Author Topic: One Month to Mars -- Methods for Very Fast Settler Transit  (Read 38111 times)

Offline LMT

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A thread exploring potential methods for speeding settler transit to Mars:  one month, safely.

A basic rationale:

One-month transit would remove the need for artificial gravity, cut consumable payload, and relieve psychological stress.  A practical consequence is increased passenger capacity.  If one-month transit raised a ship's passenger count by 50%, the number of crewed ships required for settlement would be cut by 1/3.  The corresponding fleet savings would justify considerable investment in fast transit infrastructure.

Notional parameters:

1.  Methods that could scale by, say, 2039, to enable perhaps a thousand very fast Starship-class transits per synodic window, from that time.

2.  Fast outbound transit only. 

3.  TRL2+ methods, just to give some minimum "formulated" basis for discussion of each method.
« Last Edit: 02/10/2024 04:14 pm by LMT »

Offline Emmettvonbrown

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Even in a propellant rich architecture,  would orbital mechanics allow 1 month trips ?

Offline Coastal Ron

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Even in a propellant rich architecture,  would orbital mechanics allow 1 month trips ?

Assuming virtually unlimited amounts of energy would be available, sure, point to point transportation between any two points is possible.

Whether humans would survive the trip due to the acceleration effects is another question, and of course humanity doesn't have a practical energy source to make such transits happen anytime soon.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline sdsds

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With the standard approach of a large impulsive maneuver for Earth departure followed by a coast to Mars, transit times less than 100 days are possible, but markedly more expensive in delta-v. (The attached chart was generated with an off-line variant of EasyPorkchop from sdg.aero.upm.es/index.php/online-apps/porkchop-plot.)

Continuous low-thrust options might offer better opportunities.
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Offline DanClemmensen

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Even in a propellant rich architecture,  would orbital mechanics allow 1 month trips ?

Assuming virtually unlimited amounts of energy would be available, sure, point to point transportation between any two points is possible.

Whether humans would survive the trip due to the acceleration effects is another question, and of course humanity doesn't have a practical energy source to make such transits happen anytime soon.
Assuming unlimited propellant and unlimited power, can accelerate at 1 G (10 m/s2) for half the distance and decelerate at 1 G for the other half. Max distance to Mars is about 400 million km, when Mars is exactly opposite of the Sun from Earth. (You won't want to make a straight-line trip here, so add a small amount of travel time.)

s=.5 a t2

(400 million km) /2 = .5 x 10 m/s2 x t2
200 x 109 m = .5 x 10 m/s2 x t2
4 x 1010 s2 =  t2
2 x 105 s = t
That's for the half-trip, so double it to get 400,000 seconds, which is 4.6 days for the longest 1G time needed to get to Mars.

Finding an infinite power source and infinite propellant supply is left as an exercise.
« Last Edit: 02/10/2024 06:51 pm by DanClemmensen »

Offline sdsds

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In contrast to the 2024 opportunity shown above, here's the 2025 "opportunity." Note the color scales are markedly different between the two.
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Offline joek

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...
Whether humans would survive the trip due to the acceleration effects is another question, and of course humanity doesn't have a practical energy source to make such transits happen anytime soon.

Constant ~1g acceleration/deceleration is certainly survivable and would result in Earth-Mars transit times of days-weeks. But as you stated, we don't have the technology-energy-whatever to do that.

edit: ninja'd by @DanClemmensen. (But even at 0.5G transit time is significantly reduced from 0g coast.)
« Last Edit: 02/10/2024 06:56 pm by joek »

Offline joek

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A thread exploring potential methods for speeding settler transit to Mars:  one month, safely.
...
At the risk of going OT and not addresing the direct OP issue-question, would rephrase as ...
Quote
A thread exploring potential methods for speeding settlement of Mars settler transit to Mars:  one month, safely.
.... Which seems to be the actual objective?

Reducing transit time is one answer, but not the only answer. Constraining the solution to reducing transit time eliminates other potential solutions which do not depend solely on transit time, magic energy sources, etc.


edit: Hint, e.g., see Advancing Torpor Inducing Transfer Habitats for Human Stasis to Mars.
« Last Edit: 02/10/2024 07:33 pm by joek »

Offline sdsds

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Assuming unlimited propellant and unlimited power, can accelerate at 1 G (10 m/s2) for half the distance and decelerate at 1 G for the other half. Max distance to Mars is about 400 million km, when Mars is exactly opposite of the Sun from Earth. (You won't want to make a straight-line trip here, so add a small amount of travel time.)

