Research

Human Expedition Windows to (1620) Geographos After 2055

Executive summary

(1620) Geographos is an Apollo-class near‑Earth asteroid with a highly inclined orbit (_13.3°) and Earth MOID ≈ 0.02936 au (₄.39 million km), which means its orbital path can come close to Earth’s path, but truly close flybys are rare.

From 2055 through 2200, the available close‑approach data show no Earth encounters closer than 0.02 au, none closer than 0.01 au, and no approach clearly inside 5 million km. The best (closest) post‑2055 window is 2119‑08‑27, at 0.0336166 au ≈ 5.03 million km (about a 16.8‑second one‑way light time).

Mission-wise, Geographos is not a “low‑delta‑v” crew target in the usual sense: its inclination alone implies a substantial plane-change burden compared to near‑ecliptic NEOs. A fast flyby/intercept is far more plausible than a true rendezvous/landing for chemical propulsion; a rendezvous likely needs high‑energy propulsion (e.g., nuclear thermal) or long‑duration electric mission profiles.

Data sources and method

This report combines:

• ESA NEO Portal (NEOCC/SSA) object page for Geographos, giving orbital properties, Earth MOID, and a close-approach list (1950–2126) in AU.
• JPL/CNEOS Close Approaches page for definitions and scope: it explicitly lists columns including “V relative (km/s)” and notes that close-approach data (in that interface) are not available after 2200 A.D.
• JPL Horizons manual for what a close-approach table’s CA Dist and Vrel mean (i.e., geometric closest distance and relative velocity at the nominal close-approach time).
• A secondary, non-agency compilation (Space Reference) that lists Earth close-approach distances (km) and velocities (km/s) for several future encounters. Where it overlaps ESA’s official close‑approach distances (through 2119), the distance values are consistent in practice (same encounter dates and distance scale), so it is used only to supply relative-velocity numbers where ESA’s table does not include them, and to extend indicative timing beyond 2126.

Distance conversions use 1 au = 149,597,870.7 km, consistent with standard agency usage.

Transfer times and delta‑v are order‑of‑magnitude estimates under these assumptions:

• impulsive burns, patched‑conic reasoning, no gravity assists
• departure from ~400 km LEO
• “Hohmann-like” timescale bounds based on Geographos’ perihelion/aphelion distances (q and Q) and the fact it is an Apollo with a ~1.39‑yr period

Earth close approaches from 2055 through 2200

Earth MOID

ESA lists Earth MOID = 0.02936 au, which is ₄.39 million km (minimum distance between the two osculating orbital paths, not a guarantee of an actual flyby at that distance).

Timeline of post‑2055 close approaches

The ESA object page provides official close approaches only out to 2126; the relevant subset is shown below, and later encounters (2133–2190) are included from the secondary compilation as indicative extensions.

Table: Earth close approaches for 1620 Geographos (2055–2200)

(Distances are nominal Earth‑center to asteroid‑center. “Vrel” is the asteroid’s velocity relative to Earth at closest approach as defined in JPL close‑approach tables.)

The “within 5 million km” question

• The closest post‑2055 entry in the above set is 2119‑08‑27 at ~5.029 million km, just above a 5.0 million km threshold.
• A commonly cited summary is that the 1994 ~5.0 million km close approach “will not be bettered until 2586,” implying no <5 million km encounters in 2055–2200.

So, for story/mission gating: there is no obvious “<5 Mkm” window after 2055 and before 2200; the next‑best is 2119 at essentially ₅.03 Mkm.

Best candidate windows and how they rank

Because Geographos has no <0.02 au encounters in 2055–2200 (in the available lists), the practical “windows” are all in the 0.03–0.20 au range.

A good expedition window for humans is usually a compromise between:

• distance (logistics, comms, abort energy)
• relative velocity (proxy for rendezvous/intercept difficulty)
• orbital plane mismatch (here dominated by i ≈ 13.3°)

Top six windows table

This table prioritizes (a) smaller miss distance, but also (b) avoids the very highest relative velocities when possible.

Transfer options and delta‑v estimates for a human expedition

What close-approach distance does and does not buy you

A close approach reduces:

• communications delay (seconds to a couple minutes in all these cases)
• some abort/return energy in worst-case scenarios
• resupply/launch‑cue pressure (in fiction, you can launch a “hail‑Mary” faster)

But it does not automatically mean the asteroid is an “easy rendezvous,” because rendezvous is dominated by orbit matching: inclination and heliocentric energy. Geographos’ 13.3° inclination is large enough that even idealized plane-change costs are significant compared to many “human-accessible” NEO targets.

Hohmann-like timescale (ballistic) bounds

ESA gives Geographos’ perihelion and aphelion distances (q ≈ 0.828 au, Q ≈ 1.664 au) and its ~508‑day period.

A very rough “Hohmann-like” outbound time from a 1 au orbit to meet it somewhere along its radial range is therefore on the order of:

• ₁₆₀ days if meeting near its perihelion distance (₀.83 au)
• ₂₈₀ days if meeting near its aphelion distance (₁.66 au)

Real mission designs use Lambert targeting and can be shorter or longer depending on phasing; for a story‑credible crew mission, it is reasonable to treat ₅–9 months outbound as the “ballistic” class.

