What propulsion system should we use for Mars exploration?

[Orc]

Hi all

 

For early manned exploration, pre-colonization phase chemical propulsion is quite do-able.

 

See Mars Direct as an example (https://en.wikipedia.org/wiki/Mars_Direct). Admittedly Mars Direct DOES use a small-ish nuclear reactor at the Mars side of the journey to make sure the Earth Return Vehicle is fully fueled for the trip home. But many knowledgeable space technology specialists are certain that the same results could be achieved with large solar power arrays and/or just shipping more hydrogen fuel (12 tons instead of 6). And the nuclear reactor doesn't need to be a fission device. The plan as it was originally written could get away with using DIPS (Dynamic Isotopic Power System), which is basically a conventional heat engine generator running for the heat of RTG-like heat sources.

 

Mars Direct is showing its age, as it is based on Shuttle-era technology and components. Someone could do an update assuming the availability of the heavy Falcon rocket from SpaceX.

 

Another alternative is a solar thermal booster, which is like a NERVA, except that the nuclear reactor is 1 AU away and you needs a very big solar concentrater to focus its energy. The STB heats up liquid hydrogen to NERVA like temperatures using concentrated sunlight. It boost the cargo out the Earth-Moon system and then uses the last of its propellants to put itself in a free return orbit via a lunar gravity assist. It then spends nine months getting back to earth orbit after which it is docked with a fresh fuel tank and used again. The STB grants a significant boost in performance over conventional chemical boosters and doesn't have any of the problems assocciated with NERVA.

 

Once serious colonization gets underway Aldrin cyclers boosted with STBs are likely to be the economical way to go,

 

Regards

Orc

[fredinno]

1 hour ago, Orc said:

Hi all

 

For early manned exploration, pre-colonization phase chemical propulsion is quite do-able.

 

See Mars Direct as an example (https://en.wikipedia.org/wiki/Mars_Direct). Admittedly Mars Direct DOES use a small-ish nuclear reactor at the Mars side of the journey to make sure the Earth Return Vehicle is fully fueled for the trip home. But many knowledgeable space technology specialists are certain that the same results could be achieved with large solar power arrays and/or just shipping more hydrogen fuel (12 tons instead of 6). And the nuclear reactor doesn't need to be a fission device. The plan as it was originally written could get away with using DIPS (Dynamic Isotopic Power System), which is basically a conventional heat engine generator running for the heat of RTG-like heat sources.

 

Mars Direct is showing its age, as it is based on Shuttle-era technology and components. Someone could do an update assuming the availability of the heavy Falcon rocket from SpaceX.

 

Another alternative is a solar thermal booster, which is like a NERVA, except that the nuclear reactor is 1 AU away and you needs a very big solar concentrater to focus its energy. The STB heats up liquid hydrogen to NERVA like temperatures using concentrated sunlight. It boost the cargo out the Earth-Moon system and then uses the last of its propellants to put itself in a free return orbit via a lunar gravity assist. It then spends nine months getting back to earth orbit after which it is docked with a fresh fuel tank and used again. The STB grants a significant boost in performance over conventional chemical boosters and doesn't have any of the problems assocciated with NERVA.

 

Once serious colonization gets underway Aldrin cyclers boosted with STBs are likely to be the economical way to go,

 

Regards

Orc

I'm pretty sure he nodded Mars Direct for SpaceX recently...

Also, using STB negates the point of Mars direct. For your investment, you would be better with Ion+Solar.

[shynung]

Nice to meet you, Orc.

The problem with a solar thermal rocket is similar to solar electric rocket: one would need a large surface area to catch enough energy from the sun. Thankfully, while solar panels are heavy, solar concentrators can be built lighter, by using an inflatable with half of the inner surface coated with a reflective metal, and the other half transparent.

However, a solar thermal rocket has a lower effective I_sp than a solar electric rocket(comparable to a solid-core nuclear thermal rocket), due to material thermal strength limitations. According to the Atomic Rockets site, a typical STR has a specific impulse close to 1000 seconds, while a VX-200 VASIMR electric rocket can handle 2900 seconds at the highest thrust/lowest I_sp setting.

