15 ms·

Nasa’s proposed plasma rocket would get us to Mars in 2 months

88 points by genman 2y ago

devbent 2y ago
> Shorter periods of exposure to space radiation and microgravity could help mitigate its effects on the human body. Of course once astronauts are on mars they will still be exposed to radiation, until some sort of shielding can be built. Which would be an obscene undertaking, and involves moving lots of raw and refined materials to mars. Which means hopefully the price of this rocket to get stuff off of earth is dirt cheap, because moving squishy humans to Mars, no matter the speed, is not the limiting factor! (Getting humans to Mars and keeping them alive there is!)
- sandworm101 2y ago
  >> obscene undertaking, and involves moving lots of raw and refined materials to mars. Or they can dig a hole and/or pile mars dirt on top of their living structures. Some materials are better than others at absorbing radiation but, as a general rule, mass/depth of the protection counts more than composition.
- dyauspitr 2y ago
  Building an underground chamber doesn’t seem like an impossible undertaking. Alternatively, maybe mars already has caves and tunnels.
  - OnlyMortal 2y ago
    There are tunnels that appear to have been created by volcano lava. Lava tubes.
  - heavyset_go 2y ago
    It takes a lot of energy to displace sand/dirt/rocks to build anything underground. Human-powered shovels require a lot of food and water, and machinery requires combustion and a lot of hydrocarbons.
    - deleted 2y ago
      [deleted]
    - acchow 2y ago
      Submarines run on nuclear. Wouldn't nuclear be the natural choice on mars?
      - ceejayoz 2y ago
        Those are big, and heavy. https://www.oregon.gov/energy/safety-resiliency/Pages/Naval-Nuclear-Transport.aspx https://www.oregon.gov/energy/safety-resiliency/Pages/Naval-... > The submarine reactor compartments that have been taken to Hanford are about 33 feet high and 40 feet in length. They weigh between 1,130 and 1,680 tons. Eventually, the Navy may deactivate its Ohio class submarines in the same manner. Those compartments would be much larger and heavier. Submarines don't have to get them into orbit.
        JumpCrisscross 2y ago
        In case you're serious, nobody is suggesting launching a water-cooled reactor to Mars. Between the idiot ends of the power-source spectrum bounded by, on one end, a U.S. Navy PWR and, on the other end, Martian Aramco, we have the reasonable options of solar power, batteries, RTGs and fission-powered Stirling engines [1][2]. [1] https://www.nasa.gov/directorates/stmd/tech-demo-missions-program/kilopower-hmqzw/ https://www.nasa.gov/directorates/stmd/tech-demo-missions-pr... [2] https://www.nasa.gov/tdm/fission-surface-power/ https://www.nasa.gov/tdm/fission-surface-power/
        ceejayoz 2y ago
        I think solar's the far more likely option, yes. Cheap, light, low-maintenance. Maybe fuel cells for night. RTGs aren't gonna power a good-sized base; they're a few hundred watts at best. edit: I very much hope Kilopower pans out.
        jujube3 2y ago
        What is wrong with launching a water-cooled reactor to Mars? Or more likely launching the materials needed to build it. The active components of a reactor are quite tiny -- most of the bulk is in the shielding, which won't be necessary on an already radioactive planet like Mars.
  - ortusdux 2y ago
    I still think that this would explain Musk's dalliance with tunnel boring machines.
- malfist 2y ago
  The easiest solution is to set up shop in a cooled volcano tube
- dmurray 2y ago
  Most of the materials could surely be found on Mars. A shelter built out of sandbags would be a low tech solution that would get you a large part of the way there. Further, Mars itself shields you from half the radiation (at night), the Martian atmosphere shields you from a little more, and Mars is further away from the Sun on average than an Earth-Mars spaceship. Radiation during transit really does seem like a bigger issue.
  - pmontra 2y ago
    There are also cosmic rays. They come from every direction, so even at night. An experiment measured that kind of radiation about 20 years ago https://en.wikipedia.org/wiki/Mars_Radiation_Environment_Experiment https://en.wikipedia.org/wiki/Mars_Radiation_Environment_Exp...
    - dmurray 2y ago
      The planet still shields you from half of those.
- lupusreal 2y ago
  It's not an intractable problem, just send a robot bulldozer and excavator a few years beforehand. The real problem with a Mars colony is the economics for making it anything more than a small scientific outpost / political stunt. Forget the upfront cost of the habitat/etc, how do you actually create a self sustaining Martian economy? I've never heard a realistic answer for this.
  - mongol 2y ago
    It is an interesting problem of energy. How would a robot bulldozer or excavator be powered? They require more power than a rower.
    - lupusreal 2y ago