If the goal is 30 day transfers and the means is constant thrust propulsion it likely makes sense to limit the window to the time when the planets are positioned such that the transfer is easiest.

Note also: inherent in the "accelerate then decelerate" approach is a situation where the propulsion system fails part-way through the transfer. This failure mode looks like it results in ... loss of crew.

For those so inclined, Google found:
https://escholarship.org/content/qt4m6954st/qt4m6954st.pdf
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Offline LMT

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fwiw, an optimal 29 km/s impulsive departure burn gives Mars arrival in 30 days with Vinf magnitude (entry speed) of ~ 32 km/s.
« Last Edit: 02/10/2024 09:37 pm by LMT »

Offline DanClemmensen

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #10 on: 02/10/2024 10:21 pm »
Assuming unlimited propellant and unlimited power, can accelerate at 1 G (10 m/s2) for half the distance and decelerate at 1 G for the other half. Max distance to Mars is about 400 million km, when Mars is exactly opposite of the Sun from Earth. (You won't want to make a straight-line trip here, so add a small amount of travel time.)

If the goal is 30 day transfers and the means is constant thrust propulsion it likely makes sense to limit the window to the time when the planets are positioned such that the transfer is easiest.

Note also: inherent in the "accelerate then decelerate" approach is a situation where the propulsion system fails part-way through the transfer. This failure mode looks like it results in ... loss of crew.

For those so inclined, Google found:
https://escholarship.org/content/qt4m6954st/qt4m6954st.pdf
I was not advocating a constant-acceleration mission. I was just doing the math to explore the solution space and to answer the question about survivable acceleration. Since we do not have the technology for continuous acceleration at 1 G, it would never happen that way anyway. If we postulate a science fiction scenario that has this technology, we can throw in additional science fiction engineering that makes it sufficiently reliable.  After all, Heinlein used constant acceleration to get his characters to Mars quickly in "Double Star", and if it's good enough to him, it's good enough for me.  :)

Offline deltaV

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #11 on: 02/11/2024 12:27 am »
It's possible to do fast transits to/from Mars but it's extremely expensive in money and mass. See e.g. https://www.reddit.com/r/SpaceXLounge/comments/186g74c/how_to_go_to_mars_in_45_days_without_nuclear/ for the extreme effort needed to do even 45 days. With the rocket equation making initial mass exponential in delta vee 30 days would be much harder than the already impractical 45 days.

Offline LMT

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #12 on: 02/11/2024 01:59 am »
Humorous and informative introduction to many exotic rocket notions, by Winchell Chung at Atomic Rockets:

Engine List 1

Engine List 2

Engine List 3

Offline Zed_Noir

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #13 on: 02/11/2024 02:51 am »
<snip>
I was not advocating a constant-acceleration mission. I was just doing the math to explore the solution space and to answer the question about survivable acceleration. Since we do not have the technology for continuous acceleration at 1 G, it would never happen that way anyway. If we postulate a science fiction scenario that has this technology, we can throw in additional science fiction engineering that makes it sufficiently reliable.  After all, Heinlein used constant acceleration to get his characters to Mars quickly in "Double Star", and if it's good enough to him, it's good enough for me.  :)
Project Orion (pulse nuclear) seems quite possible and achievable. Of course it isn't constant acceleration, but the net result is about the same.

Plus it is a very mature technology. ;)

Offline LMT

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #14 on: 02/11/2024 03:11 am »
<snip>
I was not advocating a constant-acceleration mission. I was just doing the math to explore the solution space and to answer the question about survivable acceleration. Since we do not have the technology for continuous acceleration at 1 G, it would never happen that way anyway. If we postulate a science fiction scenario that has this technology, we can throw in additional science fiction engineering that makes it sufficiently reliable.  After all, Heinlein used constant acceleration to get his characters to Mars quickly in "Double Star", and if it's good enough to him, it's good enough for me.  :)

Project Orion (pulse nuclear) seems quite possible and achievable...

Winterberg's 2004 "Mini Fission-Fusion-Fission Explosion" rocketry offered some theoretical advantages over Project Orion, including:

1.  "gram size amount of fissile material for each microexplosion"

2.  ignition with only "a few kg of high explosives" or, alternately, cryogenic propellant

3.  The "comparatively small yield permits [replacement of the inefficient Orion] pusher plate by a semispherical reflector" having about 20x the solid angle for thrust.

Refs.

Winterberg, F., 2004. Mini fission-fusion-fission explosions (mini-nukes). A third way towards the controlled release of nuclear energy by fission and fusion. Zeitschrift für Naturforschung A, 59(6), pp.325-336.
« Last Edit: 02/14/2024 07:55 pm by LMT »

Offline TheRadicalModerate

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #15 on: 02/11/2024 04:40 am »
Even in a propellant rich architecture,  would orbital mechanics allow 1 month trips ?