[Andem]

4 hours ago, Albert VDS said:

Sure it can put the spacecraft into an escape trajectory faster than anything else, but it doesn't matter if you do it in a few minutes, hours or even days.
Anything more efficient than chemical rockets, that can put the craft in to an escape trajectory with the same travel time, is a better choice.
Mainly because it would mean more payload can be used for supplies(food, spareparts, etc).
 

But the amount of fuel wasted in escaping the SOI is something to consider as well, as well as the way the escape burn is set up. You wouldn't want to miss the maneuver, and without enough power you will have to make several passes around the orbit which could screw with the transfer window. maybe chemical boosters to get it on an escape trajectory and mars capture?

[Albert VDS]

12 minutes ago, Andem said:

But the amount of fuel wasted in escaping the SOI is something to consider as well, as well as the way the escape burn is set up. You wouldn't want to miss the maneuver, and without enough power you will have to make several passes around the orbit which could screw with the transfer window. maybe chemical boosters to get it on an escape trajectory and mars capture?

How would it waste fuel if the propulsion is more efficient but takes longer to do a burn than chemical rockets?
Also, the optimal time to get a escape trajectory would be taken in to account with any burn time, specially with a long burn.
 

[tater]

Solar thermal doesn't require inventing new reactors, though. VASIMR is pixie dust right now for many of the claims.

[Apexazimuth]

I think a VASIMR based spacecraft could be a long term goal for an international reuseable space transit system. I'm thinking an international cooperative spacecraft like the ISS, but with a state-of-the-art propulsion system and provisions for interplanetary ejection, injection, and return.

But I want to see people walk on Mars in my lifetime, and to do that we need to use what we know and put mastery into practice.   Chemical rockets are probably the way to go for the first or at least the first few manned extra-planetary missions.  Simply because we already have the know-how.

I'd love to see nuclear thermal propulsion for interplanetary missions, but once you've brought a nuclear reactor into space, why not use it for an electrical generator to power a far, FAR more efficient electric rocket?  The biggest challenge seems to me to be getting the nuclear reactor up there in the first place.  Political hell.

Electric propulsion comes with it too many new parts that need to be designed, built, tested, redesigned, rebuilt, and retested.  I'm sure that some form of electric propulsion with be the ride of choice for astronauts of 2050 and beyond.  Until then, we've got some pretty amazing engineers designing fantastically effective cryogenic rockets.

 

[_Augustus_]

I want NERVA. SEP is good for unmanned supply craft, but not humans. VASIMR is too speculative and too large for now.

[fredinno]

5 hours ago, Andem said:

But the amount of fuel wasted in escaping the SOI is something to consider as well, as well as the way the escape burn is set up. You wouldn't want to miss the maneuver, and without enough power you will have to make several passes around the orbit which could screw with the transfer window. maybe chemical boosters to get it on an escape trajectory and mars capture?

The only reason you would is for the crewed ship to get out of the Van Allen quickly. Otherwise, Ions are still more efficient.

5 hours ago, tater said:

Solar thermal doesn't require inventing new reactors, though. VASIMR is pixie dust right now for many of the claims.

We already have ion drives, the main problem today is scaling up the systems.

[tater]

7 minutes ago, fredinno said:

We already have ion drives, the main problem today is scaling up the systems.

The problem with VASIMR is not the ion drive, it's POWER. Their fanciful fast flight times to Mars are based on a TWR that requires reactors no one is close to being able to build. Solar can work closer in, but again, for the required power they need large (heavy) arrays.

It's not impossible to make new space reactor designs, but it's not even close to off the shelf.

[Bill Phil]

56 minutes ago, tater said:

The problem with VASIMR is not the ion drive, it's POWER. Their fanciful fast flight times to Mars are based on a TWR that requires reactors no one is close to being able to build. Solar can work closer in, but again, for the required power they need large (heavy) arrays.

It's not impossible to make new space reactor designs, but it's not even close to off the shelf.

What about beamed power? How far away would that be in terms of development time?

Edited January 27, 2016 by Bill Phil

[SargeRho]

21 minutes ago, Bill Phil said:

What about beamed power? How far away would that be in terms of development time?