      They don't require more than a rover if you accept them doing their work far slower than their normal earth equivalents. Hence sending them years in advance to dig out a some holes that would only take a few days for excavators on Earth.
      - tsimionescu 2y ago
        While speed is a factor as well, you still need a lot more energy consumption to move a mass of rock&dust some distance away than to move a small rover. This immediately follows from the formula for work and the gravitational force.
        lupusreal 2y ago
        Given enough time, you can dig out a house foundation with a spoon, power is not an issue here. The less power you have available the slower you work. If your robots wear out, you send more. The real problem is finding enough time and money to waste on such a fruitless endeavor. If that can't be managed it nullifies the entire problem of digging a hole on Mars since a Mars base is nothing but a waste of time and money. Wasting time and money is table stakes.
- kallistisoft 2y ago
  As far as I know the plan has always been to use the martian regolith and water as primary radiation shielding -- same as the moon. Here is a recent (2022) paper[1] on the concept, but you can easily find scholarly work on this going back many decades... [1] https://www.sciencedirect.com/science/article/abs/pii/S0032063322001039 https://www.sciencedirect.com/science/article/abs/pii/S00320...
  - ceejayoz 2y ago
    https://en.wikipedia.org/wiki/Martian_lava_tube https://en.wikipedia.org/wiki/Martian_lava_tube have also been proposed as pre-existing possible shelters. https://en.wikipedia.org/wiki/Caves_of_Mars_Project#/media/File:Mars;_Arsia_Mons_cave_entrance_-MRO.jpg https://en.wikipedia.org/wiki/Caves_of_Mars_Project#/media/F... "HiRISE image of Mars hole 'Jeanne', about 150 meters (492 feet) across and at least 178 meters (584 feet) deep."
- phkahler 2y ago
  >> Of course once astronauts are on mars they will still be exposed to radiation, until some sort of shielding can be built. Send tunnel boring machines. There a company making electric ones.
- TheDudeMan 2y ago
  "hopefully the price of this rocket to get stuff off of earth is dirt cheap" This is not a launch technology.
  - JumpCrisscross 2y ago
    Not with that attitude!
    - mr_toad 2y ago
      Attitude isn’t going to help when the thrust to weight ratio is less than one.
    - optimalsolver 2y ago
      *altitude
      - JumpCrisscross 2y ago
        Got to have the correct attitude to gain altitude. (Attitude has a second meaning in respect of spacecraft.)
akira2501 2y ago
The distance between Mars and Earth is not fixed and is on a multi year repeating cycle. So, do they mean 2 months at the minimum distance, or the maximum?
- JumpCrisscross 2y ago
  > do they mean 2 months at the minimum distance, or the maximum This is a high delta-v vehicle, so anything on the outside of the porkchop [1]. [1] https://en.wikipedia.org/wiki/Porkchop_plot https://en.wikipedia.org/wiki/Porkchop_plot
  - akira2501 2y ago
    I'm not understanding how that plot applies here or how it answers the question.
    - perihelions 2y ago
      The orbital timing makes little difference, because the velocities involved are significantly faster than planetary orbital speeds. Longer distances will take longer times, but not proportionally longer: the limiting factor is the acceleration and deceleration. The diagram the parent linked is the conventional presentation for how to relate orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers, such as this concept. Orbital phases are not important here.
      - akira2501 2y ago
        > orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers The minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles. You're telling me this engine is so powerful it doesn't matter when you launch you'll always get there in 2 months? Isn't Mars occasionally on the other side of the Sun from us? I'm still failing to grasp this.
        2y ago
JumpCrisscross 2y ago
Zubrin gave a great talk in 2011 on VASIMR, another drawing-board nuclear magneto-plasma propulsion technology [1]. It's not only untested and unnecessary, but gets used by opponents of space exploration as a convenient reason to delay funding until the magic kit is ready. [1] https://www.youtube.com/watch?v=myYs4DCCZts https://www.youtube.com/watch?v=myYs4DCCZts
perihelions 2y ago