I did a quick workup of a 130t dry / 1500t prop / 50t payload Starship, avg Isp=369s (what I suspect Starship 3 to be, more or less), departing from a 380,000 x 300 km HEEO, and assumed that it burned dry, then was fully refueled en route.  And it doesn't work.  Even braking just before entry interface, speed is something like 13km/s, which is way too fast for Mars.

But the transit only takes 1.7 months.  Pretty close.¹

There are more extreme versions than even this:  you could brake, then refuel, brake some more, etc., but they're operationally suicidal.  And this one is already really expensive in terms of prop.  (I didn't work it out, but previous exercises like this have yielded trips that require 100 tanker launches.)

In contrast, the same Starship 3, with the same 50t payload, departing from 300 x 300, can get to Mars on one 1500t tank of prop, with enough braking delta-v to reduce entry speed to <8km/s, which might be doable, especially with an aerocapture + aerobrake before EDL.  And it only takes 3.8 months,² and about 7 tanker launches.

________
¹To get a 1 month transit time, you need v∞ = 28.5km/s, which is C3=812km²/s².  Your Mars entry interface speed is 33km/s.  Update:  just noticed that LMT had posted the same numbers up-thread.

²This is model assumes no inclination differences between Earth and Mars, and circular orbits for both planets.  So it's a bit optimistic.  But it's in the ballpark.
« Last Edit: 02/11/2024 05:01 am by TheRadicalModerate »

Offline TheRadicalModerate

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #16 on: 02/11/2024 04:52 am »
With the standard approach of a large impulsive maneuver for Earth departure followed by a coast to Mars, transit times less than 100 days are possible, but markedly more expensive in delta-v. (The attached chart was generated with an off-line variant of EasyPorkchop from sdg.aero.upm.es/index.php/online-apps/porkchop-plot.)

Continuous low-thrust options might offer better opportunities.

Just remember that there's an accuracy limit for the Lambert solver in that puppy.  If you extend the range, you need to do a (beyond my mathematical skills) sensitivity analysis on your results.

As an aside, also note that, while the EasyPorkChop y-axis is labeled "dv", the numbers are actually v∞.

Note that my numbers above aren't from EasyPorkChop; I built myself a circular, 2D model, which doesn't give you launch and arrival windows, but does a sorta-kinda OK job of computing times of flight, and lets you do an integrated estimate of the total departure, arrival, and landing delta-v budget.

Offline TheRadicalModerate

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #17 on: 02/11/2024 05:09 am »
After all, Heinlein used constant acceleration to get his characters to Mars quickly in "Double Star", and if it's good enough to him, it's good enough for me.  :)

I don't believe that photon rockets capable of 4G acceleration are quite up to TRL 2 yet.  Plus, there's the whole problem with the biosphere-destroying gamma death ray coming out the back end.  Guidance errors will be frowned upon.

Offline sdsds

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #18 on: 02/11/2024 05:13 am »
The rocketry solution for fast transfer times is to use additional upper stages stages. If we wanted to deliver a 1t payload to Mars quickly, doing it with a 130t (dry) Starship wouldn't be ... efficient.

Maybe put a ~30t upper stage inside a chomper Starship payload bay?
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Offline deltaV

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Re: One Month to Mars -- Methods for Very Fast Settler Transit
« Reply #19 on: 02/11/2024 07:15 am »
¹To get a 1 month transit time, you need v∞ = 28.5km/s, which is C3=812km²/s².

That's 22.8 km/s of delta vee from a 200 km LEO. That's a lot of delta vee! A multi-staged hydrogen/oxygen rocket with a d-log-mass-weighted-average specific impulse of 380s yields a mass ratio of exp(22800 / (9.8*380)) = 456. So you'll need around 455 launches of propellant for every launch of stuff that reaches Mars. That's not practical.

The above assumes a beefy heat shield that can handle stopping at Mars at much greater speeds than usual. If you try to stop propulsively at Mars the mass ratio gets roughly squared.

The above also assumes everything is expendable - making it reusable would make things even worse.

Multi-stage nuclear thermal propulsion would probably give somewhat better mass ratios but they'd still be obscene.

If you had years to accelerate you could do 22.8 km/s of delta vee using nuclear electric or solar electric. But that takes a lot longer than a month, especially since you'd need somewhat more delta vee with non-impulsive burns.

In summary there are good reasons why everyone usually proposes Mars missions with multi-month transit times.

 

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