Not very far. We already have it, actually, it basically just needs to be scaled up, and of course any challenges that arise from that, overcome.

https://www.youtube.com/watch?v=CDdcS8anUWg

Edited January 27, 2016 by SargeRho

[PB666]

6 hours ago, tater said:

Solar thermal doesn't require inventing new reactors, though. VASIMR is pixie dust right now for many of the claims.

pixie dust, hmm. At least if you are going to berate it, do so mindfully. Vasmir is powerful, unfortunately its heavy. and needs lots of power, we don't have source. 

[tater]

36 minutes ago, PB666 said:

pixie dust, hmm. At least if you are going to berate it, do so mindfully. Vasmir is powerful, unfortunately its heavy. and needs lots of power, we don't have source. 

I did say "for many of the claims." For their 3 month trip, they require a 4kg/kW reactor of 12MWe. That, they say (adastra) would take "moderately aggressive reactor development." The benchmark would be that we currently have either moderately, or aggressive non-development of such reactors  . The 39 day trip takes a 200MWe reactors, with lower power densities than the other one. It's not impossible, so I suppose pixie dust is an overstatement, but it's not likely to happen any time in the foreseeable future, frankly. The 12MW version is hard, but at least it could possibly happen before I'm dead.

[Kaos]

13 hours ago, Albert VDS said:

How would it waste fuel if the propulsion is more efficient but takes longer to do a burn than chemical rockets?
Also, the optimal time to get a escape trajectory would be taken in to account with any burn time, specially with a long burn.
 

Because of https://en.wikipedia.org/wiki/Oberth_effect adding to the Delta-v of a high thrust system but not for a low thrust system. I did not do the calculations myself, but I have read that a transfer from Earth to Mars needs about double the Delta-v with a low thrust than with a high thrust propulsion. Hence, a low thrust system would need more than two times the Isp to give any advantage.

[fredinno]

8 hours ago, Kaos said:

Because of https://en.wikipedia.org/wiki/Oberth_effect adding to the Delta-v of a high thrust system but not for a low thrust system. I did not do the calculations myself, but I have read that a transfer from Earth to Mars needs about double the Delta-v with a low thrust than with a high thrust propulsion. Hence, a low thrust system would need more than two times the Isp to give any advantage.

No, it's more like 1.5x.  http://i.imgur.com/SqdzxzF.png

Ion is still better in ISP, and the tech is better understood.

[Kaos]

3 hours ago, fredinno said:

No, it's more like 1.5x.  http://i.imgur.com/SqdzxzF.png

Ion is still better in ISP, and the tech is better understood.

Thank you for the link; I knew the graphics but I did not realize the number. But I find that statement rarely believable that it is a constant factor of 1.5, as it depends on the masses of the planets. Guess I should try to compute the numbers some day

[PB666]

On 1/20/2016 at 3:35 PM, Spaceception said:

We all know chemical propulsion isn't viable for our first Mars missions, too slow, too inefficient, and too primitive, so what propulsion system should we use?

NERVA? https://en.wikipedia.org/wiki/NERVA

Solar electric propulsion? https://www.nasa.gov/mission_pages/tdm/sep/index.html

VASIMR? https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket

Or the Fusion Driven Rocket (The coolest one)? https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion#MSNW_Magneto-Inertial_Fusion_Driven_Rocket

Ion driven, 0.6 m/s2 post orbital transfer acceleration. 44 xenon tanks, This particular example 16 stock dawn (which are not particularly good state of the art drives, ISP is low) the central drive kicks out about 4 times the thrust. In the game is shows about 30,000 dV, each of the spherical xenon tanks has a scaled down decoupler, and so as tanks are emptied they are ejected into space, greatly reducing the weight. Basically its designed to go from 200 km earth orbit to minimal mars orbit and back to earth again, no means is provided for re-entry, provided the naut reaches a return trajectory he can transfer to the ISS or get a pickup ship for reentry.  This craft has enough power to break kerbin orbit prograde in one orbit from 70k, starting at about angle to prograde of 250.

Habitation, single lander and a stretch version of lander capable of holding 2 people, but for supplies and space for 1 person for 3 years.

