Acta Astronautica · 2026 · Souza

The hidden shortcut to Mars, opening April 2031.

A trajectory analysis using asteroid 2001 CA21's tilted orbital plane reveals a 153-day round-trip — when conventional missions take nearly two years.

Departure window  Apr 20, 2031 Outbound  33–56 days Return  90–135 days Reference plane  CA21 ± 5°
01 · THE GEOMETRY

The long way around versus the chord across.

A standard Hohmann transfer swings nearly half-way around the Sun. The 2031 trajectory cuts a more direct path — possible only because Mars sits near opposition and the tilted reference plane lines up.

Reference path
Hohmann transfer
// minimum-energy ellipse, ~180° around Sun
Mars at launch Earth Mars at arrival Sun ~ 7–9 MONTHS
One-way duration ~259 days
2031 window · Souza
CA21-plane shortcut
// short-way Lambert transfer, near opposition
Earth Mars Sun 33d ↗ ↙ 90d return ~ 33–56 DAYS
One-way duration 33–56 days
02 · WHY 2031

The asteroid plane that closes the loop.

A 5° tilt becomes a filter.

Souza took the early 2015 predicted orbit of asteroid 2001 CA21 — highly eccentric, with a well-defined inclined plane — and treated it as a geometric template. He searched only for trajectories within ±5° of that plane.

Tested against Mars oppositions in 2027, 2029, and 2031, only the 2031 alignment produced trajectories that close into a complete round trip. The other windows either spike in energy demand or fail to return.

Ecliptic / Earth–Mars plane CA21 plane (~5° tilt) 5° Earth Mars // trajectory constrained to ±5° of CA21 plane
Round-trip duration · scaled comparison
Conventional
~900d
2031 feasible
226d
2031 extreme
153d
03 · DELTA-V & PROPULSION

The price of speed — and where you depart from.

The shortcut trades enormous fuel cost for time. And counterintuitively, lunar departure makes things worse for the high-energy cases — a consequence of the Oberth effect.

Departure ΔV from each staging point
Longer bar = more ΔV required  ·  scale: 0 → 25 km/s  ·  assumes lunar-sourced propellant
From LEO From Moon (LLO)
0 5 10 15 20 25 km/s
Hohmann transfer baseline · ~259 days one-way
LEO
3.6
LLO
1.3
✓ Moon saves 2.3 km/s · propellant free from Earth
56-day feasible shortcut v∞ ≈ 16.9 km/s · NTP required
LEO
12.4
LLO
14.4
~ +2.0 km/s ΔV, but propellant mass sourced locally
33-day extreme shortcut C3 ≈ 758 km²/s² · beyond current tech
LEO
21.9
LLO
25.0
~ +3.1 km/s ΔV, but no Earth-launch propellant cost
🌕
With lunar propellant, the Oberth penalty becomes an economic wash — or better. The ΔV numbers don't change: LLO departures still cost 2–3 km/s more than LEO for the shortcut trajectories due to the Oberth effect. But if that propellant is mined from lunar ice rather than launched from Earth's surface, the mass economics reverse dramatically. Lifting 1 kg of propellant from Earth to LEO costs roughly $2,000–6,000 at current launch prices. Sourcing it from the Moon avoids that cost entirely — meaning the "penalty" in km/s buys a far larger saving in launch mass and mission cost. For the 56-day NTP case, lunar staging with local propellant is likely the only architecturally viable path.
Propulsion capability · lunar propellant assumed
Chemical
Isp ~450 s
LH₂/LOX · e.g. RL-10, J-2X
✓ Hohmann — strongly preferred
✗ 56-day shortcut
✗ 33-day extreme
Lunar LH₂/LOX is the most tractable ISRU product. With free propellant, Hohmann from LLO becomes the cheapest Mars mission architecture possible — lower ΔV and zero Earth-launch propellant cost.
Nuclear Thermal
Isp ~900 s
NTP · e.g. NERVA heritage, DRACO
✓ Hohmann transfer
✓ 56-day feasible shortcut ★
✗ 33-day extreme
★ Best-fit architecture. NTP's high Isp means less propellant needed per km/s, and lunar LH₂ is the ideal NTP propellant. The +2.0 km/s LLO Oberth penalty is far outweighed by avoiding ~100+ tonnes of Earth-launched fuel.
Advanced / Future
Isp >1500 s
NTP+NEP hybrid · fusion · laser sail
✓ Hohmann transfer
✓ 56-day feasible shortcut
✓ 33-day extreme (theoretical)
With lunar propellant and high Isp, even the 33-day extreme case becomes architecturally conceivable — propellant mass fractions drop enough that the +3.1 km/s LLO penalty is a minor line item versus the launch cost savings.