[ExI] Use Fusion Drive To Get To Proxima Centauri

[BillK]

On Mon, 7 Jul 2025 at 15:18, <spike at rainier66.com> wrote:
>
> Ja.  Deuterium isn't rare, and the He3 is generated in route with the
> breakdown of tritium.  The big problem is storing enough tritium, because
it
> has a half-life of about 12.5 yrs.  This would make it only useful for the
> acceleration phase.  The more I have thought about that problem, the more
I
> think this will be a few thousand year mission, with lower top speed, but
> with a more plausible scheme to slow down on the other end.  This
influenced
> my comment that I can see getting into Prox orbit a lot easier than I can
> see a particular planet there.
>
> Interstellar travel is a damn tough problem.
>
> spike
> ---------------------------------------


Oh, Ye of little faith!   :)
I asked Perplexity to explain its reasoning.
Basically, it depends on developing fusion drives, fuel sourcing and
shielding.
Present tech would indeed take thousands of years of travel time, so we
won't do it that way.
See the full explanation below -
BillK


*Perplexity ---*
Is a 57-Year Fusion-Powered Mission to Proxima Centauri Feasible? Short
Answer

*According to the latest research, including the 2025 thesis by Amelie M.
Lutz, a 57-year travel time to Proxima Centauri using fusion propulsion is
theoretically feasible—but only under optimistic technological assumptions.*
Thousands of years is not inevitable, but such a short travel time depends
on major advances in fusion propulsion, fuel sourcing, and spacecraft
engineering.
Evidence from the Lutz Thesis

The thesis Lutz, 2025
<https://ppl-ai-file-upload.s3.amazonaws.com/web/direct-files/attachments/3645031/611a8c82-7b32-4255-b27d-61779940a73b/Lutz_AM_T_2025.pdf>
specifically analyzes several fusion propulsion concepts for a large-scale
(500 kg payload) mission to Proxima b (in the Proxima Centauri system, 4.2
light-years away):

   -

   *Fusion Driven Rocket (FDR) with D-He3 fuel* is identified as the only
   configuration capable of both decelerating and entering a bounded orbit at
   Proxima b, with a total mission time of about *57 years*.
   -

   Other fusion fuels and propulsion concepts (such as D-D, D-T, p-B11, or
   Inertial Electrostatic Confinement and Antimatter-Initiated Microfusion)
   either result in much longer travel times (up to 119 years for a fast
   flyby, or longer for decelerated missions) or are not currently practical
   due to fuel sourcing or reactor limitations.
   -

   The 57-year figure assumes a “slow flyby” or “bounded orbit” scenario,
   including deceleration at the destination for meaningful science return.

*Key Table (from the thesis):*
Propulsion System Fuel Mission Time (years, slow flyby)
FDR D-He3 57
FDR D-T 55 (but with much more shielding)
FDR D-D 107
FDR p-B11 119
What Makes This Possible?

   -

   *Fusion Propulsion Efficiency:* Fusion offers exhaust velocities and
   energy densities far beyond chemical or fission systems, making high-speed,
   long-duration missions feasible in principle.
   -

   *Aneutronic Fuel (D-He3):* This fuel minimizes neutron production,
   reducing the need for heavy shielding and thus improving payload fraction
   and acceleration.
   -

   *Optimized Mission Profile:* The mission design includes both
   acceleration and deceleration phases, maximizing science return.

Major Caveats

   -

   *Fusion Technology Readiness:* No fusion propulsion system has yet flown
   in space, and even ground-based reactors are only now reaching net energy
   gain. Space-qualified, high-power, long-duration fusion reactors are still
   conceptual.
   -

   *D-He3 Fuel Sourcing:* Helium-3 is extremely rare on Earth. The thesis
   assumes future breakthroughs in lunar mining or other acquisition methods.
   -

   *Engineering Challenges:* Radiation shielding, heat rejection, long-term
   reliability, and autonomous operation over decades remain unsolved at scale.
   -

   *Assumptions:* The 57-year estimate is based on idealized or optimistic
   assumptions about system performance, reactor mass, and fuel availability.

Is Thousands of Years More Likely?

   -

   *With current technology:* Yes, travel times to Proxima Centauri with
   chemical, fission, or even near-term fusion systems would be measured in
   thousands to tens of thousands of years.
   -

   *With fusion breakthroughs:* If the necessary advances in fusion
   propulsion, fuel acquisition, and spacecraft engineering are achieved,
   travel times of 50–100 years become plausible for large, instrumented
   probes.

Conclusion

*A 57-year fusion-powered mission to Proxima Centauri is not science
fiction, but it is not yet within our technological grasp.* Theoretical
studies like Lutz (2025) show that such a mission is possible with fusion
propulsion—especially using D-He3 fuel and an optimized mission profile.
However, this scenario requires significant breakthroughs in fusion
technology, fuel sourcing, and spacecraft systems. Until those advances are
realized, interstellar travel times will remain much longer.

*In summary:*

   -

   *57 years is feasible in theory,* with advanced fusion propulsion and
   D-He3 fuel.
   -

   *Thousands of years is the reality with current or near-term technology.*
   -

   *The future hinges on fusion breakthroughs and engineering innovation.*

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