Energy. 15 oversized thermonuclear generators, capable of producing 120 times the PB-NUK amount of power, six solar panels provide to 100% power at mars orbit. As you can see even distantly spaced panels do not effectively gather sunlight at critical points. I have solar driven versions of this, but I had to add a whole series of aluminum framing pieces to get the needed solar panels. Eventually it becomes a launch stability issue. (IE 60m/s at 0MSL maximal to about 160m/s at 15000 kerbin meters)

The Nucs are about 20 meters from the crew compartment are shielded by a lead-embeded metal disk, and 44 xenon tanks which scatter xrays. 

During interplanetary flight the panels can be close and the craft can be spun to generate centripetal acceleration, of course only about 0.3g, supplimental weights can be worn by travelers to increase stress on bones and muscles.

The lander is sent in advance, a separate Ion drive at mars aids in the deceleration and loss of about 30% of the reentry energy, the lander has to provide the other 60% and fuel for take off and docking. Upon Mars orbit the lander docks with the transfer ship, and pilot boards, lands and when in orbit transfers back to the transfer ship and returns to earth. This ship comes with an additional docking port that can hold supplies from automated resupply ships from earth. However the travelers quarters are cramped, for a human this would be akin to living in an oversized coffin. Not really room for two people unless they are African pygmies. 

It also has the potential to provide a hub for a space station if a suitable return ship can be sent.

Unlike other models the pilot does not need to move back and forth to special pods during solar storms, the craft is simply pointed head first at the sun. The shielding for the TNGs suffices to absorb and radiation the sun produces. 

Pros

Do-able with alot of technology already available, as long as one does not have hopes for a return trip, see below.

Cons

Requires 3 or 4 craft

Can only support 1 or 2 (pushing it) nauts

The handwaving is in an ion-drive system that is both capable of slowing down a mars lander and returning itself to Mars orbit (otherwise it will be lost). Because as of right now there are No space ships capable of landing on Mars and returning to orbit. The more fuel one has for reorbiting, the less drag/mass is produced by that mars atmosphere. The lander weight needs to come down and some means of slowing down the lander so that it can retain adequate fuel for reorbit. I have made ION drive craft capable of landing on Mun (at very great risk) about 0.2g is the limit before a whole lot of things pile on top of each other. However is a small amount of fuel one can get enough momentum vertically for ion drive to capture orbit, again the fuel adds a hell of alot of weight.

To circumvent this problem propose a martian moon as target.

You ask a bunch of amatuers in a games chat room to tell you how to get on mars, don't expect rocket science.
 

In case you are wondering:

The lander extension is a blender craft (it weight almost 2 tons), it has a built in solar panel, because if stranding a craft dead out of electricity teachs a pilot anything, always keep that power flowing.

The ion drive adapter carries two large Xenon tanks (total about 12K units) and has its own built in battery.  The more efficient capacity is a trade off for the fact it is a single function item, it can only be used for ION drives.

The spherical Xenon tanks are a blender craft. Each tank carries 7000 units. Presumably the drives could be replaced by a scaled down VASMIR (then nukes are not powerful enough) require much less gas (argon instead of xenon). Vasmir however is very heavy compared to ION drives.

The sphere tank lattice is made up of 6 pieces (for scalability and because of the non concave collision mesh restriction for single parts)

Every thing else that is not stock is a scale mod, there are no exploits, 2x rescale Factor get 8 mass, but on 4 fold power (e.g. ION Drive, or solar panels), Other than a trim of empty mass here and there for more efficient part design. One point the ION scale mod is primarily used for launch stability, so its better coupled to a 2.5 meter decoupler for the next stage.
 

 

[Nibb31]

You do know that KSP is not realistic when it comes to dV, and that ion thrusters are way overpowered in the game, dont you?

[Albert VDS]

23 hours ago, Kaos said:

Because of https://en.wikipedia.org/wiki/Oberth_effect adding to the Delta-v of a high thrust system but not for a low thrust system. I did not do the calculations myself, but I have read that a transfer from Earth to Mars needs about double the Delta-v with a low thrust than with a high thrust propulsion. Hence, a low thrust system would need more than two times the Isp to give any advantage.

But that means you can negate the loses if you do shorter burns and multiple orbits.

[Kaos]

3 hours ago, Albert VDS said:

But that means you can negate the loses if you do shorter burns and multiple orbits.

Yes, but then you need incredible many orbits and a vast amount of time. For that I would suggest low-energy transfer, it needs also a lot time, but much less than the necessary amount of orbits and can be combined with any propulsion system. Of course they are not well-suited for manned transfers, because they still need too much time, but for supplies they might help.