I love the idea of nuclear fission space propulsion. But, this concept doesn't look even mildly realistic. The first fission-electric rocket in space isn't going be f'ing 10 gigawatts [0]: it's going to be 5-6 orders of magnitude smaller, it's going to be conservatively designed and cautiously iterated, in a way that gets useful engineering data even if it doesn't work the first time (it won't). This craziness is an Nth-of-a-kind iteration you might consider attempting, >20 years* after your 1st success, after >20 years of sustained development effort. It's not a near-future plausibility. *(Coincidentally, the first serious project was cancelled about 20 years before the present day [1]. That would have been an interesting alternate history...) [0] https://www.howeindustries.net/ppr https://www.howeindustries.net/ppr [1] https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter edit: To explain my reasoning a little: 10 gigawatts is gigantic amount of violently destructive energy—thermal energy, radiation energy, mechanical and vibrational [2] energy—you're trying to squeeze into a lightweight, complex, mass-optimized aerospace device that needs to run unattended and without maintenance for many years, without failing. That's probably very hard to get right. There have been many nuclear electric reactors in space already, but remarkably none of them, in operation, had any moving parts! They were all solid-state thermoelectric converters. I believe the bulk of that design choice boils down to "it's simple and conservative". Thermoelectrics aren't impressive by any other metric—just simplicity. Even the first, smallest nuclear electric turbine in space will be a majorly impressive achievement, for whoever succeeds at it. [2] Let's not forget: https://en.wikipedia.org/wiki/Galileo_project#High_gain_antenna_problem https://en.wikipedia.org/wiki/Galileo_project#High_gain_ante...
- CaptainOfCoit 2y ago
  > This craziness is an Nth-of-a-kind iteration you might consider attempting, >20 years* after your 1st success, after >20 years of sustained development effort. It's not a near-future plausibility Fittingly, the project is part of NIAC (NASA Innovative Advanced Concepts) which is specifically for borderline outlandish, far-future ideas like magnetic sails, space elevators, nuclear propulsion, a "Lunar Crater Radio Telescope" and many other somewhat crazy ideas. From NASA: > The NASA Innovative Advanced Concepts (NIAC) Program nurtures visionary ideas that could transform future NASA missions with the creation of breakthroughs — radically better or entirely new aerospace concepts https://www.nasa.gov/stmd-the-nasa-innovative-advanced-concepts-niac/ https://www.nasa.gov/stmd-the-nasa-innovative-advanced-conce...
pmayrgundter 2y ago
Good. But it's only a few days with a million ISP from fusion.. let's raise the bar ;)
trhway 2y ago
my napkin gets almost the same with existing and relatively simple tech - solar or nuclear source of energy powering ionic drive (as the one already made and tested/flown by NASA with 3500 Isp (vs. yet to be made 5000 mentioned in the article)). Solar can actually beat nuclear if it is made as very thin, ie. light, film. I think and hope that SpaceX would end up using solar+ionic combo instead of chemical for Mars (and nuclear + ionic for beyond Mars).
ChrisMarshallNY 2y ago
The AppleTV+ alternate history show, For All Mankind, works on the theory that we got the NERVA engine working. According to that show, we should have been on Mars for the last twenty years.
credit_guy 2y ago
> could allow for crewed missions to Mars to be completed within 2 months. As it stands today with commonly used propulsion systems, a trip to Mars takes around 9 months. Both numbers are pulled out of thin air. The Hohmann transfer time between 2 planets is about half a year. Which year, you ask? The year of the inner planet, or of the outer planet. Well, it's the average of the 2 years. A Martian year is about 2 of our years, so the average is 1.5 years, divided by 2 it's 9 months. But if you are willing to burn more fuel, you can cut down the travel time. The delta-v between Earth orbit and Mars is surprisingly low. From the Moon transfer orbit to the low Mars orbit it is 2.5 km/s. The rule of thumb is that a rocket can achieve twice the delta-v of its exhaust velocity. In the case of the SpaceX Starship, the exhaust velocity is 3.7 km/s, twice that is 7.4 km/s, about 3 times the delta-v needed for the Hohmann transfer. SpaceX states they will be able to get to Mars in 6 months [1]. Musk went further and claimed that the Starship could get to Mars in as little as 80 days, and this fantastic Stack Exchange post [2] explains that maybe 80 days is slightly too optimistic, but 90 days is doable. Now this design here claims that the rocket can achieve an ISP of 5000 seconds, which means an exhaust velocity of 50 km/s. With such an exhaust velocity, basically they can pick any random number and claim they can get to Mars that fast. The shortest path between the two orbits, the radial one, is about 75 million km long. At 50 km/s, it takes 1.5 million seconds, or 17 days. Of course, this is for a one-way trip, but presumably in the far future we could preposition fuel in Mars orbit for the return trip. Maybe they thought half a month will sound too wild, so they went for the 2 month number to make it sound more realistic. The problem is that compared to the 3 months doable by SpaceX, it's not all that impressive. [1] https://www.spacex.com/humanspaceflight/mars/ https://www.spacex.com/humanspaceflight/mars/ [2] https://space.stackexchange.com/questions/57568/elon-musks-its-travel-time-to-mars-estimate https://space.stackexchange.com/questions/57568/elon-musks-i...

