Exploration and Missions
DraftEarlier sections covered orbits, propulsion and spacecraft. This one covers the destinations: what makes each one difficult, what has been found there, and how a mission goes from a question to flying hardware.
Reading order
Mission design comes first because it frames every destination page. The destinations are independent of each other. Artemis and sample return are cross-cutting programmes that draw on several.
The numbers that shape this section
Solar flux falls as the inverse square of distance, and it is the constraint that separates inner from outer solar system missions:
| Body | Distance | Solar flux | Light time, one way |
|---|---|---|---|
| Moon | 384 400 km | 1361 W/m² | 1.3 s |
| Mars | 1.52 AU | 586 W/m² | 4 to 21 min |
| Jupiter | 5.20 AU | 50 W/m² | ~43 min |
| Saturn | 9.58 AU | 15 W/m² | ~80 min |
| Neptune | 30.1 AU | 1.5 W/m² | ~4.1 h |
At the Moon, real-time teleoperation is possible. At Mars, every landing is autonomous because the ground learns the outcome after it has happened. At Saturn, a round trip exceeds two and a half hours and autonomy is not a design choice but a precondition.
Five things worth knowing
The Moon is harder than its proximity suggests. With no atmosphere, every metre per second of arrival velocity must be removed propulsively, and low lunar orbits are unstable because of mass concentrations under the maria.
Mars has the worst possible atmosphere. Too thin to stop a vehicle, too thick to ignore. A lander needs a heat shield and parachutes and descent engines, and the techniques do not scale from the one tonne demonstrated to the twenty or forty tonnes a crew would need.
Venus killed everything that landed on it within about two hours. The survival record, 127 minutes, was set by Venera 13 in 1982 and still stands. The cloud layer at 55 km, by contrast, is the most Earth-like environment off Earth.
Liquid water is common in the outer solar system, not the inner one. Tidal heating rather than sunlight maintains oceans beneath the ice of Europa, Enceladus, Titan and Ganymede, which decouples habitability from distance to the star entirely.
Small returned masses produce large science. Hayabusa returned under a milligram and settled the link between S-type asteroids and ordinary chondrites. Apollo samples sealed in 1972 were opened in 2022 with techniques that did not then exist.
Pages
Science traceability, the phase structure and why 80 per cent of cost is committed by preliminary design, cost classes and the decadal survey, concept of operations, and planetary protection.
02The MoonThe environment and the 14-day night, orbital instability from mascons, regolith and dust, polar volatiles and what is actually known about them, the Apollo record and the current commercial wave.
03MarsWhy the atmosphere is the central problem, entry descent and landing and the one-tonne limit, what the surface missions found, dust storms, in-situ resource utilisation and the human mission gap.
04VenusWhat 92 bar and 464 degrees does to hardware, the Venera survival record, radar mapping and the young surface, the habitable cloud layer, the phosphine episode and the returning missions.
05Asteroids and cometsPopulations and composition, why microgravity navigation is a different regime, the rendezvous and sample return record, DART and the momentum enhancement result, and the resource case honestly assessed.
06Outer planets and icy moonsPower, communications and patience at distance, Jupiter’s radiation environment and how mission architecture responds to it, the ocean worlds and tidal heating, Titan, and the neglected ice giants.
07Space telescopesThe three separate reasons for going above the atmosphere, segmented mirrors and co-phasing, why L2 permits passive cryogenic cooling, the major observatories, and how observing time is allocated.
08Artemis and human lunar returnThe architecture and why the profile goes through a near-rectilinear halo orbit, the lander’s orbital refuelling dependency, why the south pole, the Accords, and where the schedule risk sits.
09Sample return missionsWhy returning material beats analysing it in place, what has been returned, the Mars Sample Return architecture and its cost problem, restricted Earth return, and curation as a multi-decade obligation.