So this SEP tug weighs about as much as the payload it's pushing or perhaps a little less, takes just as long to get to where it's going as any NTR powered vehicle would, and requires additional propellant to make it back to LEO, but somehow that's cheaper and more efficient? NASA's Mars DRM 5 proposed the use of conventional solid core NTR's, downrated the efficiency of the engine of the exact type they wanted to use had demonstrated, and the transit vehicle was designed to go from LEO to LMO to LEO without refueling. Oh, and from my perspective it would be stupid to require the use of more heavy lift rockets that cost well north of a billion dollars per launch.

Impaler · 2015-01-27 00:56:43

I said that solar panel technology can be developed to high power density for modest costs, not that building the whole tug is that cheap or that the cost of launch it into LEO is cheap. This means it is pointless to try to develop nuclear POWER systems for use in inner solar-system space, solar already crushes them even the proposed Sterling RTG concepts which is what I think your talking about from LANL, that kind of system is only 4x the power of RTG's and while it would be nice past Jupiter on a probe or on planetary surfaces, but it is inferior as an in-space power source.

Every time I point out a flaw in a nuclear system you seem to jump to something else with out regard for it it is an engine or a power source or even the slightest concern for scaling or for the TRL. You've jumped now between no less then three different technologies that only the Nuclear word in common and are trying to treat them as one thing that somehow has all of the superlatives of each but none of the downsides, it's like some crazy tag-team wrestling match against team Nuclear.

You know very well that our launch vehicle costs are completely separate from our TMI vehicle development and fabrication costs so don't try to bring in any hysterics about what SLS or any other launch vehicle costs (and yes SLS costs too much), all the Initial mass on the ground costs huge money to become IMLEO, we will use the best launch vehicle we can find in the end. The lower the launch vehicle cost the less we should spend on expensive TMI stages.

If you want to go by DRM 5 then you need to actually look at what kind of payload fraction the NTR stage actually gives, it's 300 mt of NTR stages (at 875–950s ISP, not one bit of downgrading from NERVA) to push 60 mt of habitat LEO->LMO->LEO. As I said earlier SEP are looking at stage masses COMPARABLE to the payload, not 5x larger, and when I say they need a bit more propellent to do a return leg that is not with refueling at Mars, that's just another ~50% more propellent at outset so you end up with a stage that is between 1.5 -2 times the size of the payload. This simply crushes NTR which required 9 SLS launches in DRM 5, the new Boeing plan is 5-6 AND brings most hardware back to LEO for reuse so each subsequent mission is even fewer SLS launches, by your own standard NTR is what is stupid if you even take a cursory glance at the numbers.

Last edited by Impaler (2015-01-27 01:03:56)

louis · 2015-01-27 02:54:51

kbd - I think you misunderstood my point. What we don't have info on is how well people perform when put into mass-adjusted suits on a low G body like Mars or the Moon after prolonged exposure to zero G (we know they recover well on Earth, and we can probably hazard a guess they will perform quite will with special suits to simulate gravity on Mars or Moon). So you need the preceding phase of zero G to simulate the journey to Mars. That's why I argue for an analogue mission to the Moon - which is only 3 or 4 days away (so a rescue mission could be mounted).

Actually I am confused by your post - you seem to be both arguing against me and agreeing with me!

kbd512 wrote:

louis wrote:
I doubt anyone is going to send people to Mars without an analogue mission to the moon. I agree with Impaler that AG is likely to prove a very expensive diversion in terms of both money and time.
Flying a transit habitat around the moon for six months won't tell us anything that we don't already know about microgravity.
AG is too expensive or complicated whereas active radiation shielding is some sort of requirement for a Mars mission? The tech for effective particle shields to deflect protons with gigavolt energies or better is guaranteed to be far more expensive and heavier than AG. All the concepts I've seen had impressive power requirements. Are we going to power the propulsion system with our solar panels or use it to deflect radiation?
If we stop using soda cans for habitats, that'd be a good first step towards reducing radiation exposure. There are lots of better materials for absorbing radiation than aluminum.
With respect to AG, humans weren't designed for microgravity environments and there's no getting around that. Microgravity poses actual health problems and just because someone is ambulatory doesn't mean the effects aren't real or lasting. All we need is for someone's corneas to be adversely affected on the surface of Mars to put all the ridiculous hand wringing about the effects of radiation into context.
louis wrote:
We can establish how people will react by taking them to the Moon first in lunar orbit for 6 months, until landing on the lunar surface, where they can work in 1G weighted suits and their health can be assessed. The Mars habitat can be tested at the same time.
We already have plenty of data to discern the health effects of microgravity and radiation. We don't need any more human guinea pigs to tell us what we already know.
louis wrote:
I think they will be able to cope. But we have to test it first without taking them to Mars would be my view.
I don't want to find out how well the crew fares when they're tens of millions of miles from home.

RobertDyck · 2015-01-27 04:58:17

I started this discussion to critique Boeing's plan. They want to assemble a spacecraft for Mars at L2. They call it Earth/Moon L2, or EML2. The James Webb Space Telescope will be in Earth/Sun L2, because it's permanently in Earth's shadow. You don't want a space station that's permanently in shadow; it's cold and no solar power. But this Boeing plan says EML2. Why? That puts it permanently on the opposite side of Earth from the Moon. There's no reason to assemble anything there, it's just a waste of propellant. Furthermore, slide 24 of the PowerPoint mentions "EML2 Gateway". That appears to be some sort of small space station. Why another space station? Slides 63 & 64 show two TransHab modules, not just one. Don't know where the second came from. Of course they return back to their new space station before returning to Earth.

I have argued to use ISS as the "Gateway", not some new station. And not in some distant orbit that can't be reached by commercial spacecraft. I guess that's why they want it, to ensure competition can't get there: SpaceX, Orbital Sciences, Sierra Nevada, Europe's ATV, Japan's HTV, Russia's Soyuz or Progress.

Then they go on about a Deimos precursor mission. But why? Deimos is harder than Mars. There have been proposals to mine Deimos for propellant, and set up a propellant depot to refuel a reusable spacecraft for Mars settlement. But that's later, not the initial mission to Mars, and certainly not a precursor.

Mark Friedenbach · 2015-01-27 08:02:21

Robert, the EML2 point has the significant advantage of lower delta-V requirements since it's pretty much at the edge of the Earth-Moon system, gravitationally, and also has ready 24/7 access to the Moon and/or Earth for gravitational slingshots. It does make sense to have a space station there, more sense in fact than LEO.

Of course direct to Mars or LEO rendezvous makes far more sense for early missions to Mars. In the long term an EML2 station makes sense, but right now it's just pork.

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