88 points by genman 2y ago

> Shorter periods of exposure to space radiation and microgravity could help mitigate its effects on the human body. Of course once astronauts are on mars they will still be exposed to radiation, until some sort of shielding can be built. Which would be an obscene undertaking, and involves moving lots of raw and refined materials to mars. Which means hopefully the price of this rocket to get stuff off of earth is dirt cheap, because moving squishy humans to Mars, no matter the speed, is not the limiting factor! (Getting humans to Mars and keeping them alive there is!)

sandworm101 2y ago
>> obscene undertaking, and involves moving lots of raw and refined materials to mars. Or they can dig a hole and/or pile mars dirt on top of their living structures. Some materials are better than others at absorbing radiation but, as a general rule, mass/depth of the protection counts more than composition.
dyauspitr 2y ago
Building an underground chamber doesn’t seem like an impossible undertaking. Alternatively, maybe mars already has caves and tunnels.
- OnlyMortal 2y ago
  There are tunnels that appear to have been created by volcano lava. Lava tubes.
- heavyset_go 2y ago
  It takes a lot of energy to displace sand/dirt/rocks to build anything underground. Human-powered shovels require a lot of food and water, and machinery requires combustion and a lot of hydrocarbons.
  - deleted 2y ago
    [deleted]
  - acchow 2y ago
    Submarines run on nuclear. Wouldn't nuclear be the natural choice on mars?
    - ceejayoz 2y ago
      Those are big, and heavy. https://www.oregon.gov/energy/safety-resiliency/Pages/Naval-Nuclear-Transport.aspx https://www.oregon.gov/energy/safety-resiliency/Pages/Naval-... > The submarine reactor compartments that have been taken to Hanford are about 33 feet high and 40 feet in length. They weigh between 1,130 and 1,680 tons. Eventually, the Navy may deactivate its Ohio class submarines in the same manner. Those compartments would be much larger and heavier. Submarines don't have to get them into orbit.
      - JumpCrisscross 2y ago
        In case you're serious, nobody is suggesting launching a water-cooled reactor to Mars. Between the idiot ends of the power-source spectrum bounded by, on one end, a U.S. Navy PWR and, on the other end, Martian Aramco, we have the reasonable options of solar power, batteries, RTGs and fission-powered Stirling engines [1][2]. [1] https://www.nasa.gov/directorates/stmd/tech-demo-missions-program/kilopower-hmqzw/ https://www.nasa.gov/directorates/stmd/tech-demo-missions-pr... [2] https://www.nasa.gov/tdm/fission-surface-power/ https://www.nasa.gov/tdm/fission-surface-power/
        ceejayoz 2y ago
        I think solar's the far more likely option, yes. Cheap, light, low-maintenance. Maybe fuel cells for night. RTGs aren't gonna power a good-sized base; they're a few hundred watts at best. edit: I very much hope Kilopower pans out.
        jujube3 2y ago
        What is wrong with launching a water-cooled reactor to Mars? Or more likely launching the materials needed to build it. The active components of a reactor are quite tiny -- most of the bulk is in the shielding, which won't be necessary on an already radioactive planet like Mars.
- ortusdux 2y ago
  I still think that this would explain Musk's dalliance with tunnel boring machines.
malfist 2y ago
The easiest solution is to set up shop in a cooled volcano tube
dmurray 2y ago
Most of the materials could surely be found on Mars. A shelter built out of sandbags would be a low tech solution that would get you a large part of the way there. Further, Mars itself shields you from half the radiation (at night), the Martian atmosphere shields you from a little more, and Mars is further away from the Sun on average than an Earth-Mars spaceship. Radiation during transit really does seem like a bigger issue.