[Albert VDS]

59 minutes ago, Kaos said:

Yes, but then you need incredible many orbits and a vast amount of time. For that I would suggest low-energy transfer, it needs also a lot time, but much less than the necessary amount of orbits and can be combined with any propulsion system. Of course they are not well-suited for manned transfers, because they still need too much time, but for supplies they might help.

It all depends on the TWR the more efficient propulsion has. Sure ion has a too low TWR and would take ages, but something like NERVA could do the transger with 2 or 3 burns, which might end up just adding a few days. Which is not a lot over a 6-9 month trip.

[PB666]

6 hours ago, Nibb31 said:

You do know that KSP is not realistic when it comes to dV, and that ion thrusters are way overpowered in the game, dont you?

Yep I know, the kerbal ION drives are ____way____ over powered, but they are also way under ISP. It makes landing possible but it undervalues the potential dV.

However, I look at ION drives as way underpotentiated, based on latest research, even what is being used is about a half as powerful and a quarter as efficient. In fact Ion drive systems are the only deep space propulsion that actually works (proven unlike the RF resonance drive) that is as underpotentiated in terms of its current use. The Nerva, for all its worth lacks testing in a repeat use scenario, its basically been tested on a single burn, not a repetitive burn scenario after the engine is idled for 2 years.

SO lets say thrust is a tenth, and of course earth has a GM/r at minimal orbit 10 times that of kerbin, if you can break orbit in a quarter of a pass then you could break orbit in 25 passes at perigee. This lack of power has more than just inconvenience, looking at Mars entry one has to do a near perfect transfer out of earth, otherwise dV would be to high to reverse a flyby trajectory, this removes 39 day scenarios, unless alot of gas is spent on pre-SOI burning. So this basically removes ION drives from consideration from short trip scenarios, this is why I keep saying, for the technology that we currently have, a mars trip is 4 to 5 years. It gives very good reason for separating the transfer processes  Few people, lots of supplies, a small thin craft of the design I put forward. from the landing processes/reorbit processes.

You may note that I went with a single person capsule and a halfweight crew supply package, it would be about the size of a cross over SUV on the inside, which means only 1 crew. The power supplies dissipate heat at the square of the radius whereas power density increases by the cube. This also has connotations, you can not scale up in 3 dimensions, a power package can get longer, not wider, which means craft take on extremely long dimensions, or excessive weight additions for radiators. So it is not smart to send crews in one big ship but many smaller ships. This can be considered an exploit, because you may note that NASA stacks the TNGs and you would have to have huge areas of TNGs running in a wide spanning lattice to power the craft without generating so much local heat as to destroy the power unit. I have a system of piping crafted now to do this, but its an exploit to launch it, because it has impractical drag, The only way to practically use TNGs is to build the lattice in space, and each unit needs to have a shield to protect the crew. Thereare are ways to do this, you can radiate the TNGs away from the capsule. If you have to bridge the TNG over several 100 meters of axial crossection, then its better to use expandable panels.

The undeveloped technology is to embed the TNGs into the retractable radiator, the only problem there is keeping the cool until you get into space. So the basic problem is very simple, ION is great, wheres your power supply.

But the basic idea of using ION power works, but my point is that its not one ship, its multiple ships to complete a mars mission.

Edited January 28, 2016 by PB666

[Matuchkin]

I would go with VASIMR, because I actually know its capabilities.

Though, if anyone has a mega-laser-shark-zombie-kraken-spacecannon-warpdrive-tyrannosaurus rex-fluxcapacitor-jet-beam-shockwave-cruiser with them, I'll gladly consider it.

Edited January 28, 2016 by Matuchkin

[Kaos]

2 hours ago, Albert VDS said:

It all depends on the TWR the more efficient propulsion has. Sure ion has a too low TWR and would take ages, but something like NERVA could do the transger with 2 or 3 burns, which might end up just adding a few days. Which is not a lot over a 6-9 month trip.

I was speaking about low thrust systems, not about high Isp systems. I would not consider NERVA a typical low thrust system.

Indeed can the technique of multiple orbits compensate a little too small TWR. But it has its limits.