Delta‑v: what “duct-taped ISS” runs into

A useful way to separate cases:

Flyby / intercept mission (no rendezvous):

• Leave Earth on a trajectory that intersects Geographos’ path near the close approach epoch.
• Typical LEO-to-escape injection for modest hyperbolic excess velocities (v∞ ≈ 2–4 km/s) is on the order of _3.4–3.9 km/s (plus midcourse corrections).
• You do not pay the full orbit‑matching cost; you accept a high relative speed at encounter.

CNEOS/Horizons define that encounter relative speed as Vrel at close approach.

Rendezvous mission (match velocity, station-keep, “land”):

• In the worst case, if you attempted to rendezvous at the Earth close-approach instant, your required matching burn is on the order of the listed Vrel, which is ₈–17 km/s across the encounters shown—well beyond practical chemical crew vehicles.
• In better planned rendezvous profiles you reduce this, but Geographos’ high inclination means it still tends to remain a high‑delta‑v target compared to low‑inclination NEOs.

Per-window mission sketches

These are story-oriented sketches consistent with the encounter geometry above and the fact that none of the windows are ultra-close (<0.02 au).

2119-08-27 (0.0336 au) — “closest in the era” window

A fast intercept is plausible: launch weeks to a few months ahead, fly through at ~12.4 km/s relative. A true rendezvous is still demanding, but the very small Earth distance at encounter provides strong narrative advantages (tight comms, “rescue possible,” public attention).

2076-08-20 (0.0784 au, 10.2 km/s)

Best “balanced” window in this century-scale set: a manageable miss distance with lower relative speed than many. If you need a mission that almost rendezvous (slow relative drift, extended proximity ops), this is among the least punishing by Vrel.

2144-08-29 (0.0705 au, 13.5 km/s)

Close-ish but fast. It’s the kind of pass where you do “hit-and-run” operations: remote sensing, kinetic sampling, maybe high-speed harpoon capture in hard-SF terms.

2176-08-20 (0.0936 au, 9.87 km/s)

Not especially close, but relatively low Vrel. If your fiction cares about crew survivability and propulsion realism more than comms delay, this is arguably preferable to some “closer but faster” windows.

2065-03-13 and 2190-03-16 (₀.0966 au, ~12.7–13.0 km/s)

Mid-tier backups. They work fine for reconnaissance-style expeditions but are not standouts.

Feasibility notes for a crewed mission

Radiation and health risk context

Once crews leave Earth’s protective atmosphere/magnetosphere, radiation becomes a major hazard, dominated by solar energetic particles and galactic cosmic rays. NASA explicitly frames deep-space radiation as a key limiter and health risk driver for missions beyond Earth orbit.

ESA likewise emphasizes that space radiation levels are much higher than on Earth and that exposure increases with altitude and beyond shielding.

If you want a believable constraint for your story: mission duration (months) and the risk of solar particle events drive design toward storm shelters, monitoring, and either “sprint missions” or heavily shielded architectures. NASA’s Artemis/Orion work includes explicit radiation‑measurement and shielding strategies for deep‑space environments.

Abort and launch-window logic

• Launch windows for these encounters are not “single days” in practice; they’re typically a multi-week planning band, but the precise window depends on your chosen trajectory type (flyby vs rendezvous) and your propulsion. (This is why mission designers use Lambert solvers and iterate.)
• Abort options are far better for short-duration flybys (you can bias trajectories toward Earth return sooner) than for long rendezvous profiles where you commit to large plane changes and energy shifts.
• The “closest” window (2119) helps story-wise because Earth is only ~5 million km away at encounter (₁₇ s one-way light time), so you can plausibly write “rapid response” rescue politics—even if physical rescue still takes days to weeks.

Primary ephemeris links and how to reproduce the authoritative lists

To regenerate fully authoritative CA lists with both distance and Vrel out to 2200, the cleanest path is to use the JPL SBDB Close‑Approach Data (CAD) API or the JPL Horizons approach table programmatically (both are documented by JPL), or ESA’s downloadable “close encounters list” endpoints from the NEOCC automated access page.

Below are the primary pages (URLs in a code block as requested):

textCopyESA NEO Portal (1620 Geographos object page):
https://neo.ssa.esa.int/search-for-asteroids?des=1620+Geographos&tab=summary

JPL/CNEOS Close Approaches (Earth; interface scope notes include “not after 2200”):
https://cneos.jpl.nasa.gov/ca/

JPL Horizons manual (defines CA Dist and Vrel for close-approach tables):
https://ssd.jpl.nasa.gov/horizons/manual.html

JPL Horizons API documentation (how to request close-approach tables via EPHEM_TYPE=APPROACH):
https://ssd-api.jpl.nasa.gov/doc/horizons.html

JPL SBDB Close-Approach Data (CAD) API documentation:
https://ssd-api.jpl.nasa.gov/doc/cad.html

ESA NEOCC Automated Data Access (“close encounters list” endpoint is described here):
https://neo.ssa.esa.int/computer-access

If you want the “canon” in your fiction to be explicitly JPL/ESA-derived, a good in‑world line is:

• “We pulled the window from ESA NEOCC and verified the encounter geometry against Horizons definitions of CA Dist and Vrel.”