- pmontra 2y ago
  There are also cosmic rays. They come from every direction, so even at night. An experiment measured that kind of radiation about 20 years ago https://en.wikipedia.org/wiki/Mars_Radiation_Environment_Experiment https://en.wikipedia.org/wiki/Mars_Radiation_Environment_Exp...
  - dmurray 2y ago
    The planet still shields you from half of those.
lupusreal 2y ago
It's not an intractable problem, just send a robot bulldozer and excavator a few years beforehand. The real problem with a Mars colony is the economics for making it anything more than a small scientific outpost / political stunt. Forget the upfront cost of the habitat/etc, how do you actually create a self sustaining Martian economy? I've never heard a realistic answer for this.
- mongol 2y ago
  It is an interesting problem of energy. How would a robot bulldozer or excavator be powered? They require more power than a rower.
  - lupusreal 2y ago
    They don't require more than a rover if you accept them doing their work far slower than their normal earth equivalents. Hence sending them years in advance to dig out a some holes that would only take a few days for excavators on Earth.
    - tsimionescu 2y ago
      While speed is a factor as well, you still need a lot more energy consumption to move a mass of rock&dust some distance away than to move a small rover. This immediately follows from the formula for work and the gravitational force.
      - lupusreal 2y ago
        Given enough time, you can dig out a house foundation with a spoon, power is not an issue here. The less power you have available the slower you work. If your robots wear out, you send more. The real problem is finding enough time and money to waste on such a fruitless endeavor. If that can't be managed it nullifies the entire problem of digging a hole on Mars since a Mars base is nothing but a waste of time and money. Wasting time and money is table stakes.
kallistisoft 2y ago
As far as I know the plan has always been to use the martian regolith and water as primary radiation shielding -- same as the moon. Here is a recent (2022) paper[1] on the concept, but you can easily find scholarly work on this going back many decades... [1] https://www.sciencedirect.com/science/article/abs/pii/S0032063322001039 https://www.sciencedirect.com/science/article/abs/pii/S00320...
- ceejayoz 2y ago
  https://en.wikipedia.org/wiki/Martian_lava_tube https://en.wikipedia.org/wiki/Martian_lava_tube have also been proposed as pre-existing possible shelters. https://en.wikipedia.org/wiki/Caves_of_Mars_Project#/media/File:Mars;_Arsia_Mons_cave_entrance_-MRO.jpg https://en.wikipedia.org/wiki/Caves_of_Mars_Project#/media/F... "HiRISE image of Mars hole 'Jeanne', about 150 meters (492 feet) across and at least 178 meters (584 feet) deep."
phkahler 2y ago
>> Of course once astronauts are on mars they will still be exposed to radiation, until some sort of shielding can be built. Send tunnel boring machines. There a company making electric ones.
TheDudeMan 2y ago
"hopefully the price of this rocket to get stuff off of earth is dirt cheap" This is not a launch technology.
- JumpCrisscross 2y ago
  Not with that attitude!
  - mr_toad 2y ago
    Attitude isn’t going to help when the thrust to weight ratio is less than one.
  - optimalsolver 2y ago
    *altitude
    - JumpCrisscross 2y ago
      Got to have the correct attitude to gain altitude. (Attitude has a second meaning in respect of spacecraft.)

akira2501 2y ago

The distance between Mars and Earth is not fixed and is on a multi year repeating cycle. So, do they mean 2 months at the minimum distance, or the maximum?

JumpCrisscross 2y ago
> do they mean 2 months at the minimum distance, or the maximum This is a high delta-v vehicle, so anything on the outside of the porkchop [1]. [1] https://en.wikipedia.org/wiki/Porkchop_plot https://en.wikipedia.org/wiki/Porkchop_plot
- akira2501 2y ago
  I'm not understanding how that plot applies here or how it answers the question.
  - perihelions 2y ago
    The orbital timing makes little difference, because the velocities involved are significantly faster than planetary orbital speeds. Longer distances will take longer times, but not proportionally longer: the limiting factor is the acceleration and deceleration. The diagram the parent linked is the conventional presentation for how to relate orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers, such as this concept. Orbital phases are not important here.
    - akira2501 2y ago
      > orbital transfer times with orbital phases—conventions that do not apply to high-Isp transfers The minimum distance to Mars is 33.9 million miles. The maximum distance to Mars is 225 million miles. You're telling me this engine is so powerful it doesn't matter when you launch you'll always get there in 2 months? Isn't Mars occasionally on the other side of the Sun from us? I'm still failing to grasp this.
      - 2y ago

JumpCrisscross 2y ago

Zubrin gave a great talk in 2011 on VASIMR, another drawing-board nuclear magneto-plasma propulsion technology [1]. It's not only untested and unnecessary, but gets used by opponents of space exploration as a convenient reason to delay funding until the magic kit is ready. [1] https://www.youtube.com/watch?v=myYs4DCCZts https://www.youtube.com/watch?v=myYs4DCCZts

perihelions 2y ago

I love the idea of nuclear fission space propulsion. But, this concept doesn't look even mildly realistic. The first fission-electric rocket in space isn't going be f'ing 10 gigawatts [0]: it's going to be 5-6 orders of magnitude smaller, it's going to be conservatively designed and cautiously iterated, in a way that gets useful engineering data even if it doesn't work the first time (it won't). This craziness is an Nth-of-a-kind iteration you might consider attempting, >20 years* after your 1st success, after >20 years of sustained development effort. It's not a near-future plausibility. *(Coincidentally, the first serious project was cancelled about 20 years before the present day [1]. That would have been an interesting alternate history...) [0] https://www.howeindustries.net/ppr https://www.howeindustries.net/ppr [1] https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter https://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter edit: To explain my reasoning a little: 10 gigawatts is gigantic amount of violently destructive energy—thermal energy, radiation energy, mechanical and vibrational [2] energy—you're trying to squeeze into a lightweight, complex, mass-optimized aerospace device that needs to run unattended and without maintenance for many years, without failing. That's probably very hard to get right. There have been many nuclear electric reactors in space already, but remarkably none of them, in operation, had any moving parts! They were all solid-state thermoelectric converters. I believe the bulk of that design choice boils down to "it's simple and conservative". Thermoelectrics aren't impressive by any other metric—just simplicity. Even the first, smallest nuclear electric turbine in space will be a majorly impressive achievement, for whoever succeeds at it. [2] Let's not forget: https://en.wikipedia.org/wiki/Galileo_project#High_gain_antenna_problem https://en.wikipedia.org/wiki/Galileo_project#High_gain_ante...

CaptainOfCoit 2y ago
> This craziness is an Nth-of-a-kind iteration you might consider attempting, >20 years* after your 1st success, after >20 years of sustained development effort. It's not a near-future plausibility Fittingly, the project is part of NIAC (NASA Innovative Advanced Concepts) which is specifically for borderline outlandish, far-future ideas like magnetic sails, space elevators, nuclear propulsion, a "Lunar Crater Radio Telescope" and many other somewhat crazy ideas. From NASA: > The NASA Innovative Advanced Concepts (NIAC) Program nurtures visionary ideas that could transform future NASA missions with the creation of breakthroughs — radically better or entirely new aerospace concepts https://www.nasa.gov/stmd-the-nasa-innovative-advanced-concepts-niac/ https://www.nasa.gov/stmd-the-nasa-innovative-advanced-conce...

pmayrgundter 2y ago

Good. But it's only a few days with a million ISP from fusion.. let's raise the bar ;)

trhway 2y ago

my napkin gets almost the same with existing and relatively simple tech - solar or nuclear source of energy powering ionic drive (as the one already made and tested/flown by NASA with 3500 Isp (vs. yet to be made 5000 mentioned in the article)). Solar can actually beat nuclear if it is made as very thin, ie. light, film. I think and hope that SpaceX would end up using solar+ionic combo instead of chemical for Mars (and nuclear + ionic for beyond Mars).

ChrisMarshallNY 2y ago

The AppleTV+ alternate history show, For All Mankind, works on the theory that we got the NERVA engine working. According to that show, we should have been on Mars for the last twenty years.

credit_guy 2y ago

> could allow for crewed missions to Mars to be completed within 2 months. As it stands today with commonly used propulsion systems, a trip to Mars takes around 9 months. Both numbers are pulled out of thin air. The Hohmann transfer time between 2 planets is about half a year. Which year, you ask? The year of the inner planet, or of the outer planet. Well, it's the average of the 2 years. A Martian year is about 2 of our years, so the average is 1.5 years, divided by 2 it's 9 months. But if you are willing to burn more fuel, you can cut down the travel time. The delta-v between Earth orbit and Mars is surprisingly low. From the Moon transfer orbit to the low Mars orbit it is 2.5 km/s. The rule of thumb is that a rocket can achieve twice the delta-v of its exhaust velocity. In the case of the SpaceX Starship, the exhaust velocity is 3.7 km/s, twice that is 7.4 km/s, about 3 times the delta-v needed for the Hohmann transfer. SpaceX states they will be able to get to Mars in 6 months [1]. Musk went further and claimed that the Starship could get to Mars in as little as 80 days, and this fantastic Stack Exchange post [2] explains that maybe 80 days is slightly too optimistic, but 90 days is doable. Now this design here claims that the rocket can achieve an ISP of 5000 seconds, which means an exhaust velocity of 50 km/s. With such an exhaust velocity, basically they can pick any random number and claim they can get to Mars that fast. The shortest path between the two orbits, the radial one, is about 75 million km long. At 50 km/s, it takes 1.5 million seconds, or 17 days. Of course, this is for a one-way trip, but presumably in the far future we could preposition fuel in Mars orbit for the return trip. Maybe they thought half a month will sound too wild, so they went for the 2 month number to make it sound more realistic. The problem is that compared to the 3 months doable by SpaceX, it's not all that impressive. [1] https://www.spacex.com/humanspaceflight/mars/ https://www.spacex.com/humanspaceflight/mars/ [2] https://space.stackexchange.com/questions/57568/elon-musks-its-travel-time-to-mars-estimate https://space.stackexchange.com/questions/57568/elon-musks-i...